KR20190084758A - Electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrode for a lithium secondary battery. An electrode mixture comprising a bimodal electrode active material formed of big particles and small particles having different average particle diameters, a conductive material, and a binder is coated on a current collector. The weight ratio of the big particle to the small particle is 6:4 to 8:2, and the ratio of the average particle diameter (D50) of the big particle and the average particle diameter (D50) of the small particle is 4.3:1 to 2:1.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode for a lithium secondary battery, and a lithium secondary battery employing the same. BACKGROUND ART [0002]

The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery employing the same.

Lithium secondary batteries are a type of secondary battery in which charging and discharging are performed by inserting and separating lithium ions in a battery. During charging, lithium ions move from the cathode to the anode, In contrast, during discharging, the lithium ions inserted into the negative electrode move toward the positive electrode and are inserted into the active material of the positive electrode. Such a lithium secondary battery has advantages of high energy density, large electromotive force, and high capacity, and is widely used as a power source for mobile phones and notebook computers.

The lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and an electrolytic solution. The positive electrode and the negative electrode include a positive electrode active material and a negative electrode active material capable of inserting and desorbing lithium ions as described above. The separator prevents physical cell contact between the anode and cathode. Instead, the movement of the ions through the separator is free. The electrolyte serves as a passage through which ions can move freely between the anode and the cathode.

On the other hand, in the lithium secondary battery, the positive electrode current collector and the negative electrode current collector are each coated with an active material to have a constant thickness, and the separator is interposed between the current collectors to take a plurality of turns in the form of a jelly roll or a cylinder The electrode assembly can be manufactured by housing the electrode assembly in a cylindrical shape, a square can or a pouch, and sealing the electrode assembly.

On the other hand, during the process of manufacturing the battery as described above, the process of coating the electrode mixture on the current collector is subjected to a rolling process. In this case, a stress is applied to the current collector from the electrode mixture to cause a crack in the current collector Can be. When a crack occurs on the current collector, the electron transfer path is reduced and the cell resistance is increased. This may adversely affect the lifetime characteristics and the high rate charge / discharge characteristics of the battery.

In addition, if the crack is severe, a complete breakage may occur in the current collector, and there is a problem that the electrode tab portion forming the electrode is blocked when the breakage occurs, thereby losing the function of the battery cell itself.

Disclosure of the Invention The present invention has been made to solve the above problems, and it is an object of the present invention to provide a bimodal electrode active material composed of opposed and small particles having different average particle diameters, an electrode material mixture including a conductive material and a binder, And the average particle diameter (D50) of the major particles and the average particle diameter (D50) of the minor particles are within a specific range, thereby improving not only the rolling property in the rolling process during the electrode manufacturing process An electrode for a lithium secondary battery that effectively prevents a crack that may occur in an electrode in a winding process, and a lithium secondary battery employing the electrode.

In the present specification, an electrode mixture containing a bimodal electrode active material, an electrically conductive material and a binder, which are composed of major and minor particles having different average particle diameters, is applied on the current collector, and the weight ratio of the major particles: Wherein the average particle size (D50) of the major particles is in a range of 6: 4 to 8: 2, and the average particle size (D50) ratio of the minor particles is in a range of 4.3: 1 to 2:

Also, in the present specification, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, wherein at least one electrode selected from the positive electrode and the negative electrode is an electrode for the lithium secondary battery.

Hereinafter, an electrode for a lithium secondary battery and a lithium secondary battery according to a specific embodiment of the present invention will be described in detail.

As described above, according to one embodiment of the present invention, an electrode mixture containing an electrode active material in the form of a bimodal, an electrically conductive material, and a binder, which is composed of major and minor particles having different average particle diameters, Wherein the weight ratio of the major particles to the minor particles is from 6: 4 to 8: 2, and the average particle diameter (D50) of the major particles is in a range of from 4.3: 1 to 2: Can be provided.

