WO2024253471A1 - High-energy density electrochemical device comprising silicon-based particles - Google Patents

Abstract

The present invention relates to an electrochemical device capable of satisfying high energy density of 250 Wh/kg or more and excellent lifetime characteristics and stability at the same time. The electrochemical device according to the present invention comprises: a positive electrode; a negative electrode; and an electrolyte, and the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and including a porous binder scaffold and negative electrode active material particles, wherein the negative electrode active material particles include silicon-based particles.

Description

High energy density electrochemical device containing silicon particles

The present invention relates to a high energy density electrochemical device comprising silicon-based particles.

Recently, as the energy density of batteries required has increased rapidly, the development of high-capacity lithium batteries has become urgent. To this end, research on replacing existing anode materials such as graphite or silicon with lithium metal or on anode-free batteries has been proposed, but it is difficult to meet the increasingly increasing battery performance requirements by only changing the anode material. Accordingly, research on thick-film anodes with increased anode active material thickness and high-density/high-loading is actively being conducted.

However, as the negative electrode active material layer becomes thicker, problems such as physical cracks or unevenness of the negative electrode material occur during the manufacturing process, and thus it is difficult to secure stable battery performance and life characteristics, so there is a practical limit to increasing the thickness.

As a specific example, the above-mentioned thick-film type negative electrode has a fundamental problem that the negative electrode material is unevenly distributed. This causes uneven flow characteristics of lithium ions, and causes problems such as uneven charge/discharge characteristics in the thickness direction and polarization phenomena. In addition, the battery performance deteriorates due to the increase in the movement distance of lithium ions as the thickness of the negative electrode increases, and furthermore, such uneven flow characteristics of lithium ions further aggravate the problems of lithium metal precipitation and lithium dendrite formation on the surface of the negative electrode, which not only shortens the life of the battery but also lowers the stability of the battery.

Therefore, there is an urgent need for research and development of electrochemical devices that include a thick-film anode in which a high-capacity anode material, a silicon anode material, is uniformly distributed, and in which lithium metal precipitation, lithium plating, and the formation of lithium dendrites are effectively suppressed, and which have high energy density, excellent cycle characteristics, and stability.

According to one aspect of the present invention, an electrochemical device capable of simultaneously satisfying high energy density, excellent life characteristics, and stability is provided.

The tasks of the present invention are not limited to the above-described contents. Those with ordinary knowledge in the technical field to which the present invention belongs will have no difficulty in understanding additional tasks of the present invention from the overall contents of this specification.

An electrochemical device according to one embodiment of the present invention comprises a cathode, a cathode and an electrolyte, wherein the cathode comprises a cathode current collector; and an cathode active material layer formed on the cathode current collector, the cathode active material layer comprising a porous binder scaffold and cathode active material particles, wherein the cathode active material particles comprise silicon-based particles.

In an electrochemical device according to one embodiment, the electrochemical device may have an energy density of 250 Wh/kg or more.

In an electrochemical device according to one embodiment, the negative active material layer may contain at least 10 wt% of the silicon particles based on the total weight.

In an electrochemical device according to one embodiment, the negative active material particles further include graphite particles, and the negative active material layer may include at least 50 wt% of the graphite particles based on the total weight.

In an electrochemical device according to one embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

In an electrochemical device according to one embodiment, a separator may be further included.

In an electrochemical device according to one embodiment, the negative electrode may be a thick-film negative electrode having a capacity per area of a negative electrode active material layer formed on one surface of a negative electrode current collector of 4 to 15 mAh/cm2.

In an electrochemical device according to one embodiment, the negative active material layer may have negative active material particles evenly dispersed therein, and a porous binder scaffold may be present in the empty spaces between the particles.

In an electrochemical device according to one embodiment, the porous binder scaffold may be included in an amount of 0.01 to 40 parts by weight per 100 parts by weight of the negative active material particles.

In an electrochemical device according to one embodiment, the porous binder scaffold may further include a conductive material.

In an electrochemical device according to one embodiment, the porous binder scaffold may include one or two or more selected from the group consisting of a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic-based resin, an imide-based resin, and a cellulose-based resin.

In an electrochemical device according to one embodiment, the negative active material layer may further include a metal salt.

In an electrochemical device according to one embodiment, the metal salt may be included in an amount of 0.01 to 50 parts by weight per 100 parts by weight of the negative active material particles.

In an electrochemical device according to one embodiment, the metal salt may be contained in or surface-adsorbed in at least one of a porous binder scaffold and negative electrode active material particles.

In an electrochemical device according to one embodiment, the metal salt may be a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2.

[Chemical Formula 1]

[Chemical formula 2]

In the above chemical formulas 1 and 2,

n is 1 or 2;

A is a cation of valence n;

R ₁ to R ₃ are each independently a fluoro(C1-C7)alkyl or a fluoro group.

In an electrochemical device according to one embodiment, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

In an electrochemical device according to one embodiment, the electrolyte may have a ratio of the amount of electrolyte injected to the capacity of the electrochemical device (g/Ah) of less than 3.0.

In an electrochemical device according to one embodiment, lithium metal may not be deposited on the surface of a negative electrode when the electrochemical device is charged at a rate of 2.0C.

In an electrochemical device according to one embodiment, the cathode may have an electrode tortuosity (τ) of 5 or less, calculated by the following relationship.

[Relationship]

τ (Tortuosity) = (Kelectrolyte/Kelectrode)×(Porosity)

(In the above formula, Kelectrolyte means the ionic conductivity of the electrolyte, Kelectrode means the ionic conductivity of the cathode, and Porosity means the porosity of the cathode.)

In an electrochemical device according to one embodiment, the cathode may be capable of measuring wettability in a time of less than 500 seconds under the following measurement conditions.

[Measurement conditions]

At a dew point temperature of -40℃ (relative humidity of 1% or less), 1 ㎕ of propylene carbonate (PC) solvent was dropped onto the cathode surface, and the time required for the solvent to penetrate into the cathode and completely disappear was measured.

According to another embodiment of the present invention, an electrochemical device comprises a cathode, an anode, and an electrolyte, and has an energy density of 250 Wh/kg or more, wherein the anode comprises a cathode current collector; and an anode active material layer formed on the cathode current collector, the cathode active material layer comprising a binder, anode active material particles, and a conductive material; wherein the cathode active material particles comprise silicon-based particles;

When the cross-section of the above negative active material layer is analyzed by X-ray CT, the deviation among the average conductive concentration (C0) of the negative active material layer, the conductive concentration (C1) of the first active material layer corresponding to 1/3 of the thickness direction of the negative active material layer from the boundary between the negative current collector and the negative active material layer, the conductive concentration (C2) of the second active material layer corresponding to 1/3 to 2/3 of the thickness direction of the negative active material layer, and the conductive concentration (C3) of the third active material layer from 2/3 of the thickness direction of the negative active material layer to the surface is 10% or less.

In an electrochemical device according to one embodiment, the silicon particles may be included in an amount of 10 wt% or more with respect to the total weight of the negative electrode active material layer.

In an electrochemical device according to one embodiment, the conductive material may be one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF.

An electrochemical device according to one embodiment of the present invention can simultaneously satisfy high energy density, excellent life characteristics, and stability. Specifically, an electrochemical device according to one embodiment can effectively suppress the occurrence of a polarization phenomenon even when a thick film type cathode is employed, and can implement uniform charge/discharge characteristics.

In addition, the electrochemical device enables stable high-speed charging because lithium metal is not deposited on the surface of the cathode even when fast-charging with a current more than twice the magnetic capacity.

