JP5181607B2 - Method for producing electrode plate for negative electrode of non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a negative electrode plate and a non-aqueous electrolyte secondary battery used in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery has a high energy density and a high voltage, and has a memory effect during charging / discharging (when the battery is charged before it is completely discharged, Since there is no phenomenon in which the capacity decreases, it is used in various fields such as portable devices and large devices.
A typical nonaqueous electrolyte secondary battery contains a positive electrode plate and a negative electrode plate with an active material layer provided on a current collector, and a separator that is interposed between the positive and negative electrode plates and electrically cuts off both electrodes. In addition, the inner space of the container is filled with an organic electrolyte and sealed.

In recent years, development of large-capacity secondary batteries has been progressing especially for fields that require high output characteristics such as electric vehicles, hybrid vehicles, and power tools.
However, a battery with high impedance cannot make full use of its large capacity during high output charge / discharge. Therefore, a method is used in which the electrode active material layer has a large thin film area to reduce the battery impedance.
In addition, since non-aqueous electrolytes used in lithium ion secondary batteries generally have higher resistance than aqueous electrolytes, they are thin and wide electrodes compared to other batteries such as lead-acid batteries from the beginning of development. A form has been developed in which the distance between the positive electrode and the negative electrode is shortened.

The positive electrode plate and the negative electrode plate of the non-aqueous electrolyte secondary battery are mixed with a chargeable / dischargeable active material, a thickener, a binder, and a conductive agent, if necessary. By preparing a coating composition, applying the coating composition on a current collector such as a metal foil to form a coating film, drying it, and firing it as necessary to produce an electrode active material layer can get.
Conventionally, a fluorine-based resin, a polyimide resin, or the like is used as a binder for the electrode active material layer. When these binders are used, toluene, methyl ethyl ketone, N-methyl-2-pyrrolidone (NMP) or An organic solvent that is a mixture of these is used.

However, if the positive electrode plate and the negative electrode plate are made thin and have a large area from the viewpoint of high output and large capacity, it is expected that the amount of active material and organic solvent used will increase during the production of the electrode plate. When the amount of the organic solvent used is increased, the manufacturing cost of the electrode plate is increased, the apparatus for recovering the vaporized solvent is increased in size, and the possibility of adversely affecting the natural environment is increased.
In particular, when polyvinylidene fluoride (PVDF), which is one of fluororesins, is used as a binder, NMP is preferably used as a solvent for preparing a coating composition for an electrode active material layer. Since the boiling point of NMP (204 ° C.) is much higher than that of water, a large amount of energy is required for drying and removing.

Therefore, when preparing the coating composition for electrode active material layers, it has been examined to use an aqueous solvent mainly composed of water instead of the conventional organic solvent.
As a method using an aqueous solvent, a water-soluble polymer such as carboxymethyl cellulose (CMC) as a thickener and styrene butadiene rubber (SBR) as a binder are dispersed in an aqueous solvent mainly composed of water to form a slurry. A method for preparing and using a coating composition in the form of a sheet is known.

  By the way, in order for a non-aqueous electrolyte secondary battery to be used as a high-output and large-capacity power source, it is a matter of course that sustained high-output characteristics are required. It is desirable that sufficient power can be supplied to the external device immediately after the start of charging / discharging of the secondary battery.

In Patent Document 1, a reaction precursor is synthesized from a natural phosphate polymer (typically deoxyribonucleic acid (hereinafter referred to as “DNA”)) containing a manganese compound and phosphoric acid, and the reaction precursor is synthesized. It is described that a lithium ion secondary battery having an active material made of porous manganese phosphate (Mn (PO ₄ ) _x ) can be obtained by firing at a temperature at which crystallization is not performed.

  However, in Patent Document 1, DNA is only used as a phosphate source, and the temperature of heat applied when synthesizing an active material is as high as 400 to 600 ° C. It is considered denatured. Patent Document 1 aims to improve the power density and cycle characteristics, and does not mention the relationship between the addition of DNA and the initial charge / discharge efficiency.

