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

An object of the present application is to provide a slurry for a nonaqueous electrolyte secondary battery electrode capable of obtaining an electrode mixture layer showing good adhesion to a current collector. A slurry for a nonaqueous electrolyte secondary battery electrode according to one embodiment of the present application contains an electrode mixture and water, the electrode mixture containing an electrode active material, lithium carbonate, and carboxymethylcellulose or a salt thereof, the content of the lithium carbonate being in the range of 33 ppm to 300 ppm relative to the total mass of the electrode mixture.

Description

TECHNICAL FIELD

[0001] The present application 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

[0002] In recent years, as a secondary battery having high output and high energy density, a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, and allowing lithium ions or the like to move between the positive electrode and the negative electrode to perform charge and discharge has been widely used.

[0003] For example, in Patent Literature 1, a nonaqueous electrolyte secondary battery having a negative electrode including a negative electrode active material and lithium carbonate is disclosed, and it is disclosed that according to the secondary battery, a decrease in charge and discharge cycle characteristics is suppressed.

[0004] Further, for example, in Patent Literature 2, a nonaqueous electrolyte secondary battery having a negative electrode including a negative electrode active material, lithium carbonate, and carboxymethyl cellulose is disclosed, and in the nonaqueous electrolyte secondary battery, the weight of lithium carbonate with respect to the weight of the negative electrode is 1% to 10%, and it is disclosed that according to the secondary battery, safety of the battery can be achieved.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 7-235297

[0008] Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 8-138743

[0009] Patent Literature 3: Japanese Patent Application Laid-Open (JP-A) No. 2013-114959

[0010] Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 2003-272619

[0011] Patent Literature 5: International Publication No. 2012 / 002451

[0012] Patent Literature 6: International Publication No. 2012 / 011555 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] However, the negative electrode and the positive electrode can be obtained, for example, by applying a slurry containing an electrode mixture and water, the electrode mixture containing an electrode active material (a negative electrode active material or a positive electrode active material) and carboxymethyl cellulose, to an electrode current collector and drying to form an electrode mixture layer on the electrode current collector. However, the slurry containing carboxymethyl cellulose sometimes results in a decrease in coating stability on the electrode current collector and a decrease in adhesion of the electrode mixture layer to the electrode current collector due to a decrease in viscosity and the like in electrode production.

[0015] Therefore, an object of the present application is to provide a slurry for a nonaqueous electrolyte secondary battery electrode capable of obtaining an electrode mixture layer showing good adhesion to an electrode current collector and a method for producing the same. In addition, a nonaqueous electrolyte secondary battery electrode showing good adhesion of an electrode current collector to an electrode mixture layer and a nonaqueous electrolyte secondary battery are provided.

[0016] Means for solving the problem

[0017] The slurry for a nonaqueous electrolyte secondary battery electrode according to one embodiment of the present application 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 relative to the total mass of the electrode mixture.

[0018] The method for producing a slurry for a nonaqueous electrolyte secondary battery electrode according to one embodiment of the present application is a method for producing an electrode slurry by mixing 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 relative to the total mass of the electrode mixture.

[0019] The electrode for a nonaqueous electrolyte secondary battery according to one embodiment of the present application has a current collector and an electrode mixture layer on the current collector, the electrode mixture layer 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 relative to the total mass of the electrode mixture layer.

[0020] The nonaqueous electrolyte secondary battery according to one embodiment of the present application contains a positive electrode, a negative electrode, and a nonaqueous electrolyte, at least either of the positive electrode and the negative electrode being the electrode for a nonaqueous electrolyte secondary battery.

[0021] Effects of the Invention

[0022] According to the slurry for a nonaqueous electrolyte secondary battery electrode and the manufacturing method thereof according to one embodiment of the present application, an electrode mixture layer showing good adhesion to a current collector can be obtained. Further, according to the electrode for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery according to one embodiment of the present application, good adhesion of the electrode mixture layer to the current collector can be ensured. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery as one example of an embodiment.

