KR101274495B1 - Process for Preparation of Anode and Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to a method of manufacturing a negative electrode for a secondary battery in which a solid electrolyte interfacial film (SEI film) is formed on a surface of a carbon powder as a negative electrode active material, wherein lithium powder is contacted to a surface of the carbon powder by applying lithium powder to the carbon powder. And a process for injecting a lithium salt-containing electrolyte into the carbon powder having the lithium powder connected to the surface, and inducing a reaction for forming an SEI film on the surface of the carbon powder by the electrolyte. to provide.
Since the SEI film is formed on the surface of the carbon powder as the active material, the negative electrode according to the present invention may reduce the amount of irreversible lithium during the initial charge and discharge process, and thus the secondary battery using the same has excellent capacity and charge / discharge characteristics.

Description

Process for Preparation of Anode and Secondary Battery Comprising the Same

The present invention relates to a method for manufacturing a negative electrode and a secondary battery using the same. More particularly, after the lithium powder is applied to the surface of the carbon powder as a negative electrode active material, the electrolyte is injected to form a solid electrolyte interface membrane on the surface of the carbon powder It relates to a method for producing a negative electrode for a secondary battery, characterized in that to induce a reaction for the secondary battery using such a negative electrode.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

Lithium secondary batteries are manufactured by using a metal oxide such as LiCoO ₂ as a positive electrode active material and a carbon material as a negative electrode active material, placing a porous polymer separator between the negative electrode and the positive electrode, and adding a non-aqueous electrolyte containing lithium salt such as LiPF ₆ . Basically, it must be stable over the operating voltage range of the cell and have the ability to transfer ions at a sufficiently high rate.

The lithium secondary battery moves from a lithium metal oxide used as a cathode during initial charging to a carbon material in which lithium ions are used as a negative electrode, and is inserted between layers of the carbon material electrode. At this time, since lithium is highly reactive, the electrolyte solution and the lithium salt react on the surface of the carbon material negative electrode into which lithium is inserted to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the carbon material cathode, which is called a solid electrolyte interface (SEI film).

Once formed, the SEI film functions as an ion tunnel to pass only lithium ions, and the lithium ions do not react with the carbon material anode or other materials again, so that no further decomposition of the electrolyte occurs. The amount of lithium ions in the electrolyte can be reversibly maintained to maintain stable charge and discharge (J. Power Sources (1994) 51: 79-104). However, since the amount of charge consumed to form the SEI film has a property of not reversibly reacting at the time of discharging at an irreversible capacity, a decrease in discharge capacity occurs at the time of initial charging and discharging. As a result, the reversible capacity of lithium is gradually reduced, thereby reducing the discharge capacity and causing cycle degradation.

Therefore, there is a high need for a technique for solving this problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application, after extensive research and various experiments, as described later, in the secondary battery using a carbon-based material as a negative electrode active material, when the SEI film is formed on the surface of the carbon powder by a predetermined method, While it is possible to maintain stable charge and discharge by the SEI film on the surface of the carbon material, it is possible to solve problems such as the capacity decay and voltage drop due to the irreversible capacity of lithium due to the formation of the SEI film during the initial charge and discharge. The present invention has been completed.

Accordingly, the present invention is a method of manufacturing a negative electrode for a secondary battery in which a solid electrolyte interface film (SEI film) is formed on a surface of a carbon powder as a negative electrode active material.

(I) applying lithium powder to the carbon powder to bring the lithium powder into contact with the surface of the carbon powder;

(II) injecting a lithium salt-containing electrolyte into the carbon powder, the lithium powder is connected to the surface; And

(III) inducing a reaction for forming an SEI film on the surface of the carbon powder by the electrolyte solution; As shown in Fig.

In the production method of the present invention, the kind of the carbon powder is not particularly limited, and for example, a group consisting of natural graphite, artificial graphite, hard carbon, coke, and soft carbon. It may be one or two or more selected from, and preferably may be artificial graphite.

The average particle diameter of the carbon powder may be 10 to 30 μm, and the average particle diameter of the lithium powder may be 5 to 20 μm.

The lithium salt is, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ It may be selected from the group consisting of SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, C ₁ -C ₅ aliphatic carbonate, and lithium 4 phenyl borate.

The electrolyte solution is, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone , 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, Nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetra It may be selected from the group consisting of hydrofuran derivative, ether, methyl pyroionate and ethyl propionate.

