WO2015126082A1 - Electrolyte for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same and, more specifically, to an electrolyte for a lithium secondary battery, capable of reducing interfacial resistance of an electrode by comprising an electrolyte additive as an ammonium-based nitrate, and to a lithium secondary battery comprising the same. According to the present invention, a lithium secondary battery can be provided which can suppress the change in average voltage at the time of charging or discharging due to the increase in interfacial resistance of the electrode, and thus has improved charging and discharging efficiency and high-rate characteristics.

Description

Electrolyte for lithium secondary battery and lithium secondary battery having same

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery having the same, and more particularly, to a lithium secondary battery electrolyte and a lithium secondary battery having an interface resistance of the electrode by including ammonium nitrate as an electrolyte additive It relates to a battery.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, lithium secondary batteries with high energy density and operating potential, long cycle life, and low self discharge rate Batteries have been commercialized and widely used.

Such a lithium secondary battery has a structure in which an electrolyte solution containing lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode on which an active material is coated on an electrode current collector. During charging, lithium ions of the positive electrode active material are released and inserted into the active material layer of the negative electrode, and during discharging, lithium ions of the active material layer are released and inserted into the positive electrode active material, and the electrolyte serves as a medium for transferring lithium ions between the negative electrode and the positive electrode. Do it.

The electrolyte solution generally contains an organic solvent and an electrolyte salt, for example, in a mixed solvent of a highly viscous linear carbonate such as propylene carbonate and ethylene carbonate and a low viscosity chain carbonate such as diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate. And lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ are commonly used.

Lithium-containing halogen salts, such as lithium-containing fluoride salts and lithium-containing chloride salts, which are mainly used as the electrolyte salts, react very sensitively to moisture, and thus react with water present in the battery manufacturing process or in the battery to form HX, which is a strong acid. (X = F, Cl, Br, I). In particular, LiPF ₆ lithium salts are unstable at high temperatures so that anions can be thermally decomposed to produce acidic materials such as hydrofluoric acid (HF). Such acidic substances are necessarily accompanied by undesirable side reactions when present in the cell.

For example, the solid electrolyte interface (SEI) film present on the surface of the cathode can be easily destroyed due to the strong reactivity of the HX (X = F, Cl, Br, I), and thus the continuous regeneration of the SEI film Induction may increase the interfacial resistance of the negative electrode due to the increase in the amount of coating of the negative electrode. In addition, anode interface resistance may increase due to adsorption of lithium fluoride (LiF) as a by-product of the formation of hydrofluoric acid (HF). In addition, the HX may cause a rapid oxidation reaction in the battery to dissolve and degrade the positive electrode active material, and particularly when the transition metal cation contained in the lithium metal oxide used as the positive electrode active material is eluted. As the cations are deposited on the cathode, an additional cathode film is formed to further increase the cathode resistance.

On the other hand, the SEI membrane is a protective film for stabilizing the battery by inhibiting the decomposition of the carbonate-based electrolyte on the negative electrode surface is formed by the polar non-aqueous solvent of the carbonate system reacts with lithium ions in the electrolyte during the initial charging of the lithium secondary battery It serves as. However, the SEI film produced only by the organic solvent and the lithium salt is somewhat insufficient to serve as a continuous protective film, so that the charging and discharging of the battery is continuously progressed or increased electrochemical energy, especially at high temperature storage in a full charge state. It can be disintegrated slowly by heat energy. Due to the collapse of the SEI film, side reactions in which the exposed surface of the negative electrode active material and the electrolyte solvent react to decompose continuously occur, which may cause an increase in resistance of the negative electrode.

In addition to the above-described causes, the interfacial resistance between the electrode and the electrolyte may be increased by various causes, and if the interfacial resistance is increased in this way, the overall performance of the battery, such as output characteristics, may occur. For example, an increase in the resistance of a battery may cause a change in the average voltage during charge and discharge, that is, an increase in the average voltage during charge and a decrease in the average voltage during discharge, and consequently, charge and discharge with a constant current. The charge and discharge efficiency indicating the discharge capacity with respect to the capacity may be lowered.

In order to solve this problem, Patent Document 1 (Japanese Patent Laid-Open No. 5-13088) describes a method of improving the resistance of a lithium secondary battery by containing vinylene carbonate (VC) in an electrolyte solution. However, since the film formed by this method still shows high resistance, it did not show sufficient effect in suppressing the increase in resistance of the battery.

