WO2014081240A1 - Electrolyte for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

The present invention provides: an electrolyte for a lithium secondary battery, the electrolyte containing a lithium salt and a non-aqueous solvent, wherein the lithium salt contains lithium bis(fluorosulfonyl)imide (LiFSI), or lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF₆) and the non-aqueous solvent contains an ether-based solvent; and a lithium secondary battery comprising same.

Description

Electrolyte for lithium secondary battery and lithium secondary battery comprising same

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Recently, the use of secondary batteries as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized. It is becoming. Accordingly, many studies have been conducted on secondary batteries capable of meeting various needs, and in particular, there is a high demand for lithium secondary batteries having high energy density, high discharge voltage and output stability.

In particular, the lithium secondary battery used in the hybrid electric vehicle has a characteristic that can exhibit a large output in a short time, and must be used for more than 10 years under the harsh conditions in which charging and discharging by a large current is repeated in a short time, the conventional small lithium secondary battery Inevitably, better safety and output characteristics are required than batteries.

In this regard, the conventional lithium secondary battery uses a layered structure of lithium cobalt composite oxide for the positive electrode and a graphite-based material for the negative electrode, but LiCoO ₂ has good energy density and high temperature characteristics. On the other hand, since the output characteristics are poor, the high output temporarily required for oscillation and rapid acceleration, etc., is not suitable for hybrid electric vehicles (HEVs) requiring high power, and LiNiO ₂ has a manufacturing method thereof. Due to the characteristics, it is difficult to apply to the actual mass production process at a reasonable cost, lithium manganese oxides such as LiMnO ₂ , LiMn ₂ O ₄ has the disadvantage that the cycle characteristics are bad.

In recent years, a method of using a lithium transition metal phosphate material as a cathode active material has been studied. Lithium transition metal phosphate materials are classified into Naxicon-structured LixM ₂ (PO ₄ ) ₃ and Olivine-structured LiMPO ₄ , and have been studied as excellent materials at high temperature stability compared to LiCoO ₂ . .

The anode active material has a very low discharge potential of about -3V with respect to the standard hydrogen electrode potential, and exhibits a very reversible charge and discharge behavior due to the uniaxial orientation of the graphite layer, thereby providing excellent electrode life characteristics (cycle Carbon-based active materials showing life) are mainly used.

On the other hand, the lithium secondary battery is prepared by placing a porous polymer separator between the negative electrode and the positive electrode, and put a non-aqueous electrolyte containing a lithium salt such as LiPF ₆ . During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode, and during discharge, lithium ions of the carbon layer are released and inserted into the positive electrode active material, and the non-aqueous electrolyte is lithium ions between the negative electrode and the positive electrode. This serves as a moving medium. Such lithium secondary batteries should basically be stable in the operating voltage range of the battery and have the ability to transfer ions at a sufficiently fast rate.

Conventionally, a carbonate solvent is used as the non-aqueous electrolyte, but the carbonate solvent has a problem that the viscosity increases, and thus the ion conductivity is decreased. Also, when some compounds are used as an electrolyte additive, some performance of the battery is improved, but rather Often, other performance was reduced.

Therefore, there is a need for a detailed study on an electrolyte for lithium secondary batteries showing excellent output and life characteristics.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application have found that LiFSI (lithium bis (fluorosulfonyl) imide) or LiFSI (lithium bis (fluorosulfonyl) imide) and LiPF ₆ (lithium hexa When using the electrolyte solution for secondary batteries which consists of a lithium salt containing a fluoro phosphate) and the non-aqueous solvent containing an ether solvent, it confirmed that a desired effect can be achieved and came to complete this invention.

Accordingly, the present invention provides a lithium secondary battery electrolyte containing a lithium salt and a non-aqueous solvent, wherein the lithium salt is LiFSI (lithium bis (fluorosulfonyl) imide), or LiFSI (lithium bis (fluorosulfonyl) ) Imide) and LiPF ₆ (lithium hexafluoro phosphate), the non-aqueous solvent provides an electrolyte solution for a secondary battery, characterized in that it comprises an ether solvent.

