KR102436421B1 - Electrolyte for lithium secondary battery and lithium secondary battery including the same - Google Patents

Abstract

상기 식들에서,
A는 치환 또는 비치환된 지방족 탄화수소 또는 (-C₂H₄-O-C₂H₄-)n이고;
X는 할로겐이고;
n은 1 내지 10의 정수 중에서 선택된다.non-aqueous organic solvents; lithium salt; Compound (A) represented by the following formula (1); And an electrolyte for a lithium secondary battery comprising a compound (B) represented by the following formula (2) and a lithium secondary battery including the same are provided:
<Formula 1><Formula2>

In the above formulas,
A is a substituted or unsubstituted aliphatic hydrocarbon or (-C ₂ H ₄ -OC ₂ H ₄ -)n;
X is halogen;
n is selected from an integer of 1 to 10;

Description

Electrolyte for lithium secondary battery and lithium secondary battery including same

It relates to an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same.

Lithium secondary batteries are used as driving power for portable electronic devices such as video cameras, mobile phones, and notebook computers. Rechargeable lithium secondary batteries have more than three times the energy density per unit weight and high-speed charging compared to conventional lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries.

Since the lithium secondary battery operates at a high driving voltage, an aqueous electrolyte solution highly reactive with lithium cannot be used. As an electrolyte for a lithium secondary battery, an organic electrolyte is generally used. The organic electrolyte is prepared by dissolving a lithium salt in an organic solvent. It is preferable that the organic solvent is stable at high voltage, has high ionic conductivity and dielectric constant, and has low viscosity.

However, when an organic electrolyte containing a lithium salt is used as the electrolyte for a lithium secondary battery, the lifespan characteristics and high temperature stability of the lithium secondary battery may be deteriorated due to a side reaction between the negative electrode/anode and the electrolyte.

Accordingly, there is a need for an electrolyte for a lithium secondary battery capable of providing a lithium secondary battery having improved lifespan characteristics and high temperature stability.

One aspect is to provide an electrolyte solution for a lithium secondary battery comprising a combination of a novel additive for a lithium secondary battery.

Another aspect is to provide a lithium secondary battery including the electrolyte solution for a lithium secondary battery.

According to one aspect,

non-aqueous organic solvents;

lithium salt;

Compound (A) represented by the following formula (1); and

An electrolyte for a lithium secondary battery comprising a compound (B) represented by the following formula (2) is provided:

<Formula 1> <Formula 2>

In the above formulas,

A is a substituted or unsubstituted aliphatic hydrocarbon or (-C ₂ H ₄ -OC ₂ H ₄ -)n;

X is halogen;

n is selected from an integer from 1 to 10,

The substituent of the substituted aliphatic hydrocarbon is C ₁ -C ₂₀ alkyl group, C ₂ -C ₂₀ alkenyl group, C ₂ -C ₂₀ alkynyl group, C ₁ -C ₂₀ alkoxy group, halogen, cyano group consisting of hydroxy and nitro is one or more independently selected from the group

According to the other side,

anode; cathode; and

There is provided a lithium secondary battery comprising the electrolyte for a lithium secondary battery according to the above.

According to one aspect, high-temperature characteristics of a lithium secondary battery may be improved by using an electrolyte for a lithium secondary battery including a combination of a new compound.

1 is a schematic diagram of a lithium secondary battery according to an exemplary embodiment.
<Explanation of symbols for main parts of the drawing>
1: lithium secondary battery 2: negative electrode
3: positive electrode 4: separator
5: Battery case 6: Cap assembly

Hereinafter, an additive for a lithium battery electrolyte solution according to exemplary embodiments, an organic electrolyte solution including the same, and a lithium battery employing the electrolyte solution will be described in more detail.

As used herein, the term “hydrocarbon” refers to an organic compound composed of carbon and hydrogen. For example, hydrocarbons may contain single bonds, double bonds, triple bonds, or combinations thereof.

In this specification, "a" and "b" in "C _a -C _b " mean the number of carbon atoms in a specific functional group. That is, the functional group may include "a" to "b" carbon atoms. Thus, for example, a “C ₁ -C ₄ alkyl group” refers to an alkyl group having 1 to 4 carbons, ie, CH ₃ - , CH ₃ CH ₂ - , CH ₃ CH ₂ CH ₂ - , (CH ₃ ) ₂ CH -, CH ₃ CH ₂ CH ₂ CH ₂ - , CH ₃ CH ₂ CH(CH ₃ )- and (CH ₃ ) ₃ C-.

