KR101750213B1 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium manganese oxide cathode active material; Carbonaceous anode active material; And lithium tetrafluoroborate (LiBF ₄ ); And a non-aqueous electrolytic solution containing a vinylidene carbonate-based compound. The lithium secondary battery of the present invention can reduce the side reaction with the electrolyte at high voltage and prevent deterioration of the battery due to the transition metal eluted in the electrolyte solution while maintaining high capacity expression, thereby improving cycle characteristics and high temperature storage characteristics.

Description

LITHIUM SECONDARY BATTERY [0002]

The present invention relates to a lithium manganese oxide cathode active material; Carbonaceous anode active material; And lithium tetrafluoroborate (LiBF ₄ ); And a non-aqueous electrolytic solution containing a vinylidene carbonate-based compound.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and low self- It has been commercialized and widely used. In recent years, explosive demand for portable electric and electronic devices has led to a rapid increase in demand for secondary batteries. In particular, lithium secondary batteries have played a major role.

The lithium secondary battery is manufactured by using a material capable of inserting and desorbing lithium ions as a cathode and an anode, filling an organic electrolyte or a polymer electrolyte between the anode and the cathode, and inserting and removing lithium ions from the anode and the cathode And generate electrical energy by oxidation and reduction reactions at the time of the oxidation.

The use of lithium metal, a sulfur compound, or the like is considered as a negative electrode active material of such a lithium secondary battery. However, in view of safety and the like, most carbon materials are used. In this case, the capacity of the lithium secondary battery is determined by the capacity of the positive electrode, And is determined by the amount of lithium ions contained.

Generally, lithium-containing cobalt oxide (LiCoO ₂ ) is used as the cathode active material, and lithium-containing manganese oxide such as LiMnO _{2 having a} layered crystal structure and LiMn ₂ O _{4 having a} spinel crystal structure, lithium-containing nickel oxide (LiNiO ₂ ) Have been considered.

Of the above cathode active materials, LiCoO ₂ is most widely used because it has excellent lifetime characteristics and high charge / discharge efficiency. However, since cobalt used as a raw material is inferior in high temperature safety and structural safety, it is limited in price competitiveness and mass production .

On the other hand, lithium-containing nickel oxide (LiNiO ₂ ) exhibits a battery characteristic of a relatively low discharge capacity and a relatively low discharge capacity. However, a rapid phase transition of the crystal structure occurs depending on the volume change accompanying the charging / discharging cycle. When exposed to air and moisture There is a problem that safety is deteriorated rapidly.

Thus, a lithium-containing manganese oxide has been proposed as a cathode active material. Particularly, the lithium-containing manganese oxide having a spinel structure is advantageous in that it has excellent thermal stability, low cost, and easy synthesis. However, it has a disadvantage in that it has a small capacity, a deterioration in lifetime due to side reactions, and poor cycle characteristics and high temperature characteristics.

As a result, a layered lithium manganese oxide has been proposed in order to solve the low-capacity problem of spinel and ensure excellent thermal stability of the manganese-based active material. Particularly, although the lithium manganese-based oxide having a layered structure in which the content of Mn is larger than that of the other transition metal (s) has a disadvantage in that the initial irreversible capacity is somewhat large, it exhibits a very large capacity when overcharged at a high voltage. However, when charged / discharged with a high voltage equal to or higher than a flat level, the cell active material adversely affects the performance of the battery due to a side reaction (electrolytic decomposition, etc.) of the electrolyte.

Therefore, in a lithium secondary battery comprising a lithium manganese oxide as a cathode active material, there is a high need for a technique capable of suppressing side reactions of an electrolyte and increasing the performance of the battery.

Disclosure of the Invention A problem to be solved by the present invention is to provide a lithium secondary battery to which a cathode active material of lithium manganese oxide is applied in order to reduce a side reaction with an electrolyte at a high voltage and to prevent deterioration of the battery due to a transition metal eluted in the electrolyte while maintaining high- And to improve cycle characteristics and high-temperature storage characteristics of lithium secondary batteries.

In order to solve the above problems, the present invention provides a lithium secondary battery comprising: i) a cathode comprising lithium manganese oxide as a cathode active material; ii) a negative electrode comprising a carbon-based negative electrode active material; iii) a separator interposed between the anode and the cathode; And iv) a non-aqueous electrolytic solution containing lithium tetrafluoroborate (LiBF ₄ ) and a vinylidene carbonate-based compound.

