Slurry for nonaqueous electrolyte secondary battery electrode, method for producing slurry for nonaqueous electrolyte secondary battery electrode, electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

The purpose of the present invention is to provide a slurry for nonaqueous electrolyte secondary battery electrodes, said slurry being capable of obtaining an electrode mixture layer exhibiting good adhesion to a current collector. A slurry for a non-aqueous electrolyte secondary battery electrode according to one embodiment of the present invention contains an electrode mixture and water, the electrode mixture containing an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, the content of the lithium carbonate being in the range of 33 ppm to 300 ppm with respect to the total mass of the electrode mixture.

Description

[0001] This application is a divisional application of the application filed on February 21, 2020, with application number 202080016694.1 and invention title "Slurry for electrode of non-aqueous electrolyte secondary battery, method for manufacturing slurry for electrode of non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery". Technical Field

[0002] This invention relates to a slurry for electrodes of non-aqueous electrolyte secondary batteries, a method for manufacturing the slurry for electrodes of non-aqueous electrolyte secondary batteries, electrodes for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries. Background Technology

[0003] In recent years, non-aqueous electrolyte secondary batteries, which have a positive electrode, a negative electrode, and a non-aqueous electrolyte, have been widely used as high-output, high-energy-density secondary batteries. These batteries allow lithium ions to move between the positive and negative electrodes for charging and discharging.

[0004] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery having a negative electrode containing a negative electrode active material and lithium carbonate, and discloses that, according to this secondary battery, the reduction of charge-discharge cycle characteristics is suppressed.

[0005] In addition, for example, Patent Document 2 discloses a non-aqueous electrolyte secondary battery having a negative electrode comprising a negative electrode active material, lithium carbonate and carboxymethyl cellulose. In this non-aqueous electrolyte secondary battery, the weight of lithium carbonate relative to the negative electrode is 1% to 10%, and it is disclosed that the safety of the battery can be achieved according to this secondary battery.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 7-235297

[0009] Patent Document 2: Japanese Patent Application Publication No. 8-138743

[0010] Patent Document 3: Japanese Patent Application Publication No. 2013-114959

[0011] Patent Document 4: Japanese Patent Application Publication No. 2003-272619

[0012] Patent Document 5: International Publication No. 2012 / 002451

[0013] Patent Document 6: International Publication No. 2012 / 011555 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] However, negative and positive electrodes can be obtained, for example, by coating an electrode current collector with a slurry containing an electrode additive and water and drying it to form an electrode additive layer on the electrode current collector. The electrode additive contains an electrode active material (negative or positive electrode active material) and carboxymethyl cellulose. However, the slurry containing carboxymethyl cellulose sometimes suffers from reduced viscosity during electrode fabrication, leading to decreased coating stability on the electrode current collector and consequently reduced adhesion of the electrode additive layer to the electrode current collector.

[0016] Therefore, the object of the present invention is to provide a slurry for a non-aqueous electrolyte secondary battery electrode that exhibits good adhesion to the electrode current collector and a method for manufacturing the same. Furthermore, an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery exhibiting good adhesion between the electrode current collector and the electrode mixture layer are provided.

[0017] Methods for solving problems

[0018] As one aspect of the present invention, a slurry for a non-aqueous electrolyte secondary battery electrode comprises an electrode compound and water, wherein the electrode compound comprises an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the lithium carbonate is in the range of 33 ppm to 300 ppm relative to the total mass of the electrode compound.

[0019] As one aspect of the present invention, a method for manufacturing a slurry for a non-aqueous electrolyte secondary battery electrode is a method of manufacturing an electrode slurry by mixing an electrode mixture with water, wherein the electrode mixture comprises an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the lithium carbonate is in the range of 33 ppm to 300 ppm relative to the total mass of the electrode mixture.

[0020] As one aspect of the present invention, the electrode for a non-aqueous electrolyte secondary battery comprises a current collector and an electrode mixture layer on the current collector, wherein the electrode mixture layer comprises an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the lithium carbonate relative to the total mass of the electrode mixture layer is in the range of 33 ppm to 300 ppm.

