KR100826084B1 - Additives for lithium secondarty battery - Google Patents

Abstract

The present invention provides a lithium secondary battery comprising a positive electrode (C), a negative electrode (A), a separator and an electrolyte, wherein the electrolyte is (a) a nitrile group-containing compound; And (b) provides a lithium secondary battery comprising a toluene fluoride compound.

Lithium secondary battery according to the present invention by adding a toluene fluoride compound in the battery swelling phenomenon and capacity reduction during high temperature storage (> 80 ℃) caused by the nitrile group-containing compound added to the electrolyte in order to improve the high temperature cycling characteristics and safety Can be improved.

Nitrile, Toluene Fluoride, High Temperature Storage, Safety, Lithium Secondary Battery

Description

ADDITIVES FOR LITHIUM SECONDARTY BATTERY}

1 is a view showing the high-temperature (45 ° C) cycle characteristics of the 4.35V lithium secondary battery of Comparative Example 1, not using the electrolyte additive, and the 4.35V lithium secondary battery of Comparative Example 2 using the succinonitrile as the electrolyte additive.

Figure 2 is a diagram showing the high temperature (45 ℃) cycle characteristics of the 4.35V lithium secondary battery of Example 1 using a succinonitrile and 3- toluene compound as the electrolyte additive.

3A and 3B are diagrams illustrating the results of overcharging experiments of the 4.35V lithium secondary battery of Comparative Example 1 under 6V / 1A and 12V / 1A conditions, respectively.

4 is an overcharge test result of the lithium secondary battery of Comparative Example 2 under the conditions of 12V / 1A.

5 is an overcharge test result of the 4.35V lithium secondary battery of Example 1 under the conditions of 18V / 1A.

6 is a test result of a high temperature exposure (Hot box, 150 ° C.) of the lithium secondary battery of Comparative Example 1. FIG.

7 is a high-temperature exposure test result diagram of a lithium secondary battery of Comparative Example 2.

8 is a high-temperature exposure test result diagram of the lithium secondary battery of Example 1. FIG.

Figure 9 is a result of the experiment after performing the high-temperature long-term storage (30 cycles = 1 cycle: 80 ℃ 3 hours + room temperature 7 hours) of the lithium secondary batteries of Example 1, Comparative Example 2 and Comparative Example 3, respectively.

FIG. 10 is a result of the lithium secondary batteries of Example 1, Comparative Example 2, and Comparative Example 3 after high-temperature long-term storage (80 ° C. for 5 days).

The present invention relates to a lithium secondary battery having improved high temperature cycle characteristics, safety and high temperature storage characteristics.

In recent years, with the trend of miniaturization and weight reduction of electronic devices, miniaturization and weight reduction of batteries acting as power sources are also required. BACKGROUND ART Lithium-based secondary batteries have been put to practical use as small, light weight, high capacity rechargeable batteries, and are used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers.

The lithium secondary battery is composed of a positive electrode, a negative electrode, and an electrolyte, and the first charge causes lithium ions from the positive electrode active material to be inserted into a negative electrode active material, such as carbon particles, and desorbed when discharged. Charge and discharge is possible because it plays a role.

In order to manufacture a conventional 4.2V class lithium secondary battery with a high capacity, high output and high voltage battery of 4.35V or more, a process of increasing the theoretical usable capacity of the cathode active material in the battery is required. In order to increase the available capacity of the positive electrode active material, the positive electrode active material may be doped using a transition metal or a non-transition metal such as aluminum or magnesium, or the charging end voltage of the battery may be increased. As the end-of-charge voltage of a lithium secondary battery increases to 4.35V or more, the usable capacity in the battery increases by 15% or more, but as the reactivity between the positive electrode and the electrolyte increases, degradation of the surface of the positive electrode and oxidation of the electrolyte occur. Therefore, there was a problem that the high temperature cycle characteristics, safety and high temperature storage characteristics of the battery are deteriorated.

