WO2008001537A1

WO2008001537A1 - Negative electrode for polymeric electrolyte secondary battery

Info

Publication number: WO2008001537A1
Application number: PCT/JP2007/058245
Authority: WO
Inventors: Tomoyoshi Matsushima; Shinji Ishii; Yoshiki Sakaguchi; Kiyotaka Yasuda
Original assignee: Mitsui Mining & Smelting Co., Ltd.
Priority date: 2006-06-30
Filing date: 2007-04-16
Publication date: 2008-01-03
Also published as: JP2008016196A

Abstract

A negative electrode (10) for use in a polymeric electrolyte secondary battery comprises an active material layer (12) containing a particle (12a) of an active material. At least a part of the surface of the particle (12a) is coated with a metal material (13) having a poor ability of forming a lithium compound. A void is formed between the particles (12a) that are coated with the metal material (13). The active material layer has a void ratio of 15 to 45%. Preferably, the metal material (13) is present over the entire area of such a part of the surface of the particle that extends in the thickness-wise direction of the active material layer. Also preferably, the particle (12a) of the active material is composed of a silicone material, and the active material layer (12) contains a conductive carbon material in an amount of 1 to 3% by weight relative to the weight amount of the particle (12a) of the active material.

Description

Specification

Negative electrode for polymer electrolyte secondary battery

Technical field

The present invention relates to a negative electrode for a polymer electrolyte secondary battery such as a lithium polymer secondary battery.

Background art

[0002] The present applicant has previously described an active material comprising a pair of current collecting surface layers whose surfaces are in contact with an electrolytic solution, and particles of an active material having a high ability to form a lithium compound, interposed between the surface layers. A negative electrode for a non-aqueous electrolyte secondary battery provided with a layer has been proposed (see Patent Document 1). The active material layer of the negative electrode is infiltrated with a metal material having a low lithium compound forming ability, and active material particles are present in the infiltrated metal material. Since the active material layer has such a structure, the negative electrode is less likely to fall off even if it becomes fine due to expansion and contraction of the particles due to charge / discharge. As a result, the use of this negative electrode has the advantage of increasing the battery's lifetime.

[0003] By the way, as the secondary battery using the insertion and extraction of lithium ions, in addition to the non-aqueous electrolyte secondary battery, a polymer electrolyte secondary battery using a polymer gel electrolyte is known! / ヽThe The polymer gel electrolyte used in the polymer electrolyte secondary battery is of low fluidity. Therefore, even if a negative electrode for a secondary battery using a non-aqueous electrolyte, which is a highly fluid liquid, is used as it is for a negative electrode for a polymer electrolyte secondary battery, a battery having desired characteristics can be obtained. I can't.

[0004] Patent Document 1: US2006— 0115735A1

[0005] Accordingly, an object of the present invention is to provide a negative electrode for a polymer electrolyte secondary battery having further improved performance as compared with the above-described conventional negative electrode.

Disclosure of the invention

[0006] The present invention includes an active material layer containing particles of an active material, and at least a part of the surface of the particles has a low ability to form a potassium compound, is coated with a metal material !, and Voids are formed between the particles coated with a metal material, and mercury intrusion method CFIS R 1655) The negative electrode for a polymer electrolyte secondary battery is characterized in that the porosity of the active material layer measured in accordance with the above is 15 to 45%.

Brief Description of Drawings

[0007] FIG. 1 is a schematic view showing a cross-sectional structure of an embodiment of a negative electrode for a polymer electrolyte secondary battery of the present invention.

FIG. 2 is a schematic view showing an enlarged main part of a cross section of the active material layer in the negative electrode shown in FIG.

FIG. 3 (a) to FIG. 3 (d) are process diagrams showing a method for manufacturing the negative electrode shown in FIG. Detailed Description of the Invention

Hereinafter, the present invention will be described based on its preferred embodiments with reference to the drawings. FIG. 1 shows a schematic diagram of a cross-sectional structure of an embodiment of a negative electrode for a polymer electrolyte secondary battery of the present invention. The negative electrode 10 of the present embodiment includes a current collector 11 and an active material layer 12 formed on at least one surface thereof. In FIG. 1, for the sake of convenience, the active material layer 12 is formed only on one side of the current collector 11 to show the state! /, But the active material layer is formed on both sides of the current collector. Have you been?