[0021] As one aspect of the present invention, a non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode for the non-aqueous electrolyte secondary battery.

[0022] The effects of the invention

[0023] According to the non-aqueous electrolyte secondary battery electrode slurry and its manufacturing method as an embodiment of the present invention, an electrode paste layer exhibiting good adhesion to the current collector can be obtained. Furthermore, according to the non-aqueous electrolyte secondary battery electrode and the non-aqueous electrolyte secondary battery as an embodiment of the present invention, good adhesion between the current collector and the electrode paste layer can be ensured. Attached Figure Description

[0024] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method.

[0025] Figure 2 This is a schematic diagram of a device used to measure the peel strength of the negative electrode binder layer relative to the negative electrode current collector. Detailed Implementation

[0026] As mentioned above, slurries containing carboxymethyl cellulose sometimes suffer from reduced coating stability on the electrode current collector due to viscosity decreases during electrode fabrication, resulting in reduced adhesion of the electrode binder layer to the electrode current collector. Therefore, the inventors conducted in-depth research and discovered that by including a specified amount of lithium carbonate in the slurry, an electrode binder layer exhibiting good adhesion to the electrode current collector can be obtained, leading to the development of a slurry as described below.

[0027] As one aspect of the present invention, a slurry for a non-aqueous electrolyte secondary battery electrode comprises an electrode compound and water, wherein the electrode compound comprises an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the lithium carbonate is in the range of 33 ppm to 300 ppm relative to the total mass of the electrode compound.

[0028] The coating stability of slurries containing carboxymethyl cellulose on electrode current collectors is reduced due to viscosity decreases during electrode fabrication, resulting in decreased adhesion of the electrode mixture layer to the current collector. This is believed to be due to bacteria inevitably present in the slurry. Specifically, it is believed that bacterial enzymes cleave the high molecular chains of carboxymethyl cellulose, causing a decrease in the viscosity of the slurry during electrode fabrication, thus reducing the adhesion of the electrode mixture layer to the electrode current collector. However, it is believed that by including lithium carbonate in the range of 33 ppm to 300 ppm relative to the total mass of the electrode mixture, as in the slurry of one embodiment of the present invention, the activity of bacterial enzymes can be reduced, and bacterial growth can be inhibited. As a result, the cleavage of the high molecular chains of carboxymethyl cellulose is suppressed, thereby suppressing the decrease in viscosity of the slurry during electrode fabrication, thus providing an electrode mixture layer with good adhesion to the electrode current collector. On the other hand, it is believed that if the lithium carbonate content is less than 33 ppm relative to the total mass of the electrode mixture, the activity of bacterial enzymes in the slurry cannot be sufficiently reduced, and bacterial growth cannot be sufficiently inhibited. As a result, the cleavage of the carboxymethyl cellulose polymer chains cannot be sufficiently suppressed, leading to a decrease in the viscosity of the slurry during electrode fabrication, and reduced adhesion of the electrode binder layer to the electrode current collector. Furthermore, it is believed that if the lithium carbonate content exceeds 300 ppm relative to the total mass of the electrode binder, lithium carbonate itself becomes a factor reducing the adhesion of the electrode binder layer to the electrode current collector.

[0029] An electrode for a non-aqueous electrolyte secondary battery, as one aspect of the present invention, comprises a current collector and an electrode paste layer on the current collector. The electrode paste layer contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof. The content of lithium carbonate relative to the total mass of the electrode paste layer is in the range of 33 ppm to 300 ppm. The electrode for a non-aqueous electrolyte secondary battery, as one aspect of the present invention, is obtained by using the aforementioned slurry for a non-aqueous electrolyte secondary battery electrode, thus ensuring good adhesion between the current collector and the electrode paste layer. Furthermore, the non-aqueous electrolyte secondary battery using the electrode for a non-aqueous electrolyte secondary battery, as one aspect of the present invention, also ensures good adhesion between the current collector and the electrode paste layer, and further suppresses, for example, a decrease in charge-discharge cycle characteristics.

