KR101978462B1 - Lithium ion secondary battery - Google Patents

Abstract

Wherein the negative electrode has a positive electrode, a negative electrode, an electrolytic solution and a separator, and the negative electrode comprises a negative electrode active material layer formed of a composition comprising a negative electrode active material, a particulate binder and a water-soluble polymer, wherein the negative electrode active material has a specific surface area of 2 m 2 / M 2 / g, wherein the water-soluble polymer is a copolymer comprising an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit, wherein the solvent of the electrolytic solution contains 50 to 80% by volume of propylene carbonate, And 0.05% by volume to 1% by volume of vinylene carbonate.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium ion secondary battery,

The present invention relates to a lithium ion secondary battery.

Generally, a lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolytic solution may be decomposed by charging and discharging of the lithium ion secondary battery, which affects the performance of the lithium ion secondary battery. Therefore, for the purpose of improving various performance of the lithium ion secondary battery, the electrolytic solution has conventionally been examined (see Patent Documents 1 to 3).

Japanese Patent Application Laid-Open No. 2008-066062 Japanese Laid-Open Patent Publication No. 2009-076433 Japanese Laid-Open Patent Publication No. 2011-124039

If the specific surface area of the negative electrode active material of the lithium ion secondary battery is large, the place where the charge can be exchanged becomes large, and the resistance tends to decrease and the output characteristic to be improved. However, in a lithium ion secondary battery having a high output characteristic, generally, a large amount of gas is generated due to the decomposition of the solvent of the electrolyte solution. When gas is generated, the negative active material is destroyed by the gas, or ions can not be exchanged between the negative active material and the solvent in a place where gas bubbles exist, and the capacity of the lithium ion secondary battery is lowered . Therefore, the capacity of the lithium ion secondary battery, which can generate a large amount of gas, tends to decrease with charging and discharging.

In addition, for example, in a negative electrode active material using a carbonaceous active material such as graphite, the bond between the graphite layers is broken during the intercalation reaction with the negative electrode active material, and the conductive path is sometimes broken. In the lithium ion secondary battery having high output characteristics, since the above-mentioned conduction path is rapidly cut off, the capacity tends to decrease greatly with the charge and discharge.

As described above, when the decrease in the capacity accompanying the charge and discharge is large, the cycle characteristics are lowered. Therefore, the lithium ion secondary battery generally has a low cycle characteristic when the output characteristic is high, and a low output characteristic when the cycle characteristic is high. That is, in the lithium ion secondary battery, it is difficult to increase both the output characteristic and the cycle characteristic.

Therefore, studying electrolytic solution as a means for increasing the output characteristic and the cycle characteristic together has been studied. For example, it has been found that the inclusion of vinylene carbonate (VC) in the solvent of the electrolyte improves the cycle characteristics of the lithium ion secondary battery. This is presumed to be because decomposition of the solvent of the electrolytic solution is inhibited by using vinylene carbonate. For example, it has been studied to use a mixed solvent in which vinylene carbonate and a solvent other than vinylene carbonate such as propylene carbonate (PC) are combined in a lithium ion secondary battery.

However, propylene carbonate has a low viscosity at a low temperature, and precipitation at low temperature is less likely to occur than a solvent such as ethylene carbonate. Therefore, the lithium ion secondary battery using propylene carbonate as a solvent for the electrolyte solution was expected to improve the output characteristics (low temperature characteristics) at low temperatures. However, when a mixed solvent of propylene carbonate and vinylene carbonate is used as described above, the low-temperature characteristics of the lithium ion secondary battery are low. This is because, when the amount of vinylene carbonate is increased to such an extent that the improvement in the cycle characteristics can be realized, the synergistic effect of the viscosity of the electrolyte solution by vinylene carbonate becomes large at a low temperature and the viscosity of the electrolyte becomes high. do.

Therefore, in the conventional lithium ion secondary battery, the cycle characteristics are low when the low temperature characteristics are high, and the low temperature characteristics are low when the cycle characteristics are high. Therefore, development of a lithium ion secondary battery excellent in both low-temperature characteristics and cycle characteristics has been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a lithium ion secondary battery excellent in both low temperature characteristics and cycle characteristics.

The inventor of the present invention has conducted intensive studies in view of the above problems and found that when the negative electrode has a negative electrode active material layer formed of a composition containing a negative electrode active material, a particulate binder and a water-soluble polymer, (Meth) acrylic acid ester monomer unit as the water-soluble polymer, and a copolymer of propylene carbonate and vinylene carbonate as the solvent of the electrolyte at a predetermined volume ratio The present inventors have found that a lithium ion secondary battery excellent in both low-temperature characteristics and cycle characteristics can be realized, and the present invention has been accomplished.

That is, the present invention is as follows.

[1] A battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator,

Wherein the negative electrode comprises a negative electrode active material layer formed of a composition comprising a negative electrode active material, a particulate binder, and a water-soluble polymer,

The negative electrode active material has a specific surface area of 2 m 2 / g to 15 m 2 / g,

Wherein the water-soluble polymer is a copolymer comprising an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit,

Wherein the solvent of the electrolytic solution contains 50 to 80 volume% of propylene carbonate and 0.05 to 1 volume% of vinylene carbonate.

[2] The lithium ion secondary battery according to [1], wherein the negative electrode active material is one or both of a carbonaceous active material and a Si compound.

[3] The lithium ion secondary battery according to [1] or [2], wherein the particulate binder is composed of a copolymer comprising an aliphatic conjugated diene monomer unit and an ethylenically unsaturated carboxylic acid monomer unit.

[4] The lithium ion secondary battery according to any one of [1] to [3], wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer is 20% by weight to 50% by weight.

[5] The lithium ion secondary battery according to any one of [1] to [4], wherein the content of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is 1% by weight to 30% .

[6] The lithium ion secondary battery according to any one of [1] to [5], wherein the weight ratio of the particulate binder and the water-soluble polymer is from 0.5 / 99.5 to 40/60 as the water-soluble polymer / particulate binder.

[7] The lithium ion secondary battery according to any one of [1] to [6], wherein the water-soluble polymer contains a crosslinkable monomer unit and the content thereof is 0.1 wt% or more and 2 wt% or less.

[8] The water-soluble polymer according to any one of [1] to [7], wherein the water-soluble polymer contains a (meth) acrylic acid ester monomer unit other than the fluorine-containing (meth) acrylic acid ester monomer, A lithium ion secondary battery according to any one of claims 1 to 3.

[9] The lithium ion secondary battery according to any one of [1] to [8], wherein the amount of the particulate binder is 0.1 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the negative electrode active material.

The content of the aliphatic conjugated diene monomer unit in the particulate binder is 20 wt% or more and 60 wt% or less, the content of the ethylenically unsaturated carboxylic acid monomer unit is 0.1 wt% or more and 15 wt% or less, By weight based on the total weight of the lithium ion secondary battery.

According to the present invention, it is possible to realize a lithium ion secondary battery excellent in both low-temperature characteristics and cycle characteristics.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be arbitrarily changed without departing from the scope of the claims of the present invention and its equivalent scope.

In the following description, (meth) acrylic acid includes acrylic acid and methacrylic acid. Further, (meth) acrylate includes acrylate and methacrylate.

In addition, a substance which is water-soluble means that the insoluble content is less than 0.5% by weight at 25 캜 when 0.5 g of the substance is dissolved in 100 g of water. On the other hand, when a substance is insoluble in water, 0.5 g of the substance is dissolved in 100 g of water at 25 캜, and the insoluble content is 90% by weight or more.

[One. summary]

The lithium ion secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material layer formed of a composition including a negative electrode active material, a particulate binder, and a water-soluble polymer. The specific surface area of the negative electrode active material is from 2 m 2 / g to 15 m 2 / g. Further, the water-soluble polymer is a copolymer comprising an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit. The solvent of the electrolytic solution includes 50% by volume to 80% by volume of propylene carbonate and 0.05% by volume to 1% by volume of vinylene carbonate.

With such a constitution, the lithium ion secondary battery of the present invention is excellent in both low-temperature characteristics and cycle characteristics. Further, the lithium ion secondary battery of the present invention is excellent in high-temperature storage characteristics, and is normally capable of suppressing the unfolding of the battery cell by charging and discharging. The reason why such an excellent advantage is obtained is not certain, but the inventors of the present invention have investigated the reason for the following reason.

i. Low temperature characteristic

Propylene carbonate is a solvent having a low viscosity at a low temperature. Since the lithium ion secondary battery of the present invention contains a large amount of propylene carbonate as a solvent for the electrolytic solution, the viscosity of the electrolytic solution at a low temperature can be lowered. Therefore, since the solvent component of the electrolytic solution does not easily precipitate in the solvent, the internal resistance can be lowered. Therefore, it is possible to improve the output characteristics of the lithium ion secondary battery at low temperature, and it is possible to improve the low temperature characteristics.

Further, in the lithium ion secondary battery of the present invention, the amount of vinylene carbonate in the electrolytic solution was reduced. As a result, the lowering of the output at a low temperature by the vinylene carbonate can be suppressed, whereby the low temperature characteristics can be improved.

Further, in the lithium ion secondary battery of the present invention, the cycle characteristics can be increased even when the negative electrode active material having a large specific surface area is used. This makes it possible to use the negative electrode active material having a large specific surface area, so that the output characteristics can be improved. Therefore, the low-temperature characteristics can be improved.

Further, as described later, it is considered that the water-soluble polymer forms a film in the negative electrode active material layer and covers the negative electrode active material. Therefore, in the lithium ion secondary battery of the present invention, it is considered that the resistance is increased by the amount of the coating film of the water-soluble polymer and the low-temperature property is lowered. However, since the water-soluble polymer contains a fluorine-containing (meth) acrylic acid ester monomer unit, the coating film of the water-soluble polymer is excellent in ion conductivity. Therefore, in practice, in the lithium ion secondary battery of the present invention, there is no significant increase in resistance due to the coating of the water-soluble polymer.

ii. Cycle characteristics

In the lithium ion secondary battery of the present invention, the negative electrode active material layer contains a copolymer containing an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit as a water-soluble polymer. This water-soluble polymer can form a coating on the negative electrode active material layer of the lithium ion secondary battery. Since the negative electrode active material is covered with the coating, the negative electrode active material and the propylene carbonate are hardly brought into direct contact with each other in the negative electrode. Therefore, in the lithium ion secondary battery of the present invention, decomposition of propylene carbonate is suppressed, and gas is not generated well. In addition, even when a carbonaceous active material such as graphite is used as the negative electrode active material, the bonds between the graphite layers are not well broken by the propylene carbonate during the intercalation reaction. Therefore, even if the charge / discharge cycle is repeated, the capacity of the lithium ion secondary battery is not reduced so much, and the cycle characteristics can be improved.

Further, in the lithium ion secondary battery of the present invention, since the electrolyte contains vinylene carbonate, it is considered that cycle characteristics are improved by the effect of the vinylene carbonate. Since the amount of the vinylene carbonate is smaller than that of the prior art, deterioration of the low-temperature characteristics by the vinylene carbonate is little or small. Further, since the effect of the water-soluble polymer is obtained at least of the vinylene carbonate as described above, the cycle characteristics can be made sufficiently high.

Further, propylene carbonate is not decomposed well in comparison with other solvents such as ethylene carbonate, and gas is not generated well. Therefore, it is considered that the use of a large amount of propylene carbonate as a solvent contributes to the improvement of cycle characteristics.

iii. As regards compatibility with high levels of low-temperature characteristics and cycle characteristics

As described above, in the conventional lithium ion secondary battery, for example, when the specific surface area of the negative electrode active material is increased and the amount of the vinylene carbonate is decreased to improve the low temperature characteristics, the cycle characteristics are inferior. On the contrary, for example, if the specific surface area of the negative electrode active material is reduced or the amount of vinylene carbonate is increased to improve the cycle characteristics, the low temperature characteristics are inferior. For this reason, conventionally, it has been attempted to adjust the specific surface area of the negative electrode active material and the amount of the vinylene carbonate to optimize the low temperature property and the cycle property in the range in which acceptable performance can be obtained.