JP 2003-77465 A

  The present invention has been achieved in view of the above-described actual situation, and the first object thereof can be formed using an aqueous solvent-based coating composition for an active material layer, An object of the present invention is to provide an electrode plate for a non-aqueous electrolyte secondary battery negative electrode that is excellent in initial charge / discharge efficiency so that the capacity can be fully utilized during high output charge / discharge.

  The second object of the present invention is to provide a non-aqueous electrolyte secondary battery using the negative electrode plate having excellent initial charge / discharge efficiency.

The method for producing a non-aqueous electrolyte secondary battery negative electrode plate according to the present invention includes a step of forming a negative electrode active material layer on at least one surface of a current collector , and the non-aqueous electrolyte secondary battery negative electrode plate A manufacturing method of
Forming the negative electrode active material layer,
Preparing a coating composition comprising at least a negative electrode active material, DNA as a thickener, a binder, and an aqueous solvent mainly comprising water in a temperature range of 10 ° C. or higher and 100 ° C. or lower;
A step of forming a coating film by applying the coating composition onto the current collector;
Drying the coating film in a temperature range of 80 ° C. or higher and 120 ° C. or lower to remove the solvent;
A step of pressing the coating film from which the solvent has been removed in a temperature range of 20 ° C. or more and 120 ° C. or less,
It is characterized by including .

When the content of the negative electrode active material in the coating composition is 100 parts by weight, the DNA is contained in the coating composition in a range of 0.5 to 3 parts by weight. Preferably it is.
When the content of the negative electrode active material in the coating composition is 100 parts by weight, the binder is contained in the coating composition in a range of 0.5 parts by weight to 3 parts by weight. It is preferable that
The binder is preferably a material mainly composed of a rubber-based resin.

According to the present invention, when preparing a coating composition for an active material layer based on an aqueous solvent, by incorporating DNA as a thickener, the viscosity is suitable for application on a current collector. Therefore, a negative electrode active material layer based on the aqueous solvent can be formed.
Use of an aqueous solvent not only reduces the cost of the solvent itself, but also reduces the recovery cost of volatile components when drying the coating composition (decrease in drying energy), and is also environmentally friendly. Excellent.
Moreover, the negative electrode plate which has the negative electrode active material layer formed from the coating composition has high initial charge / discharge efficiency.
Moreover, according to this invention, the nonaqueous electrolyte secondary battery excellent in initial stage charge / discharge efficiency is obtained by using the electrode plate for negative electrodes based on this invention mentioned above.

  An electrode plate for a negative electrode of a non-aqueous electrolyte secondary battery according to the present invention is an aqueous system mainly composed of at least a negative electrode active material, DNA as a thickener, a binder, and water on at least one surface of a current collector. A negative electrode active material layer formed by applying a coating composition containing a solvent onto the current collector is provided.

(Negative electrode plate)
FIG. 1 is a cross-sectional view schematically showing an example of a layer configuration of a negative electrode plate (negative electrode plate) according to the present invention. In the negative electrode plate 1 of FIG. 1, a negative electrode active material layer 3 is formed on the surface side of a current collector 2. Further, FIG. 1 shows that the negative electrode active material layer 4 is formed on the back surface, but the positive electrode plate 1 according to the present invention has a negative electrode active material layer on one of both surfaces of the current collector 2. It only has to be formed. The negative electrode plate according to the present invention is not limited to the illustrated form.

The negative electrode current collector of the secondary battery is not particularly limited as long as it is a material conventionally used as a negative electrode current collector of a non-aqueous electrolyte secondary battery, but an electrolytic copper foil or a rolled copper foil A copper foil or the like is preferably used.
The thickness of the negative electrode current collector is not particularly limited, but usually about 5 to 50 μm is used.

  In the present invention, a negative electrode active material, DNA as a thickener, a binder, and water are used as components constituting the negative electrode active material layer coating composition (hereinafter referred to as “coating composition”). A main aqueous solvent may be used, and other additives such as a conductive agent may be used as necessary.

