KR102086532B1 - Non-aqueous electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention comprises: i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); And ii) lithium bis (fluorosulfonyl) imide (LiFSI) and a non-aqueous electrolyte solution containing one or more selected from the group consisting of trimethylene sulfate-based compounds represented by Formula 1; It provides a lithium secondary battery.
The non-aqueous electrolyte of the present invention can improve the low temperature and room temperature output characteristics by forming a solid SEI film at the negative electrode during initial charging of the lithium secondary battery including the same, as well as high temperature and room temperature cycle characteristics, and capacity characteristics after high temperature storage. Can improve.

Description

Non-aqueous electrolyte solution and lithium secondary battery comprising the same {NON-AQUEOUS ELECTROLYTE SOLUTION AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention is a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); And a non-aqueous electrolyte including lithium bis (fluorosulfonyl) imide (LiFSI) and a trimethylene sulfate-based compound represented by Formula 1, and a lithium secondary battery including the same.

As the technology development and demand for the Korean technology increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, crystalline or amorphous carbon or a carbon composite material is used as a negative electrode active material. The active material is applied to a current collector with a suitable thickness and length, or the active material itself is coated in a film shape to be wound or laminated with a separator, which is an insulator, to form an electrode group, and then placed in a can or a similar container, followed by injecting an electrolyte solution. A secondary battery is manufactured.

In such a lithium secondary battery, charging and discharging proceed while repeating a process of intercalating and deintercalating lithium ions from a lithium metal oxide of a positive electrode to a graphite electrode of a negative electrode. At this time, since lithium is highly reactive, it reacts with the carbon electrode to generate Li ₂ CO ₃ , LiO, LiOH, and the like to form a film on the surface of the negative electrode. Such a film is called a solid electrolyte interface (SEI) film, and the SEI film formed at the beginning of charging prevents a reaction between lithium ions and a carbon anode or other material during charging and discharging. It also acts as an ion tunnel to pass only lithium ions. This ion tunnel serves to prevent the organic solvents of the large molecular weight electrolytes that solvate lithium ions and move together to co-intercalate the carbon anodes to disrupt the structure of the carbon anodes. do.

Therefore, in order to improve the high temperature cycle characteristics and the low temperature output of the lithium secondary battery, a solid SEI film must be formed on the negative electrode of the lithium secondary battery. Once formed, the SEI membrane prevents the reaction between lithium ions and the negative electrode or other materials during repeated charge and discharge cycles by using a battery, and serves as an ion tunnel that passes only lithium ions between the electrolyte and the negative electrode. Will be performed.

To date, various non-aqueous organic solvents have been used in the non-aqueous electrolyte, and propylene carbonate is used as the non-aqueous organic solvent, but this has a problem of causing an irreversible decomposition reaction with the graphite material. To replace this, two- and three-component non-aqueous organic solvents including ethylene carbonate (EC) as a base have been used. However, ethylene carbonate has a high melting point and thus has a limited use temperature, and has a problem of causing significant battery performance deterioration at low temperatures.

KR 2009-0030237 A

The problem to be solved by the present invention is not only to improve the low temperature and room temperature output characteristics, but also to a non-aqueous electrolyte that can improve the room temperature and high temperature cycle characteristics, and capacity characteristics after high temperature storage, and a lithium secondary battery comprising the same To provide.

In order to solve the above problems, the present invention is i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); And ii) lithium bis (fluorosulfonyl) imide (LiFSI) and a trimethylene sulfate-based compound represented by Formula 1 below.

[Formula 1]

In Formula 1, R ₁ to R ₃ are each independently hydrogen, alkyl having 1 to 12 carbon atoms, alkoxy having 1 to 6 carbon atoms or halogen.

In addition, the present invention includes a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; A separator interposed between the positive electrode and the negative electrode; And it provides a lithium secondary battery comprising the non-aqueous electrolyte.

The non-aqueous electrolyte of the present invention can improve the low temperature and room temperature output characteristics by forming a solid SEI film at the negative electrode during initial charging of the lithium secondary battery including the same, as well as high temperature and room temperature cycle characteristics, and capacity characteristics after high temperature storage. Can improve.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concepts of terms in order to best describe their invention. It should be interpreted as meanings and concepts corresponding to the technical idea of the present invention based on the principle that the present invention.

