KR102022363B1 - Electrolyte for Secondary Battery and Lithium Secondary Battery Containing the Same - Google Patents

Abstract

The present invention relates to a high-voltage lithium secondary battery electrolyte and a high-voltage lithium secondary battery containing the same, and more particularly, the electrolyte thickness is not oxidized / decomposed when left at high temperature under high voltage, thereby suppressing gas generation to prevent expansion of the battery. The present invention relates to a high voltage lithium secondary battery electrolyte and a high voltage lithium secondary battery including the same, while reducing the increase rate and having excellent high temperature storage characteristics and excellent discharge characteristics at low temperatures.

Description

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

The present invention relates to a high-voltage lithium secondary battery electrolyte and a high-voltage lithium secondary battery containing the same, and more particularly, the electrolyte thickness is not oxidized / decomposed when left at high temperature under high voltage, thereby suppressing gas generation to prevent expansion of the battery. The present invention relates to a high voltage lithium secondary battery electrolyte and a high voltage lithium secondary battery including the same, while reducing the increase rate and having excellent high temperature storage characteristics and excellent discharge characteristics at low temperatures.

In recent years, the spread of portable electronic devices has been widespread, and according to the rapid miniaturization, light weight, and thinness of such portable electronic devices, the battery, which is a power source, is also compact, lightweight, and can be charged and discharged for a long time, and have high rate characteristics. Development is strongly demanded.

Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight. However, such lithium secondary batteries have safety problems such as ignition and explosion due to the use of nonaqueous electrolyte, and these problems become more serious as the capacity density of the battery increases.

In the nonaqueous electrolyte secondary battery, the deterioration in safety of the battery generated during continuous charging is a major problem. One of the causes that can affect this is the heat generated by the structural collapse of the anode. Its working principle is as follows. That is, the positive electrode active material of the non-aqueous electrolyte battery is composed of lithium-containing metal oxides capable of occluding and releasing lithium and / or lithium ions. Such a positive electrode active material is transformed into a thermally unstable structure as a large amount of lithium is released 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 the electrolyte solvent and the like. In particular, since the combustion of the electrolyte is further accelerated by the oxygen released from the anode, such a series of exothermic reactions causes the battery to ignite and burst due to thermal runaway.

A method of adding an aromatic compound as a redox shuttle additive in an electrolyte is used to control the ignition or explosion caused by the temperature rise inside the battery as described above. For example, Japanese Patent JP2002-260725 discloses a non-aqueous lithium ion battery that can prevent an overcharge current and consequent thermal runaway by using an aromatic compound such as biphenyl. In addition, U.S. Patent No. 5,879,834 also adds a small amount of aromatic compounds such as biphenyl and 3-chlorothiophene to electrochemically polymerize at abnormal overvoltage to increase internal resistance to improve battery safety. A method is described.

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

Meanwhile, high-voltage batteries (4.4V systems) have been continuously researched and developed as a way to increase the electric charge for miniaturization of batteries. In the same battery system, increasing the charge voltage generally increases the charge amount. However, safety problems such as electrolyte decomposition, lack of lithium storage space, and danger caused by the potential rise of the electrode occur. Therefore, in order to make a battery operated at a high voltage, the standard reduction potential difference between the negative electrode active material and the positive electrode active material is easily maintained large, and the overall conditions are managed by the system so that the electrolyte is not decomposed at this voltage.

Considering this point of high voltage battery, when using existing overcharge inhibitors such as biphenyl (BP) or cyclohexylbenzene (CHB) used in general lithium ion battery, many of them are decomposed during normal charge / discharge operation and only slightly It is easy to see that even at high temperatures, the battery characteristics deteriorate sharply, resulting in a shortening of the battery life. In addition, in the case of using a non-aqueous carbonate solvent which is commonly used as an electrolyte, the oxidation power is increased by charging the voltage higher than the normal charge potential of 4.2 V. As the charge and discharge cycle progresses, the decomposition reaction of the electrolyte proceeds and the life characteristics are improved. There is a problem of sudden deterioration.

Therefore, there is a continuous demand for the development of a method for improving the safety and capacity at high temperature storage without deteriorating the life characteristics of a high voltage battery (4.4V system).