The present inventors have found that, in an electrode for a lithium secondary battery, an electrode active material particle in an electrode mixture applied on a current collector is formed in a bimodal form composed of major particles and minor particles, wherein the weight ratio of the major particles to the major particles When the average particle size (D50) ratio of the particle size (D50) to the minor particle size (D50) is set within a specific range, not only the rolling property is improved in the rolling process during the electrode manufacturing process, cracks) effectively by the experiment and completed the invention.

In the electrode for a lithium secondary battery according to an embodiment of the present invention, the electrode active material in the electrode mixture formed on the current collector has a bimodal form composed of major particles and minor particles having different average particle diameters, and the weight ratio of major particles: (D50): the average particle size (D50) of the minor particles is 4.3: 1 to 2: 1, or 4: 1 to 4: 2.5: 1.

Generally, according to the prior art, it is possible to improve the bulk density and the rolling property by using an average particle size of an electrode active material as an electrode active material and an average particle size of the electrode active material. In particular, the particle size d _small / it is known that the smaller the diameter ratio (d _s / d ₁ ) measured in a _large size, the better the packing effect during rolling. However, when the packing is good and the active material particles directly contact the current collector in a large number, for example, as shown in Fig. 2, the stress applied to the current collector in the winding process performed after rolling relatively increases, Cracks are generated in the cell, the electron transfer path is reduced, and the cell resistance is increased, which may adversely affect the lifetime characteristics and the high rate charge / discharge characteristics of the cell.

In addition, in the case where the crack is severe, as shown in the example of FIG. 3, a complete disconnection may occur. In this case, the electrode tab portion forming the electrode may be blocked, .

However, according to the present invention, the electrode active material is composed of a bimodal form composed of major and minor particles having different average particle diameters, wherein the weight ratio of the major particles to the minor particles and the average particle size (D50) (D50) ratio is set to be within a specific range, the stress applied to the electrode can be minimized while improving the rolling property in the rolling process by improving the volume density, thereby effectively preventing cracks in the electrode in the winding process . Therefore, it is possible to prevent shortening of the lifetime of the battery due to the crack and deterioration of the charging / discharging characteristic of the high rate, and furthermore, the problem of the self-function of the jersey cell being lost can be prevented in advance.

Specifically, the weight ratio of the major particles to the minor particles is 6: 4 to 8: 2, the average particle diameter (D50) of the major particles, the average particle diameter (D50) : May be one. It is possible to sufficiently secure the filling density within the weight ratio range and the average particle diameter ratio of the major particle to the minor particle to improve the rolling property in the rolling process and reduce the stress applied to the current collector, .

The average particle diameter (D50) of the allergen particle according to an embodiment of the present invention may be 13 to 15 占 퐉 or 14 to 15 占 퐉, and the average particle diameter (D50) 6.5 mu m, or 4 to 6 mu m. The average particle diameter (D50) of the major particle / minor particle can be measured according to a conventional method of measuring the number average particle diameter. The particle size distribution per particle size can be measured using a particle size analyzer well known to those skilled in the art, have. .

Meanwhile, in the electrode for a lithium secondary battery according to an embodiment of the present invention, the average particle diameter (D50) value of all the particles of the electrode active material having a bimodal form composed of major and minor particles having different average particle diameters is 9 to Or 9.5 to 10.5 占 퐉, and the standard deviation SD of the particle diameter may be more than 0 and 2 or less, or 0.1 to 1.5.

According to an embodiment of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one electrode selected from the positive electrode and the negative electrode is a lithium secondary battery A battery may be provided.

The positive electrode or negative electrode is composed of a current collector and an electrode mixture applied on the current collector, and the electrode mixture may include an electrode active material, a conductive material, and a binder.

The current collector is a metal having high conductivity and is not limited as long as it can easily adhere to the electrode mixture slurry and is not reactive in the voltage range of the battery. When the current collector is a cathode current collector, it may be a foil made of aluminum, nickel, or a combination thereof, for example, or may be a laminate of the materials made of the above materials. When the current collector is an anode current collector, it may be a foil made of copper, gold, nickel or a copper alloy or a combination thereof, or may be a laminate of the materials made of the above materials.