The non-aqueous electrolyte solution of the present invention comprises: i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC); And ii) lithium bis (fluorosulfonyl) imide (LiFSI) and at least one member selected from the group consisting of trimethylene sulfate-based compounds represented by Formula 1 below.

[Formula 1]

In Formula 1, R ₁ to R ₃ are each independently hydrogen, alkyl having 1 to 12 carbon atoms, alkoxy having 1 to 6 carbon atoms or halogen.

As used herein, the term 'alkyl' means a straight, cyclic or branched hydrocarbon moiety unless stated otherwise.

As used herein, the term "alkoxy" refers to -OR _a unless stated otherwise. Group, where R _a is alkyl as defined above. Specific examples include, but are not limited to, methoxy, ethoxy, n -propoxy, isopropoxy, n -butoxy, t -butoxy, and the like.

As used herein, the term "halogen" means fluorine, chlorine, bromine or iodine unless otherwise noted.

According to one embodiment of the present invention, by adjusting the mixing ratio of propylene carbonate (PC) and ethylene carbonate (EC), which is a non-aqueous organic solvent, to solve the problems that occur when using each of propylene carbonate (PC) and ethylene carbonate (EC) By utilizing the advantages of each of these solvents, synergistic effects due to the mixing of non-aqueous organic solvents can be expressed. In addition, lithium bisfluorosulfonylimide is included under these mixed non-aqueous organic solvents, so that a solid SEI film is formed at the cathode during initial charging, so that the cathode may be generated during high temperature cycle operation as well as low temperature and room temperature output characteristics. It is possible to simultaneously improve the capacity characteristics of the lithium secondary battery by suppressing the decomposition of the surface and preventing the oxidation reaction of the electrolyte, and the trimethylene sulfate-based compound represented by Formula 1 is added to the non-aqueous electrolyte as a low resistance additive, It is possible to improve the output by lowering the resistance of the lithium secondary battery including, to form a stable layer when forming the SEI film, it is possible to improve the high temperature storage characteristics and life characteristics.

In general, ethylene carbonate (EC) as a non-aqueous organic solvent used in non-aqueous electrolytes has been mainly used in lithium secondary batteries due to its excellent affinity with carbon materials. However, when EC is used too much, CO ₂ gas is generated due to EC decomposition, which may adversely affect the performance of the secondary battery, and low temperature characteristics are poor due to high melting point characteristics and low conductivity. As a result, there is a problem in that the high power characteristic is low.

On the contrary, the non-aqueous electrolyte containing propylene carbonate has a characteristic of having high output characteristics due to excellent low temperature characteristics and high conductivity. However, propylene carbonate has a problem in that it is limited in use with graphite because it causes an irreversible decomposition reaction with the graphite material. In addition, there is a problem that a capacity decrease of the lithium secondary battery occurs due to electrode exfoliation due to propylene carbonate at high temperature cycles depending on the electrode thickness.

In particular, when propylene carbonate is used together with a lithium salt such as LiPF ₆ as a non-aqueous organic solvent, propylene carbonate may form a SEI film in a lithium secondary battery using a carbon electrode, and lithium ions solvated by propylene carbonate. Enormous capacity of irreversible reactions can occur in the intercalation between these carbon layers. This may cause a problem that the performance of the battery, such as cycle characteristics, decreases.

In addition, when lithium ions solvated by propylene carbonate are inserted into the carbon layer constituting the negative electrode, exfoliation of the carbon surface layer may proceed. This delamination can be caused by the gas generated when the solvent decomposes between the carbon layers causing a large distortion between the carbon layers. Such peeling of the surface layer and decomposition of the electrolyte may proceed continuously. As a result, when the propylene carbonate electrolyte is used in combination with the carbon-based negative electrode material, an effective SEI film may not be generated and lithium ions may not be inserted.

Thus, in the present invention, in order to overcome the problems of ethylene carbonate and propylene carbonate, and to maximize the above advantages, by mixing the amount of propylene carbonate to the existing ethylene carbonate in an appropriate composition in a non-aqueous organic solvent, It is possible to provide a non-aqueous electrolyte having excellent electrochemical affinity with a carbon layer by improving conductivity characteristics, improving output characteristics of a lithium secondary battery, and improving low temperature characteristics.