[0030] Hereinafter, an embodiment of the electrode slurry for a non-aqueous electrolyte secondary battery, which is one aspect of the present invention, will be described. The following description will cover both the negative electrode slurry and the positive electrode slurry.

[0031] <Slurry for negative electrode>

[0032] The negative electrode slurry comprises a negative electrode agent and water. The negative electrode agent comprises a negative electrode active material, lithium carbonate, carboxymethyl cellulose or its salt, and any added binder. The lithium carbonate content relative to the total mass of the negative electrode agent is in the range of 33 ppm to 300 ppm.

[0033] There are no particular restrictions on the negative electrode active material as long as it can absorb and release lithium ions. Examples include lithium metal, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, lithium-tin alloys, and other lithium alloys; carbon materials such as graphite, coke, and sintered organic materials; and metal oxides such as SnO2, SnO, and TiO2. One type can be used alone, or two or more can be used in combination.

[0034] The content of the negative electrode active material is preferably in the range of 90% to 99% by mass relative to the total mass of the negative electrode mixture, and more preferably in the range of 95% to 98% by mass.

[0035] Carboxymethyl cellulose or its salts function as thickeners to increase the viscosity of slurries used in negative electrodes, and are also presumably used as binders to bind particles of the negative electrode active material. Examples of salts of carboxymethyl cellulose include monovalent metal salts such as alkali metal salts (lithium, sodium, potassium, rubidium, cesium, etc.), divalent metal salts such as alkaline earth metal salts (calcium, magnesium, etc.), quaternary ammonium salts, amine salts, substituted amine salts (alkanolamine salts such as ethanolamine, etc.), or their complex salts.

[0036] The content of carboxymethyl cellulose or its salt is preferably in the range of 1% to 5% by mass relative to the total mass of the negative electrode compound, and more preferably in the range of 1% to 2.5% by mass.

[0037] Lithium carbonate can be, for example, inexpensive commercially available or industrial-grade products. Considering factors such as dispersibility and solubility in the negative electrode slurry, lithium carbonate is preferably pulverized before use to adjust the average and maximum particle size. The pulverization process is not particularly limited; for example, dry pulverization using a jet mill or ball mill is preferred.

[0038] The lithium carbonate content relative to the total mass of the negative electrode mixture is in the range of 33ppm to 300ppm. From the perspective of effectively inhibiting the cleavage of the carboxymethyl cellulose polymer chain caused by bacteria in the slurry and obtaining an electrode mixture layer that exhibits better adhesion to the electrode current collector, the preferred range is 66ppm to 300ppm, and more preferably 66ppm to 200ppm.

[0039] There are no particular limitations on the type of water used, but water with low impurity concentration is preferred, such as purified water such as ion-exchanged water.

[0040] Examples of binder materials include fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). Among these, considering dispersibility and solubility in negative electrode slurries, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA) are preferred. They can be used individually or in combination of two or more.

[0041] The content of the binder material is preferably in the range of 1% to 5% by mass relative to the total mass of the negative electrode agent, and more preferably in the range of 1% to 2.5% by mass.

[0042] The method for manufacturing the negative electrode slurry is as follows: First, a negative electrode active material, lithium carbonate, and carboxymethyl cellulose or its salt are mixed in a specified mass ratio. Additionally, a binder material is mixed in a specified mass ratio as needed to obtain a negative electrode mixture. The lithium carbonate content relative to the total mass of the negative electrode mixture is in the range of 33 ppm to 300 ppm. Then, by mixing the obtained negative electrode mixture with an appropriate amount of water, a negative electrode slurry can be obtained. From the perspective of reducing the activity of enzymes produced by bacteria and inhibiting bacterial growth, the pH of the negative electrode slurry is preferably in the range of 8 to 9. It should be noted that, generally, if the lithium carbonate content is within the above range, the pH of the negative electrode slurry is in the range of 8 to 9.