[0009] The active material layer 12 includes particles 12a of the active material. As the active material, a material capable of occluding and releasing lithium ions is used. Examples of such materials include silicon-based materials, tin-based materials, aluminum-based materials, and germanium-based materials. As the tin-based material, for example, an alloy containing tin, cobalt, carbon, and at least one of nickel and chromium is preferably used. In order to improve the capacity density per weight of the negative electrode, a silicon-based material is particularly preferable.

[0010] As the silicon-based material, a material capable of occluding lithium and containing silicon, for example, silicon alone, an alloy of silicon and metal, silicon oxide, or the like can be used. These materials can be used alone or in combination. Examples of the metal include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Of these metals, Cu, Ni, and Co are preferred, and Cu and Ni are preferably used because of their excellent electronic conductivity and low ability to form lithium compounds. Also, before or after incorporating the negative electrode into the battery After that, lithium may be occluded in the active material having a silicon-based material strength. A particularly preferable silicon-based material is silicon or silicon oxide having a high lithium storage capacity.

[0011] In the active material layer 12, at least a part of the surface of the particle 12a is covered with a metal material having a low ability to form a lithium compound. The metal material 13 is a material different from the constituent material of the particles 12a. Voids are formed between the particles 12a coated with the metal material. That is, the metal material covers the surface of the particle 12a in a state in which a gap is provided so that the polymer gel electrolyte can reach the particle 12a. In FIG. 1, the metal material 13 is conveniently represented as a thick line surrounding the periphery of the particle 12a. In the figure, among the particles 12a included in the active material layer 12, there is a force that is drawn so that there is no contact with other particles. In fact, each particle is in direct contact with other particles or through a metal material 13. “Low ability to form lithium compound” means that lithium does not form an intermetallic compound or solid solution, or even if lithium is formed, the amount of lithium is very small or very unstable.

[0012] The metal material 13 has conductivity, and examples thereof include copper, nickel, iron, cobalt, and alloys of these metals. In particular, the metal material 13 is preferably a highly ductile material in which even if the active material particles 12a expand and contract, the surface coating of the particles 12a is not easily broken. It is preferable to use copper as such a material.

[0013] The metal material 13 is preferably present on the surface of the active material particles 12a over the entire thickness direction of the active material layer 12. The active material particles 12 a are preferably present in the matrix of the metal material 13. As a result, even if the particles 12a expand and contract due to charge and discharge, even if they become fine powder, they are less likely to fall off. In addition, since the electronic conductivity of the entire active material layer 12 is ensured through the metal material 13, the electrically isolated active material particles 12 a are generated, particularly in the deep part of the active material layer 12. The formation of the active material particles 12a is effectively prevented. This is particularly advantageous when a semiconductor is used as the active material and electron conductivity is poor, and a material such as a silicon-based material is used. Metal material 13 is active material particles 12a throughout the thickness direction of active material layer 12 It can be confirmed by electron microscope mapping with the material 13 as a measurement target.

[0014] The metal material 13 covers the surfaces of the particles 12a continuously or discontinuously. When the metal material 13 continuously covers the surfaces of the particles 12a, it is preferable to form fine voids in the coating of the metal material 13 that allow the polymer gel electrolyte to flow. In the case where the metal material 13 discontinuously covers the surface of the particle 12a, the polymer gel electrolyte is supplied to the particle 12a through the portion of the surface of the particle 12a that is covered with the metal material 13. . In order to form the coating of the metal material 13 having such a structure, the metal material 13 may be deposited on the surface of the particle 12a by, for example, electrolytic plating according to the conditions described later.

[0015] The average thickness of the metal material 13 covering the surfaces of the active material particles 12a is preferably 0.05 to 2 / ζ πι, more preferably 0.1 to 0.25 / zm. / !, thin! /. That is, the metal material 13 covers the surface of the active material particles 12a with a minimum thickness. This prevents the dropout due to the particles 12a from expanding and contracting due to charge and discharge to be pulverized while increasing the energy density. Here, the “average thickness” is a value calculated based on a portion of the surface of the active material particle 12 a that is actually covered with the metal material 13. Accordingly, the portion of the surface of the active material particles 12a not covered with the metal material 13 is not used as the basis for calculating the average value.

