KR20210008728A - Electrolyte for rechargeable lithium battery and rechargeable lithium battery - Google Patents

Abstract

The present invention according to an embodiment relates to an electrolyte for lithium secondary battery, comprising: a non-aqueous organic solvent; lithium salt; and an additive, wherein the additive comprises at least one of (A) a compound represented by chemical formula 1, (B) a cyclic carbonate-based compound, and (C) an amphoteric lithium salt compound. The present invention also relates to a lithium secondary battery comprising the electrolyte. The electrolyte for a lithium secondary battery has improved initial resistance, resistance increase rate, and gas generation amount of the battery.

Description

Electrolyte for lithium secondary battery and lithium secondary battery including the same {ELECTROLYTE FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY}

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

Lithium secondary batteries are rechargeable, and their energy density per unit weight is three times higher than that of conventional lead storage batteries, nickel-cadmium batteries, nickel hydride batteries, and nickel zinc batteries, so notebooks, mobile phones, and power tools , It is commercialized for electric bicycles, and research and development for further energy density improvement is actively underway.

Such a lithium secondary battery includes a positive electrode including a positive electrode active material capable of intercalating and deintercalating lithium, and a negative electrode including a negative active material capable of intercalating and deintercalating lithium. It is used by injecting an electrolyte solution into a battery cell containing.

In particular, the electrolyte uses an organic solvent in which a lithium salt is dissolved, and is important in determining the stability and performance of a lithium secondary battery.

LiPF _{6, which} is most commonly used as a lithium salt of an electrolyte, has a problem in that it reacts with the solvent of the electrolyte to promote exhaustion of the solvent and generate a large amount of gas. When LiPF ₆ is decomposed, LiF and PF ₅ are generated, which causes electrolyte depletion in the battery, deterioration in high temperature performance and poor safety.

There is a need for an electrolyte solution that suppresses side reactions of such lithium salts and improves battery performance.

An embodiment provides an electrolyte solution for a lithium secondary battery with improved initial resistance, resistance increase rate, and gas generation amount of a battery.

Another embodiment provides a lithium secondary battery including the electrolyte solution having improved cycle life characteristics.

One embodiment is a non-aqueous organic solvent; Lithium salt; And an additive; wherein the additive comprises at least one of (A) a compound represented by the following Formula 1, and (B) a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound. to provide.

[Formula 1]

In Formula 1,

R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo An alkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 heteroaryl group,

L is a single bond, -O-, a substituted or unsubstituted C1 to C10 alkylene group, or in the main chain -O-, -S-, -S(=O)-, -S(=O) ₂ -, -C It is a C1-C10 alkylene group containing at least one functional group selected from (=O)-, -OC(=O)-, and -C(=O)O-.

In Formula 1, R ¹ to R ⁵ may each independently be a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C1 to C5 alkenyl group.

In Formula 1, R ¹ to R ⁵ may each independently be a substituted or unsubstituted C1 to C5 alkyl group.

L may be represented by the following formula (2).

[Formula 2]

―[CR _a R _b ] _n ―X―[CR _c R _d ] _m ―

In Chemical Formula 2,

R _a to R _d are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo An alkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 heteroaryl group,

n and m are each independently 0 to 5,

X is ―O―, ―S―, ―S(=O)―, ―S(=O) ₂ ―, ―C(=O)―, ―OC(=O)― and ―C(=O)O It is at least one selected from -.

The compound (A) may be represented by the following Chemical Formula 3-1, Chemical Formula 3-2, or a combination thereof.

[Chemical Formula 3-1] [Chemical Formula 3-2]

In Formulas 3-1 and 3-2,

R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo It is an alkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, or a substituted or unsubstituted C6 to C20 aryl group.

The compound (A) may be included in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte for the lithium secondary battery.

The cyclic carbonate-based compound (B) may be vinylene carbonate (VC), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), or a combination thereof.

The cyclic carbonate-based compound (B) may be included in an amount of 0.1% to 3% by weight based on the total amount of the electrolyte for the lithium secondary battery.

