KR102247161B1 - Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery Containing the Same - Google Patents

Abstract

The present invention provides a lithium secondary battery electrolyte and a lithium secondary battery including the same, and the secondary battery electrolyte of the present invention has excellent high temperature stability, low temperature discharge capacity, and lifetime characteristics.

Description

Lithium secondary battery electrolyte and lithium secondary battery containing the same {Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery Containing the Same}

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery containing the same, and more particularly, to a lithium secondary battery electrolyte including a boron derivative and a lithium secondary battery including the same.

Recently, the spread of portable electronic devices has been widely made, and according to the rapid miniaturization, weight reduction, and thinning of such portable electronic devices, the battery as its power source is also compact, lightweight, and capable of charging and discharging for a long time. There is a strong demand for development.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has the advantage of having a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. It is in the limelight. However, such a lithium secondary battery has safety problems such as ignition and explosion due to the use of a non-aqueous electrolyte, and such problems become more serious as the capacity density of the battery increases.

The non-aqueous electrolyte secondary battery has a major problem of deteriorating the safety of the battery generated during continuous charging. One of the causes that can affect this is heat generation due to the collapse of the structure of the anode. The principle of its operation is as follows. That is, the positive electrode active material of the nonaqueous electrolyte battery is made of a lithium-containing metal oxide that can occlude and release lithium and/or lithium ions, and such positive electrode active material is transformed into a thermally unstable structure due to the release of a large amount of lithium during overcharging. do. In such an overcharged state, when the battery temperature reaches a critical temperature due to external physical shock, such as high temperature exposure, oxygen is released from the positive electrode active material having an unstable structure, and the released oxygen causes an exothermic decomposition reaction with an electrolyte solvent and the like. In particular, since the combustion of the electrolyte solution is further accelerated by oxygen released from the anode, ignition and rupture of the battery due to thermal runaway are caused by such a cascading exothermic reaction.

In order to control ignition or explosion due to an increase in temperature inside the battery as described above, a method of adding an aromatic compound as a redox shuttle additive to an electrolyte is used. For example, Japanese Patent JP2002-260725 discloses a non-aqueous lithium ion battery capable of preventing an overcharge current and a thermal runaway phenomenon by using an aromatic compound such as biphenyl. In addition, a small amount of aromatic compounds such as biphenyl and 3-chlorothiophene are added to U.S. Patent No. 5,879,834 to improve battery safety by electrochemical polymerization under abnormal overvoltage conditions to increase internal resistance. The method for this is described.

However, in the case of using an additive such as biphenyl, the amount of biphenyl gradually decreases during the charging and discharging process when a relatively high voltage is generated locally at a general operating voltage, or when the battery is discharged at a high temperature for a long period of time. After 300 cycles of charging and discharging, there are problems in which safety cannot be guaranteed and problems of storage characteristics.

Therefore, research to improve safety at high and low temperatures while still having a high capacity retention rate is required.

Japanese Patent JP2002-260725 U.S. Patent 5,879,834

The present invention is to provide a lithium secondary battery electrolyte having excellent high-temperature and low-temperature characteristics, and a lithium secondary battery including the same, while maintaining good basic performance such as high rate charge/discharge characteristics and lifespan characteristics.

The present invention provides a lithium secondary battery electrolyte, the lithium secondary battery electrolyte of the present invention,

Lithium salt;

Non-aqueous organic solvents; And

It includes; boron derivatives represented by the following formula (1).

[Formula 1]

(In Chemical Formula 1,

R is (C1-C6)alkyl, (C2-C6)alkenyl or (C2-C6)alkynyl;

R ¹ to R ⁴ are each independently hydrogen or (C1-C10)alkyl.)

In the lithium secondary battery electrolyte according to an embodiment of the present invention, in Formula 1, preferably, R ¹ to R ⁴ may be methyl or ethyl independently of each other.