In addition, in the present invention, the above problems when the propylene carbonate and lithium salts such as LiPF ₆ are used together can be solved by combining them using lithium bisfluorosulfonylimide.

The lithium bisfluorosulfonylimide is added to the non-aqueous electrolyte as a lithium salt to form a stable and stable SEI film on the negative electrode to improve low temperature output characteristics and to suppress decomposition of the positive electrode surface that may occur during high temperature cycle operation. And oxidation reaction of electrolyte solution can be prevented.

According to one embodiment of the present invention, the mixing ratio of the propylene carbonate and the ethylene carbonate (EC) solvent as the non-aqueous organic solvent may have a significant effect in improving both low temperature and room temperature output, and capacity characteristics after high temperature storage.

The mixing ratio of propylene carbonate and ethylene carbonate (EC) may be, for example, 1: 0.1 to 2 weight ratio, preferably 1: 0.3 to 1, more preferably 1: 0.4 to 0.9, and satisfies the range of the mixing ratio. Synergistic effect by mixing two non-aqueous organic solvent may be expressed.

Propylene carbonate as the non-aqueous organic solvent according to one embodiment of the present invention may be included in an amount of 5 to 60 parts by weight, specifically 10 to 40 parts by weight based on 100 parts by weight of the non-aqueous organic solvent. When the content of the propylene carbonate is less than 5 parts by weight, a swelling phenomenon may occur in which a gas is continuously generated due to decomposition of the surface of the positive electrode during a high temperature cycle, and an initial rechargeable battery negative electrode may exceed 60 parts by weight. It is difficult to form a solid SEI film at, and high temperature properties may be degraded.

According to an embodiment of the present invention, by appropriately adjusting the ethylene carbonate within the amount of the propylene carbonate used within the mixing ratio, the low temperature and room temperature output characteristics of the lithium secondary battery of the present invention, as well as capacity characteristics after high temperature storage Can achieve the optimum effect.

According to an embodiment of the present invention, in addition to the ethylene carbonate (EC) and propylene carbonate, as a non-aqueous organic solvent that may be further included in the non-aqueous electrolyte, decomposition by an oxidation reaction or the like during charging and discharging of the battery may be minimized. There is no limitation as long as it can exhibit the desired properties with the additive.

Non-aqueous organic solvents that may be further included in the non-aqueous electrolyte according to an embodiment of the present invention, for example, ethyl propionate (EP), methyl propionate (MP), butylene carbonate ( BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) One, or mixtures of two or more thereof.

Meanwhile, according to one embodiment of the present invention, the lithium bisfluorosulfonylimide may have a concentration in the non-aqueous electrolyte solution of 0.1 mol / L to 2 mol / L, and specifically 0.5 mol / L to 1.5 mol / L Can be. When the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mol / L, the effect of improving the low temperature output and the high temperature cycle characteristics of the battery may be insignificant, and the concentration of the lithium bisfluorosulfonylimide is 2 If the mol / L exceeds, the side reaction in the electrolyte is excessively generated during charging and discharging of the battery may cause a swelling phenomenon.

In order to further prevent such side reactions, the non-aqueous electrolyte of the present invention may further include a lithium salt. The lithium salt may be used a lithium salt commonly used in the art, for example LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ And LiC ₄ BO _{8 It} may be any one selected from the group consisting of or a mixture of two or more thereof.

The mixing ratio of the lithium salt and lithium bisfluorosulfonylimide may be 1: 1 to 9 in a molar ratio. When the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide is out of the range of the molar ratio, side reactions in the electrolyte may be excessively generated during charging and discharging of the battery, and a swelling phenomenon may occur.

Specifically, the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide may be 1: 6 to 9 as a molar ratio. For example, when the mixing ratio of the lithium salt and lithium bisfluorosulfonylimide is 1: 6 or more in molar ratio, a process of forming an SEI film in a lithium ion battery, and lithium ions solvated by propylene carbonate and ethylene carbonate It can prevent the irreversible reaction of enormous capacity in the process of being inserted between the negative electrodes, suppresses the peeling of the negative electrode surface layer (for example, the carbon surface layer) and decomposition of the electrolyte solution, thereby improving the low-temperature output of the secondary battery, high temperature storage After that, the effect of improving cycle characteristics and capacity characteristics can be exerted.