Certain radical nomenclatures may include mono-radicals or di-radicals depending on the context. For example, if one substituent requires two points of connection in the other molecule, then that substituent should be understood to be a di-radical. For example, substituents that are recognized as alkyl groups requiring two points of attachment include di-radicals such as -CH ₂ - , -CH ₂ CH ₂ - , -CH ₂ CH(CH ₃ )CH ₂ - , and the like. Other radical nomenclatures clearly indicate that the radical is a diradical, such as "alkylene" or "alkenylene".

As used herein, the term "alkyl group" or "alkylene group" means a branched or unbranched aliphatic hydrocarbon group. In one embodiment, the alkyl group may be substituted or unsubstituted. The alkyl group includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a hexyl group, a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, etc. , but not limited thereto, each of which may be optionally substituted in other embodiments. In other embodiments, the alkyl group can contain from 1 to 6 carbon atoms. For example, a C1-C6 alkyl group is a methyl group. Ethyl group, propyl group, isopropyl group, butyl group. an isobutyl group, a sec-butyl group, a pentyl group, a 3-pentyl group, a hexyl group, and the like, but are not limited thereto.

As used herein, "alkenyl group" or "alkenylene group" is a hydrocarbon group having 2 to 20 carbon atoms including one or more carbon-carbon double bonds, ethenyl group, 1-propenyl group, 2-propenyl group, 2-methyl -1-propenyl group, 1-butenyl group, 2-butenyl group, cyclopropenyl group, cyclopentenyl, cyclohexenyl, cyclopentenyl, and the like, but are not limited thereto. In other embodiments, an alkenyl group may be substituted or unsubstituted. In another embodiment, the alkenyl group may have 2 to 40 carbon atoms.

As used herein, the term "alkynyl group" or "alkynylene group" refers to a hydrocarbon group having 2 to 20 carbon atoms including one or more carbon-carbon triple bonds, ethynyl group, 1-propynyl group, 1-butynyl group, 2 -Butynyl group, etc. are included, but are not limited thereto. In other embodiments, an alkynyl group may be substituted or unsubstituted. In another embodiment, the alkynyl group may have 2 to 40 carbon atoms.

As used herein, a substituent is derived from an unsubstituted parent group, wherein one or more hydrogen atoms are substituted with another atom or a functional group. Unless otherwise indicated, when a functional group is considered to be “substituted”, this means that the functional group is C ₁ -C ₂₀ alkyl, C ₂ -C ₂₀ alkenyl, C ₂ -C ₂₀ alkynyl, C ₁ -C ₂₀ alkoxy, halogen. , cyano, means substituted with one or more substituents independently selected from the group consisting of hydroxy and nitro. When a functional group is described as being “optionally substituted”, that functional group may be substituted with the aforementioned substituents.

An electrolyte for a lithium secondary battery according to an embodiment includes a non-aqueous organic solvent; lithium salt; Compound (A) represented by the following formula (1); and a compound (B) represented by the following formula (2):

<Formula 1> <Formula 2>

In the above formulas,

A is a substituted or unsubstituted aliphatic hydrocarbon or (-C ₂ H ₄ -OC ₂ H ₄ -)n;

X is halogen;

n is selected from an integer from 1 to 10,

The substituent of the substituted aliphatic hydrocarbon is C ₁ -C ₂₀ alkyl group, C ₂ -C ₂₀ alkenyl group, C ₂ -C ₂₀ alkynyl group, C ₁ -C ₂₀ alkoxy group, halogen, cyano group consisting of hydroxy and nitro at least one independently selected from the group.

Compound (A) represented by Formula 1 and compound (B) represented by Formula 2 are added to the electrolyte for a lithium secondary battery to obtain the effect of improving battery characteristics at high temperatures, such as reducing the thickness increase rate of the lithium secondary battery and improving recovery capacity can

The reason why the compound (A) and the compound (B) are added to the electrolyte to improve the performance of the lithium secondary battery will be described in more detail below, but this is to help the understanding of the present invention, and the scope of the present invention is not It is not limited to the scope.