Unless otherwise defined, technical and scientific terms used in this specification have the meaning commonly understood by a person of ordinary skill in the art to which this invention belongs, and descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention in the following description or accompanying drawings are omitted.

The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Therefore, the scope of the present invention is not limited to the embodiments described below.

The terminology used in the description of the present invention is for the purpose of describing embodiments of the present invention only and should not be taken to be limiting. Unless clearly used otherwise, the singular form includes the plural form.

The term "comprises," as used herein, is an open-ended description equivalent to the expressions "comprises," "contains," "has," or "characterized by," and does not exclude additional elements, materials, or processes not listed herein.

Units used herein, unless otherwise specified, are based on weight, and as an example, units of % or ratio mean weight% or weight ratio, and weight% means the weight % that any one component occupies in the composition among the entire composition, unless otherwise defined.

In addition, the numerical range used in this specification includes the lower and upper limits and all values within that range, the increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of the upper and lower limits of the numerical range defined in different shapes. Unless otherwise specifically defined herein, values outside the numerical range that may arise due to experimental error or rounding of values are also included in the defined numerical range.

In this specification, terms such as ‘top’, ‘upper part’, ‘top surface’, ‘bottom’, ‘lower part’, ‘bottom’, and ‘side’ are based on the drawings, and may actually vary depending on the direction in which elements or components are arranged.

Additionally, throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

In this specification, the present invention is described in detail through each embodiment according to the present invention, but each embodiment described in the specification should be considered not only to mean one embodiment but also to mean a combination with other embodiments. Therefore, the citation of a claim in the scope of the patent claims is only an example, and the technical idea of the present invention should not be interpreted only as a combination with the cited claim, and a combination with various claims is also included in the scope of the technical idea of the present invention.

The term "porous binder scaffold" as used herein refers to a structure in which a mesh structure is uniformly formed three-dimensionally by a binder, in which the binder forms a skeleton and pores are abundantly developed within the skeleton. The pores preferably have an open pore structure, and the porous mesh structure formed by the binder can act as a support in which a negative electrode active material (particle) and a conductive material can be evenly distributed. The pores may have a diameter of 0.1 ㎛ to 50 ㎛, and specifically, may have a diameter of 0.5 ㎛ to 10 ㎛. More specifically, the porous binder scaffold may be a support including fibers formed by self-assembly of an organic binder and a conductive material as a unit structure, and including a thin inner wall structure formed by secondary self-assembly of the fibrous unit structure. In other words, the binder scaffold is an open-cell foam formed by the inner wall structure, and an internal space can be partitioned by the inner wall structure. More specifically, the inner wall structure can be a porous inner wall, and the inner space can include a large number of pores compared to the pores formed in the inner wall structure. Negative active material particles can be positioned in the inner space. More specifically, the negative active material particles can be positioned in the inner space and be fixed by contact with the porous inner wall structure. A superior conductive network can be formed by the binder scaffold structure compared to a fibrous mesh structure, and excellent adhesion to the negative active material particles can be achieved.

In order to meet the performance requirements of next-generation lithium batteries, it is necessary to further increase the capacity by combining a thick-film type cathode with an increased thickness of the cathode active material layer.

However, a thick-film negative electrode with an increased negative active material layer thickness has a problem in that as the thickness of the negative active material layer increases, the negative electrode material becomes unevenly distributed, which easily causes cracks to occur during the negative electrode manufacturing process, and also reduces the life characteristics and stability of the electrochemical device including it.

The present invention solves the problems of the prior art as described above, and provides an electrochemical device, specifically a lithium secondary battery, which can simultaneously satisfy high energy density of 300 Wh/kg or more, excellent life characteristics, and stability. Here, when calculating the energy density, the weight (kg) of the electrochemical device means the weight of the final product including the weight of auxiliary materials such as a pouch and tab.

An electrochemical device according to one embodiment of the present invention comprises a cathode, a cathode and an electrolyte, wherein the cathode comprises: a cathode current collector; and a cathode active material layer formed on the cathode current collector, the cathode active material layer comprising a porous binder scaffold and cathode active material particles; wherein the cathode active material particles comprise silicon-based particles.

Here, the porous binder scaffold means a mesh structure in which the binder forms a skeleton and pores are richly developed within the skeleton, and the porous mesh structure can serve as a support in which negative electrode materials such as negative electrode active materials and conductive materials can be evenly distributed. That is, in the negative electrode according to one embodiment, by making the binder component microporous, cracks do not occur even when the negative electrode is thickened, and the negative electrode material is very evenly distributed to maintain excellent battery performance.

That is, the electrochemical device according to one embodiment can have an energy density of 250 Wh/kg or more, or 300 Wh/kg or more, and specifically, can realize a high energy density of 250 Wh/kg to 400 Wh/kg, or 300 Wh/kg to 360 Wh/kg, and can satisfy both excellent life characteristics and stability.

According to one embodiment, the electrochemical device may include the negative electrode active material layer in an amount of 50 wt% or less, 40 wt% or less, 30 wt% or less, and, but not limited to, 5 wt% or more, based on the total weight, and specifically, 5 to 50 wt%, or 10 to 50 wt%, or 15 to 50 wt%.

Additionally, the negative electrode active material particles may be included in an amount of 10 to 99 wt%, 20 to 99 wt%, 30 to 99 wt%, or 50 to 99 wt% with respect to the total weight of the negative electrode active material layer.

In addition, the negative electrode may have a negative electrode active material layer thickness of 50 ㎛ or more, or 100 ㎛ or more, or 200 ㎛ or more, or 2,000 ㎛ or less, or 1,500 ㎛ or less, or 1,000 ㎛ or less, and may be a thick-film negative electrode having a thickness of 150 to 2,000 ㎛, or 100 to 2,000 ㎛, or 100 to 1,000 ㎛, or 100 to 500 ㎛, or 200 to 500 ㎛.

In addition, the negative electrode may be a thick film negative electrode having a capacity per area of a negative electrode active material layer formed on one surface of a negative electrode current collector of 4 to 15 mAh/cm ² , 4 to 10 mAh/cm ² _, or 4 to 8 mAh/cm ² .

Additionally, the negative electrode may be a thick-film negative electrode having a negative electrode active material layer composite density (g/cc) of 1.0 to 2.5, or 1.2 to 2.3, or 1.4 to 2.0.

In addition, the cathode may have an electrode tortuosity (τ) calculated by the following relationship of 8 or less, 7 or less, 6 or less, or 5 or less, and may be, but is not limited to, 1 or more. Specifically, the electrode tortuosity may be 1 to 8, 2 to 7, 3 to 6, 3 to 5, or 3 to 4.

[Relationship]

τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity)

In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the cathode, and Porosity represents the porosity of the cathode.

An electrochemical device including such a cathode has excellent ion conductivity and can have excellent battery performance because the ion transfer path within the electrode is relatively short.

According to one embodiment, the electrochemical device may be such that lithium metal is not deposited on the surface of the negative electrode when charged at a rate of 2.0C. At this time, whether lithium metal is deposited is determined through the negative electrode potential during the charging process when charging and discharging under constant current (CC) conditions. If the negative electrode potential drops below 0 V, it is considered that lithium plating has occurred, and if it is above 0 V, on the contrary, it is considered that lithium plating has not occurred.

That is, the negative electrode active material layer according to one embodiment does not generate cracks at all even though it is high-density/high-loaded, and the negative electrode material can be very evenly distributed in the thickness direction, and uniform lithium ion flow characteristics and uniform charge/discharge characteristics in the thickness direction can be effectively maintained.

In addition, the negative electrode active material layer according to one embodiment can implement excellent mechanical properties even using a small amount of binder since the binder forms a porous scaffold structure, and thus the content of negative electrode active material particles can be further increased, thereby implementing an even better energy density.

