WO2024253469A1 - High-energy-density electrochemical device containing lithium iron phosphate - Google Patents

Abstract

The present invention relates to a high-energy-density electrochemical device containing lithium iron phosphate. The electrochemical device according to the present invention comprises a cathode, an anode and an electrolyte, wherein the cathode includes a cathode current collector and a cathode active material layer, which is formed on the cathode current collector and includes a porous binder scaffold and cathode active material particles, and the cathode active material particles include olivine-structured lithium iron phosphate-based particles on the basis of the total weight of the cathode active material layer.

Description

High energy density electrochemical device containing lithium iron phosphate

The present invention relates to a high energy density electrochemical device comprising lithium iron phosphate.

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, in addition to changing the anode material, research on thick-film anodes with increased thickness of the anode active material layer by increasing the density/high loading of the anode active material is actively being conducted.

However, as the positive electrode active material layer becomes thicker, problems such as physical cracks occurring during the manufacturing process or uneven distribution of components constituting the positive electrode, such as binders and conductive agents, throughout the volume of the positive electrode occur. Therefore, it is difficult to secure stable battery performance and life characteristics for a thick-film positive electrode, and thus there is a practical limit to increasing its thickness. A thick-film positive electrode with such unevenness causes uneven flow characteristics of lithium ions, and causes problems such as uneven charge/discharge characteristics in the thickness direction and polarization. In addition, the battery performance deteriorates due to the increase in the movement distance of lithium ions as the thickness of the positive electrode increases, and furthermore, such uneven flow characteristics of lithium ions further aggravate the problems of lithium metal precipitation and dendrite formation on the surfaces of lithium metal, graphite, and silicon negative electrodes, which not only shortens the life of the battery but also lowers the stability of the battery.

Meanwhile, lithium iron phosphate (LFP) is a promising cathode material that can be used in large-capacity secondary batteries because it is cheaper than other cathode active materials. However, it has a fatal disadvantage of low energy density compared to conventional lithium cobalt oxide (LCO) or ternary batteries such as NCM, NCA, and NCMA, despite its advantages in stability and cost-effectiveness.

Therefore, there is an urgent need for research and development of electrochemical devices with high energy density, excellent life characteristics, and stability, despite containing lithium iron phosphate as a cathode material.

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, an anode, 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 lithium iron phosphate particles having an olivine structure with respect to the total weight of the cathode active material layer.

In an electrochemical device according to one embodiment, the anode may have an electrode tortuosity (τ) of 7 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 anode, and Porosity represents the porosity of the anode.

In an electrochemical device according to one embodiment, the negative electrode may include a negative electrode active material layer containing 50 wt% or more of a graphite-based active material.

In an electrochemical device according to one embodiment, the energy density of the electrochemical device may be 180 Wh/kg to 400 Wh/kg.

In an electrochemical device according to one embodiment, the negative electrode may include a negative electrode current collector, or a negative electrode current collector and lithium metal.

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

In an electrochemical device according to one embodiment, the cathode active material layer may be included in an amount of 50 wt% or more with respect to the total weight of the electrochemical device.

In an electrochemical device according to one embodiment, the positive electrode may be a thick film having a positive electrode active material layer composite density (g/cc) of 2.2 to 2.6.

In an electrochemical device according to one embodiment, the positive electrode active material particles may be included in an amount of 80 to 99 wt% with respect to the total weight of the positive electrode active material layer.

In an electrochemical device according to one embodiment, the positive electrode may be a thick-film positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm2.

In an electrochemical device according to one embodiment, the cathode active material layer may have cathode 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 cathode 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 positive electrode 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 based on 100 parts by weight of the positive electrode 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 positive 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, the electrolyte may be included in a weight ratio of 15 to 30 parts per 100 parts by weight of the positive electrode.

In an electrochemical device according to one embodiment, a half-cell manufactured with the positive electrode may have a discharge capacity retention rate at 0.3 C of 70% or more compared to the discharge capacity at 0.1 C.

In an electrochemical device according to one embodiment, the electrochemical device may have a 0.1C discharge capacity realization ratio relative to the design capacity of 0.9 or more.