On the other hand, when the electrode active material of the electrode mixture is a cathode active material, a cathode active material capable of intercalating and deintercalating lithium, for example, a manganese spinel type active material or a lithium metal oxide may be used. Examples of the lithium metal oxide include lithium-manganese-based oxides containing lithium, lithium-nickel-manganese-based oxides, lithium-manganese-cobalt oxides and lithium-nickel-manganese-cobalt oxides.

When the electrode active material of the electrode mixture is a negative electrode active material, a negative electrode active material capable of intercalating and deintercalating lithium, for example, lithium metal, a carbon material, a metal compound, and a mixture thereof may be used. For example, low-crystalline carbon and highly-crystalline carbon may be used as the carbonaceous material. The low crystalline carbon may be at least one selected from the group consisting of soft carbon and hard carbon. The high crystalline carbon may be selected from the group consisting of natural graphite, Kish graphite, pyrolytic carbon, One or more of high temperature sintered carbon consisting of mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes. .

The metal compound may be at least one selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Or a compound containing at least one metal element. These metal compounds can be used in any form such as a single body, an alloy, an oxide (TiO ₂ , SnO _2, etc.), a nitride, a sulfide, a boride and an alloy with lithium, but an alloy with a single body, alloy, It can be increased in capacity. Among them, the film may contain at least one element selected from Si, Ge, and Sn, and more specifically, may include at least one element selected from Si and Sn in order to increase the capacity of the battery.

On the other hand, the conductive material is conductive without causing side reactions with other elements of the battery. Specific examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black (super-p), acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative, or the like.

On the other hand, the binder is a component that assists in bonding between the electrode active material and the conductive material and bonding to the current collector. Specific examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, , Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) , Sulfonated EPDM, styrene-butadiene rubber (SBR), and fluorine rubber.

The electrode according to an embodiment of the present invention can be manufactured by applying the electrode mixture mixed with the electrode active material, the conductive material and the binder on the current collector. Specifically, an electrode mixture is coated on a current collector and then pressed to produce an electrode. Specifically, in the rolling process, an electrode current collector coated with an electrode mixture is passed between two or more rotating rolls. Through this process, the electrode mixture can be adhered well onto the electrode current collector. On the other hand, the two or more rotating rolls may be in a high temperature state. Meanwhile, after the rolling process as described above, it may further include a drying step.

 Among the electrodes thus manufactured, the positive electrode may be a positive electrode mixture coated with a positive electrode mixture having a thickness of 30 to 180 占 퐉, more specifically 50 to 150 占 퐉 on the current collector. The amount of the positive electrode active material is sufficiently secured within the thickness range of the positive electrode material mixture, the battery capacity is prevented from being reduced, and the cycle characteristics and rate characteristics can be improved.

Among the electrodes thus manufactured, the negative electrode may be coated on the current collector with a negative electrode mixture of 1 占 퐉 to 180 占 퐉, more specifically, 30 占 퐉 to 150 占 퐉 thick. When the material satisfies such a thickness range within the thickness range of the negative electrode material mixture, the amount of active material in the negative electrode active material layer is sufficiently secured, the battery capacity can be prevented from being reduced, and the cycle characteristics and rate characteristics can be improved .

According to an embodiment of the present invention, there is provided a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one electrode selected from the positive electrode and the negative electrode is a lithium secondary battery Is provided.

The electrode for a lithium secondary battery may be a positive electrode or a negative electrode.

On the other hand, the separator is interposed between the positive electrode and the negative electrode and outside the positive electrode or negative electrode in a state in which the positive electrode plate and the negative electrode plate are not wound, and when the positive electrode and the negative electrode are wound together with the separator, Thereby preventing contact with a cathode or an anode located inside. On the other hand, in the case of the electrode for a lithium secondary battery constructed in accordance with the present invention, the occurrence of cracks in the electrode during the winding process is effectively suppressed.

The separator may be a polymer porous substrate which is usually used in the art as a separator, and is not particularly limited. For example, polyolefin-based porous substrates; Or a group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfite, polyethylene naphthalene , Or a mixture of two or more thereof. The polyolefin-based porous substrate may be any polyolefin-based porous substrate that is commonly used. More particularly, the present invention relates to a film formed of a polymer such as polyethylene, polypropylene, polybutylene or polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, ) Or a nonwoven fabric.

