KR20150100079A - Non-aqueous electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery including the same and, more specifically, to an electrolyte for a lithium secondary battery, capable of reducing the interfacial resistance of an electrode by including ammonium nitrate as an electrolyte addition agent, and a lithium secondary battery including the same. According to the present invention, the electrolyte can control a change in average voltage during charging and discharging, occurring due to the increased interfacial resistance of the electrode, thus a lithium secondary battery with enhanced charging and discharging efficiency and high rate characteristics can be provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery having the same. 2. Description of the Related Art [0002]

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

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

The lithium secondary battery has a structure in which an electrolyte solution containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on an electrode current collector. At the time of charging, the lithium ions of the positive electrode active material are discharged and inserted into the active material layer of the negative electrode. At the time of discharging, the lithium ions of the active material layer are released to be 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 .

The electrolytic solution generally includes an organic solvent and an electrolyte salt. For example, the electrolytic solution is mixed with a mixed solvent of a high-molecular cyclic carbonate such as propylene carbonate, ethylene carbonate and the like and a low viscosity chain carbonate such as diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, etc. , LiPF ₆ , LiBF ₄ , LiClO ₄ Or the like is generally used.

Since the lithium-containing halogen salt such as lithium-containing flame retardant and lithium-containing chloride salt, which are mainly used as the electrolyte salt, reacts very sensitively to water, it reacts with moisture present in the battery or during the manufacturing process of the battery, (X = F, Cl, Br, I). In particular, LiPF ₆ lithium salts are unstable at high temperatures, so anions can be thermally decomposed to produce acidic substances such as hydrofluoric acid (HF). Such acidic substances are essentially accompanied by undesirable side reactions when they are present in the cell.

For example, a solid electrolyte interface (SEI) film present on the cathode surface can easily be destroyed due to the strong reactivity of HX (X = F, Cl, Br, I) And the increase in the coating amount of the negative electrode may lead to an increase in the interfacial resistance of the negative electrode. In addition, the anode interface resistance can be increased due to adsorption of lithium fluoride (LiF) on the anode surface, which is a by-product at the time of forming the hydrofluoric acid (HF). In addition, the HX causes a rapid oxidation reaction in the battery, dissolving and degenerating both electrode active materials, and in particular, the transition metal cations contained in the lithium metal oxide used as the cathode active material are eluted , These cations are electrodeposited to the negative electrode to form additional negative electrode coating, thereby further increasing the negative electrode resistance.

On the other hand, the SEI film is formed by a reaction between a polar non-aqueous solvent of a carbonate-based polar non-aqueous solvent at the time of initial charging of the lithium secondary battery and a protective film formed on the surface of the negative electrode to suppress the decomposition of the carbonate- . 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 charge and discharge of the battery are continuously carried out, and in particular, when stored at a high temperature in a fully charged state, And can be gradually collapsed by thermal energy. Due to the collapse of the SEI film, a side reaction in which the surface of the exposed negative electrode active material is reacted with the electrolyte solvent is continuously generated, which may cause an increase in resistance of the negative electrode.

In addition to the above-described causes, the interface resistance between the electrode and the electrolyte can be increased by various causes, and when the interfacial resistance is increased, all the performance of the battery such as the output characteristics is deteriorated. For example, an increase in the resistance of the battery can cause an average voltage change during charging and discharging, that is, a phenomenon in which the average voltage increases during charging and the average voltage decreases during discharging. As a result, The charge / discharge efficiency indicating the discharge capacity with respect to the capacity may be lowered.

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

Also, Patent Document 2 (Japanese Patent Laid-Open Publication No. 2012-0011209) discloses an electrolyte for a lithium secondary battery comprising an alkylene sulfate having a specific structure, an ammonium compound having a specific structure, and vinylene carbonate. However, since the SEI film produced by the sulfate compound has an advantage of low resistance, it can improve the low-temperature output characteristics of the battery, but does not exhibit improvement in terms of initial efficiency and high-rate characteristics, and further improvement is required .

As described above, when a specific compound is added to an electrolytic solution to suppress the increase in battery resistance, the performance of some items is improved but the performance of other items is reduced or only some items are improved.