An electrochemical device according to another 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, comprising a binder, cathode active material particles, and a conductive material; wherein the cathode active material particles include lithium iron phosphate particles having an olivine structure, and the cathode is a thick-film cathode having a capacity per area of the cathode active material layer formed on one surface of the cathode current collector of 3.5 to 10 mAh/cm2, and when a cross-section of the cathode 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 1/3 of the thickness direction from the boundary between the cathode current collector and the cathode 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 cathode 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 cathode active material layer.

In an electrochemical device according to one embodiment, the lithium iron phosphate particles may be included in an amount of 60 wt% or more with respect to the total weight of the positive 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, despite containing lithium iron phosphate as a cathode material. Specifically, the electrochemical device can effectively suppress the occurrence of polarization phenomenon even though it employs a thick film type cathode, and can implement uniform charge/discharge characteristics.

Figure 1 shows the SEM analysis results of the anode surface manufactured in Comparative Example 1.

Figure 2 shows the results of SEM analysis of the surface of the anode manufactured in Example 1.

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 framework and pores are abundantly developed within the framework. The pores preferably have an open pore structure, and the porous mesh structure formed by the binder can act as a support in which positive electrode active material particles 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 the inner 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. Positive active material particles can be positioned in the inner space. More specifically, the positive active material particles can be positioned in the inner space and be fixed by contact with the porous inner wall structure. The binder scaffold structure can form a conductive network superior to a fibrous mesh structure, and can have excellent adhesion to the positive active material particles.

In order to meet the performance requirements of next-generation lithium batteries, it is necessary to replace the existing anode material with lithium metal or make it anode-free, and in addition, to increase the thickness of the anode active material layer by increasing the density/high loading of the anode active material to combine it with a thick film anode to further increase the capacity.

However, in the case of a thick film type cathode in which the thickness of the cathode active material layer is increased by making the cathode active material dense/loaded, as the thickness of the cathode active material layer increases, the components forming the cathode active material layer become unevenly distributed, which easily causes cracks to occur on the surface during the cathode manufacturing process, and the transfer of lithium ions in the cathode active material layer is not smooth, which reduces the output performance, lifespan, and safety of the electrochemical device.

In particular, when using lithium iron phosphate material with an olivine structure as a cathode material to manufacture a thick-film cathode with increased cathode thickness, there is a problem that cracks easily occur on the electrode surface, and the output performance, lifespan, and safety of the battery are rapidly reduced. In addition, lithium iron phosphate material with an olivine structure has a small particle size, making it difficult to thicken the electrode itself, and thus has a disadvantage of very low energy density.

The present invention has solved the problems of the prior art as described above, and an electrochemical device according to one embodiment of the present invention can simultaneously satisfy high energy density of 180 Wh/kg or more, excellent life characteristics, and stability by including a lithium iron phosphate material having an olivine structure as a cathode active material. Here, the weight (kg) of the electrochemical device when calculating the energy density 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, an anode, 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 are characterized in that they include lithium iron phosphate particles having an olivine structure with respect to the total weight of the cathode active material layer.

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 positive electrode materials such as positive electrode active material particles and conductive materials can be evenly distributed. That is, in the positive electrode according to one embodiment, cracks do not occur even when the positive electrode is thickened by making the binder component microporous, and the positive electrode material is very evenly distributed, so that excellent battery performance can be maintained.

That is, an electrochemical device according to one embodiment can realize a high energy density of 180 Wh/kg or more, or 180 Wh/kg to 400 Wh/kg, or 180 Wh/kg to 380 Wh/kg, despite containing lithium iron phosphate as a cathode material, and can satisfy both excellent life characteristics and stability.

According to one embodiment, the electrochemical device may include the cathode active material layer in an amount of 50 wt% or more, 55 wt% or more, or 60 wt% or more, or 95 wt% or less, or 90 wt% or less, or 88 wt% or less, or 50 to 90 wt%, or 60 to 90 wt%, or 60 to 85 wt%, based on the total weight.

