JP2019140040A - Manufacturing method of negative electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode for a lithium ion secondary battery, which includes a heat-resistant layer and which can suppress an increase in battery resistance. A hydrophobic resin is added to a paste A containing a negative electrode active material, and a paste B is prepared and applied to a negative electrode current collector. By drying, the negative electrode mixture layer including the negative electrode active material rich region and the hydrophobic resin rich region is formed on the surface of the negative electrode current collector. A paste C containing an aqueous solvent, a heat resistant material, and a binder is prepared, and the paste C is applied to the negative electrode mixture layer to form a heat resistant layer on the surface. The negative electrode active material rich region contains more negative electrode active material than the hydrophobic resin, the hydrophobic resin rich region contains more hydrophobic resin than the negative electrode active material, and the heat resistant layer contains the heat resistant material and the binder. [Selection diagram] Figure 2

Description

  The present disclosure relates to a method for manufacturing a negative electrode for a lithium ion secondary battery.

  Japanese Patent Laying-Open No. 2013-105681 (Patent Document 1) discloses a nonaqueous electrolyte secondary battery in which a heat-resistant layer is formed on a layer containing a negative electrode active material (that is, a negative electrode mixture layer). By forming a polyolefin-based heat-resistant layer on the negative electrode mixture layer, an improvement in battery safety is expected.

2013-105681

  The heat-resistant layer shown in Patent Document 1 includes an inorganic filler, a binder, and a granular polyolefin resin. In general, when forming a heat-resistant layer on the surface of the negative electrode mixture layer, there is a method of preparing an aqueous paste in which a granular polyolefin resin or the like is dispersed in an aqueous solvent and applying the aqueous paste to the surface of the negative electrode mixture layer. Can be used. In this specification, “aqueous solvent” refers to “water” or “a mixture of a water-miscible organic solvent and water”.

  However, it is considered that the binder contained in the aqueous paste penetrates into the negative electrode mixture layer together with the aqueous solvent. The binder that has penetrated into the negative electrode mixture layer is considered to cover the surface of the negative electrode active material contained in the negative electrode mixture layer. When a lithium ion secondary battery (hereinafter also simply referred to as “battery”) is manufactured using a negative electrode in which the surface of the negative electrode active material is coated with a binder, it is considered that the resistance of the battery increases.

  The objective of this indication is providing the manufacturing method of the negative electrode for lithium ion secondary batteries containing the heat-resistant layer which can suppress the resistance increase of a battery. Hereinafter, the negative electrode for a lithium ion secondary battery is also simply referred to as “negative electrode”.

  Hereinafter, the technical configuration and effects of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of the claims should not be limited by the correctness of the mechanism of action.

[1] A method for producing a negative electrode for a lithium ion secondary battery includes the following (a1) to (a7).
(A1) A negative electrode current collector is prepared.
(A2) A paste A containing a negative electrode active material is prepared.
(A3) A hydrophobic resin is added to the paste A to prepare a paste B containing a negative electrode active material and a hydrophobic resin.
(A4) The paste B is applied to the negative electrode current collector.
(A5) By drying the paste B, a negative electrode mixture layer including a negative electrode active material rich region and a hydrophobic resin rich region is formed on the surface of the negative electrode current collector.
(A6) A paste C containing an aqueous solvent, a heat-resistant material, and a binder is prepared.
(A7) Paste C is applied to the negative electrode mixture layer, and a heat-resistant layer is formed on the surface of the negative electrode mixture layer.
The negative electrode active material rich region contains more negative electrode active material than the hydrophobic resin, the hydrophobic resin rich region contains more hydrophobic resin than the negative electrode active material, and the heat resistant layer contains a heat resistant material and a binder.

The viscosity of the paste A prepared in (a2) above is 1100 mPa · s or more and 3400 mPa · s or more at a shear rate of 2 sec ⁻¹ . The drying in (a5) is performed in a temperature range of 120 ° C. or higher and 180 ° C. or lower. During the drying of the paste B, the negative electrode active material and the hydrophobic resin are separated into two layers by migration, a negative electrode active material rich region is formed below the thickness direction of the negative electrode mixture layer, and the thickness of the negative electrode mixture layer A hydrophobic resin rich region is formed on the upper side in the vertical direction.

