JP2009081067A - Non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery which has an excellent adhesion of a negative electrode active material mixture layer to a negative electrode core and is superior in discharge load characteristics and capacity maintenance rate. <P>SOLUTION: The non-aqueous electrolyte secondary battery 10 is provided with a wound electrode body which has a negative electrode plate 12 in which a negative electrode active material mixture layer is provided on a surface of a negative electrode core and a positive electrode plate 11 in which a positive electrode mixture layer is provided on the surface of a positive electrode core, and the negative electrode plate 12 and the positive electrode plate 11 are respectively wound through a separator. The negative electrode active material mixture layer is provided with a first negative electrode active material mixture layer which uses NH<SB>4</SB>of CMC as a thickener formed on the surface of the negative electrode core and a second negative electrode active material mixture layer which uses at least one kind selected from CMC-Na and CMC-Li as a thickener formed on the surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte secondary battery in which the adhesion of a negative electrode active material mixture layer to a negative electrode core is good, and the discharge load characteristics and capacity retention ratio are excellent. More specifically, the present invention uses a carbon material such as graphite as the negative electrode active material, and uses a salt of carboxymethyl cellulose (CMC) as a thickener, and has good adhesion of the negative electrode active material mixture to the negative electrode core, The present invention relates to a non-aqueous electrolyte secondary battery excellent in discharge load characteristics and capacity retention rate.

  Non-aqueous electrolyte secondary typified by lithium-ion secondary battery with high energy density and high capacity as a driving power source for portable electronic devices such as mobile phones, portable personal computers, portable music players, etc. Batteries are widely used. Among these, nonaqueous electrolyte secondary batteries using graphite particles as the negative electrode active material are widely used because of their high safety and high capacity.

  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 nonaqueous electrolyte secondary battery is often used. Such a rectangular non-aqueous electrolyte secondary battery is generally manufactured as follows.

  That is, on both sides of a negative electrode plate made of a negative electrode active material mixture containing a negative electrode active material on both sides of a negative electrode core made of an elongated sheet-like copper foil and the like, and on both sides of a positive electrode core made of an elongated sheet-like aluminum foil, etc. 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, and a cylindrical winding core with the negative electrode plate and the positive electrode plate insulated from each other by the separator Are wound in a spiral shape to produce a cylindrical wound electrode body. 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. The 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. The nonaqueous 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 is in direct contact with the inner surface of the battery outer can 15 that also serves as the 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 2001-273931 A JP-A-8-130035 Japanese Patent Laid-Open No. 2005-100773 JP 2005-228620 A

  These non-aqueous electrolyte secondary batteries can achieve higher capacity and higher energy density than other types of batteries, but the higher performance and smaller size of portable electronic devices as described above. Furthermore, due to the demand for weight reduction, further increase in capacity is desired. As a method for increasing the capacity of the non-aqueous electrolyte secondary battery, it is conceivable to increase the mass of the active material mixture and reduce the thickness of the core, but as a side effect, the coating thickness of the active material mixture has increased. Deterioration of winding ability of the electrode plate and expansion of the electrode plate due to repeated charge / discharge are likely to occur, the active material mixture is peeled off from the core during the electrode preparation process, and the discharge load in terms of battery characteristics There has been a problem that the capacity retention rate is deteriorated due to the deterioration of the characteristics. Such swelling of the electrode body due to repeated charge and discharge is particularly significant 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 active material mixture having the same thickness is applied to both surfaces of the negative electrode core. Therefore, 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 the usage amount of the positive electrode active material and the negative electrode active material. The theoretical battery capacity obtained from

The inventors have improved the adhesion of the negative electrode active material mixture layer to the core and the discharge load while maintaining the same thickness of each of the negative electrode active material mixture layers provided on both sides of the negative electrode core. Based on the viewpoint that the density of the negative electrode can be increased if both characteristics are improved, the inventors have conducted extensive research. As a result, the inventor found that the negative electrode active material mixture using an ammonium salt of CMC (CMC-NH ₄ ) as a thickener has good adhesion to the negative electrode core, and CMC as a thickener. The negative electrode active material mixture layer using the sodium salt of CMC-Na or the lithium salt of CMC (CMC-Li) was found to provide a negative electrode with excellent load characteristics. A first negative electrode active material mixture layer using CMC-NH ₄ as a thickener is formed, and at least one selected from CMC-Na and CMC-Li is used as a thickener on the surface. Since the negative electrode active material mixture layer 2 was formed, it was found that the adhesion of the negative electrode active material mixture layer to the core and the discharge load characteristics could be improved at the same time, and the above problems were solved. is there.

