KR102237375B1 - Electrolyte of rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

[화학식 2]

[화학식 3]

(상기 화학식 1 내지 3에서, 각 치환기의 정의는 상세한 설명에서 서술한 바와 같다)An electrolyte for a lithium secondary battery and a lithium secondary battery thereof, wherein the electrolyte is a non-aqueous organic solvent, a lithium salt, a compound of the following formula (1), a compound of the following formula (2), or a first additive that is a combination thereof, and a second additive of succinonitrile And a third additive of Formula 3 below.
[Formula 1]

[Formula 2]

[Formula 3]

(In Chemical Formulas 1 to 3, the definition of each substituent is as described in the detailed description)

Description

Electrolyte for lithium secondary battery and lithium secondary battery including the same TECHNICAL FIELD [ELECTROLYTE OF RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

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

Lithium secondary batteries are attracting attention as power sources for various electronic devices due to their high discharge voltage and high energy density.

The positive electrode active material of a lithium secondary battery is composed of lithium and a transition metal having a structure capable of intercalating lithium ions such as _{LiCoO 2} , LiMn ₂ O ₄ , and LiNi _1-x Co _x O _{2 (0 <x <1).} Oxide is mainly used.

As the negative electrode active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of intercalating/deintercalating lithium are mainly used.

An organic solvent in which a lithium salt is dissolved is used as an electrolyte for a lithium secondary battery.

One embodiment provides an electrolyte for a lithium secondary battery having excellent battery characteristics, such as a reduction in resistance during long-term storage at high temperature, capacity retention during high temperature storage, and high rate characteristics.

Another embodiment is to provide a rechargeable lithium battery including the electrolyte.

According to one embodiment, a non-aqueous organic solvent; Lithium salt; A first additive which is a compound of the following formula 1, a compound of the following formula 2, or a combination thereof; Succinonitrile second additive; And it provides an electrolyte for a lithium secondary battery comprising a third additive of the formula (3).

[Formula 1]

(In Formula 1, R _a , R _b and R _c are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group)

[Formula 2]

(In Formula 2, R _d , R _e and R _f are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group)

[Formula 3]

(In Formula 3, R _h and R _g are each independently a substituted or unsubstituted alkyl group, halogen group, alkylene group, or aryl group)

The content of the first additive may be 0.1% to 2% by weight based on the total weight of the electrolyte.

The content of the second additive may be 0.1% to 2% by weight based on the total weight of the electrolyte.

The content of the third additive may be 0.1% to 1% by weight based on the total weight of the electrolyte.

The electrolyte may further include a fourth additive, which _{is LiBF 4} , fluoroethylene carbonate, lithium bisoxalate borate, LiPO ₂ F _{2, or a combination thereof.}

Another embodiment of the present invention is a negative electrode including a negative electrode active material; A positive electrode including a positive electrode active material; And it provides a lithium secondary battery including the electrolyte.

Details of other implementations are included in the detailed description below.

The electrolyte for a lithium secondary battery according to an embodiment of the present invention can provide a lithium secondary battery that exhibits excellent battery characteristics, such as suppressing an increase in resistance during long-term storage at high temperature, improving capacity retention during storage at high temperature, and also having high rate characteristics.

1 is a schematic view of a rechargeable lithium battery according to an embodiment of the present invention.
Figure 2 is a graph showing by measuring the DC internal resistance of the battery containing the electrolyte of Examples 2 and 3 and Comparative Examples 5 and 6.
Figure 3 is a graph showing by measuring the rate of change in direct current internal resistance of a battery including the electrolyte of Example 1 and Comparative Examples 1 to 4;
Figure 4 is a graph showing by measuring the rate of change of the internal direct current resistance of the battery containing the electrolyte of Examples 2 to 5 and Comparative Examples 5 and 6.
Figure 5 is a graph measuring the AC internal resistance of the battery containing the electrolyte of Examples 2 and 3.
6 is a graph showing the measurement of the capacity recovery rate of a battery including the electrolytes of Examples 2 and 4 and Comparative Examples 5 and 6;

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

In such a lithium secondary battery, the SEI film formed by reaction with the electrolyte is formed unevenly on the surface of the negative electrode, so that side reactions occur at the negative electrode, and thus the amount of self-discharge is large or

One embodiment is a non-aqueous organic solvent; Lithium salt; A first additive including a compound of the following formula 1, a compound of the following formula 2, or a combination thereof; Succinonitrile second additive; And it provides an electrolyte for a lithium secondary battery comprising a third additive of the formula (3).

