JP2011204576A - Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery including the same, and method of manufacturing the negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compatibly improve the electrode plate strength of a negative electrode for a nonaqueous electrolyte secondary battery and improve the lithium ion-receiving performance of the negative electrode.SOLUTION: In the negative electrode for the nonaqueous electrolyte secondary battery, a negative electrode mixture layer includes graphite particles, a water-soluble polymer, and rubber particles. The amount of the water-soluble polymer is 0.6-3 pts.wt per 100 pts.wt. of the graphite particles, and the amount of the rubber particles is 0.4-1.5 pts.wt. per 100 pts.wt. of the graphite particles. The water-soluble polymer includes a first water-soluble polymer having a molecular weight of 200,000 or greater and an etherification degree of 0.8 or lower and a second water-soluble polymer having a molecular weight of 150,000 or smaller and an etherification degree of 0.8 or lower. The first water-soluble polymer covers the surfaces of the graphite particles, and the second water-soluble polymer and the rubber particles adhere the graphite particles covered with the first water-soluble polymer, to one another.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of a negative electrode for a non-aqueous electrolyte secondary battery containing graphite particles.

  A nonaqueous electrolyte secondary battery represented by a lithium ion battery has a high operating voltage and a high energy density, and is therefore widely used as a power source for driving electronic devices. Recently, the development of using non-aqueous electrolyte secondary batteries for high-power applications such as electric vehicles has been rapidly advanced, and some of them are being put into practical use.

  A negative electrode of a general nonaqueous electrolyte secondary battery includes a sheet-like negative electrode core material and a negative electrode mixture layer attached thereto. The negative electrode mixture layer contains, for example, a water-soluble polymer and rubber particles in addition to the negative electrode active material (Patent Document 1).

  As the negative electrode active material, many graphite particles capable of inserting and extracting lithium ions are used. Graphite undergoes a volume change due to charging and discharging, and the volume during charging becomes approximately 10% larger than the volume during discharging. Therefore, when the adhesive strength between the mixture layer and the core material and the binding strength between the graphite particles are low, the mixture layer is easily peeled from the core material due to the volume expansion of graphite. On the other hand, from the viewpoint of increasing the electrode plate strength, if the amount of the water-soluble polymer or rubber particles is increased, the insertion of lithium ions into the graphite particles is hindered. Therefore, the acceptability of lithium ions by the negative electrode is reduced.

  Therefore, from the viewpoint of improving the electrode plate strength, it has been proposed to include two or more water-soluble polymers in the negative electrode mixture layer (Patent Document 2). Specifically, a water-soluble polymer (for example, carboxymethylcellulose) that easily dissolves in the non-aqueous electrolyte is attached in the pores of the graphite particles, and the outer surface of the graphite particles is difficult to dissolve in the non-aqueous electrolyte. It has been proposed to attach a water-soluble polymer (eg polyvinyl alcohol).

  In the case of Patent Document 2, the water-soluble polymer that is difficult to dissolve in the nonaqueous electrolyte is prevented from entering the pores of the graphite particles. Thereby, it is considered that a relatively smooth movement of lithium ions can be secured. In addition, it is considered that the strength of the electrode plate is improved because a water-soluble polymer that is difficult to dissolve in the non-aqueous electrolyte is effectively used for binding between particles.

JP 2003-168432 A JP 2007-42285 A

  However, regardless of the degree of solubility of the water-soluble polymer in the non-aqueous electrolyte, it is considered that the insertion of lithium ions into the graphite particles is hindered when the water-soluble polymer enters the pores of the graphite particles. In addition, since a water-soluble polymer that is easily dissolved in a non-aqueous electrolyte is easily swelled by the non-aqueous electrolyte, the binding property between particles is likely to be lowered, and the negative electrode is easily expanded. That is, it is difficult to achieve a high level of improvement in electrode plate strength and improvement in lithium ion acceptability by the negative electrode.

  The present invention includes a negative electrode core material and a negative electrode mixture layer attached to the negative electrode core material, wherein the negative electrode mixture layer includes graphite particles, a water-soluble polymer, and rubber particles, The amount of molecules is 0.6-3 parts by weight per 100 parts by weight of the graphite particles, and the amount of rubber particles is 0.4-1.5 parts by weight per 100 parts by weight of the graphite particles, The water-soluble polymer includes a first water-soluble polymer having a molecular weight of 200,000 or more and an etherification degree of 0.8 or less, and a second water-soluble polymer having a molecular weight of 150,000 or less and an etherification degree of 0.8 or less, The first water-soluble polymer coats the surface of the graphite particles, and the second water-soluble polymer and the rubber particles adhere between the graphite particles coated with the first water-soluble polymer. The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery.

  The present invention also comprises (i) a step of preparing a first slurry by mixing graphite particles, a first water-soluble polymer having a molecular weight of 200,000 or more and an etherification degree of 0.8 or less, and water, ii) mixing a second water-soluble polymer having a molecular weight of 150,000 or less and a degree of etherification of 0.8 or less, rubber particles, and water into the first slurry to prepare a second slurry; iii) applying the second slurry to a negative electrode core material and drying to form a coating film; and (iv) rolling the coating film to form a negative electrode mixture layer. The amount of the first water-soluble polymer is 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles, and the amount of the second water-soluble polymer is 100 parts by weight of the graphite particles. 0.3 to 1.5 parts by weight, and the amount of the rubber particles is 0.4 to 1 per 100 parts by weight of the graphite particles. 5 parts by weight, a method of manufacturing a negative electrode for a nonaqueous electrolyte secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the improvement of the electrode plate strength of the negative electrode for nonaqueous electrolyte secondary batteries and the improvement of the acceptability of lithium ion by a negative electrode can be made compatible.

It is a block diagram which shows the outline of the apparatus for preparing a negative mix slurry. It is a longitudinal cross-sectional view which shows the outline of the in-line mixer for preparing a 1st slurry. It is the perspective view which notched a part which shows an example of a nonaqueous electrolyte secondary battery.

  The negative electrode for a non-aqueous electrolyte secondary battery of the present invention includes a negative electrode core material and a negative electrode mixture layer attached to the negative electrode core material. The negative electrode core material has a sheet shape, and the negative electrode mixture layer is formed on one surface or both surfaces of the negative electrode core material. The negative electrode mixture layer includes graphite particles, a water-soluble polymer, and rubber particles. Such a negative electrode mixture layer is obtained by applying a negative electrode mixture slurry containing graphite particles, a water-soluble polymer, rubber particles, and a liquid component (dispersion medium) to a negative electrode core material, and drying it. It is obtained by rolling the coating film.

