CN101651233A - Lithium ion secondary battery and preparation method thereof - Google Patents

Abstract

The invention provides a lithium-ion secondary battery, the lithium-ion battery includes a battery casing, a pole core and an electrolyte, the pole core and the electrolyte are hermetically accommodated in the battery casing, the pole core includes a positive pole, a negative pole and a The separator between the positive electrode and the negative electrode, the positive electrode includes a current collector and a positive electrode material, and the positive electrode material contains a positive electrode active material, a conductive agent and a binder, wherein the binder is a binder with conductive properties, and the The diaphragm is a polyimide porous film. The invention also provides a preparation method of the lithium ion secondary battery. The lithium-ion secondary battery provided by the invention significantly improves the capacity and cycle performance of the battery and significantly improves the high-rate charge-discharge performance because the conductive polymer is used as the binder of the positive electrode and the polyimide is used as the battery separator.

Description

A kind of lithium ion secondary battery and preparation method thereof

technical field

The invention relates to a lithium ion secondary battery and a preparation method thereof.

Background technique

In recent years, the rapid development of electronic technology has enabled electronic devices to be miniaturized and light in weight, and thus more and more portable electronic devices have appeared. Lithium-ion secondary batteries have become the preferred energy sources for these portable electronic devices due to their advantages of high discharge voltage, high energy density and long cycle life.

The capacity and cycle performance of lithium-ion secondary batteries are the main performance indicators of lithium-ion secondary batteries, and the capacity and cycle performance are greatly affected by the resistance of the battery. A lithium-ion secondary battery is mainly composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a current collector and a positive electrode material loaded on the current collector, and the positive electrode material contains a positive electrode active material, a conductive agent and a binder. The negative electrode includes a current collector and a negative electrode material loaded on the current collector, and the negative electrode material contains a negative electrode active material, a conductive agent and a binder. The resistance of the battery mainly includes the resistance of the positive and negative electrodes, the resistance of the electrolyte, and the resistance of the diaphragm. Traditional methods for reducing resistance include reducing the resistance of the positive electrode and/or the negative electrode by selecting the material of the current collector, the type of active material and the conductive agent.

In the battery, the performance of the positive electrode has a great influence on the performance of the battery. The performance of the traditional positive electrode is mainly determined by the performance of the positive active material and the conductive agent, while the traditional binder only provides the positive electrode active material, conductive agent and current collector. the bonding force between them. Studies have found that when the binder used has conductive properties, it can improve the rapid movement of electrons and lithium ions in the battery, thereby improving the charge and discharge capacity of the battery.

Conductive polymers or conductive polymers refer to the general designation of polymers containing π-electron conjugated structures that can be transformed from insulators to conductors or semiconductors after chemical or electrochemical doping. Since the discovery of iodine-doped polyacetylene (PA), polyaniline (PANI), polypyrrole (PPY), polythiophene (PT), polydiacetylene (PDA) and polyphenylene vinylene (PPA) have been discovered one after another. as a matrix for conductive polymers. Using polyaniline with conductive properties as a binder in lithium-ion batteries can reduce the internal resistance of the battery and increase the charge-discharge capacity. For example, CN 1809937A discloses a kind of electrode active composition for electrochemical cell, and this composition comprises active electrode material and conductive polymer. However, the capacity increased by this method is limited and cannot meet the needs of today's electronic devices for large-capacity batteries.

Contents of the invention

The object of the present invention is to provide a lithium ion secondary battery with a higher capacity in order to overcome the defect of low capacity of the lithium ion secondary battery provided by the prior art.

The invention provides a lithium ion secondary battery, which comprises a battery case, a pole core and an electrolyte, the pole core and the electrolyte are sealed and accommodated in the battery case, and the pole core includes a positive pole, a negative pole and a separator between the positive electrode and the negative electrode, the positive electrode includes a current collector and a positive electrode material, and the positive electrode material contains a positive electrode active material, a conductive agent and a binder, wherein the binder is a binder with conductive properties, And the diaphragm is a polyimide porous film.