In the conventional 4.2V class lithium secondary battery, by using an overcharge preventing agent such as cyclohexyl benzene (CHB) or biphenyl (BP), the safety is improved and an additional positive electrode is formed by forming a film on the positive electrode during high temperature long-term storage. The progress of side reaction of the over electrolyte was prevented. However, in the case of using an additive having a reaction potential of about 4.6V, such as CHB or BP in a high voltage battery of 4.35V or more, the temperature and cycle characteristics of the high temperature are drastically degraded, and the additive is decomposed too much during high temperature storage. By forming an insulator, a problem arises in that a recovery capacity is not obtained at all by preventing the movement of lithium ions.

In order to solve the above problems, as a result of using a nitrile group-containing compound, especially an aliphatic dinitrile-based compound as an electrolyte additive, the high temperature cycling characteristics and safety of a high voltage battery of 4.35V or higher are improved, but the battery becomes thick and recovery capacity is maintained at high temperature storage. There was a significant decreasing problem.

The present inventors have added a toluene fluoride compound having a reaction potential of 4.7 V or more to the electrolyte, thereby improving the high temperature cycle and safety of the battery. It has been found that an increase in thickness and a decrease in capacity can be prevented.

Accordingly, an object of the present invention is to provide a lithium secondary battery having excellent high temperature cycling characteristics and safety as well as improved high temperature storage characteristics.

The present invention provides a lithium secondary battery comprising a positive electrode (C), a negative electrode (A), a separator and an electrolyte, the electrolyte comprising: (a) a nitrile group (—CN) -containing compound; And (b) provides a lithium secondary battery comprising a toluene fluoride compound.

Hereinafter, the present invention will be described in detail.

The electrolyte according to the present invention includes a nitrile group-containing compound in a conventional electrolyte consisting of an electrolyte solvent and a lithium salt.

The lithium salt may be selected from one or more of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ) ₂ , and the electrolyte solvent is ethylene co (carbonate) carbonate. , Propylene carbonate, butylene carbonate, vinylene carbonate, sulfolane, γ-butylo lactone, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxy ethane, tetrahydrofuran and mixtures thereof The above can be used.

The nitrile group-containing compound reduces the amount of heat generated from side reactions between the electrolyte and the positive electrode and structural collapse of the positive electrode, thereby accelerating the combustion of the electrolyte and causing thermal runaway to prevent the battery from firing and rupturing. In particular, the highly polar nitrile group in the additive appears to mask active sites on the electrode surface, thereby reducing the exotherm generated from side reactions between the electrolyte and the anode and structural collapse of the anode.

The nitrile group-containing compound may be an aliphatic or aromatic compound, and mononitrile and dinitrile compounds containing 1 to 2 nitrile groups are preferable. In particular, aliphatic dinitrile compounds are more preferred.

The aliphatic dinitrile compound is a linear or branched dinitrile compound having 1 to 12 carbon atoms having one or more substituents. , 1,5-dicinopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane , 1,12-dicyanododecane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4- Dicyanopentane, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane or 1,6-dish Anodecan. In particular, succinonitrile or sebaconitrile compounds are preferred.

The maximum amount of the nitrile group-containing compound is determined depending on the solubility in the solvent used in the electrolyte, but is preferably 0.1 to 10% by weight per 100% by weight of the electrolyte. If the amount is less than 0.1% by weight, the effect of improving safety is insignificant, and if it exceeds 10% by weight, the viscosity of the electrolyte may be excessively increased, resulting in deterioration of room temperature and low temperature properties.                     

In the high-voltage lithium secondary battery of 4.35V or higher, when the above-mentioned nitrile-containing compound is used, it exhibits high temperature cycle characteristics and safety improvement effects. There was a problem with thickening and a significant drop in recovery capacity.

Thus, the present invention is characterized in that by adding a toluene fluoride compound having a reaction potential of 4.7V or more to the electrolyte, it is possible to prevent the increase in the thickness of the high-voltage battery and to minimize the reduction in recovery capacity.

The toluene fluoride compound is physically stable, has a high boiling point, is difficult to thermally decompose, and has a reaction potential of about 0.1 V higher than that of conventional CHB and biphenyl, thereby improving high temperature storage characteristics when an electrolyte is added. In addition, since there is almost no change in the reaction potential according to the progress of the cycle has the advantage that does not affect the high temperature cycle.

