CN116830291A - Negative electrode and secondary battery containing negative electrode - Google Patents
Negative electrode and secondary battery containing negative electrode Download PDFInfo
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- CN116830291A CN116830291A CN202280012333.9A CN202280012333A CN116830291A CN 116830291 A CN116830291 A CN 116830291A CN 202280012333 A CN202280012333 A CN 202280012333A CN 116830291 A CN116830291 A CN 116830291A
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Abstract
An anode and a secondary battery including the anode, the anode including an anode active material layer, wherein the anode active material layer includes a silicon-containing anode active material including a core including SiO and a carbon layer on the core, and a conductive material x And at least one metal atom, wherein 0<x<2, the at least one metal atom including at least one selected from the group consisting of Mg, li, al, and Ca, the silicon-containing anode active material having D of 0.5 or more 5 /D 50 D of 3 μm or more 5 And 4 μm to 11 μmD 50 And the conductive material comprises single-walled carbon nanotubes.
Description
Technical Field
The present application claims priority and benefit from korean patent application No. 10-2021-0107510 filed on the korean intellectual property office at month 13 of 2021 and korean patent application No. 10-2022-0008551 filed on the korean intellectual property office at month 20 of 2022, the entire contents of which are incorporated herein by reference.
The present application relates to a negative electrode including a silicon-containing negative electrode active material having a specific particle size distribution and single-walled carbon nanotubes, and a secondary battery including the negative electrode.
Background
Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is increasing, and as part of this trend, the most active research fields are the power generation and storage fields using electrochemical reactions.
At present, representative examples of electrochemical devices using such electrochemical energy include secondary batteries, and the field of use thereof is increasing. In recent years, with the development of technology and the increase in demand for portable devices such as portable computers, portable phones, and cameras, the demand for secondary batteries as an energy source has sharply increased, a great deal of research has been conducted on lithium secondary batteries having high energy density, i.e., high capacity, among such secondary batteries, and lithium secondary batteries having high capacity have been commercialized and widely used.
In general, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for inserting and extracting lithium ions from a positive electrode, and as the negative electrode active material, a silicon-containing active material having a high discharge capacity may be used.
However, silicon-containing active materials are accompanied by excessive volume changes during driving of the battery. Therefore, a problem occurs in that the service life of the battery is reduced. In order to solve these problems in the related art, the following method is used: the ratio of the silicon-containing active material used is reduced or a binder capable of exhibiting high negative electrode adhesion is used, but there is a limitation in solving the problem since the silicon-containing active material itself is not improved. Further, although a technology capable of internally accommodating volume expansion by making the silicon-containing active material porous has been used, the technology has a problem in that since the capacity per unit weight of the anode is reduced, and particles are broken when the electrode is prepared and then rolled, the effect is reduced.
Therefore, there is an urgent need to develop a negative electrode capable of effectively improving the service life characteristics of a battery while using a silicon-containing negative electrode active material.
[ related art literature ]
[ patent literature ]
(patent document 1) Korean patent No. 10-1586816
Disclosure of Invention
Technical problem
The present invention is directed to providing a negative electrode capable of improving capacity, efficiency and/or service life characteristics of a battery, and a secondary battery including the same.
Technical proposal
An exemplary embodiment of the present invention provides an anode including an anode active material layer including a silicon-containing anode active material including a core including SiO and a carbon layer on the core, and a conductive material x (0<x<2) And at least one metal atom including at least one selected from the group consisting of Mg, li, al, and Ca, the silicon-containing anode active material having D of 0.5 or more 5 /D 50 D of 3 μm or more 5 And D of 4 μm or more and 11 μm or less 50 And the conductive material comprises single-walled carbon nanotubes.
Another exemplary embodiment of the present invention provides a secondary battery including the negative electrode.
Advantageous effects of the invention
The negative electrode according to an exemplary embodiment of the present invention includes a negative electrode having a D of 0.5 or more 5 /D 50 D of 3 μm or more 5 And D of 4 μm or more and 11 μm or less 50 The silicon-containing anode active material and the single-walled carbon nanotube of the present invention enable improvement of the life characteristics of the battery because lithium ions are easily intercalated and deintercalated during charge and discharge without causing excessive side reactions with the electrolyte and without causing excessive expansion. In addition, since the silicon-containing anode active material contains at least one metal atom, and the at least one metal atom exists in the form of a metal compound such as a metal silicate, the initial efficiency of the battery can be improved.
The combined use of the silicon-containing anode active material having the above particle size distribution and single-walled carbon nanotubes can improve the conductive path between the anode active material particles, thereby improving the capacity, efficiency and life performance of the battery.
Detailed Description
Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.
The terms or words used in the present specification and claims should not be construed as limited to general or dictionary meanings, but should be construed as meanings and concepts consistent with the technical spirit of the present invention on the basis of the principle that the inventor is able to properly define concepts of the terms to best explain his/her own invention.
The terminology used in the description presented herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.
In the present invention, the terms "comprises," "comprising," or "having" are intended to mean that the existence of the feature, number, step, constituent element, or any combination thereof is achieved, and should be understood to mean that the existence or addition of one or more other features or numbers, steps, constituent elements, or any combination thereof is not precluded.
In the present specification, D 5 And D 50 Can be defined as particle sizes corresponding to 5% and 50% of the cumulative volume in the particle size distribution curve (curve of the particle size distribution curve), respectively. In addition, in the present specification, D max And D min May correspond to the maximum particle size and the minimum particle size, respectively, in the particle size distribution curve of the particles. D (D) 5 、D 50 、D max And D min The measurement can be performed by using, for example, a laser diffraction method, respectively. The laser diffraction method is generally capable of measuring particle sizes ranging from a submicron region to about several millimeters, and can obtain results with high reproducibility and high resolution. D (D) 5 And D 50 The measurement of (c) can be confirmed using a Microtrac apparatus (manufacturer: microtrac company, model name: S3500) using water and Triton-X100 dispersant at a refractive index of 1.97.
In this specification, the average length or diameter of the conductive material is measured using SEM or TEM.
In the present specification, the specific surface area can be measured by degassing an object to be measured at 130℃for 2 hours using a BET measuring apparatus (BEL-SORP-MAX, nippon Bell Co.) and N at 77K 2 Adsorption/desorption.