FIG. 1 is a conceptual cross-sectional view illustrating a configuration of a negative electrode manufactured in an embodiment of the present disclosure.
The negative electrode 200 includes a negative electrode current collector 201, a negative electrode mixture layer 202, and a heat resistant layer 203. The negative electrode mixture layer 202 includes a negative electrode active material rich region 202a and a hydrophobic resin rich region 202c. In the present specification, the “hydrophobic resin” refers to a resin that is insoluble or hardly soluble in water or a mixed solvent mainly composed of water. “Negative electrode active material rich region” refers to a region containing more negative electrode active material than hydrophobic resin. A layer containing a negative electrode active material but not containing a hydrophobic resin is also regarded as a “negative electrode active material rich region”. The “hydrophobic resin rich region” refers to a region containing more hydrophobic resin than the negative electrode active material. A layer that includes a hydrophobic resin but does not include a negative electrode active material is also considered a “hydrophobic resin-rich region”.

The viscosity of the paste A prepared in (a2) above is 1100 mPa · s or more and 3400 mPa · s or more at a shear rate of 2 sec ⁻¹ . By setting the viscosity of the paste A at the shear rate of 2 sec ⁻¹ within the above range, it is expected that an increase in resistance of the battery including the negative electrode 200 manufactured by the manufacturing method according to the present disclosure is suppressed.

  The drying of the paste B in the above (a5) is performed in a temperature range of 120 ° C. or higher and 180 ° C. or lower. It is expected that the increase in resistance of the battery including the negative electrode 200 manufactured by the manufacturing method according to the present disclosure is suppressed by drying the paste B in such a temperature range and generating migration.

“Migration” in this specification means that the negative electrode mixture layer 202 including the negative electrode active material rich region 202a and the hydrophobic resin rich region 202c shown in FIG. 1 is formed by the following phenomena (1) to (3). Indicates that
(1) Convection occurs in the paste B by drying at 120 ° C. or higher and 180 ° C. or lower.
(2) Paste B includes negative electrode active material 202b and hydrophobic resin 202d. The hydrophobic resin 202d moves to the surface layer of the paste B by convection. Thereby, the surface layer (upper part) of the paste B contains more hydrophobic resin 202d than the negative electrode active material 202b. On the other hand, the negative electrode active material 202b moves to the lower part of the paste B (that is, other than the surface layer of the paste B). Thereby, in the lower part of the paste B, the negative electrode active material 202b is contained more than the hydrophobic resin 202d.
(3) By evaporating the solvent contained in the paste B, the negative electrode mixture layer 202 including the negative electrode active material rich region 202a and the hydrophobic resin rich region 202c can be formed.

  The paste C containing the aqueous solvent, the heat resistant material 203a, and the binder 203b is applied to the negative electrode mixture layer 202, whereby the heat resistant layer 203 is formed on the surface of the negative electrode mixture layer 202 (hydrophobic resin rich region 202c). The hydrophobic resin rich region 202c includes a hydrophobic resin 202d. It is considered that the hydrophobic resin 202d suppresses the penetration of the binder 203b included in the paste C into the negative electrode mixture layer 202 together with the aqueous solvent. That is, it is expected to provide a method for manufacturing the negative electrode 200 including the heat-resistant layer 203 that can suppress an increase in battery resistance.

FIG. 1 is a conceptual cross-sectional view showing the configuration of the negative electrode for a lithium ion secondary battery of the present embodiment. FIG. 2 is a flowchart showing an outline of a method for producing a negative electrode for a lithium ion secondary battery of the present embodiment. FIG. 3 is a flowchart showing an outline of a method for manufacturing the lithium ion secondary battery of the present embodiment. FIG. 4 is a schematic diagram showing an example of the configuration of the lithium ion secondary battery of the present embodiment.

  Hereinafter, an embodiment of the present disclosure (also referred to as “this embodiment” in the present specification) will be described. However, the following description does not limit the scope of the claims.

  In the drawings of the present disclosure, the dimensional relationship is appropriately changed for convenience of explanation. The dimensional relationships shown in the drawings of the present disclosure do not represent actual dimensional relationships.

