KR20160058506A - electrolyte for lithium secondary battery and lithium secondary battery containing the same - Google Patents

Abstract

The present invention relates to an electrolyte for a secondary battery, and to a lithium secondary battery comprising the same. The lithium secondary battery applying the electrolyte for a secondary battery according to the present invention has improved electrochemical properties and life properties at room temperature and high temperature. The electrolyte for a secondary battery comprises lithium salts, a non-aqueous organic solvent, and sulfonium salts represented by chemical formula 1.

Description

[0001] The present invention relates to a secondary battery and a secondary battery containing the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery electrolyte and a lithium secondary battery comprising the same. More particularly, the present invention relates to a secondary battery electrolyte including a non-aqueous solvent, a lithium salt, and a sulfonium salt as an electrolyte additive and a lithium secondary battery comprising the same.

[0002] Recently, portable electronic devices have been widely used, and these portable electronic devices are becoming thinner, smaller, and lighter.

As a result, the secondary battery used as the power source is also small and lightweight, and can be charged and discharged for a long period of time.

 The secondary battery is classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen (Ni-MH) battery and a lithium battery according to an anode material and a cathode material. The potential and the energy density are determined. Among them, lithium secondary batteries are widely used as driving power sources for portable electronic devices such as notebook computers, camcorders, and mobile phones because of their high energy density due to the low oxidation / reduction potential and molecular weight of lithium.

However, the lithium secondary battery has a serious problem of deterioration of the safety of the battery caused by continuous charging. One of the causes that may affect the stability of the battery is heat generation due to the structural collapse of the anode. Among the secondary batteries, the battery stability according to the working principle of the non-aqueous electrolyte secondary battery is as follows.

That is, the positive electrode active material of the nonaqueous electrolyte secondary battery is composed of a lithium-containing metal oxide capable of intercalating and deintercalating lithium and / or lithium ions, etc. Such a positive electrode active material has a thermally unstable structure . When the battery temperature reaches a critical temperature due to an external physical impact such as high temperature exposure in the overcharged state, oxygen is released from the cathode active material having an unstable structure, and the released oxygen causes an exothermic decomposition reaction with the electrolyte solvent or the like. Particularly, since the combustion of the electrolytic solution is further accelerated by the oxygen released from the anode, such a series exothermic reaction causes ignition and rupture of the battery due to thermal runaway.

In addition, the positive electrode transition metal deposited on the negative electrode acts as a catalyst promoting the decomposition of the non-aqueous electrolyte, thereby generating gas inside the battery, or interfering with lithium ion migration as the SEI layer of the negative electrode progresses charge / discharge The cell performance and efficiency are significantly reduced.

Therefore, in order to solve such problems, Japanese Unexamined Patent Application Publication No. 2013-157305 proposes an electrolyte solution containing two isocyanate group-containing compounds. However, it is still required to study electrolytes having excellent lifetime characteristics and stability at high temperatures In fact.

Japanese Laid-Open Patent Publication No. 2013-157305

The present invention provides a secondary battery electrolyte comprising a sulfonium salt as an electrolyte additive.

The present invention provides a lithium secondary battery which employs the secondary battery electrolyte of the present invention and has excellent cycle characteristics and improved lifetime characteristics and output characteristics at room temperature and high temperature.

The secondary battery electrolyte of the present invention comprises a lithium salt; Non-aqueous organic solvent; And a sulfonium salt represented by the following formula (1) as an electrolyte additive, the secondary battery employing the same has excellent cycle characteristics and high temperature characteristics.

[Chemical Formula 1]

(In the formula 1,

R < ₁ > is (C1-C9) alkyl;

R is (C1-C9) alkyl, (C2-C9) alkenyl, (C1-C9) alkylthio or (C6-C12) aryl, provided that when R is alkyl, R ₁ and R are the same functional group;

X ^- is a monovalent anion.)

The sulfonium salt according to an embodiment of the present invention may be represented by the following general formula (2) or (3).