[0024] Figure 2 is a schematic view of an apparatus for measuring the peeling strength of a negative electrode mixture layer with respect to a negative electrode current collector. DETAILED DESCRIPTION

[0025] As described above, the slurry containing carboxymethyl cellulose sometimes results in a decrease in the coating stability on the electrode current collector due to a decrease in the viscosity in the electrode production or the like, and thus the adhesion of the electrode mixture layer to the electrode current collector is decreased. Therefore, the present inventors and others have made intensive studies, and as a result, it has been found that by containing a prescribed amount of lithium carbonate in the slurry, an electrode mixture layer showing good adhesion to the electrode current collector can be obtained, and thus the slurry of the following described mode has been conceived.

[0026] The slurry for a nonaqueous electrolyte secondary battery electrode according to one embodiment of the present application contains an electrode mixture and water, and the electrode mixture contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the above-described lithium carbonate is in the range of 33 ppm to 300 ppm with respect to the total mass of the above-described electrode mixture.

[0027] The slurry containing carboxymethyl cellulose has a reduced stability of coating on an electrode current collector due to a reduction in viscosity and the like in electrode production, and thus the adhesion of the electrode mixture layer to the current collector is reduced, which is considered to be caused by bacteria inevitably present in the slurry. Specifically, it is considered that the high molecular chain of carboxymethyl cellulose is cut due to an enzyme produced by the bacteria, and thus the viscosity of the slurry in electrode production and the like is reduced, and the adhesion of the electrode mixture layer to the electrode current collector is reduced. However, it is considered that the activity of the enzyme produced by the bacteria is reduced, and the propagation of the bacteria is inhibited by containing lithium carbonate in a range of 33 ppm to 300 ppm with respect to the total mass of the electrode mixture, like the slurry as one embodiment of the present application. As a result, the cutting of the high molecular chain of carboxymethyl cellulose is inhibited, and further the viscosity of the slurry in electrode production and the like is inhibited, and thus it is considered that the electrode mixture layer exhibiting good adhesion to the electrode current collector can be obtained. On the other hand, it is considered that if the content of lithium carbonate is less than 33 ppm with respect to the total mass of the electrode mixture, the activity of the enzyme produced by the bacteria in the slurry cannot be sufficiently reduced, and further the propagation of the bacteria cannot be sufficiently inhibited. As a result, the cutting of the high molecular chain of carboxymethyl cellulose cannot be sufficiently inhibited, and the viscosity of the slurry in electrode production and the like is reduced, and thus the adhesion of the electrode mixture layer to the electrode current collector is reduced. Furthermore, it is considered that if the content of lithium carbonate exceeds 300 ppm with respect to the total mass of the electrode mixture, the lithium carbonate itself becomes a factor of reducing the adhesion of the electrode mixture layer to the electrode current collector.

[0028] The electrode for nonaqueous electrolyte secondary battery as one embodiment of the present application has a current collector and an electrode mixture layer on the current collector, and the electrode mixture layer contains an electrode active material, lithium carbonate, and carboxymethyl cellulose or a salt thereof, and the content of the lithium carbonate is in a range of 33 ppm to 300 ppm with respect to the total mass of the electrode mixture layer. The electrode for nonaqueous electrolyte secondary battery as one aspect of the present application is obtained by using the slurry for electrode of nonaqueous electrolyte secondary battery as one aspect of the present application, and thus the good adhesion of the electrode current collector to the electrode mixture layer can be ensured. Furthermore, the nonaqueous electrolyte secondary battery using the electrode for nonaqueous electrolyte secondary battery as one embodiment of the present application can also ensure the good adhesion of the current collector to the electrode mixture layer, and further the reduction in, for example, charge-discharge cycle characteristics is inhibited.

[0029] Hereinafter, an embodiment of the slurry for electrode of nonaqueous electrolyte secondary battery as one embodiment of the present application will be described. Hereinafter, both of the slurry for negative electrode and the slurry for positive electrode will be described.

[0030] <Slurry for negative electrode>

[0031] The negative electrode slurry contains a negative electrode mixture and water, the negative electrode mixture contains a negative electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, and an arbitrary added binder material, and the content of lithium carbonate is in the range of 33 ppm to 300 ppm relative to the total mass of the negative electrode mixture.

[0032] 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 lithium, lithium-aluminum alloy, lithium-lead alloy, lithium-silicon alloy, and lithium-tin alloy; carbon materials such as graphite, coke, and organic sintered body; and metal oxides such as Sn02, SnO, and Ti02. One of them can be used alone, or two or more of them can be used in combination.

