KR20070074389A - Electrolyte for lithium rechargeable battery and lithium rechargeable battery comprising it - Google Patents

Abstract

Provided is an electrolyte for a lithium secondary battery, which shows excellent high-temperature and low-temperature storage characteristics while having improved lifespan characteristics. The electrolyte for a lithium secondary battery comprises: a non-aqueous organic solvent; a lithium salt; and a substituted or non-substituted glycolic anhydride and halogenated ethylene carbonate as additives, wherein the substituted or non-substituted glycolic anhydride is used in an amount of 0.1-2 wt% based on the weight of the non-aqueous organic solvent. The halogenated ethylene carbonate is used in an amount of 0.1-10 wt% based on the weight of the non-aqueous organic solvent.

Description

ELECTROLYTE FOR LITHIUM RECHARGEABLE BATTERY AND LITHIUM RECHARGEABLE BATTERY COMPRISING IT}

1 is a cross-sectional view of a rectangular lithium secondary battery shown as an embodiment of the present invention.

Figure 2 is a table showing the cycle life characteristics of the room temperature of the lithium secondary battery prepared using the electrolyte solution prepared according to Example 3, Comparative Examples 1, 2, 5 and 6 of the present invention.

3A and 3B are graphs showing room temperature cycle life characteristics of a square lithium secondary battery prepared using an electrolyte prepared according to Example 3, Comparative Examples 1, 2, 5, and 6 of the present invention.

<Description of the symbols for the main parts of the drawings>

DA: diglycolic acid anhydride FEC: fluoroethylcarbonate

VC: vinylene carbonate

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery electrolyte having excellent life characteristics and storage characteristics and a lithium secondary battery comprising the same.

With the recent rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, etc., as well as the compactness, light weight, and high functionality of the devices are becoming common. The demand for it is increasing. In particular, the rechargeable lithium secondary battery has a high energy density per unit weight of about 3 times higher than conventional lead acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries, and can be rapidly charged. Development is underway.

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, (crystalline or amorphous) carbon or a carbon composite material is used as a negative electrode active material. The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be cylindrical, square or coin type depending on the form.

The average discharge voltage of the lithium secondary battery is about 3.6 to 3.7 V, and high power can be obtained as compared with other alkaline batteries, Ni-MH batteries, and Ni-Cd batteries. However, in order to produce such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2 V. For this reason, an organic electrolyte solution in which lithium salts are dissolved in a non-aqueous organic solvent is used as an electrolyte for a lithium secondary battery. In this case, it is preferable to use an organic solvent having high ionic conductivity and high dielectric constant and low viscosity. However, since there is no single non-aqueous organic solvent that satisfies all of these conditions, a mixed solvent of a high dielectric constant organic solvent and a low dielectric constant organic solvent or a mixture of a high dielectric constant organic solvent and a low viscosity organic solvent is used. Solvent is used.

In US Pat. Nos. 6,114,070 and 6,048,637, ionic conductivity of an organic solvent is prepared by mixing dimethyl carbonate or diethyl carbonate and ethylene carbonate or propylene carbonate as a mixed solvent of chain carbonate and cyclic carbonate. A method of improving is disclosed. However, these mixed solvents can be used usually below 120 ℃ but when the temperature is higher than the gas generated by the vapor pressure there is a problem that the battery is swelled and can not be used.

U.S. Patent Nos. 5,352,548, 5,712,059 and 5,714,281 disclose electrolyte solutions comprising an organic solvent having a vinylene carbonate (VC) content of at least 20%. However, vinylene carbonate has a low dielectric constant compared to ethylene carbonate, propylene carbonate, and gamma butyrolactone, and thus has a problem in that charge and discharge characteristics and high rate characteristics of a battery are significantly reduced when used as a main solvent.

