JP2015207489A - Secondary battery and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery capable of improving cycle characteristics of the secondary battery without exposing an electrode to a high temperature in a manufacturing process and a manufacturing method of the same.SOLUTION: The secondary battery includes a negative electrode having a negative electrode foil 42a and a negative electrode mixture layer 42b. The negative electrode mixture layer 42b contains SiO-based active material particles 1 and a binder 2. Each of the SiO-based active material particles 1 is at least partially covered by a coating layer 3 composed of a resin material containing an imide bond imidized at a temperature higher than a heat-resistant temperature of the binder 2.

Description

  The present invention relates to a secondary battery and a method for manufacturing the same.

  In non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, carbon materials such as graphite have been conventionally used as negative electrode active materials. In such a conventional secondary battery, it is becoming increasingly difficult to respond to the increasing demand for higher capacity in recent years, and secondary batteries using a higher capacity negative electrode active material such as silicon have been studied. (For example, see Patent Documents 1 and 2 below).

  In patent document 1, it is supposed that it can be set as a battery of a high capacity | capacitance by using silicon as a negative electrode active material rather than using a carbon material. Further, only a specific silicon composite is used as the negative electrode active material, particles made of silicon oxide represented by SiOx (0.3 ≦ x ≦ 1.6), natural graphite, artificial It describes that a known negative electrode active material such as graphite, a fired organic compound such as a phenol resin, or a carbonaceous powder such as coke is mixed and used.

  Patent Document 1 discloses polyvinylidene fluoride (PVDF), polytetrafluoroethylene as a binder resin for binding a conductive additive added to increase the conductivity of the active material and the electrode to the current collector. Examples include fluoropolymers such as (PTFE), rubbers such as styrene butadiene rubber (SBR), and imide polymers such as polyimide.

  In Patent Document 2, an object is to obtain a non-aqueous electrolyte secondary battery having excellent cycle characteristics, an active material containing a graphite material and silicon or a silicon compound is used as a negative electrode active material, and polyimide and polyvinylpyrrolidone are used as a negative electrode binder. There is disclosed a non-aqueous electrolyte secondary battery characterized by using.

JP 2013-234088 A JP 2012-160353 A

  When silicon is used as the negative electrode active material, volume expansion and contraction associated with charge / discharge is increased as compared with conventional carbon materials. Therefore, for example, in the non-aqueous secondary battery described in Patent Document 1, the silicon composite or a mixture of the silicon composite and a known negative electrode active material is used as the negative electrode active material, and the binder resin has a relatively binding force. When weak PVDF, PTFE, SBR or the like is used, there is a possibility that the silicon composite may be repeatedly expanded and contracted as the secondary battery is charged and discharged. When the silicon composite is cracked, the cycle characteristics of the secondary battery are deteriorated.

  On the other hand, in the non-aqueous electrolyte secondary battery described in Patent Document 2, the cycle characteristics of the secondary battery are improved by using polyimide and polyvinyl pyrrolidone having a relatively strong binding force as the negative electrode binder. However, in Patent Document 2, a negative electrode slurry prepared by dissolving a precursor of a polyimide resin in N-methyl-2-pyrrolidone (NMP) and further mixing polyvinylpyrrolidone, graphite, and silicon is used as a negative electrode current collector. After applying, drying and rolling on both sides of the copper foil, heat treatment was performed in an argon atmosphere at 400 ° C. for 10 hours to produce a negative electrode. As described above, when the negative electrode current collector is exposed to a high temperature for a long time in the manufacturing process of the negative electrode, the strength of the negative electrode current collector is decreased, or the weldability to a metal such as a current collector plate is decreased. There is a risk of adversely affecting the subsequent manufacturing process of the secondary battery.

  This invention is made | formed in view of the said subject, The place made into the objective is to improve the cycling characteristics of a secondary battery, without exposing an electrode to high temperature in the manufacturing process of a secondary battery.

  In order to achieve the above object, the secondary battery of the present invention is a secondary battery including a negative electrode having a negative electrode foil and a negative electrode mixture layer, wherein the negative electrode mixture layer includes SiO-based active material particles and And the SiO-based active material particles are at least partially coated with a coating layer made of a resin material containing an imide bond imidized at a temperature higher than the heat-resistant temperature of the binder. It is characterized by that.

  According to the secondary battery of the present invention, the cycle characteristics of the secondary battery can be improved without exposing the electrode to a high temperature in the production process of the secondary battery.

The perspective view of the secondary battery which concerns on embodiment. The disassembled perspective view which shows the internal structure of the secondary battery shown in FIG. The disassembled perspective view of the electrode group shown in FIG. The expanded sectional view of the negative electrode shown in FIG. The flowchart which shows the manufacturing process of the negative electrode shown in FIG. The graph which shows the relationship between the cycle number of the secondary battery which concerns on an Example, and a capacity | capacitance maintenance factor. The graph which shows the relationship between the coverage of the silicon-type material of the secondary battery which concerns on an Example, and initial stage charge / discharge efficiency.

  Hereinafter, a secondary battery and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of a secondary battery 100 according to Embodiment 1 of the present invention. The secondary battery 100 of the present embodiment is a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, for example.