Non-limiting examples of the toluene fluoride compound include monofluorotoluene, difluorotoluene or trifluoride toluene, and the like. In particular, 2-fluorotoluene or 3-, which has a high reaction potential and little change in the reaction potential with the progress of the cycle. Toluene fluoride is preferred. In addition to the above-mentioned toluene fluoride, a compound having a reaction potential of 4.7 V or higher also has a high possibility of exhibiting equivalent safety and / or battery performance, and thus belongs to the equivalent range of the present invention.

The amount of the toluene fluoride compound added is preferably 0.1 to 10% by weight per 100% by weight of the total electrolyte. If less than 0.1% by weight, the effect of improving the high temperature storage characteristics is insignificant, and if it exceeds 10% by weight, there is a risk that excessive heat may be generated due to a decrease in viscosity of the electrolyte and an exothermic reaction of the additive.

The negative electrode active material of the present invention may use a carbon material, a lithium metal or an alloy thereof capable of occluding and releasing lithium ions, and TiO ₂ , SnO _2, and other metals capable of occluding and releasing lithium and having a potential of less than ₂ V. Metal oxides such as Li ₄ Ti ₅ O ₁₂ may also be used.

The positive electrode active material of the present invention is _a lithium transition metal complex oxide such as LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) (for example, lithium manganese composite oxides such as LiMn ₂ O ₄ , LiNiO _2, and the lithium nickel oxide, LiCoO _2, and the lithium cobalt oxide and combinations of manganese, nickel, a vanadium oxide, etc.), or chalcogenide containing a one or a lithium substituted with other transition metal for a portion of cobalt oxide (for example, g., manganese dioxide, titanium disulfide, molybdenum disulfide, etc.), etc. are used from, and preferably a lithium cobalt-based composite oxide, more preferably LiCoO ₂ can be used.

The present invention uses a positive electrode active material, such as LiCoO ₂ to provide a high voltage lithium secondary battery of 4.35V or more, preferably 4.35 to 4.7V, and the end-of-charge voltage is 4.35V or more, preferably 4.35 to 4.7V. The positive electrode active material may be increased to a range or doped with a metal selected from Al, Mg, Zr, Fe, Zn, Ga, Sn, Si, Ge, or a mixture thereof.

In order to improve the safety of the battery in the above-described voltage range, the weight ratio (A / C) per unit area of the negative electrode (A) to the positive electrode (C) can be adjusted, wherein the weight ratio per unit area of the negative electrode (A) to the positive electrode (C) ( A / C) is preferably in the range of 0.45 to 0.70. If it is less than 0.45, it is the same as the design of the existing battery, and thus, capacity valance is broken during overcharging of 4.35V or more, causing problems such as lithium dendrite growth on the surface of the negative electrode and resulting short-circuit of the battery. Will occur. If it exceeds 0.7, the lithium site of the negative electrode is unnecessarily generated and the energy density per volume / mass of the battery falls, which is not preferable.

Since the positive electrode active material such as LiCoO ₂ used in the present invention has a problem of deteriorating thermal characteristics when charged to 4.35 V or more, the specific surface area of the positive electrode active material may be adjusted to prevent this. The larger the particle size of the positive electrode active material, that is, the smaller the specific surface area, the lower the reactivity with the electrolyte solution, thereby improving thermal stability. It is preferable to use. In addition, the loading amount per unit area of the positive electrode active material and the negative electrode active material may be adjusted in order to prevent a decrease in the rate of the overall battery reaction caused by the positive electrode active material having a larger particle size than the conventional particles.

In the above, the particle size of the positive electrode active material is preferably 5 to 20㎛. If the particle size is less than 5㎛ may increase the reactivity of the positive electrode and the electrolyte may cause side effects such as lack of safety of the battery, if the particle size exceeds 20㎛ may cause a problem that the reactivity of the battery is slow.

In the above, it is preferable that the loading amount per unit area of the positive electrode is 0.01 to 0.03 g / cm ² . When the loading amount of the positive electrode is less than 0.01 g / cm ^2, problems such as deterioration of the capacity and efficiency of the battery may occur. When the amount of the positive electrode exceeds 0.03 g / cm ² , the thickness of the positive electrode increases, thereby decreasing the reactivity of the battery.