On the other hand, in order to suppress the reductive decomposition of the solvent on the negative electrode, as a means of suppressing the reductive decomposition of lithium on the negative electrode, a method of adding a compound that forms a so-called Solid Electrolyte Interface (SEI) on the negative electrode to the electrolyte solution. This is proposed in Japanese Patent Laid-Open No. 2001-6729. However, in the case of using such a film-forming additive, since the conductivity of lithium ions is low and high resistance SEI is formed on the negative electrode, an excessive amount of the additive when the discharge characteristic of the battery is significantly lowered or is excessively added in the electrolyte solution. When the battery is left at a high temperature, it is oxidized and decomposed at the anode to generate gas, and the expansion of the battery is markedly caused by an increase in the internal pressure.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrolyte solution for a lithium secondary battery that is excellent in high temperature and low temperature storage characteristics and also excellent in life characteristics.

Another object of the present invention is to provide a lithium secondary battery including the electrolyte.

In order to achieve the above object, the present invention

Non-aqueous organic solvents;

Lithium salts; And

Diglycolic anhydride and halogenated ethylene carbonate, substituted or unsubstituted by an additive,

The substituted or unsubstituted diglycolic acid anhydride is characterized in that the electrolyte solution for lithium secondary battery is 0.1 to 2% by weight relative to the non-aqueous organic solvent.

The halogenated ethylene carbonate may include 0.1 to 10% by weight based on the non-aqueous organic solvent.

The present invention also provides an electrolyte prepared according to one embodiment of the present invention; A positive electrode including a positive electrode active material capable of inserting and detaching lithium ions; And it provides a lithium secondary battery comprising a negative electrode comprising a negative electrode active material capable of inserting and detaching lithium ions.

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

The present invention relates to an electrolyte solution for a lithium secondary battery, which exhibits excellent high temperature and low temperature storage characteristics, and also has excellent room temperature and high temperature lifetime characteristics.

The electrolyte solution of the present invention includes diglycolic acid anhydride and halogenated ethylene carbonate, which may or may not be substituted with an additive. The diglycolic acid anhydride may be substituted with one or more substituents selected from the group consisting of halogen or halogen or alkyl group, alkene group or acyl group having 1 to 10 carbon atoms. The electrolyte solution of the present invention can ensure excellent life characteristics and storage characteristics by mixing and using diglycolic acid anhydride and halogenated ethylene carbonate.

As the halogenated ethylene carbonate, a compound represented by Chemical Formula 1 may be used, and fluoroethylene carbonate may be preferably used.

[Formula 1]

(Wherein X is a halogen atom, Y is H or a halogen atom, and n and m are 1 or 2).

The content of the substituted or unsubstituted diglycolic acid anhydride is 0.1 to 2% by weight with respect to the non-aqueous organic solvent, and the content of the halogenated ethylene carbonate is 0.1 to 10% by weight with respect to the non-aqueous organic solvent. The diglycolic acid anhydride and the halogenated ethylene carbonate are preferably used in combination within the above ranges, so that the life and storage characteristics of the battery are preferred. If only diglycolic acid anhydride is used in the electrolyte solution, the low temperature storage characteristics are lowered. If only halogenated ethylene carbonate is used alone, the battery life characteristics are deteriorated.

The electrolyte solution of the present invention also contains a non-aqueous organic solvent and a lithium salt. The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium battery, and the non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ It may be used in combination of one or two or more selected from the group consisting of. The concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, and if it exceeds 2.0M, the viscosity of the electrolyte is increased, there is a problem that the mobility of lithium ions decreases.

The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium battery, and the non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The non-aqueous organic solvent may include a single or mixed carbonate, ester, ether or ketone. Organic solvents should be used to have high dielectric constant (polarity) and low viscosity to increase ion dissociation and smooth ion conduction. Generally, solvents having high dielectric constant, high viscosity and low dielectric constant and low viscosity are used. It is preferable to use two or more mixed solvents configured.

In the case of the carbonate-based solvent in the non-aqueous organic solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, the cyclic carbonate and the chain carbonate are preferably used by mixing in a volume ratio of 1: 1 to 1: 9, and more preferably used by mixing in a volume ratio of 1: 1.5 to 1: 4. The performance of the electrolyte is preferable when mixed in the above volume ratio.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and the like. Can be used. Ethylene carbonate and propylene carbonate having high dielectric constants are preferred, and ethylene carbonate is preferred when artificial graphite is used as the negative electrode active material. Dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylmethyl carbonate (EMC), ethylpropyl carbonate (EPC), etc. may be used as the chain carbonate. Among these, low viscosity dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate are preferable.