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

The present invention is to solve the conventional problems, while maintaining the basic performance such as high rate charge and discharge characteristics, life characteristics, etc., the swelling of the battery is significantly improved due to the oxidation / decomposition of the electrolyte in a high voltage state The present invention provides a high voltage lithium secondary battery electrolyte having excellent high temperature storage characteristics and excellent discharge characteristics at low temperature, and a high voltage lithium secondary battery including the same.

The present invention to achieve the above object

Lithium salts;

Non-aqueous organic solvents; And

It provides a high-voltage lithium secondary battery electrolyte comprising a multi-nitrile compound represented by Formula 1;

[Formula 1]

In Formula 1, R ₁ to R ₃ are each independently cyano,-(CH ₂ ) _a -CN,-(CH ₂ ) _b -O- (CH ₂ ) _c -CN or C1-C5 alkoxycarbonyl ; R ₄ is hydrogen, cyano, — (CH ₂ ) _a —CN or — (CH ₂ ) _b —O— (CH ₂ ) _c —CN; a and c are each independently an integer from 2 to 10, b is an integer from 1 to 10; Provided that at least two of R ₁ to R ₄ are — (CH ₂ ) _m —CN or — (CH ₂ ) _m —O— (CH ₂ ) _n —CN.

In the high voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the multi-nitrile compound may be represented by the following formula (2) or:

[Formula 2]

[Formula 3]

In Formulas 2 and 3, R ₃ is cyano,-(CH ₂ ) _a -CN,-(CH ₂ ) _b -O- (CH ₂ ) _c -CN or C1-C5 alkoxycarbonyl; R ₄ is hydrogen, cyano, — (CH ₂ ) _a —CN or — (CH ₂ ) _b —O— (CH ₂ ) _c —CN; a and c are each independently an integer of 2 to 10, and b is an integer of 1 to 10.

In the electrolyte solution for a high voltage lithium secondary battery according to an embodiment of the present invention, the multinitrile compound may be selected from a multinitrile compound having the following structure:

.

.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the multi-nitrile compound may be included in 1 to 20% by weight based on the total weight of the electrolyte.

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

In the high-voltage 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 sulton, butene sultone, ethene sultone, butene sultone and propene sultone (PRS) may further include an additive selected from the group.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent may be selected from a cyclic carbonate solvent, a linear carbonate solvent and a mixed solvent thereof, the cyclic carbonate is ethylene carbonate, propylene carbonate , Butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate and mixtures thereof, the linear carbonate is dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl Propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate and mixtures thereof.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the non-aqueous organic solvent may have a mixing volume ratio of 9: 1 to 5: 5 of a linear carbonate solvent: cyclic carbonate solvent.

In the high-voltage 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 , 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 .

In the high voltage 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 high-voltage lithium secondary battery comprising the high-voltage lithium secondary battery electrolyte.

In the high-voltage lithium secondary battery electrolyte according to the present invention, at least three of the four substituents substituted with the central carbon atoms are substituents other than hydrogen, and at least two are nitrile groups, that is, cyanoalkyl groups or cyanoalkoxyalkyl groups. Including a multinitrile compound having a structure, the electrolyte is oxidized / decomposed in a high voltage state, and thus, swelling of the battery is remarkably improved, thereby exhibiting excellent high temperature storage characteristics and excellent discharge characteristics even at low temperatures.

In addition, the high-voltage lithium secondary battery including the high-voltage lithium secondary battery electrolyte according to the present invention is a phenomenon that the battery swells due to oxidation and decomposition of the electrolyte in a high voltage state while maintaining the basic performance such as high efficiency charge and discharge characteristics, life characteristics, etc. The swelling is remarkably improved to show excellent high temperature storage characteristics as well as excellent discharge characteristics even at low temperatures.

1-Oxidative decomposition voltage measurement results of Examples 1 to 4 and Comparative Example 1

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated more concretely. Unless otherwise defined in the technical terms and scientific terms used at this time, have a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs, unnecessarily obscure the subject matter of the present invention in the following description Description of known functions and configurations that may be omitted.

The present invention relates to a high voltage lithium secondary battery electrolyte for providing a battery having excellent high temperature storage characteristics and lifespan while ensuring stability of the battery in a high voltage state.

