KR20200104735A - Electrolyte Composition and Secondary Battery Using the Same - Google Patents

Abstract

The present invention provides an electrolyte composition comprising an ethylene carbonate dimer compound of a specific structure and a non-aqueous solvent, and a secondary battery comprising the electrolyte composition. The electrolyte composition according to the present invention includes an ethylene carbonate dimer compound having a specific structure, and thus forms a stable SEI film, thereby securing excellent lifespan characteristics while improving high temperature stability even when applied to a secondary battery including a silicon negative electrode.

Description

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, an electrolyte composition having improved high temperature stability even when applied to a secondary battery including a silicon anode while having excellent lifespan characteristics by forming a stable SEI film, and a secondary battery using the same. It is about the battery.

Recently, as the supply of electric vehicles and portable electronic devices increases, the demand for lithium secondary batteries with high energy density and operating potential and low self-discharge rate is rapidly increasing.

A lithium secondary battery is composed of a positive electrode and a negative electrode, each of which is coated with an active material on an electrode current collector, a separator and an electrolyte interposed therebetween, and the electrolyte is generally a lithium salt and an additive, if necessary, dissolved in an organic solvent. Use it.

During initial charging of a lithium secondary battery, lithium ions from a positive electrode active material such as lithium metal oxide migrate to the negative electrode active material and are intercalated between layers of the negative electrode active material. At this time, since lithium ions are highly reactive, the electrolyte composition and the material constituting the negative electrode active material react on the surface of the negative electrode active material to form a SEI (Solid Electrolyte Interface) film, a kind of protective film, on the surface of the negative electrode active material.

The SEI film prevents the negative electrode structure from being destroyed by intercalation of organic solvent molecules having a large molecular weight moving together with lithium ions in the electrolyte composition between the layers of the negative electrode active material. Accordingly, 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, thereby maintaining stable charging and discharging.

Accordingly, there is increasing interest in additives for forming a stable SEI film on the surface of the cathode. For example, fluoroethylene carbonate (FEC) or the like is widely used as a negative electrode film-forming agent [refer to Korean Patent Registration No. 10-0977973].

On the other hand, silicon is in the spotlight as a high-capacity cathode material because it has a higher theoretical capacity than graphite. However, in such a silicon negative electrode, a serious volume change of active material particles occurs due to repeated charging and discharging, resulting in cracks on the surface of the negative electrode. Due to such cracks, the surface of the new cathode is continuously exposed to the electrolyte, so that a thick and unstable film may be generated, and a film having an unstable structure may impair stability, particularly high temperature stability.

However, the conventional FEC used as a negative electrode film forming agent has a problem of poor high temperature stability when applied to a secondary battery including a silicon negative electrode.

Accordingly, there is a need for development of an electrolyte composition having improved high-temperature stability even when applied to a secondary battery including a silicon negative electrode while forming a stable SEI film with excellent lifespan characteristics.

Korean Patent Registration No. 10-0977973

One object of the present invention is to provide an electrolyte composition having improved high-temperature stability even when applied to a secondary battery including a silicon negative electrode while forming a stable SEI film to provide excellent lifespan characteristics.

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 composition comprising a compound represented by the following formula (1) and a non-aqueous solvent.

[Formula 1]

In one embodiment of the present invention, the compound represented by Formula 1 may be included in an amount of 0.1 to 30% by weight based on 100% by weight of the total electrolyte composition.

In one embodiment of the present invention, the electrolyte composition may further contain a lithium salt.

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

In one embodiment of the present invention, the secondary battery may include a silicon negative electrode.

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

On the other hand, the present invention provides a compound represented by the following formula (1).

[Formula 1]

The electrolyte composition according to the present invention includes an ethylene carbonate dimer compound having a specific structure, thereby forming a stable SEI film, excellent lifespan characteristics, and high temperature stability even when applied to a secondary battery including a silicon negative electrode.