<Method for producing negative electrode for lithium ion secondary battery>
FIG. 2 is a flowchart showing an outline of a method for producing a negative electrode for a lithium ion secondary battery of the present embodiment. Based on this flowchart, the negative electrode 200 described in FIG. 1 can be manufactured. The manufacturing method of the negative electrode of this embodiment includes “(a1) Preparation of negative electrode current collector”, “(a2) Preparation of paste A”, “(a3) Preparation of paste B”, “(a4) Application of paste B ", (A5) Drying of paste B", "(a6) Preparation of paste C", and "(a7) Application of paste C". Hereinafter, the manufacturing method of the negative electrode of this embodiment is demonstrated in order.

<< (a1) Preparation of negative electrode current collector >>
The method for manufacturing the negative electrode 200 of this embodiment includes preparing the negative electrode current collector 201. The negative electrode current collector 201 may be, for example, a copper (Cu) foil. The Cu foil may be a pure Cu foil or a Cu alloy foil. The negative electrode current collector 201 may have a thickness of 5 to 30 μm, for example.

  The “thickness” of each component in the present specification can be measured by, for example, a micrometer. The thickness of each configuration may be measured in a cross-sectional microscopic image of each configuration. The thickness can be measured at least three times. An arithmetic average of at least three times can be adopted as the measurement result.

<< (a2) Preparation of paste A >>
The manufacturing method of the negative electrode 200 of this embodiment includes preparing the paste A containing at least the negative electrode active material 202b. The paste A can include a binder in addition to the negative electrode active material 202b. Specifically, the paste A is prepared by mixing the negative electrode active material 202b, a binder, and a solvent. For the mixing, a general stirrer (for example, a planetary mixer, a homogenizer, etc.) can be used. The viscosity of the paste A is adjusted to be 1100 mPa · s or more and 3400 mPa · s or more at a shear rate of 2 sec ⁻¹ . The viscosity can be measured using various known viscometers. As the viscometer, there is no particular limitation on the measurement principle and measuring instrument as long as the viscosity of paste A and the viscosity range in the vicinity thereof can be measured correctly.

(Negative electrode active material and binder)
The negative electrode active material 202b should not be specifically limited. The negative electrode active material 202b may be, for example, graphite, soft carbon, hard carbon, silicon, silicon oxide, a silicon base alloy, tin, tin oxide, a tin base alloy, or the like. The graphite may be artificial graphite or natural graphite. One kind of negative electrode active material 202b may be used alone. Two or more negative electrode active materials 202b may be used in combination. The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

(solvent)
The solvent is selected according to the type of the negative electrode active material 202b and the binder. The solvent may be, for example, water or an organic solvent. For example, if the binder is CMC, water can be used as the solvent. The solvent may be an aqueous solvent. As the water-miscible organic solvent, for example, ethanol, isopropyl alcohol, acetone, tetrahydrofuran or the like may be used.

<< (a3) Preparation of paste B >>
The manufacturing method of the negative electrode 200 of this embodiment includes adding the hydrophobic resin 202d to the paste A and preparing the paste B containing the negative electrode active material 202b and the hydrophobic resin 202d. Specifically, paste B is prepared by mixing paste A and hydrophobic resin 202d. For the mixing, a general stirrer (for example, a planetary mixer, a homogenizer, etc.) can be used.

(Hydrophobic resin)
The hydrophobic resin 202d should not be particularly limited. The hydrophobic resin 202d may be, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), or the like. One kind of hydrophobic resin 202d may be used alone. Two or more hydrophobic resins 202d may be used in combination.

<< (a4) Application of paste B >>
The method for manufacturing the negative electrode 200 of the present embodiment includes applying paste B to the negative electrode current collector 201. A general coating apparatus (for example, a die coater, a gravure coater, etc.) can be used for the coating operation of the present embodiment. The paste B may be applied to both the front and back surfaces of the negative electrode current collector 201.