The amphoteric lithium salt compound (C) is lithium bis (oxalato) borate (LiBOB), lithium fluoro (oxalato) borate (LiFOB), lithium difluoro (oxalato) phosphate (LiDFOP), lithium difluoro It may be phosphate (LiPO ₂ F ₂ ) or a combination thereof.

The amphoteric lithium salt compound (C) may be included in an amount of 0.1% to 3% by weight based on the total amount of the electrolyte for the lithium secondary battery.

Another embodiment is an anode; cathode; And it provides a lithium secondary battery comprising the electrolyte.

The positive electrode includes a current collector and a positive electrode active material layer including a positive electrode active material formed on the current collector, and the positive electrode active material includes lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium cobalt. Oxide (LiCoO ₂ ), lithium manganese oxide (LiMnO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium iron phosphate (LiFePO ₄ ) It may include at least one active material selected from the group consisting of.

The electrolyte solution containing the additive composition of the present invention can suppress the initial resistance, resistance increase rate, and gas generation of the battery, and a lithium secondary battery having improved cycle life characteristics can be obtained.

1 is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention.

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.

Unless otherwise defined in the present specification,'substitution' means that the hydrogen atom in the compound is a halogen atom (F, Cl, Br or I), a hydroxy group, an alkoxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group. , Hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or salt thereof, sulfonic acid group or salt thereof, phosphoric acid or salt thereof, C1 to C20 alkyl group, C2 to C20 alkenyl group, C2 to C20 Alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C4 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkyl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to C15 It means substituted with a substituent selected from a cycloalkynyl group, a C2 to C20 heterocycloalkyl group, and combinations thereof.

In addition, unless otherwise defined in the specification,'hetero' means containing 1 to 3 heteroatoms selected from N, O, S, and P.

The electrolyte for a lithium secondary battery according to an embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive.

The non-aqueous organic solvent is introduced to provide a passage through which lithium ions in the secondary battery can move, and for example, by controlling the dissolution and dissociation degree of the electrolyte, smooth movement of lithium ions may be promoted.

As the non-aqueous organic solvent according to an embodiment, 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, decanolide, mevalonolactone, Caprolactone (caprolactone) and the like may be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used. Cyclohexanone may be used as the ketone solvent. Ethyl alcohol, isopropyl alcohol, and the like may be used as the alcohol-based solvent, and R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and as the aprotic solvent, Nitriles such as double bonds, aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. .

The non-aqueous organic solvent can be used alone or in combination of one or more, and the mixing ratio in the case of using one or more mixtures can be appropriately adjusted according to the desired battery performance, which is widely understood by those in the field. Can be.

The lithium salt actually becomes a vehicle for transporting lithium.

As the lithium salt according to an embodiment, LiPF ₆ , LiBF ₄ , 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, it is an integer of 1 to 20), LiCl, and one or two or more selected from the group consisting of LiI.

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.

The additive controls the viscosity of the electrolyte and forms a SEI (Solid Electrolyte Interface) film at the interface between the electrode active material and the separator to prevent side reactions with the electrolyte and suppress gas generation, and adjust the viscosity to prevent lithium ions. It serves to help you move smoothly.

The additives include a cathode protection additive that suppresses side reactions between electrolyte by-products and cathode by forming an SEI film on the anode surface, a cathode protection additive that suppresses side reactions between electrolyte by-products and anode by forming an SEI film on the anode surface, and lithium in the anode and cathode. And amphoteric lithium salt additives that aid in replenishment and absorption, and promote lithium insertion/removal of positive and negative active materials, thereby improving charge/discharge characteristics of a battery.

The additive according to an embodiment includes at least one of (A) a compound represented by Formula 1 below, and (B) a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound.

[Formula 1]

In Formula 1, R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted A C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 Is a heteroaryl group,

L is a single bond, -O-, a substituted or unsubstituted C1 to C10 alkylene group, or in the main chain -O-, -S-, -S(=O)-, -S(=O) ₂ -, -C It is a C1-C10 alkylene group containing at least one functional group selected from (=O)-, -OC(=O)-, and -C(=O)O-.

The (A) compound represented by the following Formula 1 may be at least one of a cathode protection additive and a cathode protection additive, the (B) cyclic carbonate-based compound may be a cathode protection additive, and (C) the compound is amphoteric lithium It is a salt compound.