As described above, when the positive electrode, the negative electrode, and the separator are prepared, a jelly roll is formed by winding the electrode assembly, dried and stored in the battery case, and the electrolyte solution is injected into the battery case. On the other hand, the type of the battery case is not particularly limited, but may be, for example, a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can.

On the other hand, the electrolyte solution may include an organic solvent and an electrolyte salt as the non-aqueous electrolyte, and the organic solvent commonly used in the electrolyte for a lithium secondary battery may be used without limitation. Typical examples are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate Any one or a mixture of two or more selected from the group consisting of mate (MF), gamma-butyrolactone (γ-BL), sulfolane and methyl acetate (MA) However, the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolytic solution well. The cyclic carbonate may contain dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as a carbonate is mixed in an appropriate ratio, a nonaqueous electrolyte having a high electric conductivity can be produced.

The electrolyte salt contained in the nonaqueous electrolyte of the present invention may be an anion selected from the group consisting of F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^{- _{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 - , and (CF ₃ CF ₂ SO ₂ ) _{2 <} N > ^- . Examples of the electrolyte salt include LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, and lithium tetraphenylborate, but are not limited thereto.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

The lithium secondary battery using the electrode for a lithium secondary battery of the present invention not only improves the rolling property in the rolling process during the electrode manufacturing process but also effectively prevents cracks in the current collector in the winding process.

Accordingly, it is possible to prevent a problem that the cell resistance is increased, the battery lifetime characteristics and the high rate charge / discharge characteristics are reduced, the complete disconnection due to cracks in the electrode is prevented, and the battery cell function is lost.

FIG. 1 shows a result of measuring stress applied to a positive electrode current collector for a lithium secondary battery according to Example 1 of the present invention. FIG.
2 is a graph showing a result of measuring stress applied to a positive electrode current collector for a lithium secondary battery according to Comparative Example 1 of the present invention.
3 is a photograph showing that an electrode crack is generated when the electrode manufactured according to Comparative Example 1 is wound.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Best Mode for Carrying Out the Invention Hereinafter, the operation and effect of the present invention will be described in more detail through specific embodiments of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

Example 1: Electrode Fabrication

(Polyvinylidene fluoride, 10 wt%) was dissolved in N-methylpyrrolidone (NMP) solvent to prepare a binder solution. Then, the binder solution and the acetylene black conductive material (super C65, average Particle diameter (D50) 30 nm) were mixed and stirred at 1500 rpm for 3 minutes.

Subsequently, a lithium cobalt oxide (LiCoO ₂ ) in which the major particle having an average particle diameter (D50) of 15 μm and the minor particle having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 8: 2 was prepared, Of 0.19: 1, and then mixed at 1500 rpm for 5 minutes to prepare a cathode active material slurry (solid content 80 wt%). At this time, the average particle diameter of the whole particles of the positive electrode active material was 10 mu m.

Next, the slurry of the prepared cathode active material was coated on an aluminum foil having a thickness of 15 탆 using a comma coater at a level of 6.3 mg / cm 2 and hot air dried to obtain a positive electrode including a first positive electrode mixture layer having a porosity of 65% Thickness: 107 mu m, positive electrode material mixture layer thickness: 92 mu m).

A roll press equipment (CIS Co., Ltd., DLC-CLPCA-2020) equipped with two upper rolls and a lower roll was prepared, and the gap between the two upper rolls and the lower rolls was set to 85 탆 .

Rolled while passing the aluminum foil formed with the positive electrode material mixture layer between the two rolls at room temperature to prepare a positive electrode (total thickness 85 占 퐉, positive electrode material mixture layer thickness 77 占 퐉) including a positive electrode mixture layer having a porosity of 55% Respectively. The positive electrode prepared after the primary rolling was allowed to stand for 1 hour. Next, the gap between the upper roll and the lower roll was set to a thickness of 67 mu m, and then rolled while passing through the positive electrode produced after the primary rolling to obtain a positive electrode including a positive electrode mixture layer having a porosity of 40 vol% Total thickness 67 mu m, positive electrode material mixture layer thickness 52 mu m). Subsequently, the anode produced after the secondary rolling was allowed to stand for 1 hour. Next, third rolling was performed at the same roll interval as the secondary rolling step to produce a positive electrode (total thickness 67 mu m, positive electrode mixture layer thickness 52 mu m) including a positive electrode mixture layer having a porosity of 40 vol%.

