JP2010238365A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery excellent in security by suppressing generation of faults in an electrode caused by coating of paint for the electrode. <P>SOLUTION: A lithium ion secondary battery 10 comprises a cathode 5 capable of discharging/occluding lithium ion, non-graphite carbon in an active material mixture, rubber binder, a negative electrode 15 including carboxymethyl cellulose (CMC) with number of polymerization 100 or more and 1,000 or less and capable of occluding/discharging lithium ion, and nonaqueous electrolytic solution. As the anode, a slurry made by dispersing a mixture of hardly-graphitized carbon, acetylene black, styrene-butadiene copolymer rubber particles and CMC (an etherification degree of 0.6 to 1.0) in water (a weight ratio: 91:4:4:1) is coated on a copper foil of 10 μm in thickness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and in particular, a non-aqueous electrolyte solution comprising a positive electrode capable of releasing / occluding lithium ions, a negative electrode capable of inserting / extracting lithium ions, and a non-aqueous electrolyte solution. Next battery.

  Recently, due to the emergence of environmental problems such as global warming, reduction of carbon dioxide emissions from automobiles has been demanded, and genuine electric vehicles powered by electric energy (PEV) and regenerative energy generated when automobiles are decelerating. Development of a hybrid electric vehicle (HEV) that can be used as a part of motive power is proceeding at a rapid pace.

  Non-aqueous electrolyte secondary batteries that utilize lithium ion storage / release reactions at electrodes are attracting attention as power sources for electric vehicles. This type of battery generally includes a positive electrode capable of releasing / occluding lithium ions, a negative electrode capable of inserting / extracting lithium ions, and a non-aqueous electrolyte. In a vehicle battery, input characteristics and cycle characteristics are very important as well as output characteristics, and these characteristics greatly depend on a negative electrode active material that occludes / releases lithium ions during charge / discharge of the battery.

  In a vehicle battery, a non-graphite carbon material having a low crystallinity, a low true density, and a lithium ion diffusion or occlusion / release reaction that easily occurs during charge / discharge is often used as a negative electrode active material. However, since non-graphitic carbon material has a large amount of pores inside and a large amount of residual gas in the negative electrode paint (slurry), when producing a negative electrode using non-graphitic carbon material, it is Electrode defects due to foam formation and rupture of small bubbles are likely to occur. Electrode defects have a major impact on battery safety. That is, when the current collector is exposed to the electrode plate in the defective portion, lithium folding occurs on the electrode plate, and the lithium folding material that has become enormous by repeated charge / discharge causes electrode short circuit / battery ignition. Therefore, it is necessary to eliminate the defects from the electrodes as much as possible. As a general solution to this problem, a technique is known in which the paint is degassed under reduced pressure before coating to reduce the amount of residual gas in the paint.

  A binder (binder) such as polyvinylidene fluoride or rubber binder is used for the electrode of the nonaqueous electrolyte secondary battery in order to bind the components (active material, conductive material, etc.) in the electrode mixture. Yes. When using water as a paint solvent, a rubber binder is often used. When using a rubber binder, a thickener is added to adjust the viscosity of the paint. Usually, carboxymethylcellulose is used for such a thickening material (for example, refer patent document 1).

JP 2008-135334 A

  When the non-graphite carbon is contained in the paint, the technique for reducing the amount of residual gas by degassing defoaming described above has a large amount of residual gas in the paint before defoaming. Cost. When the defoaming time becomes longer, the coating properties change due to solvent evaporation. In particular, when water is used as a paint solvent, the boiling point is relatively low and the amount of evaporation per unit time is large, so that the change in the properties of the paint due to solvent evaporation becomes remarkable, which is not preferable.

  On the other hand, when carboxymethyl cellulose is used as the thickener, the viscosity of the coating depends on the solid content ratio in the coating and the molecular weight of CMC. Although it is possible to reduce the solid content ratio in the paint to improve the efficiency of paint defoaming, it is not suitable for mass production of electrodes because the storage space for the paint increases. As far as the inventors know, no technology has been reported so far that improves the defoaming efficiency of the paint by using low molecular weight CMC.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that is superior in safety by suppressing the occurrence of electrode defects due to electrode paint coating.

  In order to solve the above problems, the present invention provides a nonaqueous electrolyte secondary battery, a positive electrode capable of releasing / occluding lithium ions, non-graphitic carbon in an active material mixture, a rubber binder, and a number average A negative electrode containing a carboxymethyl cellulose having a degree of polymerization of 100 or more and 1000 or less and capable of occluding / releasing lithium ions, and a non-aqueous electrolyte.

