KR20190115704A - Electrolyte of rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

The present invention relates to electrolyte for a lithium secondary battery and a lithium secondary battery including the same. The electrolyte includes: a non-aqueous organic solvent; lithium salt; a first additive which is a compound of chemical formula 1, a compound of chemical formula 2, or a combination thereof; a second additive of succinonitrile; and a third additive of chemical formula 3. In chemical formulas 1 to 3, the definition of each substituent is as described in the detailed description. The present invention provides excellent cell characteristics.

Description

ELECTROLYTE OF RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING SAME

It relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising 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.

As a cathode active material of a lithium secondary battery, 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) Oxides are mainly used.

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

As an electrolyte of a lithium secondary battery, an organic solvent in which lithium salt is dissolved is used.

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

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

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

[Formula 1]

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

[Formula 2]

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

[Formula 3]

(In Chemical 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 wt% to 2 wt% with respect to the total weight of the electrolyte.

The content of the second additive may be 0.1 wt% to 2 wt% with respect to the total weight of the electrolyte.

The content of the third additive may be 0.1% by weight 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 comprising the electrolyte.

Specific details of other embodiments are included in the following detailed description.

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

1 is a view briefly showing a lithium secondary battery according to an embodiment of the present invention.
Figure 2 is a graph showing the measurement of 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 the measurement of the DC internal resistance change rate of the battery containing the electrolyte of Example 1 and Comparative Examples 1 to 4.
Figure 4 is a graph showing the measurement of the DC internal resistance change rate of the battery containing the electrolyte of Examples 2 to 5 and Comparative Examples 5 and 6.
5 is a graph measuring the AC internal resistance of the battery including the electrolytes of Examples 2 and 3. FIG.
Figure 6 is a graph showing the measurement of the capacity recovery rate of the battery containing the electrolyte 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, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The lithium secondary battery has a non-uniform SEI film formed by reaction with an electrolyte on the surface of the negative electrode, so that side reactions occur at the negative electrode, thereby causing a large amount of self discharge.

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

[Formula 1]

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

[Formula 2]

In Formula 2, R _d , R _e, and R _f are each independently a substituted or unsubstituted alkyl group, halogen group, alkylene group, or 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 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 include triethyl phosphite, tributyl phosphite, triethyl phosphate, trimethyl phosphate, or a combination thereof. Specific examples of the third additive may include methylene methane disulfonic acid ester.

Since the electrolyte includes succinonitrile as the second additive, it is possible to suppress a phenomenon in which the metal is eluted from the positive electrode, thereby effectively suppressing the problem that the eluted metal moves, precipitates, and grows in the negative electrode. Of the nitrile-based succinonitriles can best inhibit such metal elution, it is suitable as a second additive.

In addition, by including the first additive, it is possible to suppress 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 temperature.

In addition, by including the third additive, it is possible to effectively suppress the increase in resistance during high temperature long-term storage and room temperature charging and discharging, in the case of including a carbonate solvent as a non-aqueous organic solvent, decarburization to remove CO ₂ from the carbonate solvent The oxidation reaction can be suppressed .

As such, the electrolyte according to the embodiment includes the first additive, the second additive, and the third additive together, so that the SO groups are bonded to the positive electrode, thereby suppressing electrolyte decomposition due to charge and discharge progress, and consequently, Improve storage performance.

The content of the first additive may be 0.1 wt% to 2 wt% with respect to the total weight of the electrolyte. If the content of the first additive is outside the above range, that is, less than 0.1% by weight, the effect of using the first additive is insignificant, and if the content of the first additive is more than 2% by weight, the solubility in the electrolyte decreases, and a precipitate is formed. It is not appropriate.

The content of the second additive may be 0.1 wt% to 2 wt% with respect to the total weight of the electrolyte. If the content of the second additive is outside the above range, that is, less than 0.1% by weight, the effect of using the second additive is insignificant, and when the content of the second additive is more than 2% by weight, the solubility in the electrolyte may be lowered to produce a precipitate. It's not appropriate.