According to one embodiment, the porous binder scaffold may be included in an amount of 0.01 to 40 parts by weight, or 0.01 to 20 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 5 parts by weight, or 0.01 to 1 part by weight, relative to 100 parts by weight of the negative active material particles.

As described above, the negative active material particles may include silicon-based particles.

The above silicon-based particles may be any one or a combination of two or more selected from the group consisting of silicon nanoparticles (Si), silicon oxide (SiOx: x=0.2 to 1.9), a Si-Q alloy (wherein Q is one or a combination of two or more selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, and rare earth elements, and is not Si or C), and a silicon-carbon composite. The silicon-carbon composite may be a silicon-carbon composite (Si/C) in which silicon nanoparticles (Si) are dispersed and complexed in a carbon matrix, or a silicon-carbon composite having a core-shell structure in which silicon nanoparticles form a core and have a carbon coating layer. Or, as a non-limiting example, the silicon-carbon composite may be formed by depositing a silicon (Si) layer on the surface of a graphite core, but is not limited thereto.

In one embodiment of the present invention, the negative active material layer may include 10 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, and, but not limited to, 99 wt% or less of the silicon-based particles based on the total weight, and specifically, may include 10 to 99 wt%, 20 to 80 wt%, or 30 to 70 wt%.

In one embodiment of the present invention, the negative electrode active material particles may further include graphite particles. At this time, the negative electrode active material layer may include 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, and, but not limited to, 95 wt% or less of the graphite particles based on the total weight, and specifically, may include 30 to 95 wt%, 40 to 80 wt%, or 50 to 70 wt%.

The above graphite particles may be artificial graphite, natural graphite, or a mixture of artificial graphite and natural graphite. The artificial graphite may include structured artificial graphite, secondary particles assembled from two or more artificial graphite primary particles, or a mixture thereof, and the natural graphite may include natural graphite spheroidized by mechanical force, secondary particles assembled from natural graphite primary particles, natural graphite in a flake shape, or a mixture thereof, but is not limited thereto. In addition, the graphite particles may have a structure in which artificial graphite or natural graphite is coated with amorphous carbon, but is not limited thereto.

In one embodiment of the present invention, the negative electrode active material particles may further include at least one known negative electrode active material.

The known negative electrode active material may be any material that can electrochemically absorb and release lithium ions. As a specific example, the negative electrode active material may include a carbon-based active material, a metal oxide-based active material, a metal active material, a composite thereof, or a mixture thereof.

In detail, the carbon-based active material may include, but is not limited to, soft carbon, hard carbon, composites thereof, or mixtures thereof.

In detail, metal oxide-based active materials include, but are not limited to, tin oxide, titanium oxide, nickel oxide, iron oxide (FeO), lithium-titanium oxide (LiTiO ₂ , Li ₄ Ti ₅ O ₁₂ ).

The metal active material may be any metal capable of absorbing and releasing lithium ions, and examples thereof include, but are not limited to, iron, aluminum, chromium, manganese, antimony, lead, zinc, tin, magnesium, cadmium, cesium, nickel, alloys thereof, or mixtures thereof.

The active material as a composite may be a composite of at least two materials selected from the group consisting of carbon-based active materials, silicon-based active materials, metal oxide-based active materials, and metal active materials. Representative examples of the active material in the form of a composite include, but are not limited to, a silicon-carbon composite, a silicon-silicon oxide composite, a silicon-carbon core-shell structure composite, and a metal-silicon-carbon composite.

The above porous binder scaffold may be any polymer binder commonly used in the relevant technical field, and either an aqueous polymer binder or a non-aqueous polymer binder may be used. Specifically, the polymer binder may be a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic resin, an imide-based resin, a cellulose-based resin, or the like. More specifically, the polymer binder is selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyvinylacetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, Examples include, but are not limited to, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluoroelastomer, or mixtures thereof.

Additionally, the negative active material layer according to one embodiment may further include a conductive material, in which case the conductive material may be contained or adsorbed in the porous binder scaffold.

The above conductive material is not particularly limited as long as it is commonly used in the relevant technical field, but as a non-limiting example, it may be a carbon-based conductive material, and the carbon-based conductive material may include a point-shaped carbon-based conductive material, a linear carbon-based conductive material, a plate-shaped carbon-based conductive material, or a mixture thereof. The point-shaped carbon-based conductive material may include acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon black, etc., the linear carbon-based conductive material may include carbon nanotubes, conductive carbon fibers, etc., and the plate-shaped carbon-based conductive material may include graphene, etc.

According to one embodiment, the above-described challenging material may be one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF (Vapor Grown Carbon Fiber, VGCF).

In addition, the negative electrode active material layer according to one embodiment may further include a metal salt, and the metal salt may be contained in or surface-adsorbed to at least one of the porous binder scaffold and the negative electrode active material particles. Specifically, the metal ion of the metal salt may be a metal ion (active ion) involved in an electrochemical reaction, and the salt may induce effective complexation of the carbon-based conductive material and the binder, and may remain contained in or surface-adsorbed to at least one of the porous binder scaffold structure and the negative electrode active material, and may remain in a crystal phase unique to the salt.

The metal salt may be included in an amount of 0.01 to 50 parts by weight, or 0.01 to 30 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 1 part by weight, relative to 100 parts by weight of the negative active material particles.

In addition, the weight ratio of the binder: metal salt is not particularly limited, but may be 1:0.1 to 1, 1:0.1 to 0.8, or 1:0.2 to 0.6.

The above metal salt may be a metal salt containing a sulfonyl group, in which case it may remain in the negative electrode to further improve the electrochemical properties of the negative electrode, improve the flame retardancy of the negative electrode, and further improve the wettability with respect to a liquid electrolyte.

The molecular weight (g/mole) of the above sulfonyl group-containing metal salt may be 1000 or less, specifically 500 or less, more specifically 400 or less, and may have a molecular weight of 20 or more, 50 or more, or 100 or more. In addition, the number of anions per molecule of the above sulfonyl group-containing metal salt may be 1 to 4, specifically 1 to 3, more specifically 1 to 2.

Specifically, the metal salt may be selected from the following chemical formula 1 or chemical formula 2, but is not limited thereto.

[Chemical Formula 1]

[Chemical formula 2]

(In the above chemical formulas 1 and 2,

n is 1 or 2;

A is a cation of valence n;

R ₁ to R ₃ are each independently a fluoro(C1-C7) alkyl or a fluoro group.)

For example, R ₁ to R ₃ can each independently be F, CFH ₂ , CF ₂ H, CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ or C ₅ H ₁₁ .

For example, the above A is a monovalent cation or a divalent cation, and the monovalent cation may be an alkali metal ion, and the divalent cation may be an alkaline earth metal ion or a post-transition metal ion. may be selected. Specifically, the A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

For example, the sulfonyl group-containing metal salt may be one or more selected from lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(perfluoroethanesulfonyl)imide, zinc trifluoromethanesulfonate, zinc di[bis(trifluoromethylsulfonyl)imide], and the like.

When a cross-section of the negative active material layer according to one embodiment is analyzed by X-ray CT, the deviation of the conductive material concentration (C ₁ ) of the first active material layer corresponding to 1/3 of the thickness direction of the negative active material layer from the boundary between the negative current collector and the negative active material layer, the conductive material concentration (C ₂ ) of the second active material layer corresponding to 1/3 to 2/3 of the thickness direction of the negative active material layer, and the conductive material concentration (C ₃ ) of the third active material layer from 2/3 of the thickness direction of the negative active material layer to _the surface may be 10% or less, 8% or less, 6% or less, 4% or less, 2% or less, 1% or less, or 0.1% or more. Specifically, the deviation may be 0.1 to 10%, 0.1 to 5%, 0.1 to 2%, or 0.1 to 1%.