  That is, the present invention provides a nonaqueous electrolyte secondary battery using CMC salt as a thickener, having good adhesion of the negative electrode active material mixture to the negative electrode core, and excellent discharge load characteristics and capacity retention. The purpose is to provide.

In addition, Patent Document 3 discloses a non-aqueous electrolyte secondary battery in which when CMC-NH ₄ is used as a binder for the negative electrode active material mixture, the amount of heat generated during overcharging is reduced as compared with the case where CMC-Na is used. In addition, in Patent Document 4, a non-aqueous electrolyte secondary battery having a low-temperature discharge capacity is greater when CMC-Na is used as a binder of the negative electrode active material mixture than when CMC-NH ₄ is used. Are respectively shown to be obtained. However, in Patent Documents 1 and 2, the adhesion between the negative electrode active material mixture layer and the negative electrode core when a CMC salt is used as one component of the negative electrode active material mixture and the obtained non-aqueous solution are disclosed. There is no description suggesting the discharge load characteristics of the electrolyte secondary battery.

In order to achieve the above object, the nonaqueous electrolyte secondary battery of the present invention includes a negative electrode plate having a negative electrode active material mixture layer provided on the surface of the negative electrode core, and a positive electrode mixture layer provided on the surface of the positive electrode core. A non-aqueous electrolyte secondary battery comprising a wound electrode body in which the negative electrode plate and the positive electrode plate are wound through a separator, respectively, the negative electrode active material mixture layer includes: From the first negative electrode active material mixture layer using CMC-NH ₄ as a thickener formed on the surface of the negative electrode core, and CMC-Na and CMC-Li as thickeners formed on the surface thereof. A second negative electrode active material mixture layer using at least one selected type is provided.

A nonaqueous electrolyte secondary battery including a negative electrode using only a negative electrode active material mixture layer using CMC-NH ₄ as a thickener has good adhesion between the negative electrode core and the negative electrode active material mixture layer. Thus, the capacity retention rate is excellent, but the discharge load characteristics are inferior. On the other hand, the nonaqueous electrolyte secondary battery including the negative electrode using only the negative electrode active material mixture layer using CMC-Na or CMC-Li as the thickener is excellent in capacity retention rate and discharge load characteristics. The adhesion between the negative electrode core and the negative electrode active material mixture layer is poor. Further, the nonaqueous electrolyte secondary battery including a negative electrode using a mixture of CMC-NH ₄ and CMC-Na as a thickener is excellent in capacity retention, but has a discharge load characteristic, a negative electrode core, and a negative electrode active material. Adhesion between the mixture layers is poor.

According to the non-aqueous electrolyte secondary battery of the present invention, the first negative electrode active material mixture layer using CMC-NH ₄ as a thickener as the negative electrode active material mixture layer formed on the surface of the negative electrode core. And a second negative electrode active material mixture layer using at least one selected from CMC-Na and CMC-Li as a thickener formed on the surface thereof. The second negative electrode using at least one selected from CMC-Na and CMC-Li as the second layer thickener after securing the adhesion between the negative electrode core and the material mixture layer The active material mixture layer can ensure discharge load characteristics and capacity retention. Therefore, the nonaqueous electrolyte secondary battery of the present invention is a nonaqueous electrolyte secondary battery that has good adhesion of the negative electrode active material mixture to the negative electrode core and is excellent in discharge load characteristics and capacity retention.

  The CMC salt is obtained when the viscosity of the negative electrode active material mixture layer is reduced when the degree of etherification of CMC is large, and the viscosity is increased when the degree of etherification of CMC is low. Further, the hardness of the negative electrode active material mixture layer becomes hard. Therefore, in the present invention, a negative electrode active material mixture layer having a desired hardness can be obtained by appropriately selecting the degree of etherification of CMC. In addition, various types of CMC having such a different degree of etherification are commercially available, and can be appropriately selected and employed.

  In the non-aqueous electrolyte secondary battery of the present invention, the proportion of the first negative electrode active material mixture layer is 60 mass of the total of the first and second negative electrode active material mixture layers. % Or less is preferable.