The present invention is a lithium salt; Non-aqueous organic solvents; And a multi-nitrile compound represented by Formula 1;

[Formula 1]

In Formula 1, R ₁ to R ₃ are each independently cyano,-(CH ₂ ) _a -CN,-(CH ₂ ) _b -O- (CH ₂ ) _c -CN or C1-C5 alkoxycarbonyl ; R ₄ is hydrogen, cyano, — (CH ₂ ) _a —CN or — (CH ₂ ) _b —O— (CH ₂ ) _c —CN; a and c are each independently an integer from 2 to 10, b is an integer from 1 to 10; Provided that at least two of R ₁ to R ₄ are — (CH ₂ ) _m —CN or — (CH ₂ ) _m —O— (CH ₂ ) _n —CN.

The effect as an electrolyte additive varies depending on the type of structure introduced between two nitrile groups. In the case of a compound in which a linear aliphatic hydrocarbon group is introduced in which no substituent other than a hydrogen atom is introduced between two nitrile groups, The free movement of atoms results in a relatively low dielectric constant, which easily oxidizes the electrolyte at high voltages. Therefore, when a compound containing a linear aliphatic hydrocarbon group having no substituent other than a hydrogen atom introduced between two nitrile groups is added to the electrolyte, the electrolyte is easily oxidized and decomposed at high voltage, thereby causing side reaction in the battery. However, at least three of the four substituents substituted for the central carbon atom for the high voltage lithium secondary battery according to the present invention are substituents other than hydrogen, and at least two of them are nitrile groups, that is, cyanoalkyl groups or cyanoalkoxyalkyl groups. It contains a multi-nitrile compound, which suppresses side reactions in the battery. This results in a significant improvement in swelling of the battery due to oxidation / decomposition of the electrolyte at high voltage. It shows discharge characteristics.

In the electrolyte solution for a high voltage lithium secondary battery according to an embodiment of the present invention, the multinitrile compound is represented by the following Chemical Formula 2 or 3:

[Formula 2]

[Formula 3]

In Formulas 2 and 3, R ₃ is cyano,-(CH ₂ ) _a -CN,-(CH ₂ ) _b -O- (CH ₂ ) _c -CN or C1-C5 alkoxycarbonyl; R ₄ is hydrogen, cyano, — (CH ₂ ) _a —CN or — (CH ₂ ) _b —O— (CH ₂ ) _c —CN; a and c are each independently an integer of 2 to 10, and b is an integer of 1 to 10.

In the electrolyte for a high voltage lithium secondary battery according to an embodiment of the present invention, the multinitrile compound is most preferably selected from multinitrile compounds having the following structure:

.

.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the multi-nitrile compound of Formula 1 may be included in 1 to 20% by weight based on the total weight of the secondary battery electrolyte, more preferably 1 to 15% by weight Included in%. When the content of the multi-nitrile compound of Formula 1 is less than 1% by weight, the battery does not exhibit an effect of adding an effect such as suppressing swelling of the battery during high temperature storage or a slight improvement in capacity retention rate, and a discharge capacity of a lithium secondary battery. Or if the improvement effect, such as output is insignificant and it contains more than 20 weight%, the sudden deterioration of lifetime will arise, but rather the characteristic of a lithium secondary battery will fall.

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the electrolyte is a life improvement additive for improving battery life, oxalatoborate-based compound, carbonate-based compound substituted with fluorine, vinylidene carbonate-based compound and sulfide It may further include one or two or more additives selected from the group consisting of a silyl group-containing compound.

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

[Formula 4]

(In Formula 4, R ₁₁ and R ₁₂ are each independently a halogen element or a halogenated C1 to C10 alkyl group.)

Specific examples of the oxalatoborate-based additives include LiB (C ₂ O ₄ ) F ₂ (lithium difluoro oxalatoborate, LiFOB) or LiB (C ₂ O ₄ ) ₂ (lithium bisoxalatoborate, LiBOB). Can be mentioned.

The carbonate compound substituted with fluorine may be fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluorodimethyl carbonate (FDMC), fluoroethyl methyl 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 sulfone (cyclic sulfonate), which may be used alone or in combination. Specifically, the sulfone may be represented by the following Chemical Formula 5, and may be divinyl sulfone. The sulfite may be represented by the following Chemical Formula 6, and may be ethylene sulfite or propylene sulfite. The sulfonate may be represented by the following Chemical Formula 7, and may be diallyl sulfonate. In addition, non-limiting examples of sultone include ethane sultone, propane sulton, butane sulton, ethene sultone, butene sultone, propene sultone, and the like.