In one preferred example, the process (I) is

(Ia) forming an active material layer containing carbon powder on the surface of the negative electrode current collector; (Ib) forming a lithium powder layer by applying lithium powder on the active material layer;

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The active material layer may include a binder, or a binder and a conductive agent.

The active material layer may be, for example, formed to a thickness of 100 to 200 μm, and the lithium powder layer may be formed to, for example, a thickness of 50 to 200 μm.

In some cases, after the step (Ib), may further include a step (Ic) of pressing the lithium powder layer.

Preferably, the process (III) may further comprise the step of configuring a negative electrode and a corresponding positive electrode including carbon powder and lithium powder and applying a current.

The present invention also provides a negative electrode for a secondary battery produced by the above method. As described above, the negative electrode according to the present invention is characterized in that the SEI film is already formed on the surface of the carbon powder as the negative electrode active material.

Accordingly, the present invention also provides a negative electrode active material for a secondary battery in which an SEI film is formed on the surface of the carbon powder by injecting a lithium salt-containing electrolyte solution while applying lithium powder to the carbon powder and bringing the lithium powder into contact with the surface of the carbon powder.

In addition, the present invention provides a secondary battery including the negative electrode.

As described above, the secondary battery according to the present invention, before performing the initial charge and discharge process for activation, is characterized in that the negative electrode active material includes a negative electrode having an SEI film formed on the surface of the carbon powder.

The secondary battery is not particularly limited and may be preferably a lithium secondary battery including the negative electrode.

The secondary battery according to the present invention may be preferably used as a unit battery of a medium-large battery pack including a plurality of battery cells.

As described above, since the SEI film is formed on the surface of the carbon powder as the active material, the negative electrode for the secondary battery according to the present invention may use the same to manufacture a secondary battery having improved charge and discharge characteristics.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

The present invention is a method of manufacturing a negative electrode for a secondary battery in which a solid electrolyte interface film (SEI film) is formed on a surface of a carbon powder as a negative electrode active material.

(I) applying lithium powder to the carbon powder to bring the lithium powder into contact with the surface of the carbon powder;

(II) injecting a lithium salt-containing electrolyte into the carbon powder, the lithium powder is connected to the surface; And

(III) inducing a reaction for forming an SEI film on the surface of the carbon powder by the electrolyte solution.

As described above, in the case of the lithium secondary battery, once the SEI film is formed on the surface of the negative electrode active material, the amount of lithium ions is reversibly maintained and the lifespan characteristics of the battery are also improved. However, during the initial charge / discharge process (activation process), lithium reacts with some components constituting the electrolyte to form an SEI film and is consumed at the inactive site of the negative electrode. Therefore, only about 90 to 95% of lithium ions return to the positive electrode. The fall of the discharge capacity is caused. That is, part of lithium is used to consume the irreversible portion of the negative electrode during the initial charging, and as a result, the charge and discharge efficiency may be reduced.

On the other hand, according to the present invention, in the previous step of inserting the positive electrode and the negative electrode in the battery case to inject the electrolyte to complete the secondary battery, since the negative electrode active material is already formed on the surface of the secondary battery, the initial charge and discharge process of the completed secondary battery In the lithium is not consumed for the irreversible reaction of the negative electrode can fundamentally solve the above problems.

In the conventional secondary battery manufacturing method, the concept of using a negative electrode active material in which an SEI film is already formed on the surface has not been attempted before the initial charge / discharge process. Moreover, for the formation of such SEI film, the concept of inducing a reaction for forming the SEI film on the surface of the carbon powder by the electrolyte by contacting the lithium powder on the surface of the carbon powder and injecting a lithium salt-containing electrolyte solution is completely new in the art. Technology.

In the production method of the present invention, the kind of the carbon powder is not particularly limited, and for example, a group consisting of natural graphite, artificial graphite, hard carbon, coke, and soft carbon. It may be one or two or more selected from, and preferably may be artificial graphite.

The average particle diameter of the carbon powder may be 10 to 30 μm, and if the particle size is too large, the density of the negative electrode material may be lowered. On the contrary, if the particle size is too small, the irreversible capacity of the negative electrode material is high and it is difficult to expect a desired discharge capacity. Not desirable

The average particle diameter of the lithium powder may be 5 to 20 μm, and when the particle size is too large, the contact area with the carbon powder may be small, and thus the formation of the SEI film may not be easy. It is not preferable because the cohesion force becomes large and it may be difficult to distribute uniformly on the surface of the carbon powder.