[0016] The void formed between the particles 12a coated with the metal material 13 serves as a flow path of the polymer gel electrolyte. The polymer gel electrolyte smoothly circulates in the thickness direction of the active material layer 12 due to the presence of the voids, so that the cycle characteristics can be improved. Further, the voids formed between the particles 12a also serve as a space for relieving stress caused by the volume change of the active material particles 12a due to charge and discharge. The increase in the volume of the active material particles 12a whose volume has been increased by charging is absorbed by the voids. As a result, it is difficult for the fine particles of the particles 12a to be generated, and significant deformation of the negative electrode 10 is effectively prevented. The presence of the polymer gel electrolyte in the voids also has the advantage of acting as a cushion material that relieves the stress generated by the expansion and contraction of the polymer gel electrolyte force particles 12a.

[0017] When the present inventors examined the voids formed in the active material layer 12, the active material When the porosity of the layer 12 is set to 15 to 45%, preferably 20 to 40%, more preferably 25 to 35%, the distribution of the polymer gel electrolyte in the active material layer 12 becomes extremely good, and the active material It was found to be extremely effective for stress relaxation accompanying the expansion and contraction of particles 12a. Furthermore, it has been found that the liquid retention of the polymer gel electrolyte in the voids is good. In particular, setting the upper limit to 35% is extremely effective in improving the conductivity and maintaining the strength in the active material layer, and setting the lower limit to 25% can broaden the choice of electrolyte. The porosity in this range is higher than the porosity in the conventional negative electrode active material layer, for example, the porosity in the negative electrode described in Patent Document 1 described above. By using the negative electrode 10 having such a high porosity active material layer, it is possible to use a polymer gel electrolyte which is a material having low fluidity.

[0018] The void amount of the active material layer 12 is measured by a mercury intrusion method (JIS R 1655). The mercury intrusion method is a technique for obtaining information on the physical shape of a solid by measuring the size and volume of pores in the solid. The principle of the mercury intrusion method is to apply pressure to mercury to inject it into the pores of the measurement object and measure the relationship between the pressure applied at that time and the volume of mercury that has been pushed in (intruded). In this case, mercury enters the active material layer 12 in the order of the large void force.

In the present invention, the void amount measured at a pressure of 90 MPa is regarded as the entire void amount. In the present invention, the porosity (%) of the active material layer 12 is obtained by dividing the void amount per unit area measured by the above method by the apparent volume of the active material layer 12 per unit area. Calculated by multiplying by 100.

[0020] The active material layer 12 is preferably an electrolytic plating using a predetermined plating bath on a coating film obtained by applying a slurry containing particles 12a and a binder onto a current collector and drying the slurry. And the metal material 13 is deposited between the particles 1 and 2a. The degree of precipitation of the metal material 13 affects the porosity value of the active material layer 12. In order to achieve a desired porosity, it is necessary that a space in which the plating solution can permeate is formed in the coating film. As a result of the examination by the present inventors, it was found that the particle size distribution of the active material particles 12a is a major factor in forming a space in which the plating solution can penetrate into the coating film as necessary and sufficient. did. Specifically, the particle size distribution represented by D / Ό as active material particles 12a is preferably 0. 05-0.5, more preferably 0.1 to 0.3, a desired degree of space is formed in the coating film, and sufficient penetration of the plating solution may occur. found. It has also been found that the coating film can be effectively prevented from peeling off when it is electrolyzed. D ZD force Si

The closer to 10 90, the closer the particle size of the particles 12a is to monodisperse, so it can be seen that the particle size distribution in the above range is sharp. That is, for this embodiment, it is preferable to use the particles 12a having a sharp particle size distribution. By using the particles 12a having a sharp particle size distribution, the voids between the particles can be increased when the particles 12a are packed at a high density. Conversely, when particles having a broad particle size distribution are used, small particles are likely to enter between large particles, and it is not easy to increase the voids between the particles. In addition, the use of the particles 12a having a sharp particle size distribution has an advantage that the reaction varies.

[0021] In order to obtain a negative electrode having excellent cycle characteristics, the particle size of the active material particles 12a is also important, taking into account that the particle size distribution of the active material particles 12a is within the above-mentioned range. When the particle size of the active material particles 12a is excessively large, the particles 12a are easily expanded and contracted, so that fine particles are easily formed. As a result, the generation of electrically isolated particles 12g frequently occurs. If the particle size of the active material particles 12a is too small, the gaps between the particles 12a may be too small, and the gaps may be filled by penetration penetration described later. This has a negative effect on the improvement of the cycle characteristics. Therefore, in the present embodiment, the active material particles 12a have an average particle diameter of 0.1 to 5 111, particularly 0.2 to 3 / ζ πι.