In the present invention, the negative electrode active material may be a material conventionally used as a negative electrode active material for a non-aqueous electrolyte secondary battery.
As the negative electrode active material, for example, natural graphite, artificial graphite, amorphous carbon, carbon black, or a carbonaceous material obtained by adding a different element to these components is preferably used.
Moreover, the particle shape of the negative electrode active material is not particularly limited, but for example, those having a shape such as a scale shape, a lump shape, a fiber shape, and a spherical shape can be used.

In the present invention, DNA is used as a thickener for the positive electrode active material layer coating composition based on an aqueous solvent.
DNA can be dissolved relatively easily in an aqueous solvent mainly composed of water, and after the dissolution, a thickening action is exerted on the solution to obtain a slurry-like coating composition having good coatability. It is done.
Moreover, the initial charging / discharging efficiency of the negative electrode plate which has the negative electrode active material layer formed from this coating composition can also be improved by containing DNA in a coating composition.
The reason why the initial charge / discharge efficiency of the negative electrode plate is improved by including DNA in the coating composition is not clear, but due to the special double helix structure of DNA, the negative electrode plate has conductivity. It is estimated that effects such as ionic conductivity and the like may be imparted.
Therefore, a film having high ion conductivity (hereinafter referred to as “ion permeable film”) is formed on the surface of the negative electrode active material layer formed from the coating composition containing DNA, and is uniform on the negative electrode plate. As a result of imparting effects such as conductivity and ion conductivity, the initial charge and discharge efficiency of the negative electrode plate is considered to be improved.

  A typical method for obtaining DNA is a method of extracting DNA using a fish sample such as salmon testis or scallop gonad. Among fish samples, salmon testis is preferably used because it contains a large amount of cells and can extract a large amount of DNA.

An example of a method for extracting DNA from salmon testis is given below.
First, 1 g of salmon testis is placed on a petri dish and ground with a spoonful while adding 10 ml of distilled water. The ground testis is strained with a filter and transferred to a beaker, and 30 ml of distilled water is added.
Next, in order to break the cell membrane, 4 ml of a surfactant (10% SDS solution) is added to the beaker and gently stirred. In addition, 10 ml of 2M NaCl solution is added and slowly stirred to remove protein.
The beaker is slowly stirred for about 5 minutes until the viscosity is lowered while bathing in hot water at 60 ° C. Remove the beaker from the hot water, add 30 ml of 2M NaCl solution to remove the remaining protein, and cool the solution to room temperature while stirring slowly.
Next, DNA is precipitated by adding an appropriate amount of 100% ethanol to the beaker through a stirring bar. Since the extracted DNA appears as a thread-like white structure, it can be easily wound up by stirring with a stirring bar.

The content of DNA in the coating composition is preferably 0.5 parts by weight or more and 3 parts by weight or less, when the negative electrode active material in the coating composition is 100 parts by weight. More preferably, it is 2 parts by weight or less.
When the DNA content in the coating composition is less than the above range, it becomes difficult to adjust the viscosity to be suitable for coating on the current collector, and the initial charge / discharge efficiency of the negative electrode plate is reduced. There is a case to let you. On the other hand, when the content of DNA in the coating composition exceeds the above range, the viscosity of the coating composition becomes too high, and handling may become inconvenient.

  Although DNA used as a thickener can be used alone, it can also be used in combination with water-soluble polymers such as carboxymethylcellulose (CMC) and its salts.

In the present invention, as the binder, a polymer material having good compatibility or dispersibility with a coating composition based on an aqueous solvent can be used. Among these polymer materials, a material mainly composed of a rubber-based resin is preferable because flexibility and durability can be imparted to the formed negative electrode active material layer.
Examples of rubber resins include styrene butadiene rubber (SBR), high styrene rubber (HSR), ethylene propylene rubber (EPDM), butyl rubber (IIR), chloroprene rubber (CR), butadiene rubber (BR), and isoprene rubber (IR). ), And silicone rubber. Among these, styrene butadiene rubber (SBR) is particularly preferably used.

