JPH1167277A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery with high potential, high energy density, excellent cycle characteristics by forming an adhesive layer containing a conductive filler having a particle size of the specified range and a DBP absorption of the specified ratio so as to have the dry film thickness of the specified range. SOLUTION: The mean particle size of conductive fillers is specified to 0.5 μm or less, the DBP absorption to 50 ml/100 g or less, and the dry film thickness of an adhesive layer to 0.01-5 μm. The conductive filler is preferable to be tin oxide. A positive electrode is formed by sequentially arranging an adhesive later, a positive active material containing a compound capable of absorbing/emitting lithium ions on a positive current collector. The conductive fillers having a mean particle size of 0.5 μm or less, a DBP absorption of 50 ml/100 g or less are preferably contained in the adhesive layer, and the dry film thickness of the adhesive layer is preferably 0.01-5 μm. A polymer electrolyte is preferable to be an electrolyte comprising a nonaqueous electrolyte-containing gel polymer. Thereby, the dispersion of battery performance is decreased, and cycle characteristics are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery using a polymer electrolyte (containing an electrolyte) instead of the electrolyte,
High-potential, high-energy density lithium ion battery with excellent cycle characteristics.

[0002]

2. Description of the Related Art In recent years, various devices such as a camera-integrated VTR device, an audio device, a portable computer, and a cellular phone have been reduced in size and weight, and there has been a demand for higher performance of a battery as a power supply for these devices. Is growing. Above all, development of lithium secondary batteries capable of achieving high voltage, high energy density and excellent cycle characteristics as batteries as power sources for electric vehicles has been active.

A lithium secondary battery comprises a positive electrode capable of inserting and extracting lithium ions, a negative electrode, and a non-aqueous electrolyte solution.
Generally, a positive electrode or a negative electrode in a lithium secondary battery is a paint containing a positive electrode (negative electrode) active material, a conductive material, a binder (binder), a solvent, and the like on a current collector such as an aluminum foil or a copper foil. Is applied and dried. However, the compatibility between the current collector made of metal and the active material layer made of the binder is poor, and the active material layer peels off during the manufacturing process such as the winding process, or the active material is immersed in the battery container due to the penetration of the electrolyte in the battery container. There have been problems such as the binder in the layer swelling and the active material layer being peeled off.

As a general example of the means for improving the adhesion between the current collector and the active material layer, there is a method of roughening the surface of the current collector. Examples of the surface roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. Examples of the mechanical polishing method include polishing cloth paper having abrasive particles fixed thereon, a grindstone, an emery buff, and a steel wire. There is known a method of polishing the surface of a current collector with a wire-brush provided with a brush.

[0005] However, in the above method, the binder in the active material layer swells due to the prolonged contact between the electrolyte and the active material layer in the battery container. The adhesion has not been sufficiently maintained. Furthermore, since the electrical contact between the roughened current collector and the active material layer is insufficient and non-uniform, the electrical resistance partially changes inside the electrode, and the battery performance is sufficiently brought out. Can not do.

As another means for improving the adhesion between the current collector and the active material layer, US Pat. No. 5,580,686 discloses an easy-adhesion layer containing graphite and a binder as main components. It describes a method of providing it in between. Although the graphite particles roughen the surface of the current collector and improve the electrical contact between the current collector and the active material layer through the presence of conductive graphite particles, graphite is generally bound to the binder. The step of dispersing graphite in a binder is not easy to use and takes a long time. In addition, since the paint containing graphite has high viscosity, it is difficult to apply the paint thinly on the current collector, which is disadvantageous in terms of the volume energy density of the battery. In addition, graphite is
Since the DBP oil absorption is large, a large amount of binder is required for dispersion, and the characteristics of graphite as conductive particles have not been sufficiently exhibited. As described above, the easily-adhesive layer formed using graphite having poor dispersibility in a binder has problems that the surface property is poor and the coating film is brittle.

By the way, in a conventional lithium secondary battery,
Non-aqueous electrolytes have been used as electrolytes for high-voltage batteries. However, batteries using a non-aqueous electrolyte have a risk of filtrate or ignition, and in recent years, non-aqueous electrolytes have been used to improve safety, for example, gel polymer.
An electrolyte containing an electrolytic solution has been developed. Particularly in a lithium secondary battery, heat generation and ignition resulting from an internal short circuit due to lithium dendrite deposition that occurs when a liquid electrolyte is used has become a problem, and application of a polymer electrolyte has been desired.