  In the present invention, non-graphitizable carbon can be used for non-graphitic carbon. Moreover, it is preferable that the etherification degree of carboxymethylcellulose is 0.6 or more and 1.0 or less.

  According to the present invention, by adding carboxymethyl cellulose having a number average degree of polymerization of 100 or more and 1000 or less to a negative electrode active material mixture containing non-graphitic carbon and a rubber binder, the defoaming efficiency of the paint is improved and the disadvantage of the electrode The effect that the number is reduced and the safety of the non-aqueous electrolyte secondary battery is improved can be obtained.

1 is a partially broken front view schematically showing a lithium ion secondary battery of an example to which the present invention is applicable.

  Hereinafter, an embodiment in which a nonaqueous electrolyte secondary battery according to the present invention is applied to a lithium ion secondary battery that can be used as a power source for a hybrid electric vehicle and can constitute a battery module (assembled battery) will be described. In addition, this embodiment is an example and does not restrict | limit the application range of this invention.

1. The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on both sides or one side of the positive electrode current collector. In order to improve input / output characteristics, the positive electrode current collector One side in the longitudinal direction may be cut out, for example, in a rectangular shape, and the remaining part of the cutout may be used as a positive electrode lead.

  The positive electrode current collector is capable of transmitting electrons generated by the release / occlusion reaction of lithium ions in the positive electrode mixture layer to a conductive member to be described later with low resistance, contact with a non-aqueous electrolyte, and release of lithium ions / There is no particular limitation as long as it does not deteriorate significantly due to the occlusion reaction. An example of the positive electrode current collector is aluminum foil.

  The positive electrode mixture layer includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

  It is preferable to use lithium oxide for the positive electrode active material. Examples of the lithium oxide include lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, lithium composite oxide (lithium oxide containing two or more selected from cobalt, nickel, and manganese).

  The positive electrode conductive material is not limited as long as it is a substance capable of assisting transmission of electrons generated by the lithium ion release / occlusion reaction in the positive electrode mixture layer to the positive electrode current collector. Examples of the positive electrode conductive material include graphite and acetylene black. The positive electrode binder can bind the positive electrode active material and the positive electrode conductive material, the positive electrode mixture layer and the positive electrode current collector, and is not particularly limited as long as it does not deteriorate significantly due to contact with the non-aqueous electrolyte. Absent. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF) and fluororubber.

  The method for forming the positive electrode mixture layer is not limited as long as the positive electrode mixture layer is formed on the positive electrode current collector. As an example of the method for forming the positive electrode mixture layer, a method of coating (applying) a dispersion solution of constituent materials of the positive electrode mixture layer on the positive electrode current collector can be given. Examples of the coating method include a roll coating method and a slit die coating method. Examples of the solvent for the dispersion solution include N-methyl-2-pyrrolidone (NMP) and water.

2. Negative electrode The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on both sides or one side of the negative electrode current collector. One side in the longitudinal direction may be cut out, for example, in a rectangular shape, and the remaining cutout may be used as a negative electrode lead.

  The negative electrode current collector is capable of transmitting electrons generated by the occlusion / release reaction of lithium ions in the negative electrode mixture layer to a conductive member described later with low resistance, contact with a non-aqueous electrolyte, and occlusion / There is no particular limitation as long as it does not deteriorate significantly due to the release reaction. An example of the negative electrode current collector is copper foil.

  The negative electrode mixture layer includes a negative electrode active material, a negative electrode conductive material, a negative electrode binder, and a thickener.

  When a non-graphite carbon material is used as the negative electrode active material, a great effect is exhibited. Non-graphitic carbon material refers to non-graphitizable carbon, graphitizable carbon alone or a mixture thereof. Non-graphitizable carbon has more pores than graphitizable carbon. Therefore, a particularly large effect is exhibited when non-graphitizable carbon is used. The negative electrode active material may contain graphite in addition to the non-graphitic carbon material. The negative electrode conductive material is not particularly limited as long as it is a substance capable of assisting transmission of electrons generated by the insertion / release reaction of lithium ions in the negative electrode mixture layer to the negative electrode current collector. An example of the negative electrode conductive material is acetylene black. The ratio of the negative electrode active material in the negative electrode mixture layer can be adjusted between 90 and 99.5% by weight as necessary. When it is less than 90% by weight, the capacity of the lithium ion secondary battery becomes small. On the other hand, when the amount is more than 99.5% by weight, since the ratio of the negative electrode binder is small, the binding properties of the negative electrode active material and the negative electrode conductive material, and the negative electrode mixture layer and the negative electrode current collector cannot be obtained. The reliability of the secondary battery is reduced.