Japanese Patent Application Laid-Open No. 5-13088 KR 2012-0011209 A

Disclosure of Invention Technical Problem [8] Accordingly, an object of the present invention is to provide an electrolyte solution for a lithium secondary battery, which can reduce the interfacial resistance of the electrode to suppress the change in the average voltage generated during charging and discharging, and improve the charging / discharging efficiency and the high- .

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

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

[Chemical 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 amount of the lithium salt and the organic solvent.

The compound represented by Formula 1 according to the present invention may be a compound selected from the group consisting of ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate, One selected from the group consisting of monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate. Or more.

The present invention also provides a lithium secondary battery comprising the electrolyte solution.

According to the present invention, it is possible to reduce the interfacial resistance of the electrode by providing the electrolyte for a lithium secondary battery containing the nitrate as an additive.

Therefore, it is possible to suppress the change in the average voltage during charging and discharging caused by the increase in the interface resistance of the electrode, that is, to reduce the difference between the average voltage during charging and the average voltage during discharging, A lithium secondary battery improved in charging / discharging efficiency and high-rate characteristics can be provided.

FIG. 1 is a graph showing the relationship between the discharge capacity of a coin cell manufactured according to Examples and Comparative Example at 0.5 C, 1.0 C. 1.5C and 2.0C rate discharge capacity.

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

[Chemical 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, it is difficult to maintain the performance of the SEI film formed with known organic solvents or additives until now, and in particular, the resistance of the electrode increases due to the interfacial reaction between the electrode and the electrolyte, There was a dot.

However, according to the present invention, when the nitrate salt is used as an electrolyte additive, the interface resistance of the electrode is lowered to reduce the amount of change in the average voltage generated during charging and discharging, to improve the charging and discharging efficiency, 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 amount 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 an effect of lowering the interface resistance of the electrode. On the other hand, when the content exceeds 5.0 parts by weight, the charge and discharge efficiency may be lowered.

Preferred examples of the compound represented by Formula 1 according to the present invention include ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate Selected from the group consisting of monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate, and dibutyldimethylammonium nitrate. But is not limited thereto.

The performance of the cell is largely determined by the basic electrolyte composition and the solid electrolyte interface (SEI) film formed by the reaction between the electrolyte and the electrode.

In the first rechargeable lithium battery, the surface of the carbon particles, which are the negative electrode active material, reacts with the electrolyte at the negative electrode of the battery to form an SEI film. The thus formed SEI membrane prevents the side reaction between the carbon material and the electrolyte solvent and the collapse of the negative electrode material due to the co-intercalation of the electrolyte solvent into the negative electrode material, and also fulfills the role as a conventional lithium ion tunnel. Minimize degradation. However, the SEI film formed by the conventional carbonate-based organic solvent, incombustible salt or other inorganic salt is weak, porous and dense, resulting in a reduction of the amount of reversible lithium since migration of lithium ions is not performed smoothly. As a result, the irreversible reaction due to the progress of charging / discharging was increased, resulting in a decrease in capacity and charge / discharge efficiency of the battery.

On the other hand, the ammonium-based nitrate salt represented by Formula 1 contained as an additive in the electrolytic solution of the present invention is reduced on the surface of the negative electrode material prior to other components at the time of initial charging of the battery, Respectively. Therefore, not only the conventional carbonate solvent is co-intercalated into the active material layer of the layered structure or the side reaction in which the solvent is decomposed is prevented to increase the initial efficiency of the battery, and the breakdown and regeneration of the SEI film is suppressed, Can be suppressed.

On the other hand, the lithium salt contained as an electrolyte in the electrolytic solution of the present invention can be used in a concentration range of 0.6 to 2.0M, more preferably in a range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte may be lowered and the performance of the electrolyte may be deteriorated. On the other hand, when the concentration exceeds 2.0M, the viscosity of the electrolyte may increase and the lithium ion mobility may decrease. The anion of the lithium salt may be, for example, 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 ^- .