Additionally, the positive electrode active material particles may be included in an amount of 70 to 99 wt%, 80 to 99 wt%, or 85 to 99 wt% with respect to the total weight of the positive electrode active material layer.

In addition, the positive electrode may have a positive 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 positive 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 positive electrode may be a thick film type positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm ² , 3.5 to 9 mAh/cm ² _, or 3.8 to 8 mAh/cm ² .

Additionally, the positive electrode may be a thick-film positive electrode having a positive electrode active material layer composite density (g/cc) of 2.0 to 4.0, or 2.0 to 3.0, or 2.2 to 2.6.

In addition, the electrode tortuosity (τ) calculated by the following relationship may be 10 or less, 8 or less, 7 or less, or 6 or less, and may be, but is not limited to, 1 or more. Specifically, the electrode tortuosity may be 1 to 10, 2 to 8, 3 to 7, 4 to 7, or 5 to 7.

[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 anode, and Porosity represents the porosity of the anode.

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.

Additionally, a half-cell manufactured with the positive electrode may have a discharge capacity retention rate at 0.3 C of 50% or more, or 60% or more, or 70% or more, or 74% or more, and may be from 60% to 99%, or from 70% to 98%, relative to the discharge capacity at 0.1 C. For non-limiting example, the measurement of the discharge capacity retention rate at 0.1 C and 0.3 C may be, but is not limited to, the retention rate measured after 1 charge, after 5 charges, after 10 charges, or after 30 charges.

In addition, the electrochemical device according to one embodiment may have a 0.1C discharge capacity implementation ratio relative to the design capacity of 0.8 or more, 0.85 or more, 0.9 or more, 0.95 or more, and may be from 0.8 to 1.0, or from 0.9 to 1.0, or from 0.95 to 1.0. Here, the design capacity means a theoretical value calculated from the total weight of positive active material particles included in the cell and the reversible discharge capacity of the positive active material particles.

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

In addition, the cathode 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 cathode 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 positive electrode active material particles.

The above positive electrode active material particles may include lithium iron phosphate particles represented by the following chemical formula.

[chemical formula]

LiM _x Fe _1-x PO ₄

In the above chemical formula, M is at least one metal selected from the group consisting of Co, Ni, and Mn, and 0≤x≤1, 0.0.1≤x≤0.8, or 0.01≤x≤0.6.

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

In one embodiment, the cathode active material particles may comprise less than 100 wt%, 99 wt% or less, 98 wt% or less, 97 wt% or less, 90 wt% or less, 80 wt% or less, and, but not limited to, 60 wt% or more of the lithium iron phosphate-based particles based on the total weight of the cathode active material. Specifically, the cathode active material particles may comprise 60 wt% or more and less than 100 wt%, 60 to 99 wt%, 65 to 99 wt%, 70 to 99 wt%, 80 to 99 wt%, 85 to 98 wt%, or 90 to 97 wt% of the lithium iron phosphate-based particles based on the total weight of the cathode active material particles. Alternatively, it should be understood that the cathode active material particles may comprise 100 wt% of the lithium iron phosphate-based particles based on the total weight of the cathode active material particles.

Specifically, a known positive electrode active material may be 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 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 positive electrode 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 positive 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 at least one of the porous binder scaffold and the positive 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 metal salt may induce effective complexation of the carbon-based conductive material and the binder, and may remain contained in or surface-adsorbed at least one of the porous binder scaffold structure and the positive 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, based on 100 parts by weight of the positive electrode 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 positive electrode to further improve the electrochemical properties of the positive electrode and further improve 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 positive electrode 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 a point 1/3 of the thickness of the positive electrode active material layer from the boundary between the positive electrode current collector and the positive electrode active material layer, the conductive material concentration (C ₂ ) of the second active material layer corresponding to a point from the point 1/3 to the point 2/3 of the thickness of the positive electrode active material layer, and the conductive material concentration (C ₃ ) of the third active material layer from the point _2/3 of the thickness of the positive electrode active material layer to the surface may be 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, and, but not limited to, 1% or more. Specifically, the deviation may be 1 to 10%, 1 to 7%, or 1 to 5%.