Preferably, R in Formula 1 according to an embodiment of the present invention may be methyl, ethyl, propyl, n-butyl, ethenyl, propenyl, and propargyl.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the boron derivative represented by Formula 1 may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the electrolyte is one or two selected from the group consisting of an oxalatoborate-based compound, a fluorine-substituted carbonate-based compound, a vinylidene carbonate-based compound, and a sulfinyl group-containing compound. It may further include the above additives.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the electrolyte is lithium difluoro oxalatoborate (LiFOB), lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate , Ethane sultone, propane sultone (PS), butane sultone (butane sulton), ethene sultone, butene sultone and propene sultone (PRS) may further include an additive selected from the group consisting of.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the additive may be included in an amount of 0.1% to 5.0% by weight based on the total weight of the electrolyte.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent may be selected from a cyclic carbonate-based solvent, a linear carbonate-based solvent, and a mixed solvent thereof, and the cyclic carbonate is ethylene carbonate, propylene carbonate, etc. , Butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluorine ethylene carbonate, and a mixture thereof, the linear carbonate may be selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl It may be selected from the group consisting of carbonate, methyl isopropyl carbonate, ethylpropyl carbonate, and mixtures thereof.

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

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(SO ₃ C ₂ F ₅ ) ₂ , LiN(SO ₂ F) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC ₆ H ₅ SO ₃ , LiSCN, LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), one selected from the group consisting of _{LiCl, LiI and LiB(C 2} O ₄ ) ₂ Or two or more.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the lithium salt may be present in a concentration of 0.1 to 2.0 M.

In addition, the present invention provides a lithium secondary battery comprising the lithium secondary battery electrolyte.

Since the lithium secondary battery electrolyte according to the present invention contains a boron derivative, it has excellent high-temperature storage characteristics, specifically, a high high-temperature capacity recovery rate, and a low battery thickness increase rate.

In addition, the lithium secondary battery electrolyte according to the present invention includes a boron derivative substituted with a straight-chain alkyl, alkenyl, or alkynyl, and has high discharge capacity at a low temperature as well as high temperature characteristics.

In addition, the lithium secondary battery electrolyte according to the present invention is selected from the group consisting of a boron derivative represented by Formula 1 of the present invention and an oxalatoborate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound, and a sulfinyl group-containing compound. It further includes one or two or more additives to have better life characteristics, high temperature stability, and low temperature characteristics.

In addition, the lithium secondary battery of the present invention has excellent high-temperature storage stability and low-temperature characteristics while maintaining good basic performances such as high-efficiency charge/discharge characteristics and lifespan characteristics by employing the lithium secondary battery electrolyte of the present invention containing a boron derivative.

Hereinafter, the present invention will be described in more detail. If there are no other definitions in the technical terms and scientific terms used at this time, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the following description will unnecessarily obscure the subject matter of the present invention. Description of possible known functions and configurations will be omitted.

The present invention relates to a lithium secondary battery electrolyte for providing a battery having high high-temperature storage characteristics and high-life characteristics and excellent discharge capacity at low temperatures.

The present invention is a lithium salt; Non-aqueous organic solvents; And it provides a lithium secondary battery electrolyte comprising a; and a boron derivative represented by the formula (1):

[Formula 1]

(In Chemical Formula 1,

R is (C1-C6)alkyl, (C2-C6)alkenyl or (C2-C6)alkynyl;

R ¹ to R ⁴ are each independently hydrogen or (C1-C10)alkyl.)

The secondary battery electrolyte of the present invention is a boron derivative, specifically, straight-chain alkyl, alkenyl or alkynyl, and more specifically, R in Formula 1 is substituted with straight-chain alkyl, alkenyl or alkynyl, preferably Since it contains a boron derivative of a specific structure substituted with alkyl, the capacity recovery rate and stability are high at high temperature, and the discharge capacity at low temperature is also very excellent.

In Formula 1 according to an embodiment of the present invention, preferably R may be methyl, ethyl, propyl, n-butyl, ethenyl, propenyl, and propargyl.