That is, the negative electrode active material layer is characterized by having negative electrode materials such as conductive materials and negative electrode active material particles very uniformly distributed in the thickness direction as the thickness of the negative electrode active material layer increases by forming a porous binder scaffold by microporousing the binder component.

The above anode is not particularly limited as long as it is commonly used in electrochemical devices.

In one embodiment, the positive electrode may include a positive electrode active material layer containing a positive electrode active material.

Specifically, the cathode active material may use a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, at least one of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used, and a specific example thereof may be a compound represented by one of the following chemical formulas.

Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O 4 _-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α T _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α T ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α T _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α T ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); and Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); In the above chemical formulas, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; T is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J can be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The above positive and negative electrodes may be provided by forming the positive active material layer and the negative active material layer on a positive current collector and a negative current collector, respectively. The positive current collector and the negative current collector may be any positive current collector or negative current collector used in a typical lithium secondary battery. In detail, the positive current collector or the negative current collector may be any material that has excellent conductivity and is chemically stable during charge and discharge of the battery. Specifically, the positive current collector or the negative current collector may be any material that is conductive, such as graphite, graphene, titanium, copper, platinum, aluminum, nickel, silver, gold, aluminum, or carbon nanotubes, but the present invention is not limited thereto.

The above electrolyte may be a liquid electrolyte, a solid electrolyte or a combination thereof, and specifically may be a liquid electrolyte, and the liquid electrolyte may include a non-aqueous organic solvent and a lithium salt.

The above non-aqueous organic solvent may be selected from a cyclic carbonate solvent, a linear carbonate solvent, and a mixed solvent thereof, and the cyclic carbonate solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and mixtures thereof, and the linear carbonate solvent may be selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof. Specifically, the non-aqueous organic solvent may be a mixed solvent of a cyclic carbonate solvent and a linear carbonate solvent, and a mixing volume ratio of the cyclic carbonate solvent: linear carbonate solvent may be mixed and used in a volume ratio of 1:1 to 9, or 1:1 to 4.

The lithium salt may be one or a mixture of two or more selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI, but is not limited thereto. The concentration of the lithium salt may be included in a range of 0.6 M to 2.0 M.

That is, the cathode of the electrochemical device according to one embodiment has excellent wettability with respect to the electrolyte, so that the amount of electrolyte used can be reduced while realizing a further improved energy density.

Specifically, the cathode of the electrochemical device according to one embodiment may have a time required for the evaluation of electrolyte wettability of less than 500 seconds, less than or equal to 450 seconds, less than or equal to 400 seconds, less than or equal to 350 seconds, less than or equal to 300 seconds, and, but not limited to, greater than or equal to 50 seconds, specifically, greater than or equal to 50 seconds and less than or equal to 500 seconds, 60 to 450 seconds, 70 to 400 seconds, 80 to 350 seconds, 90 to 300 seconds, or 200 to 300 seconds.

The evaluation of the electrolyte wettability of the above negative electrode is performed in a dry atmosphere with a dew point temperature of -40℃ and a relative humidity of 1% or less, and 1㎕ of propylene carbonate (PC) solvent is dropped on the surface of the negative electrode, and the time required for the solvent to penetrate into the negative electrode and completely disappear is measured. The time point at which the solvent completely disappears is observed through an optical microscope, and means the time point at which the solvent titrated on the surface of the negative electrode completely disappears from the surface of the negative electrode and the solvent cannot be observed through an optical microscope.

In addition, the electrochemical device according to one embodiment may further include a separator, and the separator is not limited to one commonly used in the relevant technical field, but as a non-limiting example, for example, may be selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or a combination thereof, may be in the form of a non-woven fabric or a woven fabric, and may optionally be used in a single-layer or multi-layer structure.

Another embodiment of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, and having an energy density of 250 Wh/kg or more, wherein the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer comprising a binder, negative electrode active material particles, and a conductive material, wherein the negative electrode active material particles comprise silicon-based particles, and when a cross-section of the negative electrode active material layer is analyzed by X-ray CT, a deviation among a conductive material concentration (C1) of a first active material layer corresponding to 1/3 of the thickness direction from the boundary between the negative electrode current collector and the negative electrode active material layer, a conductive material concentration (C2) of a second active material layer corresponding to 1/3 to 2/3 of the thickness direction of the negative electrode active material layer, and a conductive material concentration (C3) of a third active material layer from 2/3 to the surface in the thickness direction is 10% or less with respect to an average conductive material concentration (C0) of the negative electrode active material layer. Specifically, the deviation may be 8% or less, 6% or less, 4% or less, 2% or less, 1% or less, and, but not limited to, 0.1% or more, and more specifically, 0.1 to 10%, 0.1 to 5%, 0.1 to 2% or 0.1 to 1%.

Hereinafter, descriptions of the negative active material particles, binder, conductive material, positive electrode, and electrolyte are omitted as they are the same as described above.

In the above electrochemical device, the binder can form a porous binder scaffold structure forming a skeleton of a network structure in which pores are richly developed, and the porous network structure can serve as a support in which negative electrode materials such as negative electrode active material particles and conductive materials can be evenly distributed. That is, the negative electrode according to one embodiment can maintain excellent battery performance by making the binder component microporous so that the negative electrode material is very evenly distributed.

Specifically, the electrochemical device according to one embodiment can have a high energy density of 250 Wh/kg or more, or 300 Wh/kg or more, and specifically, can realize a high energy density of 250 Wh/kg to 400 Wh/kg, or 300 Wh/kg to 360 Wh/kg, and can satisfy both excellent life characteristics and stability.

According to one embodiment, the electrochemical device may include a negative electrode active material layer in an amount of 50 wt% or less, 40 wt% or less, 30 wt% or less, and, but not limited to, 5 wt% or more, based on the total weight, and specifically, 5 to 50 wt%, or 10 to 50 wt%, or 15 to 50 wt%.

Additionally, the negative electrode active material particles may be included in an amount of 10 to 99 wt%, 20 to 99 wt%, 30 to 99 wt%, or 50 to 99 wt% with respect to the total weight of the negative electrode active material layer.

In addition, the negative electrode may have a negative electrode active material layer thickness of 50 ㎛ or more, or 100 ㎛ or more, or 200 ㎛ or more, or 2,000 ㎛ or less, or 1,500 ㎛ or less, or 1,000 ㎛ or less, and may be a thick-film negative electrode of 150 to 2,000 ㎛, or 100 to 2,000 ㎛, or 100 to 1,000 ㎛, or 100 to 500 ㎛, or 200 to 500 ㎛.

In addition, the negative electrode may be a thick film negative electrode having a capacity per area of a negative electrode active material layer formed on one surface of a negative electrode current collector of 4 to 15 mAh/cm ² , 4 to 10 mAh/cm ² _, or 4 to 8 mAh/cm ² .

Additionally, the negative electrode may be a thick-film negative electrode having a negative electrode active material layer composite density (g/cc) of 1.0 to 2.5, 1.2 to 2.3, or 1.3 to 2.0.

In addition, the cathode may have an electrode tortuosity (τ) calculated by the following relationship of 8 or less, 7 or less, 6 or less, or 5 or less, and may be non-limitingly 1 or more. Specifically, the electrode tortuosity may be 1 to 8, 2 to 7, 3 to 6, 3 to 5, or 3 to 4.