[0033] The content of the negative electrode active material is preferably in the range of 90 mass% to 99 mass%, and more preferably in the range of 95 mass% to 98 mass%, relative to the total mass of the negative electrode mixture.

[0034] The carboxymethyl cellulose or the salt thereof functions as a viscosity-increasing material for increasing the viscosity of the negative electrode slurry, and is also presumed to function as a binder material for binding the particles of the negative electrode active material and the like. As the salt of the carboxymethyl cellulose, examples thereof include monovalent metal salts such as alkali metal salts (lithium salt, sodium salt, potassium salt, rubidium salt, cesium salt, and the like), divalent metal salts such as alkaline earth metal salts (calcium salt, magnesium salt, and the like), quaternary ammonium salts, amine salts, substituted amine salts (alkanolamine salts such as ethanolamine, and the like), and complex salts thereof.

[0035] The content of the carboxymethyl cellulose or the salt thereof is preferably in the range of 1 mass% to 5 mass%, and preferably in the range of 1 mass% to 2.5 mass%, relative to the total mass of the negative electrode mixture.

[0036] The lithium carbonate can use, for example, a cheap commercially available product, an industrial grade product, or the like. From the viewpoint of dispersibility or solubility in the negative electrode slurry, or the like, the lithium carbonate is preferably subjected to a pulverization treatment before use, and the average particle diameter and the maximum particle diameter are adjusted. The pulverization treatment is not particularly limited, and for example, a dry pulverization such as a jet mill or a ball mill is preferable.

[0037] The content of the lithium carbonate is in the range of 33 ppm to 300 ppm relative to the total mass of the negative electrode mixture, and from the viewpoint of being able to effectively suppress the cleavage of the high molecular chain of the carboxymethyl cellulose caused by bacteria in the slurry, and to obtain an electrode mixture layer that exhibits more excellent adhesion to the electrode current collector, it is preferably in the range of 66 ppm to 300 ppm, and more preferably in the range of 66 ppm to 200 ppm.

[0038] The water is not particularly limited, and water having a low impurity concentration is preferable, and for example, purified water such as ion exchange water can be used.

[0039] As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and the like fluororesins, polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA) and the like can be mentioned. Among them, from the viewpoint of dispersibility or solubility in the negative electrode slurry or the like, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA) are preferable. They can be used singly one kind or in combination of two or more kinds.

[0040] The content of the binder is preferably in the range of 1 to 5 mass% and more preferably in the range of 1 to 2.5 mass% with respect to the total mass of the negative electrode mixture.

[0041] The negative electrode slurry is produced by first mixing the negative electrode active material, lithium carbonate and carboxymethyl cellulose or a salt thereof in a prescribed mass ratio, and, if necessary, mixing the binder in a prescribed mass ratio, to obtain a negative electrode mixture. The content of lithium carbonate is in the range of 33 to 300 ppm with respect to the total mass of the negative electrode mixture. Then, by mixing the obtained negative electrode mixture with an appropriate amount of water, a negative electrode slurry can be obtained. From the viewpoint of reducing the activity of enzymes produced from bacteria and inhibiting the propagation of bacteria, the pH of the negative electrode slurry is preferably in the range of 8 to 9. Note that, generally, if the content of lithium carbonate is in the above range, the pH of the negative electrode slurry is in the range of 8 to 9.

[0042] <Positive electrode slurry>

[0043] The positive electrode slurry contains a positive electrode mixture and water, and the positive electrode mixture contains a positive electrode active material, lithium carbonate, carboxymethyl cellulose or a salt thereof, a binder added as necessary and a conductive material added as necessary. The content of lithium carbonate is in the range of 33 to 300 ppm with respect to the total mass of the positive electrode mixture, and, as in the case of the negative electrode slurry, it is preferably in the range of 66 to 300 ppm and more preferably in the range of 66 to 200 ppm.

[0044] As the positive electrode active material, for example, a lithium-containing transition metal oxide is included. The metal element constituting the lithium-containing transition metal oxide is, for example, at least one 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, it is preferable to include at least one selected from the group consisting of Co, Ni, Mn, and Al.

