阅读说明：本技术 非水电解质二次电池电极用浆料、非水电解质二次电池电极用浆料的制造方法、非水电解质二次电池用电极及非水电解质二次电池 (Slurry for nonaqueous electrolyte secondary battery electrode, method for producing slurry for nonaqueous electrolyte secondary battery electrode, electrode for nonaqueous electrolyte secondary batter) 是由 岩见安展 森川敬元 中森俊行 市川智浩 于 2020-02-21 设计创作，主要内容包括：本发明的目的在于提供能够得到对集电体显示良好的粘接性的电极合剂层的非水电解质二次电池电极用浆料。作为本发明的一个方式的非水电解质二次电池电极用浆料包含电极合剂和水,所述电极合剂包含电极活性物质、碳酸锂和羧甲基纤维素或其盐,上述碳酸锂的含量相对于上述电极合剂的总质量为33ppm～300ppm的范围。(The purpose of the present invention is to provide a slurry for nonaqueous electrolyte secondary battery electrodes, which enables the production of an electrode mixture layer that exhibits good adhesion to a current collector. The slurry for a nonaqueous electrolyte secondary battery electrode as one embodiment of the present invention contains an electrode mixture containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof, and water, wherein the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.)

1. A slurry for a non-aqueous electrolyte secondary battery electrode, comprising an electrode mix containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof, and water,

the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.

2. A method for producing a slurry for an electrode of a nonaqueous electrolyte secondary battery, wherein an electrode mixture containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof is mixed with water to produce a slurry for an electrode,

the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.

3. An electrode for a nonaqueous electrolyte secondary battery, comprising a current collector and an electrode mixture layer on the current collector,

the electrode mix layer contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof,

the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode material mixture layer.

4. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte,

at least one of the positive electrode and the negative electrode is the electrode for a nonaqueous electrolyte secondary battery according to claim 3.

Technical Field

The present invention relates to a slurry for a nonaqueous electrolyte secondary battery electrode, a method for producing a slurry for a nonaqueous electrolyte secondary battery electrode, an electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

Background

In recent years, nonaqueous electrolyte secondary batteries that include a positive electrode, a negative electrode, and a nonaqueous electrolyte and that charge and discharge lithium ions or the like by moving between the positive electrode and the negative electrode have been widely used as high-output, high-energy-density secondary batteries.

For example, patent document 1 discloses a nonaqueous electrolyte secondary battery including a negative electrode containing a negative electrode active material and lithium carbonate, and discloses that a decrease in charge-discharge cycle characteristics is suppressed by the secondary battery.

For example, patent document 2 discloses a nonaqueous electrolyte secondary battery including a negative electrode containing a negative electrode active material, lithium carbonate, and carboxymethyl cellulose, in which the weight of lithium carbonate relative to the negative electrode is 1% to 10%, and discloses that the safety of the battery can be achieved by the nonaqueous electrolyte secondary battery.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 7-235297

Patent document 2: japanese laid-open patent publication No. 8-138743

Patent document 3: japanese patent laid-open publication No. 2013-114959

Patent document 4: japanese patent laid-open publication No. 2003-272619

Patent document 5: international publication No. 2012/002451

Patent document 6: international publication No. 2012/011555

Disclosure of Invention

Problems to be solved by the invention

However, the negative electrode and the positive electrode can be obtained by, for example, applying a slurry containing an electrode mixture containing an electrode active material (a negative electrode active material or a positive electrode active material) and carboxymethyl cellulose and drying the slurry to form an electrode mixture layer on an electrode current collector. However, the slurry containing carboxymethyl cellulose may have a reduced coating stability on the electrode current collector due to a reduced viscosity during electrode production, or the like, and may have a reduced adhesion of the electrode mixture layer to the electrode current collector.

Accordingly, an object of the present invention is to provide a slurry for a nonaqueous electrolyte secondary battery electrode, which can obtain an electrode mixture layer exhibiting good adhesion to an electrode current collector, and a method for producing the same. Further, an electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery are provided, which exhibit good adhesion between an electrode current collector and an electrode mixture layer.

Means for solving the problems

The slurry for a nonaqueous electrolyte secondary battery electrode as one embodiment of the present invention contains an electrode mixture containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof, and water, wherein the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.