[Relationship]

τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity)

In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the cathode, and Porosity represents the porosity of the cathode.

An electrochemical device including such a cathode has excellent ion conductivity and can have excellent battery performance because the ion transfer path within the electrode is relatively short.

According to one embodiment, the negative electrode active material layer has no cracks at all even when it is high-density/high-loaded, and the negative electrode material can be very evenly distributed in the thickness direction, and uniform lithium ion flow characteristics and uniform charge/discharge characteristics in the thickness direction can be effectively maintained.

In addition, the negative electrode active material layer according to one embodiment can implement excellent mechanical properties even using a small amount of binder since the binder forms a porous scaffold structure, and thus the negative electrode active material content can be further increased, thereby implementing an even better energy density.

According to one embodiment, the porous binder scaffold may be included in an amount of 0.01 to 40 parts by weight, or 0.01 to 20 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 5 parts by weight, or 0.01 to 1 part by weight, relative to 100 parts by weight of the negative active material particles.

Additionally, the negative electrode active material layer according to one embodiment may further include a metal salt, and the metal salt may be contained in or surface-adsorbed in at least one of the porous binder scaffold and the negative electrode active material particles.

The metal salt may be included in an amount of 0.01 to 50 parts by weight, or 0.01 to 30 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 1 part by weight, based on 100 parts by weight of the negative active material particles. Since a description of the type of the metal salt is as described above, it is omitted.

In addition, the ratio (g/Ah) of the electrolyte injection amount to the capacity of the electrochemical device according to one embodiment may be less than 3.0, less than 2.0, less than 1.5, less than 1.2, or less than 1.1. At this time, the electrolyte may be a liquid electrolyte in which 1 mol of LiPF ₆ is dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1.

That is, the cathode of the electrochemical device according to one embodiment has excellent wettability with respect to the electrolyte, so that the amount of electrolyte used can be reduced while realizing a further improved energy density.

According to one embodiment of the present invention, the means for forming a porous binder scaffold by microporousing the binder component is not particularly limited, but may be, for example, using a pore former when preparing a negative electrode material slurry, and the pore former may be, for example, a mixed solvent of two or more kinds having different solubility parameters, a metal salt, or a combination thereof.

Description of the above metal salts is omitted as they are as described above.

The above mixed solvent may be, specifically, a mixed solvent of a first solvent and a second solvent having different solubility parameters, and the first solvent and the second solvent may have different solubilities with respect to the binder due to the different solubility parameters. Due to the different solubilities between the solvents, solidification of the binder may occur in a state where the solvent remains during the drying process of the negative electrode slurry, and porosity of the binder component may occur in the negative electrode due to volatilization of the residual solvent during and/or after solidification of the binder.

The difference in the solubility parameters between the first solvent and the second solvent may be 0.1 to 20, or 0.1 to 10, or 0.1 to 5, or 1 to 5, and specifically, may be 0.5 or more, 1 or more, 2 or more, 3 or more, or 4 or more, and may be 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less.

Here, the solubility parameter (based on 25°C) may be based on a known value through the Hansen solubility parameter for each substance (e.g., Charles Hansen, "Hansen Solubility Parameters: A User's Handbook" CRC Press (2007), "The CRC Handbook and Solubility Parameters and Cohesion Parameters," Allan F. M. Barton (1999)), etc.) or a value calculated by commercial software such as Molecular Modeling Pro or Dynacomp Software, and the Hansen solubility parameter for each substance is a value that is already known to those skilled in the art or can be easily calculated.

For example, when a solvent having excellent solubility in the binder is referred to as a first solvent and a solvent having poor solubility in the binder is referred to as a second solvent, the second solvent can act as a pore former, and the degree of porosity of the binder can be controlled by controlling the relative amounts of the first solvent and the second solvent. For example, the weight ratio of the first solvent to the second solvent can be 1:0.1 to 10, 1:0.1 to 5, 1:0.1 to 1, or 1:0.1 to 0.5, but is not necessarily limited thereto.

According to one embodiment of the present invention, a method for manufacturing an electrochemical device is provided, comprising: a positive electrode, a negative electrode, and an electrolyte; wherein the negative electrode comprises a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer comprising a porous binder scaffold and negative electrode active material particles; wherein the negative electrode active material particles comprise silicon-based particles.

According to one embodiment, the method for manufacturing the electrochemical device includes the steps of manufacturing a positive electrode including a positive electrode active material layer on a positive electrode current collector; the step of manufacturing a negative electrode including a negative electrode active material layer on a negative electrode current collector; the step of assembling the positive electrode and the negative electrode; and the step of injecting an electrolyte.

The order in which the steps of manufacturing the positive electrode and the steps of manufacturing the negative electrode are performed is not limited. Specifically, the negative electrode may be manufactured after the positive electrode is manufactured, or alternatively, the positive electrode may be manufactured after the negative electrode is manufactured. In addition, it goes without saying that the positive electrode and the negative electrode may be manufactured simultaneously.

Since the positive electrode, negative electrode, and electrolyte are the same as those described above, a detailed description is omitted.

The above negative active material layer includes a binder scaffold, negative active material particles, a conductive material, and a metal salt, and the negative active material particles include silicon-based particles.

According to one embodiment, the step of manufacturing the negative electrode may include a step of applying a negative electrode material slurry including the above-described negative electrode active material particles, a conductive material, a binder, and a metal salt on a (negative electrode) current collector, and a step of drying the applied negative electrode material slurry.

In addition, the manufacturing step of the positive electrode may include a step of applying a positive electrode material slurry including the positive electrode active material described above on a (positive electrode) current collector and a step of drying the applied positive electrode material slurry.

The application of the negative electrode slurry and the positive electrode slurry may be performed by one or more methods selected from spin coating, roll coating, spray coating, dip coating, flow coating, doctor blade, dispensing, inkjet printing, offset printing, stencil printing, screen printing, pad printing, gravure printing, reverse gravure printing, gravure offset printing, flexography printing, stencil printing, imprinting, xerography, slot die coating, bar coating, and roll-to-roll coating, but is not limited thereto.

After the application of the negative electrode material slurry and the positive electrode material slurry is performed, a step of drying the slurry application (the applied negative electrode material (or positive electrode material) slurry) may be performed. The drying may be performed by applying energy, or may be performed through natural drying or vacuum drying without separately applying energy. The applied energy may be thermal energy, light energy, or heat and light energy, and the application of the heat and light energy may include sequential application or simultaneous application. When light energy is applied, the light may be near-infrared light, which is a heat ray.

The above drying can be performed in a multi-stage manner, and the drying method of each stage can be the same or different. As a non-limiting example, hot air drying can be performed first, followed by vacuum drying second.

The drying temperature is not particularly limited as long as it is a temperature capable of drying the slurry coating. As a non-limiting example, the drying temperature may be performed at a temperature of 70 to 180° C., 80 to 160° C., 80 to 140° C., or 80 to 130° C. The drying time may be appropriately adjusted in proportion to the amount of the slurry coating applied.

The negative electrode material slurry can be prepared by mixing the negative electrode active material particles, conductive material, binder, and metal salt described above in the mixed solvent described above. When preparing the negative electrode material slurry, the order of adding the negative electrode active material particles, conductive material, binder, and metal salt is not particularly limited. For example, the negative electrode material slurry can be prepared by simultaneously adding and mixing the negative electrode active material particles, conductive material, binder, and metal salt to the solvent. As another example, the negative electrode material slurry can be prepared by first adding the negative electrode active material particles to a mixture in which the conductive material, binder, and metal salt are mixed. The negative electrode material slurry prepared in this way can form a more stable porous binder scaffold structure when dried later to form a negative electrode active material layer.