<< (a5) Drying of paste B >>
In the manufacturing method of the negative electrode 200 of the present embodiment, the paste B applied to the negative electrode current collector 201 is dried, so that the negative electrode active material rich region 202a and the hydrophobic resin rich region 202c are formed on the surface of the negative electrode current collector 201. Forming a negative electrode composite material layer 202 containing Drying is performed in a temperature range of 120 ° C. or higher and 180 ° C. or lower. It is considered that migration occurs in the paste B by drying the paste B in such a temperature range. Specifically, the hydrophobic resin 202d moves to the surface layer of the paste B during drying. Thereby, the surface layer (upper part) of the paste B contains more hydrophobic resin 202d than the negative electrode active material 202b. On the other hand, the negative electrode active material 202b moves to the lower part of the paste B (that is, other than the surface layer of the paste B). Thereby, in the lower part of the paste B, the negative electrode active material 202b is contained more than the hydrophobic resin 202d. In this state, the solvent contained in the paste B is evaporated, whereby the negative electrode mixture layer 202 including the negative electrode active material rich region 202a and the hydrophobic resin rich region 202c can be formed. A negative electrode active material rich region 202 a is formed on the lower side in the thickness direction of the negative electrode mixture layer 202, and a hydrophobic resin rich region 202 c is formed on the upper side in the thickness direction of the negative electrode mixture layer 202.

<< (a6) Preparation of paste C >>
The method for manufacturing the negative electrode 200 of the present embodiment includes preparing a paste C including an aqueous solvent, a heat-resistant material 203a, and a binder 203b. Specifically, the paste C is prepared by mixing the aqueous solvent, the heat-resistant material 203a, and the binder 203b. For the mixing, a general stirrer (for example, a planetary mixer, a homogenizer, etc.) can be used.

(Aqueous solvent)
The aqueous solvent may be water or a mixture of an organic solvent miscible with water and water. The water is preferably low in impurities. For example, distilled water, ion exchange water, pure water, ultrapure water, or the like may be used. As the water-miscible organic solvent, for example, ethanol, isopropyl alcohol, acetone, tetrahydrofuran or the like may be used.

(Heat resistant material)
The heat resistant material 203a may be an inorganic material. The heat resistant material 203a may be, for example, alumina, silica or the like. One kind of heat-resistant material 203a may be used alone. Two or more heat-resistant materials 203a may be used in combination.

(Binder)
The binder 203b should not be specifically limited. The binder 203b may be, for example, CMC and SBR. One kind of binder 203b may be used alone. Two or more binders 203b may be used in combination.

<< (a7) Application of paste C >>
In the manufacturing method of the negative electrode 200 of the present embodiment, the paste C prepared in (a6) above is applied to the negative electrode mixture layer 202 (hydrophobic resin rich region 202c) formed in (a5) above, Forming the heat-resistant layer 203 on the surface of the rich region 202c. The heat resistant layer 203 includes a heat resistant material 203a and a binder 203b. A general coating apparatus (for example, a die coater, a gravure coater, etc.) can be used for the coating operation of the present embodiment. The paste C applied to the hydrophobic resin rich region 202c may be dried in a temperature range of 70 ° C. or higher and 180 ° C. or lower, for example.

  From the above, the negative electrode 200 can be manufactured. The negative electrode 200 can be cut and used so as to have a predetermined planar shape (for example, a belt shape or the like) according to the specifications of the battery.

<Method for producing lithium ion secondary battery>
FIG. 3 is a flowchart showing an outline of a method for manufacturing the lithium ion secondary battery of the present embodiment. The battery manufacturing method of the present embodiment includes “(A) manufacture of negative electrode”, “(B) manufacture of positive electrode”, and “(C) manufacture of battery”. Hereinafter, the battery manufacturing method of the present embodiment will be described in order.

<< (A) Production of negative electrode >>
The manufacturing method of the battery of this embodiment includes manufacturing a negative electrode by the negative electrode manufacturing method of this embodiment described above. The details of the manufacturing method of the negative electrode of the present embodiment are as described above. The same description is not repeated here.

<< (B) Production of positive electrode >>
The manufacturing method of the battery of this embodiment includes manufacturing a positive electrode. The manufacturing method of a positive electrode should not be specifically limited. The positive electrode can be manufactured by a conventionally known method.

  For example, a positive electrode mixture paste is prepared by mixing a positive electrode active material, a conductive material, a binder, and a solvent. The positive electrode mixture paste is applied to the surface of the positive electrode current collector and dried to produce a positive electrode. The positive electrode can be cut and used so as to have a predetermined planar shape according to the specifications of the battery.

