JP2008108632A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having excellent charge and discharge characteristics in which a carbon material such as graphite is used as a negative electrode active material and then in which calboxymethylcellulose (CMC) is used as a thickening agent. <P>SOLUTION: In the nonaqueous electrolyte secondary battery 10 which has a negative electrode plate 12 in which negative electrode mixture layers containing CMC are formed on both side surfaces of a negative electrode core, and a positive electrode plate 11 in which positive electrode mixture layers are formed on both side surfaces of a positive electrode core, and which is equipped with a wound electrode body 14 around which the negative electrode plate 12 and the positive electrode plate 11 are wound through a separator 13, the negative electrode mixture layers formed on both the side surfaces of the negative electrode core have the same compositions and the same thicknesses except that physical properties of CMC are different from each other, and when a negative electrode mixture coated on the inner surface of the negative electrode core is set as A and the negative electrode mixture coated on the outer surface thereof is set as B, and then when the hardnesses of the negative electrode plates prepared by independently using the A and the B are set as F<SB>A</SB>and F<SB>B</SB>, respectively, CMC having such a property that F<SB>A</SB>becomes smaller than F<SB>B</SB>is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery excellent in charge / discharge characteristics, and in particular, a non-aqueous electrolyte excellent in charge / discharge characteristics using a carbon material such as graphite as a negative electrode active material and carboxymethyl cellulose (CMC) as a thickener. The present invention relates to a water electrolyte secondary battery.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small and thin, high capacity, excellent cycle characteristics, and stable performance are required. Yes. In the field of secondary batteries, lithium-based non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention. The proportion of lithium-based non-aqueous electrolyte secondary batteries accounts for a significant increase in the secondary battery market. Is shown.

  By the way, in a device in which this type of non-aqueous electrolyte secondary battery is used, the space for accommodating the battery is often a square (flat box shape), so the power generation element is accommodated in a rectangular outer can. The formed rectangular non-aqueous electrolyte secondary battery is often used. Such a rectangular nonaqueous electrolyte secondary battery is generally manufactured as follows.

  That is, a negative electrode plate in which a negative electrode mixture containing a negative electrode active material is applied on both sides of a negative electrode core (current collector) made of a long sheet-like copper foil and the like, and a positive electrode core made of a long and thin sheet-like aluminum foil A separator made of a microporous polyethylene film or the like is disposed between a positive electrode plate coated with a positive electrode mixture containing a positive electrode active material on both sides, and the negative electrode plate and the positive electrode plate are insulated from each other by a separator. A cylindrical wound electrode body is produced by spirally winding it on the winding core. The cylindrical electrode body is crushed with a press machine and molded into a shape that can be inserted into a rectangular battery outer can. Then, the cylindrical electrode body is accommodated in the rectangular outer can, and an electrolyte is injected to inject the rectangular nonaqueous electrolyte. Next battery.

  The configuration of such a conventional rectangular nonaqueous electrolyte secondary battery will be described with reference to the drawings. FIG. 1 is a perspective view showing a rectangular nonaqueous electrolyte secondary battery disclosed in Patent Document 1 below, cut in the vertical direction. This non-aqueous electrolyte secondary battery 10 accommodates a flat wound electrode body 14 in which a positive electrode plate 11 and a negative electrode plate 12 are wound via a separator 13 in a rectangular battery outer can 15, The battery outer can 15 is sealed with a sealing plate 16.

  The wound electrode body 14 is wound so that the positive electrode plate 11 is exposed at the outermost periphery, and the exposed outermost positive electrode plate 11 directly contacts the inner surface of the battery outer can 15 that also serves as a positive electrode terminal. And are electrically connected. The negative electrode plate 12 is formed in the center of the sealing plate 16 and is electrically connected to a negative electrode terminal 18 attached via an insulator 17 via a current collector 19.

  Since the battery outer can 15 is electrically connected to the positive electrode plate 11, in order to prevent a short circuit between the negative electrode plate 12 and the battery outer can 15, the upper end of the wound electrode body 14 and the sealing plate 16 The insulating spacer 20 is inserted between the negative electrode plate 12 and the battery outer can 15 so as to be electrically insulated.