The content of the binder resin in the coating composition is preferably 0.5 parts by weight or more and 3 parts by weight or less, based on 100 parts by weight of the negative electrode active material in the coating composition. More preferably, it is at least 2 parts by weight.
When the content of the binder resin in the coating composition is less than the above range, the effect of fixing the coating composition on the current collector is weakened and the homogeneity may be inferior. On the other hand, when the content of the binder resin in the coating composition exceeds the above range, the amount of the negative electrode active material is relatively decreased, and the conductive effect may not be sufficiently obtained.

The solvent used in the present invention is an aqueous solvent mainly composed of water. Since the solvent used in the present invention does not need to use a high-boiling organic solvent such as NMP, large energy is not required when drying the coating composition.
Aqueous solvents mainly composed of water not only reduce the cost of the solvent itself, but also reduce the cost of recovering volatile components when drying the coating composition (decrease in drying energy) and are environmentally friendly. .
The water-based solvent containing water as a main component is usually used alone. However, a water-soluble organic solvent such as alcohol may be contained in water for several percent.

Since many negative electrode active materials themselves have high conductivity, the negative electrode active material layer does not necessarily contain a conductive agent, but may be contained as necessary.
The conductive agent is not particularly limited as long as it is a material conventionally used as a conductive agent for non-aqueous electrolyte secondary batteries. For example, a carbonaceous material such as graphite, carbon black, or acetylene black Etc.
In addition, content of the electrically conductive agent in a coating composition is not specifically limited.

The preparation method of the coating composition is not particularly limited as long as it is prepared so as not to lose the thickening action of DNA and the properties such as ion conductivity.
An example of the preparation method of a coating composition is given below.
A water-based dispersion is obtained by adding and dispersing the thickener DNA in an aqueous solvent mainly composed of water, and further adding and dispersing the negative electrode active material. A slurry-like coating composition is prepared by adding a binder to the aqueous dispersion and dispersing it.
Furthermore, in addition to the above components, a conductive composition, other thickeners, and the like may be added as necessary to prepare a coating composition. Further, in order to adjust the viscosity, an aqueous solvent mainly containing water may be further added to prepare a coating composition.

As an example of the preparation method listed above, the components may be added and dispersed in sequence, or the components may be added and dispersed all at once. In addition, for dispersion of each component, the coating composition may be prepared using a dispersing machine such as a homogenizer, a ball mill, a sand mill, a roll mill, or a planetary mixer.
In addition, the dispersion time when using a disperser is not particularly limited, but is preferably 10 minutes or more and 120 minutes or less.

In the present invention, what is important in the preparation of the coating composition is that the temperature of the aqueous dispersion is sufficiently adjusted so as not to lose the characteristics of the DNA.
As an example of the temperature of the aqueous dispersion liquid that does not lose the characteristics of the DNA, a temperature range of 10 ° C. or more and 100 ° C. or less can be mentioned.

  The method of applying the coating composition onto the current collector is not particularly limited as long as the coating composition is applied so as not to lose the properties such as the thickening action of DNA and the ionic conductivity. Representative examples include coating methods such as coating, gravure coating, and die coating. Using such a coating method, the coating composition is intermittently applied to the current collector.

When the viscosity of the coating composition is relatively low, a coating method such as spraying or dip coating is preferably used. On the other hand, when the viscosity of the coating composition is relatively high, a coating method such as gravure coating or die coating is preferably used.
As the coating method used in the present invention, die coating and comma coating are preferably used.

The method for removing the solvent remaining in the coating composition coated on the current collector is not particularly limited as long as it is removed so as not to lose properties such as DNA thickening and ion conductivity. The optimum drying method is selected in consideration of the heat resistance of the composition components, the solvent removal efficiency, the uniformity of the film thickness distribution of the negative electrode active material layer after drying, and the like.
Typical examples of the drying method include drying methods such as hot air drying, contact drying, reduced pressure drying, vacuum drying, and freeze drying drying. It can also be dried by firing. Using such a drying method, the solvent remaining in the coating composition is removed.

In the present invention, what is important in removing the solvent remaining in the coating composition is that the temperature during drying is sufficiently adjusted so that the characteristics of the DNA are not lost.
As an example of the temperature at the time of drying which does not lose | disappear the characteristic of DNA, the temperature range of 80 to 120 degreeC can be mentioned.