In addition, Patent Document 2 (Domestic Patent Publication No. 2012-0011209) discloses an electrolyte solution for a lithium secondary battery containing an alkylene sulfate having a specific structure, an ammonium compound having a specific structure, and a vinylene carbonate. However, since the SEI film produced by the sulfate-based compound has the advantage of low resistance, the low-temperature output characteristics of the battery may be improved, but the improvement in initial efficiency and high rate characteristics does not show an improvement, and thus further improvement is required. .

As described above, when a specific compound is added to the electrolyte solution in order to suppress the increase in battery resistance, the performance of some items is improved, but the performance of other items is decreased, or only a few items are often improved.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Japanese Patent Application Laid-open No. Hei 5-13088

(Patent Document 2) KR2012-0011209 A

The problem to be solved by the present invention is to provide a lithium secondary battery electrolyte that can reduce the interface resistance of the electrode to suppress the change in the average voltage generated during charge and discharge, and can improve the charge and discharge efficiency and high rate characteristics .

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

In order to solve the above problems, the present invention provides a lithium secondary battery electrolyte comprising a lithium salt and an organic solvent, the electrolyte solution further comprises a nitrate represented by the formula (1). .

Formula 1

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.

Preferably, the content of the nitrate may be 0.01 to 5 parts by weight based on 100 parts by weight of the total of the lithium salt and the organic solvent.

Compound represented by the formula (1) according to the present invention is ammonium nitrate (Ammonium nitrate), tetramethylammonium nitrate (Tetramethylammonium nitrate), tetraethylammonium nitrate (Tetraethylammonium nitrate), tetrabutylammonium nitrate (Tetrabutylammonium nitrate), Monoethyltrimethylammonium nitrate, Monobutyltrimethylammonium nitrate, Monobutyltrimethylammonium nitrate, Diethyldimethylammonium nitrate and Dibutyldimethylammonium nitrate It may be abnormal.

In addition, the present invention provides a lithium secondary battery including the electrolyte.

According to the present invention, the interface resistance of the electrode can be reduced by providing an electrolyte solution for a lithium secondary battery containing the nitrate as an additive.

Therefore, it is possible to suppress the average voltage change during charge / discharge caused by the increase in the interfacial resistance of the electrode, that is, to reduce the difference between the average voltage during charging and the average voltage during discharge, thereby charging and discharging at a constant current. According to the present invention, a lithium secondary battery having improved charging and discharging efficiency and high rate characteristics can be provided.

1 is 0.5C, 1.0C compared to the 0.5C-rate discharge capacity of the coin cells prepared according to Examples and Comparative Examples. It is a graph comparing the ratio of 1.5C and 2.0C rate discharge capacity.

The present invention relates to a lithium secondary battery electrolyte comprising a lithium salt and an organic solvent, wherein the electrolyte further comprises a nitrate represented by the following formula (1).

[Formula 1]

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.

As described above, the SEI film formed of organic solvents or additives known to date is difficult to maintain the continuous performance, and in particular, the resistance of the electrode is increased due to the interfacial reaction between the electrode and the electrolyte, and it is insufficient to simultaneously achieve various performances such as output characteristics at an effective level. There was a point.

However, when the nitrate is used as an electrolyte additive according to the present invention, the interfacial resistance of the electrode is lowered to reduce the amount of change in the average voltage generated during charge and discharge, to improve the charge and discharge efficiency and to significantly improve the high rate characteristic. can do.

The content of the nitrate is preferably 0.01 to 5.0 parts by weight, more preferably 0.1 to 3.0 parts by weight based on 100 parts by weight of the total of the lithium salt and the organic solvent. If the content is less than 0.01 parts by weight, it may be difficult to obtain the effect of lowering the interface resistance of the electrode, whereas if it exceeds 5.0 parts by weight, it may cause a decrease in charge and discharge efficiency.

Preferred examples of the compound represented by Formula 1 according to the present invention include ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate ), Monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate. 1 or more types are mentioned, It is not limited to this.

The performance of the battery is highly dependent on the basic electrolyte composition and the solid electrolyte interface (SEI) film formed by the reaction between the electrolyte and the electrode.