On the other hand, in the lithium ion secondary battery of the present invention, by using a copolymer containing an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit as a water-soluble polymer, Both sides can be improved more than expected, and an effect exceeding simple optimization can be obtained.

The following points can be considered as the reason why both the low-temperature characteristic and the cycle characteristic can be improved to an expected level or higher. That is, since the ethylenic unsaturated carboxylic acid monomer unit contained in the water-soluble polymer is excellent in affinity with the negative electrode active material, a film excellent in adhesion to the surface of the negative electrode active material can be formed. Therefore, even if the negative electrode active material expands and shrinks in accordance with charge and discharge, the film can be stably maintained without peeling off the film. Further, since the film is not easily peeled off, the film is dispersed at a place other than the surface of the negative electrode active material, and the increase of the resistance of the lithium ion secondary battery can be suppressed. Further, since the fluorine-containing (meth) acrylic acid ester monomer unit contained in the water-soluble polymer increases the ion conductivity of the film, resistance increase due to the film can be suppressed. It is presumed that by these actions, both the low-temperature characteristic and the cycle characteristic can be effectively improved.

Further, according to the study of the present inventors, it has been found that the output characteristics and the cycle characteristics are inferior when vinylene carbonate is not used even when a water-soluble polymer is used (see Comparative Example 6). Taking this into account, both the low-temperature characteristics and the cycle characteristics of the lithium ion secondary battery of the present invention can be improved to an expected level or more by not only an action obtained by using a water-soluble polymer, (Meth) acrylic acid ester monomer unit and a water-soluble polymer containing an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit.

iv. High Temperature Storage Characteristics

In the lithium ion secondary battery of the present invention, as described above, the negative electrode active material is covered with the coating of the water-soluble polymer. Therefore, decomposition of the electrolytic solution is prevented not only in a low-temperature environment but also in a high-temperature environment. Therefore, even when the battery is stored in a high-temperature environment, the capacity of the lithium ion secondary battery of the present invention is not deteriorated.

v. Suppression of unfolding of the battery cell

In the lithium ion secondary battery of the present invention, since decomposition of the electrolytic solution by charge and discharge can be prevented as described above, generation of gas can be suppressed. Therefore, it is possible to suppress the swelling of the battery cell due to the generation of the gas.

Further, the coating of the water-soluble polymer covers the negative electrode active material, whereby the rigidity of the negative electrode active material layer can be enhanced. Therefore, expansion of the negative electrode by repetition of charging and discharging can be suppressed. Therefore, it is also possible to suppress the swelling of the battery cell.

[2. Negative pole]

The negative electrode has a negative electrode active material layer. Normally, the negative electrode has a current collector, and a negative electrode active material layer is formed on the surface of the current collector. At this time, the negative electrode active material layer may be formed on one surface of the current collector or on both surfaces.

[2.1. Whole house]

Generally, the current collector is formed of a material having electrical conductivity and electrochemically durable. As a material for the current collector, a metal material is preferable because it has heat resistance. Examples thereof include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold and platinum. Among them, copper is preferable as the collector for the negative electrode.

The shape of the current collector is not particularly limited, and it is preferable that the sheet is in the form of a sheet having a thickness of about 0.001 mm to 0.5 mm.

The collector may be subjected to a roughening treatment before the negative electrode active material layer is formed thereon in order to increase the bonding strength with the negative electrode active material layer. When a layer interposed between the current collector and the negative electrode active material layer is present, the current collector may be subjected to a roughening treatment before forming the layer on the current collector. Examples of the roughening method include mechanical roughening, electrolytic roughening, and chemical roughening. In the mechanical polishing, for example, a polishing forge fixed with abrasive particles, a grinding wheel, an emery buff, a wire brush having a steel wire, or the like is used.

Further, in order to increase the binding strength of the current collector and the negative electrode active material layer or to increase the conductivity, an intermediate layer may be formed on the surface of the current collector.

[2.2. Negative electrode active material layer]

The negative electrode active material layer is a layer formed of a composition comprising a negative electrode active material, a particulate binder, and a water-soluble polymer.

[2.2.1. Negative electrode active material]

The negative electrode active material is an electrode active material for the negative electrode, and is a material capable of exchanging electrons in the negative electrode of the secondary battery.

The specific surface area of the negative electrode active material is usually not less than 2 m 2 / g, usually not more than 15 m 2 / g, preferably not more than 13 m 2 / g, more preferably not more than 10 m 2 / g. By using the negative electrode active material having a specific surface area of at least the lower limit of the above range, the output characteristics of the lithium ion secondary battery can be improved. Further, by using a negative electrode active material having a specific surface area lower than the upper limit of the above range, cycle characteristics can be improved and the lifetime of the lithium ion secondary battery can be prolonged.

The specific surface area of the negative electrode active material can be measured by a BET method (apparatus: Trista II3020 series, manufactured by Shimadzu Corporation) by nitrogen gas adsorption.

As the negative electrode active material, a material capable of occluding and releasing lithium is usually used. Examples of the negative electrode active material include a carbonaceous active material and a metal-based active material.

The carbonaceous active material refers to a negative electrode active material having carbon as a main skeleton capable of intercalating lithium ions (also referred to as a dope) and desorption (also referred to as a dope). Specific examples of the carbonaceous active material include a carbonaceous material and a graphite material.

The carbonaceous material generally refers to a material having a low graphitization (that is, low crystallinity) in which a carbon precursor is heat-treated at 2000 ° C or lower and carbonized. The lower limit of the heat treatment temperature is not particularly limited, but may be, for example, 500 占 폚 or higher. Examples of the carbonaceous material include easily graphitic carbon which easily changes the structure of carbon by a heat treatment temperature, and non-graphitic carbon which has a structure similar to amorphous structure typified by glassy carbon .

As the graphitizing carbon, for example, there can be mentioned a carbon material made from tar pitch obtained from petroleum or coal as a raw material. Specific examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis gas phase grown carbon fibers. Here, MCMB is a carbon microparticle obtained by separating and extracting mesophase spherules produced in the course of heating the pitch flow at about 400 ° C. The mesophase pitch based carbon fiber is carbon fiber having mesophase pitch obtained by growing and coalescing the mesophase spheres as a raw material. The thermal decomposition vapor-grown carbon fiber is obtained by (1) a method of thermally decomposing an acrylic polymer fiber or the like, (2) a method of thermally decomposing by spinning, or (3) a method of using hydrocarbons Is a carbon fiber obtained by a catalytic vapor phase growth (catalytic CVD) method of vapor-phase thermal decomposition.

Examples of the non-graphitizable carbon include phenolic resin fired bodies, polyacrylonitrile carbon fibers, pseudo isotropic carbon, furfuryl alcohol resin fired bodies (PFA), hard carbon, and the like.

The graphite material is a graphite material having a high crystallinity close to that of graphite obtained by heat-treating graphitizing carbon at 2000 ° C or higher. The upper limit of the heat treatment temperature is not particularly limited, but may be 5000 占 폚 or lower, for example. Examples of the graphite material include natural graphite, artificial graphite and the like. Examples of the artificial graphite include artificial graphite heat-treated at a temperature of 2800 ° C or higher, graphitized MCMB heat-treated at a temperature of 2000 ° C or higher for MCMB, graphitized mesophase pitch system heat-treated at a temperature of 2000 ° C or higher for mesophase pitch- Carbon fiber and the like.

The graphite interlayer distance of the carbonaceous active material is preferably 0.340 nm or more, more preferably 0.345 nm or more, particularly preferably 0.350 nm or more, further preferably 0.370 nm or less, more preferably 0.365 nm or less, And particularly preferably 0.360 nm or less. Here, the graphite interlayer distance represents the surface interval (d value) of the (002) plane by the X-ray diffraction method. By using such a carbonaceous active material called so-called soft carbon, a lithium ion secondary battery excellent in output characteristics can be obtained without lowering the capacity per volume excessively.

Of these carbonaceous active materials, graphite materials are preferable. Among them, a graphite material whose surface is coated with a carbonaceous material is particularly preferable. For example, graphite whose surface is coated with a carbonaceous material of amorphous is preferable because it can improve the output characteristics of the lithium ion secondary battery. Conventionally, when a graphite material whose surface is coated with a carbonaceous material is used, generation of gas is remarkable. However, in the lithium ion secondary battery of the present invention, generation of gas can be suppressed, so that deterioration in performance due to the generation of gas as in the prior art can be suppressed.

The metal-based active material refers to an active material containing a metal. Typically, a metal-based active material refers to an active material having an element capable of intercalating lithium into its structure and having a theoretical capacity per unit weight of 500 mAh / g or more when lithium is inserted. The upper limit of the theoretical electric capacity is not particularly limited, but may be, for example, 5000 mAh / g or less. As the metal-based active material, for example, a lithium metal, a single metal forming the lithium alloy and an alloy thereof, and a compound thereof (for example, oxide, sulfide, nitride, silicide, carbide, phosphide, etc.) are used.

Examples of the single metal forming the lithium alloy include metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Metal. The single metal alloy forming the lithium alloy includes, for example, a compound containing the above-mentioned single metal. Among these, silicon (Si), tin (Sn), lead (Pb) and titanium (Ti) are preferable, and silicon, tin and titanium are more preferable. Therefore, as the metal-based active material, a single metal such as silicon (Si), tin (Sn), or titanium (Ti), an alloy containing these metal elements, or a compound thereof is preferable.

The metal-based active material may contain one or more non-metallic elements. For _{example, SiC, SiO x C y (} 0 <x ≤ 3, 0 <y ≤ 5), Si 3 N 4, Si 2 N 2 O, SiO x (0 <x ≤ 2), SnO x (0 < x? 2), LiSiO, LiSnO, and the like. Of these, SiO _x , SiC, and SiO _x C _y are preferable, which allow insertion and desorption of lithium on the low electric field. For example, SiO _x C _y can be obtained by firing a high-molecular material containing silicon. Among the SiO _x C _y , from the balance of the capacity and the cycle characteristics, it is preferable that the range of 0.8 ≦ x ≦ 3 and 2 ≦ y ≦ 4 be satisfied.

Examples of the oxide, sulfide, nitride, silicide, carbide, and phosphide of a lithium metal, a single metal forming the lithium alloy and an alloy thereof include oxides, sulfides, nitrides, silicides, carbides, phosphides . Of these, oxides are particularly preferable. For example, a lithium-containing metal complex oxide containing a metal element selected from the group consisting of tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide and the like and Si, Sn, Pb and Ti atoms is used.

As the lithium-containing metal composite oxide, a lithium-titanium composite oxide represented by Li _x Ti _y M _z O ₄ (0.7 ≤ x ≤ 1.5, 1.5 ≤ y ≤ 2.3, and 0 ≤ z ≤ 1.6, where M is Na, K, (Wherein _x represents an element selected from the group consisting of Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb), a lithium manganese composite oxide represented by Li _x Mn _y M _z O ₄ And M are the same as defined in the lithium titanium composite oxide). Among them, Li _4/3 Ti _5/3 O ₄ , Li ₁ Ti ₂ O ₄ , Li _4/5 Ti _11/5 O ₄ and Li _4/3 Mn _5/3 O ₄ are preferable.

Among them, a Si compound is preferable as the metal-based active material. Here, the Si compound means a compound containing silicon. By using the Si compound, the electric capacity of the secondary battery can be increased. Among Si compounds, SiC, SiO _x and SiO _x C _y are preferable. It is presumed that in the active material containing Si and C in combination, insertion and desorption of Li to Si (silicon) occur at a high electric potential, and insertion and desorption of Li to C (carbon) occurs at low electric potential. Because of this, expansion and contraction are suppressed more than other metal-based active materials, so that the charge-discharge cycle characteristics of the secondary battery can be improved.

The negative electrode active material may be used singly or in combination of two or more. For example, a carbonaceous active material and a metal-based active material may be used in combination.