  The water-soluble polymer includes a first water-soluble polymer and a second water-soluble polymer each containing an ether bond. By using multiple types of water-soluble polymers in combination, more precise material design becomes possible. Specifically, many portions of the first water-soluble polymer are directly attached to the surface of the graphite particles, and appropriately coat the surface of the graphite particles. On the other hand, many parts of the second water-soluble polymer and the rubber particles are attached to the graphite particles from the outside of the first water-soluble polymer. That is, the second water-soluble polymer and the rubber particles are bonded between the graphite particles coated with the first water-soluble polymer. By appropriately covering the surface of the graphite particles with the first water-soluble polymer, the permeability of the non-aqueous electrolyte to the negative electrode mixture layer is not hindered, and the expansion of the negative electrode and the electrode plate strength are suppressed. Easy to maintain. The second water-soluble polymer mainly contributes to suppression of negative electrode expansion and maintenance of electrode plate strength.

  The ether bond contained in the water-soluble polymer affects the network structure of the water-soluble polymer. By setting the degree of etherification to 0.8 or less, the water-soluble polymer can easily form a network structure. It is considered that the water-soluble polymer having a developed network structure can appropriately cover the surface without adhering to the surface of the graphite particles. Therefore, it becomes easy to ensure the acceptability of lithium ions by the negative electrode. Further, the development of the network structure of the water-soluble polymer enhances the binding property between the graphite particles, and the electrode plate strength is easily improved.

  However, in order to appropriately coat the surface of the graphite particles with the first water-soluble polymer having a degree of etherification of 0.8 or less that easily forms a network structure, the graphite particles and the first water-soluble polymer are applied with high shearing force. It is necessary to mix the functional polymer. In addition, the first water-soluble polymer coated on the graphite particles should not be easily detached from the graphite particles. For that purpose, it is necessary to increase the viscosity of the first water-soluble polymer.

  On the other hand, it is desirable that the second water-soluble polymer does not generate insoluble gel particles in the negative electrode mixture slurry. It is desirable that the second water-soluble polymer is once dissolved in the dispersion medium and then precipitated in the process of drying the coating film of the negative electrode mixture slurry to form a network structure with the rubber particles. For this purpose, it is necessary to reduce the viscosity of the second water-soluble polymer by reducing the molecular weight.

  From the above, when the surface of the graphite particles is coated with the first water-soluble polymer, the molecular weight of the first water-soluble polymer is preferably 200,000 or more, and preferably 300,000 or less or 250,000 or less. preferable. On the other hand, the molecular weight of the second water-soluble polymer is preferably 150,000 or less from the viewpoint of imparting an appropriate viscosity to the negative electrode mixture slurry and improving the dispersibility of the slurry solid content. The following is more preferable. Here, the molecular weight means a weight average molecular weight.

  The first viscosity ν1 at 25 ° C. of an aqueous solution containing 1% by weight of the first water-soluble polymer and the second viscosity ν2 at 25 ° C. of an aqueous solution containing 1% by weight of the second water-soluble polymer satisfy ν1> ν2. It is necessary to satisfy. However, it is not necessary to excessively increase the viscosity of the first water-soluble polymer. For example, it is preferable that 10ν2> ν1.

  The viscosity of the aqueous solution at 25 ° C. is measured at a rotational speed of 20 rpm using a Brookfield type rotational viscometer and a spindle (14.6 mm diameter).

  The first viscosity ν1 is preferably 10 to 40 Pa · s, more preferably 10 to 20 Pa · s. Further, the second viscosity ν2 is preferably 0.5 to 8 Pa · s, and more preferably 2 to 8 Pa · s. By using a water-soluble polymer having a viscosity in such a preferable range, improvement in the electrode plate strength of the negative electrode and improvement in lithium ion acceptability can be achieved in a balanced manner.

  A polysaccharide compound is preferable as the first water-soluble polymer and the second water-soluble polymer having an ether bond. Examples of water-soluble polymers include naturally occurring starch, gelatin, semi-synthetic carboxymethylcellulose (CMC), cellulose derivatives such as methylcellulose (MC), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid polymers, poly Although synthetic water-soluble polymers such as acrylamide (PAM) and polyethylene oxide (PEO) can be mentioned, polysaccharide compounds are preferred from the viewpoint of heat resistance, cost, chemical stability, and the like.

  The polysaccharide compound refers to a saccharide in which a plurality of monosaccharide molecules are polymerized by glycosidic bonds. Examples thereof include starch, amylose, amylopectin, glycogen, cellulose, and derivatives thereof. Among these, a cellulose derivative is preferable and carboxymethyl cellulose is most preferable from the viewpoints of heat resistance, cost, chemical stability, and the like. Carboxymethylcellulose may be used in the form of a sodium salt.

The degree of etherification is an index indicating the amount of ether bonds. For example, when the water-soluble polymer is a cellulose derivative, the degree of etherification of a derivative in which one of hydroxyl groups is etherified in all cellulose units is 1.0. In this case, the ether bond is a carboxymethyl group (—CH ₂ COOH), a sodium carboxymethyl group (—CH ₂ COONa) or an ammonium carboxymethyl group (—CH ₂ COONH) substituted with a part of the hydroxyl group of the glucopyranose monomer. ₄ ) included.

  The degree of etherification can be determined by various methods. For example, in the case of sodium salt of carboxymethyl cellulose (CMC-Na), it can be obtained by boiling an incinerated sample with sulfuric acid, adding a phenolphthalein indicator, and back titrating excess acid with potassium hydroxide. . Specifically, it is as follows.

[Method for measuring degree of etherification]
First, the alkalinity A of CMC-Na is measured by the following procedure.
1 g of CMC-Na powder is weighed, and 200 ml of water is added and dissolved in the flask. To this is added 5 mL of 0.05 mol / mL sulfuric acid, boiled for 10 minutes, and then cooled to room temperature. The resulting solution is titrated with a 0.1 mol / mL aqueous potassium hydroxide solution. On the other hand, in the same procedure, a blank test is performed without adding CMC-Na powder. The alkalinity A is calculated using the results of titration and blank test and the following formula (1).
A = (ed) f / M (1)
e: Volume of aqueous potassium hydroxide solution required for titration of blank test (mL)
d: Volume of aqueous potassium hydroxide solution (mL) required for titration of CMC-Na and sulfuric acid solution
f: Potency of potassium hydroxide aqueous solution (g / mL)
M: Weight of CMC-Na powder

Next, the degree of etherification DS is measured by the following procedure.
0.5 g of CMC-Na powder is weighed, wrapped in filter paper and incinerated in a crucible. This is cooled, transferred to a beaker, 250 mL of water and 35 mL of 0.05 mol / mL sulfuric acid are added, boiled for 30 minutes, and then cooled to room temperature. The resulting solution is titrated with a 0.1 mol / mL aqueous potassium hydroxide solution. The degree of etherification DS is calculated using the results of titration and the equations (2) and (3).
DS = 162W / (10000-80W) (2)
W = (af′−bf) / MA (3)
a: Volume of sulfuric acid (mL)
f ′: sulfuric acid titer (g / mL)
b: Volume of potassium hydroxide (mL)

  The total amount of the water-soluble polymer is 0.6 to 3 parts by weight, preferably 0.8 to 1.5 parts by weight, per 100 parts by weight of the graphite particles. When the total amount of the water-soluble polymer is less than 0.6 parts by weight, the slurry viscosity becomes insufficient or the electrode plate strength decreases. When the total amount of the water-soluble polymer exceeds 3 parts by weight, the negative electrode capacity decreases and the negative electrode mixture layer swells greatly.