  In the secondary battery 100 of this embodiment, a negative electrode mixture layer provided in a negative electrode described later includes SiO-based active material particles as a negative electrode active material, and the SiO-based active material particles are higher than the heat resistant temperature of the binder. The greatest feature is that at least a part of the coating layer is made of a resin material containing an imide bond imidized at a temperature. Hereinafter, the configuration of the secondary battery 100 of the present embodiment will be described in detail.

  The secondary battery 100 includes a flat box-shaped battery container 10 made of a metal material such as an aluminum alloy. The battery container 10 is a flat rectangular parallelepiped housing having an upper end surface 10a, a lower end surface 10b, a wide side surface 10c, and a narrow side surface 10d. The battery container 10 includes a flat rectangular box-shaped battery can 11 having an open top, and a rectangular plate-shaped battery lid 12 that seals the top of the battery can 11. The battery can 11 is formed in a bottomed rectangular tube shape having a rectangular opening 11a in the upper portion, for example, by deep drawing the metal material.

  Positive and negative external terminals 20 </ b> A and 20 </ b> B are provided outside the battery container 10 and on the upper surface of the battery cover 12 at both ends in the width direction of the battery container 10, that is, in the longitudinal direction of the battery cover 12. An insulating member 24 is disposed between the external terminals 20 </ b> A and 20 </ b> B and the battery lid 12, and the external terminals 20 </ b> A and 20 </ b> B are electrically insulated from the battery lid 12. The positive external terminal 20A is made of, for example, aluminum or an aluminum alloy, and the negative external terminal 20B is made of, for example, copper or a copper alloy.

  Each of the external terminals 20A and 20B includes a conductive plate 21 and a bolt 22. The conductive plate 21 has a bolt 22 inserted through a through hole provided on the outer side in the width direction of the battery case 10 from below to above. The head of the bolt 22 is disposed between the insulating member 24 and the conductive plate 21 and is electrically connected to the conductive plate 21. The conductive plate 21 has a connection terminal 23 inserted through a through hole provided on the inner side in the width direction of the battery case 10 from below to above. The connection terminal 23 is caulked at the top surface of the conductive plate 21, is plastically deformed so as to expand in diameter and is in close contact with the conductive plate 21, thereby being electrically connected to the conductive plate 21. It is electrically insulated from the lid 12.

  Between the positive and negative external terminals 20A and 20B of the battery lid 12, a gas discharge valve 13 and a liquid injection port 14 are provided. The gas discharge valve 13 is provided, for example, by thinning the battery lid 12 to form a groove 13a, and is cleaved to release the internal gas when the internal pressure of the battery container 10 exceeds a predetermined value. Thus, the pressure inside the battery container 10 is reduced. The liquid injection port 14 is used for injecting an electrolytic solution into the battery container 10, and the liquid injection plug 15 is welded and sealed by laser welding, for example.

  FIG. 2 is an exploded perspective view showing the internal structure of the secondary battery 100 shown in FIG. In FIG. 2, the battery can 11 is not shown. At both ends of the battery lid 12 in the longitudinal direction, positive and negative current collecting plates 30A and 30B are fixed to the lower surface of the battery lid 12 inside the battery container 10 via an insulating member (not shown). The positive current collector 30A is made of, for example, aluminum or an aluminum alloy, and the negative current collector 30B is made of, for example, copper or a copper alloy. The current collecting plates 30 </ b> A and 30 </ b> B each have a base portion 31 to which the base end portion of the connection terminal 23 is connected, and a terminal portion 32 extending from the base portion 31 toward the bottom surface 11 b of the battery can 11.

  The connection terminals 23 connected to the respective base portions 31 of the current collector plates 30A and 30B extend outward of the battery container 10 and penetrate the battery lid 12. The connection terminal 23 includes a through hole of an insulating member (not shown) disposed on the lower surface of the battery lid 12, a through hole of the battery lid 12, a through hole of the insulating member 24 disposed on the upper surface of the battery lid 12, and conductive The front end of the plate 21 is caulked by the upper surface of the conductive plate 21. Thereby, each base part 31 of current collection board 30A, 30B is electrically connected to the electrically conductive board 21 by the connection terminal 23, and is fixed substantially parallel to the lower surface of the battery cover 12 via an insulating member not shown. Has been. The base portions 31 and the connection terminals 23 of the current collector plates 30 </ b> A and 30 </ b> B are electrically insulated from the battery lid 12 by an insulating member (not shown) disposed on the lower surface of the battery lid 12.

  The terminal portions 32 of the positive and negative current collecting plates 30 </ b> A and 30 </ b> B extend from both sides of the base portion 31 in the thickness direction of the battery container 10 along the wide side surface 11 c of the maximum area of the battery can 11. It is formed in a plate shape extending toward 11b. Each terminal portion 32 of the current collector plates 30A and 30B extends from the outer end portion of the base portion 31 in the winding axis D direction of the electrode group 40, which will be described later, and is a current collector plate joint portion 41d at the end portion of the electrode group 40. , 42d, respectively. Thus, the positive current collector plate 30A is disposed at one end in the winding axis D direction of the electrode group 40 and is electrically connected to the positive electrode 41 (see FIG. 3), and the negative current collector plate 30B. Is disposed at the other end of the electrode group 40 in the winding axis D direction and is electrically connected to the negative electrode 42 (see FIG. 3).