  When the proportion of the first negative electrode active material mixture layer exceeds 60% by mass of the total of the first and second negative electrode active material mixture layers, the first negative electrode active material mixture layer The characteristics of the agent layer are strongly exhibited, and the adhesion and capacity retention rate between the negative electrode core and the negative electrode active material mixture layer are excellent, but the discharge load characteristics are inferior. Note that, even if the proportion of the first negative electrode active material mixture layer is small, the adhesion between the negative electrode core and the negative electrode active material mixture layer can be ensured, but the first layer and the first layer Adequate adhesion between the negative electrode active material mixture layer and the negative electrode core can be secured if the total amount of the second negative electrode active material mixture layer is 10% by mass or more.

  In the nonaqueous electrolyte secondary battery of the present invention, the negative electrode active material in the negative electrode active material mixture layer is preferably made of a carbonaceous material.

  The carbon material as the negative electrode active material has excellent properties such as high safety because dendrites do not grow, excellent initial efficiency, good potential flatness, and high density. However, it has the property of being easily peeled off from the negative electrode core in the electrode manufacturing process. Therefore, when a carbon material is used as the negative electrode active material, the effects of the present invention are remarkably exhibited. The carbon material is preferably a graphite material such as artificial graphite or natural graphite that is widely used for non-aqueous electrolyte secondary batteries.

  In the nonaqueous electrolyte secondary battery of the present invention, the wound electrode body is preferably flat.

  Since the flat wound electrode body has a portion with a smaller radius of curvature than the cylindrical wound electrode body, the adhesion between the negative electrode core body and the negative electrode active material mixture layer is reduced during production. Decline is likely to occur. However, according to the nonaqueous electrolyte secondary battery of the present invention, the positive electrode, the separator, and the negative electrode are wound into a cylindrical or elliptical cylinder and then crushed to form a flat wound electrode body. It is difficult for the adhesiveness between the negative electrode core body to be lowered. For this reason, the above-described effect of the present invention is remarkably exhibited by using a flat non-aqueous electrolyte secondary battery.

In the nonaqueous electrolyte secondary battery of the present invention, as the positive electrode active material, Li _x MO ₂ capable of reversibly occluding and releasing the lithium ions described above (where M is Co, Ni, or Mn). A lithium transition metal composite oxide represented by at least one), that is, 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), or LiFePO ₄ can be used singly 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.

  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.

[Examples 1, 3 and 5]
The nonaqueous electrolyte secondary batteries of Examples 1, 3, and 5 were produced as follows.

[Production of positive electrode]
Lithium cobaltate (LiCoO 2) ₉₅ parts by mass as a positive electrode active material was mixed with graphite 5 parts by weight as a conductive agent. 95 parts by mass of this mixture and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode active material slurry. Next, this positive electrode active material slurry was applied to both surfaces of a positive electrode core made of an aluminum foil having a thickness of 20 μm so as to have a uniform thickness. The electrode plate was passed through a dryer to remove the organic solvent, and then rolled to a thickness of 125 μm using a roll press to produce a positive electrode plate.

[Preparation of first layer negative electrode active material mixture A]
A slurry was prepared by dispersing 96 parts by mass of artificial graphite as a negative electrode active material, 2 parts by mass of CMC-NH ₄ as a thickener, and 2 parts by mass of styrene butadiene rubber (SBR) in water. This was designated as a negative electrode active material mixture A.

[Preparation of Second Layer Negative Electrode Active Material Mixture B1]
A slurry was prepared by dispersing 96 parts by mass of artificial graphite as a negative electrode active material, 2 parts by mass of CMC-Na as a thickener, and 2 parts by mass of SBR in water. This was designated as a negative electrode active material mixture B1.

[Production of negative electrode]
After applying the slurry of the negative electrode active material mixture A with a uniform thickness on both sides of the negative electrode core made of a copper foil having a thickness of 8 μm, the slurry is passed through a dryer to remove moisture, and the first layer negative electrode active material mixture An agent layer was formed. After applying the slurry of negative electrode active material mixture B1 to both surfaces of the electrode plate on which the first negative electrode active material mixture layer is formed so as to have a uniform thickness, moisture is removed by passing it through a dryer. Thus, a second negative electrode active material mixture layer was formed. Next, the electrode plate on which the first and second negative electrode active material mixture layers were formed on both sides was rolled using a roll press so that the packing density was 1.66 g / ml. The coating amount of the negative electrode active material was set such that the negative electrode charge capacity / the positive electrode charge capacity was 1.1 when the charge capacity ratio between the positive electrode and the negative electrode was 4.2 V. Here, in Example 1, the mass ratio of the first layer to the second layer is 80:20, in Example 3, the mass ratio of the first layer to the second layer is 40:60, and in Example 5, the first layer to the second layer is The two layers were applied so that the mass ratio was 35:65, and negative plates of Examples 1, 3 and 5 were produced.