The invention provides a method for preparing a lithium ion secondary battery. The method comprises winding a positive electrode, a diaphragm and a negative electrode in sequence to form a pole core, putting the pole core into a battery shell, adding electrolyte, and then sealing it, wherein the The preparation method of the positive electrode includes loading the positive electrode material on the current collector, the positive electrode material contains a positive electrode active material, a conductive agent and a binder, wherein the binder is a binder with conductive properties, and the The diaphragm is a polyimide porous film.

The use of conductive polymer as the binder of the positive electrode can reduce the internal resistance of the battery, thereby increasing the capacity of the battery; when using polyimide as a lithium-ion battery separator, due to its advantages such as large pore size and high porosity, it can increase the lithium-ion capacity. The migration speed in the electrolyte, thereby improving the capacity and cycle performance of the battery.

The inventors of the present invention have unexpectedly found that when a conductive polymer is adopted as the binder of the positive electrode and polyimide is used as the battery separator, a synergistic effect occurs, that is, the capacity and cycle performance of the battery are significantly improved, and in addition Significantly improved high rate charge and discharge performance. The 0.2C discharge capacity of the battery prepared as in Example 1 was 830 mAh, while the 0.2C discharge capacity of the batteries prepared in Comparative Examples 1, 2 and 3 were 795 mAh, 790 mAh and 780 mAh respectively The number of cycles of the battery prepared in Example 1 is 500, while the number of cycles of the battery prepared in Comparative Examples 1, 2 and 3 is 437, 431 and 420 respectively. Therefore, the combination of conductive adhesive and polyimide diaphragm performance a strong synergistic effect.

Detailed ways

The invention provides a lithium-ion secondary battery, the lithium-ion battery includes a battery casing, a pole core and an electrolyte, the pole core and the electrolyte are hermetically accommodated in the battery casing, the pole core includes a positive pole, a negative pole and a The separator between the positive electrode and the negative electrode, the positive electrode includes a current collector and a positive electrode material, and the positive electrode material contains a positive electrode active material, a conductive agent and a binder, wherein the binder is a binder with conductive properties, and the The separator is polyimide porous film (PI).

In the lithium ion secondary battery of the present invention, the porosity of the polyimide porous film can be 40-60%; the average pore diameter can be 80-100 nanometers. Its thickness may be 16-25 microns, preferably 18-22 microns.

In the lithium ion secondary battery of the present invention, the binder with conductive properties can be a conductive polymer, and the conductive polymer can be a conductive polymer used in the prior art, preferably a conductive polymer. Conductive polymers having a rate of 1-30 Siemens per centimeter (S/cm), most preferably 5-25 Siemens/cm.

In the present invention, the conductive polymer may be one or more cationized products of polyaniline, polythiophene, polypyrrole, polyacetylene, polyphenylene vinylene, and polyfuran. The degree of cationization depends on the desired conductivity. The cationization products include protonation products or metal cation products. In a preferred embodiment, the conductive polymer is a protonated product of polyaniline. Polyaniline can exist in several common forms, including its reduced form, leucoemeradine, partially oxidized emeraldine, and fully oxidized pernigraniline, whose general formula as follows:

faded emeraldine base

emeraldine base

All Nigrosine

Commonly used polyaniline exists in the form of their mixture, and its general formula is:

When 0 ≤ y ≤ 1, polyaniline is called poly-p-phenylenediamine imine, where the oxidation state of the polymer increases continuously as the value of y decreases. When y=0, it is completely reduced poly-p-phenylenediamine imine, also known as faded emeraldine base; when 0.35≤y≤0.65, it is called emeraldine base. Therefore, "faded emeraldine base", "emeraldine base", "full nigrosine" refer to polyaniline in different oxidation states. Each oxidation state can exist in its basic, protonated or cationic form. The term "protonation" refers to the addition of hydrogen ions to a polymer by contacting the polymer with a protic acid. The protic acid can be inorganic acid and organic acid. The inorganic acid is one or more of hydrochloric acid, sulfuric acid and nitric acid; the organic acid is one or more of methanesulfonic acid, toluenesulfonic acid, dodecylbenzenesulfonic acid and camphorsulfonic acid. Contacting methods and conditions are well known to those skilled in the art, and the present invention will not repeat them here.