[0043] <Positive electrode slurry>

[0044] The positive electrode slurry comprises a positive electrode agent and water. The positive electrode agent comprises a positive electrode active material, lithium carbonate, carboxymethyl cellulose or its salt, a binder material added as needed, and a conductive material added as needed. The lithium carbonate content relative to the total mass of the positive electrode agent is in the range of 33 ppm to 300 ppm, and similarly to the negative electrode slurry, it is preferably in the range of 66 ppm to 300 ppm, and more preferably in the range of 66 ppm to 200 ppm.

[0045] As a positive electrode active material, it may include, for example, a lithium-containing transition metal oxide. The metallic element constituting the lithium-containing transition metal oxide is, for example, at least one selected from 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, it is preferred to include at least one selected from Co, Ni, Mn, and Al.

[0046] The descriptions of lithium carbonate, carboxymethyl cellulose or its salts, water, and binder materials are the same as those for the negative electrode slurry, so they are omitted.

[0047] Examples of conductive materials include carbon black (CB), acetylene black (AB), Ketjen black, and graphite. They can be used individually or in combination of two or more.

[0048] The manufacturing method of the positive electrode slurry is as follows: First, a positive electrode active material, lithium carbonate, and carboxymethyl cellulose or its salt are mixed in a predetermined mass ratio. Additionally, a binder and a conductive material are mixed in a predetermined mass ratio as needed to obtain a positive electrode mixture. The lithium carbonate content relative to the total mass of the positive electrode mixture is in the range of 33 ppm to 300 ppm. Then, by mixing the obtained positive electrode mixture with an appropriate amount of water, a positive electrode slurry can be obtained. Similar to the negative electrode slurry, the pH of the positive electrode slurry is preferably in the range of 8 to 9, from the perspective of reducing the activity of enzymes produced by bacteria and inhibiting bacterial growth. It should be noted that, generally, if the lithium carbonate content is within the above range, the pH of the positive electrode slurry is in the range of 8 to 9.

[0049] The non-aqueous electrolyte secondary battery electrode slurry of this embodiment can be applied to both positive electrode slurries and negative electrode slurries, or only to either one. When applied to only one, the slurry for the other electrode preferably uses an organic solvent such as NMP instead of water as the dispersion medium. In slurries using organic solvents such as NMP instead of water as the dispersion medium, there is a tendency to exhibit high coating stability even without using carboxymethyl cellulose or its salts, thus suppressing or eliminating the amount of lithium carbonate added, which reduces the activity of enzymes produced from bacteria. Generally, in the case of positive electrode slurries, organic solvents such as NMP can be used as the dispersion medium. However, in the case of negative electrode slurries, considering factors such as coating stability, there is a tendency to prefer using water as the dispersion medium; therefore, the non-aqueous electrolyte secondary battery electrode slurry of this embodiment is preferably used at least as a negative electrode slurry.

[0050] It should be noted that electrode slurries that use organic solvents such as NMP as the dispersion medium instead of water include, for example, an electrode binder and an organic solvent such as NMP. The electrode binder includes an electrode active material, a binder material, etc. In this case, the binder material is preferably a fluoropolymer such as polytetrafluoroethylene (PTFE), polytetrafluoroethylene (PVdF), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyimide resin, acrylic resin, or polyolefin resin. Furthermore, conductive materials may be added to the electrode binder as needed.

[0051] The following describes the electrodes (positive and negative electrodes) for a non-aqueous electrolyte secondary battery according to this embodiment, and the non-aqueous electrolyte secondary battery having the electrodes.

[0052] <Non-aqueous electrolyte secondary battery>

[0053] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. (See diagram below.) Figure 1 As illustrated, the non-aqueous electrolyte secondary battery 10 includes an electrode body 14, a non-aqueous electrolyte, and a battery casing 15 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a spacer 13 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 together with the spacer 13 in between. It should be noted that the electrode body 14 is not limited to a wound type, and may also be a stacked type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one layer each with spacers in between.