In one embodiment, the negative electrode material slurry preparation step may include a step of preparing an active material mixture by mixing an ionic material (metal salt) and negative electrode active material particles, and a step of mixing the negative electrode material obtained by mixing the active material mixture, a conductive material, and a binder into the above-described mixed solvent.

The step of preparing the above active material mixture may include a step of mixing an ionic material and negative active material particles and then calcining them.

The above mixing may mean mechanical mixing through a stirring device such as a rotary mixer, and the mixing speed (rpm) and mixing time may be appropriately adjusted according to the amount of ionic material and negative electrode active material particles introduced.

The above-mentioned calcination can be performed at a temperature below the melting point of the ionic material, and is not particularly limited as long as it is a temperature higher than room temperature (20±5°C) and a temperature below the melting point (MP) of the ionic material. Non-limitingly, the temperature of the above-mentioned calcination may be 0.5 (MP) or more and less than 1 (MP), 0.5 (MP) to 0.9 (MP), or 0.6 (MP) to 0.8 (MP) with respect to the melting point (MP) of the ionic material. As a non-limiting example, when the ionic material is lithium trifluoromethanesulfonate, the above-mentioned calcination can be performed at a temperature of 150 to 300°C, 160 to 250°C, or 180 to 220°C.

Here, the heating rate during the firing may be, but is not limited to, 1 to 30°C/min, 1 to 15°C/min, 1 to 10°C/min, or 3 to 7°C/min.

The time for which the above-mentioned calcination is performed can be appropriately adjusted depending on the amount of the active material mixture introduced, and can be performed for, but not limited to, 10 to 180 minutes, 20 to 150 minutes, or 30 to 90 minutes.

Hereinafter, the present invention will be specifically described through examples. However, it should be noted that the examples described below are only intended to illustrate and concretize the present invention, and are not intended to limit the scope of the rights of the present invention. This is because the scope of the rights of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[Example 1]

1) Manufacturing of cathode

A mixture of 40 wt% of SiO _x (x=1.1) particles having an average particle size of 6 ㎛ and 50 wt% of natural graphite powder having an average particle size ( _D50 ) of 13 ㎛ as a negative electrode active material, 3 wt% of carbon black (Super-P) having an average particle size of 40 nm as a conductive material, 3 wt% of styrene-butadiene rubber, 3 wt% of carboxymethyl cellulose as a binder, and 1 wt% of lithium bis(trifluoromethanesulfonyl)imide as an additive (metal salt) (total 100 wt%) was used as the negative electrode material. Then, the negative electrode material was added to a mixed solvent of 37.5 wt% of distilled water and 7.5 wt% of propylene carbonate at 55 wt% to prepare a negative electrode material slurry (total 100 wt%). The above-mentioned negative electrode material slurry was applied to a copper film having a thickness of 8 ㎛ using a doctor blade, dried with hot air at 100 ° C., vacuum-dried at 130 ° C. for 24 hours, and rolled using a roll press to manufacture an example negative electrode including a 60 ㎛ thick negative electrode active material layer in which negative electrode active material particles are evenly distributed within a porous binder scaffold structure.

2) Manufacturing of positive electrode

A cathode material was prepared by using 94 wt% of a lithium-nickel-manganese-cobalt composite oxide (LiNi _0.9 Mn _0.05 Co _0.05 O ₂ ) as a cathode active material, 3 wt% of carbon black (Super-P) with an average particle size of 40 nm as a conductive material, and 3 wt% of polyvinylidene fluoride as a binder. Then, the cathode material was added to a single solvent of N-methyl-2-pyrrolidone in an amount of 55 wt% to prepare a cathode material slurry. The cathode material slurry was applied to a 20 ㎛ thick aluminum thin film using a doctor blade, dried with hot air at 100 ℃, vacuum-dried at 130 ℃ for 24 hours, and rolled using a roll press to prepare a cathode having a 110 ㎛ thick cathode active material layer.

3) Manufacturing of electrochemical devices

The above-mentioned positive and negative electrodes and separator (thickness 13 ㎛, SC13-D4-BP, Gelec) were laminated to manufacture a battery assembly, and an aluminum battery tab (0.1 T × 7 mm) was ultrasonically welded to the non-coated portion of the positive electrode assembly, and a nickel battery tab (0.1 T × 7 mm) was welded to the non-coated portion of the negative electrode assembly, respectively. Then, the battery assembly was placed in a formed battery pouch film (153 ㎛, DNP) and sealed. Thereafter, an electrochemical device was manufactured by injecting 2.00 g/Ah of a liquid electrolyte containing 1 mol of LiPF ₆ dissolved in a solvent containing ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[Example 2]

An electrochemical device was manufactured in the same manner as in Example 1, except that poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]) was used as an additive instead of lithium bis(trifluoromethanesulfonyl)imide during the manufacture of the negative electrode.

[Example 3]

An electrochemical device was manufactured in the same manner as in Example 1, except that a mixture of trimethylolpropane ethoxylate triacrylate and lithium trifluoromethanesulfonate in a ratio of 50:50 mass% was used instead of lithium bis(trifluoromethanesulfonyl)imide as an additive when manufacturing the negative electrode.

[Example 4]

An electrochemical device was manufactured in the same manner as in Example 1, except that cesium bis(trifluoromethanesulfonyl)imide was used instead of lithium bis(trifluoromethanesulfonyl)imide as an additive in the manufacture of the negative electrode.

[Example 5]

In the above Example 1, an electrochemical device was manufactured in the same manner as in Example 1, except that the negative electrode material was manufactured by mixing the active material mixture, conductive material, and binder after manufacturing the active material mixture during the manufacture of the negative electrode. The active material mixture was manufactured by pre-mixing lithium trifluoromethanesulfonate, natural graphite powder, and SiO _x (x=1.1) particles using a rotary mixer at 2000 rpm for 3 minutes, placing the mixture in a furnace, heating it to 200 ℃ at a heating rate of 5 ℃/min, maintaining it at that temperature for 1 hour, and then firing it. Then, the sintered product was naturally cooled to room temperature (25±5 ℃).

[Example 6]

In the above Example 1, except that 6 wt% of polyvinylidene fluoride was added instead of 3 wt% of styrene-butadiene rubber and 3 wt% of carboxymethyl cellulose as a binder during the manufacture of the negative electrode, a negative electrode material was manufactured in the same manner as in Example 1. Then, an electrochemical device was manufactured in the same manner as in Example 1, except that a negative electrode slurry was manufactured using a mixed solvent of 37.5 wt% of N-methyl-2-pyrrolidone and 7.5 wt% of propylene carbonate instead of the mixed solvent of Example 1.

[Comparative Example 1]

In the above Example 1, the negative electrode material was manufactured in the same manner as in Example 1, except that 4 wt% of the conductive material was added instead of 3 wt% of the conductive material during the manufacture of the negative electrode, and no additive was added. Then, an electrochemical device was manufactured in the same manner as in Example 1, except that distilled water was used instead of the mixed solvent of Example 1, and a negative electrode slurry of 40 wt% of distilled water and 60 wt% of the negative electrode material was manufactured, and then the negative electrode slurry was applied to a copper thin film having a thickness of 8 ㎛.

<Evaluation 1. Electrochemical device performance evaluation>

1-1. Energy density (Wh/kg)

The energy density was calculated by dividing the unit cell energy (Wh) of the electrochemical devices of the examples and comparative examples by the total weight (Kg) of the electrochemical devices. For other specific measurement conditions of energy density, energy density refers to a non-patent literature (Park, S.-H. et al. High areal capacity battery electrodes enabled by segregated nanotube networks. Nat. Energy 4, 560-567 (2019).). Here, the total weight of the electrochemical device means the weight of the final electrochemical device product including the weight of all auxiliary materials such as pouches and tabs, and the unit cell energy was measured by integrating the 0.05 C discharge graph. The results are shown in Table 1 below.