  The electrode group 40 is fixed to the battery cover 12 via the current collector plates 30A and 30B and an insulating member (not shown) by being joined to the terminal portion 32. Further, the external terminals 20A and 20B, the insulating member 24, the insulating member (not shown) on the lower surface of the battery lid 12, the current collecting plates 30A and 30B, and the electrode group 40 are assembled to the battery lid 12, so that the lid assembly is obtained. It is configured.

  An insulating case 50 that covers the electrode group 40 is disposed between the battery can 11 and the electrode group 40. The insulating case 50 includes a sheet-like sheet portion 51 and a case-like case portion 52. The insulating case 50 may be integrally formed. The insulating case 50 is made of, for example, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene (PFA), polyphenylene sulfide (PPS), or the like.

  The sheet portion 51 has a width equivalent to the width of the electrode group 40 in the winding axis D direction, and faces the current collector plate joint portion 41d to which the terminal portion 32 of the positive current collector plate 30A of the electrode group 40 is connected. The battery container 10 extends in a width direction from a position where the battery container 10 faces to a position facing the current collector plate joining portion 42d to which the terminal portion of the negative current collector plate 30B is joined. Further, the sheet portion 51 extends from the vicinity of the battery lid 12 on the front side of the battery container 10 shown in FIG. 1 to the vicinity of the lower end surface 10b along the wide side surface 10c of the battery container 10 and faces the bottom surface 10a of the battery container 10. It is folded back so as to cover the curved portion 40 b of the group 40 and extends to the vicinity of the battery lid 12 along the wide side surface 10 c on the back side of the battery case 10.

  The case portion 52 is disposed at both ends of the electrode group 40 in the winding axis D direction, and covers the current collector plate joint portions 41d and 42d of the electrode group 40 to which the terminal portions 32 of the current collector plates 30A and 30B are joined, respectively. It is provided as follows. The case portion 52 has a rectangular parallelepiped box shape in which the inner surface in the winding axis D direction and the surface on the battery lid 12 side are open, and the electrodes to which the terminal portions 32 of the current collector plates 30A and 30B are joined. Both ends of the group 40 in the winding axis D direction are covered over the entire height direction perpendicular to the lower end surface 10 b of the battery case 10.

  At the time of manufacturing the secondary battery 100, the lid assembly made of the members shown in FIG. 2 has an insulating case 50 disposed between the electrode group 40 and the current collector plates 30A and 30B and the battery can 11, and the space between them. 1 is inserted into the opening 11a of the battery can 11 shown in FIG. 1 from the bent portion 40b on the lower side of the electrode group 40 in an electrically insulated state. In the electrode group 40, the narrow side surface 11 d of the battery can 11 is located on both sides in the winding axis D direction, and the battery can 11 is arranged so that the winding axis D direction is substantially parallel to the bottom surface 11 b and the wide side surface 11 c of the battery can 11. Housed inside.

  Thus, in the electrode group 40, one curved portion 40b faces the battery lid 12, the other curved portion 40b faces the bottom surface 11b of the battery can 11, and the flat portion 40a faces the wide side surface 11c. Become. Then, in a state where the opening 11a of the battery can 11 is closed by the battery lid 12, for example, by joining the entire circumference of the battery lid 12 to the opening 11a of the battery can 11 by laser welding, the battery can 11 and the battery lid A battery container 10 composed of 12 is formed.

Thereafter, a non-aqueous electrolyte is injected into the battery container 10 through the liquid injection port 14 of the battery lid 12 and, for example, the liquid injection plug 15 is joined to the liquid injection port 14 by laser welding and sealed. The battery container 10 is sealed. Examples of the non-aqueous electrolyte injected into the battery container 10 include lithium hexafluorophosphate (LiPF ₆ ) in a mixed solution in which ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 1: 2. Can be used at a concentration of 1 mol / liter.

  FIG. 3 is an exploded perspective view in which a part of the electrode group 40 shown in FIG. 2 is developed. The electrode group 40 is a wound electrode group in which positive and negative electrodes 41 and 42 laminated with separators 43 and 44 interposed therebetween are wound around an axis parallel to the winding axis D and formed into a flat shape.

  The electrode group 40 is formed into a flat shape having a flat portion 40a facing the wide side surface 10c of the battery case 10 and a curved portion 40b facing the upper and lower end surfaces 10a and 10b. The flat portion 40a is a portion where the electrodes 41, 42 and the separators 43, 44 are laminated flat, and the curved portion 40b is a portion where the electrodes 41, 42 and the separators 43, 44 are bent and laminated in a semi-cylindrical shape. It is. The separators 43 and 44 insulate the positive electrode 41 and the negative electrode 42, and the separator 44 is wound around the outer periphery of the negative electrode 42 wound around the outermost periphery.