[Preparation of flat wound electrode body]
The positive electrode, negative electrode, and microporous membrane separator made of olefin resin prepared as described above are wound by a winder, and an insulating anti-winding tape is attached to the end of the winding and pressed to make it flat. A spirally wound electrode body was completed.

[Adjustment of non-aqueous electrolyte]
LiPF ₆ as an electrolyte salt was added to 1.0 M (mol / mol) in a non-aqueous solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 20:50:30 (1 atm, converted to 25 ° C.). The solution dissolved at a ratio of 1 liter) was used as a nonaqueous electrolyte.

[Production of batteries of Examples 1, 3 and 5]
The flat wound electrode body produced as described above and the non-aqueous electrolyte are inserted into a rectangular outer can having the same configuration as that of the conventional example described above, and a sealing plate is aligned with the opening of the outer can. The nonaqueous electrolyte secondary batteries according to Examples 1, 3, and 5 having a height of 45 mm, a width of 54 mm, and a thickness of 5.0 mm were manufactured by laser welding.

[Examples 2, 4 and 6]
The nonaqueous electrolyte secondary batteries of Examples 2, 4 and 6 were produced as follows. That is, as the positive electrode, the negative electrode active material mixture A of the first layer, and the non-aqueous electrolyte, those having the same configurations as those of Examples 1, 3, and 5 were used as they were. Further, as the negative electrode active material mixture B2 of the second layer, 96 parts by mass of artificial graphite as a negative electrode active material, 2 parts by mass of CMC-Li as a thickener, and 2 parts by mass of SBR are dispersed in water. A slurry was prepared. This was designated as a negative electrode active material mixture B2.

  Next, a slurry of the negative electrode active material mixture A was applied to both surfaces of a negative electrode core made of a copper foil having a thickness of 8 μm with a uniform thickness, and then passed through a drier to remove moisture to remove the first layer negative electrode An active material mixture layer was formed. After applying the negative electrode active material mixture B2 slurry to both surfaces of the electrode plate on which the first negative electrode active material mixture layer is formed so as to have a uniform thickness, the moisture is removed by passing through a dryer. Thus, a second negative electrode active material mixture layer was formed. Next, the electrode plate on which the first and second negative electrode active material mixture layers were formed on both sides was rolled using a roll press so that the packing density was 1.66 g / ml. The coating amount of the negative electrode active material was set such that the negative electrode charge capacity / the positive electrode charge capacity was 1.1 when the charge capacity ratio between the positive electrode and the negative electrode was 4.2 V. Here, in Example 2, the mass ratio of the first layer to the second layer is 80:20, in Example 4, the mass ratio of the first layer to the second layer is 40:60, and in Example 6, the first layer to the second layer is The negative electrode plates of Examples 2, 4 and 6 were prepared by coating so that the mass ratio of the two layers was 35:65.

  Using the negative electrode plates of Examples 2, 4 and 6 produced as described above, a flat wound electrode body was produced in the same manner as in Example 1, and then the conventional example described above together with the nonaqueous electrolyte. Example 2, 4 and 6 having a height of 45 mm, a width of 54 mm, and a thickness of 5.0 mm are inserted into a rectangular outer can having the same structure as that of No. 1, the sealing plate is aligned with the opening of the outer can, and laser welding is performed. Such a non-aqueous electrolyte secondary battery was produced.

[Comparative Examples 1-4]
As the negative electrode active material mixture for preparing the negative electrode plate of Comparative Example 2, only the negative electrode active material mixture B1 used in Example 1 was used as the negative electrode active material mixture for preparing the negative electrode plate. Only the negative electrode active material mixture B2 used in Example 2 was used, and only the negative electrode active material mixture A used in Example 1 was used as the negative electrode active material mixture for preparing the negative electrode plate of Comparative Example 3. . The negative electrode active material material mixture C is artificial graphite 96 parts by weight of the negative electrode active material, 1 part by weight of CMC-NH ₄ as a thickener, 1 mass CMC-Na for producing a negative electrode plate of Comparative Example 4 Part of the negative electrode active material mixture prepared by dispersing SBR in water

  And after apply | coating the slurry of the above-mentioned negative electrode active material mixture B1, B2, A, and C with the uniform thickness each separately on both surfaces of the negative electrode core body which consists of copper foil of thickness 8 micrometers, it passes in a drier and is water | moisture content. Was then rolled using a roll press so that the packing density was 1.66 g / ml, and negative electrode plates of Comparative Examples 1 to 4 were produced. The amount of the negative electrode active material applied here was such that the negative electrode charge capacity / the positive electrode charge capacity was 1.1 when the charge capacity ratio between the positive electrode and the negative electrode was 4.2 V.