A method for producing a slurry for a nonaqueous electrolyte secondary battery electrode according to one embodiment of the present invention is a method for producing a slurry for an electrode by mixing an electrode mixture containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof with water, wherein the content of the lithium carbonate is in a range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.

An electrode for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes a current collector and an electrode mixture layer on the current collector, wherein the electrode mixture layer contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the lithium carbonate is contained in a range of 33ppm to 300ppm with respect to the total mass of the electrode mixture layer.

A nonaqueous electrolyte secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and at least one of the positive electrode and the negative electrode is the electrode for the nonaqueous electrolyte secondary battery.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the slurry for a nonaqueous electrolyte secondary battery electrode and the method for producing the same, which are one embodiment of the present invention, an electrode mixture layer exhibiting good adhesion to a current collector can be obtained. In addition, according to the electrode for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery which are one embodiment of the present invention, good adhesion between the current collector and the electrode mixture layer can be ensured.

Drawings

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment.

Fig. 2 is a schematic diagram of an apparatus for measuring the peel strength of the negative electrode mixture layer with respect to the negative electrode current collector.

Detailed Description

As described above, the slurry containing carboxymethyl cellulose may have a reduced coating stability on the electrode current collector due to a reduced viscosity during electrode production, or the like, and may have a reduced adhesion of the electrode mixture layer to the electrode current collector. As a result of intensive studies, the present inventors have found that an electrode material mixture layer exhibiting good adhesion to an electrode current collector can be obtained by including a predetermined amount of lithium carbonate in a slurry, and have conceived of a slurry of the following embodiment.

The slurry for a nonaqueous electrolyte secondary battery electrode as one embodiment of the present invention contains an electrode mixture containing an electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof, and water, wherein the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture.

The slurry containing carboxymethyl cellulose is considered to be caused by bacteria inevitably present in the slurry, because the coating stability on the electrode current collector is lowered due to a decrease in viscosity or the like in the electrode production, and the adhesiveness of the electrode mixture layer to the current collector is lowered. Specifically, it is considered that the high-molecular chain of carboxymethyl cellulose is cut by an enzyme produced by bacteria, and thus the viscosity of the slurry in the electrode production is lowered, and the adhesiveness of the electrode mixture layer to the electrode current collector is lowered. However, it is considered that, by including lithium carbonate in the range of 33ppm to 300ppm with respect to the total mass of the electrode mixture as in the slurry as one embodiment of the present invention, the activity of the enzyme produced by the bacteria can be reduced, and the growth of the bacteria can be suppressed. As a result, it is considered that the electrode mixture layer exhibiting good adhesion to the electrode current collector can be obtained because the polymer chains of carboxymethyl cellulose are inhibited from being cut, and the viscosity of the slurry is inhibited from being lowered during the production of the electrode. On the other hand, if the content of lithium carbonate is less than 33ppm with respect to the total mass of the electrode mixture, it is considered that the activity of the enzyme generated by the bacteria in the slurry cannot be sufficiently reduced, and the growth of the bacteria cannot be sufficiently suppressed. As a result, it is not possible to sufficiently suppress the cutting of the polymer chains of carboxymethyl cellulose, and the adhesiveness of the electrode mixture layer to the electrode current collector is reduced, for example, by a decrease in the viscosity of the slurry during the production of the electrode. Further, if the content of lithium carbonate exceeds 300ppm with respect to the total mass of the electrode mixture, it is considered that lithium carbonate itself becomes a factor of reducing the adhesiveness of the electrode mixture layer to the electrode current collector.

An electrode for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes a current collector and an electrode mixture layer on the current collector, wherein the electrode mixture layer contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the lithium carbonate is contained in a range of 33ppm to 300ppm with respect to the total mass of the electrode mixture layer. Since the electrode for a nonaqueous electrolyte secondary battery according to one aspect of the present invention is obtained by using the slurry for a nonaqueous electrolyte secondary battery according to one aspect of the present invention, good adhesion between the electrode current collector and the electrode mixture layer can be ensured. In addition, a nonaqueous electrolyte secondary battery using the electrode for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention can ensure good adhesion between the current collector and the electrode mixture layer, and suppress, for example, a decrease in charge-discharge cycle characteristics.

Hereinafter, an embodiment of a slurry for a nonaqueous electrolyte secondary battery electrode, which is one embodiment of the present invention, will be described. Hereinafter, both the negative electrode slurry and the positive electrode slurry will be described.