50

Preferably there is.

[0022] The particle size distribution D / Ό and the average particle size D of the active material particles 12a are determined by laser diffraction scattering.

10 90 50

It is measured by random particle size distribution measurement or electron microscope observation (SEM observation).

[0023] In order to keep the porosity of the active material layer 12 within the above range, it is preferable to sufficiently infiltrate the plating solution into the coating film. In addition to this, it is preferable to make the conditions for depositing the metal material 13 appropriate by electrolytic plating using the plating solution. The plating conditions include the composition of the mating bath, the pH of the plating bath, and the current density of electrolysis. Regarding the pH of the plating bath, it is preferable to adjust it to more than 7 and 11 or less, particularly 7.1 or more and 11 or less. By keeping the pH within this range, the dissolution of the active material particles 12a is suppressed, the surface of the particles 12a is cleaned, and plating on the particle surfaces is promoted. Moderate voids are formed. The pH value is measured at the plating temperature.

[0024] When copper is used as the metal material 13 for plating, it is preferable to use a copper pyrophosphate bath. When nickel is used as the metal material, for example, an alkaline nickel bath is preferably used. In particular, it is preferable to use a copper pyrophosphate bath because the voids can be easily formed over the entire thickness direction of the layer even when the active material layer 12 is thickened. Further, since the metal material 13 is deposited on the surface of the active material particles 12a and the metal material 13 is less likely to be deposited between the particles 12a, the voids between the particles 12a are successfully formed. This is also preferable. When a copper pyrophosphate bath is used, the bath composition, electrolysis conditions and ρ 及び are preferably as follows.

'Copper pyrophosphate trihydrate: 85-120gZl

-Pig 13 gin Kazikum: 300-600g / l

'Potassium nitrate: 15-65gZl

'Bath temperature: 45-60 ° C

'Current density: l ~ 7AZdm ²

• pH: Add ammonia water and polyphosphoric acid to adjust the pH to 7.1 to 9.5.

[0025] Especially when using a copper pyrophosphate bath, the ratio of the weight of PO to Cu (P O ZCu

2 7 2 7

It is preferable to use one having a P ratio defined by When the P ratio is less than 5, the metal material 13 covering the active material particles 12a tends to be thick, and it may be difficult to form desired voids between the particles 12a. In addition, if a P ratio exceeding 12 is used, the current efficiency is deteriorated and gas generation is likely to occur, which may reduce the production stability. When a copper pyrophosphate bath having a P ratio of 6.5 to 10.5 is used, the size of the voids formed between the active material particles 12a and the number of polymer gels in the active material layer 12 This is very advantageous for electrolyte distribution.

[0026] When an alkaline nickel bath is used, the bath composition, electrolysis conditions, and pH are preferably as follows.

'Nickel sulfate: 100-250gZl

'Ammonium chloride: 15-30gZl 'Boric acid: 15-45gZl

'Bath temperature: 45-60 ° C

'Current density: l ~ 7AZdm ²

• pH: 25 weight ^_0/0 aqueous ammonia: 100～300GZl adjusted to be Roita8～ 11 in the range of.

When this alkaline nickel bath and the above-described copper pyrophosphate bath are compared, there is a tendency that moderate voids are formed in the active material layer 12 when the copper pyrophosphate bath is used, thereby prolonging the life of the negative electrode. It's easy to draw, so I like it.

[0027] It is also possible to appropriately adjust the characteristics of the metal material 13 by adding various additives used in electrolyte solutions for producing copper foil such as proteins, active sulfur compounds, and cellulose to the various baths described above. It is.

[0028] For the negative electrode 10 of the present embodiment, in view of the fact that the calculated void ratio of the active material layer 12 measured by the mercury intrusion method is within the above range, in lOMPa It is preferable that the calculated void ratio of the active material layer 12 measured by the mercury injection method is 10 to 40%. Further, it is preferable that the porosity calculated from the void amount of the active material layer 12 measured by the mercury intrusion method in IMPa is 0.5 to 15%. Furthermore, it is preferable that the porosity calculated from the porosity force of the active material layer 12 measured by the mercury intrusion method at 5 MPa is 1 to 35%. As described above, the mercury intrusion conditions are gradually increased in the mercury intrusion measurement. Under low pressure conditions, mercury is injected into large voids, and under high pressure conditions, mercury is injected into small voids. Therefore, the porosity measured at pressure IMPa is mainly derived from large voids. On the other hand, the porosity measured at pressure lOMPa V reflects the presence of small voids.