The lithium secondary battery of the present invention can reduce the side reaction with the electrolyte at high voltage and prevent deterioration of the battery due to the transition metal eluted in the electrolyte solution while maintaining high capacity expression, thereby improving cycle characteristics and high temperature storage characteristics.

FIG. 1 is a graph showing the results of measurement of the amount of reduction gas produced by reduction of an electrolyte solution of lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 using gas chromatography (GC) according to Experimental Example 1. FIG.
2 is a graph showing the capacity retention rate (%) according to the number of cycles of the lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 according to Experimental Example 2.
3 is a graph showing discharge resistance increase rate (%) / 100 at SOC 50% according to the number of cycles of lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 according to Experimental Example 3. FIG.
4 is a graph showing discharge resistance increase rate (%) / 100 at SOC 50% according to storage period after high-temperature storage of lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 according to Experimental Example 4. FIG.
5 is a graph showing the capacity retention ratio (%) of the lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 according to Experimental Example 5, according to the storage period after storage at a high temperature.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

A lithium secondary battery according to an embodiment of the present invention comprises i) a cathode comprising a lithium manganese-based oxide as a cathode active material; ii) a negative electrode comprising a carbon-based negative electrode active material; iii) a separator interposed between the anode and the cathode; And iv) a non-aqueous electrolytic solution comprising lithium tetrafluoroborate (LiBF ₄ ) and a vinylidene carbonate-based compound:

A lithium secondary battery according to an embodiment of the present invention includes a cathode including a cathode active material of lithium manganese oxide, a cathode including a carbon anode active material, a LiBF ₄ And a non-aqueous electrolytic solution containing a vinylidene carbonate compound at the same time, it is possible to reduce a side reaction with an electrolyte at a high voltage and prevent deterioration of the battery due to a transition metal eluted in the electrolyte solution while maintaining high capacity expression, The storage characteristics can be improved.

According to one embodiment of the present invention, the lithium manganese-based oxide may be represented by the following general formula (1);

≪ Formula 1 >

Li [Li _x Ni _a Co _b Mn _c ] O ₂ (0? X <0.5, 0 <a, b <0.6, x + a + b + c = 1, 0.4 <c <1).

Generally, a lithium secondary battery using a lithium manganese oxide having a manganese (Mn) content higher than that of other transition metal (s) as shown in Formula 1 can exhibit a large capacity at a high voltage of about 4.3 V or more. However, the lithium manganese oxide undergoes reduction decomposition of the non-aqueous electrolytic solution during charging and discharging, and the generated gas interferes with the migration of Li ions between the electrodes, thereby accelerating the precipitation of the transition metal. Particularly, when a carbonaceous anode active material is used as a cathode, transition metal ions, particularly Mn, released due to the decomposition of the electrolyte are precipitated on the surface of the carbonaceous anode active material, and Li ions are consumed, May occur. As a result, there has been a problem that it is difficult to maintain a stable cycle characteristic at a high voltage.

According to one embodiment of the present invention, the problem that can be generated while maintaining the advantages of using the cathode active material of the lithium manganese oxide is solved by simultaneously applying LiBF ₄ and a vinylidene carbonate compound as a non-aqueous electrolytic solution additive You can.

That is, the lithium secondary battery of the present invention can secure a high capacity at a high voltage by using the lithium manganese-based oxide of Formula 1, and by using LiBF ₄ , a stable LiF film is formed on the surface of the cathode, It is possible to minimize the precipitation of ions on the surface of the negative electrode. By using a vinylidene carbonate compound, a stable SEI film is formed on the surface of the negative electrode to generate excessive gas due to a side reaction of the electrolyte and suppress the reduction decomposition of the electrolyte even at a low voltage have.

Due to such an improvement, the lithium secondary battery of the present invention can suppress the reduction decomposition reaction of electrolytes even in a high voltage region of about 4.35 V as well as a low voltage region of about 2.94 V, and has a high temperature storage characteristic and a long life characteristic Can be improved.

According to one embodiment of the present invention, the vinylidene carbonate-based compound is not limited as long as the above object can be achieved. For example, the vinylidene carbonate-based compound may be vinylene carbonate (VC), vinylene ethylene carbonate (VEC), or a combination thereof. Of these, vinylene carbonate is particularly preferable.