[Formula 5]

[Formula 6]

[Formula 7]

(In Formulas 5, 6, and 7, R ₁₃ and R ₁₄ are each independently hydrogen, a halogen atom, an alkyl group of C1-C10, an alkenyl group of C2-C10, an alkyl group of halogen or C1-C10 substituted with halogen. A substituted C2-C10 alkenyl group.)

In the high-voltage 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), Fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate It may further include an additive selected from the group consisting of (diallyl sulfonate), ethane sultone, propane sulton (PS), butane sulton, ethene sultone, butene sultone and propene sultone (PS).

In the high-voltage lithium secondary battery electrolyte according to an embodiment of the present invention, the content of the additive is not significantly limited, to 0.1 to 5% by weight relative to the total weight of the electrolyte to improve the battery life in the secondary battery electrolyte, Preferably it may be included in 0.1 to 3% by weight.

In the high-voltage 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, a cyclic carbonate solvent, a linear carbonate solvent And it is preferable to select from these mixed solvents, It is most preferable to mix and use a cyclic carbonate solvent and a linear carbonate solvent. The cyclic carbonate solvent is large in polarity to sufficiently dissociate lithium ions, but has a disadvantage in that a large viscosity causes a small ion conductivity. Therefore, by using a linear carbonate solvent having a small polarity but a low viscosity in the cyclic carbonate solvent, it is possible to optimize the characteristics of the lithium secondary battery.

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

In the high-voltage 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 solvent and a linear carbonate solvent, the mixing volume ratio of linear carbonate solvent: cyclic carbonate solvent is 1: 1 to 1 It may be 9: 1, preferably used by mixing in a volume ratio of 1.5: 1 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, 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 , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC ₆ H ₅ SO ₃ , LiSCN, LiAlO ₂ , LiAlCl ₄ , LiN (C one or two selected from the group consisting of _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 abnormal.

The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M, more preferably in the range of 0.7 to 1.6 M. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, and if it exceeds 2.0 M, the viscosity of the electrolyte is increased, thereby reducing the mobility of lithium ions. The lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery.

The electrolyte solution for high voltage lithium secondary batteries of the present invention is generally stable at a temperature range of -20 ° C to 60 ° C, and maintains electrochemically stable characteristics even at a voltage of 4.4 V region, so that all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries may be used. Can be applied.

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

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

The high-voltage lithium secondary battery prepared from the high-voltage lithium secondary battery electrolyte according to the present invention exhibits low temperature discharge efficiency of 70% or more and high temperature storage efficiency of 75% or more, and increases the thickness of the battery when it is left at a high temperature for 4 to 14%. It is characterized by low.

The high voltage 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, nickel, and a composite metal oxide with lithium. The solid solution ratio between the metals may be various, 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. Specific examples of the positive electrode active material may be a compound represented by any one of the following formula:

_{Li a A 1 - b B b} D 2 ( in the above formula, 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); _{Li a E 1 - b B b} O 2 - ( in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; _{LiE 2 - b B b O 4} - ( in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) c D c; Li _a Ni _{1 -b - c} Co _b B _c D _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); _{Li a Ni 1 -b- c Co 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 a); 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, and 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, and 0 <α ≦ 2); 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, and 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, and 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 (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 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, 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 includes a negative electrode active material capable of occluding and desorbing lithium ions, and examples of the negative electrode active material include carbon materials such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, lithium metal, alloys of lithium and other elements, and the like. Can be. For example, amorphous carbon includes hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, mesophase pitch-based carbon fibers (MPCF), and the like. The crystalline carbon includes a graphite material, and specific examples thereof include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like. The carbonaceous material is preferably a material having a crystallite size (Lc) of at least 20 nm between the d002 interplanar distance of 3.35 to 3.38 Å X-ray diffraction. Other elements alloyed with lithium may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The positive electrode or the negative electrode may be prepared 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. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and as the negative electrode current collector, copper or a copper alloy may be commonly used. The positive electrode current collector and the negative electrode current collector may be in the form of a foil or a mesh.