The negative electrode active material layer formed by removing (drying) the solvent remaining in the coating composition as described above is further pressed to reduce the density of the negative electrode active material layer and the current collector. Adhesion and homogeneity can be improved.
As press work, it can carry out using a metal roll, an elastic roll, a heating roll, a roll press, a sheet press etc., for example. Among these, a roll press and a sheet press are preferably used from the viewpoint that a long sheet electrode plate can be continuously pressed.

  In the case of performing press working using a roll press, either a stereotaxic press or a constant pressure press may be used. The line speed of the press is usually 5 to 50 m / min. When the pressure of the roll press is managed by the linear pressure, the pressure is adjusted according to the diameter of the pressure roll. Usually, the linear pressure is 4.9 N (0.5 kgf / cm) to 9.8 kN (1 tf / cm). .

In the case of performing press working using a sheet press, the pressure of the press is usually 4903 to 73550 N / cm ² (500 to 7500 kgf / cm ² ), preferably 29420 to 49033 N / cm ² (3000 to 5000 kgf / cm). ² ) Adjust the pressure within the range.
If the pressing pressure is too low, it may be difficult to obtain homogeneity in the negative electrode active material layer. On the other hand, if the pressing pressure is too high, the electrode plate itself including the current collector may be destroyed.
The negative electrode active material layer may have a predetermined thickness by a single press, or may be pressed several times for the purpose of improving homogeneity.

In the present invention, what is important in the press processing is that the temperature during the press processing is sufficiently adjusted so that the characteristics of the DNA are not lost.
As an example of the temperature at the time of press working which does not lose the characteristics of DNA, a temperature range of 20 ° C. or more and 120 ° C. or less can be mentioned.

The amount of coating composition coated to a current collector on the body, the coating amount of the coating composition after drying it is preferable to coat to be in the range of ^{20g / m 2 ~250g / m 2} .
The thickness of the obtained negative electrode active material layer is preferably applied so as to be in the range of 10 μm to 200 μm, more preferably 50 μm to 170 μm after drying and pressing.

Further, the density of the obtained negative electrode active material layer is about 1.0 g / cm ³ after drying, but is 1.5 g / cm ³ or more after pressing (normally 1.5 g / cm ³ to 1. Up to about 75 g / cm ³ ).
Therefore, the capacity of the battery can be increased by improving the volume energy density by performing the pressing process without any problem. A negative electrode plate is produced through the above steps.

(Positive electrode plate)
As the positive electrode current collector, materials conventionally used as the positive electrode current collector of non-aqueous electrolyte secondary batteries can be used.
For example, aluminum foil is preferably used.
The thickness of the positive electrode current collector is not particularly limited, but usually about 5 to 50 μm is used.

As a positive electrode active material, if it is the material conventionally used as a positive electrode active material of a nonaqueous electrolyte secondary battery, it can use without being specifically limited.
Examples of the positive electrode active material include lithium composite oxides such as LiMn ₂ O ₄ (lithium manganate), LiCoO ₂ (lithium cobaltate), and LiNiO ₂ (lithium nickelate), and TiS ₂ , MnO ₂ , and MoO. ₃ , and chalcogen compounds such as V ₂ O ₅ ;

The method for preparing, coating and drying the coating composition for the positive electrode active material is not particularly limited, and a known method can be applied, and the above-described preparation and coating of the coating composition for the negative electrode active material can be applied. Methods such as construction and drying may be applied.
For example, coating a positive electrode active material layer in the form of a slurry by mixing a positive electrode active material, a thickener, a binder, a conductive agent (for example, graphite, etc.) and, if necessary, a dispersant in an organic solvent or an aqueous solvent. A composition is prepared. In addition, it is preferable that the coating composition for positive electrode active materials is also prepared using an aqueous solvent mainly composed of water.
Then, the prepared coating composition for the positive electrode active material layer is coated and dried on the positive electrode current collector to form a positive electrode active material layer to obtain a positive electrode plate.