[Formula 1]

In Formula 1, R _a , R _b and R _c are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group.

[Formula 2]

In Formula 2, R _d , R _e and R _f are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group.

[Formula 3]

In Formula 3, R _h and R _g are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group.

The alkyl group may have 1 to 6 carbon atoms. In the substituted alkyl group, the substituent may be a halogen group or an alkylene group. In addition, the alkyl group may be linear, branched or cyclic. In addition, the halogen group may be F, Cl, Br or I. In addition, the alkylene group may have 2 to 6 carbon atoms, and the aryl group may have 6 to 30 carbon atoms.

Specific examples of the first additive may include triethyl phosphite, tributyl phosphite, triethyl phosphate, trimethyl phosphate, or a combination thereof. A specific example of the third additive may be methylene methane disulfonic acid ester.

Since such an electrolyte contains succinonitrile as a second additive, it is possible to suppress a phenomenon in which the metal is eluted from the positive electrode, and thus, the problem that the eluted metal moves to the negative electrode, precipitates, and grows can be effectively suppressed. Of the nitrile-based succinonitrile, since succinonitrile can best suppress the elution of such metals, it is suitable as a second additive.

In addition, as the first additive is included, problems such as a decrease in high rate characteristics due to the use of the second additive and an increase in resistance during long-term storage at high temperatures can be suppressed.

In addition, by including the third additive, it is possible to effectively suppress an increase in resistance during long-term storage at high temperature and charge/discharge at room temperature, and when a carbonate-based solvent is included as a non-aqueous organic solvent, decarburization to remove _{CO 2 from the carbonate-based solvent} It can inhibit oxidation reactions .

As described above, since the electrolyte according to an embodiment includes the first additive, the second additive, and the third additive together, SO groups are bonded to the positive electrode, so that electrolyte decomposition due to the progress of charging and discharging can be suppressed, and as a result, high temperature Storage performance can be improved.

The content of the first additive may be 0.1% to 2% by weight based on the total weight of the electrolyte. When the content of the first additive is out of the above range, that is, less than 0.1% by weight, the effect of using the first additive is insignificant, and when it exceeds 2% by weight, the solubility in the electrolyte solution decreases, resulting in a precipitate. It can't be appropriate.

The content of the second additive may be 0.1% to 2% by weight based on the total weight of the electrolyte. When the content of the second additive is out of the above range, that is, less than 0.1% by weight, the effect of using the second additive is insignificant, and when it exceeds 2% by weight, the solubility in the electrolyte solution decreases, resulting in a precipitate. It's not appropriate.

The content of the third additive may be 0.1% to 1% by weight based on the total weight of the electrolyte. When the content of the third additive is outside the above range, that is, less than 0.1% by weight, the effect of using the third additive is insignificant, and when it exceeds 1% by weight, it reacts with lithium in the positive electrode to form a salt, A precipitate is formed, and the precipitate moves to the negative electrode, and the resulting cycle life characteristic, i.e., capacity retention, is lowered, which is not appropriate.

The mixing ratio of the first additive, the second additive, and the third additive may be appropriately adjusted within the above range.

The electrolyte may further include a fourth additive, which _{is LiBF 4} , fluoroethylene carbonate, lithium bisoxalate borate (LiBOB), LiPO ₂ F _{2, or a combination thereof.}

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used.

As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valero Lactone, mevalonolactone, caprolactone, and the like may be used.

Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have.

Ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and T-CN (T is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and as the aprotic solvent, Nitriles such as a double bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used.