  The positive electrode 41 includes a positive electrode foil 41a that is a positive electrode current collector, and a positive electrode mixture layer 41b made of a positive electrode active material mixture applied to both surfaces of the positive electrode foil 41a. One side in the width direction of the positive electrode 41 is a foil exposed portion 41c where the positive electrode mixture layer 41b is not formed and the positive foil 41a is exposed. The positive electrode 41 is wound around the winding axis D such that the foil exposed portion 41 c is disposed on the opposite side of the foil exposed portion 42 c of the negative electrode 42 in the winding axis D direction.

  The positive electrode 41, for example, a positive electrode active material mixture kneaded by adding a conductive material, a binder and a dispersion solvent to the positive electrode active material is applied to both surfaces of the positive electrode foil 41a except for one side in the width direction, It can be produced by drying, pressing and cutting. As the positive electrode foil 41a, for example, an aluminum foil with a thickness of about 20 μm can be used. The thickness of the positive electrode mixture layer 41b not including the thickness of the positive electrode foil 41a is, for example, about 90 μm.

As a material of the positive electrode active material mixture, for example, 100 parts by weight of lithium manganate (chemical formula LiMn ₂ O ₄ ) is used as the positive electrode active material, 10 parts by weight of flaky graphite as the conductive material, and 10% by weight as the binder. Part of polyvinylidene fluoride (hereinafter referred to as PVDF) and N-methylpyrrolidone (hereinafter referred to as NMP) can be used as a dispersion solvent.

  The positive electrode active material is not limited to the above-described lithium manganate. For example, another lithium manganate having a spinel crystal structure, or a lithium manganese composite oxide partially substituted or doped with a metal element may be used. Further, as the positive electrode active material, lithium cobaltate or lithium titanate having a layered crystal structure, or a lithium-metal composite oxide in which a part thereof is substituted or doped with a metal element may be used.

  The negative electrode 42 has a negative electrode foil 42a that is a negative electrode current collector, and a negative electrode mixture layer 42b made of a negative electrode active material mixture applied to both surfaces of the negative electrode foil 42a. One side in the width direction of the negative electrode 42 is a foil exposed portion 42c where the negative electrode mixture layer 42b is not formed and the negative foil 42a is exposed. The negative electrode 42 is wound around the winding axis D such that the foil exposed portion 42 c is disposed on the opposite side of the foil exposed portion 41 c of the positive electrode 41 in the winding axis D direction.

  FIG. 4 is a schematic enlarged cross-sectional view in which a part of the cross section of the negative electrode 42 shown in FIG. 3 is enlarged. The negative electrode mixture layer 42b is formed on both surfaces of the negative electrode foil 42a. In FIG. 4, only the negative electrode mixture layer 42b on one surface of the negative electrode foil 42a is illustrated, and the negative electrode mixture on the other surface is illustrated. Illustration of the layer 42b is omitted.

  In the secondary battery 100 of the present embodiment, the negative electrode mixture layer 42 b includes SiO-based active material particles 1 and a binder 2 as a negative electrode active material, and the SiO-based active material particles 1 are formed of the binder 2. The greatest feature is that at least a part of the coating layer 3 is made of a resin material containing an imide bond imidized at a temperature higher than the heat-resistant temperature. In the present embodiment, the negative electrode mixture layer 42b includes, for example, carbon-based active material particles 4 such as natural graphite as the negative electrode active material.

  The SiO-based active material particle 1 is, for example, a silicon-based active material represented by a chemical formula SiOx (where 0.8 <x <1.2), and is coarsely formed by, for example, a sieve having a mesh opening of 53 μ, 270 mesh. Are the removed particles. The entire surface or part of the surface of the SiO-based active material particles 1 is covered with the coating layer 3. The portion of the SiO-based active material particle 1 exposed from the coating layer 3 functions as a site responsible for the collection of lithium (Li) ions accompanying charge / discharge, and serves as an entrance / exit for occluding and releasing Li ions.

  The binder 2 is filled between the SiO-based active material particles 1 having the coating layer 3 and the carbon-based active material particles 4, and these are bound and held on the surface of the negative electrode foil 42a. The binder 2 is made of, for example, styrene butadiene rubber (SBR), and contains, for example, carbon or scaly graphite as a conductive material. When the binder 2 is composed of SBR, the heat resistance temperature is 100 ° C. or lower because the binder 2 is softened at a temperature of 100 ° C. or lower. Moreover, when the binder 2 is comprised by PVDF, since melting | fusing point is 150 degreeC or more and 180 degrees C or less, for example, the heat-resistant temperature will be 150 degrees C or less. The heat resistant temperature of the binder 2 is the upper limit of the temperature at which the binder 2 can maintain its function.

  The coating layer 3 is firmly bonded to the surface of the SiO-based active material particles 1 so as to cover the entire surface of the SiO-based active material particles 1 or a part of the surface. The coating layer 3 can be made of, for example, polyimide (PI) or polyamideimide (PAI). From the viewpoint of lowering the imidization temperature in the step of forming the coating layer 3, the coating layer 3 is preferably made of PAI.

  The average particle diameter of the carbon-based active material particles 4 is, for example, larger than the average particle diameter of the SiO-based active material particles 1. The ratio of the total weight of the carbon-based active material particles 4 to the total weight of the SiO-based active material particles 1 having the coating layer 3 is, for example, 95: 5. The carbon-based active material particles 4 do not have the coating layer 3, and the binder 2 is bound on the surface.