In Formula 1 according to an embodiment of the present invention, preferably R ¹ to R ⁴ may be independently methyl or ethyl.

Substituents including ``alkyl'', ``alkoxy'' and other ``alkyl'' moieties described in the present invention include all linear or branched forms, unless otherwise specified, and 1 to 10 carbon atoms, preferably 1 to 6 , More preferably, it has 1 to 4 carbon atoms.

The term "alkenyl", either alone or as part of another group described herein, refers to a straight chain, branched chain or cyclic hydrocarbon radical containing 2 to 10 carbon atoms and at least one carbon to carbon double bond. More preferred alkenyl radicals are lower alkenyl radicals having 2 to about 6 carbon atoms. The most preferred lower alkenyl radicals are those having 2 to about 4 carbon atoms.

Also alkenyl groups may be substituted at any available point of attachment. Examples of alkenyl radicals include ethenyl, propenyl, allyl, propenyl and butenyl. The terms alkenyl and lower alkenyl include radicals having cis and trans orientations, or, alternatively, E and Z orientations.

The term "alkynyl", either alone or as part of another group described herein, refers to a straight chain, branched chain or cyclic hydrocarbon radical containing 2 to 10 carbon atoms and at least one carbon to carbon triple bond. More preferred alkynyl radicals are lower alkynyl radicals having 2 to about 6 carbon atoms. Most preferred are low-gold alkynyl radicals having 2 to about 4 carbon atoms. Examples of such radicals include propargyl, butynyl, and the like. Also, the alkynyl group may be substituted at any available point of attachment.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the boron derivative of Formula 1 may be included in an amount of 0.1 to 5% by weight based on the total weight of the secondary battery electrolyte, and preferably 0.1 to 3% by weight in terms of high temperature stability. %, more preferably 1 to 3% by weight. When the content of the boron derivative of Formula 1 is less than 0.1% by weight, there is no effect of addition such as low stability at high temperature or insignificant improvement in capacity retention, and the effect of improving the discharge capacity or output of the lithium secondary battery is insignificant, and 5 If it is contained in an amount exceeding% by weight, a rapid life deterioration occurs, and the characteristics of the lithium secondary battery are rather deteriorated.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the electrolyte is an oxalate borate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound, and a sulfinyl group as a life enhancement additive for improving battery life. It may further include one or more additives selected from the group consisting of containing compounds.

The oxalatoborate-based compound may be a compound represented by the following Formula 2 or lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB).

[Formula 2]

(In Formula 2, R ₁₁ and R ₁₂ are each independently a halogen element or a halogenated C1 to C10 alkyl group.)

Specific examples of the oxalate borate-based additive include LiB(C ₂ O ₄ )F ₂ (lithium difluoro oxalate borate, LiFOB) or LiB(C ₂ O ₄ ) ₂ (lithium bis oxalate borate, LiBOB), etc. Can be lifted.

The carbonate-based compound substituted with fluorine may be fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluorodimethyl carbonate (FDMC), fluoroethylmethyl carbonate (FEMC), or a combination thereof.

The vinylidene carbonate-based compound may be vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or a mixture thereof.

The sulfinyl group (S=O)-containing compound may be sulfone, sulfite, sulfonate, and sultone (cyclic sulfonate), and these may be used alone or in combination. Specifically, the sulfone may be represented by Formula 3 below, and may be divinyl sulfone. The sulfite may be represented by Formula 4 below, and may be ethylene sulfite or propylene sulfite. The sulfonate may be represented by the following Chemical Formula 5, and may be diallyl sulfonate. In addition, non-limiting examples of sultones include ethane sultone, propane sultone, butane sulton, ethene sultone, butene sultone, propene sultone, and the like.

[Formula 3]

[Formula 4]

[Formula 5]

(In Formulas 3, 4, and 5, R ₁₃ and R ₁₄ are each independently hydrogen, a halogen atom, a C1-C10 alkyl group, a C2-C10 alkenyl group, a halogen-substituted C1-C10 alkyl group or a halogen It is a substituted C2-C10 alkenyl group.)