The non-aqueous organic solvent may be used alone or in combination of one or more. In the case of using one or more mixtures, the mixing ratio may be appropriately adjusted according to the desired battery performance, and this may be widely understood by those engaged in the art.

When the non-aqueous organic solvent is mixed and used, a mixed solvent of a cyclic carbonate and a chain carbonate or a mixed solvent of a cyclic carbonate and a propionate solvent or a cyclic carbonate, a chain carbonate and a propionate system A mixed solvent of solvents can be used. As the propionate-based solvent, methyl propionate, ethyl propionate, propyl propionate, or a combination thereof may be used.

At this time, when a cyclic carbonate and a chain carbonate, or a cyclic carbonate and a propionate solvent are mixed and used in a volume ratio of 1:1 to 1:9, the electrolyte may exhibit excellent performance. In addition, when a cyclic carbonate, a chain carbonate, and a propionate solvent are mixed and used, they may be mixed in a volume ratio of 1:1:1 to 3:3:4. Of course, the mixing ratio of the solvents may be appropriately adjusted according to desired physical properties.

The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following formula (4) may be used.

[Formula 4]

(In Formula 4, R ₁ to R ₆ are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4-trichlorobenzene, iodobenzene, 1,2-diaiodobenzene, 1,3-diaiodobenzene, 1,4-diaiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2, 3,5-trichlorotoluene, iodotoluene, 2,3-diaiodotoluene, 2,4-diaiodotoluene, 2,5-diaiodotoluene, 2,3,4-triiodotoluene, 2,3 It is selected from the group consisting of, 5-triiodotoluene, xylene, and combinations thereof.

The electrolyte for a lithium secondary battery may further include an ethylene carbonate-based compound represented by Formula 5 below to improve battery life.

[Formula 5]

(In Formula 5, R ₇ and R ₈ are each independently selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, and the R _{At least one of 7} and R ₈ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided _{that both R 7} and R ₈ are not hydrogen .)

Representative examples of the ethylene carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, or cyanoethylene carbonate. In the case of further use of such a life-improving additive, the amount of the additive may be appropriately adjusted.

The lithium salt is a material that is dissolved in an organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery, and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers, for example 1 to 20 Is an integer of), LiCl, and LiI as a supporting electrolytic salt. It is recommended to use the lithium salt concentration within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

Another embodiment provides a lithium secondary battery including the electrolyte, a positive electrode, and a negative electrode.

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

In the positive electrode active material layer, a compound capable of reversible intercalation and deintercalation of lithium (reversible intercalation compound) may be used as the positive electrode active material, specifically cobalt, manganese, nickel, and these One or more of a composite oxide of a metal and lithium selected from a combination of may be used. As a more specific example, a compound represented by any one of the following formulas may be used. Li _a A _1-b X _b D ₂ (0.90≦a≦1.8, 0≦b≦0.5); Li _a A _1-b X _b O _2-c T _c (0.90 <a <1.8, 0 <b <0.5, 0 <c <0.05); Li _a E _1-b X _b O _2-c T _c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); Li _a E _2-b X _b O _4-c T _c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b X _c O _2-α T ₂ (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 (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 G _e O ₂ (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 (0.90 <a <1.8, 0.001 <b <0.1) Li _a CoG _b O ₂ (0.90 <a <1.8, 0.001 <b <0.1); Li _a Mn _1-b G _b O ₂ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn _1-g G _g PO ₄ (0.90≦a≦1.8, 0≦g≦0.5); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO 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); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8)

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

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 contains at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. I can. The compound constituting these coating layers may be amorphous or crystalline. As a 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. The coating layer forming process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g., spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted.

According to an embodiment, as the positive active material, Li _a Ni _1-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ α ≤ 2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0≦α≦2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 ≤ α ≤ 2); Li _a Ni _1-bc Mn _b X _c O _2-α T ₂ (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 (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 G _e O ₂ (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 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1) may be used by mixing at least two of the nickel-based positive electrode active material, or in the formula of the nickel-based positive electrode active material and the positive electrode active material Other active materials other than the nickel-based positive electrode active material may be mixed and used.