[0029] As described above, the active material layer 12 is preferably prepared by subjecting a coating film obtained by applying and drying a slurry containing particles 12a and a binder to electrolysis using a predetermined plating bath. It is formed by depositing and depositing the metal material 13 between the particles 12a. Therefore, as shown in FIG. 2, the above-mentioned large void S1 is mainly derived from the space between the particles 12a, while the small void S2 described above is mainly a metal material that precipitates on the surface of the particle 12a. It is thought that it originates in the space between the crystal grains 14 of. Large void S1 is the main As a space to relieve stress caused by the expansion and contraction of the particles 12a. On the other hand, the small void S2 mainly serves as a route for supplying the polymer gel electrolyte to the particles 12a. By balancing the abundance of these large voids S1 and small voids S2, the cycle characteristics are further improved.

[0030] If the amount of the active material relative to the entire negative electrode is too small, it is difficult to sufficiently increase the energy density of the battery. On the other hand, if the amount is too large, the strength tends to decrease and the active material tends to fall off. Considering these, the thickness of the active material layer 12 is preferably 10 to 40 / ζ πι, more preferably 15 to 30 μm, and still more preferably 18 to 25 μm.

In the negative electrode 10 of the present embodiment, a thin surface layer (not shown) may be formed on the surface of the active material layer 12. Further, the negative electrode 10 may not have such a surface layer. The thickness of the surface layer is as thin as 0.25 μm or less, preferably 0.1 μm or less. There is no limit to the lower limit of the thickness of the surface layer. By forming the surface layer, the pulverized active material particles 12a can be further prevented from falling off. However, in this embodiment, by setting the porosity of the active material layer 12 within the above-described range, it is possible to sufficiently prevent the pulverized active material particles 12a from dropping without using a surface layer. Is possible.

[0032] When the negative electrode 10 is thin or has a surface layer or has the surface layer, a secondary battery is assembled using the negative electrode 10, and the battery is initially charged. The overvoltage can be reduced. This means that lithium can be prevented from being reduced on the surface of the negative electrode 10 when the secondary battery is charged. The reduction of lithium leads to the generation of dendrites that cause short circuits between the two electrodes.

When the negative electrode 10 has a surface layer, the surface layer covers the surface of the active material layer 12 continuously or discontinuously. When the surface layer continuously covers the surface of the active material layer 12, the surface layer has a large number of fine voids (not shown) that are open to the surface and communicate with the active material layer 12. Have, prefer to have. It is preferable that the fine voids exist in the surface layer so as to extend in the thickness direction of the surface layer. The fine voids allow the polymer gel electrolyte to circulate. The role of the fine voids is to supply the polymer gel electrolyte into the active material layer 12. When the surface of the negative electrode 10 is viewed in plan by an electron microscope, the fine voids are the proportion of the area covered with the metal material 13, that is, the coverage is 95% or less, particularly 80% or less. In particular, the size is preferably 60% or less.

[0034] The surface layer is composed of a metal compound having a low lithium compound forming ability. This metal material may be the same as or different from the metal material 13 present in the active material layer 12. The surface layer may have a structure of two or more layers having two or more different metal material forces. Considering the ease of production of the negative electrode 10, the metal material 13 present in the active material layer 12 and the metal material constituting the surface layer are preferably the same type.

[0035] The negative electrode 10 of the present embodiment has high resistance to bending because the porosity in the active material layer 12 is a high value. Specifically, the MIT folding resistance measured according to JIS C 6471 is preferably 30 times or more, more preferably 50 times or more. The high folding resistance is extremely advantageous since the negative electrode 10 is folded when the negative electrode 10 is folded or wound and accommodated in the battery container. As the MIT folding device, for example, Toyo Seiki Seisakusho's film folding fatigue tester (Part No. 54 9) is used, with a bending radius of 0.8 mm, a load of 0.5 kgf, and a sample size of 15 X 150 mm. can do.

