KR20130091597A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: A lithium secondary battery is provided to be able to drastically suppress the swelling phenomenon in the high temperature storage of the lithium secondary battery by containing a specific non-aqueous electrolyte solution. CONSTITUTION: A lithium secondary battery comprises a cathode containing a cathode active material which is Li_xM_yO_2, which is a lithium transition metal oxide, or a mixture of Li_xM_yO_2 and LiCoO_2; an anode containing an anode active material; a separation film; and a non-aqueous electrolyte solution containing lithium salts, an organic solvent and a dinitrile compound having ether bonding, represented by Chemical formula 1: NC-R^1-(O-R^2)_m-O-R^3-CN, which is an electrolyte additive, wherein M is Ni_(1-a-b)Mn_aCo_b, 0.05<=a<=0.4, 0.1<=b<=0.4, 0.4<=1-a-b<=0.7, x+y≒2, and 0.95<=x<=1.05. [Reference numerals] (AA) Electrode thickness variation (mm); (BB) Storage time (h); (CC) Example 2; (DD) Comparative example 1; (EE) Comparative example 2

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery capable of greatly suppressing a swelling phenomenon during high temperature storage of a lithium secondary battery.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs, and electric vehicles further expand, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s include lithium salts dissolved in an appropriate amount of a negative electrode such as a carbon material capable of occluding and releasing lithium ions, a positive electrode made of a lithium-containing oxide, and a mixed organic solvent. It consists of a nonaqueous electrolyte.

However, a lithium secondary battery using a lithium transition metal oxide or a composite oxide has a problem in that the metal component is separated from the positive electrode of the battery and stored in an unstable state when stored at high temperature in a fully charged state.

On the other hand, organic solvents currently widely used in nonaqueous electrolytes include ethylene carbonate, propylene carbonate, dimethoxyethane, gamma butyrolactone, N, N-dimethylformamide, tetrahydrofuran or acetonitrile. Such organic solvents, in general, when stored for a long time at a high temperature, may promote the decomposition due to oxidation of the electrolyte, for example, causing a so-called swelling phenomenon in which the battery swells. As a result, battery life and charge and discharge efficiency are drastically reduced, and in some cases, battery safety is greatly reduced, such as explosion of the battery.

Various nitrile compounds have been proposed to solve these problems, but they do not effectively solve the swelling phenomenon.

The present invention is to solve the above problems by adding a specific non-aqueous electrolyte to the lithium secondary battery comprising a lithium transition metal oxide or a composite oxide as a positive electrode lithium that can greatly suppress the swelling phenomenon at high temperature storage of the lithium secondary battery It is an object to provide a secondary battery.

In order to achieve the above object, the present invention is a lithium transition metal oxide Li _x M _y O ₂ (M is Ni _1-ab Mn _a Co _b [0.05≤a≤0.4, 0.1≤b≤0.4, 0.4≤1-ab ≦ 0.7], x + y ≒ 2, 0.95 ≦ _x ≦ 1.05), or a positive electrode including a positive electrode active material that is a mixture of Li _x M _y O ₂ and LiCoO ₂ ; A negative electrode comprising a negative electrode active material; Separation membrane; And a nonaqueous electrolyte including a dinitrile compound having an ether bond represented by the following Chemical Formula 1, which is a lithium salt, an organic solvent, and an electrolyte solution additive.

[Formula 1]

Here, R ¹ , R ² and R ³ are each independently alkylene having 1 to 5 carbon atoms or alkenylene having 2 to 5 carbon atoms, and m is an integer of 1 to 5 independently from each other.

According to the present invention, by using a non-aqueous electrolyte containing a lithium transition metal oxide, a compound containing a vinylene group or a vinyl group and a dinitrile compound having an ether bond together to prevent gas generation during high temperature storage to prevent battery swelling phenomenon It is possible to improve the charge and discharge cycle life.

1 is a graph showing a change in thickness according to the storage time of the lithium secondary battery of Examples 1 to 2 and Comparative Examples 1 to 2 according to the present invention.
2 is a graph showing a change in discharge capacity according to the number of cycles of the lithium secondary battery of Example 3 and Comparative Example 3 according to the present invention.