The organic solvent contained in the electrolytic solution may be any of those conventionally used in an electrolyte for a lithium secondary battery. Examples of the organic solvent include ether, ester, amide, linear carbonate, cyclic carbonate, etc., Can be used.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture 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 halides thereof, or a mixture of two or more thereof. Specific examples of the linear carbonate compound include a group consisting of dimethyl carbonate (DMC), 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 used as typical examples, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolyte well, and dimethyl carbonate and diethyl carbonate When a low viscosity and a low dielectric constant linear carbonate are mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone and? -Caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The electrolyte solution for a lithium secondary battery of the present invention may further contain an additive for forming a known SEI film within the scope of the present invention. Examples of the additive for forming the SEI film that can be used in the present invention include vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone and non-cyclic sulphone, But is not limited thereto.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, Diethyl propyl sulfite, 4,6-diethyl propyl sulfite, and 1,3-butylene glycol sulfite. The saturated sulphone includes, for example, 1,3-propane sultone, and 1,4-butane sultone. Examples of the unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, Phenolsaltone, and the like. Examples of the non-cyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

The additive for forming the SEI film may be contained in an appropriate amount depending on the specific kind of the additive, for example, 0.01 to 10 parts by weight based on 100 parts by weight of the electrolytic solution.

On the other hand, the present invention provides a lithium secondary battery comprising the nonaqueous electrolyte solution.

The lithium secondary battery is manufactured by injecting an electrolyte prepared according to the present invention into an electrode structure composed 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 the active material, the binder, and the conductive agent with a solvent to prepare a slurry, applying the slurry to a current collector such as aluminum, followed by drying and pressing.

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), Li _x MnO ₂ <x <1.3, 0 <a <1, 0 <b <1), Li _x Mn ₂ O ₄ (0.5 <x <1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ , 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 <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), or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

As the anode active material, a carbon material, lithium metal, silicon or tin, which lithium ions can be occluded and released, can be used, and metal oxides such as TiO ₂ and SnO ₂ having a potential with respect to lithium of less than ₂ V are also possible. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, artificial graphite, Kishgraphite, pyrolytic carbon, High-temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes are representative.

The binder serves to bind the active material and the conductive agent to bind to the current collector. The binder binds the active material and the conductive agent and binds the active material to the current collector. The binder includes a binder such as polyvinylidene fluoride, polypropylene, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polyvinyl alcohol, Rubber and the like which are conventionally used in a lithium ion secondary battery can be used.

Conductive agents such as artificial graphite, natural graphite, acetylene black, ketjen black, channel black, lamp black, thermal black, conductive fibers such as carbon fiber and metal fiber, conductive metal oxides such as titanium oxide, metal powders such as aluminum and nickel Can be used.

As the separator, a single olefin or olefin complex such as polyethylene (PE) and polypropylene (PP), polyamide (PA), polyacrylonitrile (PAN), polyethylene oxide (PEO), polypropylene oxide , Polyethyleneglycol diacrylate (PEGA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and the like.

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

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples.

Example  One

<Preparation of electrolytic solution>

Ethylene carbonate and ethylmethyl carbonate were mixed at a weight ratio of 3: 7 to prepare an organic solvent. Next, LiPF ₆ , which is 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 in an amount of 0.5 part by weight based on 100 parts by weight of the mixed solution to prepare an electrolytic solution.

Example  2

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

Example  3

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

Example  4

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

Example  5

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

Example  6

An electrolytic 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 electrolytic 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 electrolytic 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  One

An electrolyte was prepared in the same manner as in Example 1, except that ammonium nitrate was not added.

Comparative Example  2

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

<Manufacture of Battery>

As a cathode active material LiNi _{0 .5 Co 0 .2 Mn 0 .3 O} 2, the carbon black, polyvinylidene fluoride (PVdF) as a binder and a conductive material 91.5: 4.4: 4.1 were mixed in a weight ratio of, N- methyl Pyrrolidone to prepare a positive electrode slurry. The slurry was coated on an aluminum current collector, followed by drying and rolling to prepare a positive electrode.

Lithium metal (CHEM METAL) having a thickness of 1 mm was used as a cathode.