In one example of the present invention, the trimethylene sulfate-based compound represented by Formula 1 may be specifically R ₁ to R ₃ are each independently alkyl having 1 to 6 carbon atoms, more specifically represented by the following Formula 2 One of R ₁ or R ₃ may be methyl, and R ₂ and The other one of R ₁ or R ₃ other than methyl may be a compound (methyl trimethylene sulfate) which is hydrogen.

[Formula 2]

The content of the trimethylene sulfate-based compound represented by Formula 1 may be 0.01 to 3% by weight, specifically 0.05 to 2% by weight, and more specifically 0.6 to 1.5% by weight based on the total weight of the nonaqueous electrolyte. Can be.

When the content of the trimethylene sulfate-based compound is 0.01% by weight or more, an appropriate effect may be expected due to the addition of trimethylene sulfate-based compound, and when the content of the trimethylene sulfate-based compound is 3% by weight or less, an appropriate high temperature It is possible to prevent problems such as increasing the irreversible capacity of the battery or increasing the resistance of the battery while lowering the output and generating gas due to side reactions while exhibiting the synergistic effect of the storage and life characteristics.

The content of the trimethylene sulfate-based compound represented by Formula 1 may be adjusted according to the amount of lithium bis fluoro sulfonyl imide added, and thus the lithium bis fluoro sulfonyl imide and trimethylene sulfate-based compound may be 1: 0.001. It may be used in a weight ratio of 5 to 5, specifically, it may be used in a weight ratio of 1: 0.005 to 3, and more specifically may be used in a weight ratio of 1: 0.01 to 2.5.

On the other hand, a lithium secondary battery according to an embodiment of the present invention is a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; A separator interposed between the positive electrode and the negative electrode; And it may include the non-aqueous electrolyte.

Here, the positive electrode active material may include a manganese spinel-based active material, lithium metal oxide, or a mixture thereof. Furthermore, the lithium metal oxide may be selected from the group consisting of lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide, and lithium-nickel-manganese-cobalt oxide, and more specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _{1 - Y} Co _Y O ₂ , LiCo _{1 - Y} Mn _Y O ₂ , LiNi _{1 - Y} Mn _Y O ₂ (where 0 ≦ Y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _{2 - z} Ni _z O ₄ , LiMn _{2 - z} Co _z O ₄ (Where 0 <Z <2).

Meanwhile, as the negative electrode active material, a carbon-based negative electrode active material such as crystalline carbon, amorphous carbon or a carbon composite may be used alone or in combination of two or more thereof. Preferably, the crystalline carbon is graphite such as natural graphite and artificial graphite. (graphite) carbon.

Specifically, in the lithium secondary battery, the positive electrode or the negative electrode, for example, on the positive electrode or negative electrode current collector to prepare a slurry by mixing a mixture of a positive electrode or negative electrode active material, a conductive agent and a binder with a predetermined solvent, This slurry can be prepared by applying it onto a current collector and then drying it.

According to one embodiment of the invention, the positive electrode current collector is generally made of a thickness of 3 ㎛ to 500 ㎛. 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, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver, or the like can be used.

The positive electrode current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, 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 negative electrode current collector is generally made to a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and 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, and aluminum-cadmium alloys may 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 conductive agent used in the positive electrode or negative electrode slurry is typically added in an amount of 1 to 20 wt% based on the total weight of the mixture including the positive electrode or the negative electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent 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 whiskers such as zinc oxide and potassium titanate; Conductive 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 positive electrode or the negative electrode active material and the conductive agent to the current collector, and is usually added in an amount of 1 to 20 wt% based on the total weight of the mixture including the positive electrode or the negative electrode active material. Examples of such binders include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and polymethylmethacrylate. ), Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM ), Various types of binder polymers, such as sulfonated EPDM, styrene butyrene rubber (SBR), fluorine rubber, various copolymers, and the like may be used.