The present invention is a lithium transition metal oxide Li _x M _y O ₂ (M is Ni _{1 -a- b} Mn _a Co _b [0.05≤a≤0.4, 0.1≤b≤0.4, 0.4≤1-ab≤0.7], x + y ≒ 2, 0.95 ≦ _x ≦ 1.05), or a positive electrode including a positive electrode active material that is a mixture of Li _x M _y O ₂ and LiCoO ₂ ;

A negative electrode including a negative electrode active material;

Separation membrane; And

A lithium secondary battery comprising a nonaqueous electrolyte solution including a dinitrile compound having an ether bond represented by the following Chemical Formula 1 as a lithium salt, an organic solvent, and an electrolyte solution additive:

[Formula 1]

(Wherein R ¹ , R ² , R ³ are each independently alkylene having 1 to 5 carbon atoms or alkenylene having 2 to 5 carbon atoms, and m are each independently an integer of 1 to 5).

Hereinafter, the present invention will be described in more detail.

In the lithium secondary battery according to the present invention, the positive electrode active material is a lithium transition metal oxide Li _x M _y O ₂ (M is Ni _{1 -a- b} Mn _a Co _b [0.05≤a≤0.4, 0.1≤b≤0.4, 0.4 ≦ 1-ab ≦ 0.7], x + y ≒ 2, 0.95 ≦ _x ≦ 1.05) or by mixing Li _x M _y O ₂ and LiCoO ₂ at 20-30: 80-70 to obtain a lithium secondary battery. Capacity and cycle stability can be improved, and storage stability and high temperature safety can be improved. When LiCoO ₂ is less than 70 weight ratio in the mixing ratio of Li _x M _y O ₂ and LiCoO ₂ , there is a problem that the high temperature cycle characteristics are reduced, and when the weight ratio exceeds 80 weight ratio, there is a problem that the capacity improvement effect of the secondary battery is small.

At this time, the total molar fraction (1-ab) in the nickel (Ni) is the mole fraction containing the Ni ^{+ 2} and Ni ^{+ 3,} relative 0.4 is nickel is contained in excess with respect to the manganese and cobalt - is preferably 0.7. If the mole fraction of nickel is less than 0.4, the capacity does not improve. If the molar fraction of nickel is more than 0.7, the safety of the battery is reduced.

Li _x M _y O ₂ Or _x M _y O ₂ with LiCoO Li MO layer in a mixture of _2, preferably Ni ^{+ 2} and Ni ³⁺ coexist, some of which Ni ^{2 +} the occlusion and release layer (reversible lithium layer) is inserted in the structure il Can be. These Ni ^{2 +} is a repulsive force of the lithium ions (Li ^+), and when the size is very similar to so insert the lithium ions upon standing charge without modifying the shape of crystal structure eliminated the reversible lithium layer transition metal oxide layer (MO layer) It can serve to prevent the crystal structure collapse by. Therefore, Ni ^{2 +} is preferably contained enough to be stably supported between the at least MO layer by being inserted so do not interfere with occlusion and release of lithium ions in a reversible lithium layer can prevent the deterioration of the rate characteristics have. In other words, the mole fraction of Ni ^{2 +} into the reversible lithium layer is too high, increase in the insertion of the Ni ^{2 +} to form a rock salt structure (rock salt structure) with no electrochemical reactions locally, so not only interfere with the charging and discharging The Accordingly, the discharge capacity can be reduced. Thus, the mole fraction of Ni ^{+ 2} to be inserted into the reversible lithium layer is 0.03 for the total amount of Ni - is preferably 0.07.

It is preferable that the mole fraction (b) of the cobalt (Co) is 0.1 to 0.4, and if it is less than 0.1, sufficient rate characteristics and high powder density of the battery cannot be simultaneously achieved, and if it exceeds 0.4, the cobalt content is increased. The cost increases and the reversible capacity decreases somewhat.

The mole fraction (x) of the lithium (Li) is preferably 0.95-1.05, and when less than 0.95, the rate characteristic is lowered and the reversible capacity is decreased, and when it exceeds 1.05, the high voltage (U = 4.35V), resulting in less stability during the cycle.

In addition, as the ratio of Li to Li (M) of the transition metal (M) decreases, the amount of Ni inserted into the MO layer is gradually increased. When too much amount is lowered into the reversible lithium layer, the charging and discharging process is performed. The movement of Li ⁺ at is disturbed at the reversible capacity or the rate characteristic is reduced. On the contrary, when the ratio of Li / M is too high, the amount of Ni inserted in the MO layer is too small, which is not preferable because structural instability may be caused, resulting in deterioration of stability of the battery and deterioration of life characteristics. In addition, at an excessively high Li / M value, the amount of unreacted Li ₂ CO ₃ may increase, resulting in a large amount of impurities, which may lower chemical resistance and high temperature stability of the battery.