The electrode according to the present invention can be prepared according to a conventional method known in the art, for example, it is usually obtained by applying, rolling and drying, respectively, the positive electrode slurry and the negative electrode slurry on a current collector made of metal foil Can be.

In the above, the positive electrode slurry and the negative electrode slurry may be obtained by mixing the positive electrode active material and the negative electrode active material, respectively, with a binder, a dispersion medium, and the like, and the positive electrode slurry and the negative electrode slurry may preferably contain a small amount of a conductive agent.

As the conductive agent, any electronically conductive material which does not cause chemical change in the battery constructed can be used. For example, carbon black, such as acetylene black, Ketjen black, Farnes black, and thermal black; Natural graphite, artificial graphite, conductive yarn fibers, and the like can be used. Carbon black, graphite powder and carbon fiber are particularly preferable.

As the binder, any one of a thermoplastic resin and a thermosetting resin may be used, or a combination thereof may be used. Among these, polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) is preferable, and PVdF is particularly preferable.                     

As the dispersion medium, an organic dispersion medium such as an aqueous dispersion medium or N-methyl-2-pyrrolidone (NMP) can be used.

In the above-described positive electrode of the lithium secondary battery, the electrode plate thickness ratio A / C of the negative electrode A to the positive electrode C is appropriately 0.7 to 1.4, and particularly preferably 0.8 to 1.2. If less than 0.7, a loss of energy density per volume of the battery may be caused, and if it exceeds 1.4, a problem may occur that the reaction rate of the entire battery becomes slow.

The lithium secondary battery according to the present invention may be prepared by putting a porous separator between the positive electrode and the negative electrode according to a conventional method known in the art, and adding a non-aqueous electrolyte to which the aforementioned additive is added.

The separator may be a porous separator, for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

The external shape of the lithium ion secondary battery manufactured by the above method is not limited, but cans are cylindrical, coin-shaped, square or pouch types.

The invention is explained in more detail based on the following examples and experimental examples. However, Examples and Experimental Examples are for illustrating the present invention and are not limited to these.

Example 1. Manufacture of 4.35V class lithium secondary battery.

1-1. Manufacture of anode

A slurry was prepared by mixing 95 wt% of LiCoO ₂ having a particle size of 10 μm, 2.5 wt% of a conductive agent, and 2.5 wt% of a binder. The slurry was uniformly coated and rolled on both sides of an aluminum thin plate having a thickness of 15 μm. The positive electrode having an active material weight of 19.44 mg / cm ² was prepared .

1-2. Preparation of Cathode

A negative electrode slurry was prepared by adding and mixing 95.3 wt% of graphite material, 4.0 wt% of binder, and 0.7 wt% of a conductive agent. The negative electrode slurry was uniformly coated and rolled on both sides of a copper plate having a thickness of 10 μm and rolled to 9.56 mg / cm ^2. A negative electrode having an active material weight of was prepared. At this time, the weight ratio (A / C) per unit area of the anode (A) to the cathode (C) was 0.49.

1-3. Preparation of Electrolyte

An electrolyte solution was prepared by dissolving 1 mol of LiPF ₆ in a solution having a volume ratio of ethylene carbonate and dimethyl carbonate of 1: 2, and 3% by weight of succinonitrile and 3% by weight of 3-toluene fluoride were added thereto.

1-4. Manufacture of batteries

A 423450 square cell was manufactured using the positive electrode and the negative electrode produced by the above-described method.

[Comparative Example 1-3]. Fabrication of Lithium Secondary Battery

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that succinonitrile and 3-toluene fluoride were not used in the electrolyte.

Comparative Example 2

A lithium secondary battery was prepared in the same manner as in Example 1, except that succinonitrile was used as the electrolyte and 3-toluene was not used.

Comparative Example 3

Sebacononitrile was used instead of succinonitrile in the electrolyte, except that 3-fluorotoluene was not used. The lithium secondary battery was manufactured by the same method as Example 1 above.

Experimental Example 1. Cycle evaluation of a lithium secondary battery

A high temperature cycle evaluation experiment was performed on the 4.35V or higher lithium secondary battery manufactured according to the present invention as follows.