The lithium salt-containing electrolyte solution includes a lithium salt and an electrolyte solution, and the lithium salt-containing electrolyte solution may be the same as or different from the lithium salt-containing electrolyte solution injected into an electrode assembly having a cathode / separator / cathode structure when a secondary battery is manufactured. .

The lithium salt is, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ It may be selected from the group consisting of SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, C ₁ -C ₅ aliphatic carbonate, and lithium 4 phenyl borate.

The electrolyte solution is, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone , 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, Nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetra It may be selected from the group consisting of hydrofuran derivative, ether, methyl pyroionate and ethyl propionate.

In one preferred example, the process (I) is

(Ia) forming an active material layer containing carbon powder on the surface of the negative electrode current collector;

(Ib) applying a lithium powder on the active material layer to form a lithium powder layer; may include.

The active material layer may include a binder, a binder, and a conductive agent, and in some cases, a filler may be further included.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the negative electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the negative electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, graphite carbon black such as natural graphite or artificial graphite, acetylene black, Ketjen black, channel black, furnace black Conductive metal oxide polyphenylene derivatives, such as carbon black carbon fibers such as lamp black and summer black, conductive fibers such as metal fibers, metal powders such as carbon fluoride carbon, aluminum and nickel powder, zinc oxide oxide, and conductive whiskey titanium oxide such as potassium titanate Conductive materials, such as these, can be used.

The filler is optionally used as a component that suppresses the expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. For example, olefinic glass such as polyethylene or polypropylene may be used. Fibrous materials such as fibers and carbon fibers are used.

In the process (Ia), the negative electrode current collector may be generally 3 to 500 ㎛ thickness. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The active material layer may be prepared by, for example, applying a slurry made by mixing a negative electrode mixture including carbon powder and a binder to a solvent such as NMP on a negative electrode current collector, followed by drying and / or rolling.

In order to form an appropriate capacity and cycle characteristics of the negative electrode material and an appropriate amount of the SEI film, the active material layer is formed to a thickness of, for example, 100 to 200 μm, and the lithium powder layer is, for example, to 50 to 200 μm. It may be formed in a thickness.

However, the initially formed lithium powder layer may disappear completely through the reaction between the electrolyte solution and the active material, or only a very small amount may remain. In addition, if necessary, the remaining lithium powder layer may be washed or extinguished through reaction with other materials.

In some cases, after the step (Ib), may further include a step (Ic) of pressing the lithium powder layer.

Preferably, the process (III) may further comprise the step of configuring a negative electrode and a corresponding positive electrode including carbon powder and lithium powder and applying a current.

The above process can promote the reaction for forming the SEI film on the surface of the carbon powder by the electrolyte, and can induce the formation of a more stable SEI film. Since this process is performed before completion of the secondary battery, the corresponding cathode does not mean a cathode of the completed secondary battery.

The present invention also provides a negative electrode for a secondary battery produced by the above method. As described above, the negative electrode according to the present invention is characterized in that the SEI film is already formed on the surface of the carbon powder as the negative electrode active material before completion of the secondary battery.

Accordingly, the present invention also provides a negative electrode active material for a secondary battery in which an SEI film is formed on the surface of the carbon powder by injecting a lithium salt-containing electrolyte solution while applying lithium powder to the carbon powder and bringing the lithium powder into contact with the surface of the carbon powder.

Such negative and negative electrode active materials are novel materials that are not known per se in the art.

In addition, the present invention provides a secondary battery including the negative electrode.

As described above, the secondary battery according to the present invention, before performing the initial charge and discharge process for activation, is characterized in that the negative electrode active material includes a negative electrode having an SEI film formed on the surface of the carbon powder.

The secondary battery is not particularly limited, and may be preferably a lithium secondary battery including the negative electrode, the positive electrode, the separator, and the lithium salt-containing nonaqueous electrolyte.