In particular, as the nickel-based positive electrode active material, Li _a Ni _b1 Co _c1 X _d1 G _z1 O ₂ (0.90 ≤ a ≤1.8, 0.5 ≤ b1 ≤ 0.98, 0 <c1 ≤ 0.3, 0 <d1 ≤ 0.3, 0 ≤ z1 ≤ 0.1 , b1 + c1 + d1 + z1 = 1, X is Mn, Al or a combination thereof, and G is Cr, Fe, Mg, La, Ce, Sr, V or a combination thereof) may be appropriately used.

When these are mixed and used, this mixing ratio can be suitably mixed and used according to the desired physical properties. For example, when the nickel-based positive electrode active material and other active materials are mixed and used, the content of the nickel-based positive electrode active material may be used in an amount of 30% to 97% by weight based on the total weight of the positive electrode active material.

In the positive electrode, the content of the positive electrode active material may be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

In one embodiment, the positive active material layer may further include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

The binder may well attach the positive electrode active material particles to each other, and may also play a role of attaching the positive electrode active material to the current collector well. Representative examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrroly. Don, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but are not limited thereto. .

The conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, any material may be used as long as it does not cause chemical change and is an electron conductive material. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers, and metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers. Conductivity such as polyphenylene derivatives. And a conductive material containing a polymer or a mixture thereof.

As the current collector, an aluminum foil, a nickel foil, or a combination thereof may be used, but the present invention is not limited thereto.

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

As the negative active material, a material capable of reversibly intercalating/deintercalating lithium ions, a lithium metal, an alloy of a lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide may be used.

As a material capable of reversibly intercalating/deintercalating lithium ions, for example, a carbon material, that is, a carbon-based negative active material generally used in lithium secondary batteries may be mentioned. As a representative example of the carbon-based negative active material, crystalline carbon, amorphous carbon, or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, and fired coke.

The lithium metal alloy is a group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn An alloy of a metal selected from may be used.

The lithium-doped and undoped materials include Si, SiO _x (0 <x <2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, 16 It is an element selected from the group consisting of group elements, transition metals, rare earth elements, and combinations thereof, but not Si), Si-carbon complex, Sn, SnO ₂ , Sn-R (wherein R is an alkali metal, alkaline earth metal, 13 It is an element selected from the group consisting of a group element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and combinations thereof, but not Sn), a Sn-carbon complex, and the like. At least one of them and SiO ₂ may be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, What is selected from the group consisting of Se, Te, Po, and combinations thereof may be used.

Lithium titanium oxide may be used as the transition metal oxide.

According to one embodiment, the negative active material may be a Si-carbon composite, and the Si-carbon composite may include silicon particles and crystalline carbon. The average particle diameter (D50) of the silicon particles may be 10 nm to 200 nm. The Si-C composite may further include an amorphous carbon layer formed on at least a portion. Unless otherwise defined herein, the average particle diameter (D50) refers to the diameter of particles having a cumulative volume of 50% by volume in a particle size distribution.

According to another embodiment, the negative active material may be used by mixing two or more types of negative active materials, for example, a Si-carbon composite may be included as the first negative active material, and crystalline carbon may be used as the second negative active material. It may include. When two or more types of negative active materials are mixed and used as the negative active material, the mixing ratio thereof may be appropriately adjusted, but it may be appropriate to adjust the Si content to be 3% to 50% by weight based on the total weight of the negative active material. .

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

The content of the negative active material in the negative active material layer may be 95% to 99% by weight based on the total weight of the negative active material layer. The content of the binder in the negative active material layer may be 1% to 5% by weight based on the total weight of the negative active material layer. In addition, when a conductive material is further included, 90% to 98% by weight of the negative electrode active material, 1 to 5% by weight of the binder, and 1% to 5% by weight of the conductive material may be used.