In general, the carbonate solvent has a problem that the viscosity is large, the ion conductivity is small. On the other hand, LiFSI (lithium bis (fluorosulfonyl) imide) of the present invention, as shown in the following structural formula, the sulfonyl imide group (sulfonyl imide group) can lower the interfacial resistance lithium secondary battery comprising the same The output characteristics can be improved at low temperatures as well as at room temperature.

LiFSI (리튬 비스(플루오로설포닐) 이미드)

LiFSI (lithium bis (fluorosulfonyl) imide)

Such LiFSI may be used alone as a lithium salt of an electrolyte for a lithium secondary battery, but when used with LiPF ₆ , the effect may be maximized.

When LiFSI and LiPF ₆ are used together, the content of LiFSI may be 10% by weight or more and less than 100% by weight based on the total weight of the lithium salt, and in detail, 50% by weight or more and less than 100% by weight. When the content of the LiFSI is too small, the output characteristic effect due to the decrease in resistance is not expected, which is not preferable.

The molar concentration of the LiFSI may be 0.1 to 2 M in the electrolyte, and specifically 0.3 to 1.5 M. When the molar concentration of LiFSI is too small, the output characteristic effect due to the decrease in resistance cannot be obtained. When the molar concentration of LiFSI is too small, the viscosity of the electrolyte solution may be increased when the molar concentration of LiFSI is too high.

In this case, the molar concentration of LiPF ₆ may be 0.01 to 1 M in the electrolyte.

The ether solvent may be at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl ether, dimethoxyethane and dibutyl ether, and in detail, may be dimethyl ether or dimethoxyethane.

The electrolyte solution may further include a carbonate solvent.

In this case, the ether solvent and the carbonate solvent may be 10:90 to 90:10 based on the total volume ratio of the electrolyte, and in detail, 20:80 to 80:10. When the content of the carbonate solvent is too high, the ion conductivity of the electrolyte may be deteriorated due to the carbonate solvent having a high viscosity. If the content of the carbonate solvent is too small, the lithium salt may not be dissolved in the electrolyte, resulting in low ion dissociation. It can be undesirable.

The carbonate solvent may be, for example, a cyclic carbonate, and the cyclic carbonate may be ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2 At least one selected from the group consisting of -pentylene carbonate, and 2,3-pentylene carbonate.

In addition, the carbonate-based solvent may further include a linear carbonate, the linear carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl It includes at least one selected from the group consisting of carbonate (MPC) and ethyl propyl carbonate (EPC), in which case the cyclic carbonate and linear carbonate has a mixing ratio of 1: 4 to 4: 1 ratio based on the carbonate solvent volume ratio Can be.

The present invention provides a lithium secondary battery that is configured to include the electrolyte solution for lithium secondary batteries.

The lithium secondary battery, (i) a positive electrode containing a lithium metal phosphate of the formula (1) as a positive electrode active material; And

Li _{1 + a} M (PO _4-b ) X _b (1)

In the above formula, M is at least one member selected from the group consisting of metals of Groups 2 to 12; X is at least one selected from F, S and N, and -0.5≤a≤ + 0.5, and 0≤b≤0.1.

and (ii) a negative electrode containing amorphous carbon as the negative electrode active material.

In detail, the lithium metal phosphate may be lithium iron phosphate having an olivine crystal structure of Formula 2 below.

Li _{1 + a} Fe _1-x M ' _x (PO _4-b ) X _b (2)

Wherein M 'is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and X is selected from F, S and N At least one selected, -0.5≤a≤ + 0.5, 0≤x≤0.5, and 0≤b≤0.1.

When the values of a, b, and x are outside the above ranges, the conductivity may be lowered, the lithium iron phosphate may not be able to maintain the olivine structure, and the rate characteristics may deteriorate or the capacity may be lowered.

More specifically, the lithium iron phosphate of the olivine crystal structure may include LiFePO ₄ , Li (Fe, Mn) PO ₄ , Li (Fe, Co) PO ₄ , Li (Fe, Ni) PO ₄ , and the like. In more detail, it can be LiFePO ₄ .

That is, the lithium secondary battery of the present invention is yet to address the internal increased resistance problems that may result from the low electronic conductivity of the LiFePO ₄ by applying the LiFePO ₄ and applying an amorphous carbon as an anode active material to cathode active material, superior high-temperature stability and output Can exhibit characteristics.