The Li _x M _y O ₂ may be formed in the form of aggregates of fine powders and have an agglomerated structure having internal pores. The agglomerated structure maximizes the surface area that reacts with the electrolyte, and can increase the reversible capacity of the positive electrode while having a high rate characteristic.

In addition, the LiCoO ₂ may be included in the positive electrode active material in a form in which a part of cobalt is not substituted (doped) with other elements, and may be preferably composed of a monolithic structure. Accordingly, as the size of the particles increases, the stability of the crystal grains is improved, and the manufacturing process of the lithium secondary battery including the same is facilitated, thereby improving process efficiency.

In the lithium secondary battery according to the present invention, as the negative electrode active material, a carbon material, lithium metal, silicon or tin, etc., in which lithium ions may be occluded and released, may be used, and the potential for lithium is less than 2V TiO ₂ , Metal oxides such as SnO ₂ are also possible. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Low crystalline carbon is typical of soft carbon and hard carbon, and high crystalline carbon includes natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, and liquid crystal pitch system. High-temperature calcined carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes .

The positive electrode and / or the negative electrode may include a binder, and the binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile ), An organic binder such as polymethylmethacrylate, or an aqueous binder such as styrene-butadiene rubber (SBR) can be used together with a thickener such as carboxymethyl cellulose (CMC). Preferably, it is possible to use an aqueous binder that is excellent in adhesion and exhibits excellent adhesion even when using only a relatively small amount.

In addition, as the separator, conventional porous polymer films used as conventional separators, for example, polyolefins such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, etc. The porous polymer film made of the polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. It is not.

In the lithium secondary battery according to the present invention, the nonaqueous electrolyte includes a dinitrile compound having an ether bond represented by the following Chemical Formula 1, which is a lithium salt, an organic solvent, and an electrolyte additive.

[Formula 1]

(Wherein R ¹ , R ² , R ³ are each independently alkylene having 1 to 5 carbon atoms or alkenylene having 2 to 5 carbon atoms, and m are each independently an integer of 1 to 5)

The lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ( ^{_{CF 3) 3 PF 3 -,}} (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 ^{_{SO 2) 2 N -, (}} FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 6) 3 C -, (CF 3 SO 2 _{^{) 3 C -, CF 3 (}} CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - 1 kind selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N Can be used.

The organic solvent is a mixed solution of cyclic carbonate and linear carbonate, specifically propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethylsulperoxide, acetonitrile, dimethoxy One or more selected from the group consisting of ethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran can be used.

The dinitrile compound having an ether bond is preferably included in an amount of 0.1 to 10% by weight of the nonaqueous electrolyte. When the content is less than 0.1% by weight, there is a problem of low storage capacity at high temperature, and when the content is more than 10% by weight, the viscosity of the electrolyte is increased to decrease high rate characteristics (supplying a high output current while maintaining voltage). there is a problem.

In addition, the dinitrile compound having an ether bond is 3,5-dioxy-heptanedinitrile, 1,4-bis (cyanoethoxy) butane, bis (2-cyanoethyl) -monoformal, bis (2 -Cyanoethyl) -diformal, bis (2-cyanoethyl) -triformal, ethylene glycol bis (2-cyanoethyl) ether, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2-cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether, 3,6,9,12,15,18-hexaoxaic acid dinitrile, 1,3-bis (2-cya Noethoxy) propane, 1,4-bis (2-cyanoethoxy) butane, 1,5-bis (2-cyanoethoxy) pentane and ethylene glycol bis (4-cyanobutyl) ether One or more types selected from can be used.

In the lithium secondary battery according to the present invention, the electrolyte additive may further include a vinylene group or a compound containing a vinyl group.

In this case, the vinylene group or the compound containing a vinyl group may be included in 1% by weight to 10% by weight, preferably 1% by weight to 7% by weight, more preferably 1% by weight to 5% by weight of the nonaqueous electrolyte. If the content is less than 1% by weight, the effect of improving swelling in a high temperature environment is insignificant, and if it exceeds 10% by weight, the high rate characteristic due to the increase in the viscosity of the electrolyte decreases.