The binder is a material that plays a role of pasting the active material, mutual adhesion of the active material, adhesion with the current collector, buffering effect on the expansion and contraction of the active material, and the like, for example, polyvinylidene fluoride (PVdF), polyhexafluoro Copolymer of propylene-polyvinylidene fluoride (PVdF / HFP)), poly (vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, alkylated polyethylene oxide, polyvinyl ether, poly (methylmeth) Acrylate), poly (ethyl acrylate), polytetrafluoroethylene, polyvinylchloride, 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. When the content of the binder is too small, the adhesion between the electrode active material and the current collector is insufficient, and when the content of the binder is too large, the adhesion is improved, but the content of the electrode active material decreases by that amount, which is disadvantageous in increasing the capacity of the battery.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery constituted, and may be a graphite-based conductive agent, a carbon black-based conductive agent, a metal or a metal compound-based compound. At least one selected from the group consisting of conductive agents can be used. Examples of the graphite conductive agent include artificial graphite and natural graphite, and examples of the carbon black conductive agent include acetylene black, ketjen black, denka black, thermal black, and channel black. (channel black), and examples of the metal or metal compound conductive agent include tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ , and perovskite such as 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. If the content of the conductive agent is less than 0.1% by weight, the electrochemical properties are lowered, and if it is more than 10% by weight, the energy density per weight is reduced.

The thickener is not particularly limited as long as it can play a role of controlling the viscosity of the active material slurry. For example, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or the like may be used.

As a solvent in which an electrode active material, a binder, a conductive material, etc. are disperse | distributed, 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 high voltage 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 movement path of lithium ions, and the separator may be polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene. Polyolefin-based polymer membranes such as polyethylene, polypropylene / polyethylene / polypropylene, or multiple membranes thereof, microporous films, woven fabrics and nonwoven fabrics can be used. In addition, a film coated with a resin having excellent stability in a porous polyolefin film may be used.

The high voltage lithium secondary battery of the present invention may be formed in other shapes, such as cylindrical, pouch type, in addition to the square.

Hereinafter, examples and comparative examples of the present invention are 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 can be seen that all of the lithium salts dissociate to have a lithium ion concentration of 1 mole (1 M), so that the base electrolyte can be formed by dissolving a corresponding amount of the lithium salt such as LiPF ₆ in the base solvent to a concentration of 1 mole (1 M). .

Preparation Example 1 3- [3- (2-cyanoethoxy) -2,2-bis- (2-cyanoethoxymethyl) propoxy] propionitrile (3- [3- (2-cyanoethoxy ) -2,2-bis- (2-cyanoethoxymethyl) propoxy] propionitrile, hereinafter referred to as 'PHE22'

Pentaerythritol (21 g) and 40% aqueous potassium hydroxide solution (17 mL) were added to xylene (75 mL). Acrylonitrile (133 g) was slowly added to the solution at room temperature for 1 hour, and then stirred at room temperature for 3 hours. After toluene was added, the organic layer was washed three times with 5% aqueous sodium chloride solution and aqueous hydrochloric acid solution. Magnesium sulfate was added and dried, followed by filtration and removal of the solvent by distillation under reduced pressure to yield a colorless liquid 3- [3- (2-cyanoethoxy) -2,2-bis- (2-cyanoethoxymethyl) pro Foxy] propionitrile (52 g) was obtained.

¹ H NMR (CDCl ₃ , 500 MHz) δ 3.67 (t, 8H), 3.49 (S, 8H), 2.61 (t, 8H)

Preparation Example 2 Synthesis of diethyl 2,2-bis (2-cyanoethyl) malonate (hereinafter referred to as 'PHE24')

Diethyl malonate (50 g) and Triton B (40% methanol solution, 6.5 g) were added to dioxane (60 mL), followed by the slow addition of acrylonitrile (33 g). After stirring at 60 ° C. for 12 hours, the temperature was lowered to room temperature. After neutralizing with an aqueous 0.1 N hydrochloric acid, the reaction was added to ice water. After filtration of the precipitated product, the white solid product diethyl 2,2-bis (2-cyanoethyl) malonate (74 g) was obtained through recrystallization in ethanol.