The binder serves to attach the negative active material particles well to each other, and also serves to attach the negative active material to the current collector well. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

As the water-insoluble binder, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and C2-C8 olefin copolymer, (meth)acrylic acid and (meth)acrylate alkyl ester. Copolymers or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K or Li may be used as the alkali metal. The content of the thickener may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, any material may be used as long as it does not cause chemical change and is an electron conductive material. Examples of the conductive material are natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black, carbon-based materials such as carbon fiber, metal powders such as copper, nickel, aluminum, silver, or metal-based materials such as metal fibers, and polyphenylene derivatives And a conductive material containing a conductive polymer such as a conductive polymer or a mixture thereof.

The current collector may be selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

The positive electrode active material layer and the negative electrode active material layer are formed by mixing a negative electrode active material, a binder, and optionally a conductive material in a solvent to prepare an active material composition, and applying the active material composition to a current collector. Since such a method of forming an active material layer is widely known in the art, a detailed description thereof will be omitted herein. N-methylpyrrolidone may be used as the solvent, but is not limited thereto. In addition, when a water-soluble binder is used for the negative active material layer, water may be used as a solvent used in preparing the negative active material composition.

In addition, depending on the type of lithium secondary battery, a separator may exist between the positive electrode and the negative electrode. Polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used as such a separator, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, a polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a three-layer propylene separator may be used.

1 shows an exploded perspective view of a rechargeable lithium battery according to an embodiment of the present invention. The lithium secondary battery according to the embodiment is described as an example that has a cylindrical shape , but the present invention is not limited thereto, and may be applied to various types of batteries such as a prismatic shape and a pouch type.

Referring to FIG. 1, a lithium secondary battery 1 according to an embodiment includes an electrode assembly wound between a positive electrode 2 and a negative electrode 4 through a separator 3, and a case in which the electrode assembly is embedded ( 5) and a sealing member 6 for sealing the case 5 may be included. The anode 2, the cathode 4, and the separator 3 may be impregnated with an electrolyte (not shown).

Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

(Example 1)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture Fluoroethylene carbonate 10% by weight, LiBF ₄ 0.2% by weight, lithium bisoxalate borate 1% by weight, LiPO ₂ F ₂ 1.5% by weight, triethyl phosphite 1% by weight, succinonitrile 1% by weight and methylene methane disulfonic acid An electrolyte for a lithium secondary battery was prepared by adding 0.4% by weight of ester.

(Example 2)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.0% by weight of LiPO 2} F ₂ , 2% by weight of trimethyl phosphate, 1.0% by weight of succinonitrile, and 0.4% by weight of methylene methane disulfonic acid ester.

(Example 3)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.0% by weight of LiPO 2} F ₂ , 1% by weight of trimethyl phosphate, 1.0% by weight of succinonitrile, and 0.4% by weight of methylene methane disulfonic acid ester.

(Example 4)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.0% by weight of LiPO 2} F ₂ , 2% by weight of tributyl phosphite, 1.5% by weight of succinonitrile, and 0.4% by weight of methylene methane disulfonic acid ester.

(Example 5)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 1% by weight of tributyl phosphite, 1.5% by weight of succinonitrile, and 0.4% by weight of methylene methane disulfonic acid ester.

(Comparative Example 1)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F _{2 and 1% by weight of succinonitrile.}

(Comparative Example 2)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 1% by weight of triethyl phosphite, and 1.5% by weight of succinonitrile.

(Comparative Example 3)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 1% by weight of triethyl phosphite, and 1.0% by weight of succinonitrile.

(Comparative Example 4)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 1% by weight of succinonitrile, and 0.4% by weight of methylene methane disulfonic acid ester.

(Comparative Example 5)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 2% by weight of trimethyl phosphate, and 1.5% by weight of succinonitrile.

(Comparative Example 6)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2:1:7 by volume), and to 100% by weight of this mixture, 10% by weight of fluoroethylene carbonate, 0.2% by weight of _{LiBF 4, lithium} An electrolyte for a lithium secondary battery was prepared by adding 1% by weight of bisoxalate borate, _{1.5% by weight of LiPO 2} F ₂ , 1% by weight of trimethyl phosphate, and 1.5% by weight of succinonitrile.