[0045] As for the lithium carbonate, the carboxymethyl cellulose or its salt, the water, and the binder material, the same as the slurry for the negative electrode, so the explanation thereof is omitted.

[0046] As the conductive material, for example, carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, graphite, and the like can be cited. They can be used alone as one kind, or two or more kinds can be used in combination.

[0047] The manufacturing method of the slurry for the positive electrode is as follows: First, the positive electrode active material, the lithium carbonate, and the carboxymethyl cellulose or its salt are mixed in a manner so as to become a prescribed mass ratio, and, as necessary, the binder material and the conductive material are mixed in a manner so as to become a prescribed mass ratio, and a positive electrode mixture is obtained. The content of the lithium carbonate is in the range of 33 ppm to 300 ppm with respect to the total mass of the positive electrode mixture. Then, by mixing the obtained positive electrode mixture with an appropriate amount of water, a slurry for the positive electrode can be obtained. The pH of the slurry for the positive electrode, like the slurry for the negative electrode, from the aspect of reducing the activity of the enzyme produced from bacteria and inhibiting the propagation of bacteria, is preferably in the range of 8 to 9. Note that, generally, if the content of the lithium carbonate is in the above range, the pH of the slurry for the positive electrode is in the range of 8 to 9.

[0048] The slurry for the electrode of the non-aqueous electrolyte secondary battery of the present embodiment can be applied to both the slurry for the positive electrode and the slurry for the negative electrode, or can be applied to only either one. In the case of being applied to only either one, the slurry for the other electrode is preferably a slurry in which an organic solvent such as NMP is used instead of water as the dispersion medium. In the slurry in which an organic solvent such as NMP is used instead of water as the dispersion medium, even if the carboxymethyl cellulose or its salt is not used, there is a tendency to exhibit high coating stability, and thus the addition amount of the lithium carbonate that reduces the activity of the enzyme produced from bacteria or the like can be suppressed or can be zero. Generally, in the case of the slurry for the positive electrode, an organic solvent such as NMP can be used as the dispersion medium. However, in the case of the slurry for the negative electrode, from the aspect of coating stability and the like, there is a tendency to preferably use water as the dispersion medium, and thus the slurry for the electrode of the non-aqueous electrolyte secondary battery of the present embodiment is preferably used at least as the slurry for the negative electrode.

[0049] Note that, instead of water, an electrode slurry using an organic solvent such as NMP as a dispersion medium, for example, contains an electrode mixture containing an electrode active material, a binder material, and the like, and an organic solvent such as NMP. In this case, the binder material is preferably a fluorine resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), a polyimide-based resin, an acrylic-based resin, a polyolefin-based resin, or the like. In addition, in the electrode mixture, an electrically conductive material can be added as needed.

[0050] Hereinafter, an electrode (positive electrode, negative electrode) for a nonaqueous electrolyte secondary battery according to the present embodiment and a nonaqueous electrolyte secondary battery provided with the electrode for a nonaqueous electrolyte secondary battery will be described.

[0051] <Non-aqueous electrolyte secondary battery>

[0052] Figure 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery as one example of the embodiment. As illustrated in Figure 1 The nonaqueous electrolyte secondary battery 10 is provided with 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 is provided with 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 jelly-roll structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. Note that the electrode body 14 is not limited to the jelly-roll type, and can be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one with the separator interposed therebetween, or the like.

[0053] The nonaqueous electrolyte contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous solvent can use, for example, an ester, an ether, a nitrile, an amide, and a mixed solvent of two or more kinds thereof. The nonaqueous solvent can contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Note that the nonaqueous electrolyte is not limited to a liquid electrolyte, and can be a solid electrolyte. The electrolyte salt uses, for example, a lithium salt such as LiPF6.

[0054] The battery case 15 is composed of an outer can 16 of a bottomed cylindrical shape and a sealing body 17 that seals the opening portion of the outer can 16. Note that the battery case 15 is not limited to a cylindrical shape, and can be a metal case of a square shape (a square battery), a coin shape (a coin battery), or the like, a laminated film case (a laminated battery) composed of a metal film and a resin film stacked, or the like.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Positive electrode

[0059] 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.

[0060] The positive electrode current collector can use a foil of a metal stable in the potential range of the positive electrode such as aluminum, a film provided with the metal on the surface layer, or the like. Note that the materials constituting the positive electrode mixture layer are as described above, and the description thereof is omitted.