Melting Point: 62.2-63.5 ℃

¹ H NMR (CDCl ₃ , 500 MHz) δ 4.10 (t, 4H), 2.47 (t, 4H), 2.26 (t, 4H), 1.20 (t, 6H)

Preparation Example 3 Synthesis of 4,4-dicyano-heptanedinitrile (4,4-dicyano-heptanedinitrile, hereinafter referred to as 'PHE25')

To the aqueous solution of malononitrile (30 g) and potassium hydroxide (2.6 g) in water (200 mL) was slowly added acrylonitrile (56 g) for 1 hour and then stirred at room temperature for 2 hours. The reaction was terminated with 1N aqueous hydrochloric acid solution, extracted with ethyl acetate, and washed three times with water. The ethyl acetate solvent of the organic solvent layer was removed by distillation under reduced pressure. The solvent was removed and the resulting solid was dried in a vacuum oven to give 4,4-dicyano-heptanedinitrile (43 g).

¹ H NMR (CDCl ₃ , 500 MHz) δ 2.60 (t, 4H), 2.30 (t, 4H)

Preparation Example 4 Synthesis of 1,2,3-tris- (β-cyanoethoxy) -propane (1,2,3-tris- (β-cyanoethoxy) -propane, hereinafter referred to as 'PHE31')

Glycerol (14 g) and 40% aqueous potassium hydroxide solution (17 mL) were added to xylene (75 mL). Acrylonitrile (133 g) was slowly added to the solution at room temperature for 1 hour and stirred at room temperature for 3 hours. Toluene was added and washed three times with 5% aqueous sodium chloride solution and hydrochloric acid solution. Magnesium sulfate was added, dried, filtered and the solvent was removed by distillation under reduced pressure to obtain a colorless liquid. Purified 1,2,3-tris- (β-cyanoethoxy) -propane (35 g) was obtained by distillation under reduced pressure.

¹ H NMR (CDCl ₃ , 500 MHz) δ 3.87 (m, 1H), 3.72 (m, 6H), 3.62 (m, 6H), 2.64 (m, 6H)

Example 1-7 and Comparative Example 1-2

The electrolyte solution was a solution in which LiPF ₆ was dissolved in a mixed solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a volume ratio of 3: 7 so as to be 1.0 M solution, and the basic electrolyte solution (1M LiPF ₆ , EC / EMC = 3). It was prepared by further adding the components shown in Table 1 as: 7).

The battery to which the non-aqueous electrolyte was applied was prepared as follows.

LiNiCoMnO ₂ and LiMn ₂ O ₄ as a positive electrode active material were mixed at a weight ratio of 1: 1, polyvinylidene fluoride (PVdF) as a binder and carbon as a binder were mixed at a weight ratio of 92: 4: 4, and then N- A positive electrode slurry was prepared by dispersing in methyl-2-pyrrolidone. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode. Synthetic graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose 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 copper foil having a thickness of 15 μm, dried, and rolled to prepare a negative electrode.

A cell separator was formed by stacking a 25 μm thick polyethylene (PE) film separator between the electrodes, using a pouch having a thickness of 8 mm x 270 mm x 185 mm. Injecting the non-aqueous electrolyte, a 25Ah lithium secondary battery for EV was prepared.

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

* Ratings *

1. Capacity recovery rate after 30 days at 60 ° C (high temperature storage efficiency): After charging for 3 hours with 4.4V and 12.5A CC-CV at room temperature, and after 30 days at 60 ° C, discharge to CC up to 2.7V with 25A current. After the available capacity (%) compared to the initial dose was measured.

2. Thickness increase after 30 days at 60 ℃: After charging for 3 hours at 4.4V and 12.5A CC-CV at room temperature, the thickness of the battery is called A and the temperature is exposed to 30 ℃ at 60 ℃ and atmospheric pressure using a sealed thermostat. When the thickness of the battery, which was left unattended, the increase rate of the thickness was calculated by Equation 1 below.

[Equation 1]

(B-A) / A * 100 (%)

3. Room temperature life: After charging for 3 hours at 4.4V, 25A CC-CV at room temperature, the discharge is repeated 300 times to 2.7V, 25A current to 2.7V. At this time, the first discharge capacity was referred to as C, and the 300th discharge capacity was divided by the first discharge capacity to calculate the capacity retention rate in the lifetime.

4. -20 ℃ 1C Discharge: After charging for 3 hours at 12.5A, 4.4V CC-CV at room temperature, and leaving it at -20 ℃ for 4 hours, it is discharged to CC at 25A and discharged to CC up to 2.7V. The usable capacity (%) relative to the dose was measured.