Discolored emeraldine bases are electrically insulating, while protonated emeraldine bases are highly conductive. The protonated emeraldine base can be protonated by contacting the emeraldine base with a protic acid, such as hydrochloric acid; it can also be obtained by electrochemically oxidizing the protonated emeraldine base or Obtained by reduction of protonated all-aniline black.

The aforementioned conductive polymers can be obtained in various ways, for example, they can be obtained commercially, or can be prepared by methods known in the art.

In the lithium ion secondary battery of the present invention, the content of the binding agent, the positive electrode active material and the conductive agent is a conventional content; preferably, based on the total weight of the positive electrode active material, the conductive agent and the binding agent, the The content of the binder is 0.5-10% by weight, most preferably 0.5-2% by weight; the content of the positive electrode active material is 85-90% by weight; the content of the conductive agent is 0.5-5% by weight.

The present invention has no special limitation on the positive electrode active material, which is the same as the prior art. The positive electrode active material can be all commercially available positive electrode active materials, such as LiFePO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiMn ₂ O ₄ , LiMnO ₂ , LiNiO ₂ , LiCoO ₂ , LiVPO ₄ F, LiFeO ₂ ; or the ternary system Li _{1+ a} L _1-bc M _b N _c O ₂ , where -0.1≤a≤0.2, 0≤b≤1, 0≤c≤1, 0≤b+c≤1.0, L, M and N are one or more of Co, Mn, Ni, Al, Mg, Ga and 3d transition metal elements.

The conductive agent can be any conductive agent known in the art, for example, one or more of graphite, carbon fiber, carbon black, metal powder and fiber can be used.

The preparation method of the positive electrode can adopt various methods commonly used in the art, such as preparing the positive electrode active material, binder and conductive agent into a positive electrode material slurry with a solvent, and the addition amount of the solvent is well known to those skilled in the art. The viscosity and operability requirements of the slurry coating of the prepared positive electrode slurry can be flexibly adjusted. Then, the prepared positive electrode material slurry is drawn and coated on the positive electrode current collector, dried and pressed into sheets, and then cut into pieces to obtain positive electrodes. The drying temperature may be 80-150° C., and the drying time may be 2-10 hours.

The solvent used in the positive electrode slurry can be various solvents in the prior art, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), diethylformamide (DEF), One or more of methyl sulfoxide (DMSO), tetrahydrofuran (THF), water and alcohols. The amount of the solvent is such that the slurry can be coated on the conductive substrate. Generally, the solvent is used in an amount such that the content of the positive electrode active material in the slurry is 40-90% by weight, preferably 50-85% by weight.

The negative electrode is a negative electrode known in the art, that is, it contains a negative electrode current collector and a negative electrode material coated on the negative electrode current collector. The current collector can adopt various current collectors used in the prior art for lithium-ion secondary battery negative electrodes, such as copper foil. The present invention has no special limitation on the negative electrode material. Like the prior art, the negative electrode material layer usually includes negative electrode active material, binder and conductive agent. The negative electrode active material can be all commercially available negative electrode active materials, such as graphite and lithium titanium oxide. The conductive agent may be nickel powder and/or copper powder. Described binder can be the various binders that are used for lithium ion secondary battery negative electrode in the prior art, as can be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl fiber One or more of Sodium Sodium (CMC) and Styrene Butadiene Rubber (SBR). The preparation method of the negative electrode is similar to that of the positive electrode, and will not be described in detail here.