[0061] <Negative electrode>

[0062] The negative electrode 12 has 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 negative electrode slurry of the present embodiment to both surfaces of the negative electrode current collector, drying the coated film, thereby forming the negative electrode mixture layer on the negative electrode current collector, and calendering the negative electrode mixture layer. The negative electrode mixture layer of the negative electrode 12 produced using the negative electrode slurry of the present embodiment contains the negative electrode active material, lithium carbonate, carboxymethylcellulose or a salt thereof, and a binder material added as necessary, and the content of lithium carbonate is in the range of 33 ppm to 300 ppm with respect to the total mass of the negative electrode mixture layer. Note that, as described above, the negative electrode 12 can be produced using a slurry in which an organic solvent such as NMP is used instead of water as a dispersion medium, but it is preferable to produce using the negative electrode slurry of the present embodiment.

[0063] The negative electrode current collector can use a foil of a metal stable in the potential range of the negative electrode such as copper, a film provided with the metal on the surface layer, or the like. Note that the materials constituting the negative electrode mixture layer are as described above, and the description thereof is omitted.

[0064] <Separator>

[0065] The separator 13 can use, for example, a porous sheet having ion permeability and insulating properties. As a specific example of the porous sheet, a microporous film, a woven fabric, a nonwoven fabric, or the like can be given. As the material of the separator 13, an olefin-based resin such as polyethylene, polypropylene, a copolymer containing at least one of ethylene and propylene, cellulose, or the like is preferable. The separator 13 can be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. In addition, it can be a multilayer separator containing a polyethylene layer and a polypropylene layer, or the like. In addition, an aromatic polyamide-based resin or the like can be applied to the surface of the separator 13. In addition, a heat-resistant layer containing an inorganic filler can be formed at the interface of the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0066] Example

[0067] Hereinafter, the present application will be further described by examples, but the present application is not limited to these examples.

[0068] <Example 1>

[0069] [Positive electrode]

[0070] Zirconium of 0.1 mol% relative to cobalt, magnesium of 1 mol%, and aluminum were co-precipitated, and a thermal decomposition reaction was performed to obtain a lithium cobalt oxide containing zirconium, magnesium, and aluminum. Lithium carbonate was mixed as a lithium source, and sintering was performed at 850°C for 20 hours to obtain a lithium cobalt oxide containing zirconium, magnesium, and aluminum (LiCo 0.979 Zr 0.001 Mg 0.01 Al 0.01 O2). This was used as a positive electrode active material.

[0071] The above positive electrode active material was mixed at 95 mass%, carbon powder as a conductive material was mixed at 2.5 mass%, and polyvinylidene fluoride powder as a binder was mixed at 2.5 mass%, and this was mixed with an N-methylpyrrolidone (NMP) solution to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides of an aluminum positive electrode current collector having a thickness of 15 μm by a doctor blade method to form a positive electrode mixture layer on both sides of the positive electrode current collector. Then, calendering was performed using a calender roll, and cutting was performed to a predetermined size. This was used as a positive electrode.

[0072] [Negative electrode]

[0073] As a negative electrode active material, graphite having an average particle diameter of 22 μm was prepared. The graphite, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 97:1.5:1.0, and a predetermined amount of lithium carbonate was added to obtain a negative electrode mixture. The content of the lithium carbonate was 66 ppm relative to the total mass of the negative electrode mixture. A negative electrode slurry was prepared by adding mixed ion exchange water to the negative electrode mixture. The solid content of the negative electrode slurry was 50%.

[0074] For the prepared negative electrode slurry, a B-type viscometer (Toyo Seiki Industry TVB10) was used to measure the viscosity at the time of preparation and after 96 hours. Then, the viscosity change rate after 96 hours was calculated by the following equation. The results are shown in Table 1.

[0075] Viscosity change rate after 96 hours (%) = (viscosity after 96 hours) ÷ (viscosity at the time of preparation) x 100

[0076] The negative electrode mixture slurry that had been prepared 96 hours before was applied to both sides of a negative electrode current collector by a doctor blade method to form a negative electrode mixture layer on both sides of the negative electrode current collector. Then, calendering was performed using a calender roll, and cutting was performed to a predetermined size. This was used as a negative electrode.