Electrolyte composition 30 days after 60 ℃ Capacity retention during life -20 ℃ discharge
Volume Capacity recovery rate Thickness increase rate Example 1 Basic electrolyte solution + 10% PHE22 86% 5% 87% 79% Example 2 Basic electrolyte solution + 10% PHE24 84% 9% 84% 76% Example 3 Basic electrolyte solution + 10% PHE25 75% 10% 76% 71% Example 4 Basic electrolyte solution + 10% PHE31 83% 9% 86% 80% Example 5 Basic electrolyte solution + PHE22 10% + LiBOB 1wt% 89% 2% 89% 84% Example 6 Basic electrolyte solution + PHE22 10% + VC 1wt% 90% One% 92% 83% Example 7 Basic electrolyte solution + PHE22 10% + VC 1wt% + PS 1wt% 93% One% 91% 79% Comparative Example 1 Basic electrolyte 37% 30% 20% 55% Comparative Example 2 Basic electrolyte solution + CN- (CH ₂ ) ₄ -CN 10% 65% 16% 68% 12% Basic electrolyte solution: 1M LiPF ₆ , EC / EMC = 3: 7
PHE22: Compound of Preparation Example 1
PHE24: Compound of Preparation Example 2
PHE25: Compound of Preparation Example 3
PHE31: Compound of Preparation Example 4
LiBOB: Lithium-bis (Oxalato) Borate
VC: Vinylene carbonate
PS: 1,3-propane sultone

As described above, the high voltage lithium secondary battery including the high voltage lithium secondary battery electrolyte according to the present invention showed a low temperature discharge efficiency of at least 71% and a high temperature storage efficiency of at least 75%. In addition, it was confirmed that when the battery is left at a high temperature for a long time, the thickness increase rate of the battery is very low as 1 to 10%, and the capacity retention rate during the life is excellent as 76% or more (Examples 1 to 7). On the other hand, Comparative Examples 1 and 2 showed low temperature discharge efficiency of less than 55% and high temperature storage efficiency of less than 65%, and the thickness increase rate of the battery was very high (16-30%) when left at high temperature for a long time. The retention rate was 20% in the comparative example 1, and 68% in the comparative example 2.

In order to measure the oxidative decomposition voltages of Examples 1 to 4 and Comparative Example 1, the LSV (Pt) electrode was used as the working electrode, and the Li-metal was used as the counter electrode and the reference electrode. As a result of measuring the linear sweep voltametry, the electrolyte of Example 1 (basic electrolyte + PHE22 10%), the electrolyte of Example 2 (basic electrolyte + PHE24 10%), and the electrolyte of Example 3 compared to the basic electrolyte of Comparative Example 1 10% of PHE22, PHE24, PHE25, PHE31, and PHE21 were added to each of (Basic Electrolyte + PHE25 10%) and Example 4 (Basic Electrolyte + PHE31 10%), thereby increasing the electrolyte oxidation potential (High Oxidation Potential). It was confirmed that the decomposition in the less [Fig. 1].

In particular, when comparing Examples 1 to 4 and Comparative Example 2, the high temperature storage efficiency (Example 1: 86%, Example 2: 84%, Example 3: 75 according to the structure of the nitrile compound added to the basic electrolyte solution) %, Example 4: 83%, Comparative Example 2: 65%), the rate of increase in thickness of the battery when left at high temperature (Example 1: 5%, Example 2: 9%, Example 3: 10%, Example) 4: 9%, Comparative Example 2: 16%), low temperature discharge efficiency (Example 1: 79%, Example 2: 76%, Example 3: 71%, Example 4: 80%, Comparative Example 2: 12 %) Shows a significant difference. This difference is due to the structural properties of the nitrile compound added to the basic electrolyte, wherein at least three of the four substituents substituted for the central carbon atom are substituents other than hydrogen, At least two of the structures are nitrile groups, that is, cyanoalkyl groups or cyanoalkoxyalkyl groups, and adiponitrile (CN—CH ₂ CH) in which hydrogen atoms are introduced at all carbon atoms present between two nitrile groups of Comparative Example 2 ₂ CH ₂ CH ₂ -CN) has a different structure.