In this specification, the presence or absence of a metal element and the content of the element in the anode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma atomic emission spectrometer (ICP-OES AVIO 500 of Perkin-Elmer 7300).
<Negative electrode>
The anode according to an exemplary embodiment of the present invention is an anode including an anode active material layer, and is an anode in which the anode active material layer includes a silicon-containing anode active material including a core including SiO and a carbon layer on the core, and a conductive material x (0<x<2) And at least one metal atom including at least one selected from the group consisting of Mg, li, al, and Ca, the silicon-containing anode active material having D of 0.5 or more 5 /D 50 、3D of μm or more 5 And D of 4 μm or more and 11 μm or less 50 And the conductive material comprises single-walled carbon nanotubes.
In one exemplary embodiment of the present invention, the silicon-containing anode active material includes a core and a carbon layer on the core.
In an exemplary embodiment of the invention, the core comprises SiO x (0<x<2)。
The SiO is x (0<x<2) May correspond to the matrix in the silicon-containing anode active material. The SiO is x (0<x<2) Can be in the form of a composition comprising Si and SiO 2 And the Si may also form a phase. That is, x corresponds to SiO x (0<x<2) The number ratio of O to Si contained in the alloy. When the silicon-containing anode active material contains SiO x (0<x<2) When this is done, the discharge capacity of the secondary battery can be improved.
In one exemplary embodiment of the present invention, the core may contain metal atoms. The at least one metal atom may be present in the silicon-containing anode active material in the form of at least one of a metal atom, a metal silicate, a metal silicide, and a metal oxide.
The at least one metal atom may include at least one selected from the group consisting of Mg, li, al, and Ca. Thus, the initial efficiency of the silicon-containing anode active material can be improved.
Specifically, the metal atom may contain one or more of Mg, li, or Al. The silicon-containing anode active material of the present invention may be in a form in which particles having a relatively small size are removed, but when the metal atom is one or more of Mg, li, or Al, since even the inside of the core can be uniformly doped, the silicon-containing anode active material having the above-described characteristics can be smoothly prepared. In addition, in the silicon-containing anode active material having the particle size distribution of the present invention, the metal atoms having a low atomic number are small, so that the inside of the core can be doped more uniformly, and thus the metal atoms are most preferably Mg or Li.
The metal atoms (Li, mg, etc.) are in the form of silicon-containing particles doped with the precursorThe form of the particles may thus be distributed on the surface and/or inside the silicon-containing particles. The metal atoms are distributed on the surface and/or inside of the silicon-containing particles, so that the volume expansion/contraction of the silicon-containing particles can be controlled to an appropriate level, and can be used to prevent damage to the active material. In addition, from SiO reduction x (0<x<2) Irreversible phases in particles (e.g. SiO 2 ) In order to increase the efficiency of the active material, the metal atoms may be contained.
The metal atoms may be present in the form of metal silicates. The metal silicate may be classified into crystalline metal silicate and amorphous metal silicate.
When the metal atom is Li, li may be selected from Li 2 SiO 3 、Li 4 SiO 4 And Li (lithium) 2 Si 2 O 5 At least one form of lithium silicate from the group consisting is present in the core.
When the metal atom is Mg, mg may be as Mg 2 SiO 4 And MgSiO 3 Is present in the core in the form of at least one magnesium silicate.
In one exemplary embodiment of the present invention, the content of the metal atoms may be 0.1 parts by weight or more and 40 parts by weight or less, specifically 1 part by weight or more and 25 parts by weight or less, more specifically 2 parts by weight or more and 20 parts by weight or less, or 2 parts by weight or more and 10 parts by weight or less, with respect to 100 parts by weight of the total silicon-containing anode active material. When the content of the metal atoms exceeds the above-described range of 0.1 parts by weight or more and 40 parts by weight or less, there may be a problem in that as the content of the metal atoms increases, the initial efficiency increases, but the discharge capacity decreases, so that when the content satisfies the above-described range, an appropriate discharge capacity and initial efficiency may be achieved.
In an exemplary embodiment of the present invention, the content of the metal atoms may be 1 part by weight or more and 25 parts by weight or less, more specifically 2 parts by weight or more and 20 parts by weight or less, or 2 parts by weight or more and 10 parts by weight or less, with respect to 100 parts by weight of the total core. When the content of the metal atoms exceeds the above-described range of 1 part by weight or more and 25 parts by weight or less, there may be a problem in that as the content of the metal atoms increases, the initial efficiency increases, but the discharge capacity decreases, so that when the content satisfies the above-described range, an appropriate discharge capacity and initial efficiency can be achieved.
In one exemplary embodiment of the present invention, the silicon-containing anode active material may include a carbon layer. The carbon layer is disposed on the core and may cover at least a portion of a surface of the core. That is, the carbon layer may be in the form of partially covering the surface of the core or covering the entire surface of the core. The silicon-containing anode active material may be given conductivity by the carbon layer, and initial efficiency, service life characteristics, and battery capacity characteristics of the secondary battery may be improved.
The carbon layer may include at least one of amorphous carbon and crystalline carbon.
The crystalline carbon may further improve the conductivity of the silicon-containing anode active material. The crystalline carbon may include at least one selected from the group consisting of fullerenes, carbon nanotubes, and graphene.
The amorphous carbon can suppress expansion of the silicon-containing composite particles by properly maintaining the strength of the carbon layer. The amorphous carbon may be a carbide of at least one selected from the group consisting of tar, pitch, and other organic materials, or may be a carbonaceous material formed using hydrocarbon as a source of a chemical vapor deposition process.
The carbide of the other organic material may be a carbide of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or ketohexose, and a carbide of an organic material selected from a combination thereof.
The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane or the like. Examples of the aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, benzofuran, pyridine, anthracene, phenanthrene, and the like.