The positive electrode is prepared by, for example, applying a positive electrode mixture containing a positive electrode active material onto a positive electrode current collector and then drying the positive electrode mixture. The positive electrode mixture may include, as necessary, the conductive materials, binders, fillers, and the like described above. This may include.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals. Formula Li _{1 + y} Mn _{2 - y} O ₄ (Where y is 0 to 0.33), lithium manganese oxide lithium copper oxide (Li ₂ CuO ₂ ) such as LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Vanadium oxide chemical formula LiNi _1-y M _y O _2, such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ (where M = Co, Mn, Al, Cu, Fe, Mg Ni-site-type lithium nickel oxide represented by B, or Ga and y = 0.01 to 0.3, LiMn _2-y M _y O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta, and y LiMn ₂ O wherein a portion of Li in a lithium manganese composite oxide formula, expressed as = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Ni, Cu, or Zn, is substituted with an alkaline earth metal ion ₄ disulfide compound Fe ₂ (MoO ₄ ) ₃ , and the like, but are not limited thereto.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separator, for example, a sheet, a nonwoven fabric, or the like made of olefin polymer glass fiber or polyethylene such as polypropylene having chemical resistance and hydrophobicity is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing non-aqueous electrolyte may use a material known in the art, or may use the lithium salt-containing electrolyte as described above.

In some cases, an organic solid electrolyte, an inorganic solid non-aqueous electrolyte, or the like may be used. Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, and poly edges. Agitation lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, polymerizers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ —LiI-LiOH, Li ₃ PO ₄ —Li ₂ S-SiS ₂ , and the like, may be used.

In addition, in the electrolyte solution, for the purpose of improving the charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, and the like may be added. have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (fluoro-ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

The secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery of a medium-large battery pack including a plurality of battery cells.

Preferable examples of the above medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric power storage systems, and the like.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (15)

A method of manufacturing a negative electrode for a secondary battery in which a solid electrolyte interface film (SEI film) is formed on a surface of a carbon powder as a negative electrode active material,
(I) applying lithium powder to the carbon powder to bring the lithium powder into contact with the surface of the carbon powder;
(II) injecting a lithium salt-containing electrolyte into the carbon powder, the lithium powder is connected to the surface; And
(III) inducing a reaction for forming an SEI film on the surface of the carbon powder by the electrolyte solution;
Method for producing a negative electrode comprising a. The method of claim 1, wherein the carbon material is one or two or more selected from the group consisting of natural graphite, artificial graphite, hard carbon, coke, and soft carbon. Method for producing a negative electrode. The method of claim 1, wherein the average particle diameter of the carbon powder is 10 to 30 ㎛, the average particle diameter of the lithium powder is 5 to 20 ㎛. The method of claim 1, wherein in the lithium salt-containing electrolyte,
The lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, C ₁ -C ₅ aliphatic carbonate, and lithium 4 phenyl borate,
The electrolyte solution is N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1,2- Dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxoron, acetonitrile, nitromethane, methyl formate Methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether , Methyl pyroionate and ethyl propionate is selected from the group consisting of a method for producing a negative electrode. According to claim 1, wherein the process (I),
(Ia) forming an active material layer containing carbon powder on the surface of the negative electrode current collector; And
(Ib) forming a lithium powder layer by applying lithium powder on the active material layer; manufacturing method of a negative electrode comprising a. The method of claim 5, wherein the active material layer contains a binder, a binder, and a conductive agent. The method of claim 5, wherein the active material layer is formed to a thickness of 100 to 200 μm, and the lithium powder layer is formed to a thickness of 50 to 200 μm. The method of claim 5, wherein the step (I) further comprises a step (Ic) of pressing the lithium powder layer. The method of manufacturing a negative electrode according to claim 1, further comprising: in step (III), forming a negative electrode and a corresponding positive electrode including carbon powder and lithium powder and applying a current. A negative electrode, characterized in that produced by the manufacturing method according to any one of claims 1 to 9. Lithium powder is applied to the carbon powder and a lithium salt-containing electrolyte is injected in a state in which the lithium powder is in contact with the surface of the carbon powder, the anode active material for secondary batteries, characterized in that the SEI film is formed on the surface of the carbon powder. A secondary battery comprising the negative electrode according to claim 10. The secondary battery of claim 12, wherein the battery is a lithium secondary battery. The secondary battery of claim 12, wherein the secondary battery is used as a unit cell of a medium-large battery pack. Before performing the initial charge and discharge process for activation, the secondary battery comprising a negative electrode having an SEI film formed on the surface of the carbon powder as a negative electrode active material.