[0054] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent can be, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these solvents. The non-aqueous solvent may contain halogen-substituted derivatives in which at least a portion of the hydrogen atoms of these solvents are replaced by halogen atoms such as fluorine. It should be noted that non-aqueous electrolytes are not limited to liquid electrolytes and can also be solid electrolytes. For example, lithium salts such as LiPF6 can be used as electrolyte salts.

[0055] The battery casing 15 consists of a bottomed cylindrical outer can 16 and a sealing body 17 that closes the opening of the outer can 16. It should be noted that the battery casing 15 is not limited to a cylindrical shape, and can also be a square (square battery), a coin-shaped (coin-shaped battery) metal casing, or a laminated film casing (laminated battery) composed of a metal film and a resin film.

[0056] The outer can 16 is, for example, a bottomed cylindrical metal container. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior. The outer can 16 has, for example, a groove 22 extending inward from a portion of its side surface to support the sealing body 17. The groove 22 is preferably formed in a ring shape along the circumference of the outer can 16, with its upper surface supporting the sealing body 17.

[0057] The sealing body 17 has a structure in which a base plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except 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 respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. If the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 towards the cover 27 side, thus cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0058] The non-aqueous electrolyte secondary battery 10 has insulating plates 18 and 19 respectively disposed above and below the electrode body 14. Figure 1 In the example shown, the positive lead 20 installed on the positive electrode 11 extends towards the sealing body 17 through the through hole in the insulating plate 18, and the negative lead 21 installed on the negative electrode 12 extends towards the bottom of the outer packaging can 16 through the outer side of the insulating plate 19. The positive lead 20 is connected to the lower surface of the bottom plate 23 of the sealing body 17 by welding or the like, and the cover 27 of the sealing body 17, which is electrically connected to the bottom plate 23, becomes the positive terminal. The negative lead 21 is connected to the inner bottom surface of the outer packaging can 16 by welding or the like, and the outer packaging can 16 becomes the negative terminal.

[0059] <Positive electrode>

[0060] The positive electrode 11 comprises a positive current collector and a positive electrode additive layer formed on the positive current collector. The positive electrode 11 is obtained, for example, by coating both sides of the positive current collector with the positive electrode slurry of this embodiment, drying the coating to form a positive electrode additive layer on the positive current collector, and then calendering the positive electrode additive layer. The positive electrode additive layer of the positive electrode 11 made using the positive electrode slurry of this embodiment contains a positive electrode active material, lithium carbonate, carboxymethyl cellulose or its salt, any added binder material, and any added conductive material. The lithium carbonate content relative to the total mass of the positive electrode additive layer is in the range of 33 ppm to 300 ppm. It should be noted that, as described above, the positive electrode 11 can also be made using a slurry in which an organic solvent such as NMP is used instead of water as the dispersion medium.

[0061] The positive electrode current collector can be a foil of a metal stable within the potential range of the positive electrode, such as aluminum, or a film of the same metal disposed on its surface. It should be noted that the materials constituting the positive electrode flux layer are as described above, and their descriptions are omitted.

[0062] <Negative electrode>

[0063] The negative electrode 12 includes a negative electrode current collector and a negative electrode additive layer formed on the negative electrode current collector. The negative electrode 12 is obtained, for example, by coating both sides of the negative electrode current collector with the negative electrode slurry of this embodiment, drying the coating to form a negative electrode additive layer on the negative electrode current collector, and then calendering the negative electrode additive layer. The negative electrode additive layer of the negative electrode 12 made using the negative electrode slurry of this embodiment contains a negative electrode active material, lithium carbonate, carboxymethyl cellulose or its salt, and any added binder material. The lithium carbonate content relative to the total mass of the negative electrode additive layer is in the range of 33 ppm to 300 ppm. It should be noted that, as described above, the negative electrode 12 can be made using a slurry that uses an organic solvent such as NMP instead of water as the dispersion medium, but it is preferable to use the negative electrode slurry of this embodiment.