The ester is methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, ε-caprolactone, and the like. There may be used as the ether, tetrahydrofuran, 2-methyltetrahydrofuran, dibutyl ether and the like. As the ketone, polymethylvinyl ketone may be used.

The electrolyte solution of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by Chemical Formula 2 may be used.

[Formula 2]

In the above formula, R is halogen or an alkyl group having 1 to 10 carbon atoms and q is an integer of 0 to 6.

Specific examples of the aromatic hydrocarbon organic solvent may include benzene, fluorobenzene, bromobenzene, chlorobenzene, toluene, xylene, mesitylene, and the like, and may be used alone or in combination. In the electrolyte solution containing an aromatic hydrocarbon-based organic solvent, the volume ratio of the carbonate solvent / aromatic hydrocarbon-based organic solvent is preferably 1: 1 to 30: 1. The performance of the electrolyte solution may be desirable to be mixed in the volume ratio.

The lithium secondary battery including the electrolyte solution of the present invention includes a positive electrode and a negative electrode.

The positive electrode includes a positive electrode active material capable of inserting and detaching lithium ions, and the positive electrode active material is preferably at least one selected from cobalt, manganese, nickel, and at least one of a composite oxide with lithium. As examples, the lithium-containing compound described below can be preferably used.

Li_xMn_{One - y}M_yA₂ (One)

Li_xMn_{One - y}Myo_{2 - z}X_z (2)

Li_xMn₂O_{4 - z}X_z (3)

Li_xMn_{2 - y}M_yM '_zA₄ (4)

Li_xCo_{One - y}M_yA₂ (5)

Li_xCo_{One - y}M_yO_{2 - z}X_z (6)

Li_xNi_{One - y}M_yA₂ (7)

Li_xNi_{One - y}M_yO_{2 - z}X_z (8)

Li_xNi_{One - y}Co_yO_{2 - z}X_z (9)

Li_xNi_{One -y- z}Co_yM_zA_α 10

Li_xNi_{One -y- z}Co_yM_zO_{2 -α}X_α (11)

Li_xNi_{One -y- z}Mn_yM_zA_α (12)

Li_xNi_{One -y- z}Mn_yM_zO_{2 -α}X_α (13)

(Wherein 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is selected from the group consisting of O, F, S and P And X is selected from the group consisting of F, S and P.)

The negative electrode includes a negative electrode active material capable of inserting and detaching lithium ions, and the negative electrode active material may be a carbon material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, lithium alloy, or the like. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, mesophase pitch-based carbon fibers (MPCF), and the like. The crystalline carbon includes a graphite material, and specific examples thereof include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The carbonaceous material is preferably a material having an d002 interplanar distance of 3.35 to 3.38 Å and an Lc (crystallite size) of at least 20 nm by X-ray diffraction. As the lithium alloy, an alloy of lithium with aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium may be used.

The positive electrode or the negative electrode may be prepared by dispersing an electrode active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector. Aluminum or an aluminum alloy may be used as the positive electrode current collector, and copper or a copper alloy may be used as the negative electrode current collector. Examples of the positive electrode current collector and the negative electrode current collector include a foil, a film, a sheet, a punched one, a porous body, a foam, and the like.

The binder is a material that serves to paste the active material, the mutual adhesion of the active material, the adhesion with the current collector, the buffering effect on the expansion and contraction of the active material, and the like, for example, polyvinylidene fluoride, polyhexafluoropropylene- Copolymer of polyvinylidene fluoride (P (VdF / HFP)), poly (vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene polyethylene, polyvinyl ether, poly (methylmeth Methacrylate), poly (ethylacrylate), polytetrafluoroethylene, polyvinylchloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber and the like. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight based on the electrode active material. When the content of the binder is too small, the adhesion between the electrode active material and the current collector is insufficient, and when the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases by that amount, which is disadvantageous in increasing battery capacity.