In addition, preferred examples of the solvent include dimethyl sulfoxide (DMSO), alcohol, N-methylpyrrolidone (NMP), acetone or water and the like, and are removed in a drying process.

The separator may be a conventional porous polymer film conventionally used as a separator, for example, a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer The porous polymer film made of a polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. no.

The battery case used in the present invention may be adopted that is commonly used in the art, there is no limitation on the appearance according to the use of the battery, for example, cylindrical, square, pouch type or coin using a can (coin) type, etc.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source of a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells. Preferred examples of the medium-to-large device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Although the following Examples and Experimental Examples are further described, the present invention is not limited to these Examples and Experimental Examples.

Example 1

[Production of non-aqueous electrolyte solution]

Propylene carbonate (PC): Ethylene carbonate (EC): Ethylmethyl carbonate (EMC): LiPF ₆ based on the total amount of the non-aqueous electrolyte as a non-aqueous organic solvent and lithium salt having a composition of 3: 3: 4 (volume ratio). 0.1 mol / l was added, and 0.9 mol / l of lithium bisfluorosulfonylimide and 1 wt% of methyltrimethylene sulfate were added to prepare a non-aqueous electrolyte solution.

 [Manufacture of Lithium Secondary Battery]

96% by weight of a mixture of LiMn ₂ O ₄ and Li (Ni _0.33 Co _0.33 Mn _0.33 ) O ₂ as a positive electrode active material, ₂ % by weight carbon black as a conductive agent, 2% by weight polyvinylidene fluoride (PVdF) as a binder Was added to a solvent, N-methyl-2-pyrrolidone (NMP), to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then subjected to roll press to prepare a positive electrode.

Also, a negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive agent at 96 wt%, 3 wt%, and 1 wt%, respectively, to NMP as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film, which is a negative electrode current collector having a thickness of about 10 μm, dried to prepare a negative electrode, and then roll-rolled to prepare a negative electrode.

The positive electrode and the negative electrode prepared as described above were manufactured in a conventional manner with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), and then the non-aqueous electrolyte solution was prepared to be injected into a lithium secondary battery. The manufacture of the battery was completed.

Example 2

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the amount was changed to 0.14 mol / l and 0.86 mol / l of lithium bisfluorosulfonylimide (about 1: 6 molar ratio). Was prepared.

Example 3

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the amount was changed to 0.17 mol / l and 0.83 mol / l (about 1: 5 molar ratio) of lithium bisfluorosulfonylimide. Was prepared.

Example 4

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.5 wt% of methyltrimethylene sulfate was used.

Example 5

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that the methyltrimethylene sulfate was used at 0.5% by weight.

Example 6

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2 except that the methyltrimethylene sulfate was used at 3% by weight.

Example 7

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that trimethylene sulfate was used in place of the methyl trimethylene sulfate.

Comparative Example 1

In the same manner as in Example 1, except that ethylene carbonate (EC) was not used and a non-aqueous organic solvent having a composition of propylene carbonate (PC): ethylmethyl carbonate (DMC) = 3: 7 (volume ratio) was used. A nonaqueous electrolyte solution and a lithium secondary battery were prepared.

Comparative Example 2

In the same manner as in Example 1, except that a non-aqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (DMC) = 3: 7 (volume ratio) was used without using propylene carbonate (PC). A nonaqueous electrolyte solution and a lithium secondary battery were prepared.

Comparative Example 3

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that LiFSI and methyltrimethylene sulfate were not used.

Comparative Example 4

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that LiFSI was not used.

Comparative Example 5

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that methyltrimethylene sulfate was not used.

Experimental Example 1

<High temperature life measurement>

The lithium secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 5 were charged at 1 C up to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions at 45 ° C., followed by constant current (CC) conditions. Was discharged at 2 C up to 2.5 V, and the discharge capacity thereof was measured. This was repeated 1 to 1000 cycles, and the capacity after 1000 cycles is calculated as a capacity after 100 cycles / 1 capacity after a cycle # 100 and is shown in Table 1 as a% value.