In the lithium secondary battery electrolyte according to an embodiment of the present invention, more preferably, the electrolyte is lithium difluoro oxalatoborate (LiFOB), lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB), fluorine Roethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate ( diallyl sulfonate), ethane sultone, propane sultone (PS), butane sultone (butane sulton), ethene sultone, butene sultone and propene sultone (PRS). Specifically, lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite, ethane sultone, propane sultone , PS) may further include one or more additives selected from.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the content of the additive is not significantly limited, but in order to improve the battery life in the secondary battery electrolyte, it is 0.1 to 5% by weight, more preferably, based on the total weight of the electrolyte. It may be included in 0.1 to 3% by weight.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent may include carbonate, ester, ether, or ketone alone or a mixed solvent thereof, but a cyclic carbonate-based solvent, a linear carbonate-based solvent, and It is preferable to be selected from these mixed solvents, and most preferably, a cyclic carbonate-based solvent and a linear carbonate-based solvent are mixed and used. The cyclic carbonate solvent has a high polarity and can sufficiently dissociate lithium ions, but has a high viscosity and low ionic conductivity. Therefore, the characteristics of the lithium secondary battery can be optimized by mixing and using a linear carbonate solvent having a small polarity but a low viscosity to the cyclic carbonate solvent.

The cyclic carbonate-based solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate ate, butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and mixtures thereof, and the linear carbonate-based solvent is dimethyl carbonate, It may be selected from the group consisting of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof.

In the lithium secondary battery electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent is a mixed solvent of a cyclic carbonate-based solvent and a linear carbonate-based solvent, and the mixing volume ratio of the linear carbonate solvent: the cyclic carbonate solvent is 1 to 9: 1 It may be, and is preferably used by mixing in a volume ratio of 1.5 to 4: 1.

In the high voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the lithium salt is not limited, but LiPF ₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(SO ₃ C ₂ F ₅ ) ₂ , LiN(SO ₂ F) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC ₆ H ₅ SO ₃ , LiSCN, LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ It may be one or two or more selected from the group consisting of.

The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M, and more preferably used within the range of 0.7 to 1.6 M. When the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte is lowered and the electrolyte performance is deteriorated. When the concentration of the lithium salt is more than 2.0 M, the viscosity of the electrolyte increases, thereby reducing the mobility of lithium ions. The lithium salt acts as a source of lithium ions in the battery, thereby enabling the operation of a basic lithium secondary battery.

The lithium secondary battery electrolyte of the present invention is generally stable in the temperature range of -20℃ to 60℃ and maintains electrochemically stable characteristics even at a voltage in the 4.4V range, so it can be applied to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries. I can.

In addition, the present invention provides a lithium secondary battery comprising the lithium secondary battery electrolyte.

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

The lithium secondary battery manufactured from the lithium secondary battery electrolyte according to the present invention exhibits a high temperature storage efficiency of 70% or more, and the thickness increase rate of the battery when left at high temperature for a long period is very low, preferably 1 to 8%, rather than 1 to 20%. It is characterized by that.

The lithium secondary battery of the present invention includes a positive electrode and a negative electrode.

The positive electrode includes a positive electrode active material capable of occluding and desorbing lithium ions, and the positive electrode active material is preferably at least one selected from cobalt, manganese, and nickel, and a composite metal oxide with lithium. The solid solution ratio between metals can be made variously, and in addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, An element selected from the group consisting of Sr, V, and rare earth elements may be further included. As a specific example of the positive electrode active material, a compound represented by any one of the following formulas may be used:

Li _a A _1-b B _b D ₂ (where 0.90≦a≦1.8, and 0≦b≦0.5); Li _a E _1-b B _b O _2-c D _c (in the above formula, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); LiE _2-b B _b O _4-c D _c (where 0≦b≦0.5, 0≦c≦0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc 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 _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 _α (in the above formula, 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 (in the above formula, 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 (in the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (in the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a CoG _b O ₂ (wherein, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a MnG _b O ₂ (wherein, 0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (wherein, 0.90≦a≦1.8, 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, rare earth elements or combinations 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 contains a negative electrode active material capable of occluding and desorbing lithium ions, and such negative electrode active materials include carbon materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, lithium metal, and alloys of lithium and other elements. I can. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or less, and mesophase pitch-based carbon fibers (MPCF). As crystalline carbon, there are graphite-based materials, and specifically, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The carbon material is preferably a material having an interplanar distance of 3.35 to 3.38 Å and a crystallite size (Lc) of at least 20 nm by X-ray diffraction. Other elements forming an alloy with lithium may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

The positive or negative electrode may be prepared by dispersing an electrode active material, a binder, a conductive material, and, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and then applying the slurry composition to an electrode current collector. Aluminum or aluminum alloy may be used as the positive electrode current collector, and copper or copper alloy may be commonly used as the negative electrode current collector. The positive electrode current collector and the negative electrode current collector may be in the form of foil or mesh.

The binder is a material that plays a role in the formation of a paste of the active material, adhesion of the active material to each other, adhesion to the current collector, and buffering effect on expansion and contraction of the active material, such as polyvinylidene fluoride (PVdF), polyhexafluoro Propylene-polyvinylidene fluoride copolymer (PVdF/HFP)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly(methylmetha) Acrylate), poly(ethylacrylate), polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and the like. 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 adhesion between the electrode active material and the current collector is insufficient, and if the content of the binder is too high, the adhesion is improved, but the content of the electrode active material decreases that much, which is disadvantageous in increasing the battery capacity.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material can be used as long as it does not cause chemical change and is an electron conductive material.A graphite conductive agent, a carbon black conductive agent, a metal or a metal compound type At least one selected from the group consisting of conductive agents may be used. Examples of the graphite-based conductive agent include artificial graphite, natural graphite, and the like, and examples of the carbon black-based conductive agent include acetylene black, ketjen black, denkablack, thermal black, and channel black. (channel black), etc., and examples of metal-based or metallic compound-based conductive agents include perovskites such as _{tin, tin oxide, tin phosphate (SnPO 4} ), titanium oxide, potassium titanate, LaSrCoO ₃ , and LaSrMnO ₃ There is a substance. However, it is not limited to the conductive agents listed above.

The content of the conductive agent is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive agent is less than 0.1% by weight, the electrochemical properties decrease, and when it exceeds 10% by weight, the energy density per weight decreases.

The thickener is not particularly limited as long as it can control the viscosity of the active material slurry, but for example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and the like may be used.

As a solvent in which an electrode active material, a binder, a 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-pyrrolididone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

The lithium secondary battery of the present invention may include a separator that prevents a short circuit between the positive electrode and the negative electrode and provides a passage for lithium ions. Such separators include polypropylene, polyethylene, polyethylene/polypropylene, polyethylene/polypropylene/ Polyolefin-based polymer films such as polyethylene, polypropylene/polyethylene/polypropylene, or a multilayer thereof, microporous films, woven fabrics, and nonwoven fabrics may be used. In addition, a film coated with a resin having excellent stability on a porous polyolefin film may be used.

The lithium secondary battery of the present invention may have other shapes, such as a cylindrical shape or a pouch type, in addition to a square shape.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples. It is believed that all lithium salts dissociate in order to have a lithium ion concentration of 1 mol (1M), and a lithium salt _{such as LiPF 6} can be dissolved in a basic solvent to achieve a concentration of 1 mol (1M) to form a base electrolyte. .

[Preparation Example 1] 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2-methoxy-4,4,5,5-tetramethyl-1,3 ,2-dioxaborolane, hereinafter referred to as'PEA11') synthesis

Trimethylborate (3.7 g) and anhydrous pinacol (4.2 g) ^{were stirred at 68 o} C for 2 hours to react. After the reaction was completed, distillation under reduced pressure was performed to obtain 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2.8 g).