The lithium secondary battery of Example 1 prepared by adding succinonitrile and 3-toluene fluoride was used, and the battery of Comparative Example 1, which did not use the electrolyte additive as a control, and the succinonitrile prepared by adding the succinonitrile to the electrolyte were prepared. The battery of Comparative Example 2 was used.

Each cell was run at a charge and discharge voltage range of 3.0 to 4.35V and cycled under 1C (= 880 mA) charge and discharge current conditions. In the 4.35V constant voltage section, it was maintained at 4.35V until the current dropped to 50mA. The experiment was carried out at a temperature of 45 ℃.

As a result of the experiment, the lithium secondary battery of Comparative Example 1 (see FIG. 1) containing an electrolyte solution without an additive significantly reduced the battery cycle characteristics at high temperature, while Example 1 (which contains succinonitrile in the electrolyte solution) 2) and the lithium secondary batteries of Comparative Example 2 (see FIG. 1) showed that the high temperature cycle characteristics were improved.

Experimental Example 2 Evaluation of Safety of Lithium Secondary Battery

In order to evaluate the safety of the 4.35V or higher lithium secondary battery produced in the present invention, it was performed as follows.

2-1. Overcharge Experiment

The lithium secondary battery of Example 1 prepared by adding succinonitrile and 3-toluene fluoride was used, and the battery of Comparative Example 1, which did not use the electrolyte additive as a control, and the succinonitrile prepared by adding the succinonitrile to the electrolyte were prepared. The battery of Comparative Example 2 was used.

Each battery was charged under the conditions of 6V / 1A, 12V / 1A, and 18V / 1A, and then the state of the cells was observed.

As a result of the experiment, the lithium secondary battery of Comparative Example 1 including the electrolyte solution without using an additive rapidly increased the temperature of the battery under overcharge conditions of 6V / 1A and 12V / 1A, and caused ignition and explosion of the battery (FIGS. 3A and 3A). 3b). In comparison, the lithium secondary batteries of Example 1 and Comparative Example 2 including succinonitrile in the electrolyte showed a safe state when overcharged (see FIGS. 4 and 5).

2-2. Hot Box Experiment

The lithium secondary battery of Example 1 prepared by adding succinonitrile and 3-toluene fluoride was used, and the battery of Comparative Example 1, which did not use the electrolyte additive as a control, and the succinonitrile prepared by adding the succinonitrile to the electrolyte were prepared. The battery of Comparative Example 2 was used.

Each of the batteries in Example 1 and Comparative Example 2 was charged to 4.5V at 1C for 2 hours and 30 minutes and then maintained at a constant voltage, and placed in a convection-enabled oven at 5 ° C. per minute (5 ° C./min) from room temperature. The temperature was elevated and exposed for 1 hour at a high temperature of 150 ℃ to observe whether the battery ignited. In Comparative Example 1, each battery was charged to 4.4 V under 1C for 2 hours and 30 minutes, and then maintained in a constant voltage state.

As a result of the experiment, the lithium secondary battery charged to 4.4 V of Comparative Example 1 containing the electrolyte solution without using an additive exhibited a ignition phenomenon in the high temperature exposure experiment (see FIG. 6). On the contrary, the lithium secondary batteries of Example 1 and Comparative Example 2 containing succinonitrile in the electrolyte showed a safe state even under a charging condition of 4.5 V, indicating that succinonitrile improves the safety of the battery. (See FIGS. 7 and 8).

Experimental Example 3. High Temperature Storage Evaluation of Lithium Secondary Battery

The high temperature storage experiment was performed on the 4.35V or more lithium secondary battery manufactured in the present invention as follows.

3-1. Siemens thermal cycle

The lithium secondary battery of Example 1 prepared by adding succinonitrile and 3- toluene to the electrolyte was used, and Comparative Example 2 and Comparative Example 3 prepared by adding succinonitrile and sebaconitrile to the electrolyte, respectively, as a control. The battery of was used.