At this time, the content of the vinylidene carbonate compound can be used without limitation as long as the amount required to achieve the effect of the present invention, such as improvement of the low temperature output and cycle characteristics of the battery, can be used. For example, To 3% by weight. When the amount of the vinylidene carbonate compound is less than 1% by weight, it is difficult to sufficiently exert the effect of forming the expected SEI film upon addition. When the amount of the vinylidene carbonate compound exceeds 3% by weight, the thickness of the SEI film Is too thick to prevent formation of a LiF film produced by LiBF ₄ , thereby increasing the amount of transition metal precipitated in the cathode, thereby increasing the resistance.

In addition, the vinylidene carbonate compound remaining after forming the SEI film may be used to some extent to supplement the SEI film, but excessive amounts of the vinylidene carbonate compound may cause a side reaction with the cathode active material.

According to an embodiment of the present invention, the LiBF ₄ may form a stable LiF film on the surface of the cathode, thereby minimizing the precipitation of transition metal ions eluted in the electrolyte on the surface of the cathode.

The mixing ratio of LiBF ₄ and vinylidene carbonate compound is preferably 2: 1 to 2: 3 by weight. When the content of the vinylidene carbonate compound exceeds the range of the mixing ratio in the mixing of LiBF ₄ and the vinylidene carbonate compound, a reducing gas species such as CO, CH ₄ or C ₂ H ₆ The amount of transition metal precipitated on the surface of the negative electrode can be increased because it is difficult to form a coating film of LiBF ₄ . On the other hand, if the content of LiBF ₄ exceeds the range of the above mixing ratio, the effect of preventing the precipitation of transition metal ions may be increased, but the ion conductivity of the electrolyte may decrease and the resistance may increase.

According to an embodiment of the present invention, the concentration of LiBF ₄ in the non-aqueous electrolytic solution is preferably 0.1 mole / liter to 0.3 mole / liter, more preferably 0.125 mole / liter to 0.25 mole / liter. If the concentration of LiBF ₄ is less than 0.1 mole / l, the effect of improving cycle characteristics and high-temperature storage characteristics is insignificant. If the concentration of LiBF ₄ exceeds 0.3 mole / l, the effect of preventing the precipitation of transition metal ions But the ion conductivity of the electrolytic solution decreases, which may be a factor of increasing the resistance.

According to an embodiment of the present invention, the non-aqueous electrolytic solution may further include a lithium salt. Examples of the lithium salt include lithium salts such as LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ and LiClO ₄ , or a mixture of two or more thereof.

The molar ratio of LiBF ₄ to lithium salt is preferably 1: 4 to 1: 8. When the mixing ratio of the lithium salt and LiBF ₄ is out of the above range, the mobility of Li ions is reduced in the electrolyte solution to increase the resistance and decrease the output characteristics of the battery.

On the other hand, the non-aqueous organic solvent that can be included in the non-aqueous electrolyte solution is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery, exhibit desired characteristics together with additives, For example, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone or in combination of two or more. (EC), propylene carbonate (PC), and butylene carbonate (BC) are used as the cyclic carbonates, dimethyl carbonate (DMC) is used as the linear carbonate, and ethylene carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) are typical examples. .

According to an embodiment of the present invention, the negative electrode active material may be a carbonaceous negative electrode active material such as a crystalline carbon, an amorphous carbon or a carbon composite, either singly or in combination, Graphite carbon such as natural graphite and artificial graphite.

According to an embodiment of the present invention, the positive electrode and / or negative electrode may be prepared by mixing a binder and a solvent, a conductive agent and a dispersant, which can be ordinarily used, if necessary, and a dispersing agent, together with the positive electrode active material or the negative electrode active material, Followed by applying it to the current collector and compressing it.

Examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, poly Polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), liquefied petroleum resin (EPDM), polyvinyl alcohol, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, Various kinds of binder polymers such as polyvinylidene fluoride (EPDM), styrene butylene rubber (SBR), fluorine rubber, various copolymers and the like can be used.

The separator used according to an embodiment of the present invention may be a conventional porous polymer film conventionally used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / A porous polymer film made of a polyolefin-based polymer such as an ethylene / methacrylate copolymer may be used alone or in a laminated manner. Alternatively, a porous nonwoven fabric such as a high-melting glass fiber or a polyethylene terephthalate fiber Nonwoven fabric may be used, but the present invention is not limited thereto.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Example 1

[Preparation of non-aqueous electrolytic solution]

A mixed solvent containing a non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) and 1.0M of LiPF ₆ was added to a non- Based on the total amount, 2% by weight of LiBF ₄ and 1% by weight of vinylene carbonate (VC) were added to prepare a non-aqueous electrolytic solution.