Among the above-described negative electrode active materials, it is preferable to use one or both of a carbonaceous active material and a Si compound from the viewpoint of improving balance between cycle characteristics and output characteristics. Among them, it is particularly preferable to use only (i) a carbonaceous active material and (ii) a combination of a carbonaceous active material and a Si compound.

It is preferable that the negative electrode active material is formed into a granular shape. When the shape of the particles is spherical, a higher density of electrodes can be formed at the time of electrode formation. When the negative electrode active material is a particle, its volume average particle diameter is appropriately selected so as to balance with other constituent requirements of the lithium ion secondary battery. The specific volume-average particle size of the negative electrode active material is preferably 0.1 占 퐉 or more, more preferably 1 占 퐉 or more, further preferably 2 占 퐉 or more, particularly preferably 5 占 퐉 or more, preferably 50 占 퐉 or less 30 mu m or less, particularly preferably 25 mu m or less. When the volume average particle diameter of the carbonaceous active material as the negative electrode active material is in the above range, the amount of particulate binder can be reduced when preparing the slurry composition for negative electrode. Therefore, the capacity of the lithium ion secondary battery can be prevented from lowering, and the viscosity of the slurry composition can be easily adjusted to an appropriate range. The volume average particle diameter is a particle diameter at which the particle diameter distribution is measured by laser diffraction and the cumulative volume calculated on the small diameter side in the measured particle diameter distribution is 50%.

[2.2.2. Particulate binder]

The particulate binder is a component capable of binding the electrode active materials together or binding the electrode active material and the current collector. In the negative electrode, the particulate binder binds the negative electrode active material, thereby suppressing the desorption of the negative electrode active material from the negative electrode active material layer. The particulate binder also binds particles other than the negative electrode active material contained in the negative electrode active material layer to maintain the strength of the negative electrode active material layer.

As the particulate binder, it is preferable to use a binder having excellent performance for holding the negative electrode active material and having high binding property to the current collector. Normally, a polymer is used as the material of the particulate binder. The polymer as the material of the particulate binder may be a homopolymer or a copolymer. Among them, a copolymer containing an aliphatic conjugated diene monomer unit and an ethylenically unsaturated carboxylic acid monomer unit is preferable.

The aliphatic conjugated diene monomer unit is a structural unit obtained by polymerizing an aliphatic conjugated diene monomer. Since the aliphatic conjugated diene monomer unit is a low rigidity and flexible structural unit, the flexibility of the particulate binder can be enhanced by forming the particulate binder with a polymer containing an aliphatic conjugated diene monomer unit. Therefore, sufficient binding property of the negative electrode active material layer and the current collector can be obtained.

Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, Pentadiene, and substituted and side-chain conjugated hexadiene. Of these, 1,3-butadiene and 2-methyl-1,3-butadiene are preferable, and 1,3-butadiene is particularly preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

In the polymer forming the particulate binder, the content of the aliphatic conjugated diene monomer unit is preferably 20% by weight or more, more preferably 25% by weight or more, preferably 60% by weight or less, more preferably 50% By weight or less. When the content of the aliphatic conjugated diene monomer unit is lower than or equal to the lower limit of the above range, the binding property can be improved. When the content is less than the upper limit, flexibility of the negative electrode can be ensured. Usually, the content of the aliphatic conjugated diene monomer unit in the polymer is in agreement with the ratio (injection ratio) of the aliphatic conjugated diene monomer in the entire monomers used in the production of the polymer.

The ethylenically unsaturated carboxylic acid monomer unit is a structural unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer. Since the ethylenically unsaturated carboxylic acid monomer unit contains a carboxyl group (-COOH group) which is an acidic functional group, the adsorbability of the particulate binder to the negative electrode active material and the current collector can be increased. In addition, the ethylenically unsaturated carboxylic acid monomer unit is a structural unit having high strength. By these, when the particulate binder is formed of the copolymer containing the ethylenically unsaturated carboxylic acid monomer unit, the separation of the negative electrode active material from the negative electrode active material layer can be stably prevented and the strength of the negative electrode can be improved have.

Examples of the ethylenically unsaturated carboxylic acid monomer include monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. Among them, acrylic acid, methacrylic acid and itaconic acid are preferable from the viewpoint of stability of the slurry composition for negative electrode, and itaconic acid is particularly preferable. These may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.

In the polymer forming the particulate binder, the content of the ethylenically unsaturated carboxylic acid monomer unit is preferably 0.1% by weight or more, more preferably 1% by weight or more, preferably 15% by weight or less, By weight is not more than 10% by weight. When the content of the ethylenically unsaturated carboxylic acid monomer unit is lower than the lower limit of the above range, the binding property can be improved. When the content is less than the upper limit, the electrochemical stability of the negative electrode can be improved. Usually, the content of the ethylenically unsaturated carboxylic acid monomer unit in the polymer corresponds to the ratio (injection ratio) of the ethylenically unsaturated carboxylic acid monomer in the whole monomers used in the production of the polymer.

The polymer forming the particulate binder may contain an arbitrary structural unit in addition to the aliphatic conjugated diene monomer unit and the ethylenically unsaturated carboxylic acid monomer unit described above unless the effect of the present invention is remarkably impaired. Examples of the arbitrary monomer corresponding to any of the above structural units include aromatic vinyl monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, unsaturated monomers containing a hydroxyalkyl group, and unsaturated carboxylic acid amide monomers And the like. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the aromatic vinyl-based monomer include styrene, -methylstyrene, vinyltoluene, and divinylbenzene. Among them, styrene is preferable.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile,? -Chloracrylonitrile, and? -Ethyl acrylonitrile. Among them, acrylonitrile and methacrylonitrile are preferable.

Examples of the unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl Maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. Among them, methyl methacrylate is preferable.

Examples of the unsaturated monomer containing a hydroxyalkyl group include? -Hydroxyethyl acrylate,? -Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxy Hydroxyethyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis Hydroxyethyl maleate, and 2-hydroxyethyl methyl fumarate. Among them,? -Hydroxyethyl acrylate is preferable.

Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, and N, N-dimethylacrylamide. Among them, acrylamide and methacrylamide are preferable.

These monomers may be used singly or two or more monomers may be used in combination at an arbitrary ratio.

The polymer forming the particulate binder may be a polymer having a structure having a structure formed by polymerizing monomers used in conventional emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, Unit may be included. These may be used singly or in combination of two or more in an arbitrary ratio.

In the polymer forming the particulate binder, the content ratio of any structural unit is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, and preferably 75% by weight % Or less, more preferably 70 wt% or less, particularly preferably 65 wt% or less. Usually, the content ratio of any structural unit in the polymer corresponds to the ratio (injection ratio) of any monomer in the entire monomers used in producing the polymer.

The weight average molecular weight of the polymer forming the particulate binder is preferably 10,000 or more, more preferably 20,000 or more, preferably 5,000,000 or less, more preferably 1,000,000 or less. When the weight average molecular weight is within the above range, the strength of the negative electrode of the present invention and the dispersibility of the negative electrode active material are easily improved.

The weight average molecular weight of the particulate binder can be determined by gel permeation chromatography (GPC) from the value of polystyrene conversion using tetrahydrofuran as a developing solvent.

The glass transition temperature of the particulate binder is preferably -40 占 폚 or higher, preferably 50 占 폚 or lower, and more preferably 0 占 폚 or lower. When the glass transition temperature of the particulate binder is in the above range, the binding property and the electrode strength can be increased.

The number average particle diameter of the particulate binder is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. When the number average particle diameter of the particulate binder is in the above range, the strength and flexibility of the negative electrode can be improved. The presence of the particles can be easily measured by a transmission electron microscope, a Coulter counter, a laser diffraction scattering method or the like.

The particulate binder can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent to obtain particles of the polymer. It is possible to prevent the organic solvent from remaining in the lithium ion secondary battery by using the particulate binder polymerized in the aqueous solvent and as a result, the generation of the decomposition gas of the residual organic solvent in the use of the lithium ion secondary battery It is possible to avoid the deformation of the cell due to the deformation.

The ratio of each monomer in the monomer composition is generally the same as the content ratio of the structural unit (for example, an aliphatic conjugated diene monomer unit and an ethylenically unsaturated carboxylic acid monomer unit) in a polymer to be produced.

The aqueous solvent is not particularly limited as long as it can disperse the particulate binder. The aqueous solvent is usually selected from water-based solvents having a boiling point at normal pressure of preferably 80 占 폚 or higher, more preferably 100 占 폚 or higher, preferably 350 占 폚 or lower, more preferably 300 占 폚 or lower. Hereinafter, examples of the aqueous solvent will be given. In the following examples, the numbers in parentheses after the solvent names are the boiling points (in ° C) at normal pressure and the decimal points are rounded or discarded values.

Examples of water-based solvents include water (100); Ketones such as diacetone alcohol (169) and? -Butyrolactone (204); Alcohols such as ethyl alcohol (78), isopropyl alcohol (82) and normal propyl alcohol (97); Propylene glycol monomethyl ether 120, methyl cellosolve 124, ethyl cellosolve 136, ethylene glycol tertiary butyl ether 152, butyl cellosolve 171, 3-methoxy-3 methyl Glycol ethers such as ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271) and dipropylene glycol monomethyl ether (188) Ryu; And ethers such as 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66). Among them, water is particularly preferable from the viewpoint that there is no flammability and a dispersion of particulate binder is easily obtained. In addition, water may be used as the main solvent and an aqueous solvent other than water may be mixed in the range in which the dispersed state of the particulate binder can be ensured.

The polymerization method is not particularly limited, and any of the solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method and the like may be used. As the polymerization method, for example, any of ion polymerization, radical polymerization, living radical polymerization and the like may be used. The present invention is advantageous in that it is easy to obtain a high molecular weight material and that the polymer is obtained in a state in which the polymer is dispersed in water as it is and therefore it is not necessary to carry out redispersion treatment and can be provided for production of a slurry composition for negative electrode, Among them, the emulsion polymerization method is particularly preferable.

The emulsion polymerization method is usually carried out by a conventional method. For example, by the method described in &quot; Experimental Chemistry Lecture &quot; vol. 28, (published by Maruzen Co., Ltd., Japan Chemical Society). That is, water, a dispersing agent, an additive such as a crosslinking agent, a polymerization initiator, and a monomer are mixed so as to have a predetermined composition, and the composition in the container is stirred to emulsify the monomer or the like into water in a closed container equipped with a stirrer and a heating device , And the temperature is raised while stirring to initiate polymerization. Alternatively, the composition is emulsified and then placed in a sealed container to initiate the reaction in the same manner.

Examples of the polymerization initiator include organic peroxides such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate and 3,3,5-trimethylhexanoyl peroxide Peroxide; azo compounds such as?,? '- azobisisobutyronitrile; Ammonium persulfate; And potassium persulfate. The polymerization initiator may be used singly or in combination of two or more in an arbitrary ratio. The amount of the polymerization initiator may be 0.01 part by weight to 5 parts by weight based on 100 parts by weight of the monomer.

Examples of the dispersing agent include benzene sulfonic acid salts such as sodium dodecylbenzenesulfonate and sodium dodecylphenylether sulfonate; Alkylsulfuric acid salts such as sodium laurylsulfate and sodium tetradodecylsulfate; Sulfosuccinates such as sodium dioctylsulfosuccinate and sodium dihexylsulfosuccinate; Fatty acid salts such as sodium laurate; Ethoxy sulfates such as polyoxyethylene lauryl ether sulfate sodium salt and polyoxyethylene nonylphenyl ether sulfate sodium salt; Alkanesulfonic acid salts; Alkyl ether phosphate ester sodium salt; Nonionic emulsifiers such as polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, and polyoxyethylene-polyoxypropylene block copolymer; Gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, sodium polyacrylate, and water-soluble polymers such as polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more. Among these, preferred are benzenesulfonic acid salts such as sodium dodecylbenzenesulfonate and sodium dodecylphenylether sulfonate; Sodium lauryl sulfate, and sodium tetradodecyl sulfate. More preferably, it is a benzenesulfonic acid salt such as sodium dodecylbenzenesulfonate and sodium dodecylphenyl ether sulfonate from the viewpoint of excellent oxidation resistance. The dispersing agent may be used singly or in combination of two or more in an arbitrary ratio. The amount of the dispersant may be 0.01 part by weight to 10 parts by weight based on 100 parts by weight of the monomer.