In one exemplary embodiment of the present invention, the content of the carbon layer may be 0.1 part by weight or more and 50 parts by weight or less, 0.1 part by weight or more and 30 parts by weight or less, or 0.1 part by weight or more and 20 parts by weight or less, with respect to 100 parts by weight of the total of the silicon-containing anode active material. More specifically, the content of the carbon layer may be 0.5 parts by weight or more and 15 parts by weight or less. When the above-described range of 0.1 part by weight or more and 50 parts by weight or less is satisfied, it may be possible to prevent the capacity and efficiency of the anode active material from being lowered.
In an exemplary embodiment of the present invention, the carbon layer may have a thickness of 1nm to 500nm, specifically 5nm to 300 nm. When the above range of 1nm to 500nm is satisfied, the conductivity of the silicon-containing anode active material can be improved, so that there is an effect of improving the initial efficiency and the service life of the battery.
In one exemplary embodiment of the present invention, the silicon-containing anode active material may have D of 4 μm or more and 11 μm or less 50 . When the silicon-containing anode active material has a D of less than 4 μm 50 At this time, the particle size may be too small so that the specific surface area of the material increases, and there may be a problem in that the service life is seriously deteriorated due to many side reactions with the electrolyte. When the silicon-containing anode active material has a D of more than 11 μm 50 At this time, the granularity may be too large so that the battery may not be easily charged and discharged, and thus there may be a problem in that it is difficult to achieve capacity/efficiency during charge and discharge. Therefore, when the silicon-containing anode active material has D of 4 μm or more and 11 μm or less 50 At this time, the battery may be easily charged and discharged, so that there may be an effect of sufficiently achieving capacity and efficiency and stable life characteristics. In particular, the silicon-containing anode active material may have a D of 4.2 μm or more and 10 μm or less, specifically 4.5 μm or more and 9 μm or less, more specifically 5 μm or more and 7 μm or less 50 . In this case, in addition to the aboveIn addition to the effects, there may be an effect that an electrode can be easily prepared.
In one exemplary embodiment of the present invention, the silicon-containing anode active material may have a D of 3 μm or more 5 . D when the silicon-containing anode active material 5 At less than 3 μm, oxidation may frequently occur due to small particle size, so that there may be a problem in that the capacity and efficiency achieved are relatively small. Further, since the particle size is small, side reactions with the electrolyte during charge/discharge may increase, and thus there may be a problem in that the life characteristics are deteriorated. Therefore, when the above-mentioned range of 3 μm or more is satisfied, the content of the silicon-containing anode active material having excessively small particle size in the anode can be reduced, so that the service life and stability of the battery can be improved by reducing side reactions with the electrolyte. In particular, the silicon-containing anode active material may have a D of 3 μm or more and 5.5 μm or less, specifically 3 μm or more and 5 μm or less, more specifically 3 μm or more and 4 μm or less, or 3 μm or more and 3.6 μm or less 5 。
The silicon-containing anode active material may have a D of 0.5 or more, specifically 0.6 or more 5 /D 50 . When D is 5 /D 50 Below 0.5, the volume occupied by the undersized silicon-containing anode active material in the anode may increase, and there may be a problem in that the service life of the battery may be reduced, since side reactions with the electrolyte may increase with the increase in the specific surface area of the material. Thus, let D 5 /D 50 And satisfies 0.5 or more, thereby improving the service life characteristics of the battery. D of the silicon-containing anode active material 5 /D 50 The upper limit may be 1.
In this case, when D 5 /D 50 Less than 0.5, even if D of the silicon-containing anode active material 5 And D 50 Meeting the above range, due to the fact that the negative electrode is formed by the size and even the ratio D 50 The volume occupied by the smaller active material may increase and side reactions with the electrolyte may also increase, which may reduce the service life of the battery. Conversely, when D 5 /D 50 Satisfy 0.5 or more, but D 5 Or D 50 Not meet the upper limitIn such ranges, the average particle size may be too small or too large, thereby presenting problems in terms of service life and/or efficiency. When D is 5 Or D 50 There are problems in that capacity and efficiency are reduced due to oxidation of a large amount of silicon-containing anode active material particles, and service life characteristics are deteriorated due to excessive electrolyte side reactions. When D is 50 At high levels, the granularity is too large to facilitate charging and discharging of the battery, and thus there is a problem in that it is difficult to achieve capacity/efficiency during charging and discharging.
Thus, as in the present invention, when D of the silicon-containing anode active material 5 、D 50 And D 5 /D 50 When the above range is satisfied, the capacity, efficiency, and/or service life of the battery can be improved.
In one exemplary embodiment of the present invention, the silicon-containing anode active material may have a thickness of 1m 2 Above/g and 20m 2 Per gram of less than 1m 2 Above/g and 15m 2 Less than/g and greater than 2m 2 /g and less than 10m 2 /g, 2.5m 2 Above/g and 8m 2 BET specific surface area of not more than/g.
The BET specific surface area may have an upper limit of 20m 2 /g、18m 2 /g、15m 2 /g、10m 2 /g、8m 2 /g、5m 2 /g or 4m 2 Per g, a lower limit may be 1m 2 /g、1.5m 2 /g、2m 2 /g or 2.5m 2 /g。
In one exemplary embodiment of the present invention, the silicon-containing anode active material may have a D of 35 μm or less, specifically 30 μm or less, more specifically 25 μm or less, or 20 μm or less max . When the above-mentioned range of 35 μm or less is not satisfied, there is a problem in that the electrode may not be easily produced due to excessively large particles, and the electrode may not be uniformly produced during rolling.
The silicon-containing anode active material may have a D of 1.3 μm or more, specifically 1.5 μm or more, more specifically 1.7 μm or more, or 2 μm or more min . When the above range of 1.3 μm or more is satisfied, the specific surface area of the material may not become too large, so thatThere can be an effect that side reactions with the electrolyte can be reduced.
In one exemplary embodiment of the present invention, the silicon-containing anode active material may be formed by: preparing a prepared silicon-containing anode active material; adjusting the granularity of the prepared silicon-containing anode active material; and forming a carbon layer on the prepared silicon-containing negative electrode active material having a controlled particle size.
Specifically, in the preparation of the preliminary silicon-containing anode active material, the preliminary silicon-containing anode active material may be formed by: si powder, siO 2 Mixing the powder and the metal powder, and then gasifying the mixture; condensing the vaporized mixed gas into a solid phase; the solid phase is heat treated in an inert atmosphere.