When the additive contains (A) a compound represented by the following formula (1), and contains at least one of (B) a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound, initial resistance and resistance increase rate can be reduced, and As a result, gas generation may be suppressed, and cycle life characteristics of the battery may be improved.

The compound (A) according to an embodiment is represented by the following formula (1).

[Formula 1]

In Formula 1, R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted A C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 Is a heteroaryl group,

L is a single bond, -O-, a substituted or unsubstituted C1 to C10 alkylene group, or in the main chain -O-, -S-, -S(=O)-, -S(=O) ₂ -, -C (=O)-, -OC(=O)-, and -C(=O)O-. It is a C1-C10 alkylene containing at least one functional group selected from.

In the case of including the compound represented by (A) Formula 1 in the additive, as the compound represented by Formula 1 (A) contains a sultam group, the effect of suppressing resistance increase through formation of a solid positive/negative electrode film And, as the silyl group is included, there is an effect of stabilizing the bulk electrolyte through HF/H ₂ O capturing, and at the same time, there is a function of reducing resistance. In addition, as the sultam and silyl groups are included at the same time, a stable film-forming effect at high temperature is expressed through structural stability as well as initial resistance stabilization.

In the compound (A) according to an embodiment, R ¹ to R ⁵ in Formula 1 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C5 alkenyl group, a substituted or unsubstituted It may be a C2 to C5 alkenyl group.

In the compound (A) according to an embodiment, in Formula 1, R ¹ to R ⁵ may each independently be a substituted or unsubstituted C1 to C5 alkyl group, or a substituted or unsubstituted C2 to C5 alkyl group.

In the compound (A) according to an embodiment, the linking group L included in the formula 1 is, for example, in the main chain -O-, -S--, -S(=O)-, -S(=O) _{2 It} may be a C2 to C5 alkylene group including at least one functional group selected from -, -C(=O)-, -OC(=O)-, and -C(=O)O-.

In the compound (A) according to an embodiment, the linking group L included in Formula 1 may be, for example, represented by Formula 2 below.

[Formula 2]

―[CR _a R _b ] _n ―X―[CR _c R _d ] _m ―

In Formula 2, R ^a to R ^d are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted A C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 Is a heteroaryl group,

n and m are each independently 0 to 5,

X is ―O―, ―S―, ―S(=O)―, ―S(=O) ₂ ―, ―C(=O)―, ―OC(=O)― and ―C(=O)O It is at least one selected from -.

The compound (A) according to an embodiment may be, for example, a compound represented by any one of the following Chemical Formula 3-1, Chemical Formula 3-2, or a combination thereof.

[Chemical Formula 3-1] [Chemical Formula 3-2]

In Formulas 3-1 and 3-2, R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 Alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, or a substituted or unsubstituted C6 to C20 aryl group.

The compound (A) may be included in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte solution for the lithium secondary battery, for example, 0.1% to 5% by weight, 0.1% to 2.5% by weight, 0.2% to It may be included in an amount of 2.5 wt%, 0.2 wt% to 2.0 wt%, 0.2 wt% to 1.0 wt%, or 0.2 wt% to 0.5 wt%. When the compound (A) is contained in an amount of 10% by weight or less based on the total amount of the electrolyte for a lithium secondary battery, an increase in the amount of gas generated due to excessive film formation and decomposition gas generation can be suppressed. Resistance and resistance increase rate can be improved to improve cycle life characteristics.

The cyclic carbonate-based compound (B) according to an embodiment may be vinylene carbonate (VC), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), or a combination thereof. By including the cyclic carbonate-based compound (B) represented by the specific compound, it is possible to obtain an effect of improving the initial resistance and long-term resistance increase rate through the formation of an appropriate negative electrode film.

The cyclic carbonate-based compound (B) may be included in an amount of 0.1 to 3% by weight, for example, 0.5 to 2.0% by weight or 0.5 to 1.5% by weight, based on the total amount of the electrolyte for the lithium secondary battery. When the cyclic carbonate-based compound (B) is included in an amount of 0.1 wt% or more with respect to the total amount of the electrolyte for a lithium secondary battery, initial resistance and resistance increase rate are improved, thereby providing a lithium secondary battery with improved cycle life characteristics. In addition, when the cyclic carbonate-based compound (B) is included in an amount of 3% by weight or less based on the total amount of the electrolyte for a lithium secondary battery, an increase in initial resistance due to excessive negative electrode film formation can be suppressed. In addition, the cyclic carbonate-based compound remaining without decomposition can be prevented from being oxidatively decomposed when left to stand at a high temperature, causing self-discharge of the anode or lowering the voltage.

The amphoteric lithium salt compound (C) according to an embodiment is lithium bis (oxalato) borate (LiBOB), lithium fluoro (oxalato) borate (LiFOB), lithium difluoro (oxalato) phosphate (LiDFOP) , Lithium difluoro phosphate (LiPO ₂ F ₂ ), or a combination thereof.

The amphoteric lithium salt compound (C) may be included in an amount of 0.1 to 3% by weight, for example, 0.5 to 2.0% by weight or 0.5 to 1.5% by weight, based on the total amount of the electrolyte for the lithium secondary battery. When the amphoteric lithium salt compound (C) is contained in an amount of 0.1 wt% or more with respect to the total amount of the electrolyte for a lithium secondary battery, initial resistance and resistance increase rate are improved, thereby providing a lithium secondary battery with improved cycle life characteristics. In addition, since the amphoteric lithium salt compound (C) is the first of the compounds contained in the electrolyte to be reduced and decomposed to form a film, when it is contained in an amount of 3% by weight or less based on the total amount of the electrolyte for a lithium secondary battery, excessive formation of the film is prevented. Can be prevented and a sudden rise in initial resistance can be suppressed.

Another embodiment of the present invention is a positive electrode; cathode; And it provides a lithium secondary battery comprising the above-described electrolyte.

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

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound), specifically lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM) , Lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMnO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium iron phosphate (LiFePO ₄ ), at least one active material selected from the group consisting of.

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

In one embodiment of the present invention, the positive active material layer may 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 adheres the positive electrode active material particles well to each other, and also plays a role in attaching the positive electrode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, and polyvinyl Chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material can be used as long as it does not cause chemical change and is an electron conductive material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen Carbon-based materials such as black and carbon fiber; Metal-based materials such as metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

Al may be used as the current collector, but is not limited thereto.

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

The negative active material includes 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.

As a material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used as a carbon material, and a representative example thereof is crystalline carbon. , Amorphous carbon, or they may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, 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.

As the lithium metal alloy, in the 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 The alloy of the metal of choice can be used.

The lithium-doped and undoped materials include Si, Si-C composite, SiO _x (0 <x ≤ 2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, It is an element selected from the group consisting of a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, but not Si), Sn, SnO ₂ , Sn-R alloy (the R is an alkali metal, an alkaline earth metal, It is an element selected from the group consisting of a group 13 element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and combinations thereof, and Sn is not), and at least one of them and SiO ₂ can also 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, Tl, Ge, P, As, Sb, Bi, What is selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

The transition metal oxide may include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

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.

In one embodiment of the present invention, the negative active material layer includes a binder, and may optionally further include a conductive material. 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, the negative active material may be used in an amount of 90% to 98% by weight, a binder may be used in an amount of 1% to 5% by weight, and a conductive material may be used in an amount of 1% to 5% by weight.

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.

The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluorine rubber, and combinations thereof. The polymeric resin binder is polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, It may be selected from ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and 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 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 constituted, any material can be used as long as it does not cause chemical change and is an electron conductive material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen Carbon-based materials such as black and carbon fiber; Metal-based materials such as metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

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.

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 is a schematic diagram showing a lithium secondary battery according to an embodiment of the present invention. The lithium secondary battery according to the exemplary 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 100 according to an embodiment is disposed between a negative electrode 112, a positive electrode 114 positioned opposite to the negative electrode 112, and between the negative electrode 112 and the positive electrode 114. A battery cell containing an electrolyte (not shown) impregnating the separator 113 and the negative electrode 112, the positive electrode 114 and the separator 113, and the battery container 120 and the battery container containing the battery cell It includes a sealing member 140 for sealing 120.

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.

Fabrication of lithium secondary battery

Preparation Example 1: Synthesis of a compound represented by Formula 1a (N-methyl-N-(trimethylsilyl)-methanesulfonamide)

Under nitrogen atmosphere, N-methylmethanesulfonamide (N-methylmethanesulfonamide, 10.0 g, 91.6 mmol) and bis (trimethylsilyl) amine (bis (trimethylsilyl) amine, 29.0 g, 179.7 mmol) were catalyzed by ammonium chloride, 0.2 g ) And mixed. After stirring at 100° C. for 2 hours, the mixture was further stirred at 130° C. for 1 hour. Purified by distillation under reduced pressure to obtain a colorless transparent liquid (7.5 g, yield: 75%).

[Formula 1a]

Preparation Example 2: Synthesis of a compound represented by Formula 1b (N-methyl-N-(trimethylsilyl)-propanesulfonamide)

Proceed in the same manner as in Preparation Example 1, except that N-methylpropanesulfonamide (N-methylpropanesulfonamide, 12.57 g, 91.6 mmol) was used instead of N-methylmethanesulfonamide (N-methylmethanesulfonamide, 10.0 g, 91.6 mmol). A colorless transparent liquid (7.5 g, yield: 75%) was obtained.

[Formula 1b]

Preparation Example 3: Synthesis of a compound represented by Formula 1c (N-methyl-N-trimethylsilyloxymethanesulfonamide)

Stage 1:

Synthesis of N-hydroxy-N-methylmethanesulfonamide

After dissolving N-methylhydroxylamine hydrochloride (10.0 g, 120 mmol) in water (12 mL), the temperature was reduced to 0°C. To the prepared reaction product, an aqueous solution of K ₂ CO ₃ (16.5 g, 120 mmol) dissolved in 20 mL water was slowly added. After stirring at 0° C. for 30 minutes, tetrahydrofuran (THF, 60 mL) and methanol (15 mL) were added and stirred for 10 minutes while maintaining the temperature. Methanesulfonyl chloride (methanesulfonyl chloride, 6.85 g, 59.8 mmol) was slowly added at 0° C. and stirred for 30 minutes. Then, the reaction mixture was raised to room temperature and stirred for 4 hours. Water was added until all the white precipitated solid was dissolved, followed by extraction using diethyl ether. The extracted organic layer was dried over MgSO ₄ and filtered, and the obtained filtrate was concentrated under reduced pressure to obtain a white solid (4.96 g, yield: 66%). The obtained solid was used in the next reaction without further purification.

Step 2:

Synthesis of N-methyl-N-trimethylsilyloxymethanesulfonamide

N-hydroxy-N-methylmethanesulfonamide synthesized in step 1 was dissolved in tetrahydrofuran (THF, 50 mL) under a nitrogen atmosphere. After lowering the reaction temperature to 0°C, triethylamine (TEA, 6.02 g, 59.5 mmol) was added. Then, trimethylsilyl chloride (TMSCl, 8.89 g, 59.5 mmol) was slowly added. After the reaction was stirred at 0° C. for 2 hours, the precipitated white solid was filtered and concentrated. The obtained concentrate was purified by distillation under reduced pressure to obtain a colorless and transparent liquid (5.4 g, yield: 69%).

[Formula 1c]

Manufacturing Example 4

N,N-dimethylmethane sulfonamide (DMS, manufacturer: Aldrich) was used.

Example

Examples 1 to 5, and Comparative Examples 1 to 6

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ as a positive electrode active material, polyvinylidene fluoride as a binder, and ketjen black as a conductive material were mixed in a weight ratio of 97.3:1.4:1.3, respectively, and dispersed in N-methyl pyrrolidone to disperse the positive electrode active material slurry Was prepared. The positive electrode active material slurry was coated on an Al foil having a thickness of 15 μm, dried at 100° C., and then rolled to prepare a positive electrode.

Graphite as a negative electrode active material, polyvinylidene fluoride as a binder, and ketjen black as a conductive material were mixed at a weight ratio of 98:1:1, respectively, and dispersed in N-methyl pyrrolidone to prepare a negative electrode active material slurry. The negative active material slurry was coated on a Cu foil having a thickness of 10 μm, dried at 100° C., and then rolled to prepare a negative electrode.

A lithium secondary battery was manufactured using the prepared positive and negative electrodes, a separator made of polyethylene having a thickness of 20 μm, and an electrolyte.

The electrolyte solution was mixed by mixing LiPF ₆ at 1.0 M in a non-aqueous organic solvent (mixed in a volume ratio of EC:DMC=3:7), and by applying the types and contents of the additives shown in Table 1 below. However, the content of the additive (% by weight) is based on the total electrolyte (non-aqueous organic solvent + lithium salt + additive) content.

Manufacturing Example 1
(weight%) Manufacturing Example 2
(weight%) Manufacturing Example 4
(weight%) VC
(weight%) LiDFOP
(weight%) Comparative Example 1 - - - - - Comparative Example 2 0.25 - - - Comparative Example 3 - 0.25 - - - Comparative Example 4 - - - - 1.0 Comparative Example 5 - - - 1.0 - Comparative Example 6 - - 0.25 - - Example 1 0.25 - - - 1.0 Example 2 0.25 - - 1.0 - Example 3 0.25 - - 0.5 1.0 Example 4 0.25 - - 1.0 1.0 Example 5 0.25 - - 1.5 1.0

*Evaluation 1: Initial DC resistance, DC resistance and resistance increase rate after storage for 30 days

The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 and 6 were initially converted by the following procedure. The first cycle was discharged to 2.6V after constant current charging to 3.6V with 0.2C current, and the second cycle was CC charging to 4.2V with 0.2C current and then discharged to 2.5V.

Then, it was charged to 100% SOC (SOC, state of charge = 100%) under conditions of 4.2V cutoff constant current charging and 0.05C cutoff constant voltage charging at 1C at 60°C and stored for 30 days. Initial DC resistance (DC-IR), DC resistance after storage for 30 days, and their ratio (resistance increase rate) were calculated, and the results are shown in Table 2 below.

DC resistance is calculated from the current difference and voltage difference when different currents are applied.In the initial fully charged state, a constant current discharged at 10A for 10 seconds, a constant current discharged at 1A for 10 seconds, and then a constant current discharged at 10A for 4 seconds. , DC resistance was calculated using the equation ΔR =ΔV/ΔI from the data of 18 seconds and 23 seconds.

The resistance increase rate (ΔDC-IR) was calculated as the ratio of DC-IR after storage for 30 days to the initial DC-IR.

DC-IR (initial)
(mΩ) DC-IR (60℃, 30 days)
(mΩ) ΔDC-IR
(%) Comparative Example 1 14.1 28.9 205.0 Comparative Example 2 13.4 20.3 151.5 Comparative Example 3 14 24 171.4 Comparative Example 4 15.2 23.4 153.9 Comparative Example 5 14.3 26.5 185.3 Comparative Example 6 15.3 24.2 158.2 Example 1 13.6 19.3 141.9 Example 2 13.3 18.7 140.6 Example 3 13.1 17.6 134.4 Example 4 13.5 17.8 131.9 Example 5 13.7 17.5 127.7

Referring to Table 2, in the case of Examples 1 to 5 using an additive according to an embodiment, the initial resistance, resistance after leaving for 30 days, and resistance increase rate when left to stand at high temperature (60°C) are improved compared to Comparative Examples 1 to 6 I could confirm.

*Evaluation 2: Capacity retention and recovery rate at 60℃

The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were initially charged and charged with 100% SOC in the same manner as in Evaluation 1.

Subsequently, after preserving the lithium secondary battery charged with initial ignition and SOC 100% at 60° C. for 10 days, 20 days and 30 days, discharged at 0.2C and 2.5V cutoff to discharge capacity ratio after storage to one discharge capacity (0 days) Is shown in Table 3 below as a capacity retention rate.

On the other hand, after preserving the lithium secondary battery charged with initial Mars and SOC 100% at 60°C for 10 days, 20 days and 30 days, 4.2V cutoff constant current charging at 0.2C, 0.05C cutoff constant voltage charging 0.2C, 2.5V The discharge capacity was measured by cut-off discharge, and the ratio of the discharge capacity to the initial capacity before storage is shown as a capacity recovery rate in Table 3 below.