Further, as described above, a polymer electrolyte including an electrolyte containing an electrolytic solution in a gel polymer, etc.
Unlike a conventional lithium secondary battery, without using a separator, it is possible to substitute for a separator used in this secondary battery system, so that a positive electrode and a negative electrode can be joined with a polymer electrolyte interposed therebetween. Can be used. Since such a polymer is lighter and has a shape flexibility as compared with a liquid system, it can be formed into a thin film such as a sheet, for example.
There is an advantage that a space-saving battery can be created.

In such a lithium secondary battery using a polymer electrolyte, the positive electrode or negative electrode active material layer is formed on a current collector made of a metal. It is necessary to increase the adhesion and obtain good electrical contact. However, a sufficient effect has not been obtained even by using the above-described conventional manufacturing method such as roughening the current collector or providing an easy-adhesion layer containing graphite as a component.

[0010]

As described above, the adhesion of the active material layer to the current collector is mainly performed by roughening the current collector. The battery performance cannot be sufficiently brought out due to insufficient electrical contact between the active material layer and the active material layer. In addition, there has been a problem that the binder in the active material layer swells and the active material layer peels off from the current collector. On the other hand, in the method of providing an easy-adhesion layer containing graphite as a component, a large amount of a binder is required for dispersing the graphite, so that the properties of graphite as a conductive agent cannot be sufficiently utilized, and since the viscosity is extremely high,
It was difficult to form a thin film, and the coating film had poor surface properties and was brittle.

[0011]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and as a result of intensive studies to obtain a lithium secondary battery having a high potential, a high energy density and excellent cycle characteristics, has been developed. By providing an easy-adhesion layer using a conductive filler between the current collector and the active material layer, the adhesion and electrical contact between the current collector and the active material layer are improved, and the cycle characteristics are improved. It has been found that a lithium secondary battery that is excellent and has less variation in cycle characteristics and discharge capacity between batteries can be obtained, and has been completed.

More specifically, the average particle diameter of the conductive filler of the easy-adhesion layer of the lithium secondary battery according to the present invention and DB
It has been found that the P oil absorption is an important index for improving the properties aimed at by the present invention.
The average particle size of the conductive filler is 0.5 μm or less, DBP
It has been found that it is necessary to make the oil absorption amount 50 ml / 100 g or less, and furthermore, to make the dry film thickness of the easy-adhesion layer 0.01 to 5 μm. Thus, the average particle diameter of the conductive filler is 0.5 μm or less, and the DBP oil absorption is 50 ml / 10
0 g or less, and the dry film thickness of the easily adhesive layer is 0.01 to
By setting the thickness to 5 μm, the cycle characteristics can be improved at a high potential and a high energy density.

More preferably, the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode and a polymer electrolyte, wherein the positive electrode has an easy-adhesion layer containing a conductive filler on a positive electrode current collector, and absorbs and releases lithium ions. A positive electrode active material layer containing a possible compound is sequentially provided, the average particle diameter of the conductive filler in the easy-adhesion layer is 0.5 μm or less, the DBP oil absorption is 50 ml / 100 g or less, and the easy-adhesion The dry thickness of the layer is 0.01 to 5 μm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium secondary battery of the present invention has an electrode provided with an easy-adhesion layer between a current collector and a battery active material layer, and particularly has a polymer electrolyte as a main component. is there. First, the electrodes in the lithium secondary battery of the present invention will be described. Generally, a positive electrode or a negative electrode in a lithium secondary battery is a paint containing a positive electrode (negative electrode) active material, a conductive material, a binder (binder), a solvent, etc. on a current collector such as an aluminum foil or a copper foil. Is applied and dried to form a battery active material layer.

As the active material used for the positive electrode in the present invention, a compound capable of inserting and extracting lithium ions is used. For example, as an inorganic compound, a transition metal oxide of a transition metal such as Fe, Co, Ni, Mn, lithium, and the like are used. Complex oxides with transition metals, transition metal sulfides, and the like can be given. In particular,
Transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ ; composite oxide powders of lithium and transition metal such as lithium nickelate and lithium cobaltate; TiS
_2. Transition metal sulfide powder such as FeS. Examples of the organic compound include a conductive polymer such as polyaniline. These inorganic compounds and organic compounds may be used as a mixture.