The conductive material may be at least one selected from the group consisting of a graphite-based conductive agent, a carbon black-based conductive agent, a metal or a metal compound-based conductive agent as a material for improving electronic conductivity. Examples of the graphite conductive agent include artificial graphite and natural graphite, and examples of the carbon black conductive agent include acetylene black, ketjen black, denka black, thermal black, and channel. And black or the like, and examples of the metal or metal compound conductive agent include perovskite such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO _3. ) There is a substance. However, it is not limited to the conductive agents listed above. The content of the conductive agent is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive agent is less than 0.1% by weight, the electrochemical properties are lowered, and when the content of the conductive agent is greater than 10% by weight, the energy density per weight decreases.

The thickener is not particularly limited as long as it can play a role of controlling the viscosity of the active material slurry, for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like.

As a solvent in which an electrode active material, a binder, a conductive material, etc. are disperse | distributed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The lithium secondary battery may include a separator that prevents a short circuit between the positive electrode and the negative electrode and provides a passage for lithium ions, and such separators include polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, poly Polyolefin polymer membranes, such as propylene / polyethylene / polypropylene, or a multilayer of these, a microporous film, a woven fabric, and a nonwoven fabric can be used. In addition, a film coated with a resin having excellent stability in a porous polyolefin film may be used.

1 is a cross-sectional view of a rectangular lithium secondary battery shown as one embodiment of the present invention.

Referring to FIG. 1, in a lithium secondary battery, an electrode assembly 12 including an anode 13, a cathode 15, and a separator 14 is accommodated in a can 10 together with an electrolyte solution. It is formed by sealing the upper end with the cap assembly 20. The cap assembly 20 includes a cap plate 40, an insulating plate 50, a terminal plate 60, and an electrode terminal 30. The cap assembly 20 is combined with the insulating case 70 to seal the can 10.

The electrode terminal 30 is inserted into the terminal through-hole 41 formed in the center of the cap plate 40. When the electrode terminal 30 is inserted into the terminal through-hole 41, the tubular gasket 46 is coupled to the outer surface of the electrode terminal 30 and inserted together to insulate the electrode terminal 30 and the cap plate 40. . After the cap assembly 20 is assembled to the upper end of the can 10, the electrolyte is injected through the electrolyte injection hole 42, and the electrolyte injection hole 42 is closed by a stopper 43. The electrode terminal 30 is connected to the negative electrode tab 17 of the negative electrode 15 or the positive electrode tab 16 of the positive electrode 13 to act as a negative electrode terminal or a positive electrode terminal.

The lithium secondary battery of the present invention is not limited to the above-described shape, and any shape such as a cylindrical shape, a pouch, etc., including the positive electrode active material of the present invention and capable of operating as a battery, is possible.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred examples of the present invention and the present invention is not limited to the following examples.

Example  One

LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVDF) as a binder and carbon as a conductive agent were mixed in a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. It was. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode. Synthetic graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed in a weight ratio of 96: 2: 2, and then dispersed in water to prepare a negative electrode active material slurry. The slurry was coated on a copper foil having a thickness of 15 μm, dried, and rolled to prepare a negative electrode.

A film separator made of a polyethylene (PE) material having a thickness of 20 μm was put between the prepared electrodes and then wound and compressed, and inserted into a rectangular can. An electrolyte solution was injected into the rectangular can to prepare a lithium secondary battery. The electrolyte was prepared by dissolving 1.15 M LiPF ₆ in an ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate mixed solvent (1: 1: 1 volume ratio), and then adding diglycolic anhydride and fluoroethylene carbonate. The acid anhydride added 0.5% by weight of the organic solvent weight, and fluoroethylene carbonate added 1% by weight of the organic solvent weight.

Example  2

The same procedure as in Example 1 was conducted except that 0.5 wt% of diglycolic anhydride and 10 wt% of fluoroethylene carbonate were added.

Example  3

The same procedure as in Example 1 was conducted except that 1 wt% of diglycolic anhydride and 3 wt% of fluoroethylene carbonate were added.

Example  4

The same procedure as in Example 1 was conducted except that 1 wt% of diglycolic anhydride and 5 wt% of fluoroethylene carbonate were added.

Example  5

The same procedure as in Example 1 was conducted except that 1 wt% of diglycolic anhydride and 7 wt% of fluoroethylene carbonate were added.