1-2. Capacity implementation rate (%)

The electrochemical devices of the examples and comparative examples were charged at 0.1 C-rate to 4.4 V under constant current/constant voltage (CC/CV) conditions at 25°C and then cut-off. Thereafter, they were discharged at 0.1 C-rate to 3.0 V (CC conditions). The capacity implementation rate was evaluated as a percentage of the discharge capacity divided by the design capacity. Here, the design capacity means a value calculated from the total weight of the negative active material included in the cell and the reversible discharge capacity of the negative active material. The results are shown in Table 1 below.

division Energy density (Wh/kg) Capacity implementation rate (%) Example 1 346 94.8 Example 2 348 95.3 Example 3 345 94.5 Example 4 348 95.3 Example 5 355 97.3 Example 6 360 98.6 Comparative Example 1 218 59.7

Referring to Table 1 above, it was confirmed that the electrochemical device according to the embodiment can simultaneously implement high energy density and excellent capacity retention. That is, it can be seen that the electrochemical device according to the present invention can implement high energy density while maintaining excellent life characteristics even when employing a thick-film negative electrode. In addition, the negative electrode according to Example 1 confirmed a capacity per area of 4.4 mAh/ ^cm2 under 0.1C/0.1C conditions and a voltage range of 3.0-4.4 V.

1-3. Lithium-Plating Evaluation

In the electrochemical devices manufactured in the Examples and Comparative Examples, lithium was inserted as a reference electrode to manufacture a three-electrode cell, and the occurrence of lithium plating on the surface of the negative electrode was evaluated using the three-electrode cell. The electrochemical device was charged at a rate of 0.1 C/0.2 C/0.5 C/1.0 C/1.5 C/2.0 C/3.0 C/5.0 C up to 4.5 V under constant current (CC) conditions, and discharged at 0.2 C-rate. While the charge and discharge current of the electrochemical device was applied, the potential change of the negative and positive electrodes of the three-electrode cell was analyzed, respectively, to evaluate the deposition of lithium metal on the surface of the negative electrode. Specifically, when lithium is deposited on the surface of the negative electrode and begins to be plated during the charging process, the potential of the negative electrode changes to a negative (-) value. Accordingly, the point in time when the potential of the negative electrode begins to drop below 0 V was determined to be the point in time when lithium metal is deposited and lithium plating occurs, and the charge rate at which the potential of the negative electrode begins to drop below 0 V is shown in Table 2 below. The results of the lithium-plating evaluation of the negative electrodes manufactured in the above examples and comparative examples are shown in Table 2 below.

division Charge rate generation at negative potential below 0 V Example 1 3.0 C Example 2 3.0 C Example 3 3.0 C Example 4 3.0 C Example 5 3.0 C Example 6 3.0 C Comparative Example 1 1.5 C

As shown in Table 2 above, the electrochemical devices according to Examples 1 to 6 showed a positive (+) value in the potential of the negative electrode when charged at a rate of 2.0C, and changed to a negative (-) value only under a charge rate condition of 3.0C. On the other hand, in the case of the comparative example, the potential of the negative electrode changed to a negative (-) value when charged at a rate of 1.5C. Through this, it was confirmed that the electrochemical devices according to the examples did not cause lithium plating even when charged with a current twice the self-capacity, and that lithium plating was effectively suppressed even at a high charge rate compared to the comparative example. As a result of the evaluation of the electrochemical device, the electrochemical device according to the present invention was able to satisfy high energy density of 250 Wh/kg or more and excellent life characteristics and stability at the same time by combining a thick-film negative electrode in which the negative electrode material is very uniformly distributed in the thickness direction and a specific positive electrode. Furthermore, the electrochemical device has uniform lithium ion flow characteristics even when charged with a current more than twice its magnetic capacity, and lithium is not deposited on the surface of the negative electrode, effectively suppressing lithium plating, thereby providing a product with improved safety.

<Evaluation 2. Evaluation of cathode properties>

2-1. Evaluation of cathode appearance

The appearance of the surfaces of the negative electrodes manufactured in Example 1 and Comparative Example 1 was evaluated using a scanning electron microscope (SEM) analysis. In the case of the negative electrode manufactured in Comparative Example 1, it was confirmed that numerous cracks occurred on the electrode appearance due to uneven distribution of the conductive agent/binder during slurry coating and drying. On the other hand, in the negative electrode of Example 1, it was confirmed that no cracks occurred on the electrode appearance because the negative electrode active material coating layer was evenly applied on the current collector without mechanical deformation and a uniform binder scaffold structure was formed in the direction of the entire electrode thickness.

As a result of observing the cross-section of the negative electrode manufactured in Example 1 using a scanning electron microscope, it was confirmed that the negative active material particles were evenly distributed throughout and that the binder formed a uniform scaffold structure in the empty spaces between the particles. On the other hand, in the case of the negative electrode manufactured in the comparative example, it was found that the binders were clumped together and had an uneven microstructure and pore distribution.

2-2. Cathode X-ray CT analysis

The cross-sections of the negative electrodes manufactured in Example 1 and Comparative Example 1 were X-ray CT scanned to analyze the distribution of the conductive material, carbon black, in the thickness direction. As a result, it was confirmed that the negative electrode of Comparative Example 1 had an uneven distribution of the conductive material in the thickness direction. On the other hand, in the negative electrode of Example 1, it was confirmed that the conductive material distribution in the first active material layer corresponding to 1/3 of the thickness direction from the boundary between the negative electrode current collector and the negative electrode active material layer, the second active material layer from the 1/3 to the 2/3 point in the thickness direction, and the third active material layer from the 2/3 point in the thickness direction to the surface were all uniform. In addition, the distribution of the conductive material content (vol%) in the first active material layer, the second active material layer, and the third active material layer according to the X-ray CT scan results was quantified, and the results are shown in Table 3 below. Referring to Table 3, the negative electrode according to Example 1 showed a very low value of about 0.7% or less in the deviation of the conductive material concentration according to Equation 1 below, and through this, it was confirmed that the negative electrode active material layer of Example 1 had the conductive material very uniformly distributed.

[Formula 1]

(|C ₀ - C _n |/C ₀ ) × 100

In the above equation 1,

C ₀ is the average concentration (vol%) of the conductive material in the entire negative active material layer;

C _n is the conductive material concentration (vol%) of the nth active material layer.

division Challenge volume concentration (%) First active material layer Second active material layer Third active material layer Comparative Example 1 47 32.3 22.8 Example 1 35.2 34.8 33.5

2-3. Evaluation of ionic conductivity in the cathode Using the cathodes manufactured in the examples and comparative examples, a symmetric cell was manufactured, and a liquid electrolyte in which 1 mol of LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1 was injected to manufacture a cell for measuring ionic conductivity. The ionic resistance was measured through impedance analysis of the cell for measuring ionic conductivity, and the ionic conductivity value in the cathode was calculated. The results are shown in Table 4 below.