The vinylene group or the compound containing a vinyl group may be defined as -CH = CH- and CH ₂ = CH-, respectively, and the vinylene group or the compound containing a vinyl group is a vinylene carbonate-based compound, acryl containing a vinyl group One or more types selected from the group consisting of a latex compound, a sulfonate compound containing a vinyl group, and an ethylene carbonate compound containing a vinyl group can be used.

In addition, Compounds containing a vinylene group may be represented by the following formula (2):

[Formula 2]

Wherein R ⁴ and R ⁵ are each independently hydrogen or halogen, or substituted or unsubstituted C _1; - an alkyl group of C _6, C ₆ C ₁₂ aryl group, C ₂ C ₆ alkenyl or sulfonate groups.

In addition, at least one of R ⁴ and R ⁵ of Formula 2 may include a vinyl group.

In addition, in the lithium secondary battery according to the present invention, the nonaqueous electrolyte may further include a cyclic carbonate substituted with halogen represented by the following formula (3):

(3)

(Wherein X and Y are each independently hydrogen, chlorine or fluorine and X and Y are not simultaneously hydrogen).

The cyclic carbonate substituted with halogen may be used together with the vinylene group or the compound containing the vinyl group to improve the physical properties of the SEI film formed on the surface of the negative electrode, thereby further enhancing the battery swelling prevention effect.

The content of the cyclic carbonate substituted with halogen is preferably included in 1 to 10% by weight of the non-aqueous electrolyte. In addition, the mixing ratio of a vinylene group or a compound containing a vinyl group with a cyclic carbonate substituted with halogen may be appropriately selected depending on the specific use in which the battery is used, for example, a cyclic carbonate: vinylene group or vinyl group substituted with halogen. Contains compound may have a weight ratio of 1: 0.5-5, but is not limited thereto. When the weight ratio of the vinylene group or the compound containing a vinyl group to the cyclic carbonate substituted by halogen is less than 0.5, the high temperature charge / discharge performance is weakened. When the weight ratio exceeds 5, the interfacial resistance of the negative electrode is greatly increased and the initial performance of the battery is decreased. do. This may be because the vinylene group or the compound containing the vinyl group forms a relatively dense SEI film, but should not be construed as being limited thereto.

The organic solvent used in the nonaqueous electrolyte of the conventional lithium secondary battery has a problem of being oxidized and decomposed on the surface of the cathode during the charge and discharge process. In particular, when the lithium transition metal oxide is used as the positive electrode active material, the transition metal serves as an oxidizing agent to promote decomposition of the electrolyte, and at a high temperature, the oxidation decomposition reaction is further accelerated.

However, the dinitrile compound having an ether bond according to the present invention forms a complex on the surface of the positive electrode composed of lithium transition metal oxide, thereby suppressing the heat generation by suppressing the oxidation reaction between the nonaqueous electrolyte and the positive electrode, Internal short circuit can be prevented. In addition, various compounds are present in the nonaqueous electrolyte during charge and discharge, among which HF and PF ₆ make the nonaqueous electrolyte an acidic atmosphere, in which oxygen (-O-) in the dinitrile compound having an ether bond is a nonaqueous electrolyte. By combining with HF, PF _6, etc. in the inside, the acidic atmosphere composition can be suppressed and the oxidative decomposition reaction of the nonaqueous electrolyte can be suppressed. In addition, the performance of the secondary battery may exhibit an improved effect than the conventional additives, in particular, the capacity retention rate is excellent, the charge and discharge cycle life can be improved.

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

Therefore, the lithium secondary battery according to the present invention uses a non-aqueous electrolyte containing a lithium transition metal oxide, a compound containing a vinylene group or a vinyl group, and a dinitrile compound having an ether bond together to suppress the generation of gas during high temperature storage, thereby swelling the battery. The ring phenomenon can be prevented and the charge / discharge cycle life can be improved.

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 is not limited to the above-described embodiments.

Example 1:

Manufacture of anode

LiNi _0.53 Co _0.2 Mn _0.27 O ₂ having an average particle diameter (D ₅₀ ) of about 5 to 8 μm, which is an aggregate of fine particles of about 1 to 2 μm, and an average particle diameter of about 15 to 20 μm as a single phase structure (D _50). LiCoO ₂ with) in a ratio of 30:70 to prepare a positive electrode active material.

A slurry was prepared by mixing the prepared cathode active material with Super P as a conductive material and polyvinylidene fluoride as a binder in a weight ratio of 92: 4: 4, and then adding NMP (N-methyl pyrrolidone). The positive electrode slurry prepared above was applied to an aluminum current collector and then dried in a vacuum oven at 120 ° C. to prepare a positive electrode.