Example  6

It carried out similarly to Example 1 except adding 2 weight% of diglycolic acid anhydride, and 3 weight% of fluoroethylene carbonates.

Example  7

The same procedure as in Example 1 was conducted except that 2 wt% of diglycolic anhydride and 5 wt% of fluoroethylene carbonate were added.

Comparative example  One

It carried out similarly to Example 1 except adding only 3 weight% of diglycolic acid anhydrides.

Comparative example  2

It carried out similarly to Example 1 except adding only 3 weight% of fluoroethylene carbonates.

Comparative example  3

The same procedure as in Example 1 was conducted except that 0.1 wt% of diglycolic anhydride and 15 wt% of fluoroethylene carbonate were added.

Comparative example  4

The same procedure as in Example 1 was conducted except that 3 wt% of diglycolic anhydride and 0.1 wt% of fluoroethylene carbonate were added.

Comparative example  5

It carried out similarly to Example 1 except adding only 3 weight% of vinylene carbonates.

Comparative example  6

It carried out similarly to Example 1 except adding 1 weight% of vinylene carbonate and 3 weight% of fluoroethylene carbonate.

<Standard capacity>

Table 1 shows the standard capacity when the batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 4 were charged for 3 hours under 0.5 C / 4.2 V constant current-constant voltage conditions.

<Room temperature life characteristics>

Batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to 1 C / 4.2 V CC / CV, 0.05 C cutoff charging at 25 ° C., and 3.2 V cut-off discharge at 1 C CC. Was done. After repeating this process 300 times and 500 times, respectively, the capacity retention rate (%) at the 300th and 500th cycles of normal temperature was calculated, respectively, and the results are shown in Table 1 below.

In addition, the room temperature cycle life characteristics of the lithium secondary batteries manufactured according to Example 3, Comparative Examples 1, 2, 5, and 6 were measured in units of 10 times and measured up to 500 times, and then the capacity retention ratio was calculated as follows. 2 is shown. The cycle life characteristics and the capacity retention rate (%) thus measured are shown in the graphs of FIGS. 3A and 3B, respectively.

Capacity retention rate (%) of nth cycle = (discharge capacity of nth cycle) / (standard capacity of cell 930 mAh) * 100 (%)

<Low temperature preservation characteristic>

The cells prepared according to Examples 1 to 7 and Comparative Examples 1 to 4 were charged with 0.5 C / 4.2 V CC-CV at 25 ° C. for 3 hours, and left at 0 ° C. for 4 hours, followed by 3 V cut at 0.5 C CC. Discharge was off. Discharge capacity recovery rate (%) was calculated after leaving at low temperature, the results are shown in Table 1 below.

Discharge rate recovery after low temperature (%) = (0.5C discharge capacity after low temperature) / (0.5C discharge capacity after low temperature) * 100 (%)

<High temperature preservation characteristic>

The cells prepared according to Examples 1 to 7 and Comparative Examples 1 to 4 were charged with 0.5 C / 4.2 V CC-CV at 25 ° C. for 3 hours, left at 85 ° C. for 24 hours, and then cut 3.2 V with 0.5 C CC. -Off discharge. Discharge capacity recovery rate (%) was calculated after leaving at high temperature, the results are shown in Table 1 below.

Discharge capacity recovery rate after high temperature (%) = (0.5C discharge capacity after high temperature standing) / (0.5C discharge capacity after high temperature standing) * 100 (%)

DA addition amount (% by weight) FEC addition amount (wt%) Standard capacity (%) Room temperature 300 cycle capacity retention rate (%) Room temperature 500 cycle capacity retention rate (%) Discharge capacity recovery rate after 4 hours at 0 ℃ (%) Discharge capacity recovery rate after leaving 85 ℃ for 24 hours (%) Example 1 0.5 One 100 75 55 75 95 Example 2 0.5 10 100 88 82 50 70 Example 3 One 3 100 86 81 73 95 Example 4 One 5 100 86 81 70 96 Example 5 One 7 100 87 82 68 94 Example 6 2 3 98 85 81 65 95 Example 7 2 5 98 85 82 64 95 Comparative Example 1 3 0 96 77 50 20 70 Comparative Example 2 0 3 100 74 50 75 95 Comparative Example 3 0.1 15 100 87 81 40 61 Comparative Example 4 3 0.1 96 78 51 25 95