The prepared anode includes a bimodal type cathode active material having different sizes and a conductive material.

Example 2

An electrode was prepared in the same manner as in Example 1 except that the major particle having an average particle diameter (D50) of 15 μm and the minor particle having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 7: 3.

Comparative Example 1

An electrode was prepared in the same manner as in Example 1 except that the major particle having an average particle diameter (D50) of 15 μm and the minor particle having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 9: 1.

Comparative Example 2

An electrode was prepared in the same manner as in Example 1 except that the major particle having an average particle diameter (D50) of 15 μm and the minor particle having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 5: 5.

Comparative Example 3

An electrode was produced in the same manner as in Example 1 except that the major particle having an average particle diameter (D50) of 15 μm and the minor particle having an average particle diameter (D50) of 3 μm were used.

Comparative Example 4

An electrode was prepared in the same manner as in Example 1, except that the fine particles having an average particle diameter (D50) of 13 μm and an average particle diameter (D50) of 7 μm were used.

[Experimental Example]

Experimental Example 1: Evaluation of Stress on Anode

The stresses applied to the respective positive electrode current collectors were measured in the positive electrode for a lithium secondary battery manufactured according to Example 1 and Comparative Example 1, respectively, and the measurement results are shown in FIGS. 1 and 2, respectively. 1 and 2, it was confirmed that the stress applied to the electrode current collector in Example 1 was smaller than that in Comparative Example 1.

Experimental Example 2: Measurement of occurrence of crack in a collector

With respect to Examples 1 and 2 and Comparative Examples 1 to 4, whether or not a crack occurred in the positive electrode collector was checked and evaluated according to the following criteria. The evaluation results are summarized in the following Table 1:

* Criteria for evaluation of crack occurrence

X: No crack occurred in the electrode collector in the electrode manufactured

DELTA: Cracks were generated in the electrode collector in the produced electrode, but disconnection of the electrode current collector did not occur

O: Cracks and disconnection occurred in the electrode current collector in the produced electrode (for example, Fig. 3)

Crack occurrence Example 1 X Example 2 X Comparative Example 1 △ Comparative Example 2 O Comparative Example 3 O Comparative Example 4 O

As shown in Table 1, in Examples 1 and 2, the stress applied to the electrode current collector was reduced so that cracks did not occur on the electrode current collector. In Comparative Examples 1 to 4, cracks, Was found to occur.

Claims (6)

An electrode mixture containing a bimodal electrode active material, an electrically conductive material and a binder, made of an opposite particle and a small particle having different average particle diameters, is applied on the current collector,
Wherein the weight ratio of the major particles to the minor particles is from 6: 4 to 8: 2, and the average particle size (D50) of the major particles to the average particle size (D50) of the minor particles is from 4.3: 1 to 2: The method according to claim 1,
And an average particle diameter (D50) of the above-mentioned major particles is 13 to 15 占 퐉. Wherein the average particle size (D50) of the small particles is 3.5 to 6.5 占 퐉. The method according to claim 1,
The average particle size (D50) value of all the bimodal electrode active material particles having the average particle size different from each other is 9 to 11 占 퐉 and the standard deviation SD of the particle size is more than 0 and less than 2 , An electrode for a lithium secondary battery. A lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte solution, wherein at least one electrode selected from the positive electrode and the negative electrode is an electrode for a lithium secondary battery. An electrode mixture containing a bimodal electrode active material, an electrically conductive material and a binder, made of an opposite particle and a small particle having different average particle diameters, is applied on the current collector,
Wherein the weight ratio of the major particles to the minor particles is from 6: 4 to 8: 2, and the average particle size (D50) of the major particles to the average particle size (D50) of the minor particles is 20: 1 to 2:

Images