  Here, with reference to FIG. 5, the manufacturing process of the negative electrode 42 contained in the manufacturing process of the secondary battery 100 of this embodiment is demonstrated. FIG. 5A is a flowchart showing the manufacturing process of the negative electrode 42, and FIG. 5B is a flowchart showing details of the covering process S1 shown in FIG. 5A. The negative electrode 42 is manufactured through the coating step S1, the preparation step S2, and the coating / drying step S3 shown in FIG.

  The coating step S1 is a step of imidizing the precursor of the resin material to form the coating layer 3 made of the resin material including an imide bond on at least a part of the surface of the SiO-based active material particles 1. The coating step S1 includes a mixing step S11, a drying step S12, a pulverizing step S13, a polymerization step S14, a pulverizing step S15, and a sorting step S16 shown in FIG.

  In the mixing step S11, first, about 5% of the powder which is an aggregate of SiO-based active material particles 1 which are particles of SiOx (however, 0.8 <x <1.2) having an average particle diameter of about 5 μm. Of carbon. In addition, for example, a resin material such as PI or PAI is dissolved in a solvent such as NMP to prepare a precursor solution of the resin material. Then, these are put into a planetary mixer and mixed and stirred, for example, for about 20 minutes. As a result, a mixture of the SiO-based active material particles 1 and the precursor of the resin material is obtained.

  In the present embodiment, the total weight of the coating layer 3 formed by imidizing the precursor of the resin material is 1% or more and 5% or less of the total weight of the SiO-based active material particles 1. The weight of each material is adjusted.

  In the drying step S12, the mixture obtained in the mixing step S11 is taken out of the planetary mixer, placed on a metal foil such as aluminum, and dried in, for example, air at a temperature of about 80 ° C. for about 1 hour to evaporate the solvent. Let Furthermore, the dried mixture is dried, for example in a vacuum at a temperature of about 100 ° C. for about 2 hours to completely evaporate the solvent. Thereby, a lump containing the SiO-based active material particles 1 and the precursor of the resin material is obtained.

  In the pulverization step S13, the lump obtained in the drying step S12 is crushed roughly in a mortar, for example, and then pulverized for 10 minutes or more until it becomes sandy with a mill, and the SiO-based active material particles 1 and the resin material A powder containing the precursor is obtained.

  In the polymerization step S14, the resin material precursor is imidized by heating to a temperature of 250 ° C. or higher and 350 ° C. or lower together with the SiO-based active material particles 1. In the present embodiment, in the polymerization step, the powder obtained in the pulverization step S13 is placed on a metal foil such as aluminum, vacuum dried at a temperature of, for example, 300 ° C. and heated, and the precursor of the resin material Is polymerized to be imidized. As a result, a resin material containing an imide bond such as PI or PAI is firmly bound to the surface of the SiO-based active material particles 1.

  In the pulverization step S15, the mass of the SiO-based active material particles 1 obtained in the polymerization step S14 and a mass made of a resin material containing an imide bond such as PI or PAI is cooled to room temperature, and then, for example, in a mortar and mill Disintegrate for more than 5 minutes. Thereby, the powder of the SiO type | system | group active material particle | grains 1 with which at least one part was coat | covered with the coating layer 3 which consists of resin materials containing imide bonds, such as PI or PAI, is obtained.

  In the sorting step S16, for example, the powder obtained in the crushing step S15 is passed through a sieve having a sieve opening of 53 μm and a 270 mesh to remove coarse particles, and has a particle size in a predetermined range, and at least a part of the surface. Thus, a powder of the SiO-based active material particles 1 coated with the coating layer 3 is obtained. Thus, the covering step S1 shown in FIG.

  In the preparation step S2 shown in FIG. 5A, a slurry containing the SiO-based active material particles 1 having the coating layer 3 obtained in the coating step S1 and the binder 2 is prepared. In the present embodiment, in the preparation step S2, a slurry containing not only the SiO-based active material particles 1 having the coating layer 3 but also the carbon-based active material particles 4 is prepared as the negative electrode active material. Specifically, the ratio of the total weight of the carbon-based active material particles 4 to the total weight of the SiO-based active material particles 1 having the coating layer 3 is, for example, in the range from 95: 5 to 95: 3. And dry-mix with a planetary mixer.

  Thereafter, for example, carboxymethylcellulose (CMC) is added to the mixture as a thickener and stirred to adjust the viscosity to obtain a slurry having an appropriate viscosity. By adding and kneading, for example, styrene butadiene rubber (SBR) as a binder to this slurry, a slurry containing a negative electrode active material and a binder can be obtained. For example, 2 parts by weight of CMC and SBR can be added to 98 parts by weight of the negative electrode active material. For example, ion-exchanged water can be used to adjust the viscosity of the thickener, the binder dispersion solvent, and the slurry.

  In the coating / drying step S3 shown in FIG. 5 (a), the slurry obtained in the preparing step S2 is applied to both surfaces of the negative electrode foil 42a except for one side in the width direction, and dried to melt or soften the binder. And then press down and cut. In this embodiment, the drying temperature in the coating and drying step S3 is lower than the temperature at which the precursor of the resin material of the coating layer 3 that coats the SiO-based active material particles 1 in the coating step S1 is, for example, 120 ° C. or less. The temperature is preferably 100 ° C. or lower. As the negative electrode foil 42a, for example, a copper foil having a thickness of about 10 μm can be used.