In general, during charging and discharging of a lithium secondary battery, an anion (eg, PF ₆ ^- anion) or anion by-product (eg, PF ₅ ) of a lithium salt contained in an electrolyte for a lithium secondary battery is adsorbed to the positive electrode or negative electrode film. , there is a problem in that deterioration of battery characteristics occurs.

When the compound (A) or compound (B) is included, there is an effect of reducing the gas generated after storage at a high temperature, but when each is used alone, a film on the anode is formed to increase the initial resistance, There was this diminishing problem.

The inventors of the present application found that when compound (A) and compound (B) are included together, gas generation and resistance after high-temperature storage are reduced, as well as initial resistance is reduced, resistance reduction effect at room temperature and high temperature, and high voltage characteristics It was confirmed that this excellent effect was exhibited.

Specifically, the difluorophosphate (-PF ₂ ) group included at the terminal of the compound (A) is a thermal decomposition product of a lithium salt (eg, PF ₅ ) present in the electrolyte for a lithium battery or an anion dissociated from the lithium salt ( For example, PF ₆ ^-anions ) can be coordinated to stabilize them. By stabilizing the thermal decomposition product or dissociated anions of the lithium salt, side reactions between them and the electrolyte for a lithium secondary battery can be suppressed. Accordingly, lifespan characteristics and high temperature stability of the lithium secondary battery may be improved.

In addition, through this, it is possible to adsorb compound (B) instead of anions dissociated from lithium salts on the positive electrode or negative electrode film. Due to the sulfate functional group included in the compound (B), a polysulfate analog film is formed on the surface of the anode, thereby suppressing gas generation on the electrode surface. In addition, through the film formed by the isocyanate group (-NCO) contained in the compound (B), it is possible to suppress the deterioration of the cathode active material itself.

On the other hand, during the initial charging of the lithium secondary battery, the decomposition reaction of the electrolyte occurs on the surface of the negative electrode, because the reduction potential of the electrolyte is relatively higher than the potential of lithium. This electrolyte decomposition reaction forms a solid electrolyte interphase (SEI) on the electrode surface to suppress the movement of electrons required for the reaction between the cathode and the electrolyte, thereby preventing further decomposition of the electrolyte. Accordingly, the performance of the battery largely depends on the characteristics of the film formed on the surface of the anode, and in consideration of this, by introducing an electrolyte additive that can be decomposed before the electrolyte during the charging reaction, the SEI layer having stronger and better electrical properties formation is required.

The compound (A) contains a difluorophosphate group having excellent electrochemical reactivity at one end during the charging reaction, so that it is preferentially decomposed over the electrolyte to form an SEI film having strong and excellent electrical properties on the surface of the anode.

In addition, since the difluorophosphate (-PF ₂ ) group has excellent electrical and chemical reactivity, it can form a donor-acceptor bond with the transition metal oxide exposed on the surface of the positive electrode active material, and thus A protective layer in the form of a composite may be formed.

In addition, since the difluorophosphate attached to the transition metal oxide during the initial charging of the lithium secondary battery can be oxidized to a plurality of fluorophosphates, as a result, a more stable, ionic conductivity inactive layer is formed on the positive electrode. Accordingly, it is possible to prevent oxidative decomposition of other components of the electrolyte, and as a result, it is possible to improve the cycle characteristics of the lithium secondary battery and prevent the swelling phenomenon from occurring.

According to one embodiment, in Formula 1, A is a C ₁ -C ₂₀ aliphatic hydrocarbon; C ₁ -C substituted with one or more of C ₁ -C ₂₀ alkyl group, C ₂ -C ₂₀ alkenyl group, C ₂ -C ₂₀ alkynyl group, C ₁ -C ₂₀ alkoxy group, halogen, cyano, hydroxy and nitro ₂₀ aliphatic hydrocarbons; and (-C ₂ H ₄ -OC ₂ H ₄ -) at least one selected from _n ; n may be selected from an integer of 1 to 5.

For example, in Formula 1, A may be C ₁ -C ₂₀ alkylene, C ₂ -C ₂₀ alkenylene, or C ₂ -C ₂₀ alkynylene.

For example, in Formula 1, A may be a methylene group, an ethylene group, a propylene group, a butylene group, or an ethenylene group. For example, in Formula 1, A may be an ethylene group.

Specifically, the compound (A) represented by Formula 1 may be represented by Formula 1-1 below:

<Formula 1-1>

.

.