Alternatively, the preliminary silicon-containing anode active material may be formed by: si powder and SiO under vacuum 2 Heating and gasifying the powder, and then depositing the gasified mixed gas to form silicon-containing particles; the formed silicon-containing particles are mixed with a metal powder, and then the resulting mixture is heat-treated.
The heat treatment step may be performed at 700 to 900 ℃ for 4 to 6 hours, specifically, at 800 ℃ for 5 hours.
The metal powder may be Mg powder or Li powder.
When Mg powder is used as the metal powder, the anode active material may be prepared by vaporizing the Mg powder.
When Li powder is used as the metal powder, the anode active material may be prepared by mixing silicon-containing particles with the Li powder and then heat-treating the resultant mixture.
The silicon-containing particles may be SiO x (x＝1)。
In the preliminary silicon-containing anode active material, the Mg compound phase may contain the Mg silicate, mg silicide, mg oxide, or the like described above.
In the preliminary silicon-containing anode active material, the Li compound phase may contain the above-described Li silicate, li silicide, li oxide, or the like.
In adjusting the particle size of the preliminary silicon-containing anode active material, the particle size may be adjusted by a method such as a ball mill, a jet mill, or air classification, but the method is not limited thereto. For example, when the particle size of the preliminary silicon-containing anode active material is adjusted using a ball mill, 5 to 20 stainless steel ball media may be added, and specifically 10 to 15 stainless steel ball media may be added, but the number of stainless steel ball media is not limited thereto.
In adjusting the particle size, the milling time of the preliminary silicon-containing anode active material may be 2 hours to 5 hours, specifically 2 hours to 4 hours, more specifically 3 hours, but is not limited thereto.
In the formation of the carbon layer, the carbon layer may be prepared using a Chemical Vapor Deposition (CVD) method using a hydrocarbon gas or by carbonizing a material used as a carbon source.
Specifically, the carbon layer may be formed by: the preliminary silicon-containing anode active material is introduced into a reaction furnace, and then a hydrocarbon gas is subjected to Chemical Vapor Deposition (CVD) at 600 to 1200 ℃. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and may be heat-treated at 900 to 1000 ℃.
In one exemplary embodiment of the present invention, the anode may further include a carbonaceous anode active material. The carbonaceous anode active material may contain at least one selected from natural graphite and artificial graphite.
In one exemplary embodiment of the present invention, the silicon-containing anode active material and the carbon-containing anode active material may satisfy the following formula a.
[ A ]
2.415≤D Gr /D SiO ≤6.452
In formula A, D SiO Mean the average particle diameter (D 50 )，D Gr Mean the average particle diameter (D 50 )。
When a carbonaceous anode active material satisfying formula a is used together with the siliceous anode active material, the siliceous anode active material may be easily located in a space between the carbonaceous anode active materials to improve contact characteristics during preparation of an anode, so that there may be an effect that conductivity in the electrode becomes excellent due to easy formation of a conductive path between the electrodes.
In an exemplary embodiment of the invention, D Gr /D SiO May be 2.5 to 5, 2.5 to 4, or 3.0 to 3.5.
In one exemplary embodiment of the present invention, in the anode, a weight ratio of the silicon-containing anode active material to the carbon-containing anode active material may be 10:90 to 90:10, specifically 10:90 to 50:50, more specifically 10:90 to 30:70.
specifically, the anode may include an anode current collector and an anode active material layer on the anode current collector. The anode active material layer may contain the anode active material. In addition, the anode active material layer may further include a binder and/or a conductive material.
The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material in which the surface of aluminum or stainless steel is surface-treated with carbon, nickel, titanium, silver, or the like may be used. In particular, a transition metal such as copper or nickel, which well adsorbs carbon, may be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.
In one exemplary embodiment of the present invention, the conductive material may include single-walled carbon nanotubes (SWCNTs). The single-walled carbon nanotubes refer to carbon structures in the form of tubes comprising a single carbon layer. When the conductive material in the anode active material layer includes single-walled carbon nanotubes, charge and discharge capacity and/or service life performance of the battery can be improved. In particular, since the single-walled carbon nanotubes successfully connect the conductive paths between particles, the conductive path loss caused by the expansion of the above-described silicon-containing anode active material can be prevented. As a result, when the single-walled carbon nanotubes are included, the service life performance of the battery can be improved.
In the present specification, the length of the carbon nanotube refers to the length of a long axis passing through the center of a single carbon nanotube, and the diameter of the carbon nanotube refers to the length of a short axis passing through the center of a single carbon nanotube and perpendicular to the long axis.
The single-walled carbon nanotubes may have an average length of 0.1 μm to 50 μm, specifically 0.5 μm to 25 μm or 0.5 μm to 20 μm. More specifically, the average length may be 5 μm to 15 μm. The average length may have a lower limit of 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm and an upper limit of 50 μm, 30 μm, 25 μm, 20 μm, 15 μm, 14 μm, 13 μm, 12 μm, 11 μm or 10 μm.
With respect to the single-walled carbon nanotubes, when single-walled carbon nanotubes satisfying the conductivity, strength, and average length ranges of 0.1 μm to 50 μm described above are used together with a silicon-containing anode active material having the above-described characteristics, since the length of the carbon nanotubes is ensured to be as large as the distance between anode active material particles, it becomes easier to connect the conductive paths between the particles, so that the conductivity, strength, and/or electrolyte retention performance of the anode can be improved. In contrast, when the average length of the carbon nanotubes is short, there is a concern that conductivity may be deteriorated because it may be difficult to efficiently form the conductive path, and when the average length of the carbon nanotubes is too long, there is a concern that dispersibility may be deteriorated.
The average length of the single-walled carbon nanotubes can be calculated from the average of the results observed by SEM.
The single-walled carbon nanotubes may have an average diameter of 1nm to 20nm, specifically 1.5nm to 15 nm. More specifically, the average diameter may be 1.5nm to 5nm. The average diameter may have a lower limit of 1nm, 1.5nm or 2nm and an upper limit of 20nm, 18nm, 16nm, 14nm, 12nm, 10nm, 8nm, 6nm or 4nm.