  In this rectangular nonaqueous electrolyte secondary battery, after the wound electrode body 14 is inserted into the battery outer can 15, the sealing plate 16 is laser welded to the opening of the battery outer can 15, and then the electrolyte injection hole 21. The nonaqueous electrolytic solution is injected from the above, and the electrolytic solution injection hole 21 is sealed. Such a rectangular non-aqueous electrolyte secondary battery has an excellent effect that there is little wasted space during use, and the battery performance and battery reliability are high.

  As the negative electrode active material used in this non-aqueous electrolyte secondary battery, carbonaceous materials such as graphite and amorphous carbon have a discharge potential comparable to that of lithium metal or lithium alloy, but dendrite grows. Therefore, it is widely used because it has excellent properties such as high safety, excellent initial efficiency, good potential flatness, and high density.

As a positive electrode active material in this nonaqueous electrolyte secondary battery, Li _x MO ₂ capable of reversibly inserting and extracting lithium ions (where M is at least one of Co, Ni, and Mn) A lithium transition metal composite oxide represented by: LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like is used singly or in combination.
JP-A-2001-273931 (Claims, paragraphs [0003] to [0004], FIG. 1) JP-A-8-130035 (Claims, paragraphs [0058] to [0081])

  Since the non-aqueous electrolyte secondary battery as described above can achieve high capacity and high energy density, it is also used in cellular phones, notebook personal computers, PDAs, portable digital media players and the like. However, a further increase in capacity is desired because of the demand for higher functionality, smaller size, and lighter weight of these devices.

  As a method for increasing the capacity of the non-aqueous electrolyte secondary battery, an increase in the mass of the mixture and a reduction in the thickness of the core may be considered, but as a side effect, the winding of the electrode body due to the increase in the thickness of the mixture applied. There has been a problem that the electrode body is liable to be swollen due to deterioration of repetitiveness and repeated charge / discharge, leading to deterioration of charge / discharge characteristics. Such swelling of the electrode body due to repeated charge and discharge appears greatly in the case of a negative electrode plate having a low density and a large thickness.

  On the other hand, in Patent Document 2, the coating thickness of the positive electrode active material mixture applied on both sides of the core body is wound for the purpose of improving the winding suitability of the cylindrical electrode body for a nonaqueous electrolyte secondary battery. It is shown that the inner surface during rotation is thinner than the outer surface. However, when such a configuration is adopted, it is necessary to change the configuration of the positive electrode manufacturing means used conventionally, and the negative electrode mixture having the same thickness is applied to both surfaces of the negative electrode core. Since the active material content ratio on each of the positive electrode side and the negative electrode side becomes excessive and insufficient, the battery capacity is obtained from the usage amount of the positive electrode active material and the negative electrode active material. It will be significantly lower than the theoretical battery capacity. In addition, Patent Document 2 does not include a description suggesting that the invention described herein can be applied to a flat type non-aqueous electrolyte secondary battery.

  The inventor can suppress the swelling of the negative electrode plate if the winding characteristics of the electrode body can be improved while maintaining the same thickness of each of the negative electrode mixture layers provided on both sides of the negative electrode core. As a result of intensive research on the idea that the charge / discharge characteristics of the non-aqueous electrolyte secondary battery can be improved, it has been used as a thickener in the negative electrode mixture applied to both sides of the negative electrode core. Even if the content of each component is the same on both sides of the negative electrode core, only by changing the physical properties of the carboxymethyl cellulose (CMC) on each side, it is possible to improve winding suitability and repeat charge and discharge. Therefore, the present inventors have found that a nonaqueous electrolyte secondary battery having improved charge / discharge characteristics can be obtained and the present invention has been completed.

  That is, an object of the present invention is to provide a nonaqueous electrolyte secondary battery excellent in charge and discharge characteristics using a carbon material such as graphite as a negative electrode active material and using CMC as a thickener.