In the lithium ion secondary battery of the present invention, the electrolytic solution is a nonaqueous electrolytic solution. The non-aqueous electrolytic solution is a solution formed of an electrolyte lithium salt in a non-aqueous solvent, and conventional non-aqueous electrolytic solutions known to those skilled in the art can be used. For example, the electrolyte lithium salt can be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium hexafluorosilicate (LiSiF ₆ ) , lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl ₄ ) and lithium fluorocarbon sulfonate (LiC(SO ₂ CF ₃ ) ₃ ), LiCH ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ or one or more. Non-aqueous solvent can be selected from chain acid ester and cyclic ester mixed solution, and wherein chain acid ester can be dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), carbonic acid One or more of methyl propyl ester (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds. The cyclic acid ester can be ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sultone and other fluorine-containing, sulfur-containing or One or more of cyclic organic esters containing unsaturated bonds. In the non-aqueous electrolytic solution, the concentration of the electrolyte lithium salt is generally 0.1-2 mol/liter, preferably 0.8-1.2 mol/liter.

The preparation method of the lithium-ion secondary battery provided by the present invention is well known to those skilled in the art. Generally speaking, the method includes winding the positive pole, the negative pole and the separator between the positive pole and the negative pole in turn to form a pole core, and The pole core is placed in the battery case, the electrolyte is added, and then sealed, wherein the positive electrode includes a current collector and a positive electrode material loaded on the current collector, and the positive electrode material contains a positive electrode active material, a conductive agent and a binder, wherein , the adhesive is a conductive adhesive, and the separator is a polyimide porous film. Among them, the methods of winding and sealing are well known to those skilled in the art. The amount of electrolyte used is conventional. Among them, in a preferred embodiment, the porous polyimide film and conductive polymer are the same as the above-mentioned preferred porous polyimide film and conductive polymer. In another preferred embodiment, based on the total weight of the positive electrode active material, conductive agent and binder, the content of the binder is 0.5-10% by weight, and the content of the positive electrode active material is 85% -90% by weight, the content of the conductive agent is 0.5-5% by weight.

The lithium-ion secondary battery of the present invention will be described below by taking the 053450 battery as an example.

Example 1

This embodiment is used to illustrate the lithium ion secondary battery provided by the present invention.

Positive electrode: the positive electrode active material LiCoO ₂ , conductive agent acetylene black, conductive polymer (cationized product of polyaniline, conductivity 10S/cm, EHSY company) as binder, by weight ratio 100:5:2 Mix thoroughly with solvent NMP. Spread the dressing on both sides on aluminum foil with a thickness of 20 μm and spread evenly. Dried at 100°C, rolled, rolled and cut into positive electrode sheets, the size of the electrode sheet was 450cm (length)×44cm (width)×0.12cm (thickness), containing 7 grams of positive electrode active material.

Negative electrode: uniformly mix artificial graphite, binder SBR and CMC in deionized water at a weight ratio of 100:5:3. Apply double-sided dressing on copper foil with a thickness of 12 microns and spread evenly. Dry at 90°C, roll, roll and cut into positive pole pieces, the size of which is 480cm (length) x 45cm (width) x 0.2cm (thickness), and the weight of the negative pole material is 3.4 grams.

Diaphragm: A 20 micron thick polyimide porous film with a porosity of 40% and an average pore diameter of 90 nanometers.

Wind the above-mentioned positive and negative electrode sheets and separator into a square lithium-ion cell and put it into the square battery casing, and then inject 1 mol/liter LiPF ₆ /(EC+DEC+DMC) (EC, DEC and DMC weight The ratio is 1:1:1) electrolyte solution, sealed, and made into 053450 type lithium ion battery 1.

Example 2

This embodiment is used to illustrate the lithium ion secondary battery provided by the present invention.

Positive electrode: LiCoO ₂ as the positive electrode active material, acetylene black as the conductive agent, and conductive polymer as the binder (cationized product of polythiophene, EHSY company, conductivity 8S/cm), in a weight ratio of 100:5:0.5 Mix thoroughly with NMP. Spread the dressing on both sides on aluminum foil with a thickness of 20 μm and spread evenly. Dry at 100°C, roll, roll and cut into positive electrode pieces, the size of the electrode piece is 450cm×44cm, and the weight of the positive electrode material is 7 grams.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: A 25 micron thick polyimide porous film with a porosity of 60% and an average pore diameter of 80 nanometers.

Battery 2 was assembled according to the method of Example 1.