For example, in Formula 2, X may be -F, -Cl, -Br, or -I.

Specifically, the compound (B) represented by Formula 2 may be represented by Formula 2-1 below:

<Formula 2-1>

.

.

The content of the compound (A) represented by Formula 1 in the electrolyte for a lithium secondary battery may be 0.01 to 5% by weight based on the total weight of the electrolyte for a lithium secondary battery, but is not necessarily limited to this range, and an appropriate amount if necessary this can be used For example, the content of the compound (A) in the electrolyte for a lithium secondary battery may be 0.01 to 4 wt% based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (A) in the electrolyte for a lithium secondary battery may be 0.01 to 3% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (A) in the electrolyte for a lithium secondary battery may be 0.01 to 2% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (A) in the electrolyte for a lithium secondary battery may be 0.05 to 2% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (A) in the electrolyte for a lithium secondary battery may be 0.05 to 1% by weight based on the total weight of the electrolyte for a lithium secondary battery. Further improved battery characteristics may be obtained within the above content range. When the content of the compound (A) is out of the above content range and exceeds 5% by weight based on the total weight of the electrolyte for a lithium secondary battery, there is a problem in that the battery life is reduced.

The content of the compound (B) represented by Formula 2 in the electrolyte for a lithium secondary battery may be 0.01 to 5% by weight based on the total weight of the electrolyte for a lithium secondary battery, but is not necessarily limited to this range, and an appropriate amount may be used as needed. can be used For example, the content of the compound (B) in the electrolyte for a lithium secondary battery may be 0.01 to 4% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (B) in the electrolyte for a lithium secondary battery may be 0.01 to 3% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (B) in the electrolyte for a lithium secondary battery may be 0.01 to 2% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (B) in the electrolyte for a lithium secondary battery may be 0.05 to 2% by weight based on the total weight of the electrolyte for a lithium secondary battery. For example, the content of the compound (B) in the electrolyte for a lithium secondary battery may be 0.05 to 1% by weight based on the total weight of the electrolyte for a lithium secondary battery. Further improved battery characteristics may be obtained within the above content range. When the content of the compound (B) exceeds the total weight of the electrolyte for a lithium secondary battery out of the above content range and exceeds 5% by weight, there is a problem in that the battery life is reduced.

The content ratio of the compound (A) to the compound (B) in the electrolyte for a lithium secondary battery may be 1:1 to 1:5.

In the electrolyte for a lithium secondary battery, the non-aqueous organic solvent may include a low boiling point solvent. The low boiling point solvent means a solvent having a boiling point of 200 °C or less at 25 °C and 1 atm.

For example, the non-aqueous organic solvent is at least one selected from the group consisting of dialkyl carbonates, cyclic carbonates, linear or cyclic esters, linear or cyclic amides, aliphatic nitriles, linear or cyclic ethers, and derivatives thereof. may include.

More specifically, the non-aqueous organic solvent is dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, ethyl propionate (EP), ethyl butyrate, acetonitrile, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, gamma-valerolactone, gamma- It may include at least one selected from the group consisting of butyrolactone (GBL) and tetrahydrofuran, but is not limited thereto, and any low-boiling solvent that can be used in the art is possible.

For example, the non-aqueous organic solvent is ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, ethyl propionate (EP), propyl propionate (PP), ethyl butyrate, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, Gamma-valerolactone, gamma-butyrolactone (GBL), and may include at least one selected from the group consisting of tetrahydrofuran.

The concentration of the lithium salt in the electrolyte for a lithium secondary battery may be 0.01 to 5.0 M, but is not necessarily limited to this range, and an appropriate concentration may be used as necessary. Further improved battery characteristics may be obtained within the above concentration range.

The lithium salt used in the electrolyte for the lithium secondary battery is not particularly limited, and any lithium salt that can be used as a lithium salt in the art may be used. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiBr, CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4-phenyl boric acid Lithium, imide, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN( At least one compound selected from the group consisting of C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (x, y is 1 to 20), LiCl, and LiI may be used.

The electrolyte for a lithium secondary battery may be in a liquid or gel state. The electrolyte for a lithium secondary battery may be prepared by adding a lithium salt and a compound (A) of Formula 1 and a compound (B) of Formula 2 to the above-described non-aqueous organic solvent.