(Electrolyte)
When producing a lithium ion secondary battery which is a typical example of a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent is used as the electrolyte solution.
Examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, and LiBr, and LiB (C ₆ H ₅ ) ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC. (SO ₂ CF ₃ ) ₃ , LiOSO ₂ CF ₃ , LiOSO ₂ C ₂ F ₅ , LiOSO ₂ C ₄ F ₉ , LiOSO ₂ C ₅ F ₁₁ , LiOSO ₂ C ₆ F ₁₃ , and LiOSO ₂ C ₇ F ₁₅ An organic lithium salt;
Examples of the organic solvent used for dissolving the lithium salt include cyclic esters, chain esters, cyclic ethers, and chain ethers.

  Examples of the cyclic esters include propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.

  Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, and propionic acid alkyl ester. , Malonic acid dialkyl ester, and acetic acid alkyl ester.

  Examples of cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, and 1,4-dioxolane.

  Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. Can be mentioned.

(Non-aqueous electrolyte secondary battery)
The negative electrode current collector provided with the negative electrode active material layer obtained by the above-described method is used as a nonaqueous electrolyte secondary battery negative electrode plate.
In a non-aqueous electrolyte secondary battery, a known positive electrode plate and a negative electrode plate according to the present invention are wound through a separator such as a polyethylene porous film and stored in a battery container. And it assembles by filling a non-aqueous electrolyte in a battery container.

<Example 1>
(Preparation of aqueous DNA solution)
First, 1 g of salmon testis was placed on a petri dish and ground using a spoonful while adding 10 ml of distilled water. The ground testis was strained with a filter and transferred to a beaker, and 30 ml of distilled water was added. Next, 4 ml of a surfactant (10% SDS solution) was added to the beaker and slowly stirred in order to break the cell membrane. Furthermore, in order to remove protein, 10 ml of 2M NaCl solution was added and stirred slowly.
The beaker was slowly stirred for about 5 minutes while boiling in 60 ° C. water until the viscosity decreased. The beaker was taken out of the hot water, 30 ml of 2M NaCl solution was added to remove the remaining protein, and the solution was cooled to about room temperature while stirring slowly. Subsequently, DNA was precipitated by adding an appropriate amount of 100% ethanol to the beaker along a stir bar. Since DNA appears as a thread-like white structure, it was obtained in a state where it can be easily wound up by stirring with a stir bar.
The concentration of the obtained DNA was adjusted to 1% by weight with distilled water to prepare a 1% by weight DNA aqueous solution.

(Preparation of coating composition)
To 100 parts by weight of artificial graphite powder having an average particle diameter of 20 μm as the negative electrode active material, the DNA component of the 1 wt% DNA aqueous solution as the thickener prepared above was added to 1.5 parts by weight and dispersed. An aqueous dispersion was obtained. The viscosity was adjusted by adding distilled water as necessary.
A slurry-like coating composition is prepared by adding 1.5 parts by weight of 40% SBR dispersion (manufactured by Zeon Corporation, BM400B) as a binder to the aqueous dispersion whose concentration of DNA has been adjusted, and dispersing it. did.
In preparing the coating composition, the temperature of the aqueous dispersion was adjusted so as to be in the range of 20 to 80 ° C. to prevent DNA denaturation.

(Preparation of electrode plate for negative electrode)
The slurry-like coating composition prepared above was applied and dried on a copper foil having a thickness of 10 μm, which was a negative electrode current collector, to form a negative electrode active material layer.
At this time, the negative electrode active material layer was formed so that the coating amount of the coating composition after drying was 100 g / m ² .
When coating and drying, the temperature of the copper foil was adjusted so as to be in the range of 80 to 120 ° C. to prevent DNA denaturation.
Furthermore, after pressing using a roll press machine so that the density of the obtained negative electrode active material layer becomes 1.5 g / cm ³ , it is punched into a disk shape having a diameter of 15 mm and vacuum-dried at 120 ° C. for 12 hours. Thus, a negative electrode plate was produced.

(Preparation of non-aqueous electrolyte)
LiPF ₆ is added as a solute to a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 1: 1, and the concentration is adjusted so that the concentration of LiPF ₆ is 1 mol / l. An electrolytic solution was prepared.