The polymerization temperature and the polymerization time may be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator. The polymerization temperature is preferably 0 占 폚 or higher, more preferably 25 占 폚 or higher, particularly preferably 30 占 폚 or higher, preferably 100 占 폚 or lower, and more preferably 80 占 폚 or lower. The polymerization time is preferably 0.5 hour or more, more preferably 1 hour or more, particularly preferably 5 hours or more, preferably 50 hours or less, more preferably 30 hours or less, particularly preferably 20 Hour or less.

In the polymerization, seed polymerization may be carried out by employing seed particles.

In addition, additives such as amines may be used as a polymerization auxiliary.

The pH of the aqueous dispersion containing the particulate binder obtained by these methods may be adjusted to preferably fall within the range of 5 to 10, more preferably 5 to 9. At this time, by adjusting the pH method, for example, alkali metals (e.g., Li, Na, K, Rb, Cs) of hydroxide, ammonia, inorganic ammonium compounds (for example, NH ₄ Cl, etc), organic And a basic aqueous solution containing an amine compound (for example, ethanolamine, diethylamine, etc.) and the like are mixed with an aqueous dispersion. Among them, the pH adjustment by the alkali metal hydroxide is preferable because it improves the binding property (fill strength) between the current collector and the negative electrode active material.

The particulate binder may be a composite polymer particle composed of two or more kinds of polymers. The complex polymer particles can be obtained by polymerizing at least one kind of monomer component by a conventional method, and subsequently polymerizing at least one other monomer component and polymerizing it by a conventional method (two-step polymerization method) or the like Can be obtained. By stepwise polymerizing the monomers in this manner, particles of a core shell structure having a core layer present inside the particles and a shell layer covering the core layer can be obtained.

The amount of particulate binder is preferably at least 0.1 part by weight, more preferably at least 0.5 part by weight, particularly preferably at least 0.8 part by weight, preferably at most 10 parts by weight, more preferably at most 10 parts by weight, based on 100 parts by weight of the negative electrode active material 8 parts by weight or less, particularly preferably 5 parts by weight or less. By setting the amount of the particulate binder to a lower limit value or more of the above range, it is possible to prevent the negative active material from desorbing from the negative electrode active material layer, thereby reducing the occurrence of short-circuiting of the lithium ion secondary battery. Further, by setting the value to be the upper limit value or less, the internal resistance can be kept low and the output characteristic can be improved.

[2.2.3. Water-soluble polymer]

It is considered that the water-soluble polymer according to the present invention forms a film covering the negative electrode active material in the lithium ion secondary battery, and decomposition of the electrolytic solution is suppressed by the action of the film.

The water-soluble polymer includes an ethylenically unsaturated carboxylic acid monomer unit. For this reason, the water-soluble polymer usually has a carboxyl group (-COOH group) as an acidic functional group. Since the carboxyl group functions as an acidic functional group, the water-soluble polymer can exhibit excellent binding properties. That is, since the polar group present on the surface of the negative electrode active material interacts with the acidic functional group of the water-soluble polymer, the water-soluble polymer is retained on the surface of the negative electrode active material and a stable film can be formed.

Examples of the ethylenically unsaturated carboxylic acid monomer include an ethylenically unsaturated monocarboxylic acid and a derivative thereof, an ethylenically unsaturated dicarboxylic acid and an acid anhydride thereof and derivatives thereof. Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the derivatives of the ethylenically unsaturated monocarboxylic acids include 2-ethyl acrylic acid, isocrotonic acid,? -Acetoxy acrylic acid,? -Trans-aryloxy acrylic acid,? -Chloro-? -E-methoxy acrylic acid, and? - diamino acrylic acid. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic acid anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid and the like; Maleic acid esters such as methyl allyl maleate, diphenyl maleate, maleinanyl, maleic acid decyl, maleic acid dodecyl, maleic acid octadecyl, and maleic acid fluoroalkyl. These may be used singly or in combination of two or more in an arbitrary ratio. Of these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. The dispersibility of the obtained water-soluble polymer to water can be further increased.

In the water-soluble polymer, the content of the ethylenically unsaturated carboxylic acid monomer unit is preferably 20% by weight or more, more preferably 25% by weight or more, particularly preferably 30% by weight or more, % Or less, more preferably 45 wt% or less, particularly preferably 40 wt% or less. By making the content ratio of the ethylenically unsaturated carboxylic acid monomer unit at least the lower limit of the above range, it is possible to improve the binding property of the negative electrode (that is, the binding property between the negative electrode active material layer and the current collector) and improve the lifetime characteristics of the lithium ion secondary battery And it is possible to secure the flexibility of the negative electrode by making the upper limit or lower. Generally, the content of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer is in agreement with the ratio (injection ratio) of the ethylenically unsaturated carboxylic acid monomer in the whole monomers used in producing the water-soluble polymer .

The water-soluble polymer is a copolymer containing a fluorine-containing (meth) acrylic acid ester monomer unit in addition to the above-mentioned ethylenically unsaturated carboxylic acid monomer. Here, the fluorine-containing (meth) acrylic acid ester monomer unit is a structural unit obtained by polymerizing a fluorine-containing (meth) acrylic acid ester monomer. Since the fluorine-containing (meth) acrylic acid ester monomer unit has a high ion conductivity, it is possible to suppress an increase in resistance due to the coating of the water-soluble polymer and to improve both the output characteristics and the cycle characteristics of the lithium ion secondary battery .

Examples of the fluorine-containing (meth) acrylic acid ester monomers include monomers represented by the following formula (I).

[Chemical Formula 1]

In the above formula (I), R ¹ represents a hydrogen atom or a methyl group.

In the above formula (I), R ² represents a hydrocarbon group containing a fluorine atom. The number of carbon atoms in the hydrocarbon group is preferably 1 or more, and preferably 18 or less. The number of fluorine atoms contained in R ² may be one or two or more.

Examples of the fluorine-containing (meth) acrylic acid ester monomer represented by the formula (I) include alkyl (meth) acrylate, aryl fluoride (meth) acrylate and aralkyl fluoride (meth) acrylate. Among them, alkyl (meth) acrylate is preferred. Specific examples of such monomers include 2,2,2-trifluoroethyl (meth) acrylate,? - (perfluorooctyl) ethyl (meth) acrylate, 2,2,3,3- (Meth) acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, 1H, 1H, 9H-perfluoro-1-nonyl, Perfluorooctyl (meth) acrylate, trifluoromethyl (meth) acrylate, 3 [4 [1-trifluoromethyl-2,2-bis [bis (Trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl, and the like can be given as examples of the (meth) acrylic acid perfluoroalkyl ester. Among them, 2,2,2-trifluoroethyl methacrylate is preferable from the viewpoint of balance between cycle characteristics and output characteristics. The fluorine-containing (meth) acrylic acid ester monomers may be used singly or in combination of two or more at any ratio.

The content of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is preferably 1% by weight or more, more preferably 1.5% by weight or more, particularly preferably 2% by weight or more, By weight or less, more preferably 25% by weight or less, particularly preferably 20% by weight or less. By setting the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit to the lower limit value or more in the above range, the output characteristics of the lithium ion secondary battery can be improved and further the low temperature characteristics can be improved. In addition, the electrochemical stability can be ensured by setting it to the upper limit value or less. Usually, the content of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is such that the ratio (injection ratio) of the fluorine-containing (meth) acrylic acid ester monomer in the entire monomers used in producing the water- Match.

The water-soluble polymer may contain a crosslinkable monomer unit. The crosslinkable monomer unit is a structural unit obtained by polymerizing a crosslinkable monomer. By including the crosslinkable monomer unit, the water-soluble polymer can be crosslinked, so that the strength and stability of the coating formed of the water-soluble polymer can be increased.

As the crosslinkable monomer, a monomer capable of forming a crosslinked structure upon polymerization can be used. Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, there can be mentioned a monofunctional monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional monomer having at least two olefinic double bonds per molecule.

Examples of the thermally crosslinkable crosslinkable group contained in the monofunctional monomer include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and a combination thereof. Among them, an epoxy group is more preferable in that the crosslinking and crosslinking density can be easily controlled.

Examples of the crosslinkable monomer having an epoxy group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenylglycidyl Unsaturated glycidyl ethers such as ethers; Butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene and 1,2-epoxy-5,9-cyclododecadien Monoepoxide of diene or polyene; Alkenyl epoxide such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2-epoxy-9-decene; And glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl Glycidyl esters of unsaturated carboxylic acids such as glycidyl esters of 3-cyclohexenecarboxylic acid and glycidyl esters of 4-methyl-3-cyclohexenecarboxylic acid, and the like, .

Examples of the crosslinkable monomer having an N-methylolamide group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include (meth) acrylamides having a methylol group such as N-methylol (meth) acrylamide .

Examples of the crosslinkable monomer having an oxetanyl group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include 3 - ((meth) acryloyloxymethyl) oxetane, 3 - ((meth) acryloyl (Meth) acryloyloxymethyl) oxetane, 2- ((meth) acryloyloxymethyl) oxetane, 2- ((Meth) acryloyloxymethyl) -4-trifluoromethyl oxetane, and the like.

Examples of the crosslinkable monomer having an oxazoline group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, Methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl- , And 2-isopropenyl-5-ethyl-2-oxazoline.

Examples of the polyfunctional monomer having two or more olefinic double bonds include allyl (meth) acrylate, ethylenedi (meth) acrylate, diethyleneglycol di (meth) acrylate, triethyleneglycol di , Tetraethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diaryl ether, Trimethylolpropane-diallyl ether, allyl or vinyl ether of polyfunctional alcohols other than the above, triallylamine, methylenebisacrylamide, and divinylbenzene.

Among them, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are preferable as the crosslinkable monomer.

In the water-soluble polymer, the content of the crosslinkable monomer units is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 2% Preferably 1.5% by weight or less, particularly preferably 1% by weight or less. When the content of the crosslinkable monomer unit is within the above range, the swelling degree can be suppressed and the durability of the electrode can be enhanced. Usually, the content ratio of the crosslinkable monomer units in the water-soluble polymer is in agreement with the ratio (injection ratio) of the crosslinkable monomers in the total monomers used in the production of the water-soluble polymer.

The water-soluble polymer may contain a reactive surfactant unit. The reactive surfactant unit is a structural unit obtained by polymerizing a reactive surfactant monomer. The reactive surfactant unit constitutes a part of the water-soluble polymer and can also function as a surfactant.

The reactive surfactant monomer is a monomer having a polymerizable group capable of copolymerizing with another monomer and also having a surfactant (a hydrophilic group and a hydrophobic group). Typically, the reactive surfactant monomer has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group contained in the reactive surfactant monomer include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group. These polymerizable unsaturated groups may be used singly or in combination of two or more at any ratio.

The reactive surfactant monomer is a moiety that exhibits hydrophilicity, and usually has a hydrophilic group. The reactive surfactant monomers are classified into anionic, cationic, and nonionic surfactants depending on the kind of the hydrophilic group.

Examples of anionic hydrophilic groups include -SO ₃ M, -COOM, and -PO (OH) ₂ . Wherein M represents a hydrogen atom or a cation. Examples of cationic ions include alkali metal ions such as lithium, sodium and potassium; Alkaline earth metal ions such as calcium and magnesium; Ammonium ion; Ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; And ammonium ions of alkanolamines such as monoethanolamine, diethanolamine and triethanolamine.

Examples of the cationic hydrophilic group include -Cl, -Br, -I, and -SO ₃ OR ^X. Wherein R ^X represents an alkyl group. Examples of R ^X include a methyl group, an ethyl group, a propyl group, and an isopropyl group.

An example of a nonionic system hydrophilic group is -OH.

Examples of preferred reactive surfactant monomers include the compounds represented by the following formula (II).

(2)

In formula (II), R represents a divalent linking group. Examples of R include -Si-O- group, methylene group and phenylene group.