In the lithium secondary battery, an SEI film is formed by reacting a surface of carbon particles, which is a negative electrode active material, and an electrolyte, at a negative electrode of a battery during a first charging process. The SEI film thus formed not only prevents side reactions between the carbon material and the electrolyte solvent and the negative electrode material due to co-intercalation of the electrolyte solvent into the negative electrode material, but also faithfully plays a role as a conventional lithium ion tunnel, thereby improving battery performance. Minimize degradation. However, SEI membranes formed by conventional carbonate organic solvents, fluorine salts or other inorganic salts are weak, porous and not dense, resulting in a reduction in the amount of reversible lithium since lithium ions do not move smoothly. This increased the irreversible reaction according to the progress of charging and discharging, resulting in a decrease in the capacity and charge and discharge efficiency of the battery.

In contrast, the ammonium nitrate represented by Formula 1, which is included as an additive in the electrolyte of the present invention, is reduced on the surface of the negative electrode material before the other components at the time of initial charging of the battery, so that the SEI membrane is not only firm and dense but also excellent in stability. To form. Therefore, the conventional carbonate solvent prevents side reactions in which the co-intercalation of the layered active material layer or the solvent is decomposed, thereby increasing the initial efficiency of the battery, and also inhibits the breakdown and regeneration of the SEI film, thereby preventing interfacial resistance of the electrode. Can suppress the increase.

On the other hand, the lithium salt included as an electrolyte in the electrolyte of the present invention may be used within the concentration range of 0.6 to 2.0M, more preferably may be used in the range of 0.7 to 1.6M. When the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, and the performance of the electrolyte may be degraded. On the other hand, when the concentration of the lithium salt exceeds 2.0M, the viscosity of the electrolyte may be increased, thereby reducing the mobility of lithium ions. As the lithium salt, those conventionally used in an electrolyte for a lithium secondary battery may be used without limitation. For example, the anion of the lithium salt may be 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 5) 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 ^-It can be any one selected from the group consisting of.

As the organic solvent included in the electrolyte solution, those conventionally used in the lithium secondary battery electrolyte may be used without limitation, and for example, ethers, esters, amides, linear carbonates, and cyclic carbonates may be used alone or by mixing two or more kinds. Can be used.

Among them, carbonate compounds which are typically cyclic carbonates, linear carbonates, or mixtures thereof may be included. Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and any one selected from the group consisting of halides thereof or mixtures of two or more thereof. In addition, specific examples of the linear carbonate compound include dimethyl carbonate (dimethyl carbonate, DMC), diethyl carbonate (diethyl carbonate, DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate Any one selected or a mixture of two or more thereof may be representatively used, but is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, may be preferably used as high-viscosity organic solvents because they have high dielectric constants to dissociate lithium salts in electrolytes. When the same low viscosity, low dielectric constant linear carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be made, and thus it can be used more preferably.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used. It is not limited to this.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ε-caprolactone may be used, but is not limited thereto.

The electrolyte solution for a lithium secondary battery of the present invention may further include a conventionally known additive for forming an SEI film without departing from the object of the present invention. As the additive for forming the SEI film usable in the present invention, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, unsaturated sultone, acyclic sulfone, etc. may be used alone or in combination of two or more thereof. It may be, but is not limited thereto.

The cyclic sulfites include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfide Pite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like. 1,3-propane sultone, 1,4-butane sultone, and the like, and examples of the unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-prop Pen sulfone etc. are mentioned, As acyclic sulfone, divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone, etc. are mentioned.

The additive for forming the SEI film may be included in an appropriate amount according to the specific type of the additive, for example, 0.01 to 10 parts by weight based on 100 parts by weight of the electrolyte.

On the other hand, the present invention provides a lithium secondary battery comprising the non-aqueous electrolyte.

The lithium secondary battery is prepared by injecting an electrolyte prepared according to the present invention in an electrode structure consisting of a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode may be prepared by mixing an active material, a binder, and a conductive agent with a solvent to prepare a slurry, applying the slurry to a current collector such as aluminum, and drying and compressing the slurry.

As the cathode active material, a lithium-containing transition metal oxide may be preferably used. For example, Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), and Li _x MnO ₂ (0.5) <x <1.3), Li _x Mn ₂ O ₄ (0.5 <x <1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 <x <1.3, 0 <a <1, 0 <b <1 , 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _1-y Mn _y O ₂ (0.5 <x <1.3, 0≤y <1), Li _x Ni _1-y Mn _y O ₂ (0.5 <x <1.3, O≤y <1), Li _x (Ni _a Co _b Mn _c ) O ₄ (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _2-z Ni _z O ₄ (0.5 <x <1.3 , 0 <z <2), Li _x Mn _2-z Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <x <1.3), any one selected from the group consisting of, or a mixture of two or more thereof may be used, and the lithium-containing transition metal oxide may be coated with a metal or metal oxide such as aluminum (Al). In addition to the lithium-containing transition metal oxide, sulfide, selenide, halide, and the like may also be used.