  The amount of the first water-soluble polymer is preferably 0.3 to 1.5 parts by weight, more preferably 0.4 to 0.7 parts by weight, per 100 parts by weight of the graphite particles. If the amount of the first water-soluble polymer is less than 0.3 parts by weight, it may be difficult to attach a sufficient amount of the first water-soluble polymer to the surface of the graphite particles. When the amount of the first water-soluble polymer exceeds 1.5 parts by weight, the negative electrode capacity may decrease or the negative electrode mixture layer may swell greatly.

  The amount of the second water-soluble polymer is preferably 0.3 to 1.5 parts by weight, more preferably 0.4 to 0.8 parts by weight per 100 parts by weight of the graphite particles. When the amount of the second water-soluble polymer is less than 0.3 part by weight, the binding property between the particles becomes insufficient, and the electrode plate strength may be lowered. When the amount of the second water-soluble polymer exceeds 1.5 parts by weight, the negative electrode capacity may decrease or the negative electrode mixture layer may swell greatly.

  As the rubber particles, a polymer having rubber elasticity including a styrene unit and a butadiene unit is preferable. For example, styrene butadiene rubber (SBR) can be used. In addition to the styrene unit and the butadiene unit, a polymer having rubber elasticity containing units such as acrylonitrile, acrylic acid, methacrylic acid, 2-ethylhexyl acrylate, and butyl acrylate can also be preferably used. Such a polymer has a glass transition point of −30 to + 40 ° C., is excellent in the binding property of graphite particles in the operating temperature range of the battery, and is stable at the negative electrode potential. The content of units other than styrene units and butadiene units is preferably 0.1 to 5 mol%.

  The average particle size of the rubber particles is preferably 50 nm to 200 nm, particularly preferably 50 to 150 nm, and most preferably 100 to 120 nm. By using rubber particles having such a small particle size, it becomes easier to obtain a cooperative action between the network structure of the second water-soluble polymer and the rubber particles, and the binding property between the graphite particles becomes stronger. Strength becomes easy to improve.

The average particle size of the rubber particles is measured by, for example, a laser diffraction / scattering particle size distribution measuring device (for example, Microtrack manufactured by Nikkiso Co., Ltd.). Specifically, the cumulative volume distribution is obtained, and the particle size D _{50V at} which the cumulative volume from the large particle size side becomes 50% is obtained as the volume-based average particle size.

  The amount of rubber particles is 0.4 to 1.5 parts by weight, preferably 0.6 to 1.2 parts by weight, per 100 parts by weight of graphite particles. When the amount of the rubber particles is less than 0.4 parts by weight, the binding property between the graphite particles becomes insufficient, and the electrode plate strength decreases. When the amount of the second water-soluble polymer exceeds 1.5 parts by weight, the negative electrode capacity decreases.

  In addition, when the first water-soluble polymer coats the surface of the graphite particles, because the slipping between the graphite particles is good, the rubber particles receive a sufficient shear force during rolling of the negative electrode mixture layer, It works effectively on the surface of graphite particles. Further, since the rubber particles having a small particle size have a high probability of coming into contact with the surface of the graphite particles, a sufficient binding property is exhibited even with a small amount.

  A graphite particle is a general term for particles including a region having a graphite structure. Thus, the graphite particles include natural graphite, artificial graphite, graphitized mesophase carbon particles, and the like. The diffraction image of the graphite particles measured by the wide angle X-ray diffraction method has a peak attributed to the (101) plane and a peak attributed to the (100) plane. Here, the ratio of the peak intensity I (101) attributed to the (101) plane and the peak intensity I (100) attributed to the (100) plane is 0.01 <I (101) / I. It is preferable to satisfy (100) <0.25, and it is more preferable to satisfy 0.08 <I (101) / I (100) <0.20. The peak intensity means the peak height.

The average particle size of the graphite particles is preferably 14 to 25 μm, and more preferably 16 to 23 μm. When the average particle diameter is within the above range, the slipping property of the graphite particles in the negative electrode mixture layer is improved, the filling state of the graphite particles is improved, and it is advantageous for improving the adhesive strength between the graphite particles. The average particle diameter means D _50V in the cumulative volume distribution of graphite particles. The cumulative volume distribution of the graphite particles can also be measured by a commercially available laser diffraction / scattering particle size distribution measuring apparatus.

The average circularity of the graphite particles is preferably 0.90 to 0.95, and more preferably 0.91 to 0.94. When the average circularity is included in the above range, the slipping property of the graphite particles in the negative electrode mixture layer is improved, which is advantageous in improving the filling properties of the graphite particles and the adhesion strength between the graphite particles. The average circularity is represented by 4πS / L ² (where S is the area of the orthographic image of graphite particles, and L is the perimeter of the orthographic image). For example, the average circularity of 100 arbitrary graphite particles is preferably in the above range.

The specific surface area S of the graphite particles is preferably 3~7m ² / g, more preferably 3.5~6.5m ² / g. When the specific surface area is included in the above range, the slipperiness of the graphite particles in the negative electrode mixture layer is improved, which is advantageous for improving the adhesive strength between the graphite particles. Moreover, the suitable quantity of the 1st water-soluble polymer which coat | covers the surface of a graphite particle can be decreased. The specific surface area is measured by the BET method.

  A metal foil is preferably used for the negative electrode core material. As the metal foil, a copper foil, a copper alloy foil or the like is preferable. Of these, copper foil (which may contain components other than copper of 0.2 mol% or less) is preferable, and electrolytic copper foil is particularly preferable.

Next, the preferable form of the manufacturing method of the said negative electrode is demonstrated. FIG. 1 is a configuration diagram showing an outline of an apparatus for preparing a negative electrode mixture slurry.
This apparatus includes a premixer (first mixer) 11 for preparing a premixed slurry, an in-line mixer 12 for preparing a first slurry by performing main mixing of the premixed slurry obtained by the premixer, And a second mixer 13 for preparing a second slurry.
FIG. 2 is a longitudinal sectional view showing an outline of the in-line mixer.