  Using the negative electrode plates of Comparative Examples 1 to 4 produced as described above, a flat wound electrode body was produced in the same manner as in Example 1, and then the conventional example described above together with the nonaqueous electrolyte. Non-water according to Comparative Examples 1 to 4 having a height of 45 mm, a width of 54 mm, and a thickness of 5.0 mm by being inserted into a rectangular outer can having the same structure as described above, a sealing plate aligned with the opening of the outer can, and laser welding. An electrolyte secondary battery was produced.

[Measurement of peel strength]
The peel strength of the negative electrode plate was measured by sticking an adhesive tape to the surface of the negative electrode active material mixture layer and then measuring the strength when peeling the adhesive tape. The measured values of the peel strengths of the negative electrode plates of Examples 1 to 6 and Comparative Examples 1 to 4 are the measurement results of Comparative Example 3 consisting only of the negative electrode active material mixture layer A using CMC-NH ₄ as a thickener. Was normalized to 100 and expressed as a relative value. The results are summarized in Table 1.

[Measurement of discharge load characteristics]
About each battery of Examples 1-6 and Comparative Examples 1-4, it charges until a battery voltage will be 4.20V with a constant current of 850 mA (1 It) at 25 degreeC, and an electric current will be carried out with a constant voltage of 4.20V after that. The battery was charged to 42.5 mA, and further discharged at a constant current of 850 mA until the battery voltage reached 2.75V. The discharge capacity at this time was determined as a 1 It discharge capacity. Next, at 25 ° C., the battery is charged with a constant current of 850 mA until the battery voltage reaches 4.20 V, then charged with a constant voltage of 4.20 V until the current reaches 42.5 mA, and further a constant current of 2550 mA (3 It). The battery was discharged until the battery voltage reached 2.75V. The discharge capacity at this time was 3 It discharge capacity. And the discharge load characteristic was calculated | required based on the following formula. The results are summarized in Table 1.
Discharge load characteristic (%) = (3 It discharge capacity / 1 It discharge capacity) × 100

[Measurement of capacity maintenance ratio]
About each battery of Examples 1-6 and Comparative Examples 1-4, it charges until a battery voltage will be 4.20V with a constant current of 850 mA at 25 degreeC, and electric current will be 42.5 mA with a constant voltage of 4.20V after that. Then, the battery was discharged at 25 ° C. with a constant current of 850 mA 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

From the results shown in Table 1, the following can be understood. That is, the peel strengths of the negative electrode plates of Examples 1 to 6 are all 100% or more of the peel strength of Comparative Example 3, but the batteries of Comparative Examples 1, 2, and 4 are larger than the peel strength of Comparative Example 3. Inferior. The negative electrode plate of Comparative Example 3 is composed only of the negative electrode active material mixture layer A using CMC-NH ₄ as a thickener, but each of the negative electrode plates of Examples 1 to 6 is a lower layer on the negative electrode core. The first layer is that using CMC-NH ₄ as a thickener. Therefore, even if the second layer, which is the upper layer on the negative electrode core, contains at least one selected from CMC-Na and CMC-Li, at least the negative electrode active material mixture on the negative electrode core side is a thickener. It can be seen that a negative electrode plate with high peel strength can be obtained if CMC-NH ₄ is contained.

Moreover, although the battery of the comparative example 3 is the most inferior in the measurement result of the discharge load characteristic, the batteries of the comparative examples 1, 2, and 3 have the discharge load characteristic that is equivalent to the batteries of the first to sixth examples. I understand that. However, when these results are analyzed in more detail, the batteries of Examples 5 and 6 in which the proportion of the first layer of the lower layer using CMC-NH ₄ as the thickener is 65% by mass have a discharge load characteristic. Although it is better than that of Comparative Example 3, it is inferior to those of Examples 1 to 4 in which the proportion of the first layer is 60% by mass or less, and as a thickener, other than CMC-NH ₄ It is inferior to the thing of the comparative example 1 and the comparative example 2 containing a thing. This is probably because CMC-NH ₄ is inferior to CMC-Na or CMC-Li in the absorption of non-aqueous electrolyte. Therefore, if there are too many layers containing CMC-NH ₄ , It seems that the load characteristics were lowered due to the decrease in non-aqueous electrolyte.