Example 3

This embodiment is used to illustrate the lithium ion secondary battery provided by the present invention.

In this embodiment, the positive pole: adopt positive pole active material LiCoO ₂ , conduction agent acetylene black, conduction polymer (the cationization product of polypyrrole, EHSY company, conductivity 20S/cm) as binder, by weight Mix evenly in NMP at a ratio of 100:5:5. Spread the dressing on both sides on aluminum foil with a thickness of 20 μm and spread evenly. It is dried in a vacuum oven and then pressed.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: A 16 micron thick polyimide porous film with a porosity of 50% and an average pore diameter of 70 nanometers.

Battery 3 was assembled according to the method of Example 1.

Example 4

This embodiment is used to illustrate the lithium ion secondary battery provided by the present invention.

Positive electrode: LiCoO ₂ is used as the positive electrode active material, acetylene black as the conductive agent, and a conductive polymer as a binder (cationized product of polyacetylene, EHSY Company, conductivity 25S/cm), in a weight ratio of 100:5:10 Mix well in NMP. Spread the dressing on both sides on aluminum foil with a thickness of 20 μm and spread evenly. It is dried in a vacuum oven and then pressed.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: A 20 micron thick polyimide porous film with a porosity of 40% and an average pore diameter of 90 nanometers.

Battery 4 was assembled according to the method of Example 1.

Comparative example 1

This comparative example is used to illustrate the lithium ion secondary battery provided by the prior art.

Positive electrode: according to the method for preparing the positive electrode in Example 1, the difference is that PVDF is used as the binder.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: The same diaphragm as in Example 1 was used.

Battery C1 was assembled according to the method of Example 1.

Comparative example 2

This comparative example is used to illustrate the lithium ion secondary battery provided by the prior art.

Positive electrode: proceed according to the method for preparing the positive electrode in Example 1.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: A 20-micron polyethylene porous film with a porosity of 40% and an average pore diameter of 100 nanometers.

Battery C2 was assembled according to the method of Example 1.

Comparative example 3

This comparative example is used to illustrate the lithium ion secondary battery provided by the prior art.

Positive electrode: proceed according to the method for preparing the positive electrode in Example 1, except that PVDF is used as the binder.

Negative electrode: proceed according to the method for preparing the negative electrode in Example 1.

Diaphragm: a 20-micron polypropylene porous film with a porosity of 40% and an average pore diameter of 100 nm.

Battery C3 was assembled according to the method of Example 1.

Battery performance test

1. Test of rate discharge performance

At room temperature, the batteries prepared in Examples 1-4 and Comparative Examples 1-3 were charged to 4.2V with 1C current respectively, and after the voltage rose to 4.2 volts, they were charged with a constant voltage of 4.2 volts, and the cut-off current was 0.05C. minutes; then discharge the batteries to 3 volts with a current of 0.2C to obtain the capacity of the battery at room temperature to discharge to 3 volts with a current of 0.2C; then repeat the above charging steps, and discharge the batteries with a current of 0.5C again to obtain a battery Discharge to a capacity of 3 volts at room temperature with a current of 0.5C; then repeat the above charging steps, and discharge the batteries at a current of 1C again to obtain a capacity of 3 volts at room temperature with a current of 1C; then repeat the above charging step, and discharge the battery with a current of 2C again, to obtain the capacity of the battery at room temperature at 2C to 3 volts; then repeat the above charging steps, and discharge the battery with a current of 3C again, to obtain a battery at room temperature Discharge with 3C current to a capacitance of 3 volts; then repeat the above charging steps, and discharge the battery with a current of 5C again, and obtain the measured results of the battery at room temperature with a current of 5C to discharge to 3 volts in the table 1 in.

2. Determination of cycle performance

At room temperature, the batteries prepared in Examples 1-4 and Comparative Examples 1-3 were charged to 4.2 volts with a current of 1C, and after the voltage rose to 4.2 volts, they were charged with a constant voltage of 4.2 volts, and the cut-off current was 0.05C. 5 minutes, and then discharge the battery to 3 volts with 1C current, and obtain the capacity of the battery at room temperature with 1C current discharge to 3 volts; repeat the above charging and discharging steps until the battery capacity is 80% of the first measured capacity, stop the test, and measure The obtained results are listed in Table 1.