Experimental Example 2

Capacity characteristics after high temperature storage

The secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 5 were charged at 1 C to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions, and then to 2.5 V under constant current (CC) conditions. It discharged at 2 C, and the discharge capacity was measured. Then, after storing the secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 5 for 16 weeks at 60 ° C., the secondary batteries were again subjected to constant current / constant voltage (CC / CV) conditions at room temperature of 4.2 V / 38. Charged at 1 C until mA, then discharged at 2 C up to 2.5 V under constant current (CC) conditions, the discharge capacity was measured. The results measured by calculating the discharge capacity after 16 weeks as a percentage (discharge capacity after 16 weeks / initial discharge capacity * 100 (%)) based on the initial discharge capacity are shown in Table 1 below.

Experimental Example 3

<Output characteristics after high temperature storage>

The secondary battery prepared in Examples 1 to 7, and Comparative Examples 1 to 5 and the output was calculated using the voltage difference generated when charging and discharging for 10 seconds at 5 ° C at room temperature after 16 weeks storage at 60 ℃. The results measured by calculating the output after 16 weeks as a percentage based on the initial output (16 weeks output (W) / initial output (W) * 100 (%)) are shown in Table 1 below. The test was performed at 50% of SOC (state of charge).

Experimental Example 4

<Measurement of battery thickness increase rate>

The thickness of the secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 5 was measured, and the thickness after storage at 60 ° C. for 16 weeks was measured to determine the rate of increase in battery thickness (thickness of thickness / week 0 after 100 weeks 주 100 It is shown in Table 1 as a% value calculated as) -100.

LiPF ₆ : LiFSI additive
(weight%) Life characteristic
(%) High Temperature Storage Characteristics
(%) Volume Print Battery thickness
increase Example 1 1: 9 MTMS 1 91.6 84.1 81.2 5.3 Example 2 1: 6 MTMS 1 96.3 85.4 88.5 4.5 Example 3 1: 5 MTMS 1 86.4 80.6 79.8 4.9 Example 4 1: 9 MTMS 0.5 85.4 74.4 60.1 5.69 Example 5 1: 6 MTMS 0.5 88.3 82.6 58.6 6.12 Example 6 1: 6 MTMS 3 76.4 64.5 30.8 10.53 Example 7 1: 6 TMS 1 95.4 83.5 45.6 6.67 Comparative Example 1 1: 9 MTMS 1 78.6 67.6 56.3 10.4 Comparative Example 2 1: 9 MTMS 1 67.9 72.3 69.3 9.6 Comparative Example 3 1: 0 0 78.7 70.9 35.2 6.8 Comparative Example 4 1: 0 MTMS 1 81.9 72.9 38.5 6.64 Comparative Example 5 1: 9 0 84.2 73.2 58.6 6.3

In Table 1, MTMS represents methyltrimethylene sulfate, and TMS represents trimethylene sulfate.

Referring to Table 1, the lithium secondary batteries of Examples 1 to 3 are lithium bisfluorosulfonyl imide and methyltrimethylene sulfate together with a non-aqueous organic solvent including propylene carbonate (PC) and ethylene carbonate (EC). Comparative Example 1 does not include ethylene carbonate (EC) as a non-aqueous organic solvent, Comparative Example 2 does not include propylene carbonate (PC) as a non-aqueous organic solvent, lithium bisfluorosulfonylimide and methyl Compared with the lithium secondary battery of Comparative Example 3, which does not contain trimethylene sulfate, and Comparative Example 4, which does not contain lithium bisfluorosulfonylimide, exhibits high capacity and output even after high temperature storage with high normal temperature life characteristics. In addition, the increase rate of the battery thickness also showed a small value, it was confirmed that the excellent high temperature storage characteristics.

On the other hand, looking at the effects of the addition of lithium bisfluorosulfonylimide, when comparing the lithium secondary batteries of Example 1 and Comparative Example 4, which differ only in the addition of lithium bisfluorosulfonylimide, It was confirmed that the lithium secondary battery of Example 1 exhibited excellent excellent high-temperature storage characteristics and lifetime characteristics according to the addition of lithium bisfluorosulfonylimide, and showed excellent normal-temperature lifetime characteristics. In addition, looking at the effect of the addition amount of lithium bisfluorosulfonylimide, in the case of the lithium secondary battery of Example 1 having a LiPF ₆ : LiFSI ratio of 1: 9, Example 3 having a ratio of 1: 5 It showed somewhat better high temperature storage characteristics than lithium secondary battery.