Then, if the proportion of the negative electrode active material mixture layer containing CMC-NH ₄ as a thickener is too large, the discharge load characteristics are adversely affected. Therefore, the first layer using CMC-NH ₄ as the thickener is used. It can be seen that the occupation ratio is preferably 60% by mass or less. In addition, since the adhesiveness between the negative electrode core and the negative electrode active material mixture layer can be ensured even if the proportion of the first negative electrode active material mixture layer is small, the first layer and the first layer If it is 10 mass% or more of the total of the second negative electrode active material mixture layer, good discharge load characteristics can be achieved while ensuring the adhesion between the negative electrode active material mixture layer and the negative electrode core.

Moreover, although the measurement result of a capacity | capacitance maintenance rate is very favorable with 78% or more in Examples 1-4, the result of 72-74% in Examples 5 and 6 and Comparative Examples 1-4. It has become. This is because the difference in the composition of the thickener does not affect the capacity maintenance rate so much, but the first layer of the lower layer includes a negative electrode active material mixture layer containing CMC-NH ₄ salt as a thickener. This indicates that a very good capacity retention rate can be achieved when the proportion of the first layer is 60% by mass or less.

  Therefore, comprehensively judging the results shown in Table 1, it can be seen that the batteries of Comparative Examples 1 and 2 have good discharge load characteristics but low adhesion of the negative electrode active material mixture layer. Moreover, although the battery of the comparative example 3 has favorable adhesiveness of a negative electrode active material mixture layer, it turns out that the discharge load characteristic is low. Furthermore, the battery of Comparative Example 4 does not reach the batteries of Examples 1 to 6 in terms of discharge load characteristics and adhesion. In addition, since the substantially same effect is show | played in the case where a thickener is CMC-Na and the case of CMC-Li, even if CMC-Na and CMC-Li are mixed as a thickener. It is clear that the same effects as those obtained when CMC-Na or CMC-Li is used alone are produced.

Therefore, if good results are obtained with respect to all of the adhesion, discharge characteristics, and capacity retention rate of the negative electrode active material mixture layer, the first negative electrode active material mixture layer is thickened. A material containing CMC-NH ₄ salt is used as the agent, and a material containing at least one selected from CMC-Na and CMC-Li is used as the negative electrode active material mixture in the second layer. The proportion of the negative electrode active material mixture layer may be 5% by mass to 10% by mass and 60% by mass or less of the total of the first and second negative electrode active material mixture layers. Recognize.

It is a perspective view which cut | disconnects and shows the conventional square nonaqueous electrolyte secondary battery to the vertical direction.

Explanation of symbols

10: Nonaqueous electrolyte secondary battery 11: Positive electrode plate 12: Negative electrode plate 13: Separator 14: Flat wound electrode body 15: Rectangular battery outer can 16: Sealing plate 17: Insulator 18: Negative electrode terminal 19: Collection Electrode 20: Insulating spacer 21: Electrolyte injection hole

Claims (4)

A negative electrode plate in which a negative electrode active material mixture layer is provided on the surface of the negative electrode core; and a positive electrode plate in which a positive electrode mixture layer is provided on the surface of the positive electrode core. In a non-aqueous electrolyte secondary battery including a wound electrode body wound through a separator,
The negative electrode active material mixture layer includes a first negative electrode active material mixture layer using an ammonium salt of carboxymethyl cellulose as a thickener formed on the surface of the negative electrode core, and a thickener formed on the surface thereof. A non-aqueous electrolyte secondary battery comprising a second negative electrode active material mixture layer using at least one selected from a sodium salt and a lithium salt of carboxymethyl cellulose as an agent.   The proportion of the first negative electrode active material mixture layer is 10% by mass or more and 60% by mass or less of the total of the first and second negative electrode active material mixture layers. The nonaqueous electrolyte secondary battery according to claim 1.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material in the negative electrode active material mixture layer is made of a carbonaceous material.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the wound electrode body is a flat shape.

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