A lithium secondary battery according to another embodiment includes a positive electrode; It includes an anode and an electrolyte for a lithium secondary battery according to the above. The form of the lithium secondary battery is not particularly limited, and includes a lithium ion battery, a lithium ion polymer battery, a lithium sulfur battery, and the like.

For example, in the lithium secondary battery, the negative electrode may include at least one of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material. And, the operating voltage of the lithium secondary battery may be 4.2V or more, for example, it may be 4.3V or more, for example, it may be 4.45V or more.

For example, the lithium secondary battery may be manufactured by the following method.

First, an anode is prepared.

For example, a positive electrode active material composition in which a positive electrode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the above-listed shapes and may be in a shape other than the above-mentioned shapes.

The cathode active material is a lithium-containing metal oxide, and any one commonly used in the art may be used without limitation. For example, one or more of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof include Li _a A _1-b B ¹ _b D ¹ ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B ¹ _b O _2-c D ¹ _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B ¹ _b O _4-c D ¹ _c (wherein 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B ¹ _c D ¹ _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 ¹ _c O _2-α F ¹ _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B ¹ _c O _2-α F ¹ ₂ (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B ¹ _c D ¹ _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 ¹ _c O _2-α F ¹ _α (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B ¹ _c O _2-α F ¹ 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 (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 (in the above formula, 0.90 ≤ a ≤ 1.8, 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 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiI ¹ O 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); A compound represented by any one of the formulas of LiFePO ₄ may be used:

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 is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _g O _{2 g} (g=1, 2), LiNi _1-g Mn _g O _{2 g} (0<g<1), LiNi _1-gk Co _g Mn _k O ₂ (0≤g≤g≤ 0.5, 0≤k≤0.5), LiFePO ₄ and the like.

Specifically, the positive electrode may include a positive electrode active material having a layered structure.

For example, the cathode active material may be represented by the following Chemical Formula 3:

<Formula 3>

LiCo _1-s M _'s O ₂

In the above formula, M' is at least one selected from the group consisting of Ni, Mn, Al, Cu, Fe, Mg, Cr, Zn, B, and Ga, and 0 ≤ s ≤ 0.5.

For example, the cathode active material may be represented by the following Chemical Formula 4:

<Formula 4>

Li _t (Ni _1-uv Co _u Al _v )O ₂

In the above formula, 0.96≤t≤1.05, 0≤u≤0.2, 0≤v≤0.1).

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include a coating element compound of oxide or hydroxide of the coating element, oxyhydroxide of the coating element, oxycarbonate of the coating element, or hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

Carbon black, graphite fine particles, etc. may be used as the conductive material, but are not limited thereto, and any conductive material that can be used as a conductive material in the art may be used.

Examples of the binder include vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymer. may be used, but is not limited thereto, and any binder that can be used as a binder in the art may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but the solvent is not limited thereto and any solvent that can be used in the art may be used.

The content of the positive electrode active material, the conductive material, the binder and the solvent is a level commonly used in a lithium secondary battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

Next, the cathode is prepared.

For example, a negative electrode active material composition is prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a negative electrode plate.

The negative active material may be any material that can be used as an anode active material for a lithium secondary battery in the art. For example, it may include at least one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) an element or a combination element thereof, but not Si), Sn-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, and not Sn ) and so on. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, or Te.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, plate-like, flake-like, spherical or fibrous graphite, such as natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low-temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, and the like.

In the negative electrode active material composition, the same conductive material, binder, and solvent may be used as in the positive electrode active material composition.

The content of the negative electrode active material, the conductive material, the binder, and the solvent is a level commonly used in a lithium secondary battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

Any of the separators may be used as long as they are commonly used in lithium secondary batteries. Those having low resistance to ion movement of the electrolyte and excellent in electrolyte moisture content may be used. For example, it may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a separator that can be wound up such as polyethylene or polypropylene is used for a lithium ion battery, and a separator having excellent electrolyte impregnation ability for a lithium secondary battery may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated and dried on the electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled from the support is laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

Next, the above-described electrolyte for a lithium secondary battery is prepared.