¹ H NMR (CDCl ₃ , 500 MHz) δ 3.57 (s, 2H), 1.22 (s, 12H)

[Production Example 2] 2-isopropyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2-isopropoxy-4,4,5,5-tetramethyl-1,3 ,2-dioxaborolane, hereinafter referred to as'PEA12') synthesis

Triisopropylborate (5.5 g) and anhydrous pinacol (3.9 g) ^{were stirred at 68 o} C for 2 hours to react. After the reaction was completed, distillation under reduced pressure was performed to obtain 2-isopropyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (2.1 g).

¹ H NMR (CDCl ₃ , 500 MHz) δ 4.32 (m, 1H), 1.24 (s, 12H), 1.19 (d, J = 6.1 Hz, 6H)

[Example 1-6 and Comparative Example 1-3]

_{The electrolyte is a solution obtained by dissolving LiPF 6} to a 1.0 M solution in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a volume ratio of 3: 7 and the basic electrolyte solution (1M LiPF ₆ , EC/EMC = 3). : 7) was prepared by additionally adding the components shown in Table 1 below.

A battery to which the non-aqueous electrolyte is applied was manufactured as follows.

_{LiNiCoMnO 2} and LiMn ₂ O ₄ as a positive electrode active material are mixed in a weight ratio of 1:1, polyvinylidene fluoride (PVdF) as a binder and carbon as a conductive agent are mixed in a weight ratio of 92:4:4, and then N- Disperse in methyl-2-pyrrolidone to prepare a positive electrode slurry. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried and rolled to prepare a positive electrode. Artificial graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethylcellulose as a thickener were mixed in a weight ratio of 96:2:2, and then dispersed in water to prepare a negative electrode active material slurry. The slurry was coated on a 15 μm-thick copper foil, dried, and rolled to prepare a negative electrode.

A 25 μm-thick polyethylene (PE) film separator was stacked between the prepared electrodes, and a cell was constructed using a pouch having a size of 8 mm in thickness x 270 mm in width x 185 mm in length. , The non-aqueous electrolyte was injected to prepare a 25Ah class lithium secondary battery for EV.

The performance of the thus prepared EV 25Ah class battery was evaluated as follows. The evaluation items are as follows.

*Evaluation items*

1. -20℃ 1C discharge capacity: After charging at room temperature with 25A, 4.2V CC-CV for 3 hours, leaving at -20℃ for 4 hours with a current of 25A, discharging to 2.7V by CC, and then using the available capacity compared to the initial capacity (%) was measured.

2. Capacity recovery rate at 60℃ for 30 days: After charging with 4.2V, 25A CC-CV at room temperature for 3 hours, and leaving at 60'C for 30 days, with a current of 25A, after discharging to 2.7V at CC, the recovery rate compared to the initial capacity (% ) Was measured.

3. Thickness increase rate after 30 days at 60℃: After charging with 4.2V, 25A CC-CV at room temperature for 3 hours, the thickness of the battery is called A, and 30 days at 60℃ and atmospheric pressure using a sealed thermostat. When the thickness of the left battery is B, the rate of increase in thickness was calculated as shown in Equation 1 below.

[Equation 1]

(B-A)/A × 100(%)

4. Room temperature life: After charging at room temperature with 4.4V, 50A CC-CV for 3 hours, discharge up to 2.7V with 2.7V, 50A current 500 times. At this time, the first discharge capacity was denoted C, and the capacity retention rate during the lifetime was calculated by dividing the 300th discharge capacity by the first discharge capacity.

As shown in Table 1, it can be seen that the lithium secondary battery containing the lithium secondary battery electrolyte according to the present invention showed a high capacity recovery rate even after 30 days at 60℃, and the thickness increase rate was also very low, 3 to 18%.