Furthermore, when the predetermined electrolyte solution according to the present invention is applied together, it can exhibit excellent room temperature and low temperature output characteristics as compared with the case of using a carbonaceous solvent.

The lithium metal phosphate may be composed of secondary particles in which primary particles and / or primary particles are physically aggregated.

The average particle diameter of the primary particles is 1 nanometer to 300 nanometers, the average particle diameter of the secondary particles may be 1 micrometer to 40 micrometers, and in detail, the average particle diameter of the primary particles is 10 nanometers to 100 nanometers, and the average particle diameter of the secondary particles may be 2 micrometers to 30 micrometers, and more specifically, the average particle diameter of the secondary particles may be 3 micrometers to 15 micrometers.

If the average particle diameter of the primary particles is too large, the desired ion conductivity improvement cannot be exhibited. If too small, the battery manufacturing process is not easy. If the average particle diameter of the secondary particles is too large, the bulk density decreases. When too small, process efficiency cannot be exhibited and it is not preferable.

The specific surface area (BET) of these secondary particles can be 3 to 40 m ² / g.

The lithium iron phosphate of the olivine crystal structure may be coated with, for example, conductive carbon in order to increase electronic conductivity, and in this case, the content of the conductive carbon may be 0.1 wt% to 10 wt% based on the total weight of the positive electrode active material. It may be, in detail may be 0.5% to 5% by weight. When the amount of the conductive carbon is too large, the amount of lithium metal phosphate is relatively decreased, so that the overall battery characteristics are reduced. When the amount is too small, the electron conductivity improvement effect cannot be exhibited, which is not preferable.

The conductive carbon may be applied to the surface of each of the primary particles and the secondary particles, for example, coating the surface of the primary particles to a thickness of 0.1 nanometer to 100 nanometers, and the surface of the secondary particles to 1 nanometer to It can be coated to a thickness of 300 nanometers. For the primary particles coated with conductive carbon of 0.5 wt% to 1.5 wt% based on the total weight of the positive electrode active material, the thickness of the carbon coating layer may be about 0.1 nanometers to 2.0 nanometers.

In the present invention, the amorphous carbon is a carbon-based compound except crystalline graphite, and may be, for example, hard carbon and / or soft carbon. When crystalline graphite is used, electrolyte decomposition may occur, which is not preferable.

The amorphous carbon may be prepared by a heat treatment at a temperature of 1800 degrees Celsius or less, for example, hard carbon is prepared by thermal decomposition of a phenol resin or furan resin, and soft carbon is coke, needle coke or pitch (Pitch) ) Can be prepared by carbonizing.

XRD spectrum of the anode to which such amorphous carbon is applied is shown in FIG. 1.

Hereinafter, a configuration of a lithium secondary battery according to the present invention will be described.

The lithium secondary battery includes a cathode prepared by applying the mixture of the cathode active material, the conductive material and the binder as described above on a cathode current collector, followed by drying and pressing, and a cathode manufactured using the same method, in which case, In some cases, a filler may be further added to the mixture.

The positive electrode current collector is generally made in a thickness of 3 micrometers to 500 micrometers. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is typically added in an amount of 1% by weight to 50% by weight based on the total weight of the mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive material to the current collector, and is generally added in an amount of 1% by weight to 50% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode current collector is generally made in a thickness of 3 micrometers to 500 micrometers. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The lithium secondary battery may have a structure in which a lithium salt-containing electrolyte is impregnated into an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 micrometer to 10 micrometers, and the thickness is generally 5 micrometers to 300 micrometers. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing electrolyte is composed of the non-aqueous organic solvent electrolyte and the lithium salt described above, and may additionally include an organic solid electrolyte, an inorganic solid electrolyte, and the like, but are not limited thereto.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymerizers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

In addition, in the electrolyte solution, for the purpose of improving the charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. . In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. Carbonate), PRS (Propene sultone) may be further included.

The present invention provides a battery module comprising the lithium secondary battery as a unit cell and a battery pack including the battery module.

The battery pack may be used as a power source for devices requiring high temperature stability, long cycle characteristics, high rate characteristics, and the like.

Examples of the device may be an electric vehicle including an electric vehicle, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., but the secondary battery according to the present invention Since shows excellent room temperature and low temperature output characteristics, it can be preferably used in a hybrid electric vehicle in detail.