The above object of the present invention can be achieved by the following configurations. That is, the non-aqueous electrolyte secondary battery of the present invention includes a negative electrode plate in which a negative electrode mixture layer containing CMC is provided on both sides of the negative electrode core, and a positive electrode mixture layer on both sides of the positive electrode core. In a non-aqueous electrolyte secondary battery comprising a wound electrode body in which each of the negative electrode plate and the positive electrode plate is wound via a separator, the positive electrode plate is provided on both side surfaces of the negative electrode core. The negative electrode mixture layers have the same composition and the same thickness except that the physical properties of CMC are different from each other. The negative electrode mixture applied to the inner surface of the negative electrode core is A, and the negative electrode mixture is applied to the outer surface. And B and A and B are each independently used in the same amount, and when the negative electrode plate has a hardness of F _A and F _B , respectively, F _A <F _B It is characterized by using carboxymethylcellulose.

In the nonaqueous electrolyte secondary battery of the present invention, Li _x MO ₂ capable of reversibly occluding and releasing lithium ions as a positive electrode active material (where M is at least one of Co, Ni, and Mn). A lithium transition metal composite oxide represented by the following: LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn ₂ O ₄ , LiCo _x Mny _y Ni _z O ₂ (x + y + z = 1), LiFePO ₄ or the like can be used alone or in combination.

  In the nonaqueous electrolyte secondary battery of the present invention, carbonates, lactones, ethers, esters, etc. can be used as the nonaqueous solvent (organic solvent) constituting the nonaqueous solvent electrolyte. Two or more of these solvents can be mixed and used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3-oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned.

In addition, as a solute of the nonaqueous electrolyte in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L.

  The present invention provides the nonaqueous electrolyte secondary battery, wherein the degree of etherification of carboxymethyl cellulose in the negative electrode mixture A is greater than the degree of etherification of carboxymethyl cellulose in the negative electrode mixture B. To do.

  In the non-aqueous electrolyte secondary battery according to the present invention, the wound electrode body is a flat shape.

  In the non-aqueous electrolyte secondary battery according to the present invention, the negative electrode active material in the negative electrode mixture is made of a carbonaceous material.

  By providing the above configuration, the present invention has the following excellent effects. That is, according to the present invention, the negative electrode mixture layers provided on both side surfaces of the negative electrode core have the same composition and the same thickness although the physical properties of the CMCs contained therein are different. Therefore, there is no difference in the amount of active material involved in the electrochemical reaction. Therefore, the battery capacity is not lowered due to the difference in the thickness of the mixture layer provided on both side surfaces of the core as in the conventional example.

In addition, when the negative electrode mixture applied to the inner surface of the negative electrode core is A, the negative electrode mixture applied to the outer surface is B, and the same amount of A and B is used alone to produce a negative electrode plate When the hardness of the negative electrode plate is F _A and F _B , since carboxymethyl cellulose having a property of F _A <F _B is used, the negative electrode mixture layer on the outer surface is formed when the wound electrode body is formed. Is harder than the hardness of the negative electrode mixture layer on the inner surface. Therefore, when the wound electrode body is formed by winding each of the negative electrode plate and the positive electrode plate through a separator, each negative electrode mixture layer is less likely to be distorted, and can be wound densely. Even when the charge / discharge cycle is repeated, the negative electrode mixture layer is difficult to expand, and a nonaqueous electrolyte secondary battery excellent in charge / discharge characteristics is obtained.

  In addition, according to the nonaqueous electrolyte secondary battery of the present invention, when the degree of etherification of CMC is increased, the viscosity of the negative electrode mixture layer obtained is decreased (softened), and the degree of etherification of CMC is reduced. Since the hardness of the negative electrode mixture layer obtained by increasing the viscosity increases (hardens), the negative electrode mixture layer having a desired hardness can be obtained by appropriately selecting the degree of etherification of CMC. Will be able to. In addition, various types of CMC having such a different degree of etherification are commercially available, and can be appropriately selected and employed.