  For the first mixer, for example, a mixer equipped with impeller type, sawtooth blade type or rotor type rotary blades can be used as the stirring blade 11a. In the first mixer 11, the first raw material graphite particles, the first water-soluble polymer containing an ether bond, and water are mixed to prepare a premixed slurry. In that case, it is preferable to finally control the amount of the first water-soluble polymer contained in the premixed slurry to be 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles. In the mixing by the first mixer 11, a mixture composed of graphite particles, the first water-soluble polymer and water is mixed at a shear rate of 500 (1 / s) or less, for example.

  The viscosity of the premixed slurry at 25 ° C. is preferably controlled to 100 Pa · s or less, preferably 50 Pa · s or less so that the premixed slurry can be easily transferred to the in-line mixer 12.

  In the case of the apparatus shown in FIG. 1, the premixed slurry is transferred by the feed pump 14 to the in-line mixer 12 to which a high shear force can be applied. In the case where the preparation from the first slurry to the second slurry is continuously performed, an in-line mixer is suitable. As the delivery pump 14, a screw pump is preferable.

An inline rotor / stator mixer is preferably used for the inline mixer 12. This mixer includes a fixed stator 12a and a rotor 12b that rotates at high speed with a small clearance between the stator 12a and the inner wall of the stator. Among these, it is preferable to use a fill mix manufactured by Primix Co., Ltd. (Primix) as an inline rotor / stator mixer.
However, it is not always necessary to continuously perform a series of steps using these apparatuses. A desired slurry can be obtained without continuously performing a series of steps. Moreover, you may use the other mixer which can provide a high shearing force to the contents. For example, an IKA rotor stator mixer may be used.

  In the premixed slurry, the graphite particles that are not sufficiently dispersed and the first water-soluble polymer that is not sufficiently dissolved can be sufficiently dispersed and dissolved by the in-line mixer 12. In the in-line mixer, it is necessary to apply a sufficient shearing force to the premixed slurry and to appropriately form a network coating film of the first water-soluble polymer on the surface of the graphite particles. Specifically, the premixed slurry obtained by premixing is preferably main-mixed at a shear rate of 10,000 (1 / s) to 100,000 (1 / s), preferably 10,000 (1 / s) to 40000 (1 More preferably, the main mixing is performed at a shear rate of / s).

  In this mixing, it is preferable to control the mixing conditions so that the viscosity of the first slurry at 25 ° C. is 5 to 50 Pa · s. If the viscosity is within this range, it is considered that the graphite particles and the first water-soluble polymer are sufficiently uniformly dispersed, and a suitable covering state of the graphite particles by the water-soluble polymer is obtained.

  As shown in FIG. 2, the inline mixer includes a rotor 12 b integrated with a rotating shaft 21. Centrifugal force is generated when the rotor 12b rotates at a high speed. Due to this centrifugal force, the premixed slurry is continuously drawn into the rotor 12b from the inlet 22. The slurry is spouted from the plurality of window holes 23 provided in the rotor 12b by centrifugal force, and passes through the clearance between the stator 12a and the rotor 12b. At that time, the slurry receives a strong shearing force. The slurry ejected from the window hole 23 stays for a while while rotating in the in-line mixer. Thereafter, the slurry passes through the dam plate 24, moves to the overflow container 25, and is guided to the discharge port 26. As shown in FIG. 2, it is preferable that the periphery of the stator 12 a be covered with an outer container 27 in order to provide a cooling water passage 27 b for circulating the cooling water.

  The mixing conditions (especially shear efficiency) are the shape of the stator 12a and the rotor 12b included in the in-line mixer 12, the clearance between the stator 12a and the rotor 12b, the rotational speed (peripheral speed) of the rotor 12b, the residence time (the premixed slurry is mixed) It is controlled by changing parameters such as the time from when it is drawn into the machine until it is guided outside.

  For the second mixer 13, a mixer having impeller-type, sawtooth blade-type, or rotor-type rotary blades can be used as the stirring blade 13a, similar to the first mixer. In the second mixer, the first slurry derived from the in-line mixer 12 is mixed with the second water-soluble polymer containing an ether bond as the second raw material, rubber particles, and water, and the second slurry. To prepare. From the viewpoint of increasing the mixing efficiency, the concentration of the aqueous solution of the second water-soluble polymer is preferably 1.5 to 2% by weight. The rubber particles are preferably used in a state of being uniformly dispersed in water or an emulsion. At that time, the amount of the first water-soluble polymer finally contained in the second slurry (negative electrode mixture slurry) is controlled to be 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles. It is preferable. The amount of the rubber particles contained in the negative electrode mixture slurry is preferably controlled so as to be 0.4 to 1.5 parts by weight per 100 parts by weight of the graphite particles. In the mixing by the second mixer, a mixture of the first slurry, the second water-soluble polymer, the rubber particles, and water is mixed at a shear rate of 500 (1 / s) or less, for example.

  The viscosity of the negative electrode mixture slurry at 25 ° C. is preferably controlled to 3 to 10 Pa · s so that transfer to another apparatus and coating can be easily performed.

  The viscosity of the premixed slurry, the first slurry, and the negative electrode mixture slurry at 25 ° C. is measured using a Brookfield rotary viscometer and a spindle (14.6 mm).

  The BET specific surface area of the graphite particles appropriately coated with the first water-soluble polymer is reduced by about 10 to 50% compared to the specific surface area (initial specific surface area) before being coated. Further, in addition to the first water-soluble polymer, the BET specific surface area in the dry state of the graphite particles appropriately coated with the second water-soluble polymer and the rubber particles is reduced by about 20 to 70% compared to the initial specific surface area. To do. Therefore, the degree of coating can be known to some extent by drying the first slurry and the second slurry and measuring the specific surface area of the solid content.

  The obtained negative electrode mixture slurry is applied to a negative electrode core material and dried to form a coating film. The method for applying the negative electrode mixture slurry to the negative electrode core material is not particularly limited. For example, the negative electrode mixture slurry is applied in a predetermined pattern on the raw material of the negative electrode core material using a die coat. The drying temperature of the coating film is not particularly limited.

  The coated film after drying is rolled with a rolling roll and controlled to a predetermined thickness. By rolling, the adhesive strength between the negative electrode mixture layer and the negative electrode core material and the adhesive strength between the graphite particles are increased. The negative electrode mixture layer thus obtained is cut into a predetermined shape together with the negative electrode core material, whereby the negative electrode is completed.