As the active material used for the negative electrode, a compound capable of inserting and extracting lithium ions is used, and examples thereof include graphite and coke. Cokes are particularly preferable from the viewpoint of safety. The particle size of the active material of the positive electrode and the negative electrode may be appropriately selected in consideration of other components of the battery, but is usually 1 to 30 μm, and particularly 1 to 10 μm.
m, especially 3 to 8 μm, is preferred because it has an effect that the porosity in the active material layer can be easily controlled.

The binder must be stable with respect to the electrolytic solution and the like, and is desired to have weather resistance, chemical resistance, heat resistance, flame retardancy and the like. Further, a material having excellent ion conductivity is desirable, and examples thereof include a cross-linkable polyethylene oxide resin. More preferably, it is desirable to introduce an acryl group, a methacryl group or the like into the terminal of the polyethylene oxide resin, and to crosslink with heat, ultraviolet rays or the like.

The conductive substance is not particularly limited as long as it can impart conductivity by mixing an appropriate amount of the compound powder capable of inserting and extracting lithium.
Examples include carbon powder such as bon black and graphite, and metal powder that is stable at the electrode potential used. The DBP oil absorption of these conductive substances is preferably 120 ml / 100 g or more, particularly preferably 150 ml / 100 g or more because the electrolyte retains the electrolyte. The weight ratio with the active material is 98 /
A range of 2 to 90/10 is preferred. If the weight ratio with the active material is greater than 98/2, the conductivity of the conductive material will not be exhibited, and the resistance of the electrode coating will increase. If the weight ratio to the active material is smaller than 90/10, the dispersion of the conductive material becomes difficult, and the charge / discharge capacity also decreases due to the decrease in the weight of the active material.

As the solvent, those capable of dissolving the binder and drying easily are preferable, and examples thereof include acrylonitrile and dimethyl carbonate. As a current collector, an aluminum foil is generally used for a positive electrode, and a copper foil is used for a negative electrode. In addition, instead of using a negative electrode composed of a negative electrode current collector and a negative electrode active material layer, a Li metal foil can be used as the negative electrode material.

In the present invention, an easy-adhesion layer containing a conductive filler is provided between the current collector and the active material layer. In the present invention, the average particle size of the conductive filler in the easily adhesive layer is 0.5 μm or less. By specifying such a value, a remarkable effect of improving cycle characteristics can be obtained because good adhesiveness can be maintained. This is due to the effect that the conductive filler having an average particle size of 0.5 μm or less imparts an appropriate surface roughness to the surface of the easily adhesive layer. When the average particle diameter of the conductive filler exceeds 0.5 μm, the surface of the easy-adhesion layer is too rough, and the electrical contact between the easy-adhesion layer and the active material layer is insufficient and uneven. In addition, the electric resistance partially changes inside the electrode, and the battery performance cannot be sufficiently brought out.

In the present invention, the DBP oil absorption of the conductive filler in the easily adhesive layer is 50 ml / 100 g.
It is as follows. By specifying such a value, it is possible to disperse the conductive filler with an appropriate amount of binder in order to exhibit the conductivity of the conductive filler. Further, since a coating of the conductive filler in a good dispersion state can be obtained, not only the thinning of the easy-adhesion layer is possible, but also the dispersion of the surface properties of the easy-adhesion layer is reduced, so that the active adhesive layer and the active adhesive layer can be effectively used. Uniform electrical contact with the material layer can be maintained. On the other hand, the conductive filler D
If the BP oil absorption exceeds 50 ml / 100 g, the proportion of the binder required for dispersing the conductive filler increases, the electrical resistance of the easily adhesive layer increases, and the effect of the conductive filler cannot be obtained.