  As a method for producing non-graphitizable carbon, an organic polymer compound such as a furfuryl alcohol resin is carbonized at 300 to 700 ° C. in an inert gas stream, and then heated to 900 to 1500 ° C. to reach the ultimate temperature. The method of hold | maintaining for 0 to 30 hours is illustrated. Further, as a method for producing graphitizable carbon, after carbonizing coal or pitch at 300 to 700 ° C. in an inert gas stream, the temperature is raised to 900 to 1500 ° C. and 0 to 30 hours at the ultimate temperature. The method of holding is illustrated.

  As the negative electrode binder, it is preferable to use a rubber binder. Here, the rubber binder refers to a binder having rubber obtained by polymerizing one or more kinds of monomer mixtures having double bond sites. Examples of the rubber binder include styrene-butadiene copolymer rubber (SBR) and modified products thereof, acrylonitrile-butadiene copolymer rubber and modified products thereof, acrylic rubber and modified products thereof. The shape of the rubber binder is preferably a particle shape having a particle size of about 0.1 to 1.0 μm, but is not limited thereto.

  Moreover, the ratio of a negative electrode binder can be adjusted between 0.5 to 10 weight% as needed. When it is more than 10% by weight, the capacity of the lithium ion secondary battery becomes small. On the other hand, when the content is less than 0.5% by weight, since the proportion of the negative electrode binder is small, the binding properties of the negative electrode active material and the negative electrode conductive material, and the negative electrode mixture layer and the negative electrode current collector cannot be obtained. The reliability of the secondary battery is reduced. In addition, when forming the negative electrode mixture layer by a method of coating the dispersion solution of the constituent material of the negative electrode mixture layer on the negative electrode current collector, the dispersion solution may be contained in the negative electrode mixture layer as necessary. A surfactant for ensuring the dispersion stability of the rubber binder therein and / or an antifoaming agent that suppresses foaming during coating due to the addition of the surfactant may be included. An example of a surfactant is sodium n-dodecyl sulfate (SDS). Examples of the antifoaming agent include n-octanol and polysiloxane.

  In the present embodiment, the use of carboxymethyl cellulose (CMC) having a number average polymerization degree of 100 or more and 1000 or less as a thickener exhibits a suitable effect. Use of CMC having a number average degree of polymerization of less than 100 is not preferable because the coating does not sufficiently thicken and the electrode is difficult to apply. On the other hand, if CMC having a number average degree of polymerization of more than 1000 is used, the paint cannot be sufficiently defoamed, and a number of defects occur on the coated electrode, so that a safe battery cannot be produced. The degree of etherification of CMC is not limited as long as this effect is not inhibited, but is preferably 0.6 to 1.0. When the degree of etherification is less than 0.6, the viscosity of the paint increases and defoaming becomes difficult. On the other hand, when the degree of etherification is larger than 1.0, the interaction with the negative electrode current collector becomes weak, and the negative electrode mixture layer tends to peel off from the negative electrode current collector, which is not preferable. The degree of etherification is the average number of carboxymethyl groups contained in the unit skeleton of cellulose, and can theoretically take a value from 0 to 3. Moreover, the ratio of a thickener can be adjusted between 0.5 to 5 weight% as needed. If the amount is more than 5% by weight, the coating is excessively thickened and electrode coating becomes difficult, which is not preferable. On the other hand, when the amount is less than 0.5% by weight, the viscosity of the paint is not sufficient and electrode coating becomes difficult, which is not preferable.

  The method for forming the negative electrode mixture layer is not limited as long as the negative electrode mixture layer is formed on the negative electrode current collector. As an example of the method for forming the negative electrode mixture layer, there is a method in which a dispersion solution of constituent materials of the negative electrode mixture layer is applied onto the negative electrode current collector. Examples of the coating method include a roll coating method and a slit die coating method. In addition, water is used as a solvent for the dispersion solution.