[0036] The current collector 11 in the negative electrode 10 may be the same as that conventionally used as the current collector of the negative electrode for a polymer electrolyte secondary battery. It is preferable that the current collector 11 has a low ability to form a lithium compound as described above and has a metal material strength. Examples of such metal materials are as described above. In particular, it is preferably made of copper, nickel, stainless steel or the like. Also, it is possible to use a copper alloy foil represented by Corson alloy foil. Further, as the current collector, a metal foil having a normal tensile strength (JIS C 2318) of preferably 500 MPa or more, for example, a copper film layer formed on at least one surface of the aforementioned Corson alloy foil can be used. Furthermore, it is also preferable to use a current collector having a normal elongation CFIS C 2318) of 4% or more. This is because when the tensile strength is low, stress is generated due to the stress when the active material expands, and when the elongation is low, the current collector may crack. By using these current collectors, it is possible to further improve the folding resistance of the negative electrode 10 described above. The thickness of the current collector 11 is preferably 9 to 35 / ζ πι in consideration of the balance between maintaining the strength of the negative electrode 10 and improving the energy density. When copper foil is used as the current collector 11, chromate treatment, triazole compound and imidazole compound are used. It is preferable to carry out an antifungal treatment using an organic compound such as

Next, a preferred method for producing the negative electrode 10 of the present embodiment will be described with reference to FIG. In this production method, a coating film is formed on the current collector 11 using a slurry containing active material particles and a binder, and then the coating is electrolyzed.

First, a current collector 11 is prepared as shown in FIG. Then, a slurry containing active material particles 12 a is applied onto the current collector 11 to form a coating film 15. The surface roughness of the coating film forming surface of the current collector 11 is preferably 0.5 to 4 / ζ πι at the maximum height of the contour curve. When the maximum height exceeds 4 m, the accuracy of forming the coating film 15 is reduced, and current concentration tends to occur at the protrusions. When the maximum height is less than 0, the adhesion of the active material layer 12 tends to decrease. As the active material particles 12a, those having the above-described particle size distribution and average particle size are preferably used.

[0039] In addition to the active material particles, the slurry contains a binder and a diluting solvent. The slurry may also contain a small amount of conductive carbon material particles such as acetylene black and graphite. In particular, when the active material particles 12a also have a silicon-based material force, it is preferable that the conductive carbon material is contained in an amount of 1 to 3% by weight with respect to the weight of the active material particles 12a. When the content of the conductive carbon material is less than 1% by weight, the viscosity of the slurry is lowered and the sedimentation of the active material particles 12a is promoted, so that it is difficult to form a good coating film 15 and a uniform void. Become. On the other hand, if the content of the conductive carbon material exceeds 3% by weight, plating nuclei concentrate on the surface of the conductive carbon material, and a good coating is formed.

[0040] As the binder, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene monomer (EPDM), or the like is used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material particles 12a in the slurry is preferably about 30 to 70% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. A dilute solvent is added to these to form a slurry.

[0041] The formed coating film 15 has a large number of minute spaces between the particles 12a. The current collector 11 on which the coating film 15 is formed is immersed in a plating bath containing a metal material having a low ability to form a lithium compound. By immersion in the plating bath, the plating solution penetrates into the minute space in the coating film 15. And reaches the interface between the coating film 15 and the current collector 11. Under this condition, electrolytic plating is performed to deposit metal species on the surface of the particles 12a (hereinafter, this plating is also referred to as penetration plating). The penetration is performed by using the current collector 11 as a force sword, immersing the counter electrode as the anode in the plating bath, and connecting both electrodes to the power source.

[0042] It is preferable that the deposition of the metal material by the penetration adhesion proceeds by applying one side force of the coating film 15 to the other side. Specifically, as shown in FIGS. 3B to 3D, the interfacial force between the coating film 15 and the current collector 11 is also electrolyzed so that the deposition of the metal material 13 proceeds toward the coating film surface. Make a mess. By precipitating the metal material 13 in this way, the surface of the active material particles 12a can be successfully coated with the metal material 13, and a void is successfully formed between the particles 12a coated with the metal material 13. can do. In addition, the porosity of the voids can be easily set within the preferred range described above.

[0043] As described above, the conditions for the penetration for depositing the metal material 13 include the composition of the plating bath, the pH of the plating bath, and the current density of electrolysis. Such conditions are as described above.

[0044] As shown in FIGS. 3 (b) to (d), the deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. When plating is performed, in the forefront portion of the precipitation reaction, fine particles 13a that have a substantially constant thickness and also have a nucleating force of the metal material 13 are present in layers. As the precipitation of the metal material 13 proceeds, the adjacent fine particles 13a are combined to form larger particles, and when the deposition proceeds further, the particles are combined to continuously cover the surface of the active material particles 12a. It becomes like this.