The content of the third additive may be 0.1% by weight 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 the content of the third additive is more than 1% by weight, it reacts with lithium of the positive electrode to form a salt. It is not suitable because it produces a precipitate, which moves to the cathode, and thus the cycle life characteristics, i.e. capacity retention, are lowered.

Mixing ratios of the first additive, the second additive, and the third additive may be appropriately adjusted and used within the content of the above ranges, respectively.

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 cell 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.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used. The ester solvent may be 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 can be used.

Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran 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 solvent, and as the aprotic solvent, T-CN (T is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, Nitriles such as double bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, and the like.

The non-aqueous organic solvent may be used alone or in admixture of one or more. The mixing ratio in the case of mixing more than one can be appropriately adjusted according to the desired cell performance, which can be widely understood by those skilled in the art.

When the nonaqueous organic solvent is mixed and used, a mixed solvent of cyclic carbonate and chain carbonate, or a mixed solvent of cyclic carbonate and propionate solvent or cyclic carbonate, chain carbonate and propionate system Mixed solvents of solvents may be used. As the propionate solvent, methyl propionate, ethyl propionate, propyl propionate, or a combination thereof may be used.

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

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

As the aromatic hydrocarbon-based organic solvent may be used an aromatic hydrocarbon compound of the formula (4).

[Formula 4]

(In Formula 4, R _{One To} R _{6 It} is the same or different from each other and is selected from the group consisting of hydrogen, halogen, alkyl group of 1 to 10 carbon atoms, haloalkyl group and combinations thereof.)

Specific examples of the aromatic hydrocarbon 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-dioodobenzene, 1,3-dioiobenzene, 1,4-dioiobenzene, 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-dioodotoluene, 2,4-diaodotoluene, 2 , 5-diaodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

The lithium secondary battery electrolyte may further include an ethylene carbonate compound of Formula 5 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 C1-5 alkyl group, wherein 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 using such life improving additives, the amount thereof can be properly adjusted.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery and to promote 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 1), LiCl and LiI include one or more selected from the group consisting of supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, 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 cathode active material layer, as the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used, and specifically, cobalt, manganese, nickel, and these At least one of a complex oxide of a metal and lithium selected from the combination of More specific examples may be used a compound represented by any one of the following formula. 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 0 _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 0 _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 0 _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 0 _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, what has a coating layer on the surface of this compound can also be used, or the compound and the compound which have a coating layer can also be used in mixture. The coating layer may include at least one coating element compound selected from the group consisting of oxides of the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements and hydroxycarbonates of the coating elements. Can be. The compounds 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. The coating layer forming process may use any coating method as long as it can be coated with the above compounds by a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating or dipping method). Detailed descriptions thereof will be omitted since they can be understood by those skilled in the art.

According to one embodiment, 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) as the cathode active material; Li _a Ni _1-bc Co _b X _c 0 _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 0 _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 0 _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 0 _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); At least two kinds of nickel-based positive electrode active materials such as Li _a NiG _b O ₂ (0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1) may be mixed and used, or in the chemical formulas 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, the nickel-based positive 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.

When using these in mixture, this mixing ratio can be mixed suitably according to the target physical property. For example, when the nickel-based positive electrode active material and another active material are mixed and used, the content of the nickel-based positive electrode active material may be used in an amount of 30 wt% to 97 wt% 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 cathode 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% by weight to 5% by weight based on the total weight of the positive electrode active material layer, respectively.

The binder may attach the positive electrode active material particles to each other well and may also attach the positive electrode active material to the current collector. Representative examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrroli Don, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto. .

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electron conductive material without causing chemical change in the battery. Examples of the conductive material include conductive materials such as carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives such as metallic materials such as metal fibers. And conductive materials containing polymers or mixtures thereof.

The current collector may be aluminum foil, nickel foil, or a combination thereof, but is not limited thereto.

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

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

Examples of a material capable of reversibly intercalating / deintercalating the lithium ions include carbon materials, that is, carbon-based negative electrode active materials generally used in lithium secondary batteries. Representative examples of the carbon-based negative active material may be crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate, 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, calcined coke, and the like.

Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of metals selected from can be used.