  Further, according to the non-aqueous electrolyte secondary battery of the present invention, when the wound electrode body is formed, each negative electrode mixture layer is hardly distorted and can be wound tightly. Even when the flat wound electrode body is crushed after being wound into a cylindrical shape, there is little gap, and there is little residual strain, so the negative electrode mixture layer is less likely to expand even after repeated charge / discharge cycles. Thus, a flat non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics can be obtained.

  In addition, according to the nonaqueous electrolyte secondary battery of the present invention, the carbonaceous material such as graphite and amorphous carbon as the negative electrode active material has a discharge potential comparable to that of lithium metal or lithium alloy, but dendrite. Is known to have excellent properties such as high safety, excellent initial efficiency, good potential flatness, and high density. However, when such a carbonaceous material is used as the negative electrode active material, the effect of the present invention is remarkably exhibited.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples illustrate non-aqueous electrolyte secondary batteries for embodying the technical idea of the present invention, and are not intended to specify the present invention to these examples. The present invention can be equally applied to various modifications without departing from the technical idea shown in the claims.

  First, a method for producing a positive electrode common to Examples and Comparative Examples, a method for preparing negative electrode mixtures A and B, a method for measuring negative electrode plate strength, a method for preparing a non-aqueous electrolyte, a method for measuring charge / discharge characteristics, and a battery thickness A measurement method will be described.

[Production of positive electrode]
Lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material uses lithium carbonate (Li ₂ CO ₃ ) as a lithium source as a starting material, and tricobalt tetroxide (Co ₃ O ₄ ) as a cobalt source. Were weighed and mixed in a predetermined amount, and then calcined at 850 ° C. for 24 hours in an air atmosphere to obtain lithium cobalt oxide. This was ground to an average particle size of 14 μm with a mortar to obtain a positive electrode active material.

  95 parts by mass of the positive electrode active material thus produced and 5 parts by mass of graphite powder as a conductive agent were mixed. A positive electrode active material slurry was prepared by dispersing 95% by mass of this mixture and 5 parts by mass of polyvinylidene fluoride (PVdF) powder as a binder in an N-methylpyrrolidone (NMP) solution. Next, it apply | coated to both surfaces of the positive electrode core body which consists of an aluminum foil with a thickness of 20 micrometers by the doctor blade method. This positive electrode plate was passed through a drier to remove NMP that was necessary when the slurry was produced, and then rolled to a thickness of 125 μm using a roll press to produce a positive electrode plate.

[Preparation of negative electrode mixture A]
96 parts by mass of artificial graphite as a negative electrode active material, 2 parts by mass of CMC having a degree of etherification of 1.20 as a first thickener, and 2 parts by mass of styrene butadiene rubber (SBR) latex are dispersed in water. Thus, a negative electrode active material slurry was prepared. This was designated as negative electrode mixture A.

[Preparation of negative electrode mixture B]
96 parts by mass of artificial graphite as a negative electrode active material, 2 parts by mass of CMC having a degree of etherification of 0.65 as a second thickener, and 2 parts by mass of styrene butadiene rubber (SBR) latex are dispersed in water. Thus, a negative electrode active material slurry was prepared. This was designated as negative electrode mixture B.

[Measurement of hardness F _A and F _B of electrode plate]
Hardness F _B of the negative electrode plate with a hardness F _A and the negative electrode mixture B of the negative electrode plate using a negative electrode mixture A were measured as follows. First, the negative electrode mixture A or the negative electrode mixture B was applied to both sides of a negative electrode core made of a copper foil having a thickness of 8 μm with a uniform thickness. This negative electrode plate was passed through a dryer to remove moisture, and then rolled using a roll press so that the packing density was 1.60 / mL. A negative electrode sample b composed of the agent B was obtained. These negative electrode samples a and b were cut out to have a size of 2 cm × 5 cm, respectively, and subjected to strength measurement.

As shown in FIG. 2, the strength of the negative electrode plate is such that each negative electrode sample a or b is arched against a plate having a width of 3 cm, and the negative electrode sample a or b has a height of 25 mm × 6 mm × height from the upper center. The force applied when a 60 mm SUS test plate was propelled at a speed of 20 mm / min was measured with a load cell, and the numerical values displayed first were obtained as the hardnesses F _A and F _B of the respective negative electrode samples a and b. It was. The results are shown in Table 1.