[0045] The penetration staking is terminated when the metal material 13 is deposited in the entire thickness direction of the coating film 15. By adjusting the end point of plating, a surface layer (not shown) can be formed on the upper surface of the active material layer 12. In this way, the target negative electrode is obtained as shown in FIG. 3 (d).

[0046] After the penetration, the negative electrode 10 is preferably subjected to an antifouling treatment. As the antifungal treatment, for example, an organic antifungal using a triazole compound such as benzotriazole, carboxybenzotriazole, tolyltriazole and imidazole, or an inorganic protective using cobalt, nickel, chromate or the like can be employed. [0047] The negative electrode 10 thus obtained is suitably used as a negative electrode for a polymer electrolyte secondary battery such as a lithium ion polymer secondary battery. In this case, the positive electrode of the battery is prepared by suspending a positive electrode active material and, if necessary, a conductive agent and a binder in a suitable solvent to prepare a positive electrode mixture, applying this to a current collector, drying, roll rolling, It can be obtained by pressing, cutting and punching. The active material layer of the positive electrode is previously impregnated with a polymer gel electrolyte to be combined. As the positive electrode active material, conventionally known positive electrode active materials such as lithium-containing metal composite oxides such as lithium nickel composite oxide, lithium mangan composite oxide, lithium cobalt composite oxide and the like are used. As a positive electrode active material, LiCoO

2 Also preferably used is a lithium transition metal composite oxide containing at least both Zr and Mg and a lithium transition metal composite oxide having a layered structure and containing at least both Mn and Ni be able to. The use of a positive electrode active material can be expected to increase the end-of-charge voltage without deteriorating charge / discharge cycle characteristics and thermal stability. The average primary particle diameter of the positive electrode active material is 5 μm or more and 10 μm or less, and the weight average molecular weight of the binder used for the positive electrode is preferably 3 in view of the balance between packing density and reaction area. Preferably, the polyvinylideneidene is from 50,000 to 2,000,000. This is because it can be expected to improve the discharge characteristics in a low temperature environment.

[0048] The polymer gel electrolyte includes a matrix polymer, an organic solvent, and a lithium salt. As the matrix polymer, polyethylene oxide, polypropylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, polyfluoride bur, polyacrylic acid, polymethacrylic acid, polyacrylonitrile, polycarbonate, polyethylene glycol and the like can be used. Lithium salts include LiCIO, LiAlCl, LiPF, LiAsF, LiSb

4 4 6 6

Examples thereof include F, LiBF, LiSCN, LiCl, LiBr, Lil, LiCFSO, and LiCFSO. Yes

6 4 3 3 4 9 3

Examples of the organic solvent include ethylene carbonate, jetyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, y-butyrolatone, and the like.

Example

[0049] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to such embodiments. [Example 1]

A current collector having an electrolytic copper foil strength of 18 / zm in thickness was acid-washed at room temperature for 30 seconds. After the treatment, it was washed with pure water for 15 seconds. A slurry containing Si particles was applied on the current collector to a thickness of 15 m to form a coating film. The composition of the slurry was particles: styrene butadiene rubber (binder): acetylene black = 100: 1.7: 2 (weight ratio). The average particle size D of Si particles is 2

50

5 / z m. The particle size distribution D ZD was 0.07. Average particle size D and particle size distribution

10 90 50

D ZD is a microtrack particle size distribution measuring instrument (No. 9320-X10) manufactured by Nikkiso Co., Ltd.

10 90

0).

[0051] The current collector on which the coating film was formed was immersed in a copper pyrophosphate bath having the following bath composition, and by electrolysis, copper penetrated into the coating film to form an active material layer. did. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source.

'Copper pyrophosphate trihydrate: 105gZl

• Potassium pyrophosphate: 450g / l

'Potassium nitrate: 30gZl

• P ratio: 7.7

'Bath temperature: 50 ° C

• Current density: 3AZdm ²

• pH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

[0052] The penetration staking was terminated when copper was deposited over the entire thickness direction of the coating film, and washed with water and subjected to an anti-bacterial treatment with benzotriazole (BTA) to obtain a target negative electrode.

[Examples 2 to 5]

Si particles with the average particle size D and particle size distribution D / Ό shown in Table 1 are used.

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A negative electrode was obtained in the same manner as in Example 1 except that.