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

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

In one embodiment, the negative electrode includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material may be a material commonly used in a negative electrode of a lithium secondary battery. Specifically, the negative electrode active material may be a material capable of lithium intercalation. More specifically, the negative electrode active material may be one or more selected from, but is not limited to, lithium (metallic lithium), graphitizable carbon, non-graphitizable carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, Fe oxide (FeO), lithium-titanium oxide (LiTiO ₂ , Li ₄ Ti ₅ O ₁₂ ), mixtures thereof, or composites thereof.

According to one embodiment, the negative electrode may include a negative electrode active material layer containing 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, and not limited to 99 wt% or less of a graphite-based active material, specifically 50 to 99 wt%, 60 to 99 wt%, 70 to 99 wt%, 80 to 99 wt%, or 90 to 99 wt%.

At this time, the graphite-based active material may be artificial graphite or natural graphite. As a non-limiting example, the graphite-based active material may be natural graphite.

According to another embodiment, the negative electrode may include a negative current collector, or a negative current collector and lithium metal.

That is, an electrochemical device according to one embodiment may be a lithium metal battery including the above-described thick-film positive electrode; a negative electrode including a negative electrode current collector and lithium metal formed on the negative electrode current collector; and an electrolyte.

In addition, an electrochemical device according to one embodiment may be an anode-free lithium battery including the above-described thick-film positive electrode; a negative electrode current collector; and an electrolyte.

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.

For example, the liquid electrolyte may have a ratio of the amount of electrolyte injected to the capacity of the electrochemical device according to one embodiment (g/Ah) of less than 3.0, less than 2.0, less than 1.5, less than 1.2, or less than 1.1. In addition, the liquid electrolyte may be included in a weight ratio of 15 to 30, or a weight ratio of 15 to 25, or a weight ratio of 15 to 20, with respect to 100 parts by weight of the positive electrode.

That is, the positive electrode 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.

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, wherein the positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising a binder, positive electrode active material particles, and a conductive material; wherein, when a cross-section of the positive electrode 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 direction from a boundary between the positive electrode current collector and the positive electrode active material layer, a conductive material concentration (C2) of a second active material layer corresponding to a point 1/3 to 2/3 of the thickness direction of the positive electrode active material layer, and a conductive material concentration (C3) of a third active material layer from the point 2/3 of the thickness direction of the positive electrode active material layer to the surface is 10% or less.

Hereinafter, descriptions of the positive electrode active material particles, binder, conductive material, negative 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 positive electrode materials such as positive electrode active material particles and conductive materials can be evenly distributed. That is, the positive electrode according to one embodiment can maintain excellent battery performance by making the binder component microporous so that the positive electrode material is very evenly distributed.

Specifically, an electrochemical device according to one embodiment can realize a high energy density of 180 Wh/kg or more, or 180 Wh/kg to 400 Wh/kg, or 180 Wh/kg to 380 Wh/kg, and can satisfy both excellent life characteristics and stability.

According to one embodiment, the electrochemical device may include the cathode active material layer in an amount of 50 wt% or more, 55 wt% or more, or 60 wt% or more, or 95 wt% or less, or 90 wt% or less, or 88 wt% or less, or 50 to 90 wt%, or 60 to 90 wt%, or 60 to 85 wt%, based on the total weight.

Additionally, the positive electrode active material particles may be included in an amount of 70 to 99 wt%, 80 to 99 wt%, or 85 to 99 wt% with respect to the total weight of the positive electrode active material layer.

The above cathode active material particles may include 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, 95 wt% or more, and, but not limited to, less than 100 wt% of the lithium iron phosphate-based particles based on the total weight of the cathode active material particles. Specifically, it may include 60 wt% or more and less than 100 wt%, 60 to 99 wt%, 65 to 99 wt%, 70 to 99 wt%, 80 to 99 wt%, 85 to 98 wt%, or 90 to 97 wt%. Alternatively, it goes without saying that the above cathode active material particles may include 100 wt% of the lithium iron phosphate-based particles based on the total weight of the cathode active material particles.

