KR20190101772A - Electrolyte Composition and Secondary Battery Using the Same - Google Patents

Abstract

The present invention provides an electrolyte composition comprising a cyclic carbonate compound in which one of adjacent carbon atoms is substituted with a methylene ether group and a non-aqueous solvent, and a secondary battery comprising the electrolyte composition. The electrolyte composition according to the present invention comprises a cyclic carbonate compound in which one of adjacent carbon atoms is substituted with a methylene ether group, thereby lowering the viscosity of the electrolyte composition and increasing ion conductivity to enhance output characteristics and enable fast charging, as well as a stable negative electrode coating formation. Therefore, the life characteristics of the secondary battery can be significantly increased.

Description

Electrolytic solution and secondary battery using the same {Electrolyte Composition and Secondary Battery Using the Same}

The present invention relates to an electrolyte composition and a secondary battery using the same, and more particularly, lowers the viscosity of the electrolyte composition, increases ion conductivity, improves output characteristics, enables high-speed charging, and forms a stable negative electrode film, thereby improving life characteristics. It relates to an excellent electrolyte composition and a secondary battery using the same.

During the initial charging of the lithium secondary battery, lithium ions derived from the positive electrode active material such as lithium metal oxide move to the negative electrode active material such as graphite and are inserted between the layers of the negative electrode active material. At this time, since lithium ions are highly reactive, the electrolyte composition and the carbon constituting the negative electrode active material react on the surface of the negative electrode active material such as graphite to generate compounds such as Li ₂ CO ₃ , Li ₂ O, LiOH, and Li ₂ SO ₄ . These compounds form a SEI (Solid Electrolyte Interface) film, which is a kind of protective film, on the surface of an anode active material such as graphite.

The SEI film acts as an ion tunnel, passing only lithium ions. The SEI film is an effect of such an ion tunnel, and prevents the negative electrode structure from being destroyed by intercalation of an organic solvent molecule having a large molecular weight moving with lithium ions in the electrolyte composition between the layers of the negative electrode active material. Therefore, by preventing contact between the electrolyte composition and the negative electrode active material, decomposition of the electrolyte composition does not occur, and the amount of lithium ions in the electrolyte composition is reversibly maintained to maintain stable charge and discharge.

Accordingly, interest in additives for improving the life characteristics by forming a stable SEI film on the surface of the cathode is increasing. For example, Korean Patent No. 10-0515298 discloses an electrolyte composition using a cyclic carbonate compound substituted with halogen, cyano or nitro as an electrolyte additive.

However, the electrolyte additive is difficult to lower the viscosity of the electrolyte composition, the output characteristics of the secondary battery is difficult or high-speed charging, as well as the flexibility of the formed film is small, cracks are generated by repeated shrinkage expansion of the negative electrode during long-term life evaluation There is a problem that it is difficult to suppress a decrease in battery capacity.

Republic of Korea Patent No. 10-0515298

One object of the present invention is to provide an electrolyte composition excellent in lifespan characteristics by lowering the viscosity of the electrolyte composition and increasing ion conductivity to improve output characteristics, enable high-speed charging, and to form a stable cathode film.

Another object of the present invention is to provide a secondary battery using the electrolyte composition.

On the other hand, the present invention provides an electrolyte solution composition comprising a compound represented by the following formula (1) and a non-aqueous solvent.

[Formula 1]

Where

R is a C ₁ -C ₄ alkyl group, C ₁ -C ₄ haloalkyl group or C ₁ -C ₄ trialkylsilyl group.

On the other hand, the present invention provides a secondary battery comprising the electrolyte composition.

The electrolyte composition according to the present invention includes a cyclic carbonate compound in which one of the adjacent carbon atoms is substituted with a methylene ether group, has a low viscosity and high ion conductivity, thereby improving output characteristics of the secondary battery and enabling high-speed charging, as well as a stable negative electrode film. Formation of the secondary battery can significantly increase the life characteristics of the secondary battery.

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

One embodiment of the present invention relates to an electrolyte solution composition comprising a compound represented by the following formula (1) and a non-aqueous solvent.

[Formula 1]

Where

R is a C ₁ -C ₄ alkyl group, C ₁ -C ₄ haloalkyl group or C ₁ -C ₄ trialkylsilyl group.