On the other hand, the lithium secondary battery employing the electrolytic solution of Comparative Example 1 that does not contain the boron derivative of the present invention exhibited low capacity retention at high temperature and discharge capacity at low temperature. Very low.

In addition, the electrolyte solutions of Comparative Example 2 and Comparative Example 3 contain an additive having a structure different from that of the boron derivative of the present invention, so that the battery characteristics at high and low temperatures are very low.

This is considered to be due to the structure of boron represented by Formula 1 of the present invention. Specifically, PEA12 having a branched structure in which the substituent of R in Formula 1 of the present invention is not a straight chain, has a large volume due to the branched chain. It is judged that the characteristics at low and high temperatures are low because a thick film is formed on the surface of the furnace and the resistance is increased.

However, in the case of PEA11, which is a boron derivative of the present invention, it is determined that R in Formula 1 is substituted with a linear alkyl group to have high and low temperature characteristics.

In addition, the secondary battery electrolyte of the present invention is a boron derivative represented by Formula 1 of the present invention and lithium bisoxalatoborate (LiB(C ₂ O ₄ ) ₂ , LiBOB), vinylene carbonate (VC), vinylethylene carbonate (VEC). , Ethylene sulfite (ethylene sulfite), ethane sultone, propane sultone (propane sulton, PS) by further including one or more additives selected from the high-temperature storage stability, low-temperature discharge capacity and life characteristics to further improve the secondary battery electrolyte of the present invention The lithium secondary battery comprising a has very high efficiency, stability and life characteristics.

As described above, the embodiments of the present invention have been described in detail, but those of ordinary skill in the art to which the present invention pertains, the present invention without departing from the spirit and scope of the present invention defined in the appended claims. It will be possible to implement the invention by various modifications. Therefore, changes in the embodiments of the present invention will not be able to depart from the technology of the present invention.

Claims (13)

Lithium salt;
Non-aqueous organic solvents;
Boron derivatives represented by the following formula (1); And
Lithium difluoro oxalate borate (LiFOB), lithium bis oxalate borate (LiB(C ₂ O ₄ ) ₂ , LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC) , Divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate, ethane sultone, propane sulton (PS), butane sultone sulton), ethene sultone, butene sultone, and propene sultone (PS):
[Formula 1]

(In Chemical Formula 1,
R is straight-chain (C1-C6)alkyl;
R ¹ to R ⁴ are each independently hydrogen or (C1-C10)alkyl.) The method of claim 1,
R ¹ to R ⁴ are each independently methyl or ethyl secondary battery electrolyte. The method of claim 1,
R is methyl or ethyl secondary battery electrolyte. The method of claim 1,
The boron derivative is a secondary battery electrolyte that is contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte. delete delete The method of claim 1,
The additive is a secondary battery electrolyte containing 0.1 to 5.0% by weight based on the total weight of the electrolyte. The method of claim 1,
The non-aqueous organic solvent is a secondary battery electrolyte selected from a cyclic carbonate-based solvent, a linear carbonate-based solvent, and a mixed solvent thereof. The method of claim 8,
The cyclic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and mixtures thereof, and the linear carbonate is dimethyl carbonate, diethyl carbonate, dipropyl A secondary battery electrolyte selected from the group consisting of carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof. The method of claim 8,
The non-aqueous organic solvent is a secondary battery electrolyte in which the mixing volume ratio of the linear carbonate solvent: the cyclic carbonate solvent is 1 to 9: 1. The method of claim 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(SO ₃ C ₂ F ₅ ) ₂ , LiN(SO ₂ F) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC ₆ H ₅ SO ₃ , LiSCN, LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ One or more secondary battery electrolytes selected from the group consisting of. The method of claim 1,
The lithium salt is a secondary battery electrolyte present in a concentration of 0.1 to 2.0 M. A lithium secondary battery comprising the secondary battery electrolyte according to any one of claims 1 to 4 and 7 to 12.