< slurry for negative electrode >

The slurry for a negative electrode contains a negative electrode mixture containing a negative electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, and an optional binder, and water, and the content of the lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the negative electrode mixture.

The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions, and examples thereof include lithium alloys such as metallic lithium, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, and lithium-tin alloys, carbon materials such as graphite, coke, and sintered organic materials, and SnO₂、SnO、TiO₂And the like. These can be used alone in 1 kind, also can be combined with more than 2 kinds.

The content of the negative electrode active material is, for example, preferably in the range of 90 to 99 mass%, and more preferably in the range of 95 to 98 mass%, based on the total mass of the negative electrode mixture.

It is presumed that carboxymethyl cellulose or a salt thereof functions as a thickener for increasing the viscosity of the slurry for a negative electrode and also functions as a binder for binding particles of a negative electrode active material and the like. Examples of the salt of carboxymethyl cellulose include monovalent metal salts such as alkali metal salts (lithium salts, sodium salts, potassium salts, rubidium salts, cesium salts, and the like), divalent metal salts such as alkaline earth metal salts (calcium salts, magnesium salts, and the like), quaternary ammonium salts, amine salts, substituted amine salts (alkanolamine salts such as ethanolamine, and the like), and double salts thereof.

The content of the carboxymethyl cellulose or a salt thereof is, for example, preferably in the range of 1 to 5 mass%, and preferably in the range of 1 to 2.5 mass%, based on the total mass of the negative electrode mixture.

For example, inexpensive commercial products and industrial-grade products can be used as lithium carbonate. From the viewpoint of dispersibility or solubility in the slurry for a negative electrode, it is preferable that lithium carbonate is pulverized before use to adjust the average particle diameter and the maximum particle diameter. The pulverization treatment is not particularly limited, and for example, dry pulverization such as a jet mill and a ball mill is preferable.

The content of lithium carbonate may be in the range of 33ppm to 300ppm with respect to the total mass of the negative electrode mixture, and is preferably in the range of 66ppm to 300ppm, and more preferably in the range of 66ppm to 200ppm, from the viewpoint of effectively suppressing the cleavage of the polymer chain of carboxymethyl cellulose by bacteria in the slurry and obtaining an electrode mixture layer exhibiting more excellent adhesion to the electrode current collector.

The water is not particularly limited, but water having a low impurity concentration is preferable, and for example, purified water such as ion-exchanged water can be used.

Examples of the binder include fluorine resins such as Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyvinylpyrrolidone (PVP), Polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). Among them, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA) are preferable from the viewpoint of dispersibility or solubility in the slurry for a negative electrode. These can be used alone in 1 kind, also can be combined with more than 2 kinds.

The content of the binder is, for example, preferably in the range of 1 to 5 mass%, and preferably in the range of 1 to 2.5 mass%, based on the total mass of the negative electrode mixture.

The method for producing the slurry for the negative electrode is as follows: first, a negative electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof are mixed so as to have a predetermined mass ratio, and a binder is mixed so as to have a predetermined mass ratio as needed, thereby obtaining a negative electrode mixture. The content of lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the negative electrode mixture. Then, the obtained negative electrode mixture is mixed with an appropriate amount of water to obtain a negative electrode slurry. The pH of the slurry for a negative electrode is preferably in the range of 8 to 9 in terms of reducing the activity of enzymes produced from bacteria and suppressing the propagation of bacteria. In general, if the lithium carbonate content is in the above range, the pH of the slurry for a negative electrode is in the range of 8 to 9.

< slurry for Positive electrode >

The slurry for a positive electrode contains a positive electrode mixture containing a positive electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, a binder added as needed, and a conductive material added as needed, and water. The content of lithium carbonate may be in the range of 33ppm to 300ppm with respect to the total mass of the positive electrode mixture, and as in the case of the negative electrode slurry, is preferably in the range of 66ppm to 300ppm, and more preferably in the range of 66ppm to 200 ppm.

The positive electrode active material includes, for example, a lithium-containing transition metal oxide. The metal element constituting the lithium-containing transition metal oxide is, for example, at least 1 selected from the group consisting of magnesium (Mg), aluminum (Al), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), tin (Sn), antimony (Sb), tungsten (W), lead (Pb), and bismuth (Bi). Among these, at least 1 kind selected from Co, Ni, Mn, and Al is preferably contained.