Preparation of nonaqueous electrolyte

A 1M LiPF ₆ solution having a composition of EC: PC: DEC = 3: 2: 5 was used as an electrolyte, in which 2% by weight of vinylene carbonate (VC), 3% by weight of fluoroethylene carbonate (FEC) and ethylene glycol were used. A nonaqueous electrolyte was prepared by adding 3% by weight of bis (2-cyanoethyl) ether.

Manufacture of lithium secondary battery

Artificial graphite was used as the negative electrode active material, a lithium polymer battery was manufactured by a conventional method, and an aluminum laminate packaging material was used. Thereafter, the prepared electrolyte was injected into the assembled lithium secondary battery to complete the lithium secondary battery.

Example 2:

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5 wt% of ethylene glycol bis (2-cyanoethyl) ether was added.

Example 3:

And the above embodiment except that a positive active material of about 1 ~ 2 ㎛ of the micro-particle aggregate of _{LiNi 0 .53 Co 0 .2 Mn 0} .27 O 2 having an average particle diameter (D ₅₀₎ of from about 5 ~ 8 ㎛ of only A lithium secondary battery was manufactured in the same manner as in Example 1.

Comparative Example 1:

A lithium secondary battery was manufactured in the same manner as in Example 1, except that ethylene glycol bis (2-cyanoethyl) ether was not added to the nonaqueous electrolyte.

Comparative Example 2;

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5% by weight of succinonitrile was added to the nonaqueous electrolyte instead of ethylene glycol bis (2-cyanoethyl) ether.

Comparative Example 3:

Only about _{1 ~ 2 ㎛ LiNi 0 .53 Co} 0 .2 Mn 0 .27 O 2 having an average particle diameter (D ₅₀₎ of from about 5 ~ 8 ㎛ of aggregates of fine particles of a positive electrode active material, and ethylene in the non-aqueous electrolyte A lithium secondary battery was manufactured in the same manner as in Example 1, except that 5% by weight of succinonitrile was added instead of glycol bis (2-cyanoethyl) ether.

Experimental Example 1: High Temperature Stability Test of Lithium Secondary Battery

After fully charging the lithium secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 to 4.2V and storing them at 90 ° C. for 4 hours, the initial thickness and thickness change (Δt) of the lithium secondary battery were respectively stored. It measured and the result is shown in Table 1 and FIG.

Yes Δt (mm) Example 1 3.24 Example 2 2.52 Comparative Example 1 4.00 Comparative Example 2 3.95

As shown in Table 1, the secondary batteries of Examples 1 and 2 according to the present invention can be seen that the increase in thickness (swelling phenomenon) during long time storage at high temperature compared to the secondary batteries of Comparative Examples 1 and 2 is suppressed. It turns out that ethylene glycol bis (2-cyanoethyl) ether is superior in swelling phenomenon suppression effect than succinonitrile which is a dinitrile compound.

In addition, as shown in FIG. 1, since the secondary battery of Example 2 according to the present invention has a smaller change in thickness than the secondary batteries of Comparative Examples 1 and 2 as the storage time increases, the swelling phenomenon is suppressed. Able to know.

Experimental Example 2: Evaluation of Charge / Discharge Performance of Lithium Secondary Battery

The lithium secondary batteries prepared in Example 3 and Comparative Example 3 were charged at a constant current of 1C = 980 mA at 45 ° C., and after the voltage of the battery became 4.2 V until the charge current value reached 50 mA at 4.2 V constant voltage. Charged once. The battery charged once was discharged at a constant current of 1C until the battery voltage reached 3V and the discharge capacity of one cycle was examined. Subsequently, 300 cycles of the above charging and discharging were repeated, and the results are shown in FIG. 2.

As shown in Figure 2, it can be seen that the lithium secondary battery of Example 3 according to the present invention has an effect of improving the charge and discharge cycle life at a higher temperature than the lithium secondary battery of Comparative Example 3.