  The positive electrode current collector may be, for example, an aluminum (Al) foil. The Al foil may be a pure Al foil or an Al alloy foil. The Al foil may have a thickness of 10 to 30 μm, for example.

A positive electrode mixture layer can be formed by applying the positive electrode mixture paste to the surface of the positive electrode current collector and drying it. The positive electrode mixture layer may be formed on both the front and back surfaces of the positive electrode current collector. In the present embodiment, the positive electrode mixture layer may be compressed so that the positive electrode mixture layer has a predetermined density. In the present embodiment, the positive electrode mixture layer can be compressed so that the positive electrode mixture layer has a density of 2 to ⁴ g / cm ³ , for example. The positive electrode mixture layer after compression may have a thickness of 10 to 200 μm, for example. The positive electrode mixture layer can be formed to include, for example, 80 to 98% by mass of a positive electrode active material, 1 to 15% by mass of a conductive material, and 1 to 5% by mass of a binder.

(Positive electrode active material)
The positive electrode active material electrochemically occludes and releases lithium ions. The positive electrode active material is a powder. The positive electrode active material should not be particularly limited. The positive electrode active material is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _x Co _y Me _z O ₂ (wherein Me is at least one of Mn or Al, and x, y, and z are 0 < x <1, 0 <y <1, 0 <z <1, x + y + z = 1), LiMn ₂ O ₄ , LiFePO _4, or the like. Examples of the positive electrode active material represented by the general formula: LiNi _x Co _y Me _z O ₂ include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.82 Co _0.15 Al _0.03 O ₂ etc. are mentioned. One type of positive electrode active material may be used alone, or two or more types of positive electrode active materials may be used in combination. The positive electrode active material may have an average particle diameter of 1 to 30 μm, for example.

(Conductive material)
The conductive material has electronic conductivity. The conductive material is a powder. The conductive material should not be particularly limited. The conductive material may be, for example, carbon black, scaly graphite or the like. One type of conductive material may be used alone, or two or more types of conductive materials may be used in combination.

(Binder)
The binder should not be particularly limited. The binder may be, for example, PVdF, PTFE, CMC, polyacrylic acid (PAA), or the like. One kind of binder may be used alone, or two or more kinds of binders may be used in combination.

(solvent)
A solvent is suitably selected according to the kind of binder. For example, when the binder is PVdF, N-methyl-2-pyrrolidone (NMP) can be used as the solvent.

<< (C) Battery Production >>
The battery manufacturing method of the present embodiment includes manufacturing a battery including at least a positive electrode, a negative electrode 200, and an electrolytic solution having lithium ion conductivity.

  FIG. 4 is a schematic diagram illustrating an example of the configuration of the battery 1000 according to the present embodiment. Here, the electrode group 500 is manufactured. The electrode group 500 can be manufactured by, for example, laminating the positive electrode 100, the separator 300, the negative electrode 200, and the separator 300 in this order, and winding them in a spiral shape.

(Separator)
The separator 300 is a porous sheet. The separator 300 is electrically insulating. For example, the separator 300 may have a thickness of 5 to 50 μm (typically 10 to 25 μm). Separator 300 can be made of, for example, polyethylene (PE), polypropylene (PP), or the like. Separator 300 may have a multilayer structure. For example, the separator 300 may be configured by laminating a polypropylene porous layer, a polyethylene porous layer, and a polypropylene porous layer in this order.

(Case)
Case 800 is prepared. Case 800 is a sealed container. Case 800 may be made of metal such as Al alloy, stainless steel (SUS), iron (Fe), and the like. Case 800 may be made of resin. Case 800 may be a bag made of an aluminum laminate film or the like. The case 800 may include a current interrupt mechanism (CID), a gas discharge valve, a liquid injection hole, and the like (none of which are shown).

  Case 800 is cylindrical. However, the battery of this embodiment should not be limited to a cylindrical battery. The battery of this embodiment may be, for example, a square battery or a laminate type battery.

  The electrode group 500 is housed in the case 800. The positive electrode 100 and the negative electrode 200 are welded to a portion to be an external terminal.