Lithium carbonate, carboxymethyl cellulose or a salt thereof, water, and a binder are the same as the negative electrode slurry, and therefore, descriptions thereof are omitted.

Examples of the conductive material include carbon materials such as Carbon Black (CB), Acetylene Black (AB), ketjen black, and graphite. These can be used alone in 1 kind, also can be combined with more than 2 kinds.

The method for producing the slurry for the positive electrode is as follows: first, a positive electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof are mixed so as to have a predetermined mass ratio, and a binder and a conductive material are mixed so as to have a predetermined mass ratio as needed, to obtain a positive electrode mixture. The content of lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the positive electrode mixture. Then, the obtained positive electrode mixture is mixed with an appropriate amount of water to obtain a positive electrode slurry. The pH of the slurry for positive electrode is preferably in the range of 8 to 9 from the viewpoint of reducing the activity of enzymes generated from bacteria and suppressing the propagation of bacteria, as in the slurry for negative electrode. In general, if the lithium carbonate content is in the above range, the pH of the positive electrode slurry is in the range of 8 to 9.

The slurry for a nonaqueous electrolyte secondary battery electrode of the present embodiment may be applied to both the slurry for a positive electrode and the slurry for a negative electrode, or may be applied to only either one. In the case of applying to either one, the slurry for the other electrode preferably contains an organic solvent such as NMP as a dispersion medium instead of water. In the slurry containing an organic solvent such as NMP as a dispersion medium instead of water, since high coating stability tends to be exhibited without using carboxymethyl cellulose or a salt thereof, the amount of lithium carbonate added to reduce the activity of enzymes produced from bacteria can be suppressed or reduced to zero. In general, in the case of slurry for a positive electrode, an organic solvent such as NMP can be used as a dispersion medium. However, in the case of the slurry for a negative electrode, there is a tendency that water is preferably used as a dispersion medium from the viewpoint of coating stability and the like, and therefore, the slurry for a nonaqueous electrolyte secondary battery electrode of the present embodiment is preferably used at least as the slurry for a negative electrode.

The electrode slurry containing an organic solvent such as NMP as a dispersion medium instead of water contains, for example, an electrode mixture containing an electrode active material, a binder, and the like, and an organic solvent such as NMP. In this case, the binder is preferably a fluororesin such as Polytetrafluoroethylene (PTFE) or polytetrafluoroethylene (PVdF), polyvinylpyrrolidone (PVP), Polyacrylonitrile (PAN), a polyimide-based resin, an acrylic resin, a polyolefin-based resin, or the like. In addition, a conductive material may be added to the electrode mixture as needed.

The following describes an electrode (positive electrode, negative electrode) for a nonaqueous electrolyte secondary battery of the present embodiment and a nonaqueous electrolyte secondary battery including the electrode.

< nonaqueous electrolyte Secondary Battery >

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. As illustrated in fig. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode body 14, a nonaqueous electrolyte, and a battery case 15 that houses the electrode body 14 and the nonaqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13 interposed between the positive electrode 11 and the negative electrode 12. The electrode body 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The electrode body 14 is not limited to a wound type, and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated by 1 sheet with a separator interposed therebetween.

The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of the nonaqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of 2 or more of them. The nonaqueous solvent may contain a halogen-substituted compound in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine. The nonaqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte. The electrolyte salt is, for example, LiPF₆And the like lithium salts.

The battery case 15 includes a bottomed cylindrical outer can 16 and a sealing member 17 for sealing an opening of the outer can 16. The battery case 15 is not limited to a cylindrical shape, and may be a metal case such as a rectangular battery or a coin-shaped battery, or a laminate film case (laminate battery) in which a metal film and a resin film are laminated.

The outer can 16 is, for example, a metal container having a bottomed cylindrical shape. A gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure the sealing property inside the battery. The outer can 16 has, for example, a recessed portion 22, a part of the side surface portion of which protrudes inward, and which supports the sealing body 17. The recessed portion 22 is preferably formed in a ring shape along the circumferential direction of the outer can 16, and supports the sealing member 17 on the upper surface thereof.

Sealing body 17 has a structure in which bottom plate 23, lower valve element 24, insulating member 25, upper valve element 26, and cover 27 are stacked in this order from electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk shape or an annular shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their central portions, and an insulating member 25 is interposed between their peripheral portions. If the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push the upper valve body 26 upward toward the lid 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is cut off. If the internal pressure further rises, the upper valve body 26 is broken and the gas is discharged from the opening of the lid 27.

The nonaqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 disposed above and below the electrode assembly 14. In the example shown in fig. 1, a positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing member 17 through a through hole of the insulating plate 18, and a negative electrode lead 21 attached to the negative electrode 12 extends toward the bottom of the outer can 16 through the outside of the insulating plate 19. Positive electrode lead 20 is connected to the lower surface of bottom plate 23 of sealing member 17 by welding or the like, and cover 27 of sealing member 17 electrically connected to bottom plate 23 serves as a positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

< Positive electrode >

The positive electrode 11 includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The positive electrode 11 is obtained, for example, by applying the slurry for a positive electrode of the present embodiment to both surfaces of a positive electrode current collector, drying the coating film to form a positive electrode mixture layer on the positive electrode current collector, and rolling the positive electrode mixture layer. The positive electrode mixture layer of the positive electrode 11 produced using the slurry for a positive electrode of the present embodiment contains a positive electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, an optional binder, and an optional conductive material, and the content of lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the positive electrode mixture layer. As described above, the positive electrode 11 can be produced using a slurry in which an organic solvent such as NMP is used as a dispersion medium instead of water.

As the positive electrode current collector, a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, a film in which the metal is disposed on the surface layer, or the like can be used. The materials constituting the positive electrode material mixture layer are as described above, and the description thereof is omitted.

< negative electrode >

The negative electrode 12 includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode 12 is obtained, for example, by applying the slurry for a negative electrode of the present embodiment to both surfaces of a negative electrode current collector, drying the coating film to form a negative electrode mixture layer on the negative electrode current collector, and rolling the negative electrode mixture layer. The negative electrode mixture layer of the negative electrode 12 produced using the slurry for a negative electrode of the present embodiment contains a negative electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, and an optional binder, and the content of lithium carbonate is in the range of 33ppm to 300ppm with respect to the total mass of the negative electrode mixture layer. As described above, the negative electrode 12 can be produced using a slurry in which an organic solvent such as NMP is used as a dispersion medium instead of water, but it is preferable to produce the negative electrode slurry of the present embodiment.

As the negative electrode current collector, a foil of a metal such as copper that is stable in the potential range of the negative electrode, a film in which the metal is disposed on the surface layer, or the like can be used. The materials constituting the negative electrode mixture layer are as described above, and the description thereof is omitted.

< spacer >

For example, a porous sheet having ion permeability and insulation properties can be used as the spacer 13. Specific examples of the porous sheet include a microporous film, a woven fabric, and a nonwoven fabric. As a material of the spacer 13, olefin resin such as polyethylene, polypropylene, a copolymer containing at least one of ethylene and propylene, cellulose, and the like are preferable. The spacer 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Further, a multilayer spacer including a polyethylene layer, a polypropylene layer, and the like may be used. Further, an aramid resin or the like may be applied to the surface of the spacer 13. In addition, a heat-resistant layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

Examples

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.

< example 1>

[ Positive electrode ]

Zirconium in an amount of 0.1 mol% relative to cobalt, magnesium in an amount of 1 mol% relative to cobalt, and aluminum were coprecipitated and subjected to a thermal decomposition reaction to obtain cobaltosic oxide containing zirconium, magnesium, and aluminum. Lithium carbonate as a lithium source was mixed thereto, and the mixture was sintered at 850 ℃ for 20 hours to obtain lithium cobaltate (LiCo) containing zirconium, magnesium and aluminum_0.979Zr_0.001Mg_0.01Al_0.01O₂). This was used as a positive electrode active material.

The positive electrode active material was mixed so that the mass of the positive electrode active material was 95%, the mass of the carbon powder as the conductive material was 2.5%, and the mass of the polyvinylidene fluoride powder as the binder was 2.5%, and the mixture was mixed with an N-methylpyrrolidone (NMP) solution to prepare a positive electrode slurry. This slurry for a positive electrode was applied to both surfaces of a positive electrode current collector made of aluminum and having a thickness of 15 μm by a doctor blade method, and positive electrode mixture layers were formed on both surfaces of the positive electrode current collector. Then, calendering is performed using a calender roll, and cut into a prescribed size. This was used as a positive electrode.