3. Battery production The positive electrode and the negative electrode are arranged via a separator to form an electrode group. Such an electrode group can be classified into a wound type and a laminated type electrode group. Examples of the wound electrode group include a cylindrical shape, a rectangular parallelepiped shape, an elliptical shape, and a flat shape. The stacked electrode group is a type in which a separator is interposed between a positive electrode and a negative electrode, or a type in which the separator is configured in a bag shape and either the positive or negative electrode is accommodated in the separator and the positive and negative electrodes are stacked. It may be. Therefore, it is not particularly limited to the mode of the electrode group (separate type such as a wound type and a laminated type).

  The positive electrode current collector and the negative electrode current collector are connected to an external terminal via a conductive member. In general, a battery for a vehicle uses a current collecting ring as a conductive member, but is not limited thereto. Moreover, although a battery can and a battery cover (cap) are often used for the external terminal, it is not limited thereto. In general, a gasket is interposed between the battery can and the battery lid. The conductive member may be a member different from the positive electrode current collector and the negative electrode current collector. In addition, when the notch remainder is formed as a positive electrode lead or a negative electrode lead, the notch tip is joined to the conductive member (for example, ultrasonic welding).

  The separator is a sheet-like substance that permeates lithium ions that move through the non-aqueous electrolyte while isolating the positive electrode and the negative electrode, and may be composed of a substance that does not deteriorate significantly due to contact with the non-aqueous electrolyte. There is no limit. Examples of the separator include a polyethylene porous film and a polypropylene porous film.

  It is preferable that the electrode group is housed in a battery can or a film container together with a non-aqueous electrolyte and has a sealed structure. There is no restriction | limiting also in the shape of a battery can, A cylindrical shape, a rectangular parallelepiped shape, an ellipse thru | or a flat shape can be used.

  As needed, you may have the insulator for avoiding (insulating) a contact with an electrode group, a battery can, a battery cover, or a current collection member. The insulator is not limited as long as it is made of a material that does not deteriorate significantly due to contact with the non-aqueous electrolyte. Examples of the insulator include a polyethylene plate. In addition, the battery can or the battery lid may be provided with a cleavage valve in order to prevent an increase in the battery internal pressure.

As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in a carbonate solvent can be used. Examples of the lithium salt include lithium fluorophosphate (LiPF ₆ ), lithium fluoroborate (LiBF ₆ ), and the like. Examples of carbonate solvents include ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), methyl ethyl carbonate (MEC), or a mixture of solvents selected from one or more of the above solvents. Can be mentioned.

  Next, examples of lithium ion secondary batteries manufactured according to the above embodiment will be described with reference to the drawings. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
As shown in FIG. 1, in the battery of Example 1, the positive electrode mixture layer 2 was formed on both surfaces of the positive electrode current collector 1. As the positive electrode current collector, an aluminum foil having a thickness of 20 μm was used. A mixture (weight fraction 80:10:10) of a positive electrode active material (lithium manganate), a positive electrode conductive material (a mixture of graphite and acetylene black), and a positive electrode binder (PVDF) is dispersed in NMP to form a slurry. Was made. This slurry was applied to both surfaces of the positive electrode current collector 1 by a roll coating method to form a positive electrode mixture layer.

  Thereafter, the positive electrode mixture layer was dried at 120 ° C. and pressed to prepare a positive electrode 5 having a thickness of 90 μm. The width and length of the positive electrode were 54 mm and 450 mm, respectively. Further, a positive electrode tab 3 made of aluminum was attached to an end of the produced positive electrode current collector 1.

  Next, the negative electrode mixture layer 12 was formed on both surfaces of the negative electrode current collector 11. As shown in Table 1 below, in the battery of Example 1, non-graphitizable carbon was used as the negative electrode active material. The non-graphitizable carbon was prepared by holding a furfuryl alcohol resin in a nitrogen stream at a temperature of 500 ° C. for 5 hours, then raising the temperature to 1200 ° C. and performing a heat treatment for 1 hour. A copper foil having a thickness of 10 μm was used as the negative electrode current collector 11. Negative electrode active material, negative electrode conductive material (acetylene black), negative electrode binder (styrene-butadiene copolymer rubber particles: number average particle diameter 0.15 μm), thickener (carboxymethyl cellulose: number average polymerization degree 600, ether The mixture (weight ratio: 91: 4: 4: 1) with a degree of conversion of 0.6) was dispersed in water to prepare a paint. The solid content of the paint (slurry) was 50 weight percent, and the viscosity of the paint was 2400 mPa. This paint was applied to both surfaces of the negative electrode current collector 11 by a roll coating method to form a negative electrode mixture layer on both surfaces of the negative electrode current collector. The number of electrode defects due to the formation of small bubbles and the burst of small bubbles during coating was visually confirmed to be two per square meter.