3. Determination of battery internal resistance

The batteries made in Examples 1-4 and Comparative Examples 1-3 were charged at 0.1C (120 mA) for 16 hours at an ambient temperature of 20±5°C. After charging, they were left to stand for 1 hour, and then The internal resistance was tested with an internal resistance meter produced by Guangzhou Lanqi Company, and the measured results are listed in Table 1.

Table 1

As can be seen from Table 1, the electric capacity and cycle performance of the battery prepared in Example 1-4 are significantly higher than those of the battery prepared in Comparative Example 1-3; and the internal resistance is significantly lower than that of Comparative Example 1-3 The internal resistance of the prepared battery. Therefore, the combined use of conductive adhesives and polyimide separators exhibits a strong synergistic effect.

Claims (12)

1. A lithium-ion secondary battery, the lithium-ion battery includes a battery casing, a pole core and an electrolyte, the pole core and the electrolyte are sealed and accommodated in the battery casing, the pole core includes a positive pole, a negative pole and a battery located between the positive pole and the electrolyte. The separator between the negative electrodes, the positive electrode includes a current collector and a positive electrode material loaded on the current collector, the positive electrode material contains a positive electrode active material, a conductive agent and a binder, and it is characterized in that the binder is a conductive material binder, and the diaphragm is a polyimide porous film. 2. The lithium ion secondary battery according to claim 1, wherein the porosity of the polyimide porous film is 40-60%, and the average pore diameter is 80-100 nanometers. 3. The lithium ion secondary battery according to claim 1 or 2, wherein the thickness of the polyimide porous film is 16-25 microns. 4. The lithium ion secondary battery according to claim 1, wherein the conductive binder is a conductive polymer, and the conductive polymer has a conductivity of 1-30 Siemens per centimeter. 5. The lithium-ion secondary battery according to claim 4, wherein the conductive polymer is one or more of polyaniline, polythiophene, polypyrrole, polyacetylene, polyphenylene vinylene, and polyfuran Protonated product or cationized product. 6. The lithium ion secondary battery according to claim 1, wherein, based on the total weight of the positive electrode active material, the conductive agent and the binder, the content of the binder is 0.5-10% by weight, and the The content of the positive electrode active material is 85-90% by weight, and the content of the conductive agent is 0.5-5% by weight. 7. A method for preparing a lithium-ion secondary battery as claimed in claim 1, the method comprising winding the positive electrode, the diaphragm and the negative electrode in sequence to form a pole core, placing the pole core in the battery case, adding electrolyte, and then sealing , wherein, the preparation method of the positive electrode includes loading the positive electrode material on the current collector, the positive electrode material contains a positive electrode active material, a conductive agent and a binder, and it is characterized in that the binder is an adhesive with conductive properties. binder, and the diaphragm is a polyimide porous film. 8. The method for preparing a lithium-ion secondary battery according to claim 7, wherein the porosity of the polyimide porous film is 40-60%, and the average pore diameter is 80-100 nanometers. 9. The method for preparing a lithium ion secondary battery according to claim 7 or 8, wherein the thickness of the polyimide porous film is 16-25 microns. 10. The method for preparing a lithium-ion secondary battery according to claim 7, wherein the conductive binder is a conductive polymer, and the conductive polymer has a conductivity of 1-30 Siemens per centimeter. 11. The method for preparing a lithium-ion secondary battery according to claim 10, wherein the conductive polymer is one of polyaniline, polythiophene, polypyrrole, polyacetylene, polyphenylene vinylene, polyfuran or Several cationization products. 12. The method for preparing a lithium ion secondary battery according to claim 8, wherein, based on the total weight of the positive electrode active material, the conductive agent and the binder, the content of the binder is 0.5-10% by weight , the content of the positive electrode active material is 85-90% by weight, and the content of the conductive agent is 0.5-5% by weight.