[Comparative Examples 1 and 2]

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It was. Further, in place of the copper pyrophosphate bath used in Example 1, a copper sulfate bath having the following composition was used. The current density was 5AZdm ² and the bath temperature was 40 ° C. DSE electrode is used for anode It was. A DC power source was used as the power source. A negative electrode was obtained in the same manner as Example 1 except for these.

[Comparative Examples 3 and 4]

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[0056] [Evaluation]

The negative electrodes obtained in the examples and comparative examples were measured with a mercury porosimeter. The results are shown in Table 1. Separately, lithium ion polymer secondary batteries were manufactured using the negative electrodes obtained in Examples and Comparative Examples. LiCo Ni Mn O is used as the positive electrode

1/3 1/3 1/3 2 The positive electrode active material layer was impregnated with the following polymer gel electrolyte. The Porimage Le electrolyte, polyacrylonitrile 6 wt ^_0/0, 40 weight ethylene carbonate ^_0/0, the oxygenate chill carbonate 44 wt%, was used containing LiPF 10 wt%. Obtained

6

Further, the capacity retention rate up to 100 cycles was measured for the secondary battery. The capacity retention rate was calculated by measuring the discharge capacity at each cycle, dividing the value by the initial discharge capacity, and multiplying by 100. The charging conditions were 0.5C and 4.2V, and constant current * constant voltage (CCCV). The discharge conditions were 0.5C and 2.7V, and constant current (CC). However, the first cycle was set to 0.05C, the 2nd to 4th cycles were set to 0.1C, the 5th to 7th cycles were set to 0.5C, and the 8th to 10th cycles were set to 1C. The results are shown in Table 1.

[0057] [Table 1]

As is clear from the results shown in Table 1, it can be seen that the secondary battery including the negative electrode of the example has better cycle characteristics than the secondary battery including the negative electrode of the comparative example. In the table Although not shown, in the negative electrode of each example, it was confirmed that electrical conduction was established between the front and back sides.

Industrial applicability

According to the present invention, a low-fluidity, even a polymer gel electrolyte can be circulated through the active material layer with a necessary and sufficient path so that the polymer gel electrolyte can easily reach the active material layer. Therefore, the entire region in the thickness direction of the active material layer is used for the electrode reaction. As a result, cycle characteristics are improved. In addition, even if fine particles are generated due to the expansion and contraction of the particles due to charge and discharge, the particles do not easily fall off.

Claims

The scope of the claims

[1] An active material layer including particles of an active material is provided, and at least a part of the surface of the particles is covered with a metal material having a low ability to form a lithium compound and is coated with the metal material. A negative electrode for a polymer electrolyte secondary battery, wherein voids are formed between the particles, and the porosity of the active material layer is 15 to 45%.

2. The negative electrode for a polymer electrolyte secondary battery according to claim 1, wherein the metal material is present on the surface of the particles over the entire thickness direction of the active material layer.

[3] The particle size distribution of the particles according to claim 1, wherein the particle size distribution is 0.05 to 0.5 expressed by D ZD.

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Or a negative electrode for a polymer electrolyte secondary battery according to item 2.

[4] The average particle diameter of the particles according to claim 1, wherein the average particle diameter is 0.1 to 5 / ζ πι in terms of D.

50

A negative electrode for a polymer electrolyte secondary battery.

[5] The active material particles are composed of a silicon-based material, and the active material layer includes a conductive carbon material in an amount of 1 to 3% by weight based on the weight of the active material particles. The negative electrode for a polymer electrolyte secondary battery as described in the paragraph.

6. The negative electrode for a polymer electrolyte secondary battery according to claim 1, wherein the coating of the metal material is formed by electrolytic plating using a plating bath having a pH of more than 7 and 11 or less.

[7] The negative electrode for a polymer electrolyte secondary battery according to claim 1, wherein the porosity of the active material layer measured by mercury porosimetry (JIS R 1655) at lOMPa is 10 to 40%.

[8] The negative electrode for a polymer electrolyte secondary battery according to claim 1, wherein the porosity of the active material layer measured by the mercury intrusion method (JIS R 1655) at IMPa is 0.5 to 15%.

[9] The polymer electrolyte according to claim 1, wherein the maximum peak value of the pore size distribution of the voids of the active material layer measured by mercury porosimetry (JIS R 1655) is between 100 and 2000 nm. Battery negative electrode.

[10] A polymer electrolyte secondary battery comprising the negative electrode for a polymer electrolyte secondary battery according to claim 1.