* Battery manufacturing

LiNi _0.88 Co _0.105 Al _0.015 O ₂ 96% by weight of a positive electrode active material, 2% by weight of Ketjen Black conductive material, and 2% by weight of polyvinylidene fluoride were mixed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on an aluminum foil, dried, and rolled to prepare a positive electrode.

A negative electrode active material slurry was prepared by mixing 96% by weight of a graphite negative active material, 2% by weight of Ketjen Black conductive material, and 2% by weight of polyvinylidene fluoride in an N-methylpyrrolidone solvent. The negative electrode active material slurry was coated on copper foil, dried, and rolled to prepare a negative electrode.

Using the prepared positive electrode, negative electrode, and electrolytes prepared according to Examples 1 to 5 and Comparative Examples 1 to 6, a lithium secondary battery was manufactured by a conventional method.

*Direct current internal resistance (DC-IR)

After storing the prepared battery at high temperature (60°C) for 90 days, direct current internal resistance (DC-IR) was measured. The DC internal resistance measurement is performed with the battery at 0.2C twice, and then SOC (State of charge) 50% discharge (when the battery is charged and discharged at 4.2V, when the total charging capacity of the battery is 100%, 50 It measured while carrying out the state of discharging so that it might become% discharge capacity).

Among the measured DC internal resistance results, the results of up to 60 days for the batteries containing the electrolytes of Examples 2 and 3 and Comparative Examples 5 and 6 are shown in FIG. 2.

In addition, the DC internal resistance change rate from the measured result to 30 days was calculated, and the results for the battery including the electrolyte of Example 1 and Comparative Examples 1 to 4 are shown in FIG. 3, and Examples 2 to 5 and Comparative Examples Fig. 4 shows the results of the rate of change of the DC internal resistance up to 60 days of the battery containing the electrolytes of 5 and 6.

As shown in FIG. 2, it can be seen that the DC internal resistance of the batteries containing the electrolytes of Examples 2 and 3 is smaller than that of the batteries containing the electrolytes of Comparative Examples 5 and 6.

In addition, as shown in FIG. 3, in the case of a battery including the electrolyte of Example 1 containing all of triethyl phosphite, succinonitrile, and methylene methane disulfonic acid ester, the DC-IR change rate was the smallest, The battery containing the electrolyte of Comparative Example 1 containing only succinonitrile has a large DC-IR change rate, and in the case of the battery containing the electrolytes of Comparative Examples 2 and 3 containing triethyl phosphite and succinonitrile, succino It can be seen that the DC-IR rate of change is increased compared to the battery containing the electrolyte of Comparative Example 1 containing only nitrile. In addition, it can be seen that the battery including the electrolyte of Comparative Example 4 containing only succinonitrile and methylene methane disulfonic acid ester also exhibited a greater DC-IR change rate compared to the battery including the electrolyte solution of Example 1.

In addition, as shown in FIG. 4, it can be seen that the rate of change of DC-IR of the batteries containing the electrolytes of Examples 2 to 5 was also less than that of the batteries containing the electrolytes of Comparative Examples 5 and 6.

From these results, it can be seen that when all of the trialkyl phosphite, succinonitrile, and methylene methane disulfonic acid ester are included, the increase in resistance is very small when stored at high temperature, but when none of them is included, the increase in resistance increases. have. In particular, it can be seen that, among the trialkyl phosphites, Example 1 using triethyl phosphite is the most excellent in the resistance reduction effect.

* AC internal resistance (AC-IR: Alternating Current, Internal resistance)

After storing the prepared battery at high temperature (60°C) for 90 days, the AC internal resistance (DC-IR) was measured. AC internal resistance measurement is performed by charging and discharging the battery to a 100% discharge capacity after storing the battery at a high temperature, at room temperature (25°C), 4.2V (SOC (State of charge) 100 (when the total charging capacity of the battery is 100%)). Condition) was measured with a Hioki meter.

Among the results, the results of Examples 2 and 3 are shown in FIG. 5. As shown in FIG. 5, it can be seen that the AC internal resistance of the batteries including the electrolytes of Examples 2 and 3 were similar.