Then, a coin cell was prepared by using a porous polyethylene membrane (manufactured by Tonen Co., Ltd.) as a separator together with the prepared positive electrode and negative electrode, and injecting the prepared electrolyte solution.

<Evaluation method>

(1) Charging / discharging efficiency

The prepared coin cell was allowed to stand at a constant temperature of 25 DEG C for 24 hours and then subjected to a constant current of 0.1 C at a constant current of 4.2 V using a lithium secondary battery charge / discharge device (Toyo-System Co., LTD, TOSCAT- C was charged under a constant voltage condition with a termination current and discharged at 0.1 C under a constant current condition to 3.0 V to measure the charging and discharging capacity of the first cycle and the charging and discharging efficiency was calculated according to the following equation, And efficiency.

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

(2) Average voltage

The prepared coin cell was charged and discharged in the region of 3.0 to 4.2 V at a rate of 0.2 C, and a voltage (charge average voltage) and a discharge voltage of 50% in the depth of discharge (DOC) (DOD) (discharge average voltage) were measured, and the results are shown in Table 1 below. The difference between the charge average voltage and the discharge average voltage was calculated and expressed as a voltage difference.

(3) Rate characteristics

Table 1 shows discharge capacities of the prepared coin cells according to their respective c-rates after charging and discharging in the region of 3.0 to 4.2 V at 0.5 C, 1.0 C, 1.5 C and 2.0 C, respectively. The ratio of the discharge capacity at 0.5 C, 1.0 C, 1.5 C, and 2.0 C versus the discharge capacity at the c-rate of 0.5 C is shown in FIG.

0.1C / 0.1C ( mAh ) 0.2C / 0.2C (V) Rate characteristic  ( mAh ) Charging capacity Discharge capacity Charging and discharging  efficiency Charge average voltage Discharge average voltage Voltage difference 0.5C discharge 1.0C discharge 1.5 C 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 charging and discharging at 0.1C, and 0.2C / 0.2C means charging and discharging at 0.2C.

As shown in Table 1, the coin cells of Examples 1 to 8, in which the additive according to the present invention was used as an electrolytic solution, showed that the difference in average voltage generated during charging and discharging was remarkably reduced as compared with Comparative Examples 1 and 2 And it can be seen that the resistance in the cell is reduced. As the resistance decreases, it can be seen that the charging / discharging efficiency is improved when charging / discharging is performed with a constant current.

1 and FIG. 1 showing the results of the high-rate discharge characteristics of the coin cell using the electrolytic solution prepared according to Examples 1 to 8 and Comparative Examples 1 and 2, It can be confirmed that the coin cell has improved high-rate characteristics as compared with the coin cells of the comparative examples 1 and 2.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments but is to be construed as being limited only by the appended claims. Should be construed as being included in the scope of the present invention.

Claims (7)

1. An electrolyte for a lithium secondary battery comprising a lithium salt and an organic solvent,
Wherein the electrolytic solution further comprises a nitrate salt represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]

In Formula 1, R ₁ to R ₄ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms. The method according to claim 1,
The compound represented by the above formula (1) may be at least one selected from the group consisting of ammonium nitrate, tetramethylammonium nitrate, tetraethylammonium nitrate, tetrabutylammonium nitrate, monoethyltrimethylammonium And at least one selected from the group consisting of monoethyltrimethylammonium nitrate, monobutyltrimethylammonium nitrate, diethyldimethylammonium nitrate and dibutyldimethylammonium nitrate. A non-aqueous electrolyte for a lithium secondary battery. The method according to claim 1,
Wherein 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. The method according to claim 1,
The anion of the lithium salt is selected from the group consisting of 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 ^- And an electrolyte solution for a lithium secondary battery. The method according to claim 1,
Wherein the organic solvent is at least one selected from the group consisting of ether, ester, amide, linear carbonate and cyclic carbonate. The method according to claim 1,
Wherein the electrolytic solution further comprises at least one selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone, and acyclic sulphone. A lithium secondary battery comprising the electrolyte according to any one of claims 1 to 6.

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