As used herein, an alkyl group of C ₁ -C ₄ refers to a straight or branched hydrocarbon having 1 to 4 carbon atoms, for example methyl, ethyl, n-propyl, i-propyl, n-butyl, i -Butyl, t-butyl, and the like, but are not limited thereto.

As used herein, a C ₁ -C ₄ haloalkyl group refers to a straight or branched hydrocarbon of 1 to 4 carbon atoms substituted with one or more halogens selected from the group consisting of fluorine, chlorine, bromine and iodine, for example Trifluoromethyl, trichloromethyl, trifluoroethyl, and the like, but are not limited thereto.

As used herein, a C ₁ -C ₄ trialkylsilyl group refers to a silyl group substituted with three C ₁ -C ₄ alkyl groups, including but not limited to trimethylsilyl, triethylsilyl, and the like.

In one embodiment of the invention, R is methyl, trifluoroethyl or trimethylsilyl.

In one embodiment of the present invention, the compound represented by the formula (1) is to lower the viscosity of the electrolyte composition, increase the ion conductivity to improve the output characteristics and to enable fast charging. In addition, the compound represented by Chemical Formula 1 has a low LUMO (Lowest Unoccupied Molecular Orbital) and has a high reductive decomposition tendency, thereby reducing and decomposing before the non-aqueous solvent in the electrolyte composition to form a stable film on the surface of the negative electrode to improve the life characteristics can do. In addition, a flexible film is formed by a cyclic carbonate compound in which one of the adjacent carbon atoms is substituted with a methylene ether group, and cracks are suppressed even in repeated charge and discharge, thereby ensuring long-term life characteristics.

The compound represented by Chemical Formula 1 may be obtained by using a commercially available one or manufactured and used by a method known in the art.

The compound represented by Formula 1 may be included in an amount of 0.05 to 20% by weight based on 100% by weight of the total electrolyte composition. When the compound represented by Chemical Formula 1 is included in an amount of less than 0.05% by weight, the effect of improving the ionic conductivity due to a decrease in viscosity may be insignificant. When the compound represented by the amount of more than 20% by weight, the ether group interacts with lithium There is a fear that the ion conductivity is lowered.

In one embodiment of the present invention, the non-aqueous solvent serves as a medium through which ions involved in the electrochemical reaction of the cell can move.

The non-aqueous solvent may be one that is commonly used in the art without particular limitation. For example, the nonaqueous solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or another aprotic solvent. These may be used alone or in combination of two or more.

As the carbonate solvent, a chain carbonate solvent, a cyclic carbonate solvent, a fluoro carbonate solvent, or a combination thereof can be used.

The chain carbonate solvent is, for example, diethyl carbonate (DEC), dimethyl carbonate (dimethyl carbonate, DMC), dipropyl carbonate (DPC), methylpropyl carbonate (methylpropyl carbonate, MPC), Ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) or a combination thereof, and the cyclic carbonate solvent is, for example, ethylene carbonate (EC), propylene carbonate (propylene) carbonate, PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or a combination thereof.

As the fluoro carbonate solvent, for example, fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene Carbonate, 4,4,5,5-tetrafluoroethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene Carbonate, 4,4,5-trifluoro-5-methylethylene carbonate, or a combination thereof.

The ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone ), Caprolactone, methyl formate, and the like can be used.

Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. This can be used.

Cyclohexanone may be used as the ketone solvent.

Ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent.

Examples of other aprotic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, Formamide, dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate and the like can be used.

In one embodiment of the invention, the non-aqueous solvent may comprise ethylene carbonate. In the case where ethylene carbonate is included as the non-aqueous solvent, dissociation of the electrolyte in the electrolyte composition may be promoted to further increase the ionic conductivity, which is advantageous in view of the output characteristics and the fast charging characteristics of the secondary battery.

The electrolyte solution composition according to one embodiment of the present invention may further include a lithium salt.

The lithium salt serves as a source of lithium ions in the battery, and serves to promote the movement of lithium ions between the positive electrode and the negative electrode.

Examples of the lithium salt are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiN (SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO _3, include _{LiClO 4, LiAlO 2, LiAlCl 4} , LiCl, LiI, LiB (C 2 O 4) 2 ( lithium bis (oxalate reyito) borate (lithium bis (oxalato) borate), LiBOB), etc. have. These may be used alone or in combination of two or more.

The concentration of the lithium salt may be 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte composition may have appropriate conductivity and viscosity.

One embodiment of the present invention relates to a secondary battery comprising the electrolyte composition described above.

Since the secondary battery according to the present invention includes the electrolyte composition of the present invention comprising the compound represented by Formula 1 having a low LUMO, a stable SEI film may be formed on the surface of the negative electrode during initial charging (chemical conversion step), thereby providing excellent life characteristics. .

In addition, since the secondary battery according to the present invention includes the electrolyte solution composition of the present invention including the compound represented by Formula 1 to lower the viscosity of the electrolyte composition and increase the ionic conductivity, the output characteristics are excellent and high-speed charging is possible.

In one embodiment of the present invention, the secondary battery may be a lithium secondary battery, for example, may be a lithium ion secondary battery.

The lithium secondary battery includes a positive electrode, a negative electrode and the above-described electrolyte composition.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

The positive electrode current collector may be used without particular limitation as long as it has conductivity without causing chemical change in the battery. Specifically, the positive electrode current collector may include aluminum, copper, stainless steel, nickel, titanium, calcined carbon, surface treated with carbon, nickel, titanium, silver, or the like on the surface of copper or stainless steel, aluminum-cadmium alloy, or the like. It can be used, in particular aluminum can be used. The positive electrode current collector may have various forms such as a foil, a net, a porous body, and the like, and may form fine irregularities on the surface to enhance the bonding strength of the positive electrode active material.

The positive electrode current collector may have a thickness of 3 to 500 μm.

The positive electrode active material layer includes a positive electrode active material, a binder, and optionally a conductive material.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specifically, the cathode active material may be one or more of a complex oxide or a composite phosphate of cobalt, manganese, nickel, aluminum, iron, or a combination of metal and lithium. More specifically, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate.

The binder attaches the positive electrode active material particles to each other and serves to attach the positive electrode active material to the positive electrode current collector. Specifically, as the binder, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl Pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used.

The conductive material is used to impart conductivity to the electrode, and may be used without limitation as long as it has electronic conductivity without causing chemical change. Specifically, examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal materials such as copper, nickel, aluminum, and silver; Conductive polymers, such as a polyphenylene derivative, etc. can be used.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

The negative electrode current collector may be used without particular limitation so long as it has conductivity without causing chemical change in the battery. Specifically, the negative electrode current collector may be copper, aluminum, stainless steel, nickel, titanium, calcined carbon, surface treated with carbon, nickel, titanium, silver, or the like on the surface of copper or stainless steel, aluminum-cadmium alloy, or the like. Can be used, in particular copper can be used. The negative electrode current collector may have various forms such as a foil, a net, a porous body, and the like, and may form fine irregularities on the surface to enhance the bonding strength of the negative electrode active material.

The negative electrode current collector may have a thickness of 3 to 500 μm.

The negative electrode active material layer includes a negative electrode active material, a binder, and optionally a conductive material.

As the negative electrode active material, a material capable of reversible intercalation and deintercalation of lithium ions, a lithium metal, an alloy of lithium metal, a material doped and undoped with lithium, a transition metal oxide, and the like may be used.

The material capable of reversible intercalation and deintercalation of lithium ions is a carbon-based material, and crystalline carbon, amorphous carbon, or a combination thereof may be used. Examples of the crystalline carbon include amorphous, plate, flake, spherical or fibrous graphite, and may be natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metals selected may be used.

The lithium doped and undoped materials include Si, Si-C composites, SiO _x (0 <x <2), Si-Q alloy (Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, An element selected from the group consisting of Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, not Si), Sn, SnO ₂ , Sn-R alloys (wherein R is an alkali metal, an alkaline earth metal, Element selected from the group consisting of Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and not Sn). SiO ₂ can also be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, One selected from the group consisting of S, Se, Te, Po, and a combination thereof can be used.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

The binder serves to attach the negative electrode active material particles to each other and to attach the negative electrode active material to the negative electrode current collector. Specifically, the same binder as that used for the positive electrode active material layer may be used as the binder.

The conductive material is used to impart conductivity to the electrode, and may be used without limitation as long as it has electronic conductivity without causing chemical change. Specifically, the same conductive material as that used for the positive electrode active material layer may be used.

The positive electrode and the negative electrode may be prepared by a manufacturing method commonly known in the art.

Specifically, the positive electrode and the negative electrode are prepared by mixing each active material, a binder and optionally a conductive material in a solvent to prepare an active material composition, and applying the active material composition to a current collector.

N-methylpyrrolidone (NMP), acetone, water and the like may be used as the solvent.

The positive electrode and the negative electrode may be separated by a separator. The separator may be used without particular limitation as long as it is commonly used in the art. In particular, it is suitable that it is low with respect to the ion migration in electrolyte solution, and excellent in the water-moisture capability of electrolyte solution. The separator may be a material selected from glass fiber, polyester, teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) and combinations thereof, and may be in the form of a nonwoven fabric or a woven fabric. The separator may have a pore diameter of 0.01 to 10 μm and a thickness of 3 to 100 μm. The separator may be a single film or a multilayer film.

The lithium secondary battery may be manufactured by a manufacturing method commonly known in the art.

Specifically, the lithium secondary battery is obtained by obtaining a laminate through a separator between the positive electrode and the negative electrode, the laminate is wound or folded to be accommodated in the battery container, injecting the electrolyte composition in the battery container and sealed with a sealing member It can manufacture.

The battery container may be cylindrical, rectangular, thin film, or the like.

The secondary battery may be used in a mobile phone, a portable computer, an electric vehicle, and the like. In addition, the secondary battery may be used in a hybrid vehicle in combination with an internal combustion engine, a fuel cell, a supercapacitor, and the like, and may be used in an electric bicycle or a power tool that requires high power, high voltage, and high temperature driving.

Hereinafter, the present invention will be described in more detail with reference to Examples, Comparative Examples and Experimental Examples. These examples, comparative examples and experimental examples are only for illustrating the present invention, it is apparent to those skilled in the art that the scope of the present invention is not limited thereto.

Example  1: Preparation of Electrolyte Composition

LiPF ₆ was added to 1.3 M in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 4: 6, and the compound represented by the following formula (2) was added to 100 wt% of the total electrolyte composition: The electrolyte composition was prepared by adding in an amount of% by weight.

[Formula 2]

Example  2: Preparation of Electrolyte Composition

An electrolyte solution composition was prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 3 was used instead of the compound represented by Chemical Formula 2.

[Formula 3]

Example  3: Preparation of Electrolytic Solution Composition

An electrolyte solution composition was prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 4 was used instead of the compound represented by Chemical Formula 2.

[Formula 4]

Comparative example  1: Preparation of Electrolyte Composition

An electrolyte solution composition was prepared in the same manner as in Example 1 except that the compound represented by Chemical Formula 2 was not added.

Comparative example  2: Preparation of Electrolyte Composition

An electrolyte solution composition was prepared in the same manner as in Example 1 except for using the compound represented by the following Formula a instead of the compound represented by the Formula 2.

[Formula a]

Experimental Example  One:

A secondary battery was prepared using the electrolyte composition prepared in Examples and Comparative Examples. The secondary battery was measured by the following method, and the results are shown in Table 1 below. In addition, the viscosity and ionic conductivity of each electrolyte composition were measured, and the results are shown in Table 1 below.

<Manufacture of secondary battery>

The mixture was mixed in a weight ratio of 5:; (Timcal Ltd. Super-P) and PVDF (polyvinylidene fluoride) binder _{90 LiNi 1/3 Co 1/} 3 Mn 1/3 O 2 powder, a carbon conductive material as the positive electrode active material: 5 To the positive electrode slurry was prepared by adding N-methylpyrrolidone (NMP) as a solvent so that the solid content was 60% by weight. The positive electrode slurry was coated to a thickness of about 40 μm on a 15 μm thick aluminum foil. It was dried at room temperature, dried again at 120 ° C., and rolled to prepare a positive electrode.