2-4. Evaluation of the electrode tortuosity of the cathode

The measured ionic conductivity values in the cathode were used to calculate the electrode curvature of the cathode using the MacMullin number (N _m ) formula. N _m can be defined as follows:

N _m = K _electrolyte / K _electrode = Tortuosity / Porosity

K _electrolyte refers to the ionic conductivity of the liquid electrolyte, and K _electrode refers to the ionic conductivity of the cathode measured at 25°C according to the examples and comparative examples. The liquid electrolyte was prepared by adding 1 M LiPF ₆ to a cosolvent containing ethylene carbonate (EC)/diethyl carbonate (DEC) in a volume ratio of 1:1. The ionic conductivity of the cathode was calculated by measuring the conductivity in the thickness direction of the electrode after filling the cathode with a 1 M LiPF ₆ EC/DEC solution. The porosity was measured using a mercury porosimeter (Mercury Porosimet, AutoPore V, Micromeritics) according to ASTM D 4284-83. Specifically, a pre-weighed cathode sample was placed in a mercury porosimeter cell, and the cell was filled with mercury to a given pressure range (30 psia to 60,000 psia) to measure the pore volume within the cathode. The tortuosity was finally calculated from the measured porosity and McMullin number. The measured electrode tortuosity is shown in Table 4 below.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Curvature 4.1 3.8 3.9 3.7 3.2 3.1 5.8 Ionic conductivity
(mS/cm) 0.46 0.5 0.49 0.52 0.59 0.62 0.33

Referring to Table 4 above, it was confirmed that the negative electrode according to the embodiment had improved curvature within the electrode compared to the negative electrode according to the comparative example. The curvature of the electrode (cathode) is affected by the pore structure formed within the electrode, and when the conductive agent and binder are unevenly distributed, a high curvature value is measured, which can be expected to result in a longer ion transfer path within the electrode and a decrease in battery performance. In the case of Comparative Example 1, it can be confirmed that the uneven distribution of the conductive agent and binder became more severe due to the high electrode loading, and the curvature of the electrode significantly increased. On the other hand, the electrode manufactured according to the embodiment evenly distributes the negative electrode active material within the uniformly formed porous binder scaffold structure by inducing interaction between the conductive agent, binder, and metal salt to suppress the unbalanced movement of the conductive agent and binder that occurs during electrode drying, and it can be confirmed that the curvature within the electrode does not significantly increase even with high electrode loading. In addition, in the case of the cathode of the embodiment, it was confirmed that by controlling the timing of adding the metal salt during the slurry preparation, the interaction between the conductive agent, binder and metal salt can be more easily induced, thereby further improving the structural characteristics of the porous binder scaffold.

2-5. Evaluation of electrolyte wettability (seconds) of the cathode

At a dew point temperature of -40℃ (relative humidity of 1% or less), 1 ㎕ of propylene carbonate (PC) solvent was dropped onto the surface of the cathode manufactured in the examples and comparative examples, and the time required for the solvent to penetrate into the electrode and completely disappear was measured, and the time required is shown as the required time in Table 5 below. The time point at which the solvent completely disappears is observed with the naked eye through an optical microscope, and means the time point at which the solvent titrated on the surface of the cathode completely disappears from the surface of the cathode.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 time taken
(candle) 287 297 300 287 253 291 632

Referring to Table 5 above, the negative electrodes of Examples 1 to 6 took a shorter time for the electrolyte to completely penetrate compared to the comparative examples, and it was confirmed that the electrolyte wettability was significantly improved through this. Through this, the negative electrode according to one embodiment exhibits excellent electrolyte wettability, thereby reducing the injection time or aging time of the manufacturing process, thereby increasing work efficiency, and improving the uniformity of battery performance. As described above, the present invention has been described by limited embodiments, but this has been provided only to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains can make various modifications and variations from this description. Therefore, the spirit of the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below, as well as the claims, fall within the scope of the spirit of the present invention.

Claims (23)

Contains a positive electrode, a negative electrode and an electrolyte, The negative electrode comprises a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer comprising a porous binder scaffold and negative electrode active material particles; An electrochemical device, wherein the negative active material particles include silicon particles. In paragraph 1, The above electrochemical device is an electrochemical device having an energy density of 250 Wh/kg or more. In paragraph 1, An electrochemical device, wherein the negative active material layer contains at least 10 wt% of the silicon particles based on the total weight. In the second paragraph, The above negative active material particles further include graphite particles, An electrochemical device, wherein the negative active material layer contains at least 50 wt% of the graphite particles based on the total weight. In paragraph 1, An electrochemical device, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. In paragraph 1, An electrochemical device further comprising a separator. In paragraph 1, An electrochemical device, wherein the above negative electrode is a thick-film negative electrode having a capacity per area of a negative electrode active material layer formed on one surface of a negative electrode current collector of 4 to 15 mAh/cm2. In paragraph 1, An electrochemical device, wherein the negative active material layer comprises negative active material particles evenly dispersed therein, and a porous binder scaffold exists in the empty space between the particles. In Article 8, An electrochemical device, wherein the porous binder scaffold is included in an amount of 0.01 to 40 parts by weight per 100 parts by weight of the negative active material particles. In Article 8 An electrochemical device, wherein the porous binder scaffold further comprises a conductive material. In Article 8 An electrochemical device, wherein the porous binder scaffold comprises one or more selected from the group consisting of a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic-based resin, an imide-based resin, and a cellulose-based resin. In Article 8 An electrochemical device, wherein the negative active material layer further includes a metal salt. In Article 12, An electrochemical device, wherein a metal salt is included in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the negative active material particles. In Article 12, An electrochemical device, wherein the metal salt is contained in or surface-adsorbed in at least one of a porous binder scaffold and negative active material particles. In Article 12, An electrochemical device, wherein the metal salt is a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2. [Chemical Formula 1]

[Chemical formula 2]

In the above chemical formulas 1 and 2, n is 1 or 2; A is a cation of valence n; R ₁ to R ₃ are each independently a fluoro(C1-C7)alkyl or a fluoro group. In Article 15 The above A is an electrochemical device comprising lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium. In paragraph 1, The above electrolyte is an electrochemical device, wherein the ratio (g/Ah) of the amount of electrolyte injected to the capacity of the electrochemical device is less than 3.0. In paragraph 1, The above electrochemical device is an electrochemical device in which lithium metal is not deposited on the surface of the negative electrode when charged at a rate of 2.0C. In the first paragraph, The above cathode is an electrochemical device having an electrode tortuosity (τ) of 5 or less, calculated by the following relationship. [Relationship] τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity) (In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the cathode, and Porosity represents the porosity of the cathode.) In the first paragraph, The above negative electrode is an electrochemical device, wherein the wettability evaluation time measured under the following measurement conditions is less than 500 seconds. [Measurement conditions] At a dew point temperature of -40℃ (relative humidity of 1% or less), 1 ㎕ of propylene carbonate (PC) solvent was dropped onto the cathode surface, and the time required for the solvent to penetrate into the cathode and completely disappear was measured. Contains a positive electrode, a negative electrode and an electrolyte, and has an energy density of 250 Wh/kg or more; The above negative electrode comprises a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector, the negative electrode active material layer comprising a binder, negative electrode active material particles, and a conductive material; The above negative active material particles include silicon particles, An electrochemical device, wherein when a cross-section of the negative active material layer is analyzed by X-ray CT, a deviation of a conductive material concentration (C1) of a first active material layer corresponding to a point 1/3 of the thickness of the negative active material layer from the boundary between the negative current collector and the negative active material layer, a conductive material concentration (C2) of a second active material layer corresponding to a point from the point 1/3 to the point 2/3 of the thickness of the negative active material layer, and a conductive material concentration (C3) of a third active material layer from the point 2/3 of the thickness of the negative active material layer to the surface is 10% or less. In Article 21, An electrochemical device, wherein the silicon particles are contained in an amount of 10 wt% or more based on the total weight of the negative electrode active material layer. In Article 21, An electrochemical device wherein the above-mentioned challenge material is one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF.