KR102211172B1 - Electrolyte of rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

An electrolyte for a lithium secondary battery and a lithium secondary battery thereof, wherein the electrolyte includes a non-aqueous organic solvent; Lithium salt; A first additive represented by LiSO ₃ X (wherein X is halogen); And a succinonitrile second additive.

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 active material, various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of intercalating/desorbing 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 high rate characteristics and reduced resistance during long-term storage at high temperatures.

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

According to one embodiment, a non-aqueous organic solvent; Lithium salt; A first additive represented by LiSO ₃ X (wherein X is halogen); And it provides an electrolyte for a lithium secondary battery comprising a second succinonitrile additive. X may be F.

The content of the first additive may be 0.1% to 5% 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 electrolyte may further include a third 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.

The positive active material may be represented by Formula 3 below.

[Formula 3]

Li _a Ni _x M _1-x O ₂

(In Formula 3, 0.9 ≤ a ≤ 1.1, 0.5 ≤ x ≤ 0.93,

M is Mn, Al, Co, Mg, Ba, B, La, Y, Ti, Zr, Mn, Si, V, P, Mo, W, F, or a combination thereof.)

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

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

1 is a schematic view of a rechargeable lithium battery according to an embodiment of the present invention.
2 is a graph showing a change in resistance after storage at a high temperature of batteries including the electrolytes of Examples 1 to 5 and Comparative Example 1. FIG.
3 is a graph showing the measurement of the capacity recovery rate after high temperature storage of the batteries containing the electrolytes of Examples 1 to 5 and Comparative Example 1. FIG.
4 is a graph showing a change in resistance after storage at a high temperature of batteries including the electrolytes of Examples 6 to 9;

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.

One embodiment is a non-aqueous organic solvent; Lithium salt; A first additive represented by LiSO ₃ X (wherein X is halogen); And it provides an electrolyte for a lithium secondary battery comprising a second succinonitrile additive.

The first additive is LiSO ₃ X, which may serve to improve high temperature storage performance. In this case, X is a halogen, for example, it may be F, Cl, Br, I, At, or a combination thereof. According to one embodiment, X may be F. When X is halogen, in a battery using this electrolyte, there may be an advantage of effectively forming a film on the negative electrode, and in particular, when F is the advantage of further improving the cycle life characteristics (capacity retention rate) of the negative electrode. Can be obtained.

In addition, such an electrolyte includes succinonitrile as a second additive, and can form a thin film on the positive electrode, thereby suppressing the elution of metallic foreign substances from the positive electrode, so that the eluted foreign substances move to the negative electrode and precipitate. And it is possible to effectively suppress the problem of growth, and thereby suppress a decrease in initial resistance.

However, the second additive may cause problems such as a decrease in high rate characteristics and an increase in resistance during long-term storage at high temperatures, but the electrolyte of one embodiment further comprises the first additive having not only an effect of improving high temperature storage performance, but also protecting an anode interface. Since it includes, it is possible to suppress the problem caused by the use of the second additive.

As described above, when the first additive and the second additive are used together, the initial resistance decrease and the anode interface protection function can be enhanced, thereby improving the high rate characteristics, and suppressing the increase in resistance during long-term storage at high temperatures. I can.

The content of the first additive may be 0.1% to 5% by weight based on the total weight of the electrolyte, and according to one embodiment, may be 0.5% to 2% by weight. If 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 if it exceeds 5% by weight, it is appropriate because a precipitate may be formed due to solubility problems. Not.

The content of the second additive may be 0.1% by weight to 2% by weight based on the total weight of the electrolyte, and according to one embodiment, it may be 0.25% by weight to 2% by weight, and according to another embodiment, 0.25% by weight It may be more than 1.5% by weight. 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 resistance increases and is not appropriate.

The electrolyte may further include a third additive that is LiBF ₄ , fluoroethylene carbonate, lithium bisoxalate borate (LiBOB), LiPO ₂ F _2, or a combination thereof.

When the third additive is further included, the content of the third additive may be 0.1% by weight to 1% by weight based on 100% by weight of the total electrolyte. When the third additive is further included, it is possible to improve the cycle life characteristics (capacity retention) of the negative electrode in a battery using this electrolyte, and especially when used in an amount within the above range, the high temperature storage characteristics are more effectively improved. I can make it.

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

The carbonate-based solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl 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 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, which 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 of Formula 1 may be used.

[Formula 1]

(In Formula 1, R ₁ to R ₆ are the same 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 ,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.

The electrolyte for a rechargeable lithium battery may further include an ethylene carbonate-based compound represented by Formula 2 below to improve battery life.

[Formula 2]

(In Formula 2, 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 C 1 to C 5 alkyl group, 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. When further use of such a life-improving additive is used, 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 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 effectively move.

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 de-intercalation 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 <a <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, and D is from the group consisting of O, F, S, P, and combinations thereof. Is selected; 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 formation 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, the positive electrode active material may be a nickel-based positive electrode active material represented by Formula 3 below. As the nickel-based positive electrode active material promotes electrolyte decomposition at high temperature, the high-temperature performance generally deteriorates somewhat compared to the cobalt-based positive electrode active material, but the electrolyte containing the first and second additives according to one embodiment is used as a nickel-based positive electrode. When used together with an active material, the first and second additives can suppress the nickel-based positive electrode active material from decomposing the electrolyte solution at high temperature, and thus, deterioration in high-temperature performance can be effectively prevented. Accordingly, it is appropriate to use the electrolyte including the first and second additives according to one embodiment together with a positive electrode including a nickel-based positive electrode active material, since the effect can be more maximized.

[Formula 3]

Li _a Ni _x M _1-x O ₂

In Formula 3, 0.9 ≤ a ≤ 1.1, 0.5 ≤ x ≤ 0.93, M is Mn, Al, Co, Mg, Ba, B, La, Y, Ti, Zr, Mn, Si, V, P, Mo, W , F or a combination thereof.

A specific example of the intercalation compound may be a compound represented by Formula 4 below.

[Formula 4]

Li _a Ni _x Co _y T _z O ₂

In Formula 4, 0.9 ≤ a ≤ 1.1, 0.5 ≤ x ≤ 0.93, 0.05 ≤ x ≤ 0.3, 0.01 ≤ z ≤ 0.1, x + y + z = 1, T is Mn or Al

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 serve to attach 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-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as polyphenylene derivatives. And conductive materials containing polymers or mixtures thereof.

The current collector may be an aluminum foil, a nickel foil, or a combination thereof, but 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 calcined coke.

The lithium metal alloy includes lithium, 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, and 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) means 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 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 to the negative active material to the current collector. 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 including 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 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.

As the current collector, 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 a combination thereof may be used.

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 then 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. As the solvent, N-methylpyrrolidone or the like may be used, 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, a separator may exist between the positive electrode and the negative electrode depending on the type of lithium secondary battery. 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 exemplary embodiment is described as an example of a prismatic shape, but the present invention is not limited thereto, and may be applied to various types of batteries such as a cylindrical shape and a pouch type.

Referring to FIG. 1, a rechargeable lithium battery 100 according to an embodiment includes an electrode assembly 40 wound between a positive electrode 10 and a negative electrode 20 through a separator 30, and the electrode assembly 40. ) May include a built-in case 50. The anode 10, the cathode 20, and the separator 30 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.

(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 An electrolyte for a lithium secondary battery was prepared by adding 10% by weight of fluoroethylene carbonate, 0.2% by weight of LiBF ₄ , 1% by weight of lithium bisoxalate borate, 1.5% by weight of LiPO ₂ F _{2 and} 1% by weight of succinonitrile.

(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 For lithium secondary batteries by adding 10% by weight of fluoroethylene carbonate, 0.2% by weight of LiBF ₄ , 1% by weight of lithium bisoxalate borate, 1.5% by weight of LiPO ₂ F ₂ , 0.1% by weight of LiSO ₃ F and 1% by weight of succinonitrile The electrolyte was prepared.

(Example 2)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the LiSO ₃ F content was changed to 0.5% by weight.

(Example 3)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the LiSO ₃ F content was changed to 1% by weight.

(Example 4)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the LiSO ₃ F content was changed to 1.5% by weight.

(Example 5)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the LiSO ₃ F content was changed to 2% by weight.

* Battery manufacturing

LiNi _0.8 Co _0.1 Mn _0.1 O ₂ 96 wt% of a cathode active material, ₂ wt% of Ketjen Black conductive material, and 2 wt% of polyvinylidene fluoride were mixed in an N-methylpyrrolidone solvent to prepare a cathode 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 a Ketjen Black conductive material, and 2% by weight of polyvinylidene fluoride in an N-methylpyrrolidone solvent. The negative 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 Example 1, a lithium secondary battery was manufactured by a conventional method. At this time, the amount of electrolyte injected was 3.8g.

*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, and the results are shown in FIG. 2.

The DC internal resistance measurement was performed by performing the battery conversion process twice at 0.2C, and then discharging SOC 50% (State of charge) 50% (when charging and discharging the battery at 4.2V, the total charging capacity of the battery was 100%. At this time, it was measured while carrying out the state of discharging to a 50% discharge capacity).

As shown in FIG. 2, in the case of the battery including the electrolyte of Examples 1 to 5 including both LiSO ₃ F and succinonitrile, compared to the battery including the electrolyte of Comparative Example 1 including only succinonitrile, It can be seen that the DC-IR rate of change was small. In particular, in the case of Examples 3 to 5 in which the LiSO ₃ F content is 1.0% to 2.0% by weight, it can be seen that the DC-IR change rate is very small.

From this result, when only succinonitrile is used in the electrolyte, the resistance increases during high temperature storage, whereas when succinonitrile and LiSO ₃ F are used together in the electrolyte, the increase in resistance during high temperature storage can be suppressed. Can be seen.

* Dose recovery rate evaluation

The prepared battery was charged and discharged once at 0.3C, and the discharge capacity was measured. Subsequently, the obtained battery was stored at a high temperature (60°C) for 60 days, and then charged and discharged once at 0.3C, and the discharge capacity was measured. The ratio of the discharge capacity to the discharge capacity before high temperature storage and after storage for 60 days was calculated, and the result is shown in FIG. 3 as a capacity recovery capacity.

As shown in FIG. 3, it can be seen that the capacity recovery rate of the batteries using the electrolytes of Examples 1 to 5 is superior to that of Comparative Example 1.

(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 For lithium secondary batteries by adding 10% by weight of fluoroethylene carbonate, 0.2% by weight of LiBF ₄ , 1% by weight of lithium bisoxalate borate, 1.5% by weight of LiPO ₂ F ₂ , 2.0% by weight of LiSO ₃ F and 0.25% by weight of succinonitrile The electrolyte was prepared.

(Example 7)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the succinonitrile content was changed to 0.5% by weight.

(Example 8)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the succinonitrile content was changed to 1% by weight.

(Example 9)

An electrolyte for a lithium secondary battery was prepared in the same manner as in Example 1, except that the succinonitrile content was changed to 1.5% by weight.

* Battery manufacturing

LiNi _0.8 Co _0.1 Mn _0.1 O ₂ 96 wt% of a cathode active material, ₂ wt% of Ketjen Black conductive material, and 2 wt% of polyvinylidene fluoride were mixed in an N-methylpyrrolidone solvent to prepare a cathode 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 a Ketjen Black conductive material, and 2% by weight of polyvinylidene fluoride in an N-methylpyrrolidone solvent. The negative 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 6 to 9, a lithium secondary battery was manufactured by a conventional method. At this time, the amount of electrolyte injected was 5.8g.

*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, and the results are shown in FIG. 4.

The DC internal resistance measurement was performed by performing the battery conversion process twice at 0.2C, and then discharging SOC 50% (State of charge) 50% (when charging and discharging the battery at 4.2V, the total charging capacity of the battery was 100% At this time, it was measured while carrying out the state of discharging to a 50% discharge capacity).

As shown in FIG. 4, it can be seen that as the content of succinonitrile increases, the DC-IR change rate increases during high temperature storage.

The present invention is not limited to the above embodiments, but may be manufactured in a variety of different forms, and a person of ordinary skill in the art to which the present invention pertains to 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 not limiting.

Claims (7)

Non-aqueous organic solvents;
Lithium salt;
A first additive represented by LiSO ₃ X (wherein X is halogen); And
Succinonitrile second additive
Including,
The content of the first additive is 0.5% by weight to 2% by weight based on the total weight of the electrolyte,
The content of the second additive is 0.25% by weight or more and less than 1.5% by weight based on the total weight of the electrolyte. delete delete The method of claim 1,
Wherein X is F, an electrolyte for a lithium secondary battery. The method of claim 1,
The electrolyte is LiBF ₄ , fluoroethylene carbonate, lithium bisoxalate borate, LiPO ₂ F ₂ Or a lithium secondary battery electrolyte further comprising a third additive that is a combination thereof. 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, 4 and 5
Lithium secondary battery comprising a. The method of claim 6,
The positive electrode active material is a lithium secondary battery represented by the following formula (3).
[Formula 3]
Li _a Ni _x M _1-x O ₂
(In Formula 3, 0.9 ≤ a ≤ 1.1, 0.5 ≤ x ≤ 0.93,
M is Mn, Al, Co, Mg, Ba, B, La, Y, Ti, Zr, Mn, Si, V, P, Mo, W, F, or a combination thereof.)

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