The ratio between the conductive filler and the binder in the easy-adhesion layer is preferably from 95/5 to 10/90. If the ratio of the conductive filler to the binder is more than 95/5, it becomes difficult to disperse the conductive filler. If the ratio is less than 10/90, the conductivity of the conductive filler cannot be obtained. Further, in the present invention, the dry film thickness of the easily adhesive layer is 0.01 to 5 μm.
It is. Here, the dry film thickness refers to the film thickness of the easy-adhesion layer measured after applying an easy-adhesion paint on the current collector and performing a process of drying the contained solvent. By defining the dry film thickness to such a value, a remarkable effect that the electrical contact resistance with the active material layer can be reduced and the volume energy density of the battery can be improved while maintaining good adhesiveness can be obtained. . If the dry film thickness of the easy-adhesion layer is less than 0.01 μm, the mechanical strength of the easy-adhesion layer is weak, and the easy-adhesion layer is easily damaged. On the other hand, when the dry film thickness of the easy-adhesion layer exceeds 5 μm, the electrical resistance of the easy-adhesion layer increases, which may deteriorate the rate characteristics and the cycle characteristics. In addition, making the easy-adhesion layer thicker is disadvantageous in terms of improving the volume energy density of the battery.

As the conductive filler in the present invention,
Examples include conductive metal or metal compound powders. For example, a metal compound such as Ag or Pt, a metal compound such as tin oxide, zinc oxide, or titanium oxide, or a metal compound such as tin oxide doped with Sb or Al can be used. From the viewpoint, tin oxide is preferred. As the binder for the easy-adhesion layer, polymer compounds such as vinyl chloride resin and urethane resin, as well as alkali metal silicate agents can be used, and alkali metal silicate is preferred from the viewpoint of reactivity with the current collector. Agents are preferred. In addition, in order to enhance the dispersibility of the conductive filler, a surfactant may be added at the time of preparing the paint for the easily adhesive layer.

The method of forming the easy-adhesion layer and the electrode active material layer on the current collector is not particularly limited, but is a common coat, a squeeze coat, a lip coat, a die coat, and a bar. A coating method such as a coat and a gravure coat is used, and an easy-adhesive and an electrode active material are sequentially formed. After forming the electrode, particularly the positive electrode, as described above, pressure may be applied to the active material-containing layer by calendaring, pressing, or the like. The pressure at this time varies depending on the material forming the active material, but is generally 500 to 2000 kgf / cm ^2.
And it is sufficient.

In the present invention, the easy-adhesion layer may be provided on either the positive electrode or the negative electrode, but is preferably formed on the positive electrode. Next, the polymer electrolyte will be described.
Generally, a polymer electrolyte containing an electrolyte solution in a gel polymer (hereinafter, this may be simply referred to as a polymer electrolyte) is used as the polymer electrolyte.

The electrolyte contained in the gel polymer is preferably a non-aqueous electrolyte, which is generally obtained by dissolving an electrolyte in a non-aqueous solvent. As the electrolyte solution used for the polymer electrolyte, the electrolyte is stable with respect to the positive electrode active material and the negative electrode active material, and lithium ions can move to perform an electrochemical reaction with the positive electrode active material or the negative electrode active material. Any non-aqueous substance can be used.

Specifically, LiPF ₆ , LiAsF ₆ , L
iSbF ₆ , LiBF ₄ , LiClO ₄ , LiI, Li
Br, LiCl, LiAlCl, LiHF ₂ , LiSC
N, LiSO ₃ CF _{2 and the} like. Among them, LiPF ₆ and LiClO ₄ are particularly preferable. The content of these electrolytes in the electrolyte is generally 0.5 to
2.5 mol / l.

The solvent for dissolving the polymer electrolyte is not particularly limited, but a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.
Acyclic carbonates such as tetrahydrofuran,
One or a mixture of two or more of glymes such as 2-methyltetrahydrofuran and dimethoxyethane, lactones such as γ-butyllactone, sulfur compounds such as sulfolane, and nitriles such as acetonitrile can be mentioned. Among these, cyclic carbonates such as ethylene carbonate and propylene carbonate, and acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are particularly preferred. One or a mixed solution of two or more selected from -bonettes is preferred.

The above-mentioned electrolyte solution is immersed in a polymer such as polyethylene oxide, polypropylene oxide, an isocyanate crosslinked product of polyethylene oxide, phenylene oxide, or a phenylene sulfide polymer to prepare a gel electrolyte. The shape of the lithium secondary battery of the present invention can be various shapes such as a cylindrical shape, a box shape, a paper type, and a card type.