[0064] The negative electrode current collector can be a foil of a metal such as copper that is stable within the potential range of the negative electrode, or a film of the same metal disposed on its surface. It should be noted that the materials constituting the negative electrode binder layer are as described above, and their descriptions are omitted here.

[0065] <spacer>

[0066] The spacer 13 can be made of a porous sheet material, for example, that has ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The preferred material for the spacer 13 is polyethylene, polypropylene, olefin resins such as copolymers containing at least one of ethylene and propylene, cellulose, etc. The spacer 13 can be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it can be a multilayer spacer containing a polyethylene layer and a polypropylene layer. Furthermore, an aromatic polyamide resin or similar material can be coated on the surface of the spacer 13. Additionally, a heat-resistant layer containing inorganic fillers can be formed at the interface between the spacer 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0067] Example

[0068] The present invention will be further illustrated below by way of examples, but the present invention is not limited to these examples.

[0069] <Example 1>

[0070] [positive electrode]

[0071] Zirconium (0.1 mol% relative to cobalt), magnesium (1 mol% relative to cobalt), and aluminum were co-precipitated and subjected to thermal decomposition to obtain cobalt tetroxide containing zirconium, magnesium, and aluminum. Lithium carbonate, used as a lithium source, was then mixed into the precipitate and sintered at 850°C for 20 hours to obtain lithium cobalt oxide (LiCo) containing zirconium, magnesium, and aluminum. 0.979 Zr 0.001 Mg 0.01 Al 0.01 O2). It is used as the positive electrode active material.

[0072] A slurry for the positive electrode was prepared by mixing the above-mentioned positive electrode active material (95% by mass), carbon powder (2.5% by mass) as a conductive material, and polyvinylidene fluoride powder (2.5% by mass) as a binder material, and then mixing it with an N-methylpyrrolidone (NMP) solution. This slurry was then coated onto both sides of a 15 μm thick aluminum positive electrode current collector using a doctor blade method, forming a positive electrode binder layer on both sides of the current collector. The mixture was then calendered using calendering rollers and cut to a specified size. This was used as the positive electrode.

[0073] [negative electrode]

[0074] As the negative electrode active material, graphite with an average particle size of 22 μm was prepared. A mixture of graphite, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 97:1.5:1.0 was prepared, and a specified amount of lithium carbonate was added to obtain the negative electrode mixture. The lithium carbonate content relative to the total mass of the negative electrode mixture was 66 ppm. Mixed deionized water was added to this negative electrode mixture to prepare a negative electrode slurry. The solids content of the negative electrode slurry was 50%.

[0075] For the prepared negative electrode slurry, the viscosity was measured during preparation and after 96 hours using a Type B viscometer (Toki Sangyo TVB10). The viscosity change rate after 96 hours was then calculated using the following formula. The results are recorded in Table 1.

[0076] Viscosity change rate (%) after 96 hours = (viscosity after 96 hours) ÷ (viscosity at the time of preparation) × 100

[0077] The negative electrode slurry, which has undergone 96 hours of preparation, is coated onto both sides of the negative electrode current collector using a scraper method, forming a negative electrode slurry layer on both sides of the current collector. Then, it is calendered using calendering rollers and cut to the specified size. This is then used as the negative electrode.

[0078] For the negative electrode of Example 1, using Figure 2 The apparatus shown measures the peel strength of the negative electrode binder layer relative to the negative electrode current collector. Figure 2The apparatus shown includes: a base 131 on which a test subject 132 is placed; an adhesive member 133 for fixing the test subject 132; a chuck 134 for fixing one end of the test subject 132 and connected to a lifting platform 138; a bearing portion 135 for allowing the base 131 to slide horizontally; a spring 136 for applying force uniformly during the sliding of the base 131; a fixing portion 137 for connecting the spring 136; a lifting platform 138 connected to the base 131 via a line 139 and a pulley 140; and a line 141 for lifting... The platform 138 is connected to the gripping fixture 142; the load sensor 143 is connected to the gripping fixture 142 and is used to detect the load on the lifting platform 138; the support 144 supports the load sensor 143; the drive 146 moves the support 144 up and down; the linear sensor 147 detects the amount of movement of the gripping fixture 142; the support column 145 has the drive 146 and the linear sensor 147 built into it; the support platform 148 supports the base 131, and the support platform 148 and the support column 145 are fixed to the base 150.