In the formula (II), R ³ represents a hydrophilic group. An example of R ³ is -SO ₃ NH ₄ .

In the formula (II), n represents an integer of 1 or more and 100 or less.

Another example of a preferable reactive surfactant monomer is a compound having a polymerization unit based on ethylene oxide and a polymerization unit based on butylene oxide and having an alkenyl group having a terminal double bond and -SO ₃ NH ₄ For example, trade names &quot; Latex PD-104 &quot; and &quot; Latex PD-105 &quot;, manufactured by Kao Corporation).

The reactive surfactant monomers may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

In the water-soluble polymer, the content of the reactive surfactant unit is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5% Preferably not more than 4% by weight, particularly preferably not more than 2% by weight. The dispersibility of the slurry composition for negative electrode can be improved by setting the content ratio of the reactive surfactant unit to the lower limit value or more in the above range. In addition, by setting it to the upper limit value or less, the durability of the negative electrode can be improved.

The water-soluble polymer may contain a (meth) acrylic acid ester monomer unit other than the fluorine-containing (meth) acrylic acid ester monomer unit. The (meth) acrylic acid ester monomer unit is a structural unit obtained by polymerizing a (meth) acrylic acid ester monomer. Among the (meth) acrylic acid ester monomers, the fluorine-containing (meth) acrylic acid ester monomers are distinguished from the (meth) acrylic acid ester monomers as the fluorine-containing (meth) acrylic acid ester monomers.

Examples of the (meth) acrylic acid ester monomers include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, Alkyl acrylate esters such as acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; And examples of the monomer include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, Methacrylic acid such as methacrylic acid, methacrylic acid such as methacrylic acid, methacrylic acid, methacrylic acid, etc., such as acrylate, methacrylate, Alkyl esters and the like. The (meth) acrylic acid ester monomers may be used singly or in combination of two or more in an arbitrary ratio.

The content of the (meth) acrylic acid ester monomer unit in the water-soluble polymer is preferably 30% by weight or more, more preferably 35% by weight or more, particularly preferably 40% by weight or more, By weight or less. By making the amount of the (meth) acrylic acid ester monomer unit equal to or more than the lower limit value in the above range, the binding property of the negative electrode active material to the current collector can be increased, and the flexibility of the negative electrode can be increased by setting it to the upper limit value.

The water-soluble polymer may contain an arbitrary structural unit in addition to the structural unit described above. Examples of the arbitrary structural unit include structural units obtained by polymerizing any of the following monomers. The monomers may be used singly or two or more monomers may be used in combination at an arbitrary ratio.

The optional monomers include, for example, styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, Styrene-based monomers such as styrene-based monomers; Amide-based monomers such as acrylamide; Alpha, beta -unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Olefin monomers such as ethylene and propylene; Halogen-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; And heterocyclic vinyl compound monomers such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole. Examples of the optional monomer include monomers containing a phosphoric acid group, such as compounds containing a phosphoric acid group and an allyloxy group, and phosphoric acid group-containing (meth) acrylic acid esters. Examples of the compound containing a phosphoric acid group and an allyloxy group include 3-allyloxy-2-hydroxypropane phosphoric acid. Examples of the (meth) acrylic acid ester containing a phosphoric acid group include dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl- Methacryloyloxyethylphosphate, diethyl-2-methacryloyloxyethylphosphate, monoisopropyl-2-methacryloyloxyethylphosphate, diethyl-2-methacryloyloxyethylphosphate, 2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono n-butyl-2-methacryloyloxyethyl phosphate, di- , Mono butoxyethyl-2-methacryloyloxyethyl phosphate, dibutoxyethyl-2-methacryloyloxyethyl phosphate, mono (2-ethylhexyl) -2- methacryloyloxyethyl phosphate, di 2-ethylhexyl) -2-methacryloyloxyethyl phosphate, and the like. The. Examples of the optional monomers include monomers containing a sulfonic acid group. Examples of the monomer containing a sulfonic acid group include monomers in which one conjugated double bond of a diene compound such as isoprene and butadiene is sulfonated, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, sulfoethylmethacrylate, Sulfonic acid group-containing monomers or salts thereof such as acrylate; Monomers or salts thereof containing an amide group and a sulfonic acid group, such as 2-acrylamido-2-methylpropanesulfonic acid (AMPS); And 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS), and salts or salts thereof containing a hydroxyl group and a sulfonic acid group.

In the water-soluble polymer, the content ratio of any structural unit is preferably 20% by weight or more, more preferably 25% by weight or more, particularly preferably 30% by weight or more, preferably 70% Preferably not more than 65% by weight, particularly preferably not more than 60% by weight. Usually, the content ratio of any structural unit in the polymer corresponds to the ratio (injection ratio) of any monomer in the entire monomers used in producing the polymer.

The weight average molecular weight of the water-soluble polymer is usually smaller than that of the polymer forming the particulate binder. The weight average molecular weight of the water-soluble polymer is preferably 500 or more, more preferably 1000 or more, particularly preferably 5000 or more, preferably 500000 or less, more preferably 250000 or less, particularly preferably 100000 or less. By setting the weight average molecular weight of the water-soluble polymer to a lower limit value or more of the above range, the strength of the water-soluble polymer can be increased and the coating covering the negative electrode active material can be stabilized. As a result, the cycle characteristics and the output characteristics of the lithium ion secondary battery can be improved. By setting the content at or below the upper limit, the water-soluble polymer can be softened. As a result, for example, it is possible to suppress the unfolding of the negative electrode and to improve the binding property of the negative electrode active material layer to the current collector.

The weight average molecular weight of the water-soluble polymer can be determined as a value in terms of polystyrene using a solution in which 0.85 g / ml of sodium nitrate is dissolved in a 10% by volume aqueous solution of dimethylformamide by GPC as a developing solvent.

The glass transition temperature of the water-soluble polymer is preferably 0 占 폚 or higher, more preferably 5 占 폚 or higher, preferably 100 占 폚 or lower, more preferably 70 占 폚 or lower. When the glass transition temperature of the water-soluble polymer is in the above-mentioned range, adhesion and flexibility of the negative electrode can be achieved. The glass transition temperature of the water-soluble polymer can be adjusted by combining various monomers.

The water-soluble polymer preferably has a viscosity of 0.1 mPa s or more, more preferably 0.5 mPa s or more, particularly preferably 1 mPa-s or more, in the case of a 1 wt% aqueous solution, Is 20,000 mPa s or less, more preferably 15,000 mPa s or less, and particularly preferably 10,000 mPa s or less. By setting the viscosity above the lower limit of the above range, the strength of the water-soluble polymer can be increased and the durability of the negative electrode can be improved. In addition, by setting it to the upper limit value or less, the coating property of the slurry composition for negative electrode can be improved, and the binding strength of the current collector and the negative electrode active material layer can be improved. The viscosity can be adjusted, for example, according to the molecular weight of the water-soluble polymer. The viscosity is a value measured at 25 캜 and a rotation speed of 60 rpm using an E-type viscometer. The pH of the aqueous solution at the time of measuring the viscosity is 8.

There is no particular limitation on the method for producing the water-soluble polymer. For example, a monomer composition containing an ethylenically unsaturated carboxylic acid monomer and a fluorine-containing (meth) acrylic acid ester monomer and, if necessary, other monomers is polymerized in an aqueous solvent to prepare a water-soluble polymer You can.

The proportion of each monomer in the monomer composition is usually in the range of from 0.1 to 20 parts by weight, preferably from 1 to 100 parts by weight, of a structural unit in a water-soluble polymer (e.g., an ethylenically unsaturated carboxylic acid monomer unit, a fluorine-containing (meth) acrylic acid ester monomer unit, Active agent unit, etc.).

The aqueous solvent used for the polymerization reaction can be, for example, the same as the preparation of the particulate binder. The order of the polymerization reaction may be the same as that in the production of the particulate binder. As a result, a reaction solution containing a water-soluble polymer is usually obtained. The obtained reaction solution is usually acidic, and the water-soluble polymer is often dispersed in an aqueous solvent. The water-soluble polymer thus dispersed in the water-soluble solvent can be usually used in an aqueous solvent by adjusting the pH of the reaction solution to, for example, 7 to 13. The water-soluble polymer may be extracted from the reaction solution thus obtained. However, usually, a negative electrode can be produced by using water as an aqueous medium, preparing a slurry composition for a negative electrode by using a water-soluble polymer dissolved in the water, and using the slurry composition.

Examples of a method for alkalizing the pH to 7 to 13 include an aqueous solution of an alkali metal such as an aqueous solution of lithium hydroxide, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide and the like; An aqueous solution of an alkaline earth metal such as an aqueous solution of calcium hydroxide and an aqueous solution of magnesium hydroxide; And an aqueous solution of an alkali such as an aqueous ammonia solution is mixed with the reaction solution. The above-mentioned alkali aqueous solution may be used singly or in combination of two or more in an arbitrary ratio.

The amount of the water-soluble polymer is preferably 0.01 parts by weight or more, more preferably 0.03 parts by weight or more, particularly preferably 0.05 parts by weight or more, preferably 20 parts by weight or less, more preferably 0.05 parts by weight or less 15 parts by weight or less, particularly preferably 10 parts by weight or less. By setting the amount of the water-soluble polymer to not less than the lower limit of the above range, the cycle characteristics of the lithium ion secondary battery can be improved. In addition, by setting it to the upper limit value or less, the low temperature characteristics of the lithium ion secondary battery can be improved.

The weight ratio of the particulate binder and the water-soluble polymer is preferably 0.5 / 99.5 or more, more preferably 1.0 / 99.0 or more, particularly preferably 1.5 / 98.5 or more, and more preferably 40 / 60 or less, more preferably 30/70 or less, particularly preferably 20/80 or less. By setting the content ratio of the particulate binder and the water-soluble polymer to the lower limit value or more in the above range, it is possible to improve the binding properties of the negative electrode and the life characteristics of the lithium ion secondary battery. In addition, by setting it to be not more than the upper limit value, it is possible to improve flexibility of the negative electrode and low temperature characteristics of the lithium ion secondary battery.

[2.2.4. Any component]

The composition for forming the negative electrode active material layer may contain an arbitrary component as long as it does not significantly impair the effect of the present invention, in addition to the negative electrode active material, particulate binder and water-soluble polymer. Examples thereof include a conductive material (also referred to as a conductive material), a reinforcing material, a dispersant, a leveling agent, and an antioxidant.

The conductive imparting material is a component that can improve the electrical contact between the negative electrode active materials. By including the conductive material, the discharge load characteristic of the lithium ion secondary battery can be improved.

Examples of the conductivity-imparting material include conductive carbon such as acetylene black, ketjen black, carbon black, vapor grown carbon fiber, and carbon nanotube. In addition, carbon powder such as graphite and fibers or foils of various metals may be used. The conductive imparting material may be used singly or in combination of two or more in an arbitrary ratio.

The amount of the conductive agent is preferably 0.01 parts by weight or more, more preferably 1 part by weight or more, preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material .

As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers may be used, for example. The reinforcing materials may be used singly or in combination of two or more in an arbitrary ratio. By using a reinforcing material, a strong and flexible electrode can be obtained and excellent long-term cycle characteristics can be obtained.

The amount of the reinforcing material is preferably 0.01 parts by weight or more, more preferably 1 part by weight or more, preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material. By setting the amount of the reinforcing material within the above range, high capacity and high load characteristics can be obtained.

Examples of the dispersing agent include anionic compounds, cationic compounds, nonionic compounds, and polymeric compounds. The kind of the specific dispersant can be selected according to the negative electrode active material and the conductive material to be used. The dispersant may be used singly or in combination of two or more at any ratio.

The amount of the dispersant is preferably 0.01 wt% to 10 wt% in the negative electrode active material layer. When the amount of the dispersing agent is in the above range, the stability of the slurry composition for the negative electrode can be improved, a smooth electrode can be obtained, and a high battery capacity can be realized.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorochemical surfactants, and metal surfactants. The leveling agent may be used singly or two or more kinds thereof may be used in combination at an arbitrary ratio. By using the leveling agent, it is possible to prevent cratering that occurs during coating and to improve the smoothness of the negative electrode.