As the negative electrode active material, a carbon material, lithium metal, silicon, tin, or the like, which can normally occlude and release lithium ions, may be used, and a metal oxide such as TiO ₂ and SnO ₂ having a potential of less than ₂ V may be used. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low-crystalline carbon, and high crystalline carbon is natural graphite, artificial graphite, Kishgraphite, pyrolytic carbon, 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 are typical.

The binder binds the active material and the conductive agent to fix the current collector, and polyvinylidene fluoride, polypropylene, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polyvinyl alcohol, styrene butadiene Those commonly used in lithium ion secondary batteries, such as rubber, can be used.

Examples of the conductive agent include artificial graphite, natural graphite, acetylene black, ketjen black, channel black, lamp black, thermal black, conductive fibers such as carbon fibers and metal fibers, conductive metal oxides such as titanium oxide, metal powders such as aluminum and nickel, and the like. This can be used.

In addition, as a separator, a single olefin or a complex of olefins such as polyethylene (PE) and polypropylene (PP), polyamide (PA), polyacrylonitrile (PAN), polyethylene oxide (PEO), and polypropylene oxide (PPO) , Polyethylene glycol diacrylate (PEGA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC) and the like can be used.

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.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

<Production of electrolyte solution>

Ethylene carbonate and ethylmethyl carbonate were mixed in a weight ratio of 3: 7 to prepare an organic solvent. Next, LiPF ₆ as a lithium salt was dissolved in the organic solvent to prepare a LiPF ₆ mixed solution having a lithium salt concentration of 1M. Next, ammonium nitrate was added to the mixed solution at 0.5 parts by weight based on 100 parts by weight of the mixed solution to prepare an electrolyte solution.

Example 2

An electrolyte solution was prepared in the same manner as in Example 1, except that tetramethylammonium nitrate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 3

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 4

An electrolyte solution was prepared in the same manner as in Example 1, except that tetrabutylammonium nitrate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 5

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 0.1 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 6

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 1.0 part by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 7

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 2.0 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Example 8

An electrolyte solution was prepared in the same manner as in Example 1, except that tetraethylammonium nitrate was added in an amount of 3.0 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

Comparative Example 1

In Example 1, ammonium nitrate was not added, and the rest of the electrolyte was prepared in the same manner.

Comparative Example 2

An electrolyte was prepared in the same manner as in Example 1, except that lithium difluorophosphate was added in an amount of 0.5 parts by weight based on 100 parts by weight of the mixed solution instead of ammonium nitrate.

<Manufacture of battery>

After mixing NiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material at a weight ratio of 91.5: 4.4: 4.1, N-methyl-2-pyrrolidone A positive electrode slurry was prepared by dispersing in a slurry, and the slurry was coated on an aluminum current collector, followed by drying and rolling to prepare a positive electrode.

In addition, a lithium metal (manufactured by CHEM METAl) having a thickness of 1 mm was used as the cathode.

Then, a porous polyethylene membrane (manufactured by Tonen) was used as a separator together with the prepared anode and cathode, and the coin cell was prepared by pouring the prepared electrolyte solution.

<Evaluation method>

(1) charging and discharging efficiency

After allowing the prepared coin cell to stand at a constant temperature of 25 ℃ for 24 hours, using a lithium secondary battery charger (Toyo-System Co., LTD, TOSCAT-3600), the conditions to make a constant current to 4.2V at 0.1C and 0.05 The charge and discharge capacity of the first cycle was measured by charging C under constant voltage condition as the termination current, and discharging under constant current condition to 3.0V at 0.1 C. The charge and discharge capacity is calculated in Table 1 by calculating the charge and discharge efficiency according to the following equation. And efficiency.

Charge / discharge efficiency (%) = discharge capacity / charge capacity

(2) average voltage

Charged and discharged in the 3.0 ~ 4.2V range at 0.2C rate for the manufactured coin cell, the voltage (charge average voltage) and 50% depth of discharge at 50% charge (depth of discharge, DOC) , DOD) and the voltage (discharge average voltage) were measured and shown in Table 1 below. The difference between the average charging voltage and the average discharge voltage was calculated and expressed as a voltage difference.