In addition, the positive electrode may have a positive 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 positive 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 positive electrode may be a thick film positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm ² , 3.5 to 9 mAh/cm ² _, or 3.8 to 8 mAh/cm ² .

Additionally, the positive electrode may be a thick-film positive electrode having a positive electrode active material layer composite density (g/cc) of 2.0 to 4.0, or 2.0 to 3.0, or 2.2 to 2.6.

In addition, the electrode tortuosity (τ) calculated by the following relationship may be 10 or less, 8 or less, 7 or less, or 6 or less, and may be, but is not limited to, 1 or more. Specifically, the electrode tortuosity may be 1 to 10, 2 to 8, 3 to 7, 4 to 7, or 5 to 7.

[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 anode, and Porosity represents the porosity of the anode.

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.

Additionally, a half-cell manufactured with the positive electrode may have a discharge capacity retention rate at 0.3 C of 50% or more, or 60% or more, or 70% or more, or 74% or more, and may be from 60% to 99%, or from 70% to 98%, relative to the discharge capacity at 0.1 C. For non-limiting example, the measurement of the discharge capacity retention rate at 0.1 C and 0.3 C may be, but is not limited to, the retention rate measured after 1 charge, after 5 charges, after 10 charges, or after 30 charges.

In addition, the electrochemical device according to one embodiment may have a 0.1C discharge capacity implementation ratio relative to the design capacity of 0.8 or more, 0.85 or more, 0.9 or more, 0.95 or more, and may be from 0.8 to 1.0, or from 0.9 to 1.0, or from 0.95 to 1.0. Here, the design capacity means a theoretical value calculated from the total weight of the positive active material included in the cell and the reversible discharge capacity of the positive active material.

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

In addition, the cathode 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 cathode 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 positive electrode active material particles.

In addition, the positive 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 positive 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 positive electrode 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 2.0, less than 1.5, less than 1.2, or less than 1.1. In addition, the liquid electrolyte may be included in a weight ratio of 10 to 30, or a weight ratio of 10 to 25, or a weight ratio of 15 to 25 with respect to 100 parts by weight of the positive electrode.

That is, the positive electrode 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 cathode material slurry, and the pore former may be, for example, a mixed solvent of two or more having different solubility parameters, a metal salt, or a combination thereof.

A description of the above metal salt is omitted as it is the same 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 cathode material slurry, and porosity of the binder component may occur in the cathode 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, an negative electrode, and an electrolyte; wherein the positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer comprising a porous binder scaffold and positive electrode active material particles; wherein the positive electrode active material particles comprise lithium iron phosphate particles having an olivine structure with respect to the total weight of the positive electrode active material layer.

According to one embodiment, the method for manufacturing the electrochemical device includes the steps of manufacturing a positive electrode including a current collector and a positive electrode active material layer on the current collector; the step of manufacturing a negative electrode; the step of assembling the positive electrode and the negative electrode; and the step of injecting an electrolyte. Since the positive electrode, the negative electrode, and the electrolyte are the same as those described above, a detailed description thereof will be omitted.

According to one embodiment, the step of manufacturing the positive electrode may include a step of applying a positive electrode slurry including the positive electrode active material particles, a conductive material, a binder, and a metal salt as described above onto a current collector; and a step of drying the applied positive electrode slurry.

The application of the cathode 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 cathode slurry is performed, a step of drying the slurry application (the applied cathode slurry) can be performed. The drying can be performed by applying energy, or can be performed through natural drying or vacuum drying without separately applying energy. The applied energy can be thermal energy, light energy, or thermal and light energy, and the application of thermal and light energy can include sequential application or simultaneous application. When light energy is applied, the light can 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 above drying temperature is not particularly limited as long as it is a temperature capable of drying the cathode material slurry. As a non-limiting example, the drying temperature may be performed at a temperature of 90 to 180° C., 100 to 160° C., 100 to 140° C., or 100 to 130° C. The drying time may be appropriately adjusted in proportion to the amount of the cathode material slurry applied.