Examples of materials that can be doped and undoped with lithium include Si, SiO _x (0 <x <2), and Si-Q alloys (wherein Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, and 16). An element selected from the group consisting of group elements, transition metals, rare earth elements, and combinations thereof, not Si), Si-carbon composites, Sn, SnO ₂ , Sn-R (wherein R is an alkali metal, an alkaline earth metal, 13 An element selected from the group consisting of group elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and not Sn), Sn-carbon composites, and the like. At least one of them may be used by mixing with SiO ₂ . 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, 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 electrode active material may be a Si-carbon composite, 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 at least in part. Unless otherwise defined herein, the average particle diameter (D50) refers to the diameter of the particles having a cumulative volume of 50% by volume in the particle size distribution.

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

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

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

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

The water-insoluble binder includes polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and olefin copolymers having 2 to 8 carbon atoms, and (meth) acrylic acid and (meth) acrylic acid alkyl esters. Copolymers or combinations thereof.

When using a water-soluble binder as the negative electrode binder, it may further include a cellulose-based compound that can impart viscosity as a thickener. As this cellulose type compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, these alkali metal salts, etc. can be used in mixture of 1 or more types. Na, K or Li may be used as the alkali metal. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electron conductive material without causing chemical change in the battery. Examples of the conductive material include carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black, carbon fiber, metal powders such as copper, nickel, aluminum, and silver, or polyphenylene derivatives of metals such as metal fibers. And conductive materials containing conductive polymers such as these or mixtures thereof.

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

The cathode active material layer and the anode active material layer are formed by mixing an anode 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 the method of forming the active material layer is well known in the art, detailed description thereof will be omitted. 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 electrode active material layer, water may be used as a solvent used when preparing the negative electrode active material composition.

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

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

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

Hereinafter, examples and comparative examples of the present invention are described. Such 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 volume ratio) and added to 100% by weight of the mixture. 10 wt% fluoroethylene carbonate, 0.2 wt% LiBF ₄ , 1 wt% lithium bisoxalate borate, 1.5 wt% LiPO ₂ F ₂ , 1 wt% triethyl phosphite, 1 wt% succinonitrile and methylene methane disulfonic acid 0.4 wt% of the ester was added to prepare an electrolyte for a lithium secondary battery.

(Example 2)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2: 1: 7 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 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 volume ratio) and 100% by weight of the mixture was 10% by weight of fluoroethylene carbonate, 0.2% by weight of LiBF ₄ , lithium 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 were added to prepare an electrolyte for a lithium secondary battery.

(Comparative Example 6)

1.5M LiPF ₆ was added to a mixed solvent of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (2: 1: 7 volume ratio) and 100% by weight of the mixture was 10% by weight of fluoroethylene carbonate, 0.2% by weight of LiBF ₄ , lithium 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 were added to prepare an electrolyte for a lithium secondary battery.

* Battery manufacturing

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

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

Using a prepared positive electrode, a negative electrode and the electrolyte 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)

The prepared battery was stored at a high temperature (60 ° C.) for 90 days, and then DC internal resistance (DC-IR) was measured. DC internal resistance measurement is 50% of SOC (State of charge) discharge after carrying out two chemical conversion processes at 0.2C (when charging and discharging the battery at 4.2V, the total charge capacity of the battery is 100%. And the discharged state so as to be the% discharge capacity.

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

In addition, the change rate of the DC internal resistance up to 30 days from the measured result was obtained, and the results of 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. 4 shows results of DC internal resistance change rate up to 60 days of the battery including the electrolytes 5 and 6.

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

In addition, as shown in FIG. 3, the battery containing the electrolyte of Example 1 containing all of triethyl phosphite, succinonitrile and methylene methane disulfonic acid ester showed the smallest DC-IR change rate. The battery including the electrolyte solution of Comparative Example 1, which does not contain only succinonitrile, has a large DC-IR change rate, and in the case of the battery including the electrolyte of Comparative Examples 2 and 3 containing triethyl phosphite and succinonitrile, It can be seen that the DC-IR change rate is higher than that of the battery containing the electrolyte of Comparative Example 1 containing only succinonitrile. In addition, it can be seen that the battery containing the electrolyte of Comparative Example 4 containing only succinonitrile and methylene methane disulfonic acid ester also showed a greater DC-IR change rate than the battery containing the electrolyte solution of Example 1.