Since the single-walled carbon nanotubes satisfying the above-described average diameter range of 1nm to 20nm have flexible characteristics, there is an effect that contact between anode active material particles is not easily broken even when the single-walled carbon nanotubes are physically damaged. Conversely, when the average diameter of the carbon nanotubes is too large, there may be a concern that the electrode density may be lowered, and when the average diameter of the carbon nanotubes is too small, it may be difficult to disperse the carbon nanotubes, so that there may be a concern that the preparation processability of the dispersion may be deteriorated.
The average diameter of the single-walled carbon nanotubes can be calculated from the average of the results observed by TEM.
The single-walled carbon nanotubes may have a diameter of 200m 2 /g to 2000m 2 /g, in particular 250m 2 /g to 1500m 2 BET specific surface area per gram. When used meets the 200m requirement 2 /g to 2000m 2 In the case of single-walled carbon nanotubes of the range of/g, the single-walled carbon nanotubes may be easily dispersed even with a small amount of conductive material, so that there is an effect of being able to effectively attach the particles.
The content of the single-walled carbon nanotubes may be 0.005 to 1 part by weight, specifically 0.01 to 0.1 part by weight or 0.04 to 0.06 part by weight, relative to 100 parts by weight of the total negative electrode active material layer. When the above-described range of 0.005 to 1 part by weight is satisfied, there may be an effect of minimizing side reactions of the electrolyte caused by a high specific surface area while promoting contact of conductive paths between the silicon-containing anode active material particles.
The weight ratio of the silicon-containing anode active material to the single-walled carbon nanotubes in the anode active material layer may be 92:8 to 99.99:0.01, specifically 97:3 to 99.98:0.02. more specifically, the weight ratio may be 99:1 to 99.8:0.2. when 92 above is satisfied: 8 to 99.99: when the range is 0.01, the conductive path of the silicon-containing anode active material can be more effectively ensured.
In the present specification, the average size of the silicon-containing anode active material refers to the arithmetic average of the sizes of all the silicon-containing anode active materials, and is calculatedThe average particle diameter value is measured as the number distribution by Particle Size Distribution (PSD) analysis. That is, the average size of the silicon-containing anode active material is equal to D 50 Different values, D 50 Refers to the median value of the particle size distribution.
In general, since the factors of the particle shape are not considered in the particle size distribution measured by the volume distribution of the Particle Size Distribution (PSD) analysis, the average size of the silicon-containing anode active material is the result calculated by assuming that the particles are spheres having the same volume value. Thus, particle size observed and measured by SEM may be different from particle size distribution results measured by volume distribution of PSD analysis.
In one exemplary embodiment of the present invention, the average size of the silicon-containing anode active material measured when the anode is analyzed by surface SEM is 4.5 μm or more. The average size may be 20 μm or less, 15 μm or less, or 10 μm or less.
In one exemplary embodiment of the present invention, the average size of the silicon-containing anode active material measured when the anode is analyzed by cross-sectional SEM is 2 μm or more. The average size may be 15 μm or less, 10 μm or less, or 8 μm or less. In the case of cross-sectional SEM analysis, the measured particle size tends to be smaller than that of surface SEM analysis, depending on the location of the particles.
A battery including the silicon-containing anode active material having the average size as described above has an effect of improving charge/discharge capacity and/or service life performance.
The SEM analysis may be performed with a Scanning Electron Microscope (SEM), and in this case, a scanning electron microscope S-4800 manufactured by Hitachi corporation may be used, but the scanning electron microscope is not limited thereto.
The anode active material layer may further include a binder. The adhesive may comprise at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and a material whose hydrogen is replaced with Li, na, ca, or the like, and may further contain various copolymers thereof.
In one exemplary embodiment of the present invention, the anode may be prepared by: preparing a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent; forming a negative electrode active material layer by applying the negative electrode slurry to at least one surface of a current collector, drying and rolling the current collector; and drying the current collector in which the anode active material layer is formed.
<Secondary battery>
The secondary battery according to still another exemplary embodiment of the present invention may include the negative electrode in the above-described exemplary embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is identical to the above-described negative electrode. Since the anode has been described in detail, a detailed description thereof will be omitted. The secondary battery may be a lithium ion secondary battery.
The positive electrode may include a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector and including a positive electrode active material.
In the positive electrode, the positive electrode current collector is not particularly limited as long as the positive electrode current collector has conductivity without causing chemical changes to the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material in which the surface of aluminum or stainless steel is surface-treated with carbon, nickel, titanium, silver, or the like may be used. Further, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and the adhesion of the positive electrode active material may also be enhanced by forming fine irregularities on the surface of the current collector. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric body.
The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material includes: layered compounds, e.g. lithium cobalt oxide (LiCoO) 2 ) And lithium nickel oxide (LiNiO) 2 ) Or a compound substituted with more than one transition metal; lithium iron oxides, e.g. LiFe 3 O 4 The method comprises the steps of carrying out a first treatment on the surface of the Lithium manganese oxides, e.g. of formula Li 1+c1 Mn 2-c1 O 4 (0≤c1≤0.33)、LiMnO 3 、LiMn 2 O 3 And LiMnO 2 The method comprises the steps of carrying out a first treatment on the surface of the Lithium copper oxide (Li) 2 CuO 2 ) The method comprises the steps of carrying out a first treatment on the surface of the Vanadium oxides, e.g. LiV 3 O 8 、V 2 O 5 And Cu 2 V 2 O 7 The method comprises the steps of carrying out a first treatment on the surface of the Ni-site lithium nickel oxide, expressed as chemical formula LiNi 1-c2 M c2 O 2 (here, M is at least one selected from the group consisting of Co, mn, al, cu, fe, mg, B and Ga, and c2 satisfies 0.01.ltoreq.c2.ltoreq.0.3); lithium manganese composite oxide, expressed as chemical formula LiMn 2-c3 M c3 O 2 (where M is at least one selected from the group consisting of Co, ni, fe, cr, zn and Ta, and c3 satisfies 0.01.ltoreq.c3.ltoreq.0.1) or Li 2 Mn 3 MO 8 (here, M is at least one selected from the group consisting of Fe, co, ni, cu and Zn); liMn in which Li in the chemical formula is partially replaced with alkaline earth metal ions 2 O 4 Etc., but is not limited thereto. The positive electrode may be Li metal.
The positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder, in addition to the positive electrode active material.
In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and may be used without particular limitation as long as the positive electrode conductive material has electron conductivity without causing chemical changes in the battery to be constituted. Specific examples thereof include: graphite, such as natural graphite or artificial graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, any one or a mixture of two or more thereof may be used.
The positive electrode binder is used to improve the bonding between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, any one of which or a mixture of two or more thereof may be used.
The separator separates the anode and the cathode and provides a path for lithium ion movement, and can be used without particular limitation as long as the separator is generally used as a separator in a secondary battery, and in particular, a separator having excellent electrolyte moisturizing ability and low resistance to ion movement in an electrolyte is preferable. Specifically, a porous polymer film, for example, a porous polymer film formed of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of glass fibers having a high melting point, polyethylene terephthalate fibers, or the like, may also be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.
Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used to prepare lithium secondary batteries.
In particular, the electrolyte may comprise a non-aqueous organic solvent and a metal salt.
As the nonaqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate can be used.
In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate may be preferably used as cyclic carbonates because cyclic carbonates have a high dielectric constant as a high-viscosity organic solvent to thereby dissociate lithium salts well, and cyclic carbonates may be more preferably used because they may be mixed with linear carbonates having a low viscosity and a low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio and used for preparing an electrolyte having a high conductivity.
As the metal salt, a lithium salt which is a material easily dissolved in the nonaqueous electrolyte, for example, as an anion of the lithium salt, one or more selected from the group consisting of: f (F) - 、Cl - 、I - 、NO 3 - 、N(CN) 2 - 、BF 4 - 、ClO 4 - 、PF 6 - 、(CF 3 ) 2 PF 4 - 、(CF 3 ) 3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、CF 3 SO 3 - 、CF 3 CF 2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - Sum (CF) 3 CF 2 SO 2 ) 2 N - 。
In the electrolyte, for the purpose of improving the service life characteristics of the battery, suppressing the decrease in the battery capacity, and improving the discharge capacity of the battery, in addition to the above electrolyte constituent components, one or more additives, for example, halogenated alkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substitutedOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.
According to still another exemplary embodiment of the present invention, there is provided a battery module including the above secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the above secondary batteries having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium-to-large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.
Mode for carrying out the invention
Hereinafter, preferred embodiments will be set forth to facilitate understanding of the present invention, but the embodiments are provided only for illustrating the present invention, and it is apparent to those skilled in the art that various modifications and variations are possible within the scope and technical spirit of the present invention, and such modifications and variations are also natural within the scope of the appended claims.
< examples and comparative examples >
Example 1-1
(1) Preparation of silicon-containing anode active material
Si and SiO therein are reacted in a reaction furnace 2 1, the method comprises the following steps: 1 and 6g of Mg, and the resulting mixture is heated under vacuum at a sublimation temperature of 1400 ℃. Thereafter, vaporized Si, siO 2 The mixed gas with Mg reacts in the cooling zone under vacuum with a cooling temperature of 800 ℃ and condenses into a solid phase. Thereafter, a preliminary silicon-containing anode active material was prepared by performing heat treatment at a temperature of 800 ℃. Thereafter, after 15 stainless steel ball media were introduced into the preliminary silicon-containing anode active material using a ball mill, the preliminary silicon-containing anode active material was prepared to have D by pulverizing the preliminary silicon-containing anode active material for 3 hours 50 Size=6 μm. Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-containing anode active material was placed in the hot zone of the CVD apparatus, and methane was blown into the hot zone at 900 ℃ using Ar as a carrier gas, and at 10 -1 The reaction was carried out under the support for 20 minutes to prepare a silicon-containing anode active material having a carbon layer formed on the surface.
D of the silicon-containing anode active material 5 /D 50 0.5, D 50 6 μm, D max 19 μm, D min Is 2 μm.
(2) Preparation of negative electrode
After adding the silicon-containing anode active material, artificial graphite, and carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) as binders to a dispersion liquid of single-walled carbon nanotubes using distilled water as a dispersion medium and carboxymethyl cellulose (CMC) as a dispersant, the resultant mixture was stirred, and then an anode slurry was prepared by adding distilled water (solid content=50 parts by weight) thereto. The negative electrode slurry was applied to a copper (Cu) metal thin film as a negative electrode current collector and having a thickness of 20 μm and dried. In this case, the temperature of the circulated air was 60 ℃. Subsequently, a negative electrode having a negative electrode active material layer disposed on the negative electrode current collector was prepared by rolling the negative electrode current collector and drying the negative electrode current collector in a vacuum oven at 130 ℃ for 12 hours.
In the anode active material layer, a silicon-containing anode active material, artificial graphite (D 50 =18 μm), single-walled carbon nanotubes, carboxymethyl cellulose (CMC) and styrene-butadiene rubber in a weight ratio of 14.63:82.92:0.05:1.2:1.2. in this case, in CMC, the weight of CMC added as a binder: weight of CMC added as dispersant = 1.14:0.06. in the negative electrode active material layer, the average length of the individual single-walled carbon nanotubes was 10 μm and the average diameter was 2nm.
Examples 1 to 2
A silicon-containing anode was produced in the same manner as in example 1-1 except that 10 stainless steel ball media were added thereto.
Examples 1 to 3
A silicon-containing anode was produced in the same manner as in example 1-1 except that single-walled carbon nanotubes having an average length of 25 μm and an average diameter of 16nm were used.
Example 2-1
In the method of example 1-1, mg was not used, 6g of Li metal powder was added thereto after synthesizing 94g of SiO particles, and heat treatment was performed at a temperature of 800 ℃ in an inert atmosphere to prepare a preliminary silicon-containing anode active material. Thereafter, after 15 stainless steel ball media were introduced into the preliminary silicon-containing anode active material using a ball mill, the preliminary silicon-containing anode active material was prepared to have D by pulverizing the preliminary silicon-containing anode active material for 3 hours 50 Size=6 μm. Thereafter, while maintaining an inert atmosphere by flowing Ar gas, the preliminary silicon-containing anode active material is subjected toPlaced in a hot zone of a CVD apparatus, and methane was blown into the hot zone at 900 ℃ using Ar as a carrier gas, at 10 -1 The reaction was carried out under the support for 20 minutes to prepare a silicon-containing anode active material having a carbon layer formed on the surface.