(2)

(3)

(In the above formulas 2 and 3,

R ₁₁ and R ₁₂ are independently of each other (C 1 -C 9) alkyl;

X ^- is _{N (SO 2 CF 3) 2} -, N (SO 2 C 2 F 5) 2 -, N (SO 2 F) 2 -, OSO 2 CF 3 -, O (SO 3 C 2 H 5) - , ^{_{O (SO 3 CH 3) -}} , BF 4 -, PF 6 -, SbF ₆ ^- or CF ₃ CO ₂ ^- ).

In the above formulas (2) and (3) according to an embodiment of the present invention, R and R ₁₁ are each independently (C 1 -C 5) alkyl; X ^- is _{N (SO 2 CF 3) 2} -, N (SO 2 C 2 F 5) 2 -, ^{_{O (SO 3 CH 3) -}} , OSO 2 CF 3 -, O (SO ₃ C ₂ H ₅ ) ^- or N (SO ₂ F) ₂ ^- .

The sulfonium salt according to an embodiment of the present invention may be included in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution.

In the electrolyte for a secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent or a mixture thereof. Based solvent is selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) and methyl propyl carbonate And the cyclic carbonate solvent is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), vinylethylene carbonate and fluoroethylene carbonate. Is a mixture of two or more, and the linear ester solvent is a single or a mixture of two or more selected from the group consisting of methyl propionate, ethyl propionate, propyl acetate, butyl acetate and ethyl acetate, and the cyclic ester- And may be a single or a mixture of two or more selected from the group consisting of lactone, caprolactone, and valerolactone.

In the electrolyte for a secondary battery according to an embodiment of the present invention, the volume ratio of the non-aqueous organic solvent to the linear carbonate solvent: cyclic carbonate solvent may be 1 to 9: 1.

In the electrolyte of the secondary battery according to an embodiment of the present invention, the lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , _{LiN (C 2 F 5 SO 3} ) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) 2. _{LiSCN, LiN (C x F 2x} + 1 SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2, LiF 2 BC 2 O ₄ , LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiP (C ₂ O ₄ ) ₃ and LiPO ₂ F ₂ .

In the secondary battery electrolyte according to an embodiment of the present invention, the lithium salt may be present at a concentration of 0.6 to 2.0M.

The present invention also provides a lithium secondary battery comprising the secondary battery electrolyte according to the present invention, wherein the lithium secondary battery comprises: a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium; b) a negative electrode comprising a negative electrode active material capable of intercalating and deintercalating lithium; c) a secondary battery electrolyte of the present invention; And d) a separator.

The secondary battery electrolyte of the present invention contains the sulfonium salt represented by the above formula (1) as an electrolyte additive, so that the secondary battery employing the secondary battery electrolyte of the present invention has remarkably improved cycle characteristics, It is very good.

The lithium secondary battery of the present invention uses the secondary battery electrolyte of the present invention including a sulfonium salt to reduce the resistance of the battery at a high temperature and thus has high storage stability at a high temperature and excellent cycle characteristics at room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing AC impedance of Example 3 and Comparative Example 1. Fig.

Hereinafter, the present invention will be described in more detail. Unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the following description, And a description of the known function and configuration will be omitted.

The present invention provides a secondary battery electrolyte and a lithium secondary battery comprising the same, wherein the secondary battery electrolyte includes a sulfonium salt.

More particularly, the present invention relates to a lithium salt; Non-aqueous organic solvent; And a sulfonium salt represented by the following general formula (1).

[Chemical Formula 1]

(In the formula 1,

R < ₁ > is (C1-C9) alkyl;

R is (C1-C9) alkyl, (C2-C9) alkenyl, (C1-C9) alkylthio or (C6-C12) aryl, provided that when R is alkyl, R ₁ and R are the same functional group;

X ^- is a monovalent anion.)

The secondary battery electrolyte of the present invention includes the sulfonium salt of Formula 1 as an electrolyte additive, thereby reducing the resistance of the battery and improving cycle characteristics and lifetime characteristics at high temperature and room temperature.

Preferably, R ₁ is (C ₁ -C 5) alkyl and R is (C 1 -C 9) alkyl or (C ₁ -C 9) alkylthio, according to one embodiment of the present invention. When R is alkyl, R ₁ and R are the same functional group.

In the present invention, when R is alkyl, R ₁ and R are the same functional groups. For example, when R is methyl, R ₁ is methyl and when R is ethyl, R ₁ is ethyl.

Preferably, Formula 1 according to an embodiment of the present invention may be represented by the following Formula 2 or 3 in view of having long-life characteristics at room temperature or high temperature and high cycle characteristics.

(2)

(3)

(In the above formulas 2 and 3,

R ₁₁ and R ₁₂ are independently of each other (C 1 -C 9) alkyl;

X ^- is _{N (SO 2 CF 3) 2} -, N (SO 2 C 2 F 5) 2 -, N (SO 2 F) 2 -, OSO 2 CF 3 -, O (SO 3 CH 3) -, O (SO ₃ C ₂ H ₅ ) ^- , BF ₄ ^- , PF ₆ ^- , SbF ₆ ^- or CF ₃ CO ₂ ^- ).

Preferably, R 2 and R ₁₁ in the general formulas (2) and (3) are independently (C 1 -C 5) independently from each other in terms of long life and high cycle characteristics at room temperature by increasing the high temperature stability and storage characteristics by reducing the resistance of the battery at a high temperature. Alkyl; X ^- is _{N (SO 2 CF 3) 2} -, N (SO 2 C 2 F 5) 2 -, O (SO ₃ CH ₃ ) ^- , OSO ₂ CF ₃ ^- , O (SO ₃ C ₂ H ₅ ) ^- or N (SO ₂ F) ₂ ^- For example, triethylsulfonium bis (trifluoromethanesulfonyl) imide, trimethylsulfonium methylsulfate, dimethylmethylsulfonium bistrifluoromethanesulfonylimide (diethylsulfonium bis (trifluoromethanesulfonyl) imide Dimethyl (methylthio) sulfonium Bis (trifluoromethanesulfonyl) imide) or dimethyl methylthiosulfonium trifluoromethanesulfonate (Dimethyl (methylthio) sulfonium trifluoromethanesulfonate).

The substituents comprising " alkyl " and other " alkyl " moieties described in this invention encompass both linear and branched forms. The term " aryl " in the present invention means an organic radical derived from an aromatic hydrocarbon by the removal of one hydrogen, and may be a single or fused ring containing 4 to 7, preferably 5 or 6 ring atoms, A ring system, and a form in which a plurality of aryls are connected by a single bond. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, indenyl, fluorenyl, and the like.

&Quot; Alkenyl " as used in the present invention means a straight, branched or cyclic hydrocarbon radical containing from 2 to 10 carbon atoms and at least one carbon to carbon double bond.

&Quot; Aryl " in the present invention means an organic radical derived from an aromatic hydrocarbon by one hydrogen elimination and is a single or fused ring containing 4 to 7, preferably 5 or 6 ring atoms, And includes a form in which a plurality of aryls are connected by a single bond. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, indenyl, fluorenyl, and the like.

In the secondary battery electrolyte according to an embodiment of the present invention, the sulfonium salt of Formula 1 may be contained in an amount of 0.05-10 wt%, more preferably 0.5-5 wt%, based on the total weight of the electrolyte solution. If the content of the sulfonium salt of the formula 1 is less than 0.05 wt%, the effective SEI film can not be formed, and the lifetime of the lithium secondary battery is insufficiently improved. When the content of the sulfonium salt is more than 10 wt%, a thick and highly resistant SEI film is formed The effect of increasing the charge / discharge efficiency may be insignificant, and the lifetime performance may be deteriorated.

In the electrolyte of the secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent or a mixture thereof, A solvent, a cyclic carbonate-based solvent or a mixed solvent thereof, and it is most preferable to use a mixture of a linear carbonate-based solvent and a cyclic carbonate-based solvent. The cyclic carbonate solvent has a large polarity, which can sufficiently dissociate lithium ions, but has a disadvantage in that the ion conductivity is low due to the high viscosity. Therefore, by using a linear carbonate solvent having a low polarity but a low viscosity in the cyclic carbonate solvent, the characteristics of the lithium secondary battery can be optimized.

The linear carbonate solvent may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) and methyl propyl carbonate And the cyclic carbonate solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2- Terephthalene carbonate, terephthalene carbonate, tilene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), vinylethylene carbonate and fluoroethylene carbonate, and the linear ester solvent is methyl propionate, ethyl propionate Propionate, propyl acetate, butyl acetate, and ethyl acetate. Mixture, and the cyclic ester-based solvent may be alone or a mixture of two or more selected from the group consisting of a lactone with the lactone, caprolactone and ballet as gamma -butyrolactone.

In the electrolyte for a secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a linear carbonate solvent and a cyclic carbonate solvent, wherein the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent is 1 to 9: 1, preferably in a volume ratio of 2: 8 to 8: 2, in terms of life characteristics and storage characteristics of the battery.

Preferably, in the electrolyte for a secondary battery according to an embodiment of the present invention, the non-aqueous organic solvent may be ethylene carbonate, propylene carbonate, ethyl methyl carbonate or a mixture thereof.

In the secondary battery electrolyte according to one embodiment of the invention, the lithium salt include, but are not limited _{to, LiPF 6, LiClO 4, LiAsF} 6, LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiSCN, LiN (C x F 2x} + 1 SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2, One or a mixture of two or more selected from the group consisting of LiF ₂ BC ₂ O ₄ , LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiP (C ₂ O ₄ ) ₃ and LiPO ₂ F ₂ And may preferably be lithium hexafluorophosphate (LiPF ₆ ).

The concentration of the lithium salt is preferably in the range of 0.6 to 2.0 M, and more preferably in the range of 0.8 to 1.5 M, considering the properties related to the electric conductivity and the viscosity associated with the lithium ion mobility. When the concentration of the lithium salt is less than 0.6M, the electric conductivity of the electrolytic solution is lowered, so that the performance of the electrolytic solution which transfers ions at a high speed between the anode and the cathode of the secondary battery decreases. When the concentration exceeds 2.0M, the viscosity of the electrolytic solution increases, There is a problem that the mobility of the mobile terminal is reduced. The lithium salt acts as a source of lithium ions in the battery, thereby enabling operation of a basic lithium secondary battery.

The secondary battery electrolyte of the present invention is electrochemically stable in a temperature range of -20 ° C to 60 ° C, so that the life of the battery can be prolonged when applied to the lithium secondary battery, and the safety and reliability of the lithium secondary battery are improved. Accordingly, the secondary battery electrolyte can be applied to any lithium secondary battery such as a lithium ion battery, a lithium polymer battery, and the like without limitation.

The present invention also provides a lithium secondary battery comprising: a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium; b) a negative electrode comprising a negative electrode active material capable of intercalating and deintercalating lithium; c) the secondary battery electrolyte of the present invention; And d) a separator.

The lithium secondary battery is manufactured by a conventional method, and the battery manufactured by using the electrolyte solution containing the electrolyte additive of the present invention is excellent in the room temperature and high temperature service life characteristics.

Non-limiting examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

An anode according to an embodiment of the present invention includes a current collector and a cathode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material capable of absorbing and desorbing lithium, a binder, a conductive material, and the like. The positive electrode active material is preferably a composite metal oxide of lithium and at least one element selected from cobalt, manganese, and nickel. In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Sr, V, and a rare earth element. Specific examples of the positive electrode active material may include a compound represented by any one of the following formulas:

Li _a A _1-b B _b D ₂ wherein, in the formula, 0.90? A? 1.8, and 0? B? 0.5; Li _a E _1-b B _b O _{2 -c} D _c wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); _{Li (3-f) Fe 2} (PO 4) 3 (0≤ f ≤ 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The negative electrode according to an embodiment of the present invention includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer may include a negative electrode active material capable of intercalating and deintercalating lithium, a binder, a conductive material, and the like. As the negative electrode active material, a carbon material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber, a lithium metal, an alloy of lithium and other elements, and the like can be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1500 ° C. or lower, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an interplanar distance of 3.35 to 3.38 angstroms and a crystallite size (Lc) of at least 20 nm by X-ray diffraction. Other elements constituting the alloy with lithium may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The anode and / or the cathode according to an embodiment of the present invention may be manufactured by dispersing an electrode active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector have. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and copper or a copper alloy may be used as the negative electrode current collector. The anode current collector and the anode current collector may be in the form of a foil or a mesh.

The binder according to one embodiment of the present invention acts as a paste for the active material, mutual adhesion of the active material, adhesion to the current collector, buffering effect on expansion and contraction of the active material, and the like. Anything is possible. For example, there may be mentioned polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, Polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP)), poly (vinyl acetate), alkylated polyethylene oxide, polyvinyl Butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, polyacrylonitrile, , Epoxy resin, nylon, and the like can be used, but the present invention is not limited thereto. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesive force between the electrode active material and the current collector is insufficient. If the content of the binder is too large, the adhesive force is improved but the content of the electrode active material is reduced accordingly.

The conductive material according to one embodiment of the present invention is used for imparting conductivity to an electrode, and any material can be used as an electron conductive material without causing any chemical change in the battery. As the conductive material, at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material may be used. Examples of the black graphite conductive material include artificial graphite and natural graphite. Examples of the carbon black conductive material include acetylene black, ketjen black, denkablack, thermal black, channel black black or the like. Examples of metal or metal compound conductive agents include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ and LaSrMnO ₃ have. However, the present invention is not limited to the above-mentioned conductive materials. The content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive material is less than 0.1% by weight, the electrochemical characteristics are deteriorated, and when it exceeds 10% by weight, the energy density per weight is decreased.

The thickening agent according to an embodiment of the present invention is not particularly limited as long as it can control the viscosity of the active material slurry. For example, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and the like are used .

As the solvent in which the electrode active material, the binder, the conductive material and the like are dispersed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The secondary battery of the present invention may include a separator to prevent a short circuit between the positive electrode and the negative electrode and to provide a path for the lithium ion. The separator may be a polypropylene, a polyethylene, a polyethylene / polypropylene, a polyethylene / polypropylene / , Polyolefin-based polymer membranes such as polypropylene / polyethylene / polypropylene, or multi-membranes thereof, microporous films, woven fabrics and nonwoven fabrics. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The lithium secondary battery of the present invention may have other shapes such as a cylindrical shape, a pouch shape, and the like.

The present invention will be described in detail with reference to the following examples. However, the following examples are only illustrative of the present invention and the scope of the present invention is not limited thereby.

[Example 1]

LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material were mixed at a weight ratio of 92: 4: 4 and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry . This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode.

Acetylene black as a conductive material and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 92: 1: 7 and dispersed in N-methyl-2-pyrrolidone as an anode active material to obtain an anode active material slurry . This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode.

A thickness of 20 mu m Polyethylene (PE) film A separator was stacked and wound and compressed to form a cell using a pouch having a size of 6 mm x 35 mm x 60 mm and a secondary cell electrolyte was injected to prepare a lithium secondary battery .

The secondary battery electrolyte was prepared by dissolving LiPF ₆ to a concentration of 1.0 M in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) (EC: EMC = 3: 7 by volume), and then adding triethylsulfonium bistrifluoromethane 0.5% by weight of triethylsulfonium bis (trifluoromethanesulfonyl) imide was added to the above-prepared pouch to prepare a secondary battery.

[Example 2]

0.5% by weight of trimethylsulfonium methylsulfate was added instead of 0.5% by weight of triethylsulfonium bis (trifluoromethanesulfonyl) imide to the electrolyte for the secondary battery of Example 1, A secondary battery was manufactured in the same manner.

[Example 3]

Instead of adding 0.5% by weight of triethylsulfonium bis (trifluoromethanesulfonyl) imide to the electrolyte for the secondary battery of Example 1, (dimethyl) (methylthio) sulfonium bistrifluoro Except that 0.5 wt% of dimethyl (methylthio) sulfonium bis (trifluoromethanesulfonyl) imide was added to the secondary battery.

[Comparative Example 1]

Except that 0.5% by weight of triethylsulfonium bis (trifluoromethanesulfonyl) imide was not added to the secondary battery electrolyte of Example 1. The secondary batteries were produced in the same manner as in Example 1, except that the triethylsulfonium bis (trifluoromethanesulfonyl) imide .

[Comparative Example 2]

The secondary battery electrolyte of Example 1 was used in the same manner as in Example 1 except that 0.5% by weight of triethylsulfonium bis (trifluoromethanesulfonyl) imide was used instead of diethyl methylsulfonium bistrifluoromethane sulfonylimide (methylsulfonium bis (trifluoromethanesulfonyl) imide) as a positive electrode active material was prepared in the same manner as in Example 1.

[Property evaluation 1: 4.2V cycle life property evaluation at room temperature (25 DEG C)] [

The discharge capacities of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were measured at 300 cycles of charging 1 C to 4.2 V and then discharging at 1 C, and the discharge capacity and the initial capacity were measured, Respectively.

Initial capacity (mAh) 300 times capacity
(mAh) percentage(%) Improvement rate (% in comparison with Comparative Example 1) Example 1 893.38 834.02 93.35 4.79 Example 2 888.05 852.34 95.97 7.41 Example 3 889.57 856.92 96.33 7.77 Comparative Example 1 905.23 801.68 88.56 - Comparative Example 2 890.31 809.20 90.89 2.33

As shown in Table 1, the electrolytic solution of Examples 1 to 3 of the present invention at room temperature (25 ° C) exhibited excellent cycle performance ratio with respect to the initial capacity at 4.2 V of 300 cycles by 4% or more as compared with Comparative Examples 1 and 2.

Among them, the electrolytic solution of Example 3 in which 0.5% by weight of (dimethyl) (methylthio) sulfonium bis (trifluoromethanesulfonyl) imide (Dimethyl And 96.33% of the capacity and the initial capacity, respectively.

[Property evaluation 2: 4.3V cycle life property evaluation at room temperature (25 DEG C)] [

The discharge capacities of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were measured at 300 cycles of charging 1 C to 4.3 V and then discharging at 1 C, and the discharge capacity and the percentage relative to the initial capacity were measured. Respectively.

Initial capacity (mAh) 300 times capacity
(mAh) percentage(%) Improvement rate (% in comparison with Comparative Example 1) Example 1 946.75 871.16 92.02 5.33 Example 2 954.17 884.23 92.67 5.98 Example 3 948.64 882.33 93.01 6.32 Comparative Example 1 952.03 825.31 86.69 - Comparative Example 2 950.26 841.46 88.55 1.86

As shown in Table 2, even when the electrolytic solution of Examples 1 to 3 of the present invention at room temperature (25 ° C) was 4.3 V and 300 cycles, the cycle capacity ratio to the initial capacity was superior to those of Comparative Examples 1 and 2 by 3.0% , 0.5% by weight of dimethylmethylthiosulfonium bis (trifluoromethanesulfonyl) imide (Dimethyl (methylthio) sulfonium bis) was added to the electrolyte solution of Example 3, and trimethylsulfonium methylsulfate The electrolyte solution of Example 2 added with the weight% showed a higher lifetime improvement rate than the electrolyte solution of Comparative Example 1.

[Property evaluation 3: Evaluation of battery resistance characteristics after storage at high temperature (70 ° C)] [

Each of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 was charged at 1 C to 4.2 V and then stored at a high temperature (70 ° C.) for 7 days. After charging 1 C to 4.2 V and then conducting 1 C discharge twice, And the alternating current impedance was measured.

Resistance value
(Z / Ohm) Example 1 0.0410 Example 2 0.0452 Example 3 0.0371 Comparative Example 1 0.0464 Comparative Example 2 0.0458

As shown in Table 3, the electrolytic solution of Examples 1 to 3 of the present invention showed lower resistance than the electrolytic solutions of Comparative Examples 1 and 2, and then stored at a high temperature (70 ° C) for 7 days. The electrolytic solution of Example 3 exhibits the lowest resistance value.

Also, as shown in FIG. 1, the additive containing a sulfonium cation improves the performance of the battery by reducing the resistance at the anode in the low frequency region.

As described above in Evaluation 1 to 3, the secondary cell electrolyte according to the present invention shows improved lifetime characteristics at room temperature and high-temperature storage characteristics by using an additive containing a sulfonium cation.

Claims (10)

Lithium salts;
Non-aqueous organic solvent; And
1. A secondary battery electrolyte comprising a sulfonium salt represented by the following formula (1).
[Chemical Formula 1]

(1)
R &lt; ₁ &gt; is (C1-C9) alkyl;
R is (C1-C9) alkyl, (C2-C9) alkenyl, (C1-C9) alkylthio or (C6-C12) aryl, provided that when R is alkyl, R ₁ and R are the same functional group;
X ^- is a monovalent anion.) The method according to claim 1,
Wherein the sulfonium salt is represented by the following general formula (2) or (3).
(2)

(3)

(In the above formulas 2 and 3,
R ₁₁ and R ₁₂ are independently of each other (C 1 -C 9) alkyl;
X ^- is selected from the group consisting of N (SO ₂ CF ₃ ) ₂ ^- , N (SO ₂ C ₂ F ₅ ) ₂ ^- , N (SO ₂ F) ₂ ^- , O (SO ₃ CH ₃ ) ^- , OSO ₂ CF ₃ ^- (SO ₃ C ₂ H ₅ ) ^- , BF ₄ ^- , PF ₆ ^- , SbF ₆ ^- or CF ₃ CO ₂ ^- ). 3. The method of claim 2,
R and R &lt; ₁₁ &gt; independently from each other are (C1-C5) alkyl;
X ^- is _{N (SO 2 CF 3) 2} -, N (SO 2 C 2 F 5) 2 -, ^{_{O (SO 3 CH 3) -}} , OSO ₂ CF ₃ ^- , O (SO ₃ C ₂ H ₅ ) ^- or N (SO ₂ F) ₂ ^- . The method according to claim 1,
Wherein the sulfonium salt is contained in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution. The method according to claim 1,
The non-aqueous organic solvent may be a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, a cyclic ester solvent or a mixed solvent thereof. 6. The method of claim 5,
The linear carbonate solvent may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC) and methyl propyl carbonate And the cyclic carbonate solvent is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (BC), 2,3-butylene carbonate, 1,2- Terephthalene carbonate, terephthalene carbonate, tilene carbonate, 2,3-pentylene carbonate, vinylene carbonate (VC), vinylethylene carbonate and fluoroethylene carbonate, and the linear ester solvent is methyl propionate, ethyl propionate Propionate, propyl acetate, butyl acetate, and ethyl acetate. Mixture, and the cyclic ester solvent is gamma-butyrolactone, secondary battery electrolyte is selected alone or in mixture of two or more from the group consisting of a lactone with caprolactone and ballet. 6. The method of claim 5,
Wherein the non-aqueous organic solvent has a mixing volume ratio of linear carbonate solvent: cyclic carbonate solvent of 1 to 9: 1. The method according to claim 1,
The lithium salt is _{LiPF 6, LiClO 4, LiAsF 6} , LiBF 4, LiSbF 6, LiAlO 4, LiAlCl 4, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (C 2 F 5 SO 3) 2, LiN ( C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . _{LiSCN, LiN (C x F 2x} + 1 SO 2) (C y F 2y + 1 SO 2) ( in this example, x, y are natural numbers), LiCl, LiI, LiB ( C 2 O 4) 2, LiF 2 BC 2 Wherein the electrolyte solution is a mixture of one or more selected from the group consisting of Li ₂ PO ₄ , LiPF ₄ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiP (C ₂ O ₄ ) ₃ and LiPO ₂ F ₂ . The method according to claim 1,
Wherein the lithium salt is present in a concentration of 0.4 to 2.0M. a) a positive electrode comprising a positive electrode active material capable of intercalating and deintercalating lithium;
b) a negative electrode comprising a negative electrode active material capable of intercalating and deintercalating lithium;
c) a secondary battery electrolyte according to any one of claims 1 to 9; And
d) a separator;
&Lt; / RTI &gt;

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