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

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

[Formula 1]

In one embodiment of the present invention, the compound represented by Formula 1 may improve life characteristics by forming a stable SEI film having high crosslinking density and chemical resistance on the surface of the negative electrode during initial charging and discharging. In addition, the compound represented by Chemical Formula 1 may improve stability at high temperatures, particularly at a high temperature of 60°C, even when applied to a secondary battery including a silicon anode having a large volume change during charging and discharging.

In one embodiment of the present invention, the compound represented by Formula 1 may be included in an amount of 0.1 to 30% by weight, preferably 1 to 10% by weight, based on 100% by weight of the total electrolyte composition. When the compound represented by Formula 1 is included in an amount of less than 0.1% by weight, the ability to form a stable SEI film may decrease, and when it is included in an amount of more than 30% by weight, the resistance of the coating may increase and output may decrease.

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 battery can move.

As the non-aqueous solvent, those commonly used in the art may be used without particular limitation. For example, as the non-aqueous solvent, a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or other aprotic solvent may be used. These may be used alone or in combination of two or more.

As the carbonate-based solvent, a chain carbonate-based solvent, a cyclic carbonate-based solvent, a fluorocarbonate-based solvent thereof, or a combination thereof may be used.

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

Examples of the fluorocarbonate-based solvent include fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 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 combinations thereof.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, butyl propionate, γ-butyrolactone, decanolide, valero. Lactone, mevalonolactone, caprolactone, methyl formate, ethyl formate, propyl formate, and the like may be used.

As the ether solvent, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Can be used.

Cyclohexanone may be used as the ketone solvent.

Ethyl alcohol, isopropyl alcohol, and the like may be used as the alcohol-based solvent.

Examples of the other aprotic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 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.

The electrolyte composition according to an 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 promotes the movement of lithium ions between the positive electrode and the negative electrode.

Examples of the lithium salt include 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 , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiCl, LiBr, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate), LiBOB), Li (CH ₃ CO ₂ ), Li(CF ₃ S0 ₃ ), Li(FSO ₂ ) ₂ N, Li(CF ₃ SO ₂ ) ₃ C, and the like. 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 an 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 contains the electrolyte composition of the present invention containing the compound represented by Formula 1, a stable SEI film can be formed on the surface of the negative electrode during the initial charging (formation step), so it has excellent life characteristics and Even when applied to a secondary battery including a silicon anode having a large volume change during discharge, it has excellent stability at high temperatures, particularly at a high temperature of 60°C.

Therefore, in one embodiment of the present invention, the secondary battery may particularly include a silicon negative electrode.

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

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

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 changes in the battery. Specifically, the positive electrode current collector includes aluminum, copper, stainless steel, nickel, titanium, calcined carbon, a surface-treated copper or stainless steel surface with carbon, nickel, titanium, silver, etc., and an aluminum-cadmium alloy. Can be used, in particular aluminum can be used. The positive electrode current collector may have various shapes such as a foil, a net, and a porous material, and may form fine irregularities on the surface to enhance the bonding strength of the positive electrode active material.

The thickness of the positive electrode current collector may be 3 to 500 μm.

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

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

The binder serves to attach the positive electrode active material particles to each other and 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 can be used without limitation as long as it does not cause chemical change and has electronic conductivity. Specifically, the conductive material includes carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; Metallic materials such as copper, nickel, aluminum, and silver; Conductive polymers, such as a polyphenylene derivative, can be used.

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

The negative electrode current collector is not particularly limited and may be used as long as it has conductivity without causing chemical changes to the battery. Specifically, the negative electrode current collector includes copper, aluminum, stainless steel, nickel, titanium, calcined carbon, a surface-treated copper or stainless steel surface with carbon, nickel, titanium, silver, etc., and an aluminum-cadmium alloy. Can be used, in particular copper can be used. The negative electrode current collector may have various shapes such as a foil, a net, and a porous material, and may enhance the bonding strength of the negative active material by forming fine irregularities on the surface.

The thickness of the negative electrode current collector may be 3 to 500 μm.

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

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

The material capable of reversible intercalation and deintercalation of lithium ions is a carbon-based material, and may be crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include amorphous, plate-like, 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, and fired coke.

As the lithium metal alloy, in the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn The alloy of the metal of choice can be used.

The lithium-doped and undoped materials include Si, Si-C composite, SiO _x (0 <x <2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, It is an element selected from the group consisting of a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, but not Si), Sn, SnO ₂ , Sn-R alloy (where R is an alkali metal, alkaline earth metal, It is an element selected from the group consisting of a group 13 element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and combinations thereof, and Sn is not), and at least one of them and 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, What is selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

The transition metal oxide may include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

In one embodiment of the present invention, the negative electrode active material is particularly Si, Si-C composite, SiO _x (0 <x <2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 element, 14 It is an element selected from the group consisting of a group element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, and not Si).

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

The conductive material is used to impart conductivity to the electrode, and can be used without limitation as long as it does not cause chemical change and has electronic conductivity. Specifically, the conductive material may be the same as that used for the positive electrode active material layer.

The positive electrode and the negative electrode can be manufactured 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 then applying the active material composition to a current collector.

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

The positive and negative electrodes may be separated by a separator. The separator may be used without particular limitation as long as it is commonly used in the art. Particularly, it is suitable that the electrolyte composition has a low resistance to ion migration and excellent moisture-retaining ability of the electrolyte composition. 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 can be manufactured by a manufacturing method commonly known in the art.

Specifically, in the lithium secondary battery, a laminate is obtained by interposing a separator between a positive electrode and a negative electrode, and then the laminate is wound or folded to be accommodated in a battery container, and an electrolyte composition is injected into the battery container and sealed with a sealing member. Can be manufactured.

The battery container may be a cylindrical shape, a square shape, or a thin film type.

The secondary battery may be used for mobile phones, portable computers, electric vehicles, and the like. In addition, the secondary battery may be used in a hybrid vehicle, etc., in combination with an internal combustion engine, a fuel cell, a supercapacitor, etc., and may also be used in electric bicycles and power tools that require high output, high voltage and high temperature driving.

One embodiment of the present invention relates to a compound represented by the following formula (1).

[Formula 1]

The compound represented by Formula 1 may be prepared by reacting vinylene carbonate and 2,2,3,3-tetrafluoro-1,4-butanediol in the presence of a base.

Triethylamine or the like may be used as the base.

Hereinafter, the present invention will be described in more detail by Examples, Comparative Examples and Experimental Examples. These Examples, Comparative Examples and Experimental Examples are for illustrative purposes only, and it is obvious to those skilled in the art that the scope of the present invention is not limited thereto.

Synthesis example 1: Synthesis of a compound represented by Formula 1

After adding vinylene carbonate (170 g, 2 mol) to 140 ml of monoglyme and stirring vigorously, 2,2,3,3-tetrafluoro-1,4-butanediol (130 g, 0.8 mol) was added to the stirred solution. ) And triethylamine (295.5 g, 2.92 mol) were added at -5°C under an inert atmosphere. Then, the resulting mixture was stirred at 2 to 4° C. for 7 hours and then at room temperature overnight. The reaction mixture was diluted with 2 L of diethyl ether and the formed suspension was filtered. The filtrate was evaporated using a rotary evaporator, and the residue was distilled under reduced pressure (0.5 mmHg) to obtain a compound represented by Formula 1 as 200 g of white solid having a boiling point of 78 to 82°C/0.5 mmHg (yield: 74.9% ).

¹ H-NMR (400MHz, CDCl ₃ ): δ=4.25-4.45 (m, 6H), 4.65-4.75 (m, 2H), 5.95-6.05 (m, 2H)

Example 1: Preparation of electrolyte composition

LiPF ₆ as a lithium salt was added to a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 so as to be 1.0M, and then represented by Formula 1 with respect to 100% by weight of the total electrolyte composition. The resulting compound was added in an amount of 2% by weight to prepare an electrolyte solution composition.

Example 2: Preparation of electrolyte composition

An electrolyte composition was prepared in the same manner as in Example 1, except that the compound represented by Formula 1 was added in an amount of 0.1% by weight.

Example 3: Preparation of electrolyte composition

An electrolyte composition was prepared in the same manner as in Example 1, except that the compound represented by Formula 1 was added in an amount of 10% by weight.

Comparative example 1: Preparation of electrolyte composition

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

Comparative example 2: Preparation of electrolyte composition

An electrolyte composition was prepared in the same manner as in Example 1, except that the compound represented by Formula 1 was added in an amount of 40% by weight.

Comparative example 3: Preparation of electrolyte composition

An electrolyte composition was prepared in the same manner as in Example 1, except that fluoroethylene carbonate was added instead of the compound represented by Chemical Formula 1.

Experimental example One:

A secondary battery was manufactured as follows using the electrolyte composition prepared in the Examples and Comparative Examples, and the room temperature life characteristics and high temperature stability at this time were measured by the following method, 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 N-methylpyrrolidone (NMP) as a solvent was added to a solid content of 60% by weight to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil having a thickness of 15 μm to a thickness of about 40 μm. It was dried at room temperature, dried again at 120° C., and then rolled to prepare a positive electrode.

N-methylpyrrolidone in a mixture of artificial graphite, carbon-coated silicon oxide, styrene-butadiene rubber, and carboxymethylcellulose as an anode active material in a weight ratio of 85:5:5:5, and a solid content of 60% by weight It was added so as to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil having a thickness of 10 μm to a thickness of about 40 μm. It 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, negative electrode, and electrolyte composition and a polyethylene separator.

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

(1) Room temperature life characteristics

The secondary battery that had undergone the formation step was charged at a constant current at 25° C. with a current of 1.0 C until the voltage reached 4.2 V, and charged at a constant voltage until the current reached 0.05 C while maintaining 4.2 V. Subsequently, the cycle of discharging with a constant current of 1.0 C was repeated 300 times until the voltage reached 2.5 V during discharge.

The capacity retention ratio (%) in the 300th cycle of each secondary battery was calculated by Equation 1 below.

[Equation 1]

Capacity retention rate [%] = [Discharge capacity at the 300th cycle / Discharge capacity at the first cycle] × 100

(2) High temperature stability

The secondary battery that had undergone the formation step was charged at a constant current at 25° C. with a current of 1.0 C until the voltage reached 4.2 V, and charged at a constant voltage until the current reached 0.05 C while maintaining 4.2 V. Then, while storing the charged secondary battery at 60° C., the voltage was measured every 24 hours using a multimeter, and the residual voltage was measured at a high temperature of the charged cell to measure the high temperature voltage storage stability.

When measuring the 15th day of each secondary battery, the voltage retention ratio (%) was calculated by Equation 2 below.

[Equation 2]

Voltage retention rate[%]=[open circuit voltage on the 15th day/initial open voltage]×100

Room temperature life characteristics High temperature stability Example 1 91.5% 89.5% Example 2 87.1% 81.4% Example 3 91.3% 89.6% Comparative Example 1 76.3% 70.3% Comparative Example 2 81.9% 76.2% Comparative Example 3 86.3% 78.6%

As shown in Table 1 above, the secondary battery manufactured using the electrolyte composition containing the ethylene carbonate dimer compound of a specific structure according to the present invention was at room temperature compared to the secondary battery manufactured using the electrolyte composition of Comparative Examples 1 to 3 It was confirmed that not only had more excellent life characteristics, but also improved stability at high temperatures.

As described above, a specific part of the present invention has been described in detail, and it is obvious that this specific technology is only a preferred embodiment for those of ordinary skill in the art to which the present invention belongs, and the scope of the present invention is not limited thereto. Do. Those of ordinary skill in the art to which the present invention belongs will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Therefore, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (7)

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

The electrolyte composition of claim 1, wherein the compound represented by Formula 1 is contained in an amount of 0.1 to 30% by weight based on 100% by weight of the total electrolyte composition. The electrolytic solution composition according to claim 1, further comprising a lithium salt. A secondary battery comprising the electrolyte composition according to any one of claims 1 to 3. The secondary battery according to claim 4, comprising a silicon negative electrode. The secondary battery according to claim 4, which is a lithium secondary battery. Compound represented by the following formula (1):
[Formula 1]