That is, the adiponitrile compound of Comparative Example 2 is a structure in which the carbon atom existing between two nitrile groups is not substituted by a substituent other than hydrogen, and the mobility of atoms in the molecule is relatively free and relatively low in dielectric constant, It does not effectively block the anode surface. Therefore, when a compound containing a linear aliphatic hydrocarbon group in which no substituent other than hydrogen is introduced between two nitrile groups of Comparative Example 2 is added to the electrolyte, the electrolyte is easily oxidatively decomposed at high voltage and causes side reaction in the battery. In addition, the high temperature storage efficiency and the low temperature discharge efficiency are lowered, and the thickness increase rate of the battery increases when it is left at a high temperature for a long time. In addition, it was confirmed that the low-temperature discharge characteristics of the nitrile compound and the adiponitrile of Comparative Example 2 were worse than that of Comparative Example 1 without adding the nitrile compound.

However, in the electrolyte solution for high voltage lithium secondary batteries according to the present invention, at least three of the four substituents substituted for the central carbon atoms are substituents other than hydrogen, and at least two of them are nitrile groups, that is, cyanoalkyl groups or cyanoalkoxy. It contains an alkyl group of multinitrile compounds, which suppresses side reactions in the battery. This causes the electrolyte to be oxidized / decomposed under high voltage, thereby significantly improving the swelling of the battery, thereby exhibiting excellent high temperature storage characteristics as well as low temperature. Also exhibits excellent discharge characteristics.

Although described in detail with respect to embodiments of the present invention as described above, those of ordinary skill in the art, without departing from the spirit and scope of the invention as defined in the appended claims Various modifications may be made to the invention. Therefore, changes in the future embodiments of the present invention will not be able to escape the technology of the present invention.

Claims (13)

Lithium salts;
Non-aqueous organic solvents; And
An electrolytic solution for a lithium secondary battery comprising a multinitrile compound represented by Formula 1;
[Formula 1]

In Formula 1, R ₁ and R ₂ are each independently cyano, — (CH ₂ ) _a —CN, or C 1 -C 5 alkoxycarbonyl; R ₃ and R ₄ are each independently cyano or-(CH ₂ ) _a -CN; a is an integer from 2 to 10; At least two or more of R ₁ to R ₄ are — (CH ₂ ) _a —CN. The method of claim 1,
The multinitrile compound is a lithium secondary battery electrolyte represented by the following formula (2):
[Formula 2]

In Formula 2, R ₃ and R ₄ are each independently cyano, or C1-C5 alkoxycarbonyl. The method of claim 2,
The multi-nitrile compound is selected from the multi-nitrile compound of the structure of the lithium secondary battery electrolyte:

. The method of claim 1,
The multinitrile compound is a lithium secondary battery electrolyte that is contained in 1 to 20% by weight based on the total weight of the electrolyte. The method of claim 1,
The electrolyte solution further comprises one or two or more additives selected from the group consisting of an oxalatoborate compound, a carbonate compound substituted with fluorine, a vinylidene carbonate compound and a sulfinyl group-containing compound. The method of claim 5,
The electrolyte solution is lithium difluoro oxalatoborate (LiFOB), lithium bisoxalatoborate (LiB (C ₂ O ₄ ) ₂ , LiBOB), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), divinyl sulfone, ethylene sulfite, propylene sulfite, diallyl sulfonate, ethane sulfone, propane sulton (PS), butane Butane sulton, ethene sultone, butene sultone and propene sultone (PRS) further comprises an additive selected from the group consisting of lithium secondary battery electrolyte. The method of claim 5,
The additive is a lithium secondary battery electrolyte containing 0.1 to 5.0% by weight relative to the total weight of the electrolyte. The method of claim 1,
The non-aqueous organic solvent is a lithium secondary battery electrolyte selected from a cyclic carbonate solvent, a linear carbonate 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, vinyl ethylene carbonate, fluoroethylene carbonate and mixtures thereof, and the linear carbonate is dimethyl carbonate, diethyl carbonate, dipropyl An electrolyte for a lithium secondary battery 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 linear carbonate solvent: cyclic carbonate solvent mixing volume ratio of 1: 1 to 9: 1 lithium secondary battery electrolyte. The method of claim 1,
The lithium salt may be 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 , 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 water), LiCl, LiI and LiB (C ₂ O ₄ ) ₂ One or two or more of the electrolyte for a lithium secondary battery selected from the group consisting of. The method of claim 1,
The lithium salt is a lithium secondary battery electrolyte present at a concentration of 0.1 to 2.0 M. A lithium secondary battery comprising the lithium secondary battery electrolyte according to any one of claims 1 to 12.

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