In the present invention, the graphite particles are coated with the first water-soluble polymer having a network structure, and the cooperative action between the second water-soluble polymer having a network structure and the rubber particles is obtained. In addition, the binding property between the graphite particles is strong, and the electrode plate strength is improved. Specifically, as the binder strength between the graphite particles in the negative electrode mixture layer, 98 N / cm ² or more, more can be achieved 150~250N / cm ^2. Further, the binding strength between the negative electrode core material and the negative electrode mixture layer can be 15 N / m or more, and further 20 to 30 N / m can be achieved. By improving the electrode plate strength, even when the number of charge / discharge cycles of the battery is increased, swelling of the negative electrode mixture layer is suppressed, and peeling of the negative electrode mixture layer from the negative electrode core material is significantly suppressed.

The binding strength between the graphite particles is measured as follows.
[Measurement method of binding strength between graphite particles]
A 2 cm × 3 cm negative electrode piece is cut out from the negative electrode having the negative electrode mixture layer formed on both sides. The negative electrode mixture layer is peeled off from one surface of the negative electrode piece, and the negative electrode mixture layer on the other surface is left as it is. The other surface of the negative electrode piece is attached to an adhesive layer of a double-sided tape (product number: No. 515, manufactured by Nitto Denko Corporation) attached on a glass plate. Next, the negative electrode core material is peeled from the negative electrode piece to expose the negative electrode mixture layer. Thereby, the sample for a measurement which the negative mix layer adhered to the single side | surface of a double-sided tape is produced.

The double-sided tape side of this measurement sample is attached to the tip of a probe (tip diameter: 0.2 cm) of a tacking tester (trade name: TAC-II, manufactured by Resuka Co., Ltd.). Next, the measurement probe is pressed against the negative electrode mixture layer under the following conditions, and separated to perform a peel test. In this peeling test, the maximum load at which peeling occurs between graphite particles is measured. The value obtained by dividing the maximum load obtained by the cross-sectional area (0.031 cm ² ) of the probe is the binding strength (N / cm ² ) between the graphite particles.

<Test conditions>
Measurement probe indentation speed 30 mm / min Measurement probe indentation time 10 seconds Measurement probe indentation load 3.9 N
Measuring probe pulling speed 600mm / min

Further, the binding strength between the negative electrode core material and the negative electrode mixture layer is measured as follows.
[Measurement method of binding strength between negative electrode core material and negative electrode mixture layer]
The negative electrode was cut to prepare a test piece having a width of 15 mm and a length of 80 mm. A double-sided tape (No. 151 manufactured by Nitto Denko Corporation) was attached to the negative electrode mixture layer on one side of the test piece and fixed to a smooth stainless steel (SUS) substrate. The SUS board | substrate with which the test piece was fixed was installed so that it might become horizontal. Next, one end of the negative electrode core material in the longitudinal direction of the test piece is attached to a tensile tester (trade name: Tensilon Universal Tester RTC1210, It was fixed to a movable jig of A & D). And the movable jig was moved so that the negative mix layer and core material of a test piece may peel at a speed | rate of 20 mm / min. At that time, the tensile direction was always maintained at 90 ° with respect to the SUS substrate on which the test piece was fixed. The numerical value of the stable tensile strength when 30 mm or more of the test piece was peeled was read and used as the binding strength between the negative electrode core material and the negative electrode mixture layer.

  The non-aqueous electrolyte secondary battery of the present invention includes the above-described negative electrode and positive electrode, a separator interposed therebetween, and a non-aqueous electrolyte. The shape of the battery is not particularly limited, but may be a cylindrical shape, a square shape, a flat shape, a coin shape, or the like.

  FIG. 3 is a perspective view schematically showing the configuration of the nonaqueous electrolyte secondary battery 1 according to one embodiment of the present invention. In FIG. 3, in order to show the structure of the principal part of the battery 30, the part is notched and shown. The battery 30 is a rectangular battery in which a flat electrode group 32 and a nonaqueous electrolyte are accommodated in a rectangular battery case 31.

  The electrode group 32 includes a positive electrode, a negative electrode, and a separator (all not shown). The positive electrode lead 33 connects the positive electrode core material and a sealing plate 34 having a function as a positive electrode terminal. The negative electrode lead 35 connects the negative electrode core material and the negative electrode terminal 36. The gasket 37 insulates the sealing plate 34 and the negative electrode terminal 36. The sealing plate 34 is joined to the open end of the rectangular battery case 31 and seals the rectangular battery case 31. A liquid injection hole (not shown) is formed in the sealing plate 34. The liquid injection hole is closed by a sealing plug 38 after the nonaqueous electrolyte is injected into the rectangular battery case 31. The electrode group 32 can be produced by interposing a separator between the positive electrode and the negative electrode, winding them, and press-molding the wound body into a flat shape.

For the positive electrode, for example, a positive electrode mixture slurry containing a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride is applied to a positive electrode core material such as an aluminum foil, dried, and rolled. Can be obtained. As the positive electrode active material, a lithium-containing transition metal composite oxide is preferable. Typical examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , Li _x Ni _y M _z Me _{1- (y + z)} O _{2 + d, and the} like. Among these, lithium nickel-containing composite oxides are preferable because high capacity can be secured.

Specific lithium nickel-containing composite oxides include, for example, the general formula (1):
_{Li x Ni y M z Me 1-} (y + z) O 2 + d (1)
(M is at least one element selected from the group consisting of Co and Mn, Me is at least one element selected from the group consisting of Al, Cr, Fe, Mg, and Zn; 98 ≦ x ≦ 1.10, 0.3 ≦ w ≦ 1.0, 0 ≦ z ≦ 0.7, 0.9 ≦ (y + z) ≦ 1.0 and −0.01 ≦ d ≦ 0.01 ).

  As the separator, a microporous film made of polyethylene or polypropylene is generally used. The thickness of the separator is, for example, 10 to 30 μm.

The non-aqueous electrolyte has lithium ion conductivity, includes a solute (supporting salt) and a non-aqueous solvent, and further includes various additives as necessary. Solutes include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ and the like. Solutes can be used alone or in combination of two or more. The solute is preferably added at a ratio of 0.5 to 2 moles per liter of the nonaqueous solvent. Nonaqueous solvents include cyclic carbonates, chain carbonates, and cyclic carboxylic acid esters. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate. Examples of chain carbonic acid esters include diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone and γ-valerolactone. A non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types.

Next, the present invention will be specifically described based on examples and comparative examples. However, the present invention is not limited to the following examples.
In each example and comparative example, the viscosity of the aqueous solution and slurry at 25 ° C. was measured at a rotation speed of 20 rpm using a Brookfield rotary viscometer and a 14.6 mm diameter spindle.
Example 1
(1) Preparation of positive electrode LiNi _0.82 Co _0.15 Al _0.03 O ₂ (positive electrode active material) 100 parts by weight, acetylene black (conductive agent) 1 part by weight, polyvinylidene fluoride (binder) 1 part by weight and N-methyl-2 -Pyrrolidone 25 weight part was mixed with the double arm type kneader, and the positive mix slurry was prepared. The positive electrode mixture slurry was applied to both sides of a 15 μm thick strip-shaped aluminum foil (positive electrode core material), dried, and then the coated film was rolled to prepare a positive electrode plate. The total thickness of the positive electrode mixture layers on both sides and the positive electrode core material was 120 μm. Thereafter, the positive electrode plate was cut into a predetermined size to obtain a strip-shaped positive electrode.