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

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

The step of preparing the above active material mixture may include a step of mixing an ionic material and positive electrode 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 positive 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 positive electrode

A cathode material was prepared by mixing 94 wt% of lithium iron phosphate (LiFePO ₄ ) active material having an olivine structure and an average particle size of 7 ㎛, 2 wt% of carbon black (Super-P) having an average particle size of 40 nm as a conductive material, 3 wt% of polyvinylidene fluoride as a binder, and 1 wt% of lithium trifluoromethanesulfonate as a salt ionic material (total 100 wt%). The cathode material was added to a mixed solvent of 32.5 wt% of N-methyl-2-pyrrolidone and 7.5 wt% of propylene carbonate to an amount of 60 wt% to prepare a cathode material slurry. The above cathode material slurry was applied to a 20 ㎛ thick aluminum 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 manufacture a cathode including a 121 ㎛ thick cathode active material layer in which cathode active material particles are evenly distributed within a porous binder scaffold structure.

The positive electrode active material loading of the above positive electrode was 29.2 mg/cm2, and the composite density was 2.4 g/cc.

2) Manufacturing of cathode

A mixture of 96 wt% of natural graphite with an average particle size of 20 ㎛ as an anode active material, 1 wt% of carbon black (Super-P) with an average particle size of 40 nm as a conductive material, and 1.5 wt% of CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber) as a binder (total 100 wt%) was used as the anode material. The anode material slurry was prepared by adding 60 wt% of the above anode material to 40 wt% of distilled water. The above anode material slurry was applied to a 20 ㎛ thick copper thin film 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 prepare an anode including a 74 ㎛ thick anode active material layer.

The negative active material loading of the above negative electrode was 13.7 mg/cm2, and the composite density was 1.65 g/cc.

3) Manufacturing of electrochemical devices

The manufactured 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 2.72 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 instead of lithium trifluoromethanesulfonate as the salt ionic material in the manufacture of the positive 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 50:50 mass% ratio was used instead of lithium trifluoromethanesulfonate as the salt ionic material in the manufacture of the positive 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 trifluoromethanesulfonate as the salt ionic material in the manufacture of the positive electrode.

[Example 5]

In the above Example 1, an electrochemical device was manufactured in the same manner as in Example 1, except that the positive 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 positive electrode. The active material mixture was manufactured by pre-mixing lithium trifluoromethanesulfonate and lithium iron phosphate active material 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. The fired product was then naturally cooled to room temperature (25±5 ℃).

[Example 6]

In the above Example 1, an electrochemical device was manufactured in the same manner as in Example 1, except that a silicon composite cathode manufactured by the following method was used instead of the cathode of Example 1.

4) Manufacturing of silicon composite cathode

A mixture of 76 wt% of natural graphite and 20 wt% of silicon oxide as negative active materials, 1 wt% of carbon black (Super-P) with an average particle size of 40 nm as a conductive material, and 1.5 wt% of CMC and SBR as binders (total 100 wt%) was used as the negative electrode material. Thereafter, the negative electrode material slurry was prepared by adding 60 wt% of the above-mentioned negative electrode material to 40 wt% of distilled water. The above-mentioned negative electrode slurry was applied onto a 20 ㎛ thick copper 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 silicon composite negative electrode including a 50 ㎛ thick negative electrode active material layer.

[Example 7]

An electrochemical device was manufactured in the same manner as in Example 1, except that a 50 μm thick lithium metal anode rolled onto an 8 μm thick copper foil current collector was used instead of the anode in Example 1.

[Comparative Example 1]

In the above Example 1, an electrochemical device was manufactured in the same manner as in the above Example 1, except that 94 wt% of lithium iron phosphate (LiFePO ₄ ) active material was used as a positive electrode active material, 2 wt% of carbon black (Super-P) having an average particle size of 40 nm was used as a conductive material, and 4 wt% of polyvinylidene fluoride was used as a binder to manufacture a positive electrode slurry.

<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 3.6 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 2.8 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 positive electrode active material included in the cell and the reversible discharge capacity of the positive electrode active material. The results are shown in Table 1 below.