As shown in FIG. 1 , the lithium secondary battery 1 includes a positive electrode 3 , a negative electrode 2 , and a separator 4 . The above-described positive electrode 3 , negative electrode 2 , and separator 4 are wound or folded and accommodated in the battery case 5 . Then, electrolyte for a lithium secondary battery is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium secondary battery 1 . The battery case may have a cylindrical shape, a prismatic shape, a thin film type, or the like. For example, the lithium secondary battery may be a large-sized thin-film battery. The lithium secondary battery may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is laminated in a bi-cell structure, impregnated with an organic electrolyte, and the obtained result is accommodated in a pouch and sealed, a lithium ion polymer battery is completed.

In addition, a plurality of the battery structure is stacked to form a battery pack, and the battery pack can be used in any device requiring high capacity and high output. For example, it can be used in a laptop, a smartphone, an electric vehicle, and the like.

In addition, since the lithium secondary battery has excellent lifespan characteristics and high rate characteristics, it can be used in an electric vehicle (EV). For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV). In addition, it can be used in fields requiring a large amount of power storage. For example, it can be used for electric bicycles, power tools, and the like.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

(Production of electrolyte for lithium secondary battery)

Example 1

Lithium salt containing 1.15M LiPF ₆ , ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propylene propionate (PP) 2:1:2:5 volume ratio mixed solvent , 7 wt% of fluoroethylene carbonate (FEC) and 1 wt% and 1 wt% of Compound 1 and Compound 2 having the following structures were added to prepare an electrolyte for a lithium secondary battery.

compound 1 compound 2

Comparative Example 1

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that Compound 1 and Compound 2 were not added.

Comparative Example 2

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1 wt% of Compound 1 was added and Compound 2 was not added.

Comparative Example 3

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that 1 wt% of Compound 2 was added.

(Manufacture of lithium secondary battery)

Example 2

(Manufacture of anode)

LiNi _0.8 Co _0.15 Al _0.05 O ₂ 96.0 wt% as a positive electrode active material, 2.0 wt% of Carbon black as a conductive material, and 2.0 wt% of PVDF as a binder were mixed, added to N-methyl-2-pyrrolidone solvent, and then added to a mechanical stirrer was dispersed for 30 minutes to prepare a cathode active material composition. The cathode active material composition was applied to a thickness of about 60 μm on an aluminum foil current collector having a thickness of 12 μm using a doctor blade, dried in a hot air dryer at 100° C. for 0.5 hours, and then again under vacuum and 120° C. conditions for 4 hours. It was dried and rolled to prepare a positive electrode in which a positive electrode active material layer was formed on a current collector.

(Production of cathode)

98 wt% of graphite and 2 wt% of a binder were mixed as an anode active material, added to distilled water, and dispersed for 60 minutes using a mechanical stirrer to prepare an anode active material composition. The negative active material composition was applied to a thickness of about 60 μm on a copper current collector having a thickness of 10 μm using a doctor blade, dried in a hot air dryer at 100° C. for 0.5 hours, and then dried again under vacuum and 120° C. conditions for 4 hours. and rolling to prepare a negative electrode having a negative electrode active material layer formed on the current collector.

(Assembly of lithium secondary battery)

A lithium secondary battery was manufactured using the electrolyte prepared in Example 1 as the electrolyte and the positive electrode, the negative electrode, and the 18 μm thick polyethylene separator coated with ceramic.

Comparative Examples 4 to 6

A lithium secondary battery was manufactured in the same manner as in Example 2, except that the electrolyte for a lithium secondary battery prepared in Comparative Examples 1 to 3 was used instead of the electrolyte for a lithium secondary battery prepared in Example 1, respectively.

evaluation example 1: 300 cycles post characteristics Assessment - capacity retention rate

The lithium secondary batteries prepared in Example 2 and Comparative Examples 4 to 6 were charged with a constant current to 4.25V at room temperature (25°C) and high temperature (45°C), respectively, at a rate of 1C, and then to 4.25V. After repeating the charge/discharge cycle of charging at a constant voltage until the current reached 0.05C while maintaining it, the discharge capacity was measured and the results of comparing the capacity retention rate are shown in Table 1 below.

The capacity retention rate is defined by Equation 1 below.

<Equation 1>

Capacity retention rate [%] = [discharge capacity after 300 ^th cycle / standard capacity] × 100 (the above standard capacity is the discharge capacity at 2 ^nd cycle)

Capacity retention rate at room temperature (%) Capacity retention at high temperature (%) Example 2 100.5 114 Comparative Example 4 100 100 Comparative Example 5 99.6 100.3 Comparative Example 6 99.3 99.5

As shown in Table 1, the lithium secondary battery of Example 2 including the electrolyte for a lithium secondary battery of the present invention includes not only the lithium secondary battery of Comparative Example 4 that does not include Compound 1 and Compound 2, but also the comparative lithium secondary battery containing only Compound 1. Compared to the lithium secondary battery of Example 5 or Comparative Example 6 including only Compound 2, the capacity retention rate at room temperature and high temperature was significantly improved.