[Measurement of battery thickness]
The battery thickness was determined by measuring the battery thickness with a micrometer after repeating 300 cycles of charge and discharge.

[Preparation of non-aqueous electrolyte]
A solution in which LiPF ₆ as an electrolyte salt is dissolved at a rate of 1.0 mol / L in a non-aqueous solvent in which EC, EMC, and DEC are mixed at a volume ratio of 20:50:30 (1 atm, converted to 25 ° C.) Was a non-aqueous electrolyte.

[Measurement of charge / discharge characteristics]
At 25 ° C., the battery is charged at a constant current of 850 mA until the battery voltage reaches 4.20 V, then charged at a constant voltage of 4.20 V until the current reaches 42.5 mA, and then at a constant current of 850 mA at 25 ° C. The battery was discharged until the battery voltage reached 2.75V. The discharge capacity at this time was determined as the discharge capacity of the first cycle. Next, the above charge / discharge cycle was repeated 300 times, and the discharge capacity at the 300th time was determined as the discharge capacity at the 300th cycle. And the capacity | capacitance maintenance factor was calculated | required with the following formulas.
Capacity maintenance rate (%)
= (Discharge capacity at 300th cycle / Discharge capacity at 1st cycle) × 100

[Production of negative electrode]
When preparing a wound electrode body, a negative electrode core made of copper foil having a thickness of 8 μm is coated with the negative electrode mixture A on the inner surface and the negative electrode mixture B on the outer surface with a uniform thickness. Applied. The negative electrode plate was passed through a dryer to remove moisture, and then rolled using a roll press so that the packing density was 1.60 / mL. The charging capacity ratio between the positive electrode and the negative electrode was such that (negative electrode charging capacity) / (positive electrode charging capacity) = 1.1 when the battery voltage was 4.2V.

[Production of wound electrode body]
The flat electrode body was completed by winding the positive electrode, the negative electrode, and a separator made of a microporous film made of an olefin resin with a winder, attaching an insulating winding tape, and pressing.

[Production of battery]
The flat wound electrode body is inserted into a rectangular battery outer can as shown in FIG. 1, and a sealing body is fitted into the opening of the rectangular battery outer can and laser welded. A predetermined amount of electrolyte was injected, and the electrolyte solution injection hole was sealed to produce the nonaqueous electrolyte secondary battery of the example. The size of the prismatic nonaqueous electrolyte secondary battery according to the obtained example is 50 mm high, 34 mm wide, and 46 mm thick.

  The charge / discharge test of 300 cycles as described above was performed on the non-aqueous electrolyte secondary battery of the example manufactured in this way, and the capacity retention rate at the 300th cycle was obtained and the thickness of the battery was measured. The results are shown in Table 1.

[Comparative Examples 1-3]
When preparing a wound electrode body, a negative electrode core made of copper foil having a thickness of 8 μm is coated with the negative electrode mixture B on the inner surface and the negative electrode mixture A on the outer surface with a uniform thickness. A nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the coating was performed. Similarly, the negative electrode mixture B is formed on the inner surface of the negative electrode core made of copper foil having a thickness of 8 μm, and the negative electrode mixture B is formed on the outer surface with a uniform thickness. A nonaqueous electrolyte secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the coating was performed in this manner. Similarly, the negative electrode mixture A is formed on the inner surface of the negative electrode core made of copper foil having a thickness of 8 μm, and the negative electrode mixture A is uniformly formed on the outer surface. A nonaqueous electrolyte secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the coating was performed in the same manner. The 300 cycles of charge / discharge tests as described above were performed on each of the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 3 thus obtained, and the capacity retention rate at the 300th cycle was determined. The results are shown in Table 2 together with the results of Example 1.