Claims (14)

Li _x M _y O ₂ , which is a lithium transition metal oxide (M is Ni _{1 -ab} Mn _a Co _b [0.05 ≦ a ≦ 0.4, 0.1 ≦ _b ≦ 0.4, 0.4 ≦ _{1- ab} ≦ 0.7], and x + y ≒ 2 0.95 ≦ _x ≦ 1.05), or a positive electrode including a positive electrode active material which is a mixture of Li _x M _y O ₂ and LiCoO ₂ ;
A negative electrode comprising a negative electrode active material;
Separation membrane; And
A lithium secondary battery comprising a nonaqueous electrolyte solution including a dinitrile compound having an ether bond represented by the following Chemical Formula 1 as a lithium salt, an organic solvent, and an electrolyte solution additive:
[Formula 1]

(Wherein R ¹ , R ² , R ³ are each independently alkylene having 1 to 5 carbon atoms or alkenylene having 2 to 5 carbon atoms, and m are each independently an integer of 1 to 5).
The method according to claim 1,
The _x M _y O ₂ mixture with Li of LiCoO ₂ is Li _x M _y O ₂ with LiCoO ₂ is 20 - 30:80 - 70 wherein the lithium secondary battery of the mixture in a weight ratio of.
The method according to claim 1,
Li _x M _y O ₂ (M is Ni _{1 -a- b} Mn _a Co _b [0.05 ≦ a ≦ 0.4, 0.1 ≦ _b ≦ 0.4, 0.4 ≦ 1-ab ≦ 0.7], and x + y ≒ 2, 0.95≤x≤1.05) or the Li _x M _y O ₂ with lithium ions between the transition metal oxide layer (MO layer) of a mixture of LiCoO ₂ and the occlusion and release, the molar fraction of Ni ^{+ 2} of the total amount of lithium ions are Ni The lithium secondary battery, characterized in that 0.03 to 0.07.
The method according to claim 1,
The lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ( ^{_{CF 3) 3 PF 3 -,}} (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 ^{_{SO 2) 2 N -, (}} FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 6) 3 C -, (CF 3 SO 2 _{^{) 3 C -, CF 3 (}} CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - 1 species is selected from the group consisting of Lithium secondary battery, characterized in that.
The method according to claim 1,
The organic solvent is propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethylsulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane And at least one selected from the group consisting of gamma-butyrolactone, propylene sulfite and tetrahydrofuran.
The method according to claim 1,
The dinitrile compound having an ether bond is contained in an amount of 0.1 to 10% by weight of the nonaqueous electrolyte.
The method according to claim 1,
The dinitrile compound having an ether bond is 3,5-dioxa-heptanedinitrile, 1,4-bis (cyanoethoxy) butane, bis (2-cyanoethyl) -monoformal, bis (2-sia Noethyl) -diformal, bis (2-cyanoethyl) -triformal, ethylene glycol bis (2-cyanoethyl) ether, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2 -Cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether, 3,6,9,12,15,18-hexaoxaic acid dinitrile, 1,3-bis (2-cyanoe Methoxy) propane, 1,4-bis (2-cyanoethoxy) butane, 1,5-bis (2-cyanoethoxy) pentane and ethylene glycol bis (4-cyanobutyl) ether Lithium secondary battery characterized in that at least one.
The method according to claim 1,
The nonaqueous electrolyte additive further comprises a vinylene group or a compound containing a vinyl group.
The method according to claim 1,
The vinylene group or the compound containing a vinyl group is a lithium secondary battery, characterized in that contained in the amount of 1 to 10% by weight of the non-aqueous electrolyte.
The method according to claim 8,
The vinylene group or the compound containing a vinyl group is one selected from the group consisting of a vinylene carbonate compound, an acrylate compound containing a vinyl group, a sulfonate compound containing a vinyl group, and an ethylene carbonate compound containing a vinyl group. The lithium secondary battery characterized by the above.
The method according to claim 8,
The compound containing the vinylene group is a lithium secondary battery, characterized in that represented by the following formula (2):
(2)

Where R ⁴ And R ⁵ are each independently hydrogen or halogen, or C ₁ unsubstituted or substituted with halogen; - an alkyl group of C _6, C ₆ C ₁₂ aryl group, C ₂ C ₆ alkenyl or sulfonate groups.
The method of claim 11,
At least one of R ⁴ and R ⁵ of the general formula (2) comprises a vinyl group.
The method according to claim 1 or 8,
The non-aqueous electrolyte lithium secondary battery further comprises a cyclic carbonate substituted with halogen represented by the formula (3):
(3)

(Wherein X and Y are each independently hydrogen, chlorine or fluorine and X and Y are not simultaneously hydrogen).
The method according to claim 13,
The cyclic carbonate substituted with halogen is a lithium secondary battery, characterized in that contained in the amount of 1 to 10% by weight of the non-aqueous electrolyte.

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