(2) Production of Negative Electrode Using a device similar to that shown in FIG. 1, a negative electrode mixture slurry was prepared by the following procedure.
(I) Preparation of Premixed Slurry Natural graphite particles (average particle size 20 μm, BET specific surface area 6.2 m ² / g) 2000 g, carboxymethyl cellulose (CMC) 10 g as a first water-soluble polymer, water 1200 g, sawtooth blade The mixture was put into a premixer (first mixer) equipped with a rotary rotor and mixed. The rotation speed of the first mixer was 2000 rpm, and the mixing time was 10 minutes. The shear rate at this time was 500 (1 / s).

The degree of etherification of CMC as the first water-soluble polymer was 0.6, the weight average molecular weight was 250,000, and the viscosity of a 1% by weight aqueous solution at 25 ° C. was 18.5 Pa · s.
The viscosity of the obtained premixed slurry at 25 ° C. was 50 Pa · s.

(Ii) Preparation of First Slurry The premixed slurry was supplied to a Fillmix FM80-50 type, which is an in-line mixer, at a flow rate of 600 g / min with a delivery pump, and was finally mixed. The rotor speed (peripheral speed) of the Fillmix FM80-50 type was 20 m / s, the clearance between the rotor and the stator was 2 mm, and the residence time was about 30 seconds. The shear rate at this time was 10,000 (1 / s).

The viscosity of the first slurry at 25 ° C. was 30 Pa · s.
A part of the first slurry was recovered, dried, and the BET specific surface area of the solid content was measured and found to be 3.7 m ² / g. That is, the specific surface area was reduced by about 40% from the initial specific surface area. From this, it can be understood that the surface of the graphite particles is appropriately coated with the first water-soluble polymer.

(Iii) Preparation of Second Slurry (Negative Electrode Mixture Slurry) The first slurry that passed through the film mix FM80-50 type was sent to a second mixer having a sawtooth blade type rotary blade and stored. Thereafter, 10 g of CMC to be the second water-soluble polymer, 700 g of water, 50 g of an emulsion (solid content concentration 40 wt%) of rubber particles (styrene butadiene rubber, glass transition point −10 ° C.) having an average particle diameter of 120 nm, Was put into the same mixer and further mixed. The rotation speed of the second mixer was 2000 rpm, and the mixing time was 10 minutes.

The degree of etherification of CMC, which is the second water-soluble polymer, was also 0.6, but the weight average molecular weight was 80,000, and the viscosity of a 1 wt% aqueous solution at 25 ° C. was 6.2 Pa · s.
The viscosity of the obtained second slurry (negative electrode mixture slurry) at 25 ° C. was 7 Pa · s.

A part of the negative electrode mixture slurry was recovered, dried, and the BET specific surface area of the solid content was measured and found to be 2.6 m ² / g. That is, the specific surface area was reduced by about 58% from the initial specific surface area. From this, it can be understood that the surface of the graphite particles appropriately coated with the first water-soluble polymer is further appropriately coated with the second water-soluble polymer and the rubber particles.

  The negative electrode mixture slurry was applied to both sides of a 10 μm thick tough pitch copper foil (negative electrode core material, copper purity: 99.9%, softening temperature: 170 ° C.), dried, and then the coated film was rolled to produce a negative electrode plate did. The total thickness of the negative electrode mixture layers on both sides and the negative electrode core material was 150 μm. Thereafter, the negative electrode plate was cut into a predetermined size to obtain a strip-shaped negative electrode.

The binding strength between the graphite particles of the obtained negative electrode was 196 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 25 N / cm.

(3) Preparation of nonaqueous electrolyte 1 part by weight of vinylene carbonate was added to 99 parts by weight of a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 to obtain a mixed solvent. Thereafter, LiPF ₆ was dissolved in a mixed solvent so as to have a concentration of 1.0 mol / L to prepare a nonaqueous electrolyte.

(4) Production of electrode group An electrode group was produced using the obtained positive electrode, negative electrode and non-aqueous electrolyte.
Specifically, one end of the aluminum lead was connected to the positive electrode core material. One end of the nickel lead was connected to the negative electrode core material. These were wound by interposing a separator having a thickness of 16 μm (polyethylene microporous film, trade name: Hypore, manufactured by Asahi Kasei Co., Ltd.) between the positive electrode and the negative electrode. The obtained wound body was pressed under an environment of 25 ° C. to produce a flat electrode group. The press pressure was 0.5 MPa.

(5) Battery assembly The obtained electrode group was inserted into a stainless steel prismatic battery case. A resin frame was attached to the upper part of the electrode group. The resin frame body separates the electrode group from the stainless steel sealing plate and prevents the aluminum lead or nickel lead from contacting the battery case. The other end of the aluminum lead was connected to the lower surface of the sealing plate. The other end of the nickel lead was connected to a stainless steel negative electrode terminal. The negative electrode terminal was disposed on the sealing plate via a polypropylene gasket. A sealing plate was placed in the opening of the battery case and welded. A predetermined amount of nonaqueous electrolyte was injected into the battery case from the injection hole of the sealing plate. Thereafter, the liquid injection port was closed with a plug to produce the nonaqueous electrolyte secondary battery of the present invention.

[Battery capacity evaluation]
For the battery of Example 1, the charge / discharge cycle was repeated three times under the following conditions, and the third discharge capacity was determined to be the battery capacity. The results are shown in Table 1.
Constant current charging: 200mA, end voltage 4.2V
Constant voltage charge: end current 20 mA, rest time 20 minutes Constant current discharge: current 200 mA, end voltage 2.5 V, rest time 20 minutes

[Charge / discharge cycle characteristics evaluation]
About the battery of Example 1, the following charging / discharging cycle was repeated 500 times at 45 degreeC.
Constant current charging: Charging current value 500 mA / end-of-charge voltage 4.2 V
Constant voltage charging: Charging voltage value 4.2V / end-of-charge current 100mA
Constant current discharge: discharge current value 500 mA / discharge end voltage 3 V
And according to the following formula | equation, the capacity | capacitance maintenance factor (%) was calculated | required. The results are shown in Table 1.
Capacity retention rate (%) = (500th discharge capacity / first discharge capacity) × 100

[Battery expansion evaluation]
For the battery after charge / discharge cycle characteristics evaluation (after 500 cycles), the amount of swelling of the battery was measured. The amount of swelling of the battery was set to a value (mm) obtained by subtracting the thickness of the battery before evaluation of charge / discharge cycle characteristics from the thickness of the battery after evaluation of charge / discharge cycle characteristics. The results are shown in Table 1.