[0077] For the negative electrode of Example 1, the peeling strength of the negative electrode mixture layer relative to the negative electrode current collector was measured using the device shown in FIG. 1. Figure 2 Figure 2 ​The illustrated device includes a base 131 on which a test object 132 is placed; an adhesive member 133 for fixing the test object 132; a chuck 134 that fixes one end of the test object 132 and is connected to a pulling stage 138; a bearing site 135 that allows the base 131 to slide horizontally; a spring 136 that uniformly applies force when the base 131 slides; a fixing portion 137 that connects the spring 136; the pulling stage 138 that is connected to the base 131 via a wire 139 and a pulley 140; a wire 141 for connecting the pulling stage 138 to a gripping clamp 142; a load sensor 143 that is connected to the gripping clamp 142 and is used to detect the load of the pulling stage 138; a support portion 144 that supports the load sensor 143; a driving portion 146 that moves the support portion 144 up and down; a linear sensor 147 that detects the amount of movement of the gripping clamp 142; a support column 145 in which the driving portion 146 and the linear sensor 147 are built in; a support stage 148 that supports the base 131, and the support stage 148 and the support column 145 are fixed to a base 150.

[0078] As the test object 132, a negative electrode cut to a size of 15 mm in length and 120 mm in width was used. The negative electrode (test object 132) was fixed to the base 131 by the adhesive member 133, and one end thereof was fixed by the chuck 134. The driving portion 146 was activated, and the gripping clamp 142 was pulled at a certain speed, whereby the pulling stage 138 was pulled, and in conjunction therewith, the chuck 134 was pulled, whereby the negative electrode active material layer was peeled from the negative electrode current collector. The stress at that time was measured by the load sensor 143. After the measurement, a pulling test was performed using only the device from which the negative electrode had been removed, and the component of the force when only the base 131 slid was measured. The component of the force when only the base 131 slid was subtracted from the stress when the negative electrode active material layer was peeled from the negative electrode current collector, and converted into per unit length (m), whereby the peeling strength of the negative electrode active material layer was calculated. The results are shown in Table 1.

[0079] [Non-aqueous electrolyte]

[0080] A solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 30:70 was prepared, and lithium hexafluorophosphate (LiPF6) was dissolved therein so as to have a concentration of 1 mol / L. Further, 2.0 wt% of vinylene carbonate (VC) with respect to the total amount of the electrolyte was dissolved, thereby preparing a non-aqueous electrolyte.

[0081] [Non-aqueous electrolyte secondary battery]

[0082] The above-described positive electrode and negative electrode were wound with a separator composed of a micro-porous film made of polyethylene, and a tape made of polypropylene was attached to the outermost periphery, thereby producing a cylindrical electrode body. Then, the electrode body was pressed to produce a flat spiral electrode body.

[0083] A sheet-shaped laminate prepared from a 5-layer structure of a resin layer (polypropylene) / adhesive material layer / aluminum alloy layer / adhesive material layer / resin layer (polypropylene) was folded back to form a bottom, thereby forming a cup-shaped electrode body housing space. The above flat electrode body and the above nonaqueous electrolyte were inserted into the above housing space in a glove box under an argon atmosphere. Then, the inside of the exterior body was depressurized, the nonaqueous electrolyte was impregnated into the spacer, and the opening of the exterior body was sealed, thereby producing a nonaqueous electrolyte secondary battery having a height of 62 mm, a width of 35 mm, and a thickness of 3.6 mm.

[0084] [Evaluation of capacity retention rate in charge / discharge cycle]

[0085] After constant current charging (current 1 It = 800 mA, termination voltage 4.2 V) - constant voltage charging (voltage 4.2 V, termination current 40 mA) were performed at a temperature environment of 25°C, discharging was performed at a current value of 800 mA to 2.75 V. This charge / discharge was performed for 300 cycles, and the capacity retention rate in the charge / discharge cycle was calculated based on the following formula. The results are shown in Table 1.