The amount of the leveling agent is preferably 0.01 wt% to 10 wt% in the negative electrode active material layer. When the amount of the leveling agent is in the above range, the productivity, smoothness and battery characteristics at the time of electrode production are excellent.

Examples of the antioxidant include phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds and polymer type phenol compounds. Among them, the polymer type phenol compound is a polymer having a phenol structure in the molecule. The polymer type phenolic compound preferably has a weight average molecular weight of preferably 200 or more, more preferably 600 or more, further preferably 1000 or less, more preferably 700 or less.

The amount of the antioxidant is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, preferably 10% by weight or less, and more preferably 5% by weight or less, in the negative electrode active material layer. Thus, the slurry composition is excellent in stability, battery capacity and cycle characteristics.

The composition for forming the negative electrode active material layer may contain a component included in the negative electrode slurry composition used for producing the negative electrode active material layer.

[2.2.5. Thickness of negative electrode active material layer]

The thickness of the negative electrode active material layer is preferably 1 占 퐉 or more, more preferably 5 占 퐉 or more, particularly preferably 30 占 퐉 or more, preferably 300 占 퐉 or less, more preferably 250 占 퐉 or less, 200 탆 or less, particularly preferably 100 탆 or less. When the thickness of the negative electrode active material layer is in the above range, balanced power density and energy density can be achieved.

[2.3. Manufacturing method of negative electrode]

The production method of the negative electrode is not particularly limited. For example, a negative electrode may be obtained by preparing a slurry composition for a negative electrode, applying the slurry composition to the surface of the current collector, and drying the negative electrode active material layer on the surface of the current collector.

The slurry composition for negative electrode is a slurry composition comprising a negative electrode active material, a particulate binder, a water-soluble polymer and an aqueous solvent. Further, the slurry composition may contain components other than the negative electrode active material, the binder, the water-soluble polymer and the aqueous solvent, if necessary. The amount of the negative electrode active material, the binder and the water-soluble polymer, and if necessary, the amount of the constituent components is usually equal to the amount of each component contained in the negative electrode active material layer. In such a slurry composition, a part of the water-soluble polymer is dissolved in an aqueous solvent, but a part of the water-soluble polymer is adsorbed on the surface of the negative electrode active material, so that the negative electrode active material is covered with a stable layer (coating film) The dispersibility of the active material in a solvent is improved. For this reason, the slurry composition for negative electrode has good coatability when applied to a current collector.

As the aqueous solvent of the slurry composition for the negative electrode, the same solvent as the aqueous solvent used in the polymerization of the particulate binder and the water-soluble polymer may be used. Among them, it is preferable to use water as an aqueous solvent.

The amount of the water-based solvent is preferably adjusted appropriately so that the slurry composition is suitable for the subsequent steps. Concretely, the amount of the solid content of the slurry composition is preferably 30% by weight or more, more preferably 40% by weight or more, preferably 70% by weight or less, more preferably 60% by weight or less And used. Here, the solid content of the slurry composition refers to a substance remaining as a constituent component of the negative electrode active material layer after drying and heating of the slurry composition.

In addition, the slurry composition for negative electrode may contain a compounding agent such as a preservative, a thickener, and the like.

As the preservative, it is preferable to use a benzoisothiazoline-based compound represented by the following formula (III), 2-methyl-4-isothiazolin-3-one or a mixture thereof, More preferable.

(3)

In the formula (III), R ⁴ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. When the benzoisothiazoline-based compound represented by the formula (III) and the 2-methyl-4-isothiazolin-3-one are used in combination, the ratio thereof is 1:10 to 10: 1 in terms of weight ratio . The amount of the preservative in the slurry composition is preferably 0.001 part by weight to 0.1 part by weight, more preferably 0.001 part by weight to 0.05 part by weight, more preferably 0.001 part by weight to 0.01 part by weight, based on 100 parts by weight of the total of the particulate binder and the water- Particularly preferred.

The particulate binder and the water-soluble polymer are obtained by polymerization in the above-described manner, preferably in an aqueous solvent. Therefore, the particulate binder and the water-soluble polymer are usually stored as a dispersion or solution of an aqueous system. Therefore, in general, the quality tends to deteriorate due to the propagation of microorganisms. On the other hand, deterioration of such quality can be prevented by using a preservative.

Examples of the thickener include cellulose polymers such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (Modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts; (Modified) polyvinyl alcohols, copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, polyvinyl alcohols such as maleic anhydride or maleic acid, or copolymers of fumaric acid and vinyl alcohol; Polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, various modified starches, and acrylonitrile-butadiene copolymer hydrides. Among them, cellulosic polymers and their ammonium salts and alkali metal salts; (Modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts are preferred. These may be used singly or in combination of two or more in an arbitrary ratio. Here, "(modified) poly" means "unmodified poly" or "modified poly". The amount of the thickening agent in the slurry composition is preferably 0.1 wt% to 10 wt%. Since the dispersing property of the negative electrode active material in the slurry composition can be enhanced by the presence of the thickening agent in the above range, a smooth electrode can be obtained. This makes it possible to realize excellent load characteristics and cycle characteristics.

The slurry composition for negative electrode may be prepared by mixing the above-mentioned negative electrode active material, particulate binder, water-soluble polymer, aqueous solvent, and optionally used optional components.

As the apparatus used for mixing, any apparatus capable of uniformly mixing the above components can be used. Examples thereof include a bead mill, a ball mill, a roll mill, a sand mill, a pigment disperser, a brain ball, an ultrasonic disperser, a homogenizer, a planetary mixer, and a fill mix. Particularly, it is particularly preferable to use a ball mill, a roll mill, a pigment disperser, a cerebellum, and a planetary mixer in order to disperse at a high concentration.

The viscosity of the slurry composition is preferably 10 mPa s or more, more preferably 100 mPa s or more, and preferably 100,000 mPa or more, from the viewpoints of uniform coatability and time-course stability of the slurry composition Pa · s or less, and more preferably 50,000 mPa · s or less. Here, the viscosity is a value measured by a B-type viscometer at 25 ° C and a rotation speed of 60 rpm.

The solid content concentration of the slurry composition is not particularly limited as long as it is capable of being coated and immersed and has a viscosity having fluidity, but it is generally from 10% by weight to 80% by weight.

The negative electrode active material layer can be formed by applying the slurry composition for negative electrode on a member such as a current collector, and if necessary, drying and heating. When a layer interposed between the current collector and the negative electrode active material layer is present in the lithium ion secondary battery, the slurry composition may be applied on the layer. The method of application is not particularly limited. For example, methods such as a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a soaking method may be used.

The drying conditions of the layer of the slurry composition formed on the current collector are not particularly limited. For example, it may be set at 120 ° C or more for 1 hour or more. Examples of the drying method include drying by hot air, hot air and low-humidity air; Vacuum drying: A drying method by irradiation of energy rays such as infrared rays, far-infrared rays, and electron beams can be mentioned.

After the layer of the slurry composition is dried, it is preferable to carry out the pressure treatment, for example, using a die press or a roll press, if necessary. The negative electrode active material layer having a low porosity can be obtained by the pressure treatment. The porosity is preferably 5% or more, more preferably 7% or more, preferably 15% or less, more preferably 13% or less. By setting the porosity to the lower limit of the above range, it becomes easy to obtain a high volume capacity, and the negative electrode active material layer can be prevented from being peeled off from the current collector. In addition, a high charging efficiency and a high discharge efficiency can be obtained by setting the amount to be not more than the upper limit value.

When the negative electrode active material layer contains a curable polymer, it is preferable to cure the polymer after formation of the negative electrode active material layer.

[3. Positive]

The positive electrode usually comprises a current collector and a positive electrode active material layer formed on the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and a binder for the positive electrode.

As the current collector of the positive electrode, a material usually formed of a material having electrical conductivity and electrochemically durable is used. The collector of the positive electrode may be the same as the collector used for the negative electrode of the present invention, for example. Among them, aluminum is particularly preferable.

As the positive electrode active material, a material capable of inserting and desorbing lithium ions is used. Such a positive electrode active material is largely classified into an inorganic compound and an organic compound.

Examples of the positive electrode active material composed of an inorganic compound include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and a transition metal.

Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Examples of transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ and the like. Of these, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle stability and capacity.

Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like.

The lithium-containing composite metal oxide includes, for example, a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co-Ni-Mn, Lithium complex oxides, and lithium composite oxides of Ni-Co-Al.

Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganese oxide (LiMn ₂ O ₄ ) or Li [Mn _3/2 M _1/2 ] O ₄ (LiMn ₂ O ₄ ) in which a part of Mn is substituted with another transition metal Where M is Cr, Fe, Co, Ni, Cu, etc.).

As the lithium-containing composite metal oxide having olivine structure, for example, Li _X MPO ₄ (where M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Ti, Al, Si, B and Mo, and X represents a number satisfying 0? X? 2).

Examples of the positive electrode active material composed of an organic compound include conductive polymer compounds such as polyacetylene and poly-p-phenylene.

Further, a positive electrode active material composed of a composite material in which an inorganic compound and an organic compound are combined may be used.

Further, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and this composite material may be used as a positive electrode active material. The iron-based oxide tends to lack electrical conductivity, but by using the composite material as described above, it can be used as a high-performance positive electrode active material.

Further, the above-mentioned compound may be partially substituted with an element to use as a positive electrode active material.

A mixture of the inorganic compound and the organic compound may be used as the positive electrode active material.

The positive electrode active material may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The volume average particle diameter of the particles of the positive electrode active material is preferably 1 占 퐉 or more, more preferably 2 占 퐉 or more, preferably 50 占 퐉 or less, and more preferably 30 占 퐉 or less. By setting the volume average particle diameter of the particles of the positive electrode active material within the above range, it is possible to reduce the amount of the binder when preparing the positive electrode active material layer and suppress the decrease in capacity of the secondary battery. In order to form the positive electrode active material layer, a slurry composition for a positive electrode containing a positive electrode active material and a binder is usually prepared. The viscosity of the positive electrode slurry composition is easily adjusted to a suitable viscosity, A uniform positive electrode can be obtained.

The amount of the positive electrode active material in the positive electrode active material layer is preferably 90 wt% or more, more preferably 95 wt% or more, preferably 99.9 wt% or less, more preferably 99 wt% or less. By setting the content of the positive electrode active material within the above range, the capacity of the lithium ion secondary battery can be increased, flexibility of the positive electrode, and adhesion of the current collector and the positive electrode active material layer can be improved.

Examples of the binder for the positive electrode include a binder such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, Resins such as ronitril derivatives; A soft polymer such as an acrylic soft polymer, a diene soft polymer, an olefin soft polymer, and a vinyl soft polymer can be used. One kind of binder may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.

The positive electrode active material layer may contain components other than the positive electrode active material and the binder, if necessary. Examples thereof include conductive materials, reinforcing materials, leveling agents, antioxidants, thickeners, and the like. These components may be used singly or in combination of two or more in an arbitrary ratio.

The thickness of the positive electrode active material layer is preferably 5 占 퐉 or more, more preferably 10 占 퐉 or more, preferably 300 占 퐉 or less, and more preferably 250 占 퐉 or less. When the thickness of the positive electrode active material layer is in the above-mentioned range, it is possible to realize both high load characteristics and high energy density characteristics.

The positive electrode can be produced, for example, in the same manner as the negative electrode described above.

[4. Electrolyte]

The electrolytic solution includes a solvent and a supporting electrolyte dissolved in the solvent.

As the electrolyte contained in the electrolytic solution, a lithium salt is usually used. Lithium salts include, for _{example, LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. Of these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferably used because they easily dissolve in solvents and exhibit a high degree of dissociation. These may be used singly or in combination of two or more in an arbitrary ratio. Generally, the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity, so that the lithium ion conductivity can be controlled depending on the type of the supporting electrolyte.