  Thereafter, the negative electrode mixture layer was dried at 120 ° C. and pressed to prepare a negative electrode 15 having a thickness of 80 μm. The width and length of the negative electrode were 56 mm and 500 mm, respectively. Further, a nickel negative electrode tab 13 was attached to the end of the produced negative electrode current collector 11.

An electrode group 40 was produced in which the produced positive electrode 5 and negative electrode 15 were spirally wound through a separator 21 (thickness 25 μm, width 58 mm) made of a polyethylene porous film. The electrode group 40 was inserted into the battery can 41 together with the insulator 31 made of polyethylene, and an axial core (not shown) serving as a winding center of the electrode group 40 was fixed to the battery can 41. Thereafter, the negative electrode tab 13 was welded to the inner bottom surface of the battery can 41, and the positive electrode tab 3 was welded to the bottom surface of the positive electrode terminal 51. Then, a non-aqueous electrolyte (1.0 mol / liter LiPF ₆ dissolved in a 1: 1: 1 mixed solvent by volume ratio of EC, DMC, and DEC) is injected into the battery can 41, and a positive electrode terminal 51 was caulked and sealed to the battery can 41 via a gasket, and the assembly of the lithium ion secondary battery 10 having a diameter of 18 mm and a length of 65 mm was completed.

  The positive electrode terminal 51 also serves as a battery sealing lid, and is provided with a cleavage valve that cleaves and releases the pressure inside the battery when the pressure inside the battery rises. By evaluating input / output characteristics of a lithium ion secondary battery having a charge depth of 50% according to the conditions of JIS D713: 2003, it was found that the output density of the battery was 3500 W / kg and the input density was 3300 W / kg. .

(Example 2)
The battery of Example 2 is the same as the battery of Example 1 except for the negative electrode mixture layer (the positive electrode, the dimensions of the battery, the output density is 3500 W / kg, and the input density is 3300 W / kg). Explanation of members is omitted, and only different portions are described in detail (the same applies to the batteries of Example 3 and Comparative Examples 1 and 2 described later).

  As shown in Table 1, in the battery of Example 2, graphitizable carbon was used for the negative electrode active material. The graphitizable carbon was prepared by holding coal pitch in a nitrogen stream at a temperature of 500 ° C. for 5 hours, and then heating to 1400 ° C. and heat-treating for 1 hour. Negative electrode active material, negative electrode conductive material (acetylene black), negative electrode binder (styrene-butadiene copolymer rubber particles: number average particle diameter 0.15 μm), thickener (carboxymethyl cellulose: number average polymerization degree 600, ether The mixture (weight ratio: 91: 4: 4: 1) with a degree of conversion of 1.0) was dispersed in water to prepare a paint. The solid content of the paint was 50 weight percent, and the viscosity of the paint was 2000 mPa. This paint was applied to both surfaces of the negative electrode current collector by a roll coating method to form a negative electrode mixture layer on both surfaces of the negative electrode current collector. The number of electrode defects resulting from the formation of small bubbles and the burst of small bubbles during coating was visually confirmed to be 3 per square meter.

Example 3
As shown in Table 1, in the battery of Example 3, non-graphitizable carbon produced by the same method as in Example 1 described above was used as the negative electrode active material. Negative electrode active material, negative electrode conductive material (acetylene black), negative electrode binder (styrene-butadiene copolymer rubber particles: number average particle size 0.15 μm), thickener (carboxymethyl cellulose: number average degree of polymerization 1000, ether A mixture (weight ratio: 91: 4: 4: 1) with a degree of conversion of 0.7) was dispersed in water to prepare a paint. The solid content rate of the paint was 50 weight percent, and the viscosity of the paint was 4000 mPa. This paint was applied to both surfaces of the negative electrode current collector by a roll coating method to form a negative electrode mixture layer on both surfaces of the negative electrode current collector. The number of electrode defects due to the formation of small bubbles and the bursting of small bubbles during coating was visually confirmed to be 5 per square meter.