[0030]

As described above, the features of the present invention are to regulate the particle size of the conductive filler in the easy-adhesion layer, the DBP oil absorption, and the dry film thickness of the easy-adhesion layer in the lithium secondary battery using the polymer electrolyte. It is in. Hereinafter, the present invention will be described specifically.

[0031]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In each example, evaluation was performed by the following method. (Adhesion) The adhesion between the easy-adhesion layer and the positive electrode active material layer is as follows:
The evaluation was made based on the time required for peeling the positive electrode active material layer when the positive electrode was immersed in the electrolytic solution. Propylene carbonate was used as the electrolytic solution, and the size of the positive electrode was formed to 13 mmφ and evaluated.

(Initial Discharge Capacity [mAH / g]) The initial discharge capacity was calculated as the discharge capacity per positive electrode weight. For the evaluation, five identical batteries were prepared from the same sheet, and the variation in the initial discharge capacity was also evaluated. (Cycle Characteristics) The cycle characteristics were evaluated based on the number of cycles at which the capacity retention ratio became 80% or less, when the initial discharge capacity was 1. For evaluation, five identical batteries were prepared from the same sheet, and the variation in cycle characteristics was also evaluated.

Example 1 An easily adhesive layer paint was prepared according to the composition shown below and applied to an aluminum substrate. The following materials were used as the raw materials for the easily adhesive layer paint. Conductive filler: Tin oxide powder (manufactured by Mitsubishi Materials Corporation; average particle size: 0.03 μm, DBP oil absorption: 30 ml / 100 g) 40 parts by weight Binder: 20% aqueous solution of Li ₂ Si ₁₅ O ₁₁ (manufactured by Aldrich) 90 parts by weight Part Surfactant: Triton X-100 (manufactured by Alidrich) 1 part by weight Water: 150 parts by weight

The material for the easily adhesive layer was subjected to a dispersion treatment to form a paint, and was applied on an aluminum foil having a thickness of 20 μm using a bar coater so that the dry film thickness became 0.01 μm. The drying conditions of the coating film are as follows: after pre-drying at 200 ° C. for 90 seconds, and further, in an electric furnace at 400 ° C. Ar atmosphere for dehydration.
Let dry for hours. Subsequently, a paint for a positive electrode was prepared according to the composition shown below, and was applied on the aluminum substrate with an easy-adhesion layer described above, and was evaluated as a positive electrode for a Li battery. The following were used as raw materials for the positive electrode paint.

Positive electrode material: LiCoO ₂ powder (manufactured by FMC) 88 parts by weight Conductive material: acetylene black (manufactured by Denki Kagaku Kogyo) 4 parts by weight Binder: Photomer 4050 (manufactured by Henkel) 8 parts by weight Solvent: DMC (dimethyl carboxyl) Bonnet, manufactured by Mitsubishi Chemical Corporation) 100 parts by weight Crosslinking initiator: Trignox 42 (manufactured by Akuzo Nobel) 0.1 part by weight

The above positive electrode material was kneaded and dispersed to form a paint, which was then applied to the aluminum foil with an easy-adhesion layer prepared above using a doctor blade to a thickness of 150 μm. Thereafter, the coating film was dried and crosslinked at 120 ° C. to obtain a sheet on which the electrode material was applied. Next, press pressure is 800kgf
/ Cm ² . Thereafter, the coating film was impregnated with propylene carbonate as an electrolytic solution and punched into a predetermined shape to form a positive electrode. Next, an electrolyte having a thickness of 50 μm was applied on the positive electrode obtained here, and crosslinked by ultraviolet rays to form a gel electrolyte layer. A metal Li foil was laminated as a negative electrode on the gel electrolyte layer to obtain a sheet-like battery.

Example 2 A sheet-like battery was obtained in the same manner as in Example 1 except that the dry film thickness of the easy-adhesion layer was changed to 5 μm. Example 3 As a conductive filler, the average particle diameter was 0.01 μm, and D
A sheet-shaped battery was obtained in the same manner as in Example 1, except that tin oxide having a BP oil absorption of 45 ml / 100 g was used.