In recent years, research has been actively conducted to use a lithium secondary battery in a power storage device that converts unused power into physical or chemical energy and stores it as an electric energy when needed.

1 is a graph showing the XRD spectrum of the anode to which the amorphous carbon of the present invention is applied;

2 is a graph showing room-temperature output characteristics of lithium secondary batteries in Experimental Example 1;

3 is a graph showing the low-temperature resistance of lithium secondary batteries measured in Experimental Example 2 by electrochemical impedance spectroscopy (EIS);

4 is a graph showing low-temperature output characteristics of lithium secondary batteries in Experimental Example 3;

5 is a graph showing capacity retention rates and resistance increase rates of lithium secondary batteries in Experimental Example 4; And

6 is a graph showing room temperature resistance of lithium secondary batteries in Experimental Example 5. FIG.

<Example 1>

86% by weight of LiFePO ₄ , 8% by weight of Super-P (conductive agent) and 6% by weight of PVdF (binder) were added to NMP as a cathode active material to prepare a cathode mixture slurry. It was coated on one surface of aluminum foil, dried and pressed to prepare a positive electrode.

A negative electrode mixture slurry was prepared by adding 93.5 wt% of soft carbon, 2 wt% of Super-P (conductive agent), 3 wt% of SBR (binder), and 1.5 wt% of thickener as a negative electrode active material to H ₂ O as a solvent, and a copper foil. Coating, drying, and pressing on one side of the negative electrode was prepared.

After preparing the electrode assembly by laminating the positive electrode and the negative electrode using CelgardTM as a separator, 0.1 M LiPF ₆ and 0.9 M of LiPF ₆ were mixed with lithium salt in a mixed solvent of ethylene carbonate and dimethoxyethane in a volume ratio of 8 based on the volume ratio. A lithium secondary battery was prepared by adding a lithium non-aqueous electrolyte solution containing M LiFSI.

<Example 2>

A lithium secondary battery was manufactured in the same manner as in Example 1, except that only 1 M LiFSI was used as the lithium salt in Example 1.

<Example 3>

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.5 M LiPF ₆ and 0.5 M LiFSI were used as lithium salts in Example 1.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1 M LiPF ₆ was used as a lithium salt.

Experimental Example 1

The room temperature output characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 were measured and shown in FIG. 2.

Each cell obtained the resistance of each SOC through HPPC (Hybrid Pulse Power Characterization) test and compared the output at SOC 50%.

According to Figure 2, it can be seen that the battery of Example 1 according to the present invention has a higher room temperature output characteristics than the battery of Comparative Example 1.

Experimental Example 2

The lithium secondary batteries prepared in Example 1 and Comparative Example 1 were shown in FIG. 3 by measuring AC impedance by EIS (Electrochemical Impedance Spectroscopy) at a low temperature of 30 degrees Celsius.

Each cell was cooled to 30 degrees Celsius at room temperature set to 50% SOC, and then measured by comparing the AC impedance.

According to FIG. 3, it can be seen that the battery of Example 1 according to the present invention has higher low temperature resistance characteristics than the battery of Comparative Example 1.

Experimental Example 3

The low-temperature output characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 were measured and shown in FIG. 4.

Each cell was cooled to 30 degrees Celsius at room temperature, set to SOC 50%, and then discharged for 10 seconds at a constant voltage (120 mA) to compare the outputs.

According to Figure 4, it can be seen that the battery of Example 1 according to the present invention has a higher low-temperature output characteristics than the battery of Comparative Example 1.

Experimental Example 4

High temperature durability of the lithium secondary batteries prepared in Example 1 and Comparative Example 1 was measured and shown in FIG. 5.

Each cell was stored at 60 degrees Celsius storage chamber for 1 week at room temperature, adjusted to SOC 50%, followed by room temperature HPPC TEST. Figure 5 shows storage capacity and resistance increase rate by room temperature HPPC TEST after 10 weeks of storage. Indicated.

According to Figure 5, it can be seen that the battery of Example 1 according to the present invention has a higher temperature durability than the battery of Comparative Example 1.

Experimental Example 5

The resistance is measured at room temperature of the lithium secondary batteries prepared in Examples 1 to 3 and shown in FIG. 6.