Example 2
A negative electrode was produced in the same manner as in Example 1 except that the amount of the first water-soluble polymer used was changed to 14 g. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 80 Pa · s, and the viscosity of the first slurry was 50 Pa · s.
The BET specific surface area of the dried solid content of the first slurry was 3.2 m ² / g.

The viscosity of the second slurry at 25 ° C. was 9 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.4 m ² / g.

The binding strength between the graphite particles of the negative electrode was 215 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 29 N / cm.

Example 3
A negative electrode was produced in the same manner as in Example 1 except that the amount of the first water-soluble polymer used was changed to 6 g. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 45 Pa · s, and the viscosity of the first slurry was 20 Pa · s.
The BET specific surface area of the dried solid content of the first slurry was 4.3 m ² / g.

The viscosity of the second slurry at 25 ° C. was 5 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 3.5 m ² / g.

The binding strength between the graphite particles of the negative electrode was 88 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 20 N / cm.

<< Comparative Example 1 >>
A negative electrode mixture slurry was prepared in the same manner as in Example 1 except that the film mix FM80-50 type was not passed. Specifically, the premixed slurry was moved directly from the first mixer to the second mixer. A negative electrode was produced in the same manner as in Example 1 except that the negative electrode mixture slurry thus obtained was used. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 45 Pa · s.
The BET specific surface area of the dried solid content of the premixed slurry was 4.4 m ² / g.

The viscosity of the second slurry at 25 ° C. was 11 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 3.3 m ² / g.

The binding strength between the graphite particles of the negative electrode was 88 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 17 N / cm.

<< Comparative Example 2 >>
A CMC having a molecular weight of 80,000 and a 1 wt% aqueous solution of 6.2 Pa · s is used as the first water-soluble polymer, and a CMC having a molecular weight of 250,000 and a 1 wt% aqueous solution of 18.5 Pa · s is used as the second water-soluble polymer. A negative electrode was produced in the same manner as in Example 1 except that it was used as a conductive polymer. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 20 Pa · s, and the viscosity of the first slurry was 15 Pa · s.
The shear rate in the main mixing was 10,000 (1 / s).
The BET specific surface area of the dried solid content of the first slurry was 3.4 m ² / g.

The viscosity of the second slurry at 25 ° C. was 18 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.9 m ² / g.

The binding strength between the graphite particles of the negative electrode was 127 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 19 N / cm.
Moreover, the surface state of the negative electrode was nonuniform. This is probably because the second water-soluble polymer was not sufficiently dissolved in the second slurry.

<< Comparative Example 3 >>
A negative electrode was prepared in the same manner as in Example 1 except that CMC having a viscosity of 2.0 Pa · s, an etherification degree of 1.0, and a weight average molecular weight of 40,000 was used as the second water-soluble polymer. . A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 55 Pa · s, and the viscosity of the first slurry was 30 Pa · s.
The BET specific surface area of the dried solid content of the first slurry was 3.7 m ² / g.

The viscosity of the second slurry at 25 ° C. was 3 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.6 m ² / g.

The binding strength between the graphite particles of the negative electrode was 58 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 13 N / cm.

<< Comparative Example 4 >>
A negative electrode was prepared in the same manner as in Example 1 except that CMC having a viscosity of 2.0 Pa · s, an etherification degree of 1.0, and a weight average molecular weight of 40,000 was used as the first water-soluble polymer. . A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 20 Pa · s, and the viscosity of the first slurry was 10 Pa · s.
The shear rate in the main mixing was 10,000 (1 / s).
The BET specific surface area of the dried solid content of the first slurry was 3.2 m ² / g.

The viscosity of the second slurry at 25 ° C. was 4 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.5 m ² / g.

The binding strength between the graphite particles of the negative electrode was 58 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 13 N / cm.

The results of Examples 2-3 and Comparative Examples 1-4 are shown in Table 1.
In Table 1, the interparticle strength is the binding strength between the graphite particles, and the peel strength is the binding strength between the negative electrode core material and the negative electrode mixture layer.

  From Table 1, it is clear that the batteries of Examples 1 to 3 have high peel strength and interparticle strength, excellent capacity retention, and small battery swelling.

  On the other hand, in the comparative example 1, all the evaluation results are inferior to those of the examples, and the amount of swelling of the battery is particularly large. This is considered to be because the electrode plate strength was lowered because the graphite particles could not be sufficiently coated with the first water-soluble polymer.

  Also in Comparative Example 2, all the evaluation results are inferior to those of the Examples, and in particular, the capacity retention rate is degraded. This is because the first water-soluble polymer and the second water-soluble polymer were exchanged, so that the graphite particles were not properly coated with the water-soluble polymer, but were excessively coated, and the lithium ion acceptance by the negative electrode was reduced. Is considered to be the cause.

  Also in Comparative Example 3, all the evaluation results are inferior to those of the Examples, and the amount of swelling of the battery is particularly large. This is probably because the degree of etherification of the second water-soluble polymer exceeds 0.8 and a sufficient network structure cannot be formed, so that the electrode plate strength is reduced.

  Also in Comparative Example 4, all the evaluation results are inferior to those of the Examples. In particular, the capacity retention rate is greatly deteriorated, and the amount of swelling of the battery is also large. This is because the degree of etherification of the first water-soluble polymer exceeds 0.8, so the graphite particles are not properly coated with the water-soluble polymer, but are excessively coated, and the lithium ion acceptance by the negative electrode is reduced. It is thought that this is because the electrode plate strength was reduced.

When the negative electrode was taken out from the batteries of Examples 1 to 4 and the cross section was observed with a transmission electron microscope, the first water-soluble polymer covered the surface of the graphite particles, and the second water-soluble polymer and the rubber particles were It can be observed that the graphite particles coated with the first water-soluble polymer are adhered to each other.
On the other hand, when the negative electrode is taken out from the battery of Comparative Example 1 and the cross section thereof is observed in the same manner, the first water-soluble polymer can be distinguished from the second water-soluble polymer, but the first water-soluble polymer is composed of graphite particles. It can be observed that the ratio of covering the surface is very small.

Example 4
A negative electrode was produced in the same manner as in Example 1, except that CMC having a viscosity of 4.5 Pa · s, an etherification degree of 0.8, and a weight average molecular weight of 70,000 was used as the second water-soluble polymer. . A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the second slurry at 25 ° C. was 4 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.6 m ² / g.

The binding strength between the graphite particles of the negative electrode was 176 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 21 N / cm.