(3) rate characteristics

Table 1 shows the discharge capacities according to the c-rates after charging and discharging in the 3.0 to 4.2 V region at 0.5 C, 1.0 C, 1.5 C, and 2.0 C for the manufactured coin cells. In addition, the ratio of the discharge capacities at 0.5C, 1.0C, 1.5C, and 2.0C when the c-rate is 0.5C is shown in FIG. 1.

Table 1

	0.1C / 0.1C (mAh)			0.2C / 0.2C (V)			Rate characteristic (mAh)
	Charging capacity	Discharge capacity	Charge and discharge efficiency	Average charging voltage	Discharge average voltage	Voltage difference	0.5C discharge	1.0C discharge	1.5C discharge	2.0C discharge
Example 1	4.844	4.261	87.96%	3.802	3.772	0.030	4.120	3.989	3.017	1.320
Example 2	4.849	4.263	87.92%	3.794	3.769	0.025	4.126	3.994	3.053	1.246
Example 3	4.844	4.259	87.92%	3.793	3.770	0.023	4.126	3.975	3.062	1.221
Example 4	4.851	4.264	87.90%	3.791	3.769	0.022	4.127	3.995	3.075	1.236
Example 5	4.866	4.263	87.61%	3.799	3.769	0.030	4.131	4.002	3.011	1.202
Example 6	4.836	4.253	87.94%	3.793	3.769	0.024	4.125	4.001	3.089	1.233
Example 7	4.838	4.250	87.85%	3.797	3.770	0.027	4.109	3.974	3.045	1.134
Example 8	4.841	4.250	87.79%	3.799	3.771	0.028	4.106	3.965	2.927	1.032
Comparative Example 1	4.883	4.241	86.86%	3.811	3.746	0.065	4.114	3.669	1.502	0.499
Comparative Example 2	5.596	4.301	76.86%	3.800	3.723	0.077	4.119	2.863	0.482	0.194

* 0.1C / 0.1C, 0.2C / 0.2C: 0.1C / 0.1C means charged and discharged at 0.1C, 0.2C / 0.2C means charged and discharged at 0.2C.

Looking at the Table 1, it can be seen that in the case of the coin cells of Examples 1 to 8 using the additive according to the present invention in the electrolyte, the difference in the average voltage generated during charging and discharging significantly reduced compared to Comparative Examples 1 to 2 It can be seen that this reduces the resistance in the battery. As the resistance is reduced, it can be seen that the charging and discharging efficiency is improved when charging and discharging at a constant current.

In addition, referring to Tables 1 and 1 showing the results of the high-rate discharge characteristics of the coin cell to which the electrolytes prepared according to Examples 1 to 8 and Comparative Examples 1 to 2 were applied, Examples 1 to 8 of the present invention In the case of the coin cell, it can be seen that the high rate characteristic is improved compared to the coin cells of Comparative Examples 1 to 2.

As described above, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to explain the protection scope of the present invention, which should be interpreted by the following claims, and all technical ideas within the equivalent scope thereof. Should be construed as being included in the scope of the present invention.

Claims (7)

1. In a lithium secondary battery electrolyte containing a lithium salt and an organic solvent,

   The electrolyte solution is a lithium secondary battery electrolyte further comprises a nitrate represented by the formula (1):

   [Formula 1]

   

   In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.
2. The method of claim 1,

   The compound represented by Formula 1 is ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate, tetrabutylammonium nitrate, monoethyltrimethylammonium Monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, monoethyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate. A non-aqueous electrolyte for lithium secondary batteries.
3. The method of claim 1,

   The amount of the nitrate is 0.01 to 5 parts by weight based on 100 parts by weight of the total amount of the lithium salt and the organic solvent electrolyte solution for a lithium secondary battery.
4. The method of 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 5) 3 C -, (CF 3 SO 2 _{^{) 3 C -, CF 3 (}} CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - is any one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N An electrolyte for lithium secondary batteries, characterized in that.
5. The method of claim 1,

   The organic solvent is at least one selected from the group consisting of ether, ester, amide, linear carbonate and cyclic carbonate electrolyte for lithium secondary battery.
6. The method of claim 1,

   The electrolyte solution further comprises at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, unsaturated sultone and acyclic sulfone.
7. A lithium secondary battery comprising the electrolyte solution of any one of claims 1 to 6.

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