Capacity retention rate (%) Capacity recovery rate (%) (0 days) (10 days) (20 days) (30 days) (0 days) (10 days) (20 days) (30 days) Comparative Example 1 100 90.1 87.5 86.5 100 93.5 92.1 90.7 Comparative Example 2 100 91.3 90.2 89.5 100 95.8 95.1 93.9 Comparative Example 3 100 90.5 88.4 86.5 100 93.3 91.8 90.5 Comparative Example 4 100 90.6 90.3 88.6 100 94 93.2 92.8 Comparative Example 5 100 89.9 89 87.3 100 95.2 94.6 93.8 Comparative Example 6 100 89.3 88.7 86.4 100 93.4 91.8 89.3 Example 1 100 90.8 90.6 90.3 100 97.5 96.4 94.3 Example 2 100 91.2 90.5 90.2 100 97.5 96.4 94.6 Example 3 100 91.5 91 90.6 100 98.1 96.3 95.1 Example 4 100 91.8 91.3 90.8 100 98.1 96.7 94.9 Example 5 100 91.2 90.9 90.5 100 98.1 96.1 94.8

Referring to Table 3, it was confirmed that the lithium secondary batteries prepared in Examples 1 to 5 improved both the capacity retention rate and the capacity recovery rate compared to Comparative Examples 1 to 6.

*Evaluation 3: Cycle life characteristics and resistance increase rate

The lithium secondary batteries prepared in Example 1, Examples 3 to 5, and Comparative Examples 1, 2, 4 and 5 were initially charged with 100% chemical conversion and SOC in the same manner as in Evaluation 1.

Initially, charge the lithium secondary battery 100% charged with Mars and SOC at a constant current of 0.2C, 4.2V cutoff at 25℃, charge with a constant voltage of 4.2V, 0.05C cutoff, and discharge 0.2C, 2.5V cutoff constant current as one cycle. , A total of 200 cycles were performed. The ratio of the 200 cycle discharge capacity to the one cycle discharge capacity is shown in Table 4 below as cycle life characteristics (0.2C).

Initially, a lithium secondary battery charged with 100% of Hwaseong and SOC was charged with a constant current of 1C and 4.2V cutoff at 25°C, charged with a constant voltage of 4.2V and 0.05C, and then discharged at a constant current with a cutoff of 1C and 2.5V as 1 cycle. 200 cycles were run. The 200 cycle discharge capacity ratio to the one cycle discharge capacity is shown in Table 4 below as cycle life characteristics (1C).

On the other hand, after 200 cycles, DC resistance (DC-IR) was calculated by applying a 1C current for 10 seconds and measuring the voltage drop, and the 200 cycle DC resistance increase rate (ΔDC-IR) for the initial DC resistance was calculated, and the following In Table 4, it is shown as DC-IR (200 cy) and ΔDC-IR, respectively.

Cycle life characteristics (0.2C)
(%) Cycle life characteristics (1C)
(%) DC-IR (200 cy)
(mΩ) ΔDC-IR
(%) Comparative Example 1 95.6 92.1 24.9 35 Comparative Example 2 97.0 93.5 21.2 18 Comparative Example 4 95.6 92.7 21.0 19 Comparative Example 5 96.2 92.8 22.9 24 Example 1 97.5 93.7 20.5 12 Example 3 97.8 96.3 19.5 7 Example 4 98.1 94.9 19.3 8 Example 5 98.0 95.4 18.9 4

Referring to Table 4, the lithium secondary batteries prepared in Examples 1 and 3 to 5 are compared with Comparative Examples 1, 2, 4 and 5, the initial discharge capacity, cycle life characteristics, direct current resistance (DC-IR) and charging. It was confirmed that the discharge cycle DC resistance increase rate (ΔDC-IR) was improved.

*Evaluation 4: High-temperature gas generation

The lithium secondary batteries prepared in Examples 3 to 5 and Comparative Examples 1, 2, 4 and 5 were initially converted in the same manner as in Evaluation 1. Subsequently, the lithium secondary battery that was initially converted was degassed, placed in a pouch, and stored in an oven at 60° C. for 30 days. Thereafter, the volume change of the pouch was measured, and it was converted into a mass change using the Archimedes method, and is shown as the amount of gas generated in Table 5 below.