[0079] As the test subject 132, a negative electrode cut to a length of 15 mm and a width of 120 mm was used. This negative electrode (test subject 132) was fixed to the base 131 using an adhesive member 133, and one end was secured with a chuck 134. The drive unit 146 was activated, lifting the gripping clamp 142 at a certain speed, thereby pulling the lifting platform 138 and simultaneously lifting the chuck 134, thus peeling the negative electrode adhesive layer from the negative electrode current collector. The stress at this time was measured using a load sensor 143. After measurement, a pull-up test was performed using only the device with the negative electrode removed, and the force component during the sliding of only the base 131 was measured. The peel strength of the negative electrode adhesive layer was calculated by subtracting the force component during the sliding of only the base 131 from the stress during the peeling of the negative electrode adhesive layer from the negative electrode current collector, and converting the result to a unit length (m). The results are recorded in Table 1.

[0080] [Non-aqueous electrolytes]

[0081] A non-aqueous electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF6) in a solvent prepared by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 30:70. Then, 2.0 wt% of ethylene carbonate (VC) relative to the total electrolyte is dissolved in the solvent.

[0082] [Non-aqueous electrolyte secondary battery]

[0083] The positive and negative electrodes are wound around a spacer made of a microporous membrane made of polyethylene, and polypropylene tape is attached to the outermost periphery to form a cylindrical electrode body. Then, it is pressed to form a flat spiral electrode body.

[0084] A sheet-like laminate consisting of five layers—a resin layer (polypropylene), an adhesive layer, an aluminum alloy layer, another adhesive layer, and another resin layer (polypropylene)—is prepared. This aluminum laminate is then folded back to form a bottom, creating a cup-shaped electrode housing. Inside a glove box under an argon atmosphere, the flat electrode and the non-aqueous electrolyte are inserted into this housing. The internal pressure of the outer casing is then reduced, allowing the non-aqueous electrolyte to permeate into the spacer. The opening of the outer casing is then sealed, thus fabricating a non-aqueous electrolyte secondary battery with a height of 62 mm, a width of 35 mm, and a thickness of 3.6 mm.

[0085] [Evaluation of capacity retention during charge-discharge cycles]

[0086] Under a temperature environment of 25°C, constant current charging (current 1It = 800mA, termination voltage 4.2V) followed by constant voltage charging (voltage 4.2V, termination current 40mA) was performed, and then discharge to 2.75V at a current of 800mA. This charge-discharge cycle was performed 300 times, and the capacity retention rate during the charge-discharge cycle was calculated based on the following formula. The results are recorded in Table 1.

[0087] Capacity maintenance rate = (X2 / X1) × 100

[0088] X1: Discharge capacity in the first cycle

[0089] X2: Discharge capacity at the 300th cycle

[0090] <Example 2>

[0091] In the preparation of the negative electrode slurry, the lithium carbonate content relative to the total mass of the negative electrode mixture was set to 166 ppm. Otherwise, the negative electrode slurry was prepared in the same manner as in Example 1. Furthermore, the negative electrode slurry of Example 2 was used, and the negative electrode and non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1.

[0092] <Example 3>

[0093] In the preparation of the negative electrode slurry, the lithium carbonate content relative to the total mass of the negative electrode agent was set to 300 ppm. Otherwise, the negative electrode slurry was prepared in the same manner as in Example 1. Furthermore, the negative electrode slurry of Example 3 was used, and the negative electrode and non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1.