(Production of three-electrode coin cell)
Using the negative electrode plate prepared above as a working electrode, metallic lithium as a counter electrode and a reference electrode, and a porous polyethylene sheet as a separator, the non-aqueous electrolyte prepared above was injected, and three of Example 1 were injected. A polar coin cell was prepared and subjected to the following charge / discharge test.

(Test method)
(Charge / discharge test)
The charge / discharge test was performed on the three-pole coin cell produced above in an environment of 25 ° C.
1C (capacitance; means discharge rate. 1C is a current value at which a battery having a nominal capacity value is discharged at a constant current and discharge is completed in just one hour. In this embodiment, 6.2 mA is used. The battery was charged to 0.01 V with respect to the reference electrode.
Thereafter, the charging was completed by performing constant voltage charging at 0.01 V with respect to the reference electrode until the charging current became 5% or less (that is, 0.3 mA or less) of the discharge rate 1C.
Thereafter, the operation was stopped for 10 minutes, and the discharge was performed at a constant 1 C until the voltage reached 2.0 V with respect to the reference electrode.
With the horizontal axis as the discharge capacity (discharge time) and the vertical axis as the cell voltage, the charge / discharge curve at 1C was calculated to determine the discharge capacity (mAh / g) at 1C.
The charge capacity (initial charge capacity) of the first cycle and the discharge capacity (initial discharge capacity) of the first cycle are measured, and each measured value is converted per weight of the negative electrode active material. Charge / discharge efficiency (%) was calculated.

<Comparative Example 1>
The tripolar coin cell of Comparative Example 1 was prepared in the same manner as in Example 1 except that the DNA used as the thickener in Example 1 was changed to CMC sodium salt (Sellogen 4H, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). It produced and used for the charging / discharging test.

(result)
Table 1 shows the results of the charge / discharge test of the tripolar coin cell produced in Example 1 and Comparative Example 1.

(Summary of results)
From the results of the charge / discharge test described in Table 1, the following can be understood.
The tripolar coin cell of Comparative Example 1 had a low initial charge / discharge efficiency due to the fact that it was a negative electrode plate produced using a conventional CMC sodium salt as a thickener.
In contrast, the tripolar coin cell of Example 1 was excellent in initial charge / discharge efficiency because it was a negative electrode plate produced using DNA as a thickener.

FIG. 1 is a cross-sectional view of a main part of a negative electrode plate for a nonaqueous electrolyte secondary battery according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode plate 2 Current collector 3 Negative electrode active material layer 4 Negative electrode active material layer

Claims (4)

A method for producing a negative electrode plate for a nonaqueous electrolyte secondary battery comprising a step of forming a negative electrode active material layer on at least one surface of a current collector ,
Forming the negative electrode active material layer,
Preparing a coating composition comprising at least a negative electrode active material, DNA as a thickener, a binder, and an aqueous solvent mainly comprising water in a temperature range of 10 ° C. or higher and 100 ° C. or lower;
A step of forming a coating film by applying the coating composition onto the current collector;
Drying the coating film in a temperature range of 80 ° C. or higher and 120 ° C. or lower to remove the solvent;
A step of pressing the coating film from which the solvent has been removed in a temperature range of 20 ° C. or more and 120 ° C. or less,
The manufacturing method of the electrode plate for nonaqueous electrolyte secondary battery negative electrodes characterized by including . When the content of the negative electrode active material in the coating composition is 100 parts by weight,
In the range of 0.5 to 3 parts by weight of the DNA,
The method for producing an electrode plate for a non-aqueous electrolyte secondary battery negative electrode according to claim 1, wherein the electrode plate is contained in the coating composition. When the content of the negative electrode active material in the coating composition is 100 parts by weight,
In the range of 0.5 parts by weight or more and 3 parts by weight or less of the binder,
The method for producing an electrode plate for a nonaqueous electrolyte secondary battery negative electrode according to claim 1 or 2, wherein the electrode plate is contained in the coating composition. The method for producing an electrode plate for a nonaqueous electrolyte secondary battery negative electrode according to any one of claims 1 to 3, wherein the binder is a material mainly composed of a rubber-based resin.

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