(Electrolyte)
An electrolyte is prepared. The electrolytic solution contains a solvent and a Li salt. The solvent is aprotic. The solvent may be, for example, a mixture of a cyclic carbonate and a chain carbonate. The mixing ratio may be, for example, “cyclic carbonate: chain carbonate = 1: 9 to 5: 5” by volume ratio. The cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate (PC), or the like. One cyclic carbonate may be used alone. Two or more cyclic carbonates may be used in combination. The chain carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or the like. One type of chain carbonate may be used alone. Two or more chain carbonates may be used in combination.

Li salt is a supporting electrolyte. The electrolytic solution may contain, for example, 0.5 to 2 mol / l Li salt. Li salt, _{e.g., LiPF 6, LiBF 4, Li} [N (FSO 2) 2], may be _{Li [N (CF 3 SO 2} ) 2] and the like. One Li salt may be used alone. Two or more kinds of Li salts may be used in combination.

  The electrolytic solution may further contain various additives. The electrolytic solution may contain, for example, an additive of 0.01 to 0.1 mol / l. The additive may be, for example, vinylene carbonate (VC), propane sultone (PS), cyclohexylbenzene (CHB), biphenyl (BP), lithium bisoxalatoborate (LiBOB), and the like. One additive may be used alone. Two or more additives may be used in combination.

  The electrolytic solution is stored (injected) in the case 800. After the electrolytic solution is stored, the case 800 is sealed. Thus, the battery 1000 can be manufactured.

  Examples of the present disclosure are described below. However, the following description does not limit the scope of the claims.

<Example 1>
In Example 1, the negative electrode 200 was manufactured according to the flowchart of FIG. Then, the battery 1000 was manufactured according to the flowchart of FIG.

<< (A) Production of negative electrode >>
1. Preparation of paste A etc. [(a1) and (a2)]
The following materials were prepared:
Negative electrode active material: Natural graphite Binder: CMC
Solvent: Water Negative electrode current collector: Cu foil

Paste A was prepared by mixing natural graphite, CMC, and water. The viscosity of the paste A was 3400 mPa · s at a shear rate of 2 sec ⁻¹ .

2. Preparation and application of paste B [(a3) and (a4)]
The following materials were prepared:
Hydrophobic resin: PTFE

  Paste B was prepared by adding PTFE to paste A. The solid content composition of the paste B was “natural graphite: CMC: PTFE = 98.5: 1: 0.5” by mass ratio. Paste B was applied to the surface (both front and back surfaces) of the negative electrode current collector 201.

3. Drying paste B (a5)
Paste B applied to the surface of the negative electrode current collector 201 was dried at 120 ° C. Migration occurred during drying, and a negative electrode active material rich region 202a and a hydrophobic resin rich region 202c were formed. On the surface of the negative electrode current collector 201, the negative electrode mixture layer 202 including the negative electrode active material rich region 202a and the hydrophobic resin rich region 202c was formed. It is confirmed that the negative electrode active material rich region 202a is formed on the lower side in the thickness direction of the negative electrode mixture layer 202, and the hydrophobic resin rich region 202c is formed on the upper side in the thickness direction of the negative electrode mixture layer 202a. It was.

4). Preparation of paste C and formation of heat-resistant layer [(a6) and (a7)]
The following materials were prepared:
Heat resistant material: Alumina Binder: SBR
Thickener: CMC
Solvent: Water Negative electrode current collector: Cu foil

  Paste C was prepared by mixing alumina, SBR, CMC, and water. The solid content composition of the paste C was “alumina: SBR: CMC = 96: 2: 2” by mass ratio. The heat-resistant layer 203 was formed by applying the paste C to the surface of the hydrophobic resin-rich region 202c and drying. Thereby, the negative electrode 200 was manufactured. The negative electrode 200 was compressed. The negative electrode 200 has a belt-like planar shape.