  Thereby, as shown in FIG. 4, the binder 2 is formed between the SiO-based active material particles 1 having the coating layer 3, and the negative electrode mixture layer 42b is formed on the surface of the negative electrode foil 42a. In the present embodiment, the layer of the binder 2 is also formed between the SiO-based active material particles 1 having the coating layer 3 and the carbon-based active material particles 4 and between the carbon-based active material particles 4. The thickness of the negative electrode mixture layer 42b not including the thickness of the negative electrode foil 42a is, for example, about 70 μm. As described above, the negative electrode 42 including the negative electrode mixture layer 42b including the binder 2 between the particles of the negative electrode active material can be manufactured.

In the present embodiment, the negative electrode active material includes both the SiO-based active material particles 1 and the carbon-based active material particles 4. However, only the SiO-based active material particles 1 may be used as the negative electrode active material. Further, the carbon-based active material particles 4 are not limited to the above-described natural graphite into which lithium ions can be inserted and removed, and carbonaceous materials such as amorphous carbon, various artificial graphite materials, coke, Si, Sn, etc. These compounds (for example, SiO, TiSi ₂ etc.) or a composite material thereof may be used. The particle shape of the negative electrode active material is not particularly limited, and a particle shape such as a scale shape, a spherical shape, a fiber shape, or a lump shape can be appropriately selected.

  The binder used for the positive electrode and negative electrode mixture layers 41b and 42b is not limited to PVDF and SBR. Examples of the binder include polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, and vinylidene fluoride. Polymers such as propylene fluoride, chlorochloroprene, and acrylic resins, and mixtures thereof may be used.

  Further, the axis when winding the positive electrode 41 and the negative electrode 42 with the separators 43 and 44 shown in FIG. 3 interposed therebetween is, for example, any of the positive foil 41a, the negative foil 42a, and the separators 43 and 44. Alternatively, a resin sheet having a high bending rigidity can be used.

  In the winding axis D direction of the electrode group 40, the width of the negative electrode mixture layer 42 b of the negative electrode 42 is wider than the width of the positive electrode mixture layer 41 b of the positive electrode 41. A negative electrode 42 is wound around the innermost and outermost circumferences of the electrode group 40. Thus, the positive electrode mixture layer 41b is sandwiched between the negative electrode mixture layer 42b from the innermost periphery to the outermost periphery of the electrode group 40.

  The foil exposed portions 41c and 42c of the positive electrode 41 and the negative electrode 42 are bundled by the flat portion 40a of the electrode group 40 to form the current collector plate joint portions 41d and 42d (see FIG. 2). The current collector plate joints 41d and 42d of the positive electrode 41 and the negative electrode 42 are joined to the terminal portions 32 of the positive and negative current collector plates 30A and 30B, for example, by ultrasonic welding or the like. Thereby, on the positive electrode side and the negative electrode side, the external terminals 20A and 20B are electrically connected to the positive and negative electrodes 41 and 42 constituting the electrode group 40 via the current collector plates 30A and 30B, respectively.

  In addition, in the winding axis D direction of the electrode group 40, the width of the separators 43 and 44 is wider than the width of the negative electrode mixture layer 42b, but the foil exposed portions 41c and 42c of the positive electrode 41 and the negative electrode 42 are separators, respectively. Projecting outward in the width direction from the ends in the width direction of 43 and 44. Therefore, the separators 43 and 44 do not hinder the foil exposed portions 41c and 42c from being bundled and welded.

  Hereinafter, the operation of the secondary battery 100 and the manufacturing method thereof according to the present embodiment will be described.

  The secondary battery 100 of the present embodiment is connected to the external terminals 20A and 20B of other secondary batteries 100 by fastening a bus bar (not shown) to the bolts 22 of the external terminals 20A and 20B shown in FIG. Used as an assembled battery. The secondary battery 100 stores electric power supplied from the outside via the external terminals 20A and 20B in the electrode group 40 via the connection terminal 23 and the current collector plates 30A and 30B shown in FIG. Further, the electric power stored in the electrode group 40 is supplied to the outside from the external terminals 20A and 20B via the current collector plates 30A and 30B and the connection terminal 23.

  As the secondary battery 100 is charged and discharged, the SiO-based active material particles 1 and the carbon-based active material particles 4 included in the negative electrode mixture layer 42b shown in FIG. The change in volume becomes larger than that of the carbon-based active material particles 4. Therefore, in the conventional secondary battery using PVDF, SBR or the like having a relatively weak binding force as the binder resin, that is, the binder 2, the SiO-based active material particles 1 are cracked due to repeated expansion and contraction. There was a possibility that the cycle characteristics of the battery would deteriorate. In the conventional secondary battery using polyimide (PI) and polyvinylpyrrolidone (PVP) as the negative electrode binder, that is, the binder 2, the negative electrode foil 42a is formed when the binder 2 is formed by imidizing PI. When exposed to high temperatures, the strength and weldability are reduced, which may adversely affect the manufacturing process of the secondary battery 100.