Next, a silicon-containing anode was prepared using the silicon-containing anode active material prepared by the above method instead of the silicon-containing anode active material of example 1-1.
Example 2-2
A silicon-containing anode was produced in the same manner as in example 2-1 except that 10 stainless steel ball media were added thereto.
Comparative example 1-1
A silicon-containing anode was produced in the same manner as in example 1-1 except that the pulverization time was changed to 8 hours.
Comparative examples 1 to 2
A silicon-containing anode was produced in the same manner as in example 1-1 except that the pulverization time was changed to 1 hour.
Comparative examples 1 to 3
A silicon-containing anode was produced in the same manner as in example 1-1 except that the pulverization time was changed to 5 hours.
Comparative examples 1 to 4
A silicon-containing anode was produced in the same manner as in example 1-1 except that 10 stainless steel ball media were added thereto, and the pulverizing time was changed to 5 hours.
Comparative examples 1 to 5
A silicon-containing anode was produced in the same manner as in example 1-1 except that 30 stainless steel ball media were added thereto, and the pulverization time was changed to 8 hours.
Comparative examples 1 to 6
A silicon-containing anode was produced in the same manner as in example 1-1 except that 30 stainless steel ball media were added thereto, and the pulverization time was changed to 1 hour.
Comparative examples 1 to 7
A silicon-containing anode was produced in the same manner as in example 1-1 except that 30 stainless steel ball media were added thereto.
Comparative example 2-1
A silicon-containing anode was produced in the same manner as in example 2-1 except that the pulverization time was changed to 8 hours.
Comparative example 2-2
A silicon-containing anode was produced in the same manner as in example 2-1 except that the pulverization time was changed to 1 hour.
Comparative examples 2 to 3
A silicon-containing anode was produced in the same manner as in example 2-1 except that the pulverization time was changed to 5 hours.
Comparative examples 2 to 4
A silicon-containing anode was produced in the same manner as in example 2-1 except that 10 stainless steel ball media were added thereto, and the pulverizing time was changed to 5 hours.
Comparative examples 2 to 5
A silicon-containing anode was produced in the same manner as in example 2-1 except that 30 stainless steel ball media were added thereto, and the pulverization time was changed to 8 hours.
Comparative examples 2 to 6
A silicon-containing anode was produced in the same manner as in example 2-1 except that 30 stainless steel ball media were added thereto, and the pulverization time was changed to 1 hour.
Comparative examples 2 to 7
A silicon-containing anode was produced in the same manner as in example 2-1 except that 30 stainless steel ball media were added thereto.
Comparative example 3-1
A silicon-containing anode was produced in the same manner as in embodiment 1-1 except that carbon black was used instead of the single-walled carbon nanotubes.
In the anode active material layer, the weight ratio of the silicon-containing anode active material, the artificial graphite, the carbon black, the carboxymethyl cellulose, the styrene-butadiene rubber and the dispersing agent is 14.49:82.11:1:1.2:1.2.
comparative example 3-2
A silicon-containing anode was produced in the same manner as in example 1-1, except that a multi-walled carbon nanotube (MWCNT) was used instead of the single-walled carbon nanotube.
In the anode active material layer, the weight ratio of the silicon-containing anode active material, the artificial graphite, the multi-wall carbon nanotube (MWCNT), the carboxymethyl cellulose, the styrene-butadiene rubber and the dispersant was 14.63:82.92:0.05:1.2:1.2.
The silicon-containing negative electrodes prepared in examples and comparative examples are shown in table 1 below.
TABLE 1
Particle size analysis of the silicon-containing anode active material was confirmed using a Microtrac apparatus (manufacturer: microtrac company, model name: S3500) using water and Triton-X100 dispersant at a refractive index of 1.97.
Specific surface area was degassed at 130℃for 2 hours by using BET measuring equipment (BEL-SORP-MAX, nippon Bell Co.) and N was carried out at 77K 2 Adsorption/desorption.
The content of metal atoms was confirmed by ICP analysis using an inductively coupled plasma atomic emission spectrometer (ICP-OES AVIO 500 of Perkin Elmer 7300).
Physical properties of the conductive materials used in the examples and comparative examples are shown in table 2 below.
TABLE 2
The average length and/or particle size of the conductive material used was measured by SEM, the average diameter thereof was measured by TEM, and the average diameter was measured by BET measurement method at N 2 The specific surface area was measured under adsorption/desorption and deaeration at 200 ℃ for 8 hours.
< experimental example: evaluation of discharge capacity, initial efficiency and service life (Capacity Retention Rate) characteristics ]
The negative electrode active materials in examples and comparative examples were used to prepare a negative electrode and a battery, respectively.
Cutting lithium (Li) metal sheet into 1.7671cm 2 The lithium (Li) metal thin film obtained by rounding was used as the positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte in which vinylene carbonate was dissolved in a mixed volume ratio of 7 in 0.5 parts by weight was injected thereto to prepare a lithium coin half cell: 3 (EMC) and Ethylene Carbonate (EC) and is also dissolved with 1M LiPF 6 。
The discharge capacity, initial efficiency and capacity retention were evaluated by charging and discharging the prepared battery, as shown in table 3 below.
For cycle 1 and cycle 2, the battery was charged and discharged at 0.1C, and from cycle 3, the battery was charged and discharged at 0.5C. The 300 th cycle was completed in the charged state (lithium was contained in the negative electrode).
Charging conditions: CC (constant current)/CV (constant voltage) (5 mV/0.005C current cut-off)
Discharge conditions: CC (constant current) Condition 1.5V
The discharge capacity (mAh/g) and initial efficiency (%) were derived from the results during the first charge/discharge. Specifically, the initial efficiency (%) was derived by the following calculation.
Initial efficiency (%) = (discharge capacity after 1 st discharge/1 st charge capacity) ×100
The charge retention rates were each derived by the following calculation.