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

From these results, it can be seen that when the trialkyl phosphite, succinonitrile, and methylene methane disulfonic acid esters are all included, the increase in resistance at high temperature storage is very small, but the increase in resistance is not included in any of them. have. In particular, it can be seen that Example 1 using triethyl phosphite is the most excellent among the trialkyl phosphites.

* AC-IR: Alternating Current, Internal resistance

The prepared battery was stored at a high temperature (60 ° C.) for 90 days, and then the AC internal resistance (DC-IR) was measured. The AC internal resistance measurement was performed by charging and discharging the battery to a 100% discharge capacity when the battery was stored at a high temperature and then stored at room temperature (25 ° C.) at 4.2 V (state of charge) 100 (when the total charge capacity of the battery was 100%. Under conditions) and 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 battery including the electrolytes of Examples 2 and 3 appeared similarly.

* High temperature storage characteristics: evaluation of recovery capacity

Charged and discharged the produced battery once at 0.2C at 0.2C to measure the charge and discharge capacity (initial charge-discharge capacity), and store the battery at 60 ° C for 10 days, and then charge and discharge once at 0.2C. Charge and discharge capacity (10-day charge and discharge capacity), and after storing the battery for 30 days at 60 ℃, once charged and discharged at 0.2C, charge and discharge capacity (30 days charge and discharge capacity) ) Was measured. Subsequently, after storing the obtained battery for 60 days at 60 degreeC, it charged and discharged once at 0.2 C, and measured the charging / discharging capacity (60-day charging / discharging capacity).

The 10-day charge-discharge capacity ratio (which is the recovery capacity), the 30-day charge-discharge capacity ratio, and the 60-day charge-discharge capacity ratio with respect to the measured initial charge-discharge capacity were obtained, respectively. Among the results, the results of the 30-day charge-discharge capacity ratio and the 30-day charge-discharge capacity ratio 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 the 60-day charge-discharge capacity ratio were used as recovery capacity, and the results of Examples 2 and 3 and Comparative Examples 5 and 6 are shown in FIG. 6.

30 days charge and discharge capacity ratio (%) 60 days charge and 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 battery containing the electrolytes of Examples 1 to 5 are very excellent compared to the battery containing the electrolyte of Comparative Example 2.

In addition, as shown in Figure 6, it can be seen that the capacity recovery rate after storing 60 days at a high temperature of the battery containing the electrolyte of Examples 2 and 3 is superior to the battery containing the electrolyte of Comparative Examples 5 and 6. .

From these results, it can be seen that the case where all of the trialkyl phosphite, succinonitrile and methylene methane disulfonic acid ester is included is superior to the case where none of them is included, and the high temperature storage characteristics are excellent.

The present invention is not limited to the above embodiments, but may be manufactured in various forms, and a person skilled in the art to which the present invention pertains has another specific form without changing the technical spirit or essential features of the present invention. It will be appreciated that the present invention may be practiced as. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (6)

Non-aqueous organic solvents;
Lithium salts;
A first additive which is a compound of Formula 1, a compound of Formula 2, or a combination thereof;
Succinonitrile second additive; And
To include a third additive of the formula
Electrolyte for lithium secondary battery.
[Formula 1]

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

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

(In Chemical 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,
The content of the first additive is a lithium secondary battery electrolyte 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% by weight to 2% by weight of the electrolyte for a lithium secondary battery based on the total weight of the electrolyte. The method of claim 1,
The content of the third additive is 0.1 wt% to 1 wt% of an electrolyte for a lithium secondary battery based on the total weight of the electrolyte. The method of claim 1,
The electrolyte further comprises a _fourth additive which is LiBF ₄ , fluoroethylene carbonate, lithium bisoxalate borate, LiPO ₂ F _2, or a combination thereof. A negative electrode including a negative electrode active material;
A positive electrode including a positive electrode active material; And
The electrolyte of any one of claims 1 to 5
Lithium secondary battery comprising a.