In addition, looking at the effect of the addition of the trimethylene sulfate-based compound, when comparing the lithium secondary battery of Example 1 and Comparative Example 5, which differ only in the addition of methyltrimethylene sulfate, the lithium secondary battery of Example 1 The addition of methyltrimethylene sulfate resulted in better room temperature life characteristics, and better output after high temperature storage.

On the other hand, when looking at the effect of the addition amount of methyltrimethylene sulfate, in the case of Examples 1 to 5 containing 0.5 to 1% by weight of methyltrimethylene sulfate relative to the total weight of the non-aqueous electrolyte solution 3% by weight of methyltrimethylene sulfate Excellent effect compared to Example 6,

Claims (17)

i) a non-aqueous organic solvent comprising propylene carbonate (PC) and ethylene carbonate (EC);
ii) lithium salts;
iii) Lithium bis (fluorosulfonyl) imide (LiFSI) and
iv) a trimethylene sulfate-based compound represented by Formula 1 below,
The lithium bis fluoro sulfonyl imide: the trimethylene sulfate-based compound represented by Formula 1 may include a nonaqueous electrolyte comprising a weight ratio of 1: 0.005 to 1: 3:
[Formula 1]

In Formula 1, R ₁ to R ₃ are each independently hydrogen, alkyl having 1 to 12 carbon atoms, alkoxy having 1 to 6 carbon atoms or halogen.
The method of claim 1,
The mixing ratio of the propylene carbonate and ethylene carbonate is 1: 0.1 to 2 by weight ratio non-aqueous electrolyte.
delete The method of claim 1,
The mixing ratio of the lithium salt and lithium bisfluorosulfonylimide is 1: 1 to 9 as the molar ratio.
The method of claim 4, wherein
The mixing ratio of the lithium salt and lithium bisfluorosulfonylimide is 1: 6 to 9 as a molar ratio nonaqueous electrolyte.
The method of claim 1,
The lithium bisfluorosulfonyl imide has a concentration in the non-aqueous electrolyte solution of 0.1 mol / L to 2 mol / L non-aqueous electrolyte.
The method of claim 1,
The content of the propylene carbonate is 5 parts by weight to 60 parts by weight based on 100 parts by weight of the non-aqueous organic solvent.
The method of claim 7, wherein
The content of the propylene carbonate is 10 parts by weight to 40 parts by weight based on 100 parts by weight of the non-aqueous organic solvent.
The method of claim 1,
The R ₁ to R ₃ are each independently hydrogen or alkyl having 1 to 6 carbon atoms.
The method of claim 1,
Any one of R ₁ or R ₃ is methyl, R ₂ , and A non-aqueous electrolyte solution other than methyl of R ₁ or R ₃ is hydrogen.
The method of claim 1,
The content of the trimethylene sulfate-based compound represented by Formula 1 is 0.01% to 3% by weight based on the total weight of the nonaqueous electrolyte.
The method of claim 1,
The content of the trimethylene sulfate-based compound represented by Formula 1 is 0.05% to 2% by weight based on the total weight of the nonaqueous electrolyte. The method of claim 1,
The non-aqueous organic solvent is ethyl propionate (EP), methyl propionate (MP), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl Non-aqueous electrolyte further comprising any one selected from the group consisting of carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC), or a mixture of two or more thereof.
The method of claim 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) A non-aqueous electrolyte solution which is any one selected from the group consisting of ₃ and LiC ₄ BO ₈ or a mixture of two or more thereof.
A positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; A separator interposed between the positive electrode and the negative electrode; And
A lithium secondary battery comprising the nonaqueous electrolyte of claim 1.
The method of claim 15,
The cathode active material is a lithium secondary battery which is a manganese spinel-based active material, lithium metal oxide or a mixture thereof.
The method of claim 16,
The lithium metal oxide is a lithium secondary battery selected from the group consisting of lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt-based oxide and lithium-nickel-manganese-cobalt-based oxide.