Example 4 As a conductive filler, the average particle diameter was 0.5 μm, and DB
A sheet-shaped battery was obtained in the same manner as in Example 1, except that tin oxide having a P oil absorption of 20 ml / 100 g was used. Comparative Example 1 A sheet-shaped battery was obtained in the same manner as in Example 1 except that the easy-adhesion layer was not provided.

Comparative Example 2 A sheet-like battery was prepared in the same manner as in Example 1 except that the aluminum substrate was polished with abrasive cloth to which abrasive particles were fixed without providing an easy-adhesion layer. Obtained. Comparative Example 3 A sheet-shaped battery was obtained in the same manner as in Example 1, except that graphite having an average particle diameter of 6 μm and a DBP oil absorption of 120 ml / 100 g was used as the conductive filler.

Comparative Example 4 Graphite having an average particle diameter of 6 μm and a DBP oil absorption of 120 ml / 100 g was used as a conductive filler.
A sheet-shaped battery was obtained in the same manner as in Example 1, except that the dry film thickness of the easy-adhesion layer was 5 μm. Comparative Example 5 Example 1 except that the dry film thickness of the easily adhesive layer was 10 μm.
A sheet-shaped battery was obtained in the same manner as described above.

Comparative Example 6 A sheet-shaped battery was obtained in the same manner as in Example 1, except that the dry film thickness of the easy-adhesion layer was changed to 0.005 μm. Comparative Example 7 As a conductive filler, the average particle diameter was 1.0 μm, and DB
A sheet-shaped battery was obtained in the same manner as in Example 1 except that tin oxide having a P oil absorption of 15 ml / 100 g was used.

Comparative Example 8 As the conductive filler, the average particle diameter was 0.005 μm,
A sheet-shaped battery was obtained in the same manner as in Example 1, except that tin oxide having a DBP oil absorption of 60 ml / 100 g was used. Examples 1 to 3 and Comparative Examples 1 to 8 were evaluated for adhesion, initial discharge capacity, and cycle characteristics, and the results are shown in Table 1.

[0043]

Table 1 Adhesive property Initial discharge capacity Cycle characteristics (mAh / g) (Cycle) Example 1 No peeling in 24 hours 125 ± 2 300 or more Example 2 No peeling in 24 hours 123 ± 2 300 or more Example 3 Peel in 20 hours 117 ± 5 300 ± 7 Example 4 Peel in 18 hours 115 ± 6 280 ± 9 Comparative Example 1 Peel in 1 minute 122 ± 5 30 ± 20 Comparative Example 2 Peel in 20 minutes 119 ± 15 50 ± 18 Compare Example 3 Peeled in 6 hours 115 ± 12 100 ± 10 Comparative Example 4 Peeled in 6 hours 113 ± 18 100 ± 18 Comparative Example 5 Peeled in 18 hours 108 ± 10 180 ± 18 Comparative Example 6 Peeled in 20 hours 118 ± 18 200 ± 20 Comparative Example 7 Peeled off in 10 hours 105 ± 14 150 ± 20 Comparative Example 8 Peeled out in 8 hours 110 ± 18 120 ± 23

[0044]

The lithium battery using the easy-adhesion layer of the present invention has good adhesiveness, has little variation in battery performance, and has excellent cycle characteristics.

Claims (4)

[Claims] 1. A lithium secondary battery in which an easy-adhesion layer is provided between a current collector and a battery active material layer, wherein in the easy-adhesion layer,
Average particle size is 0.5 μm or less and DBP oil absorption is 50 m
A lithium secondary battery comprising 1/100 g or less of a conductive filler, wherein the dry film thickness of the easy-adhesion layer is 0.01 to 5 μm. 2. The lithium secondary battery according to claim 1, wherein the conductive filler is tin oxide. 3. A lithium secondary battery comprising a positive electrode, a negative electrode and a polymer electrolyte, wherein the positive electrode comprises a positive electrode current collector, an easy-adhesion layer, and a positive electrode active material layer containing a compound capable of inserting and extracting lithium ions. Having an average particle diameter of 0.5 μm or less and a DBP oil absorption of 50 ml /
A lithium secondary battery comprising 100 g or less of a conductive filler, and a dry film thickness of the easy-adhesion layer is 0.01 to 5 μm. 4. The lithium secondary battery according to claim 3, wherein the polymer electrolyte is an electrolyte comprising a gel polymer containing a non-aqueous electrolyte.