Evaluation Example 2: Characteristic evaluation after 300 cycles - thickness

The lithium secondary batteries prepared in Example 2 and Comparative Examples 4 to 6 were charged with a constant current to 4.25V at room temperature (25°C) and high temperature (45°C), respectively, at a rate of 1C, and then to 4.25V. After repeating the charge/discharge cycle of constant voltage charging until the current reached 0.05C while maintaining the thickness, the thickness was measured, and the results of comparing the increase rate of the thickness based on the initial thickness are shown in Table 2 below.

Thickness increase rate at room temperature (%) Thickness increase rate at high temperature (%) Example 2 4.6 14.2 Comparative Example 4 7.9 14.6 Comparative Example 5 7.6 14.4 Comparative Example 6 7.9 14.8

As shown in Table 2, the lithium secondary battery of Example 2 including the electrolyte for a lithium secondary battery of the present invention includes not only the lithium secondary battery of Comparative Example 4 that does not include Compound 1 and Compound 2, but also the comparative lithium secondary battery containing only Compound 1. Compared to the lithium secondary battery of Comparative Example 6 containing only Example 5 or Compound 2, the effect of reducing the thickness increase rate at room temperature and high temperature was significantly improved.

Evaluation Example 3: Capacity retention rate evaluation at high temperature (45°C) according to the content of compound 1 and compound 2

Prepared in the same manner as in Example 2, except that the lithium secondary batteries prepared in Example 2 and Comparative Examples 4 to 6 and Compound 1 and Compound 2 in the amounts shown in Table 3 below were included. A charge/discharge cycle of constant current charging to 4.25V at a high temperature (45°C) at a high temperature (45°C), followed by constant voltage charging until the current becomes 0.05C while maintaining 4.25V for 300 After repeated times, the discharge capacity was measured, and the results of comparing the capacity retention rate are shown in Table 3 below.

The capacity retention rate was evaluated in the same manner as in Evaluation Example 1.

Content of compound 1 (%) Content of compound 2 (%) Capacity retention rate (%) Example 2 1.0 1.0 114.0 Example 3 0.05 0.05 103.0 Example 4 1.0 0.05 105.0 Example 5 0.05 1.0 108.3 Example 6 2.0 1.0 104.0 Example 7 2.0 2.0 107.0 Example 8 5.0 5.0 102.0 Comparative Example 4 0 0 100 Comparative Example 5 1.0 0 100.3 Comparative Example 6 0 1.0 99.5 Comparative Example 7 0.01 0 100.1 Comparative Example 8 0.05 0 100.1 Comparative Example 9 2.0 0 99.5 Comparative Example 10 5.0 0 98.5 Comparative Example 11 0 0.01 99.2 Comparative Example 12 0 0.05 99.0 Comparative Example 13 0 2.0 99.3 Comparative Example 14 0 5.0 99.3

As shown in Table 3, when the electrolyte for a lithium secondary battery of the present invention is used, as in the lithium secondary batteries of Examples 2 to 8, as well as the lithium secondary battery of Comparative Example 4 that does not contain both Compounds 1 and 2, Compared with the lithium secondary batteries of Comparative Examples 5 to 14 including only one of Compound 1 or 2, it can be confirmed that excellent high-temperature capacity retention rate is exhibited.

In particular, among the lithium secondary batteries of Examples 2 to 8 including both compounds 1 and 2, the lithium secondary batteries of Example 2 each containing 1 wt% of compounds 1 and 2 are the lithium secondary batteries of other Examples 3 to 8. It can be seen that the high temperature capacity retention rate is significantly superior even compared to .