[ negative electrode ]

Graphite having an average particle diameter of 22 μm was prepared as a negative electrode active material. Taking graphite: carboxymethyl cellulose (CMC): the mass ratio of styrene-butadiene rubber (SBR) was 97: 1.5: 1.0, and a predetermined amount of lithium carbonate was added to obtain a negative electrode mixture. The lithium carbonate content was 66ppm based on the total mass of the negative electrode mixture. To this negative electrode mixture, ion-exchanged water was added and mixed to prepare a negative electrode slurry. The solid content of the slurry for a negative electrode was 50%.

The viscosity of the prepared negative electrode slurry was measured at the time of preparation and after 96 hours, using a B-type viscometer (east china industry TVB 10). Then, the viscosity change rate after 96 hours was determined by the following equation. The results are shown in Table 1.

Viscosity change rate (%) after 96 hours (viscosity after 96 hours)/(viscosity at the time of manufacture) × 100

The negative electrode mixture slurry obtained after 96 hours from the production was applied to both surfaces of the negative electrode current collector by a doctor blade method, and negative electrode mixture layers were formed on both surfaces of the negative electrode current collector. Then, the sheet was rolled with a calender roll and cut into a predetermined size. This was used as a negative electrode.

For the negative electrode of example 1, the peel strength of the negative electrode mixture layer with respect to the negative electrode current collector was measured using the apparatus shown in fig. 2. The apparatus shown in fig. 2 comprises: a base 131 on which a test object 132 is placed; an adhesive member 133 for fixing the test object 132; a chuck 134 which fixes one end of the test object 132 and is connected to the pull stage 138; a bearing portion 135 for horizontally sliding the base 131; a spring 136 for uniformly applying a force when the base 131 slides; a fixing portion 137 to which the spring 136 is connected; a pulling table 138 connected to the base 131 via a wire 139 and a pulley 140; a wire 141 for connecting the pulling stage 138 with the grasping jig 142; a load sensor 143 connected to the gripping jig 142 and detecting a load of the pulling stage 138; a support 144 that supports the load sensor 143; a driving unit 146 for moving the support 144 up and down; a linear sensor 147 that detects the amount of movement of the grasping jig 142; a support 145 having a drive unit 146 and a linear sensor 147 built therein; and a support base 148 for supporting the base 131, wherein the support base 148 and the support column 145 are fixed to the base 150.

The negative electrode cut into a size of 15mm in the vertical direction and 120mm in the horizontal direction was used as the specimen 132. The negative electrode (test object 132) is fixed to the base 131 by an adhesive member 133, and one end thereof is fixed by a chuck 134. The driving unit 146 is started to pull up the gripping jig 142 at a constant speed, whereby the pulling table 138 is pulled, and the chuck 134 is pulled up in association therewith, whereby the negative electrode mixture layer is peeled off from the negative electrode current collector. The stress at this time is measured by the load cell 143. After the measurement, a pulling test was performed only by the present apparatus with the negative electrode removed, and only the force component when the base 131 slid was measured. The peel strength of the negative electrode mixture layer is determined by subtracting the component of the force when only the base 131 slides from the stress when the negative electrode mixture layer is peeled from the negative electrode current collector, and converting the component into the unit length (m). The results are shown in Table 1.

[ non-aqueous electrolyte ]

For Ethylene Carbonate (EC) and ethyl methyl carbonate (MEC) to be 30: 70, dissolving lithium hexafluorophosphate (LiPF)₆) So that the concentration thereof becomes 1 mol/L. Further, Vinylene Carbonate (VC) was dissolved in an amount of 2.0 wt% based on the total amount of the electrolyte, thereby preparing a non-aqueous electrolyte.

[ nonaqueous electrolyte Secondary Battery ]

The positive electrode and the negative electrode were wound with a separator made of a microporous polyethylene film interposed therebetween, and a polypropylene tape was attached to the outermost periphery of the separator to produce a cylindrical electrode body. Then, pressing was performed to make a flat spiral electrode body.

A sheet-like laminate having a 5-layer structure of resin layer (polypropylene)/adhesive material layer/aluminum alloy layer/adhesive material layer/resin layer (polypropylene) was prepared. Then, the aluminum laminate was folded back to form a bottom portion, thereby forming a cup-shaped electrode body housing space. The flat electrode body and the nonaqueous electrolyte are inserted into the storage space in a glove box under an argon atmosphere. Then, the inside of the package was depressurized to impregnate the inside of the separator with the nonaqueous electrolyte, and the opening of the package was sealed, thereby producing a nonaqueous electrolyte secondary battery having a height of 62mm, a width of 35mm, and a thickness of 3.6 mm.