[Production of lithium secondary battery]

Li ₁ as a cathode active material _{. 07} Ni _{0 . 25} Mn _{0 . 42} Co _{0 . 26} O ₂ (NMP) as a binder, 3 wt% of polyvinylidene fluoride (PVdF) as a binder was added to the positive electrode mixture slurry . The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a roll press to prepare a positive electrode.

Further, as a negative electrode active material, a mixture of natural graphite and soft carbon 9: 1, a mixture of SBR and CMC 2.2: 1 as a binder, carbon black as a conductive agent in an amount of 96 wt%, 3 wt% and 1 wt% Was added to NMP as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to produce a negative electrode.

The prepared positive electrode and negative electrode were sandwiched between a polyethylene separator and a polypropylene mixed separator, followed by preparing a polymer type battery by a conventional method, and then injecting the prepared non-aqueous electrolyte solution to complete the production of a lithium secondary battery.

Example 2

A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that 3% by weight of vinylene carbonate (VC) was added based on the total amount of the nonaqueous electrolytic solution in the preparation of the nonaqueous electrolytic solution of Example 1, A secondary battery was manufactured.

Comparative Example 1

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that vinylene carbonate (VC) was not used in the preparation of the non-aqueous electrolytic solution of Example 1 above.

Comparative Example 2

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that LiBF ₄ was not used and 3% by weight of vinylene carbonate (VC) was added to the non-aqueous electrolytic solution of Example 2 A battery was prepared.

Experimental Example 1

&Lt; Measurement of reducing gas amount using gas chromatography (GC)

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were charged at 0.1 C up to 4.6 V / 42.6 mA under constant current / constant voltage (CC / CV) conditions at 45 ° C., 0.1 C, which was repeatedly carried out at 1 to 500 cycles. The amount of reducing gas generated by the decomposition of the electrolyte after 500 cycles was measured using gas chromatography (GC-FID / TCD). The results are shown in Fig.

As can be seen from FIG. 1, in the case of a secondary battery using a non-aqueous electrolytic solution containing LiBF ₄ but not including vinylene carbonate (VC), the reduction gas analysis after 500 cycles showed that CH ₄ and C ₂ H ₆ , While LiBF ₄ And VC in Examples 1 and 2 using a non-aqueous electrolytic solution, the reduction gas was remarkably reduced as compared with Comparative Example 1. In particular, when the VC content was increased to 3 wt% based on the total amount of the non-aqueous electrolytic solution, the amount of reducing gas generated due to the reduction of the electrolytic solution was drastically decreased.

Experimental Example 2

&Lt; Measurement of capacity retention rate &

The lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were charged at 4.degree. C. to 4.35 V / 40.65 mA at a constant current / constant voltage (CC / CV) condition at 45.degree. , And the discharge capacity thereof was measured. This was repeated with 1 to 500 cycles, and the measured capacity retention rate is shown in Fig.

As can be seen from FIG. 2, the lithium secondary batteries of Examples 1 and 2 according to the present invention exhibited similar capacity retention ratios as those of Comparative Example 1 up to the 250th cycle, but after about 250 cycles, Respectively. In particular, from the 300th cycle onwards, the capacity retention ratios of the lithium secondary batteries of Examples 1 and 2 were substantially maintained, but the lithium secondary battery of Comparative Example 1 dropped sharply. In the lithium secondary battery of Comparative Example 2 not containing LiBF ₄ , the graph rapidly dropped from the 100th cycle.

Thus, according to an embodiment of the present invention, LiBF ₄ And VC were used, the discharge capacity characteristics of the lithium secondary batteries of Examples 1 and 2 using the non-aqueous electrolytic solution were significantly superior to those of Comparative Examples 1 and 2 in accordance with the cycle characteristics at 45 ° C.

Experimental Example 3

&Lt; Measurement of increase rate of discharge resistance to the number of cycles &

The lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were charged at 4.35 V at room temperature and then discharged at 5 C for 5 seconds at an SOC of 50% (charge depth) to measure the resistance. This was performed at 0, 100, 300, and 500th cycles, and the resistance increase rate (%) / 100 against the number of cycles was shown in FIG.