Example 5
A negative electrode was produced in the same manner as in Example 1 except that CMC having a viscosity of 16 Pa · s in a 1% by weight aqueous solution, a degree of etherification of 0.7, and a weight average molecular weight of 230,000 was used as the first water-soluble polymer. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 42 Pa · s, and the viscosity of the first slurry was 20 Pa · s.
The shear rate in the main mixing was 10,000 (1 / s).
The BET specific surface area of the dried solid content of the first slurry was 4.0 m ² / g.

The viscosity of the second slurry at 25 ° C. was 5 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.9 m ² / g.

The binding strength between the graphite particles of the negative electrode was 176 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 23 N / cm.

Example 6
A negative electrode was produced in the same manner as in Example 5 except that the same second water-soluble polymer as in Example 4 was used. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the second slurry at 25 ° C. was 4 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 2.8 m ² / g.

The binding strength between the graphite particles of the negative electrode was 147 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 21 N / cm.

Example 7
A negative electrode was produced in the same manner as in Example 1 except that CMC having a viscosity of 20 Pa · s in a 1% by weight aqueous solution, a degree of etherification of 0.5, and a weight average molecular weight of 200,000 was used as the first water-soluble polymer. A battery was prepared and evaluated in the same manner as in Example 1 using the obtained negative electrode.

The viscosity of the premixed slurry at 25 ° C. was 65 Pa · s, and the viscosity of the first slurry was 45 Pa · s.
The shear rate in this mixing was 15000 (1 / s).
The BET specific surface area of the dried solid content of the first slurry was 3.9 m ² / g.

The viscosity of the second slurry at 25 ° C. was 8 Pa · s.
The BET specific surface area of the dried solid content of the second slurry was 3.0 m ² / g.

The binding strength between the graphite particles of the negative electrode was 225 N / cm ² .
The binding strength between the negative electrode core material and the negative electrode mixture layer was 28 N / cm.
The results of Examples 4-7 are shown in Table 2.

From Table 2, it is clear that the batteries of Examples 4 to 7 have high peel strength and interparticle strength, are excellent in capacity retention, and have a small amount of battery swelling.
When the negative electrode was taken out from the batteries of Examples 4 to 7 and the cross section was observed with a transmission electron microscope, the first water-soluble polymer covered the surface of the graphite particles, and the second water-soluble polymer and the rubber particles were It can be observed that the graphite particles coated with the first water-soluble polymer are adhered to each other.

  The negative electrode of the present invention and the nonaqueous electrolyte secondary battery including the negative electrode are useful as a power source for portable electronic devices. Examples of portable electronic devices include personal computers, mobile phones, mobile devices, personal digital assistants (PDAs), portable game devices, and video cameras. Further, the negative electrode of the present invention and the non-aqueous electrolyte secondary battery comprising the same are a main power source or auxiliary power source for driving an electric motor in a hybrid electric vehicle, a fuel cell vehicle, a plug-in HEV, and the like, an electric tool, a vacuum cleaner, and a robot. It is also expected to be used as a drive power source.

11 Preliminary mixer (first mixer)
DESCRIPTION OF SYMBOLS 11a Stirring blade 12 Inline mixer 12a Stator 12b Rotor 13 2nd mixer 13a Stirring blade 14 Feeding pump 21 Shaft 22 Inlet 23 Window hole 24 Scallop 25 Overflow container 26 Discharge port 27 Outer container 27b Cooling water flow path 30 Nonaqueous electrolyte Secondary battery 31 Battery case 32 Electrode group 33 Positive electrode lead 34 Sealing plate 35 Negative electrode lead 36 Negative electrode terminal 37 Gasket 38 Sealing

Claims (10)

Including a negative electrode core material and a negative electrode mixture layer attached to the negative electrode core material,
The negative electrode mixture layer includes graphite particles, a water-soluble polymer, and rubber particles,
The amount of the water-soluble polymer is 0.6 to 3 parts by weight per 100 parts by weight of the graphite particles,
The amount of the rubber particles is 0.4 to 1.5 parts by weight per 100 parts by weight of the graphite particles,
The water-soluble polymer includes a first water-soluble polymer having a molecular weight of 200,000 or more and an etherification degree of 0.8 or less, and a second water-soluble polymer having a molecular weight of 150,000 or less and an etherification degree of 0.8 or less,
The first water-soluble polymer coats the surface of the graphite particles,
The negative electrode for a non-aqueous electrolyte secondary battery, wherein the second water-soluble polymer and the rubber particles are bonded between graphite particles coated with the first water-soluble polymer. The amount of the first water-soluble polymer is 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles,
The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the amount of the second water-soluble polymer is 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles.   The first viscosity ν1 at 25 ° C. of an aqueous solution containing 1% by weight of the first water-soluble polymer and the second viscosity ν2 at 25 ° C. of an aqueous solution containing 1% by weight of the second water-soluble polymer are ν1> ν2. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the first viscosity ν1 is 10 to 40 Pa · s, and the second viscosity ν2 is 0.5 to 8 Pa · s. Negative electrode.   The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the rubber particles have an average particle size of 50 to 200 nm.   A nonaqueous electrolyte secondary battery comprising the negative electrode according to any one of claims 1 to 5, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte. (I) a step of mixing a graphite particle, a first water-soluble polymer having a molecular weight of 200,000 or more and an etherification degree of 0.8 or less, and water to prepare a first slurry;
(Ii) a step of mixing the first slurry with a second water-soluble polymer having a molecular weight of 150,000 or less and a degree of etherification of 0.8 or less, rubber particles, and water to prepare a second slurry;
(Iii) applying the second slurry to the negative electrode core material and drying to form a coating film;
(Iv) rolling the coating film to form a negative electrode mixture layer,
The amount of the first water-soluble polymer is 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles,
The amount of the second water-soluble polymer is 0.3 to 1.5 parts by weight per 100 parts by weight of the graphite particles,
The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries whose quantity of the said rubber particle is 0.4-1.5 weight part per 100 weight part of said graphite particles.   The first viscosity ν1 at 25 ° C. of an aqueous solution containing 1% by weight of the first water-soluble polymer and the second viscosity ν2 at 25 ° C. of an aqueous solution containing 1% by weight of the second water-soluble polymer are ν1> ν2. The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries of Claim 7 which satisfy | fills. Step (i) is a first step in which the graphite particles and the aqueous solution of the first water-soluble polymer are premixed;
9. A non-aqueous electrolyte according to claim 7, comprising a second step of subjecting the premixed slurry obtained by the premixing to a main mixing at a shear rate of 10,000 (1 / s) to 100,000 (1 / s). A method for producing a negative electrode for a secondary battery.   The non-aqueous electrolyte according to claim 9, wherein the first step is performed with a premixer, and the obtained premixed slurry is continuously transferred to an inline mixer, and the second step is performed with the inline mixer. A method for producing a negative electrode for a secondary battery.

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