  From the results shown in Table 2, the following can be understood. That is, when the negative electrode mixture applied to both surfaces as in Comparative Example 2 is a negative electrode mixture B containing CMC having a degree of etherification of 0.65, the battery thickness is that of Example 1 when charge and discharge are repeated. Compared to this, it is recognized that the wound electrode body is distorted, and as a result, the cycle characteristics are deteriorated. Moreover, when the negative electrode mixture applied to both surfaces as in Comparative Example 3 is a negative electrode mixture A containing CMC having a degree of etherification of 1.25, the battery thickness is more than that of Comparative Example 2 when charging and discharging are repeated. Further, since the increase is further increased, the wound electrode body is greatly distorted, and as a result, it is recognized that the cycle characteristics are particularly deteriorated.

On the other hand, referring to the description in Table 1 above, the negative electrode plate of Comparative Example 2 corresponds to the negative electrode sample b, the negative electrode plate of Comparative Example 3 corresponds to the negative electrode sample a, and has a relationship of F _A <F _B. . Therefore, when the hardness of the negative electrode mixture layer is reduced (softened), the expansion is greatly caused by repetition of the charge / discharge cycle as compared with the hardened material (hard), which increases the battery thickness and the capacity retention rate. It can be seen that this has led to a decline.

  Further, the negative electrode plate of Example 1 and the negative electrode plate of Comparative Example 1 are those in which the arrangement relationship of the negative electrode mixture layers on both sides of the core is opposite to each other. The capacity of Example 1 was maintained as negative electrode mixture B containing CMC having a degree of etherification of 0.65 and negative electrode mixture A containing CMC having a degree of etherification of 1.20. The rate is large and the battery thickness is also small. From this, by having a certain degree of hardness as the negative electrode mixture layer on the outer side at the time of forming the wound electrode body, swelling due to repeated charge / discharge cycles is suppressed, and the wound electrode body is distorted. In addition, since the inner side when forming the wound electrode body is made softer than the outer side, the force applied to the wound electrode body when forming the wound electrode body can be reduced. It is recognized that the load on the separator or the like can be suppressed and the cycle characteristics are improved.

  In Example 1, CMCs having a degree of etherification of 0.65 and 1.20 were used. However, the CMC having a lower degree of etherification is not limited to this. If CMC with a higher degree of etherification is used on the inner side, the same effect can be obtained. That is, a commercially available CMC having a degree of etherification of about 0.4 to 1.6 is readily available, but a CMC having a smaller degree of etherification has a degree of etherification of about 0.4 to 0.8. CMC having a higher degree of etherification may be appropriately selected from about 0.9 to 1.6.

It is a perspective view which cut | disconnects and shows the conventional square nonaqueous electrolyte secondary battery to the vertical direction. It is a figure which shows the intensity | strength measuring method of a negative electrode plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery 11 Positive electrode plate 12 Negative electrode plate 13 Separator 14 (Flat shape) Winding electrode body 15 (Square shape) Battery outer can 16 Sealing plate 17 Insulator 18 Negative electrode terminal 19 Current collector 20 Insulating spacer 21 Electrolyte injection hole

Claims (4)

A negative electrode plate having a negative electrode mixture layer containing carboxymethyl cellulose provided on both sides of the negative electrode core; and a positive electrode plate having a positive electrode mixture layer provided on both sides of the positive electrode core; In the non-aqueous electrolyte secondary battery provided with a wound electrode body in which the positive electrode plate is wound through a separator,
The negative electrode mixture layers provided on both side surfaces of the negative electrode core have the same composition and the same thickness except that the physical properties of carboxymethyl cellulose are different from each other.
A negative electrode mixture applied to the inner surface of the negative electrode core is A, a negative electrode mixture applied to the outer surface is B, and the negative electrode plate when the negative electrode plate is prepared using A and B independently. _A non-aqueous electrolyte secondary battery using carboxymethyl cellulose having such a property that F _A <F _B when the hardness is F _A and F _B , respectively.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the degree of etherification of carboxymethyl cellulose in the negative electrode mixture A is greater than the degree of etherification of carboxymethyl cellulose in the negative electrode mixture B. 3.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the wound electrode body has a flat shape.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material in the negative electrode mixture is made of a carbonaceous material.

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