* High temperature storage characteristics: Evaluation of recovery capacity

The manufactured battery was charged and discharged once at 60°C at 0.2C, and the charge/discharge capacity (initial charge/discharge capacity) was measured, and the battery was stored at 60°C for 10 days, and then charged and discharged once at 0.2C. To measure the charge/discharge capacity (10-day charge/discharge capacity), and after storing the battery at 60°C for 30 days, charge/discharge once at 0.2C, and charge/discharge capacity (30-day charge/discharge capacity) ) Was measured. Subsequently, the obtained battery was stored at 60° C. for 60 days, then charged and discharged once at 0.2 C, and the charge/discharge capacity (60-day charge/discharge capacity) was measured.

To the measured initial charge/discharge capacity, the charge/discharge capacity ratio for 10 days (which is a capacity recovery capacity), the charge/discharge capacity ratio for 30 days, and the charge/discharge capacity ratio for 60 days were obtained, respectively. Among the results, the 30-day charge-discharge capacity ratio and the 30-day charge-discharge capacity ratio results of Examples 1 to 5 and Comparative Example 2 are shown in Table 1 below.

In addition, the measured 30-day charge-discharge capacity ratio and 60-day charge-discharge capacity ratio were used as the capacity recovery capacity, and among the results, the results of Examples 2 and 3 and Comparative Examples 5 and 6 are shown in FIG. 6.

30-day charge/discharge capacity ratio (%) 60-day charge/discharge capacity ratio (%) Example 1 93.2 89.1 Example 2 94 92.1 Example 3 93.8 92.1 Example 4 92.9 89.0 Example 5 94.0 89.7 Comparative Example 2 92.2 85.2

As shown in Table 1, it can be seen that the high-temperature storage characteristics of the batteries containing the electrolytes of Examples 1 to 5 are very superior to those of the batteries containing the electrolyte of Comparative Example 2.

In addition, as shown in FIG. 6, it can be seen that the capacity recovery rate of the batteries containing the electrolytes of Examples 2 and 3 after storage at high temperature for 60 days is superior to that of the batteries containing the electrolytes of Comparative Examples 5 and 6. .

From these results, it can be seen that the case of including all of the trialkyl phosphite, succinonitrile and methylene methane disulfonic acid ester has superior high-temperature storage characteristics compared to the case not including any of these.

The present invention is not limited to the above embodiments, but may be manufactured in a variety of different forms, and those of ordinary skill in the art to which the present invention pertains, other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that it can be implemented with. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

Claims (6)

Non-aqueous organic solvents;
Lithium salt;
A first additive which is a compound of the following formula 1, a compound of the following formula 2, or a combination thereof;
Succinonitrile second additive;
A third additive of Formula 3 below; And
LiBF ₄ , fluoroethylene carbonate, lithium bisoxalate borate, LiPO ₂ F ₂ or a combination of the fourth additive consisting of
Electrolyte for lithium secondary battery.
[Formula 1]

(In Formula 1, R _a , R _b and R _c are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group)
[Formula 2]

(In Formula 2, R _d , R _e and R _f are each independently a substituted or unsubstituted alkyl group, a halogen group, an alkylene group, or an aryl group)
[Formula 3]

(In Formula 3, R _h and R _g are each independently a substituted or unsubstituted alkyl group, halogen group, alkylene group, or aryl group) The method of claim 1,
An electrolyte for a lithium secondary battery in which the content of the first additive is 0.1% to 2% by weight based on the total weight of the electrolyte. The method of claim 1,
The content of the second additive is 0.1% to 2% by weight based on the total weight of the electrolyte lithium secondary battery electrolyte. The method of claim 1,
The content of the third additive is 0.1% to 1% by weight based on the total weight of the electrolyte lithium secondary battery electrolyte. delete A negative electrode including a negative active material;
A positive electrode including a positive electrode active material; And
The electrolyte of any one of claims 1 to 4
Lithium secondary battery comprising a.

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