As shown in 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 anode.

<Evaluation 2. Bipolar property evaluation>

2-1. Bipolar appearance evaluation

The appearance of the surfaces of the positive electrodes manufactured in Example 1 and Comparative Example 1 was evaluated using a scanning electron microscope (SEM) analysis. The SEM analysis results of the positive electrodes according to Comparative Example 1 and Example 1 are shown in FIGS. 1 and 2, respectively. Referring to FIGS. 1 and 2, in the case of the positive electrode manufactured in Comparative Example 1, it was confirmed that numerous cracks occurred in the electrode appearance due to uneven distribution of the conductive agent/binder during slurry coating and drying. On the other hand, in the case of the positive electrode of Example 1, it was confirmed that the positive 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, so that no cracks occurred in the electrode appearance.

In addition, when observing the cross-section of the positive electrode manufactured in Example 1 using a scanning electron microscope, it was confirmed that the positive electrode 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 positive 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. Bipolar X-ray CT analysis

The cross-sections of the positive 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. It was confirmed that the positive electrode of Comparative Example 1 had an uneven distribution of the conductive material in the thickness direction. On the other hand, the positive electrode of Example 1 had a uniform distribution of the conductive material in the first active material layer corresponding to 1/3 of the thickness direction from the boundary between the positive electrode current collector and the positive electrode active material layer, the second active material layer from 1/3 to 2/3 of the thickness direction, and the third active material layer from 2/3 to the surface. 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 2 below. Referring to Table 2, the positive electrode according to Example 1 showed a very low value of about 5% or less in the deviation of the conductive material concentration according to Equation 1 below, and through this, it was confirmed that the positive 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 throughout the positive electrode active material layer;

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

2-3. Evaluation of ionic conductivity within the anode

A symmetric cell was manufactured using the positive electrodes manufactured in the Examples and Comparative Examples, and a liquid electrolyte containing 1 mol of LiPF ₆ dissolved in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio 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 inside the positive electrode was calculated. The results are shown in Table 3 below.

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

The measured ionic conductivity values in the anode were used to calculate the electrode curvature of the anode 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 anode according to the examples and comparative examples measured at 25 ℃. 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 anode was calculated by measuring the conductivity in the thickness direction of the electrode after filling the anode 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 anode sample was placed in a mercury porosimeter cell, and the cell was filled with mercury up to a given pressure range (30 psia to 60,000 psia) to measure the pore volume inside the anode. The final curvature was calculated from the measured porosity and McMullin number. The measured electrode curvature is shown in Table 3 below.

As shown in Table 2 above, it was confirmed that the positive electrode according to the embodiment had improved curvature within the electrode compared to the positive electrode according to the comparative example. The curvature of the electrode is affected by the pore structure formed within the electrode, and when the conductive agent and the 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 positive 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. Half-cell performance evaluation

A half cell was manufactured using the positive electrode manufactured in Example 1, and the capacity was measured under 0.1 C/0.1 C charge/discharge conditions and 0.1 C/0.3 C charge/discharge conditions, respectively, and the discharge capacity retention rate according to the rate (C-rate) was evaluated. Specifically, the half cell was manufactured in the same manner as the method for manufacturing the electrochemical device, except that a 200 ㎛ thick lithium metal was used as the negative electrode.

The above half-cell was charged to 3.6 V at 0.1 C-rate under constant current/constant voltage (CC/CV) conditions at 25 ℃ and then cut-off. Thereafter, it was discharged to 2.8 V at 0.1 C-rate (CC conditions) and the discharge capacity under 0.1 C/0.1 C charge/discharge conditions was measured. In addition, the C-rate was changed to 0.3 C and the discharge capacity under 0.1 C/0.3 C charge/discharge conditions was measured. The relative discharge capacity at 0.3 C was defined as the value obtained by dividing the measured discharge capacity at 0.1 C by the discharge capacity at 0.3 C, and the discharge capacity retention rate was calculated by multiplying the relative discharge capacity at 0.3 C by 100. The results are shown in Table 4 below.