[0086] Capacity retention rate = (X2 / X1) x 100

[0087] X1: discharge capacity of the 1st cycle

[0088] X2: discharge capacity of the 300th cycle

[0089] [Example 2]

[0090] In the production of the slurry for the negative electrode, the content of lithium carbonate was set to 166 ppm with respect to the total mass of the negative electrode mixture, and the slurry for the negative electrode was produced in the same manner as in Example 1, except for this. Further, the negative electrode and the nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except for this, using the slurry for the negative electrode of Example 2.

[0091] [Example 3]

[0092] In the production of the slurry for the negative electrode, the content of lithium carbonate was set to 300 ppm with respect to the total mass of the negative electrode mixture, and the slurry for the negative electrode was produced in the same manner as in Example 1, except for this. Further, the negative electrode and the nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except for this, using the slurry for the negative electrode of Example 3.

[0093] [Example 4]

[0094] In the production of the slurry for the negative electrode, the content of lithium carbonate was set to 33 ppm with respect to the total mass of the negative electrode mixture, and the slurry for the negative electrode was produced in the same manner as in Example 1, except for this. Further, the negative electrode and the nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except for this, using the slurry for the negative electrode of Example 4.

[0095] <Comparative Example 1>

[0096] In the production of the slurry for the negative electrode, lithium carbonate was not used, and otherwise, the slurry for the negative electrode was produced in the same manner as in Example 1. Further, using the slurry for the negative electrode of Comparative Example 1, a negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1.

[0097] <Comparative Example 2>

[0098] In the production of the slurry for the negative electrode, the content of lithium carbonate was set to 1 mass% with respect to the total mass of the negative electrode mixture, and otherwise, the slurry for the negative electrode was produced in the same manner as in Example 1. Further, using the slurry for the negative electrode of Comparative Example 2, a negative electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1.

[0099] Further, the viscosity change rate after 96 hours of the slurries for the negative electrode of Examples 2 to 4 and Comparative Examples 1 to 2, the peeling strength of the negative electrode mixture layer in the negative electrode of Examples 2 to 4 and Comparative Examples 1 to 2, and the capacity maintenance rate in the charge-discharge cycle of the nonaqueous electrolyte secondary batteries of Examples 2 to 4 and Comparative Examples 1 to 2 were measured in the same manner as in Example 1. The results thereof are shown in Table 1. Note that, for Comparative Example 2, it was confirmed that the peeling strength of the negative electrode mixture layer was reduced due to the addition of excess lithium carbonate to the negative electrode, and thus the measurement of the capacity maintenance rate was not performed.

[0100] [Table 1]

[0101]

[0102] The lower the value of the viscosity change rate after 96 hours of Table 1 (the lower than 100%), the more the slurry is reduced in viscosity. Thus, according to the results of the viscosity change rate after 96 hours of Table 1, it can be said that the viscosity reduction of the slurries for the negative electrode of Examples 1 to 4 is suppressed as compared with the slurries for the negative electrode of Comparative Examples 1 to 2. Further, along therewith, the peeling strength of the negative electrode mixture layer of Examples 1 to 4 shows a higher value than the peeling strength of the negative electrode mixture layer of Comparative Examples 1 to 2. That is, it can be said that by using the slurries for the negative electrode of Examples 1 to 4, an electrode mixture layer showing good adhesion to the current collector can be obtained. Further, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 show a higher value in the capacity maintenance rate in the charge-discharge cycle than the nonaqueous electrolyte secondary battery of Comparative Example 1, and the reduction in the charge-discharge cycle characteristics is suppressed.

[0103] Explanation of Reference Numerals

[0104] 10: nonaqueous electrolyte secondary battery, 11: positive electrode, 12: negative electrode, 13: separator, 14: electrode body, 15: battery case, 16: outer can, 17: sealing body, 18, 19: insulating plate, 20: positive electrode lead, 21: negative electrode lead, 22: slot entry portion, 23: bottom plate, 24: lower valve body, 25: insulating member, 26: upper valve body, 27: lid, 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 300 ppm relative to the total mass of the electrode mixture, the pH of the slurry for a nonaqueous electrolyte secondary battery electrode is in a range of 8 to 9.

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 300 ppm relative to the total mass of the electrode mixture, the pH of the slurry for a nonaqueous electrolyte secondary battery electrode is in a range of 8 to 9.

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 is formed by applying the slurry for a nonaqueous electrolyte secondary battery electrode according to claim 1 on the current collector and drying, and 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 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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