Capacity retention (%) = (300 th discharge capacity/1 st discharge capacity) ×100
TABLE 3
| Discharge capacity (mAh/g) | Initial efficiency (%) | Capacity retention (%) | |
| Example 1-1 | 512 | 87.1 | 90 |
| Examples 1 to 2 | 515 | 87.1 | 95 |
| Examples 1 to 3 | 511 | 86.9 | 88 |
| Example 2-1 | 500 | 89.6 | 90 |
| Example 2-2 | 502 | 89.6 | 95 |
| Comparative example 1-1 | 510 | 86.6 | 85 |
| Comparative examples 1 to 2 | 505 | 86.2 | 83 |
| Comparative examples 1 to 3 | 511 | 86.1 | 83 |
| Comparative examples 1 to 4 | 511 | 86.1 | 83 |
| Comparative examples 1 to 5 | 505 | 86.2 | 83 |
| Comparative examples 1 to 6 | 503 | 86.1 | 81 |
| Comparative examples 1 to 7 | 509 | 86.6 | 86 |
| Comparative example 2-1 | 496 | 89.0 | 85 |
| Comparative example 2-2 | 493 | 87.4 | 83 |
| Comparative examples 2 to 3 | 496 | 88.7 | 83 |
| Comparative examples 2 to 4 | 496 | 88.7 | 83 |
| Comparative examples 2 to 5 | 495 | 88.7 | 83 |
| Comparative examples 2 to 6 | 493 | 87.4 | 82 |
| Comparative examples 2 to 7 | 496 | 89.1 | 85 |
| Comparative example 3-1 | 500 | 85.0 | 75 |
| Comparative example 3-2 | 505 | 86.3 | 80 |
The negative electrode according to the invention comprises D 5 /D 50 Is more than 0.5, D 5 Is more than 3 mu m, D 50 A silicon-containing anode active material of 4 μm or more and 11 μm or less and containing single-walled carbon nanotubes as a conductive material.
Since the anode active material particles have an appropriate D 5 、D 50 And D 5 /D 50 The negative electrode has the effects of suppressing side reactions with the electrolyte, promoting charge and discharge, whereby capacity/efficiency is sufficiently achieved and life characteristics are stabilized.
Further, when the anode active material satisfying the particle size distribution and the single-walled carbon nanotube are used, the conductive paths between the particles satisfying the particle size distribution are more easily connected, so that the conductive path loss due to expansion of the silicon-containing anode active material can be prevented.
When the particle size distribution is not satisfied, i.e., D 5 /D 50 Less than 0.5, D 5 Less than 3 μm or D 50 When a negative electrode active material smaller than 4 μm is used together with single-walled carbon nanotubes, there is a problem in that the negative electrode active material is excessively used during the cycle progress due to an increase in side reaction with an electrolyte, and thus deterioration frequently occurs, so that the service life characteristics are deteriorated. When D is to 50 When a negative electrode active material larger than 11 μm is used together with single-walled carbon nanotubes, there is a problem in that the volume difference due to the swelling phenomenon of the negative electrode active material is too large, and the service life is reduced because the disconnection of the conductive path cannot be prevented.
In table 3, in examples 1-1 to 1-3 and 2-1 and 2-2, a negative electrode including a negative electrode active material satisfying a specific particle size and single-walled carbon nanotubes as a conductive material was used, and it was confirmed that the discharge capacity, initial efficiency and capacity retention were excellent.
It can be confirmed that examples 1-1 and 1-2 are negative electrode active materials containing Mg, and do not satisfy D 5 /D 50 Value or not satisfy D 5 Value sum D 50 The comparative examples 1-1 to 1-7 of the values are excellent in all of the discharge capacity, initial efficiency and capacity retention. Further, it can be confirmed that examples 2-1 and 2-2 are anode active materials containing Li, and are excellent in discharge capacity, initial efficiency, and capacity retention ratio as compared with comparative examples 2-1 to 2-7.
In contrast, comparative examples 1 and 5 do not satisfy the D of the present invention 5 /D 50 、D 5 And D 50 。
Comparative examples 1-1 and 1-4 satisfy the D of the present invention 5 /D 50 But does not satisfy D 5 Or D 50 It can be confirmed that capacity, efficiency and service life are reduced as compared with the examples.
In particular, even D 5 /D 50 At least 0.5, when D 5 Less than 3 μm or D 50 At less than 4 μm, the overall particle size is too small so that the specific surface area of the material becomes large and oxidation frequently occurs. It can thus be confirmed that the capacity, efficiency and service life are lower than those in the examples due to frequent occurrence of side reactions with the electrolyte during charge/discharge.
In addition, even D 5 /D 50 At least 0.5, when D 50 When exceeding 11 μm, the overall particle size is too large to confirm that the capacity, efficiency and service life are reduced compared to the examples because the battery is not easily charged and discharged.
In addition, when D 5 /D 50 Less than 0.5, the negative electrode is formed by a negative electrode having a specific value D 50 The volume occupied by the negative electrode active material of a much smaller size increases, so that it can be confirmed that, compared with the examples, the side reaction with the electrolyte increasesAdditionally, capacity, efficiency and service life are reduced.
Comparative examples 3-1 and 3-2 are cases where dot-shaped conductive material carbon black is used or multi-wall carbon nanotubes are used instead of single-wall carbon nanotubes, and even if the same anode active material as in example 1 is used, it is not easy to secure a conductive path between particles, so that it can be confirmed that, in particular, the service life of the battery is significantly reduced.
Thus, by adjusting D 5 、D 50 And D 5 /D 50 The range of negative electrode active materials used with single-walled carbon nanotube conductive materials to reduce side reactions with electrolytes and ensure conductive paths can readily improve the capacity, efficiency, and/or service life of the battery.
Claims (17)
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| KR1020220008551A KR20230025315A (en) | 2021-08-13 | 2022-01-20 | Negative electrode and secondary battery comprising the negative electrode |
| KR10-2022-0008551 | 2022-01-20 | ||
| PCT/KR2022/011863 WO2023018184A1 (en) | 2021-08-13 | 2022-08-09 | Negative electrode and secondary battery including negative electrode |
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