N-methylpyrrolidone was added to a mixture of artificial graphite, styrene-butadiene rubber, and carboxymethyl cellulose in a weight ratio of 90: 5: 5 as a negative electrode active material such that a solid content of 60% by weight was added to prepare a negative electrode slurry. . The negative electrode slurry was coated to a thickness of about 40 μm on a 10 μm thick copper foil. This was dried at room temperature, dried again at 120 ° C., and then rolled to prepare a negative electrode.

A secondary battery was manufactured using the positive electrode, the negative electrode and the electrolyte composition, and a polyethylene separator.

The prepared secondary battery was charged with a constant current at 25 ° C. with a current of 0.2 C until the voltage reached 4.2 V, and then discharged with a constant current of 0.2 C until the voltage reached 2.5 V. Subsequently, constant current charging was performed at a current of 0.5 C until the voltage reached 4.2 V, and constant voltage was charged until the current became 0.05 C while maintaining 4.2 V. Subsequently, it discharged with the constant current of 0.5C until the voltage reached 2.5V at the time of discharge (chemical conversion step).

(1) Normal Temperature Life Characteristics

The secondary battery that passed through the formation step was charged with constant current until the voltage reached 4.2V at a current of 1.33C at 25 ° C, and constant voltage charged until the current became 0.05C while maintaining 4.2V. Subsequently, the cycle of discharging with a constant current of 1.33C was repeated 100 times until the voltage reached 2.5V at the time of discharge.

The capacity retention ratio (%) at the 100th cycle of each secondary battery was calculated by Equation 1 below.

[Equation 1]

Capacity retention rate [%] = [discharge capacity at 100th cycle / 1 discharge capacity at cycle 1] x 100

(2) high temperature life characteristics

The measurement was performed in the same manner as the normal temperature lifespan measurement method except that the measurement conditions were set to 45 ° C. instead of 25 ° C. and the number of times was 300.

(3) viscosity

The viscosity of the electrolyte composition was measured at 25 ° C. using an RS150 viscometer.

(4) ion conductivity

Ion conductivity of the electrolyte composition was measured at 25 ° C using an Inolab® 740 instrument.

Room temperature life characteristics High Temperature Life Characteristics Viscosity (mPacm) Ion Conductivity (mS / cm) Example 1 71% 65% 3.5 8.9 Example 2 77% 70% 3.7 8.8 Example 3 81% 74% 3.7 8.8 Comparative Example 1 35% 22% 4.0 8.7 Comparative Example 2 82% 73% 4.2 8.4

As shown in Table 1, a secondary battery prepared using an electrolyte composition comprising a cyclic carbonate compound in which one of the adjacent carbon atoms according to the present invention is substituted with a methylene ether group has excellent life characteristics even at room temperature as well as at high temperature. I could confirm it. In addition, it was confirmed that the electrolyte composition including the cyclic carbonate compound in which one of the adjacent carbon atoms according to the present invention was substituted with a methylene ether group had a low viscosity and a high ionic conductivity as compared with the electrolyte compositions of Comparative Examples 1 and 2. Therefore, it was found that the secondary battery using the electrolyte composition according to the present invention had excellent output characteristics and was capable of high-speed charging.

Having described the specific part of the present invention in detail, it is apparent to those skilled in the art that this specific technology is only a preferred embodiment, which is not intended to limit the scope of the present invention. Do. Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Therefore, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.

Claims (7)

An electrolyte composition comprising the compound represented by Formula 1 and a non-aqueous solvent:
[Formula 1]

Where
R is a C ₁ -C ₄ alkyl group, C ₁ -C ₄ haloalkyl group or C ₁ -C ₄ trialkylsilyl group. The electrolyte composition according to claim 1, wherein R is methyl, trifluoroethyl or trimethylsilyl. The electrolyte composition of claim 1, wherein the compound represented by Formula 1 is included in an amount of 0.05 to 20 wt% based on 100 wt% of the total electrolyte composition. The electrolyte solution of claim 1, wherein the nonaqueous solvent comprises ethylene carbonate. The electrolyte solution composition according to claim 1, further comprising a lithium salt. A secondary battery comprising the electrolyte solution composition according to any one of claims 1 to 5. The secondary battery of claim 6, wherein the secondary battery is a lithium secondary battery.