<< (B) Production of positive electrode >>
The following materials were prepared:
Positive electrode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM)
Conductive material: AB
Binder: PVdF
Solvent: NMP
Positive electrode current collector: Al foil

  A positive electrode mixture paste was prepared by mixing NCM, AB, PVdF, and NMP. The mixing ratio of the solid content is “NCM: AB: PVdF = 93: 4: 3 (mass ratio)”. The positive electrode mixture paste was applied to the surface (both front and back surfaces) of the positive electrode current collector and dried. Thereby, the positive electrode 100 was manufactured. The positive electrode 100 was compressed. The positive electrode 100 has a belt-like planar shape.

<< (C) Battery Production >>
A separator 300 made of polyethylene was prepared. The separator 300 has a belt-like planar shape. The positive electrode 100, the separator 300, the negative electrode 200, and the separator 300 were laminated in this order, and these were further spirally wound. Thereby, the electrode group 500 was manufactured. A cylindrical case 800 was prepared. The electrode group 500 was housed in the case 800.

An electrolytic solution having the following composition was prepared.
Solvent: [EC: DMC: EMC = 3: 4: 3 (volume ratio)]
Supporting electrolyte: LiPF ₆ (1 mol / l)

  An electrolyte was injected into the case 800. Case 800 was sealed. As described above, the battery 1000 according to Example 1 was manufactured. Battery 1000 has a rated capacity of 500 mAh.

<Example 2 to Example 6>
As shown in Table 1 below, the negative electrode 200 and the battery 1000 were manufactured in the same manner as in Example 1 except that the viscosity of the paste A and the temperature for drying the paste B were changed.

<Comparative Example 1>
As shown in Table 1 below, the viscosity of the paste A was changed, the hydrophobic resin was not added to the paste A, the paste A was applied to the negative electrode current collector 201, and the paste A was applied at 130 ° C. By drying, the negative electrode mixture layer 202 was formed on the surface of the negative electrode current collector 201, the composition of the negative electrode mixture layer 202 was changed, and the layer containing the CMC on the surface of the negative electrode mixture layer 202 (hereinafter referred to as the negative electrode mixture layer 202) The negative electrode 200 was manufactured in the same manner as in Example 1 except that the heat resistant layer 203 was not formed, and the battery 1000 was manufactured. That is, in Comparative Example 1, the hydrophobic resin rich region 202c and the heat resistant layer 203 are not formed. A binder layer is formed on the surface of the negative electrode mixture layer 202. The binder layer does not contain a hydrophobic resin (PTFE).

<Comparative example 2>
As shown in Table 1 below, the negative electrode 200 was manufactured and the battery 1000 was manufactured in the same manner as in Comparative Example 1 except that the heat-resistant layer 203 was formed on the surface of the binder layer.

<Comparative Example 3>
As shown in Table 1 below, the composition of the negative electrode mixture layer 202 was changed, and the paste containing CMC and PTFE on the surface of the negative electrode mixture layer 202 (hereinafter also referred to as “post-coating paste”) Except that a layer containing a hydrophobic resin (hydrophobic resin layer) is formed on the surface of the negative electrode mixture layer 202 by applying (this coating method is also described as “post-coating”) and drying. The negative electrode 200 was manufactured in the same manner as in Comparative Example 1, and the battery 1000 was manufactured. That is, in Comparative Example 3, the surface of the negative electrode mixture layer 202 is formed by post-coating a hydrophobic resin layer.

<Comparative Example 4>
As shown in Table 1 below, except that the viscosity of the paste A was changed, the negative electrode 200 was manufactured in the same manner as in Example 1, and the battery 1000 was manufactured.

<Comparative Example 5>
As shown in Table 1 below, except that the temperature for drying the paste B was changed, the negative electrode 200 was manufactured in the same manner as in Example 1, and the battery 1000 was manufactured.

<Evaluation>
The SOC of battery 1000 was adjusted to 50%. The battery 1000 was discharged for 10 seconds at a current rate of 10 C in a 25 ° C. environment. The amount of voltage drop 10 seconds after the start of discharge was measured. The battery resistance was calculated from the relationship between the voltage drop amount and the current rate. The results are shown in the column “Battery resistance” in Table 1 below. In Table 1, the value shown in “Battery resistance” is a relative evaluation of the initial resistance values of other examples and comparative examples, with the initial resistance value in comparative example 1 being 100%. The smaller the value, the smaller the initial resistance value.