Claims (19)

non-aqueous organic solvents;
lithium salt;
Compound (A) represented by the following formula (1); and
An electrolyte for a lithium secondary battery comprising a compound (B) represented by the following formula (2):
<Formula 1><Formula2>

In the above formulas,
A is a substituted or unsubstituted aliphatic hydrocarbon or (-C ₂ H ₄ -OC ₂ H ₄ -)n;
X is halogen;
n is selected from an integer from 1 to 10,
The substituent of the substituted aliphatic hydrocarbon is C ₁ -C ₂₀ alkyl group, C ₂ -C ₂₀ alkenyl group, C ₂ -C ₂₀ alkynyl group, C ₁ -C ₂₀ alkoxy group, halogen, cyano group consisting of hydroxy and nitro at least one independently selected from the group. According to claim 1,
In Formula 1, A is a C ₁ -C ₂₀ aliphatic hydrocarbon; C ₁ -C substituted with one or more of C ₁ -C ₂₀ alkyl group, C ₂ -C ₂₀ alkenyl group, C ₂ -C ₂₀ alkynyl group, C ₁ -C ₂₀ alkoxy group, halogen, cyano, hydroxy and nitro ₂₀ aliphatic hydrocarbons; and (-C ₂ H ₄ -OC ₂ H ₄ -) at least one selected from _n ; n is selected from an integer of 1 to 5, an electrolyte for a lithium secondary battery. According to claim 1,
In Formula 1, A is a C ₁ -C ₂₀ alkylene group, a C ₂ -C ₂₀ alkenylene group, or a C ₂ -C ₂₀ alkynylene group, the electrolyte for a lithium secondary battery. According to claim 1,
In Formula 1, A is a methylene group, an ethylene group, a propylene group, a butylene group, or an ethenylene group, the electrolyte for a lithium secondary battery. According to claim 1,
The compound (A) represented by the formula (1) is a compound represented by the following formula 1-1, an electrolyte for a lithium secondary battery:
<Formula 1-1>

. According to claim 1,
In Chemical Formula 2, X is -F, -Cl, -Br, or -I, an electrolyte for a lithium secondary battery. According to claim 1,
The compound (B) represented by the formula (2) is a compound represented by the following formula (2-1), an electrolyte for a lithium secondary battery:
<Formula 2-1>

. According to claim 1,
An electrolyte for a lithium secondary battery in which the content of the compound (A) is 0.01 to 5% by weight based on the total weight of the electrolyte for a lithium secondary battery. According to claim 1,
An electrolyte for a lithium secondary battery in which the content of the compound (B) is 0.01 to 5% by weight based on the total weight of the electrolyte for a lithium secondary battery. According to claim 1,
An electrolyte for a lithium secondary battery wherein the content ratio of the compound (A) to the compound (B) is 1:1 to 1:5. According to claim 1,
The non-aqueous organic solvent is ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), Fluoroethylene carbonate (FEC), butylene carbonate, ethyl propionate (EP), propyl propionate (PP), ethyl butyrate, acetonitrile, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, gamma-valero An electrolyte for a lithium secondary battery comprising at least one selected from the group consisting of lactone, gamma-butyrolactone (GBL) and tetrahydrofuran. According to claim 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiBr, CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4-phenyl boric acid Lithium, imide, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN( C _x F _2x+1 SO ₂ ) (C _y F _2y+1 SO ₂ ) (x, y is 1 to 20), LiCl and LiI electrolyte for a secondary battery comprising at least one selected from the group consisting of. According to claim 1,
An electrolyte for a lithium secondary battery, wherein the concentration of the lithium salt is 0.01 to 5.0 M. anode; cathode; and
A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to any one of claims 1 to 13. 15. The method of claim 14,
A lithium secondary battery wherein the negative electrode includes at least one of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material. 15. The method of claim 14,
A lithium secondary battery wherein the positive electrode includes a positive electrode active material having a layered structure. 15. The method of claim 14,
A lithium secondary battery having an operating voltage of 4.2V or more of the lithium secondary battery. 17. The method of claim 16,
The cathode active material is a lithium secondary battery represented by Formula 3:
<Formula 3>
LiCo _1-s M _'s O ₂
In the above formula,
M' is at least one selected from the group consisting of Ni, Mn, Al, Cu, Fe, Mg, Cr, Zn, B, and Ga,
0 ≤ s ≤ 0.5. 17. The method of claim 16,
The cathode active material is a lithium secondary battery represented by the following Chemical Formula 4:
<Formula 4>
Li _t (Ni _1-uv Co _u Al _v )O ₂
In the above formula,
0.96≤t≤1.05, 0≤u≤0.2, 0≤v≤0.1).

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