DA: diglycolic acid anhydride, FEC: fluoroethylene carbonate,

As can be seen from Table 1, FIGS. 2 to 3A and 3B, the present invention comprises 0.1 to 2 wt% of diglycolic acid anhydride and 0.1 to 10 wt% of fluoroethylene carbonate based on the weight of the non-aqueous organic solvent. The electrolyte solutions of Examples 1 to 7 showed good life characteristics and storage characteristics of the battery. The electrolyte solution of Comparative Example 1 containing only diglycolic acid anhydride has poor cold storage characteristics, and the electrolyte solution of Comparative Example 2 containing only fluoroethylene carbonate has poor battery life characteristics. Moreover, the electrolyte solution of Comparative Examples 3 and 4 to which the diglycolic acid anhydride or fluoroethylene carbonate was added excessively has low low temperature storage characteristic or high temperature storage characteristic, and its life characteristics are not good.

The electrolyte solution of Comparative Example 6 containing vinylene carbonate and fluoroethylene carbonate instead of diglycolic acid anhydride has a very high shelf life characteristics compared to the electrolyte solution of Example 3 containing diglycolic acid anhydride and fluoroethylene carbonate in the same ratio. Appeared to fall.

As described above, the electrolyte according to the present invention provides a lithium secondary battery having excellent life characteristics and storage characteristics.

Although the present invention has been described with reference to the above embodiments, it is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (15)

Non-aqueous organic solvents; Lithium salts; And Diglycolic acid and halogenated ethylene carbonate, optionally substituted with an additive, The substituted or unsubstituted diglycolic acid anhydride is 0.1 to 2% by weight relative to the non-aqueous organic solvent. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the halogenated ethylene carbonate is 0.1 to 10% by weight based on the non-aqueous organic solvent. The electrolyte of claim 1, wherein the substituted diglycolic acid anhydride is substituted with one or more substituents selected from the group consisting of halogen or an alkyl group having 1 to 10 carbon atoms, an alkene group or an acyl group. The electrolyte for a lithium secondary battery according to claim 1, wherein the halogenated ethylene carbonate is a compound represented by the following Chemical Formula 1. [Formula 1]

(Wherein X is a halogen atom, Y is H or a halogen atom, and n and m are 1 or 2). The electrolyte solution for lithium secondary batteries according to claim 4, wherein the halogenated ethylene carbonate is fluoroethylene carbonate. The electrolyte of claim 1, wherein the non-aqueous organic solvent comprises at least one solvent selected from the group consisting of carbonates, esters, ethers, and ketones. The electrolyte solution for a lithium secondary battery according to claim 6, wherein the carbonate is a mixed solvent of cyclic carbonate and chain carbonate. 8. The group according to claim 7, wherein the cyclic carbonate is made of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate and 2,3-pentylene carbonate Electrolyte for lithium secondary battery, characterized in that at least one solvent selected from. 8. The lithium secondary of claim 7, wherein the chain carbonate is at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylmethyl carbonate and ethylpropyl carbonate. Battery electrolyte. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. The electrolytic solution for a lithium secondary battery according to claim 10, wherein the aromatic hydrocarbon organic solvent is an aromatic compound represented by the following Chemical Formula 2. [Formula 2]

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and q is an integer of 0 to 6). The method of claim 11, wherein the aromatic hydrocarbon-based organic solvent is at least one solvent selected from the group consisting of benzene, fluorobenzene, chlorobenzene, bromobenzene, toluene, xylene, mesitylene and mixtures thereof. An electrolyte solution for lithium secondary batteries. The electrolyte of claim 10, wherein the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent are mixed in a volume ratio of 1: 1 to 30: 1. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI, characterized in that at least one selected from the group consisting of Electrolyte for lithium secondary battery. The electrolyte of any one of claims 1 to 14; A positive electrode including a positive electrode active material capable of inserting and detaching lithium ions; And A lithium secondary battery comprising a negative electrode comprising a negative electrode active material capable of inserting and detaching lithium ions.

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