  On the other hand, in the secondary battery 100 of the present embodiment, the SiO-based active material particles 1 are formed by the coating layer 3 made of a resin material containing an imide bond imidized at a temperature higher than the heat resistance temperature of the binder 2. At least a portion is coated. Thereby, the volume change at the time of expansion and contraction of the SiO-based active material particles 1 is reduced by the coating layer 3 made of a tough resin material having a binding force higher than that of the binder 2, or the SiO-based active material particles 1 Side reactions such as reductive decomposition of the electrolytic solution occurring on the surface can be suppressed, and cracking of the SiO-based active material particles 1 can be suppressed.

  In addition, the secondary battery 100 of the present embodiment has a PI or PAI formed on the surface of the SiO-based active material particles 1 before the coating and drying step S3 in which the binder 2 is formed on the negative electrode foil 42a when the negative electrode 42 is manufactured. It has coating process S1 which forms the coating layer 3 which consists of resin materials containing imide bonds, such as. The drying temperature in the coating / drying step S3 is lower than the temperature at which the precursor of the resin material of the coating layer 3 is imidized and polymerized in the coating step S1. Therefore, it can avoid exposing the negative electrode foil 42a to the high temperature required for imidation polymerization.

  Therefore, according to the secondary battery 100 and the manufacturing method thereof of the present embodiment, the cycle characteristics of the secondary battery 100 can be improved without exposing the negative electrode 42 to a high temperature in the manufacturing process.

  Moreover, when the resin material of the coating layer 3 is PAI, the temperature required for imidation polymerization is lowered as compared with the case of PI, which contributes to simplification of the manufacturing process of the secondary battery 100 and reduction of manufacturing cost. . Moreover, when the binder 2 contains SBR, the softness | flexibility of the binder 2 can be improved and durability of the negative mix layer 42b can be improved. In addition, the negative electrode mixture layer 42b includes the carbon-based active material particles 4, so that the negative electrode mixture layer 42b includes only the SiO-based active material particles 1 as the negative electrode active material. Expansion and contraction can be suppressed.

  Further, the coating step S1 includes a polymerization step S14 in which the precursor of the resin material of the coating layer 3 is imidized by heating to a temperature of 250 ° C. or higher and 350 ° C. or lower together with the SiO-based active material particles 1. Thereby, the tough coating layer 3 made of a resin material containing an imide bond such as PI or PAI firmly bound to the surface of the SiO-based active material particles 1 can be formed.

  Moreover, coating process S1 has mixing process S11, drying process S12, and grinding | pulverization process S13 before superposition | polymerization process S14. Thereby, in polymerization process S14, the precursor of the resin material of the coating layer 3 made into powder and the SiO type | system | group active material particle 1 can be heated. Accordingly, in the polymerization step S14, the coating layer 3 is more uniform and denser on the surface of the SiO-based active material particles 1 than in the case where the precursor of the resin material of the coating layer 3 and the SiO-based active material particles 1 are massive. Can be formed.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention. For example, in the above-described embodiments and examples, the example in which the present invention is applied to the prismatic secondary battery has been described. However, the present invention is not limited to the prismatic secondary battery, and for example, non-aqueous electrolysis such as a cylindrical shape or a laminate type. It can be applied to all negative electrodes of liquid secondary batteries.

[Example]
Examples of the secondary battery and the manufacturing method thereof according to the present invention will be described below.

  The negative electrodes of Examples 1 and 2 and Comparative Example 1 were manufactured based on the manufacturing method described in the above embodiment. In the negative electrodes of Examples 1 and 2, the total weight of PAI as the resin material of the coating layer was 3% and 5% with respect to the total weight of the SiO-based active material particles, respectively. On the other hand, in the negative electrode of Comparative Example 1, the total weight of PAI as the resin material of the coating layer with respect to the total weight of the SiO-based active material particles was 0% (no coating layer). In the negative electrodes of Examples 1 and 2 and Comparative Example 1, the ratio of the total weight of the carbon-based active material particles to the total weight of the SiO-based active material particles having the coating layer was 95: 3. These negative electrodes were overlapped with positive electrodes through separators, respectively, to produce small cells of Examples 1, 2 and 3, and the initial cycle characteristics were measured. In addition, the charging / discharging method of each small cell is as follows.

Charge: 0.5C constant current constant voltage charge, constant voltage value 4.2V, 0.01C termination Discharge: 0.5C constant current, 2.7V termination

  FIG. 6 shows the number of cycles and capacity maintenance rate of the small cells of Examples 1 and 2 and Comparative Example 1 with the horizontal axis as the number of charge / discharge cycles (cycle) and the vertical axis as the capacity maintenance rate (%) of each cell. It is a graph which shows a relationship.

  In FIG. 6, the measurement result of the small cell of Example 1 (PAI: 3%) is indicated by a white triangle mark and a broken line, and the measurement result of the small cell of Example 2 (PAI: 5%) is indicated by a white circle. The measurement result of the small cell of Comparative Example 1 (PAI: 0%) is indicated by a black square mark and an alternate long and short dash line. From the above results, in the small cell using the SiO-based active material particles having the coating layers of Examples 1 and 2, the cycle characteristics are more than in the small cell using the SiO-based active material particles having no coating layer of Comparative Example 1. Has been confirmed to improve.