<Result>
In Examples 1 to 6, an increase in battery resistance was suppressed as compared with Comparative Example 1. In Examples 1 to 6, the hydrophobic resin rich region 202c including the hydrophobic resin 202d is formed by migration. It is considered that the binder 203b included in the paste C is prevented from penetrating into the negative electrode mixture layer 202 by the hydrophobic resin rich region 202c. Accordingly, it is considered that the surface of the negative electrode active material 202b included in the negative electrode mixture layer 202 is suppressed from being covered with the binder 203b, and an increase in battery resistance is suppressed.

  In Comparative Example 1, the battery resistance was higher than that of the example. It is considered that CMC (binder) contained in the binder layer formed on the surface of the negative electrode mixture layer 202 penetrates into the negative electrode mixture layer 202, and the CMC (binder) covers the surface of the negative electrode material 202a. Thereby, it is thought that battery resistance increased.

  Comparative Example 2 had higher battery resistance than Comparative Example 1. It is considered that the battery resistance is increased because the heat-resistant layer 203 is provided.

  Comparative Example 3 had a higher battery resistance than Comparative Example 1. The hydrophobic resin layer is formed by “post-coating” of forming a negative electrode mixture layer 202 and then applying a post-coating paste to the surface of the negative electrode mixture layer 202. Therefore, it is considered that CMC (binder) contained in the post-coating paste penetrates into the negative electrode mixture layer 202 and the CMC (binder) covers the surface of the negative electrode material 202a. Thereby, it is thought that battery resistance increased.

Comparative Example 4 had higher battery resistance than Comparative Example 1. The viscosity of the paste A used in Comparative Example 4 was 3700 mPa · s at a shear rate of 2 sec ⁻¹ and was not in the range of 1100 mPa · s to 3400 mPa · s. For this reason, it is considered that the negative electrode 200 capable of suppressing the increase in battery resistance was not obtained.

  Comparative Example 5 had a higher battery resistance than Comparative Example 1. In Comparative Example 5, the paste B was dried at 110 ° C. and not at a temperature of 120 ° C. or higher and 180 ° C. or lower. For this reason, it is considered that the negative electrode 200 capable of suppressing the increase in battery resistance was not obtained.

  The embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope determined by the description of the scope of claims includes meanings equivalent to the scope of claims and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 100 Positive electrode, 200 Negative electrode (negative electrode for lithium ion secondary batteries), 201 Negative electrode collector, 202 Negative electrode compound material layer, 202a Negative electrode active material rich area | region, 202b Negative electrode active material, 202c Hydrophobic resin rich area | region, 202d Hydrophobic resin , 203 heat-resistant layer, 203a heat-resistant material, 203b binder, 300 separator, 500 electrode group, 800 case, 1000 battery (lithium ion secondary battery).

Claims (1)

Preparing a negative electrode current collector,
Preparing a paste A containing a negative electrode active material;
Adding a hydrophobic resin to the paste A, and preparing a paste B containing the negative electrode active material and the hydrophobic resin;
Applying the paste B to the negative electrode current collector;
Forming the negative electrode mixture layer including a negative electrode active material rich region and a hydrophobic resin rich region on the surface of the negative electrode current collector by drying the paste B;
Preparing a paste C containing an aqueous solvent, a heat-resistant material, and a binder;
Applying the paste C to the negative electrode mixture layer, and forming a heat-resistant layer on the surface of the negative electrode mixture layer,
The negative electrode active material rich region includes more of the negative electrode active material than the hydrophobic resin,
The hydrophobic resin-rich region contains more hydrophobic resin than the negative electrode active material,
The heat-resistant layer includes the heat-resistant material and the binder,
The viscosity of the paste A is 1100 mPa · s or more and 3400 mPa · s or more at a shear rate of 2 sec ⁻¹ .
The drying is performed in a temperature range of 120 ° C. or more and 180 ° C. or less, and during the drying of the paste B, the negative electrode active material and the hydrophobic resin are separated into two layers by migration, and the thickness of the negative electrode mixture layer The manufacturing method of the negative electrode for lithium ion secondary batteries by which the said negative electrode active material rich area | region is formed below the thickness direction, and the said hydrophobic resin rich area | region is formed above the thickness direction of the said negative mix layer.

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