The concentration of the supporting electrolyte in the electrolytic solution is preferably 1% by weight or more, more preferably 5% by weight or more, further preferably 30% by weight or less, more preferably 20% by weight or less. If the amount of the supporting electrolyte is excessively large or excessively large, the ion conductivity may be lowered and the charging characteristics and the discharging characteristics of the lithium ion secondary battery may be deteriorated.

As the solvent contained in the electrolytic solution, those containing propylene carbonate and vinylene carbonate are used.

The amount of the propylene carbonate in the solvent is usually 50 vol% or more, usually 80 vol% or less, preferably 75 vol% or less, and more preferably 70 vol% or less. By setting the amount of propylene carbonate to the lower limit value or more in the above range, the output characteristics of the lithium ion secondary battery can be improved. In addition, by setting it to the upper limit value or less, the cycle characteristics can be improved, and the service life of the battery can be increased.

The amount of vinylene carbonate in the solvent is usually 0.05 vol% or more, preferably 0.1 vol% or more, more preferably 0.15 vol% or more, and usually 1.0 vol% or less, preferably 0.8 vol% Or less, more preferably 0.6 vol% or less. By using vinylene carbonate at a lower limit value or higher in the above range, the cycle characteristics of the lithium ion secondary battery can be improved. Further, since the water-soluble polymer is used in the lithium ion secondary battery of the present invention, it is possible to improve cycle characteristics even when the amount of vinylene carbonate is reduced. Therefore, since the amount of vinylene carbonate can be reduced to suppress the viscosity increase of the electrolytic solution, it is also possible to improve the low-temperature characteristics of the lithium ion secondary battery.

As the solvent of the electrolytic solution, any solvent other than propylene carbonate and vinylene carbonate may be used in combination with propylene carbonate and vinylene carbonate. Examples of optional solvents include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); esters such as? -butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds such as sulfolane and dimethylsulfoxide, and the like are used. Particularly, carbonates such as dimethyl carbonate, ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity tends to be obtained and the use temperature range is wide. These solvents may be used alone, or two or more solvents may be used in combination at an arbitrary ratio. The lower the viscosity of the solvent used, the higher the lithium ion conductivity, so that the lithium ion conductivity can be controlled depending on the type of the solvent.

The electrolytic solution may optionally contain an optional compounding agent.

[5. Separator]

As the separator, a porous substrate having pores is usually used. Examples of the separator include (a) a porous separator having pores, (b) a porous separator having a polymer coat layer formed on one side or both sides thereof, (c) a porous separator formed with a porous resin coat layer containing an inorganic ceramic powder, etc. . Examples thereof include solid polymers such as polypropylene-based, polyethylene-based, polyolefin-based or aramid-based porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer Polymer films for electrolytes or gelated polymer electrolytes; A separator coated with a gelled polymer coat layer; And a separator coated with a porous film layer made of an inorganic filler and a dispersing agent for an inorganic filler.

[6. Manufacturing Method of Lithium Ion Secondary Battery]

The production method of the lithium ion secondary battery is not particularly limited. For example, the negative electrode and the positive electrode described above may be polymerized through a separator, and the battery may be wrapped or folded according to the shape of the battery, placed in a battery container, and then filled with an electrolyte solution. Also, if necessary, for example, X-Fund metal; An overcurrent prevention element such as a fuse or a PTC element; A lead plate or the like may be inserted so as to prevent an increase in pressure inside the battery and overcharge discharge. The shape of the battery may be, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, or a flat type.

Example

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following embodiments, and may be arbitrarily changed without departing from the scope of the claims of the present invention and its equivalent scope. In the following description, &quot;% &quot; and &quot; part &quot; representing amounts are based on weight unless otherwise specified. The operations described below were carried out under normal temperature and normal pressure conditions unless otherwise noted.

The artificial graphite used in the following examples and comparative examples had a structure in which a surface of a portion formed of a graphite material having high crystallinity was coated with a low-crystallinity amorphous carbonaceous material.

[How to measure]

(1) Method for evaluating high-temperature storage characteristics

A lithium ion secondary battery of a laminate type cell was prepared and allowed to stand for 24 hours under an environment of 25 캜. Thereafter, charging and discharging operations were carried out under the environment of 25 캜 by a constant current method of 0.1 C at 4.2 volts and discharging to 3.0 volts, and the initial capacity C0 was measured. The sample was further charged at 4.2 V under an environment of 25 캜 and stored at 60 캜 for 30 days. Thereafter, charging and discharging were performed up to 4.2 volts by the constant current method of 0.1 C and discharged to 3.0 volts, and the capacity C1 after high-temperature storage was measured. The high-temperature storage characteristics were evaluated by the capacity retention rate? C1 indicated by? C1 = C1 / C0 x 100 (%). The higher the value, the better the high-temperature storage characteristics.

(2) Evaluation method of high temperature cycle characteristics

A lithium ion secondary cell of a laminate type cell was fabricated and allowed to stand at 25 캜 for 24 hours. Thereafter, charge and discharge operations were carried out under the environment of 25 캜 by the constant current method of 0.1 C up to 4.2 volts and discharging to 3.0 volts, and the initial capacity C0 was measured. The charging and discharging operation in which the battery was charged to 4.2 volts at a constant current of 1 C under the environment of 60 占 폚 and discharged to 3.0 volts was repeated 1000 times (1000 cycles), and the capacity C2 after 1000 cycles was measured. The high temperature cycle characteristics were evaluated by the capacity retention rate? C2 indicated by? C2 = C2 / C0 x 100 (%). The higher the value, the better the high-temperature cycle characteristics.

(3) Evaluation method of low temperature characteristics

A lithium ion secondary cell of a laminate type cell was fabricated and allowed to stand at 25 캜 for 24 hours. Thereafter, charging operation was performed up to 4.2 volts by the constant current method of 0.1 C. Thereafter, discharge was performed by the constant current method of 1 C under the environment of -10 DEG C, and the voltage V after 15 seconds from the start of discharge was measured. The low-temperature characteristics were evaluated by a voltage change? V indicated by? V = 4.2 volts-V. The smaller the value, the better the low-temperature characteristics.

(4) Evaluation method of cell inflation rate

A lithium ion secondary cell of a laminate type cell was fabricated and allowed to stand at 25 캜 for 24 hours. Thereafter, charging and discharging operations were carried out under the environment of 25 캜 at a constant current of 0.1 C at 4.2 volts and discharging to 3.0 volts, and the initial cell volume M0 was measured. The sample was further charged at 4.2 V under an environment of 25 캜 and stored at 60 캜 for 30 days. Thereafter, charging and discharging were carried out under the environment of 25 캜 by the constant current method of 0.1 C at 4.2 volts and discharging to 3.0 volts, and the cell volume M1 after high temperature storage was measured. The inflating rate ΔM of the cell was calculated as ΔM = (M1 - M0) / M0 × 100 (%). The lower this value is, the smaller the swelling is, and the better.

(5) Method of measuring the specific surface area of the negative electrode active material

The specific surface area of the negative electrode active material was measured by the BET method by nitrogen gas adsorption using a "Tristar II3020 series" measuring apparatus manufactured by Shimadzu Corporation.

[Example 1]

(1-1. Production method of water-soluble polymer)

32.5 parts of methacrylic acid (ethylenically unsaturated carboxylic acid monomer), 7.5 parts of 2,2,2-trifluoroethylmethacrylate (fluorine-containing (meth) acrylic acid ester monomer) were placed in a 5 MPa pressure vessel equipped with a stirrer, , 0.8 part of ethylene dimethacrylate (crosslinkable monomer), 58.0 parts of butyl acrylate (arbitrary monomer), 20 parts of ammonium polyoxyalkylene alkyl ether sulfate (reactive surfactant monomer, trade name: Latex PD-104 ), 0.6 part of t-dodecylmercaptan, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate (polymerization initiator) were placed and sufficiently stirred. Thereafter, the polymerization was started by heating to 60 占 폚. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the water-soluble polymer. To the mixture containing the water-soluble polymer, 10% aqueous ammonia was added to adjust the pH to 8. Thus, an aqueous solution containing the desired water-soluble polymer was obtained.

(1-2. Production method of particulate binder)

Into a 5 MPa pressure vessel equipped with a stirrer, 33.5 parts of 1,3-butadiene (aliphatic conjugated diene monomer), 3.5 parts of itaconic acid (ethylenically unsaturated carboxylic acid monomer), 63 parts of styrene (arbitrary monomer) 4 parts of sodium sulfonate (emulsifier), 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate (polymerization initiator) were put and sufficiently stirred. Thereafter, the polymerization was started by heating to 50 占 폚. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the particulate binder. To the mixture containing the particulate binder, a 5% aqueous solution of sodium hydroxide was added to adjust the pH to 8. Thereafter, unreacted monomers were removed by distillation under reduced pressure. Thereafter, it was cooled to 30 캜 or lower. Thus, an aqueous dispersion containing a desired particulate binder was obtained.

(1-3) Process for producing a binder composition comprising a water-soluble polymer and a particulate binder [

The aqueous solution containing the water-soluble polymer obtained above was diluted with ion-exchanged water and the concentration was adjusted to 5%. This was mixed with the aqueous dispersion containing the particulate binder obtained above so as to have a weight ratio of particulate binder: water-soluble polymer = 95.0: 5.0 in terms of solid content to obtain a binder composition.

(1-4. Preparation of Slurry Composition for Negative Electrode)

Artificial graphite having a specific surface area of 5.5 m &lt; 2 &gt; / g (volume average particle diameter: 24.5 mu m) was prepared as a negative electrode active material.

100 parts of artificial graphite and 1% aqueous solution of carboxymethyl cellulose (&quot; BSH-12 &quot;, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener were added to a planetary mixer equipped with a dispenser. Further, ion exchange water was added to adjust the solid concentration to 55%. Thereafter, they were mixed at 25 DEG C for 60 minutes. Next, the solid content was adjusted to 52% with ion-exchanged water. Thereafter, the mixture was further mixed at 25 DEG C for 15 minutes to obtain a mixed solution.

To the mixed solution, 1.0 part of the binder composition obtained in the above (1-3) was added in an amount corresponding to the solid content, and ion-exchanged water was added thereto to adjust the final solid content concentration to 50%. And further mixed for 10 minutes. This was degassed under reduced pressure to obtain a negative electrode slurry composition having excellent flowability.

(1-5. Preparation of negative electrode)

The slurry composition for negative electrode obtained in the above (1-4) was coated on a copper foil having a thickness of 20 mu m as a current collector with a comma coater so that the film thickness after drying was about 150 mu m and dried. This drying was carried out by conveying the copper foil in an oven at 60 캜 for 2 minutes at a speed of 0.5 m / min. Thereafter, the substrate was subjected to heat treatment at 120 캜 for 2 minutes to obtain a negative electrode raw material. The original negative electrode was rolled by a roll press to obtain a negative electrode having a negative active material layer having a thickness of 80 mu m.

(1-6. Preparation of positive electrode)

As a binder for the positive electrode, a 40% aqueous dispersion containing an acrylate polymer having a glass transition temperature Tg of -40 캜 and a number average particle diameter of 0.20 탆 was prepared. The above acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture comprising 78% 2-ethylhexyl acrylate, 20% acrylonitrile, and 2% methacrylic acid.

100 parts of LiCoO ₂ having a volume average particle diameter of 12 탆 as a positive electrode active material and 1 part of a 1% aqueous solution of carboxymethylcellulose ("BSH-12" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener, , 5 parts of a 40% aqueous dispersion of the acrylate polymer corresponding to the solid content, and ion-exchanged water were mixed. The amount of ion-exchanged water was adjusted so that the total solid concentration became 40%. These were mixed by a planetary mixer to prepare a positive electrode slurry composition.

The above-described slurry composition for a positive electrode was applied on a 20 mu m thick aluminum foil as a current collector with a comma coater so as to have a thickness of about 200 mu m after drying and dried. This drying was carried out by conveying the aluminum foil in an oven at 60 ° C for 2 minutes at a rate of 0.5 m / min. Thereafter, it was heat-treated at 120 DEG C for 2 minutes to obtain a positive electrode plate. The original plate of the positive electrode was rolled by a roll press to obtain a positive electrode.