[ evaluation of capacity maintenance ratio in Charge-discharge cycle ]

In a temperature environment of 25 ℃, constant current charging (current 1It is 800mA, end voltage 4.2V) -constant voltage charging (voltage 4.2V, end current 40mA) was performed, and then, discharge was performed to 2.75V at a current value of 800 mA. The charge and discharge were cycled 300 times, and the capacity retention rate in the charge and discharge cycle was determined based on the following formula. The results are shown in Table 1.

Capacity retention rate (X2/X1) × 100

X1: discharge capacity of 1 st cycle

X2: discharge capacity at 300 th cycle

< example 2>

A slurry for a negative electrode was prepared in the same manner as in example 1, except that the content of lithium carbonate was 166ppm based on the total mass of the negative electrode mixture in the preparation of the slurry for a negative electrode. A negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the slurry for a negative electrode in example 2 was used.

< example 3>

A slurry for a negative electrode was prepared in the same manner as in example 1, except that the content of lithium carbonate was set to 300ppm based on the total mass of the negative electrode mixture in the preparation of the slurry for a negative electrode. A negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the slurry for a negative electrode in example 3 was used.

< example 4>

A slurry for a negative electrode was prepared in the same manner as in example 1, except that the content of lithium carbonate was 33ppm based on the total mass of the negative electrode mixture in the preparation of the slurry for a negative electrode. A negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the slurry for a negative electrode in example 4 was used.

< comparative example 1>

A negative electrode slurry was prepared in the same manner as in example 1, except that lithium carbonate was not used for preparing the negative electrode slurry. A negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the slurry for a negative electrode in comparative example 1 was used.

< comparative example 2>

A slurry for a negative electrode was prepared in the same manner as in example 1, except that the content of lithium carbonate was 1 mass% based on the total mass of the negative electrode mixture in the preparation of the slurry for a negative electrode. A negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the slurry for a negative electrode in comparative example 2 was used.

In addition, the viscosity change rate after 96 hours of the negative electrode slurry of examples 2 to 4 and comparative examples 1 to 2, the peel strength of the negative electrode mixture layer in the negative electrodes of examples 2 to 4 and comparative examples 1 to 2, and the capacity retention rate in the charge/discharge cycle of the nonaqueous electrolyte secondary batteries of examples 2 to 4 and comparative example 1 were measured in the same manner as in example 1. The results are set forth in Table 1. In comparative example 2, it was confirmed that the peel strength of the negative electrode mixture layer was decreased by adding an excessive amount of lithium carbonate to the negative electrode, and thus the capacity retention rate was not measured.

[ Table 1]

The lower the value of the viscosity change rate after 96 hours in table 1 (the lower the value is than 100%), it means that the viscosity of the slurry is more lowered. Therefore, from the results of the viscosity change rate after 96 hours in table 1, it can be said that the slurry for negative electrodes of examples 1 to 4 has a lower viscosity than the slurry for negative electrodes of comparative examples 1 to 2. In addition, the peel strength of the negative electrode mixture layers of examples 1 to 4 showed a higher value than that of the negative electrode mixture layers of comparative examples 1 to 2. That is, it can be said that by using the slurry for a negative electrode of examples 1 to 4, an electrode mixture layer exhibiting good adhesion to a current collector can be obtained. In addition, the nonaqueous electrolyte secondary batteries of examples 1 to 4 exhibited a higher value of capacity retention rate in charge and discharge cycles than the nonaqueous electrolyte secondary battery of comparative example 1, and the deterioration of charge and discharge cycle characteristics was suppressed.

Description of the reference numerals

10: nonaqueous electrolyte secondary battery, 11: positive electrode, 12: negative electrode, 13: spacer, 14: electrode body, 15: battery case, 16: outer can, 17: sealing body, 18, 19: insulating plate, 20: positive electrode lead, 21: anode lead, 22: groove-in portion, 23: bottom plate, 24: lower valve body, 25: insulating member, 26: upper valve body, 27: cover, 28: and (7) a gasket.