3, after the battery was charged at 4.35 V, the rate of increase in discharge resistance at an SOC of 50% with respect to the number of cycles was measured according to Examples 1 and 2 of the present invention using LiBF ₄ And VC was used as a non-aqueous electrolytic solution was LiBF ₄ The discharge resistance increase rate of the lithium secondary battery of Comparative Example 1 using the non-aqueous electrolytic solution containing only the non-aqueous electrolyte was significantly increased. Especially after 100th cycle, it can be seen that the resistance increase rate is significantly increased in Comparative Examples 1 and 2, and that the output of the battery can be reduced.

Thus, it can be seen that the first and second embodiments of the present invention do not have a high rate of resistance increase until the 500th cycle, and that the output characteristics of the battery are superior to those of Comparative Examples 1 and 2.

Experimental Example 4

&Lt; Measurement of discharge resistance increase rate at high temperature storage period >

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were filled with 4.35 V, stored at 60 DEG C for 1 to 4 weeks, and then discharged while SOC was 50% to 5C for 10 seconds. 4 shows the discharge resistance increase rate (%) / 100 at SOC 50% for the storage period of 1 to 4 weeks.

Referring to FIG. 4, in Example 1, the rate of increase in discharge resistance was significantly lower than that in Comparative Example 1 from the beginning of the storage period at 60 ° C. On the other hand, the discharge resistance increase rate of Example 2 and Comparative Example 1 were similar to each other at the first week of the storage period, but it was confirmed that the discharge resistance increase rate of Comparative Example 1 increased significantly after one week. In addition, at the fourth week of the storage period, Examples 1 and 2 showed a marked difference in the discharge resistance increase rate as compared with Comparative Example 1.

Thus, it can be seen that, even after storage at a high temperature of 60 캜 of 4.35 V, the discharge resistance increase rate of Examples 1 and 2 of the present invention is significantly lower than that of Comparative Example 1 even if the storage period is increased.

Experimental Example 5

&Lt; Measurement of capacity retention rate at high temperature storage period >

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were charged at 1 C to 4.35 V / 40.65 mA under a constant current / constant voltage (CC / CV) condition at room temperature. And the discharge capacity thereof was measured. The capacity retention ratio after storage for 1 to 4 weeks is shown in Fig.

Referring to FIG. 5, Example 1 of the present invention from the first week of the storage period has a significantly higher capacity retention rate than Comparative Example 1. That is, the capacity retention ratios of Examples 1 and 2 were maintained at 80% or more even at the 4th storage period at 60 ° C, and in particular, the capacity retention ratio was about 90% in Example 1.

Therefore, it can be seen that the lithium secondary batteries of Examples 1 and 2 have an effect of improving the capacity characteristics even when the storage period after storage at high temperature is increased as compared with the lithium secondary battery of Comparative Example 1. [

Claims (8)

i) a cathode comprising a lithium manganese-based oxide as a cathode active material;
ii) a negative electrode comprising a carbon-based negative electrode active material;
iii) a separator interposed between the anode and the cathode; And
iv) a non-aqueous electrolytic solution comprising lithium tetrafluoroborate (LiBF ₄ ) and a vinylidene carbonate-based compound,
The vinylidene carbonate compound is contained in an amount of 1 to 3% by weight based on the total weight of the non-aqueous electrolytic solution,
The mixing ratio of the lithium tetrafluoroborate to the vinylidene carbonate compound is 2: 1 to 2: 3 by weight,
The lithium secondary battery according to claim 1, wherein the lithium manganese oxide is represented by the following formula (1).
&Lt; Formula 1 >
Li [Li _x Ni _a Co _b Mn _c ] O ₂ (0? X <0.5, 0 <a, b <0.6, x + a + b + c = 1, 0.4 <c <1).
The method according to claim 1,
Wherein the non-aqueous electrolytic solution further comprises a lithium salt.
3. The method of claim 2,
Wherein the mixing ratio of the lithium tetrafluoroborate to the lithium salt is 1: 4 to 1: 8 in terms of molar ratio.
delete The method according to claim 1,
Wherein the vinylidene carbonate compound is vinylene carbonate, vinylene ethylene carbonate, or a combination thereof.
3. The method of claim 2,
The lithium salt may be any one selected from the group consisting of LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and CF ₃ SO ₃ Li And a mixture of two or more thereof.
The method according to claim 1,
Wherein the concentration of the lithium tetrafluoroborate in the non-aqueous electrolytic solution is 0.1 mole / liter to 0.3 mole / liter.
The method according to claim 1,
Wherein the carbonaceous anode active material comprises graphite carbon.

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