(1-7 Preparation of Separator)

A single-layer polypropylene separator ("Celgard 2500" manufactured by Celgard Corporation) was cut into a square of 5 × 5 cm 2.

(1-8. Preparation of lithium ion secondary battery)

As an exterior of the battery, an aluminum-containing sheath was prepared. The positive electrode obtained in the above (1-6) was cut into a square of 4 x 4 cm 2, and the surface of the collector side was arranged so as to be in contact with the aluminum-covered sheath. On the surface of the positive electrode active material layer of the positive electrode, a square separator obtained in the above (1-7) was disposed. The negative electrode obtained in the above (1-5) was cut into a square of 4.2 x 4.2 cm 2, and this was placed on the separator so that the surface of the negative electrode active material layer side faced the separator.

The electrolytic solution was injected thereon so as to leave no air. In the above electrolytic solution, LiPF ₆ having a concentration of 1 M was used as the electrolyte. PC: VC = 19.5: 10: 70: 0.5 (volume ratio) was used as the solvent for the electrolytic solution, and ethylene carbonate (EC), diethyl carbonate (DEC), propylenecarbonate (PC) and vinylene carbonate As a solvent.

Further, in order to seal the openings of the aluminum foil, a heat seal at 150 DEG C was carried out and the aluminum sheath was closed to prepare a lithium ion secondary battery.

The obtained lithium ion secondary battery was evaluated for high temperature storage characteristics, high temperature cycle characteristics, low temperature characteristics, and cell swelling rate.

[Example 2]

In the same manner as in Example 1 except that the amount of 2,2,2-trifluoroethyl methacrylate was changed to 3 parts and the amount of butyl acrylate was changed to 62.5 parts in the above (1-1) , And a lithium ion secondary battery were manufactured and evaluated.

[Example 3]

In the same manner as in Example 1 except that the amount of 2,2,2-trifluoroethyl methacrylate was changed to 18 parts and the amount of butyl acrylate was changed to 47.5 parts in the above (1-1) , And a lithium ion secondary battery were manufactured and evaluated.

[Example 4]

The procedure of Example 1 was repeated except that the mixing ratio of the aqueous solution containing the water-soluble polymer and the aqueous dispersion of the particulate binder was changed so that the particulate binder: water-soluble polymer = 98.0: In the same manner, a lithium ion secondary battery was produced and evaluated.

[Example 5]

The procedure of Example 1 was repeated except that the mixing ratio of the aqueous dispersion containing the water-soluble polymer and the aqueous dispersion of the particulate binder was changed so that the particulate binder: water-soluble polymer = 90.0: In the same manner, a lithium ion secondary battery was produced and evaluated.

[Example 6]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 19.8: 10: 70: 0.2 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[Example 7]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 19.2: 10: 70: 0.8 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[Example 8]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 24.5: 20: 55: 0.5 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[Example 9]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 14.5: 10: 75: 0.5 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[Example 10]

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the amount of methacrylic acid was changed to 22 parts and the amount of butyl acrylate was changed to 68.5 parts in the above (1-1) Respectively.

[Example 11]

A lithium ion secondary battery was produced in the same manner as in Example 1 except that the amount of methacrylic acid was changed to 48 parts and the amount of butyl acrylate was changed to 42.5 parts in the above (1-1) Respectively.

[Example 12]

A lithium ion secondary battery was produced in the same manner as in Example 1 except that artificial graphite having a specific surface area of 2.5 m 2 / g (volume average particle diameter: 12 μm) was used as the negative electrode active material in the above (1-4) Respectively.

[Example 13]

A lithium ion secondary battery was produced in the same manner as in Example 1 except that artificial graphite (volume average particle diameter: 13 占 퐉) having a specific surface area of 8.9 m2 / g was used as the negative electrode active material in (1-4) Respectively.

[Example 14]

A mixture containing artificial graphite and SiOC in graphite / SiOC = 85/15 (weight ratio) was prepared. The specific surface area of this mixture was 6.4 m &lt; 2 &gt; / g.

A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that a mixture containing artificial graphite and SiOC was used as the negative electrode active material in the above (1-4).

[Example 15]

A mixture containing artificial graphite and SiC in graphite / SiC = 85/15 (weight ratio) was prepared. The specific surface area of this mixture was 7.1 m 2 / g.

A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that a mixture containing artificial graphite and SiC was used as the negative electrode active material in the above (1-4).

[Comparative Example 1]

An aqueous dispersion containing a particulate binder was obtained in the same manner as in the above (1-2) of Example 1, except that the amount of 1,3-butadiene was changed to 65.5 parts and the amount of styrene was changed to 31 parts.

(1-4) of Example 1 except that 0.95 part by weight of the aqueous dispersion solution containing the particulate binder prepared in Comparative Example 1 corresponding to the solid content was used instead of the binder composition obtained in the above (1-3) To prepare a negative electrode slurry composition.

A negative electrode was prepared in the same manner as in (1-5) above using the negative electrode slurry composition thus obtained, and the negative electrode was used to produce a lithium ion secondary battery in the same manner as in (1-8) above , Respectively.

[Comparative Example 2]

An aqueous dispersion containing the particulate binder prepared in (1-2) above was used in an amount of 0.95 parts by weight in terms of solid content instead of the binder composition obtained in the above (1-3). Artificial graphite having a specific surface area of 1.2 m &lt; 2 &gt; / g (volume average particle diameter: 21 mu m) was used as the negative electrode active material. A negative electrode slurry composition was prepared in the same manner as in (1-4) of Example 1 except for these points.

A negative electrode was prepared in the same manner as in (1-5) above using the negative electrode slurry composition thus obtained, and the negative electrode was used to produce a lithium ion secondary battery in the same manner as in (1-8) above , Respectively.

[Comparative Example 3]

An aqueous dispersion containing the particulate binder prepared in (1-2) above was used in an amount of 0.95 parts by weight in terms of solid content instead of the binder composition obtained in the above (1-3). Artificial graphite having a specific surface area of 18 m &lt; 2 &gt; / g (volume average particle diameter: 3.2 mu m) was used as the negative electrode active material. A negative electrode slurry composition was prepared in the same manner as in (1-4) of Example 1 except for these points.

A negative electrode was prepared in the same manner as in (1-5) above using the negative electrode slurry composition thus obtained, and the negative electrode was used to produce a lithium ion secondary battery in the same manner as in (1-8) above , Respectively.

[Comparative Example 4]

Artificial graphite having a specific surface area of 5.5 m &lt; 2 &gt; / g (volume average particle diameter: 24.5 mu m) was prepared as a negative electrode active material. 100 parts of the above artificial graphite and 12% N-methylpyrrolidone solution of polyvinylidene fluoride (&quot; 7208 &quot;, manufactured by Kuraray Co., Ltd.) as a soluble binder were added to a planetary mixer equipped with a disper / RTI &gt; Further, N-methylpyrrolidone was added to adjust the solid concentration to 55%. This was degassed under reduced pressure to obtain a negative electrode slurry composition having excellent flowability.

Using the obtained negative electrode slurry composition, a negative electrode was prepared in the same manner as in (1-5) of Example 1, and using this negative electrode, a lithium ion secondary A battery was prepared and evaluated.

[Comparative Example 5]

(1-1) of Example 1 except that 2,2,2-trifluoroethyl methacrylate was not used and the amount of butyl acrylate was changed to 65.5 parts. &Lt; / RTI &gt;

An aqueous dispersion containing a particulate binder was obtained in the same manner as in (1-2) of Example 1 except that the amount of 1,3-butadiene was changed to 65.5 parts and the amount of styrene was changed to 31 parts .

In the same manner as in item (1-3) of Example 1 except that the aqueous dispersion solution containing the water-soluble polymer prepared in Comparative Example 5 and the particulate binder was used in this way, a binder containing a water-soluble polymer and a particulate binder A composition was obtained. Using this binder composition, lithium ion secondary batteries were produced and evaluated in the same manner as in (1-4) to (1-8).

[Comparative Example 6]

(EC), diethyl carbonate (DEC) and propylene carbonate (PC) as a solvent for the electrolytic solution were mixed in a volume ratio of EC: DEC: PC = 20: 10: 70 A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that a solvent was used.

[Comparative Example 7]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 18.8: 10: 70: 1.2 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[Comparative Example 8]

(EC: DEC: PC: VC = 1) as the solvent of the electrolytic solution in the above (1-8), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and vinylene carbonate 39.5: 30: 40: 0.5 was used as the positive electrode active material, a lithium ion secondary battery was produced and evaluated.

[result]

The results of Examples and Comparative Examples are shown in Tables 1 to 6. Here, the abbreviations in the table are as follows. In the following Tables 1 to 6, the unit "%" in the column of "amount of VC" and "amount of PC" is based on volume.

Monomer A: aliphatic conjugated diene monomer

BD: 1,3-butadiene

Monomer B: Ethylenically unsaturated carboxylic acid monomer

IA: Itaconic acid

Monomer I: Fluorine-containing (meth) acrylic acid ester monomer

TFEMA: 2,2,2-Trifluoroethyl methacrylate

Monomer II: Ethylenically unsaturated carboxylic acid monomer

MAA: methacrylic acid

VC: vinylene carbonate

PC: propylene carbonate

EC: ethylene carbonate

DEC: Diethyl carbonate

PVDF: polyvinylidene fluoride

ΔC1: Capacity retention rate indicating the evaluation result of high temperature storage characteristics

? C2: Capacity retention rate indicating the evaluation result of the high temperature cycle characteristic

ΔV: voltage change

ΔM: cell inflation rate

[Review]

In Examples, excellent results were obtained in both of the high temperature cycle characteristics and the low temperature characteristics as compared with the Comparative Examples. Also, in any of the examples, it can be seen that a lithium ion secondary battery excellent in high-temperature storage characteristics could be realized. In addition, it was confirmed in the examples that the generation of gas could be suppressed in the Examples in that the cells were less inflated than the Comparative Examples.

Claims (10)

A positive electrode, a negative electrode, an electrolyte, and a separator,
Wherein the negative electrode comprises a negative electrode active material layer formed of a composition comprising a negative electrode active material, a particulate binder, and a water-soluble polymer,
The negative electrode active material has a specific surface area of 2 m 2 / g to 15 m 2 / g,
Wherein the water-soluble polymer is a copolymer comprising an ethylenically unsaturated carboxylic acid monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit,
Wherein the solvent of the electrolytic solution contains 50 to 80 volume% of propylene carbonate and 0.05 to 1 volume% of vinylene carbonate. The method according to claim 1,
Wherein the negative electrode active material is one or both of a carbonaceous active material and a Si compound. The method according to claim 1,
Wherein the particulate binder is composed of a copolymer comprising an aliphatic conjugated diene monomer unit and an ethylenically unsaturated carboxylic acid monomer unit. The method according to claim 1,
Wherein the content of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer is 20 wt% to 50 wt%. The method according to claim 1,
The content of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is 1 to 30% by weight. The method according to claim 1,
Wherein the weight ratio of the particulate binder and the water-soluble polymer is a water-soluble polymer / particulate binder = 0.5 / 99.5 to 40/60. The method according to claim 1,
Wherein the water-soluble polymer contains a crosslinkable monomer unit and the content thereof is 0.1 wt% or more and 2 wt% or less. The method according to claim 1,
Wherein the water-soluble polymer contains a (meth) acrylic acid ester monomer unit other than the fluorine-containing (meth) acrylic acid ester monomer and the content of the (meth) acrylic acid ester monomer unit is 30 wt% or more and 70 wt% or less. The method according to claim 1,
Wherein the amount of the particulate binder is 0.1 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the negative electrode active material. The method of claim 3,
Wherein the content of the aliphatic conjugated diene monomer unit in the particulate binder is 20 wt% or more and 60 wt% or less and the content of the ethylenically unsaturated carboxylic acid monomer unit is 0.1 wt% or more and 15 wt% Ion secondary battery.