Each cell was charged up to 4.35V with a charging current of 1C (maintained at constant voltage until the current dropped to 18mA at 4.35V) and GSM pulse discharge was performed to 3.1V to confirm the initial discharge capacity. After charging again under the same conditions as 4.35V, and then repeated 30 cycles to store 3 hours at 80 ℃ / 7 hours at room temperature. After completion of 30 cycles, cell thickness change, OCV (open circuit voltage) change, and impedance (impedance) change were measured, respectively, and then pulse discharge was performed under GSM conditions to measure the remaining capacity of the battery. After the remaining capacity was measured and charged and discharged three times, the GSM recovery capacity of the battery was measured.

As a result, the 4.35V class lithium secondary battery of Example 1 using the succinonitrile and 3-fluoride toluene compound as electrolyte additives was compared with the batteries of Comparative Examples 2 and 3 using succinonitrile and sebaconitrile as electrolyte additives, respectively. It did not swell and showed high temperature long term storage properties (see FIG. 9).

3-2. High temperature long term storage characteristics test (80 ℃ 5 days Siemens storage)

The lithium secondary battery of Example 1 prepared by adding succinonitrile and 3-toluene fluoride was used, and Comparative Example 2 and Comparative Example 3 prepared by adding succinonitrile and sebaconitrile to the electrolyte as control, respectively. The battery of was used.

The recovery capacity of the batteries was measured by performing the same method as Experimental Example 3-1 (Siemens thermal cycle) except that each battery was stored at 80 ° C. for 5 days.

Experimental results showed that after storing for 5 days at a temperature of 80 ℃ the cell thickness of Comparative Examples 2 and 3 significantly increased (see FIG. 10). When the succinonitrile or sebaconnitrile compound containing a nitrile group-containing compound is used as an electrolyte additive of a high voltage battery of 4.35 V or higher, the battery safety and high temperature cycle characteristics are improved, but the thick insulation formed by decomposition of the dinitrile compound during high temperature long-term storage The layer makes the cell thicker, indicating a decrease in recovery capacity. On the other hand, the 4.35V class lithium secondary battery of Example 1 using the succinonitrile and 3-fluoride toluene compound as the electrolyte additive did not show swelling of the battery even after long-term storage at a high temperature of 80 ° C (see FIG. 10).

Thus, the present invention can significantly improve the problems in high temperature storage caused by nitrile group-containing compounds, which are high temperature cycle characteristics and safety enhancers of high voltage batteries of 4.35 V or more, by using a toluene fluoride compound having a reaction potential of 4.7 V or more. I could confirm that there is.

The lithium secondary battery according to the present invention can improve the battery swelling phenomenon and capacity drop during the high temperature storage caused by the nitrile group-containing compound added to the electrolyte in order to improve the high temperature cycle characteristics and safety by adding a toluene fluoride compound.

Claims (9)

In a lithium secondary battery comprising a positive electrode (C), a negative electrode (A), a separator and an electrolyte solution, the electrolyte solution is (a) Nitrile group (-CN) containing compound; And (b) toluene fluoride compounds A lithium secondary battery comprising: a charge end voltage of the battery is 4.35V or more. The lithium secondary battery according to claim 1, wherein the nitrile group-containing compound is an aliphatic or aromatic nitrile compound containing 1 to 2 nitrile groups. The lithium secondary battery of claim 1, wherein the nitrile group-containing compound is a succinonitrile or sebaconitrile compound. The lithium secondary battery of claim 1, wherein the amount of the nitrile group-containing compound is 0.1 to 10 wt% per 100 wt% of the electrolyte. The lithium secondary battery of claim 1, wherein the toluene fluoride compound comprises toluene 2-fluoride, 3-toluene fluoride, or both thereof. The lithium secondary battery of claim 1, wherein the amount of the toluene fluoride compound is 0.1 to 10 wt% per 100 wt% of the electrolyte. delete The method of claim 1, wherein the lithium secondary battery is Al, Mg, Zr, Fe, Zn, Ga, Sn in the positive electrode active material that the charge end voltage of the battery ranges from 4.35 to 4.7V or the positive electrode can occlude and release lithium Lithium secondary battery is prepared by doping at least one metal selected from the group consisting of, Si and Ge. The lithium secondary battery of claim 1, wherein a weight ratio (A / C) per unit area of the negative electrode (A) to the positive electrode (C) is 0.45 to 0.70.

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