  Next, the negative electrodes of Examples 1 and 2 and Comparative Example 1 described above were manufactured, and the total weight (PAI coating amount) of PAI as the resin material of the coating layer with respect to the total weight of the SiO-based active material particles was 1%. The negative electrode of Example 3 was manufactured in the same manner. In each negative electrode, the ratio of the total weight of the carbon-based active material particles, the total weight of the SiO-based active material particles having the coating layer, and the total weight of the binder composed of the binder and the thickener is 95. The slurry was adjusted so as to be 3: 2 and applied to the negative electrode foil. Using these negative electrodes, a half cell having metallic lithium as a counter electrode was prepared, and the initial charge / discharge efficiency of the negative electrode was measured. FIG. 7 shows a value obtained by dividing the discharge capacity when charging and discharging are performed under the following conditions by the charge capacity.

Charge: 0.5C constant current constant voltage charge, constant voltage value 0.01V vs Li metal, 0.01C termination Discharge: 0.5C constant current, 1.5V vs Li metal termination

  FIG. 7 is a graph showing the relationship between the initial charge / discharge efficiency and the PAI coverage, with the vertical axis representing the initial charge / discharge efficiency (%) and the horizontal axis representing the PAI coverage (wt%). Example 1 (PAI coating amount: 3 wt%), Example 2 (PAI coating amount: 5 wt%) and Example 3 (PAI coating amount: 1 wt%) and Comparative Example 1 (PAI coating amount: 0 wt%) In comparison, it was confirmed that any of the small cells of Examples 1 to 3 showed higher initial charge / discharge efficiency than the small cell of Comparative Example 1.

  In addition, the initial charge / discharge efficiency of the small cells of each example is the highest in the small cell of Example 3 (PAI coating amount: 1 wt%), and the lowest in the small cell of Example 2 (PAI coating amount: 5 wt%). It was. That is, if the total weight of the coating layer is 1% or more and 5% or less of the total weight of the SiO-based active material particles, higher initial charge / discharge efficiency can be obtained than when the coating layer is not provided. It was confirmed that a higher initial charge / discharge efficiency could be obtained if the total weight of the substance particles was 1% or more and 3% or less.

DESCRIPTION OF SYMBOLS 1 ... SiO type | system | group active material particle, 2 ... Binder, 3 ... Coating layer, 4 ... Carbon type active material particle, 42 ... Negative electrode, 42a ... Negative electrode foil, 42b ... Negative electrode mixture layer, 100 ... Secondary battery

Claims (11)

A secondary battery comprising a negative electrode having a negative electrode foil and a negative electrode mixture layer,
The negative electrode mixture layer includes SiO-based active material particles and a binder,
The secondary particles characterized in that the SiO-based active material particles are at least partially covered with a coating layer made of a resin material containing an imide bond imidized at a temperature higher than the heat resistance temperature of the binder. battery.   The secondary battery according to claim 1, wherein the resin material is polyamideimide.   The secondary battery according to claim 2, wherein the binder includes styrene butadiene rubber.   The secondary battery according to claim 2, wherein a total weight of the coating layer is 1% or more and 5% or less of a total weight of the SiO-based active material particles.   The secondary battery according to claim 2, wherein the negative electrode mixture layer includes carbon-based active material particles. A method for manufacturing a secondary battery including a negative electrode having a negative electrode foil and a negative electrode mixture layer,
A coating step of imidizing a precursor of a resin material to form a coating layer made of the resin material including an imide bond on at least a part of the surface of the SiO-based active material particles;
A preparation step of preparing a slurry containing the SiO-based active material particles having the coating layer and a binder;
Coating and drying step of forming the negative electrode mixture layer containing the binder by applying the slurry to the negative electrode foil and drying it,
The method for producing a secondary battery, wherein a drying temperature in the coating drying step is lower than a temperature at which the precursor is imidized in the coating step.   The secondary battery according to claim 6, wherein the covering step includes a polymerization step in which the precursor is imidized by heating to a temperature of 250 ° C. or more and 350 ° C. or less together with the SiO-based active material particles. Manufacturing method. The coating step includes
Before the polymerization step, a mixing step of obtaining a mixture of the SiO-based active material particles and the precursor solution, and a lump containing the SiO-based active material particles and the precursor by drying the mixture A drying step to obtain, and a pulverizing step to obtain a powder containing the SiO-based active material particles and the precursor by pulverizing the lump.
The method for manufacturing a secondary battery according to claim 7, wherein the powder is heated in the polymerization step.   In the coating step, after the polymerization step, the SiO-based active material particles and the resin material are crushed to obtain the SiO-based active material particles at least partially coated on the coating layer. The method for producing a secondary battery according to claim 7, further comprising a crushing step and a selection step of sieving the powder on a sieve.   The method for manufacturing a secondary battery according to claim 7, wherein the drying temperature in the coating and drying step is 120 ° C. or lower.   The method for manufacturing a secondary battery according to claim 7, wherein in the preparation step, the slurry containing carbon-based active material particles is adjusted.

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