Referring to Table 4 above, the measurement results show that the half cell of the positive electrode according to Example 1 effectively maintains the discharge capacity even when the rate increases. That is, the positive electrode according to one embodiment has uniform lithium ion flow characteristics and excellent output characteristics even when the thickness increases. In addition, the positive electrode according to Example 1 was confirmed to have a capacity per area of 4 mAh/cm2 under 0.1 C/0.1 C conditions and a voltage range of 2.8-3.6 V.

Although the present invention has been described by limited embodiments, this has only been provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those with ordinary skill 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 following claims, as well as variations equivalent to the claims, are considered to fall within the scope of the spirit of the present invention.

Claims (26)

Contains a positive electrode, a negative electrode and an electrolyte, The above positive electrode comprises a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer comprising a porous binder scaffold and positive electrode active material particles; An electrochemical device, wherein the positive electrode active material particles include lithium iron phosphate particles having an olivine structure with respect to the total weight of the positive electrode active material layer. In the first paragraph, The above-mentioned positive electrode is an electrochemical device having an electrode tortuosity (τ) of 7 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 anode, and Porosity represents the porosity of the anode.) In paragraph 1, An electrochemical device, wherein the negative electrode includes a negative electrode active material layer containing 50 wt% or more of a graphite-based active material. In paragraph 1, An electrochemical device having an energy density of 180 Wh/kg to 400 Wh/kg. In paragraph 1, An electrochemical device, wherein the negative electrode comprises a negative current collector, or a negative current collector and lithium metal. In paragraph 1, An electrochemical device further comprising a separator. In paragraph 1, An electrochemical device, wherein the cathode active material layer is included in an amount of 50 wt% or more based on the total weight of the electrochemical device. In paragraph 1, The above positive electrode is an electrochemical device having a thick film type positive electrode active material layer composite density (g/cc) of 2.2 to 2.6. In paragraph 1, An electrochemical device, wherein the positive electrode active material particles are included in an amount of 80 to 99 wt% based on the total weight of the positive electrode active material layer. In paragraph 1, An electrochemical device, wherein the positive electrode is a thick film positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm2. In paragraph 1, An electrochemical device, wherein the positive electrode active material layer comprises positive electrode active material particles evenly dispersed therein, and a porous binder scaffold exists in the empty space between the particles. In Article 11, An electrochemical device, wherein the porous binder scaffold is included in an amount of 0.01 to 40 parts by weight based on 100 parts by weight of the positive electrode active material particles. In Article 11 An electrochemical device, wherein the porous binder scaffold further comprises a conductive material. In Article 11 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 11, An electrochemical device, wherein the positive electrode active material layer further includes a metal salt. In Article 15, An electrochemical device, wherein the metal salt is contained in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the positive electrode active material particles. In Article 15, An electrochemical device, wherein the metal salt is contained in or surface-adsorbed in at least one of a porous binder scaffold and positive electrode active material particles. In Article 15, 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 18 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, An electrochemical device, wherein the electrolyte is included in a weight ratio of 15 to 30 parts per 100 parts by weight of the positive electrode. In paragraph 1, An electrochemical device, wherein a half-cell manufactured with the above positive electrode has a discharge capacity retention rate at 0.3 C of 70% or more compared to the discharge capacity at 0.1 C. In paragraph 1, The above electrochemical device is an electrochemical device having a 0.1C discharge capacity realization ratio of 0.9 or more compared to the design capacity. Contains a positive electrode, a negative electrode and an electrolyte, The above positive electrode comprises a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer comprising a binder, positive electrode active material particles, and a conductive material; The above cathode active material particles include lithium iron phosphate particles having an olivine structure, The above positive electrode is a thick film type positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm2. An electrochemical device, wherein when a cross-section of the positive electrode 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 positive electrode active material layer from the boundary between the positive electrode current collector and the positive electrode 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 positive electrode 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 positive electrode active material layer to the surface is 10% or less. In Article 24, An electrochemical device, wherein the lithium iron phosphate particles are included in an amount of 60 wt% or more based on the total weight of the positive electrode active material layer. In Article 24, 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.

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