[0094] <Example 4>

[0095] In the preparation of the negative electrode slurry, the lithium carbonate content was set to 33 ppm relative to the total mass of the negative electrode mixture. Otherwise, the negative electrode slurry was prepared in the same manner as in Example 1. Furthermore, the negative electrode slurry of Example 4 was used, and the negative electrode and non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1.

[0096] <Comparative Example 1>

[0097] In the preparation of the negative electrode slurry, lithium carbonate was not used; otherwise, the negative electrode slurry was prepared in the same manner as in Example 1. Furthermore, the negative electrode slurry of Comparative Example 1 was used; otherwise, the negative electrode and non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1.

[0098] <Comparative Example 2>

[0099] In the preparation of the negative electrode slurry, the lithium carbonate content was set to 1% by mass relative to the total mass of the negative electrode mixture. Otherwise, the negative electrode slurry was prepared in the same manner as in Example 1. Furthermore, the negative electrode slurry of Comparative Example 2 was used, and a negative electrode and a non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1.

[0100] In addition, the viscosity change rate of the negative electrode slurry of Examples 2-4 and Comparative Examples 1-2 after 96 hours, the peel strength of the negative electrode binder layer in the negative electrodes of Examples 2-4 and Comparative Examples 1-2, and the capacity retention rate of the non-aqueous electrolyte secondary battery of Examples 2-4 and Comparative Example 1 during charge-discharge cycles were measured in the same manner as in Example 1. The results are recorded in Table 1. It should be noted that for Comparative Example 2, it was confirmed that the peel strength of the negative electrode binder layer decreased due to the addition of excessive lithium carbonate to the negative electrode; therefore, the capacity retention rate was not measured.

[0101] [Table 1]

[0102]

[0103] The lower the viscosity change rate (below 100%) in Table 1 after 96 hours, the greater the viscosity reduction of the slurry. Therefore, based on the viscosity change rate results after 96 hours in Table 1, it can be said that the viscosity reduction of the negative electrode slurries of Examples 1-4 is suppressed compared to that of Comparative Examples 1-2. Furthermore, the peel strength of the negative electrode binder layer of Examples 1-4 is higher than that of the negative electrode binder layer of Comparative Examples 1-2. That is, it can be said that by using the negative electrode slurries of Examples 1-4, an electrode binder layer exhibiting good adhesion to the current collector can be obtained. In addition, the non-aqueous electrolyte secondary batteries of Examples 1-4 show higher capacity retention rates during charge-discharge cycles compared to the non-aqueous electrolyte secondary battery of Comparative Example 1, and the reduction in charge-discharge cycle characteristics is suppressed.

[0104] Explanation of reference numerals in the attached figures

[0105] 10: Non-aqueous electrolyte secondary battery; 11: Positive electrode; 12: Negative electrode; 13: Spacer; 14: Electrode body; 15: Battery casing; 16: Outer can; 17: Sealing body; 18, 19: Insulating plate; 20: Positive electrode lead; 21: Negative electrode lead; 22: Tank inlet; 23: Bottom plate; 24: Lower valve body; 25: Insulating component; 26: Upper valve body; 27: Cover; 28: Gasket.

Claims

1. A slurry for a nonaqueous electrolyte secondary battery electrode, comprising an electrode mixture and water, the electrode mixture comprising an electrode active material, pulverized lithium carbonate, and carboxymethyl cellulose or a salt thereof, the content of the lithium carbonate is in a range of 33 ppm to 66 ppm or 166 ppm to 300 ppm relative to the total mass of the electrode mixture.

2. A method for producing a slurry for a nonaqueous electrolyte secondary battery electrode, wherein an electrode mixture comprising an electrode active material, pulverized 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 a range of 33 ppm to 66 ppm or 166 ppm to 300 ppm relative 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 mixture layer comprises an electrode active material, pulverized lithium carbonate, and carboxymethyl cellulose or a salt thereof, the content of the lithium carbonate is in a range of 33 ppm to 66 ppm or 166 ppm to 300 ppm relative to the total mass of the electrode mixture layer.

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

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