(Comparative Example 1)
As shown in Table 1, in the battery of Comparative Example 1, non-graphitizable carbon prepared by the same method as in Example 1 described above was used as the negative electrode active material. Negative electrode active material, negative electrode conductive material (acetylene black), negative electrode binder (styrene-butadiene copolymer rubber particles: number average particle size 0.15 μm), thickener (carboxymethyl cellulose: number average degree of polymerization 2000, ether The mixture (weight ratio: 91: 4: 4: 1) with a degree of conversion of 0.6) was dispersed in water to prepare a paint. The solid content of the paint was 50 weight percent, and the viscosity of the paint was 12000 mPa. This paint was applied to both surfaces of the negative electrode current collector by a roll coating method to form a negative electrode mixture layer on both surfaces of the negative electrode current collector. The number of electrode defects caused by the formation of small bubbles and the bursting of small bubbles during coating was visually confirmed to be 50 per square meter.

(Comparative Example 2)
As shown in Table 1, in the battery of Comparative Example 2, graphitizable carbon prepared by the same method as in Example 2 described above was used as the negative electrode active material. Negative electrode active material, negative electrode conductive material (acetylene black), negative electrode binder (styrene-butadiene copolymer rubber particles: number average particle diameter 0.15 μm), thickener (carboxymethyl cellulose: number average degree of polymerization 2000, ether The mixture (weight ratio: 91: 4: 4: 1) with a degree of conversion of 1.0) was dispersed in water to prepare a paint. The solid content rate of the coating material was 50 weight percent, and the viscosity of the coating material was 10,000 mPa. This paint was applied to both surfaces of the negative electrode current collector by a roll coating method to form a negative electrode mixture layer on both surfaces of the negative electrode current collector. The number of electrode defects due to the formation of small bubbles and the bursting of small bubbles during coating was visually confirmed to be 30 per square meter.

(test)
100 batteries of each of the examples and comparative examples were produced, and safety was evaluated by measuring the voltage drop of the battery after the charge / discharge cycle test at high temperature. It is generally known that a battery short path (micro short circuit) is formed when a lithium break-out generated by a defect of the negative electrode breaks through a separator between the positive electrode and the negative electrode, thereby causing smoke and ignition of the battery. Since the short path is also a cause of the voltage drop of the battery, the safety of the battery can be evaluated by measuring the voltage drop.

  Specifically, in an environment of 50 ° C., (1) the battery was charged at 10 C up to 4.1 V, (2) the battery was discharged 1000 times at 2.7 V at 10 C, and then the battery was charged to 4.1 V. . Thereafter, the battery was allowed to stand for one day, and the voltage of each battery was measured, and whether or not it was a safe battery was evaluated depending on whether or not it showed a voltage of 4.08 V or higher. The evaluation results are shown in Table 2 below.

  As shown in Table 2, all the batteries of Examples 1 to 3 exhibited a voltage of 4.08V or more. From this, it was found that the batteries of Examples 1 to 3 were safe batteries. On the other hand, in the battery of Comparative Example 1, there were 8 batteries whose voltage dropped to less than 4.08V. Moreover, in the battery of Comparative Example 2, there were five batteries whose voltage dropped to less than 4.08V. From this, it was found that the batteries of Comparative Examples 1 and 2 were likely to emit smoke or ignite.

  In consideration of Tables 1 and 2, the battery of the example using CMC having a number average degree of polymerization of 1000 or less has a small number of defects on the electrode plate, and the voltage drop of the battery after 1000 cycle tests is suppressed. Recognize. As a cause of this, when a CMC having a number average degree of polymerization of 1000 or less is used, the occurrence of electrode defects due to the formation of small bubbles and the bursting of small bubbles during coating is suppressed, and the electrode during charge / discharge cycles is suppressed. It is thought that upper lithium folding was suppressed. Therefore, the batteries of Examples 1 to 3 are safe batteries in which the formation of a short path due to lithium folding on the negative electrode plate, which is a cause of smoke and fire, is suppressed.

  Since the present invention provides a non-aqueous electrolyte secondary battery excellent in safety by suppressing the occurrence of electrode defects due to electrode paint coating, it contributes to the manufacture and sale of non-aqueous electrolyte secondary batteries. Have industrial applicability.

5 Positive electrode 10 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
15 Negative electrode 40 Electrode group 41 Battery can 51 Positive electrode terminal

Claims (3)

A positive electrode capable of releasing / occluding lithium ions;
A negative electrode containing non-graphite carbon, a rubber binder, and carboxymethylcellulose having a number average degree of polymerization of 100 or more and 1000 or less in the active material mixture and capable of occluding / releasing lithium ions;
A non-aqueous electrolyte,
A non-aqueous electrolyte secondary battery comprising:   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-graphitic carbon is non-graphitizable carbon.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the degree of etherification of the carboxymethyl cellulose is 0.6 or more and 1.0 or less.

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