According to Figure 6, it can be seen that the resistance is lowered at room temperature as the molar concentration of LiFSI used as a lithium salt increases. This is a result of the improved output characteristics due to the reduced resistance caused by LiFSI.

As described above, the secondary battery according to the present invention can increase the ionic conductivity by using an electrolyte solution for a secondary battery comprising a lithium salt containing LiFSI and a non-aqueous solvent containing an ether solvent, and thus, excellent room temperature and low temperature. Output characteristics and improved high temperature life characteristics.

When used with lithium iron phosphate and amorphous carbon of the olivine crystal structure, the battery internal resistance can be reduced, further improving the life characteristics and output characteristics, it can be suitably used for hybrid electric vehicles.

Claims (19)

In a lithium secondary battery electrolyte comprising a lithium salt and a non-aqueous solvent, the lithium salt is LiFSI (lithium bis (fluorosulfonyl) imide), or LiFSI (lithium bis (fluorosulfonyl) imide) and LiPF ₆ (lithium hexafluoro phosphate), wherein the non-aqueous solvent comprises an ether solvent. The method of claim 1, wherein the molar concentration of LiFSI is an electrolyte solution for a lithium secondary battery, characterized in that 0.1 to 2 M in the electrolyte. The lithium secondary battery electrolyte of claim 1, wherein the content of the LiFSI is 10% by weight or more and less than 100% by weight based on the total weight of the lithium salt. The lithium secondary battery electrolyte of claim 1, wherein the content of the LiFSI is 50% by weight or more and less than 100% by weight based on the total weight of the lithium salt. The method of claim 1, wherein the ether solvent is at least one selected from the group consisting of tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl ether, dimethoxyethane and dibutyl ether electrolyte solution for a lithium secondary battery. The electrolyte solution for lithium secondary batteries according to claim 1, wherein the electrolyte solution further comprises a carbonate solvent. The electrolyte of claim 6, wherein the ether solvent: the carbonate solvent is 10:90 to 90:10 based on the total volume ratio of the electrolyte. The method of claim 6, wherein the carbonate solvent is a cyclic carbonate, the cyclic carbonate is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2 A pentylene carbonate, and an electrolyte solution for a lithium secondary battery, characterized in that at least one selected from the group consisting of 2,3-pentylene carbonate. The method of claim 8, wherein the carbonate solvent further comprises a linear carbonate, the linear carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), It is one or more selected from the group consisting of methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC), the cyclic carbonate and linear carbonate has a mixing ratio of 1: 4 to 4: 1 ratio based on the carbonate solvent volume ratio The lithium secondary battery electrolyte characterized by the above-mentioned. A lithium secondary battery comprising the electrolyte for lithium secondary battery according to claim 1. The method of claim 10, wherein the lithium secondary battery, (i) a positive electrode comprising lithium metal phosphate of Formula 1 as a positive electrode active material; And Li _{1 + a} M (PO _4-b ) X _b (1) In the above formula, M is at least one member selected from the group consisting of metals of Groups 2 to 12; X is at least one selected from F, S and N, and -0.5≤a≤ + 0.5, and 0≤b≤0.1. (ii) a negative electrode containing amorphous carbon as a negative electrode active material; lithium secondary battery comprising a. The lithium secondary battery according to claim 11, wherein the lithium metal phosphate is lithium iron phosphate having an olivine crystal structure of Formula 2 below: Li _{1 + a} Fe _1-x M ' _x (PO _4-b ) X _b (2) Where M 'is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, X is at least one selected from F, S and N, -0.5 a +0.5, 0 x 0.5, 0 b 0.1. The lithium secondary battery of claim 12, wherein the lithium iron phosphate of the olivine crystal structure is LiFePO ₄ . 13. The lithium secondary battery of claim 12, wherein the lithium iron phosphate of the olivine crystal structure is coated with conductive carbon. The lithium secondary battery of claim 11, wherein the amorphous carbon is hard carbon and / or soft carbon. A battery module comprising the lithium secondary battery according to claim 10 as a unit cell. A battery pack comprising a battery module according to claim 16. A device comprising a battery pack according to claim 17. 19. The device of claim 18, wherein the device is a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

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