Gas generation amount (mg) Comparative Example 1 82 Comparative Example 2 42 Comparative Example 4 67 Comparative Example 5 38 Example 3 29 Example 4 31 Example 5 34

Referring to Table 5, in the lithium secondary batteries prepared in Examples 3 to 5, it is determined that the amount of gas generated is reduced due to the increase in thermal stability due to the solid SEI film. On the other hand, Comparative Examples 1, 2, 4, and 5 were found to have a higher gas generation amount compared to the Example.

Although a preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and it is possible to implement various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings. It is natural to fall within the scope of the invention.

100: lithium secondary battery
112: cathode
113: separator
114: anode
120: battery container
140: sealing member

Claims (12)

Non-aqueous organic solvents; Lithium salt; And an additive,
The additive is (A) a compound represented by the following formula (1), and
(B) containing at least one of a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound,
Electrolyte for lithium secondary battery:
[Formula 1]

In Formula 1,
R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo An alkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 heteroaryl group,
L is a single bond, -O-, a substituted or unsubstituted C1 to C10 alkylene group, or in the main chain -O-, -S-, -S(=O)-, -S(=O) ₂ -, -C (=O)-, -OC(=O)-, and -C(=O)O-. In claim 1,
The R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C1 to C5 alkenyl group,
Electrolyte for lithium secondary batteries. In claim 1,
The R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C5 alkyl group,
Electrolyte for lithium secondary batteries. In claim 1,
The L is represented by the following formula (2),
Electrolyte for lithium secondary battery:
[Formula 2]
―[CR _a R _b ] _n ―X―[CR _c R _d ] _m ―
In Chemical Formula 2,
R _a to R _d are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo An alkyl group, a substituted or unsubstituted C3 to C10 heterocycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C6 to C20 aryl group or a substituted or unsubstituted C2 to C20 heteroaryl group,
n and m are each independently 0 to 5,
X is ―O―, ―S―, ―S(=O)―, ―S(=O) ₂ ―, ―C(=O)―, ―OC(=O)― and ―C(=O)O It is at least one selected from -. In claim 1,
The compound (A) is represented by the following formula 3-1, formula 3-2, or a combination thereof,
Electrolyte for lithium secondary battery:
[Chemical Formula 3-1] [Chemical Formula 3-2]

In Formula 3-1 and Formula 3-2,
R ¹ to R ⁵ are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cyclo It is an alkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, or a substituted or unsubstituted C6 to C20 aryl group. In claim 1,
The compound (A) is contained in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte for the lithium secondary battery,
Electrolyte for lithium secondary batteries. In claim 1,
The cyclic carbonate-based compound (B) is vinylene carbonate (VC), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), or a combination thereof,
Electrolyte for lithium secondary batteries. In claim 1,
The cyclic carbonate-based compound (B) is contained in an amount of 0.1% to 3% by weight based on the total amount of the electrolyte for the lithium secondary battery,
Electrolyte for lithium secondary batteries. In claim 1,
The amphoteric lithium salt compound (C) is lithium bis (oxalato) borate (LiBOB), lithium fluoro (oxalato) borate (LiFOB), lithium difluoro (oxalato) phosphate (LiDFOP), lithium difluoro Phosphate (LiPO ₂ F ₂ ) or a combination thereof,
Electrolyte for lithium secondary batteries. In claim 1,
The amphoteric lithium salt compound (C) is contained in an amount of 0.1% to 3% by weight based on the total amount of the electrolyte for the lithium secondary battery,
Electrolyte for lithium secondary batteries. anode; cathode; And comprising the electrolyte solution of any one of claims 1 to 10,
Lithium secondary battery. In clause 11,
The positive electrode includes a current collector and a positive electrode active material layer including a positive electrode active material formed on the current collector,
The positive electrode active material is lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMnO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium iron phosphate. (LiFePO ₄ ) containing at least one active material selected from the group consisting of,
Lithium secondary battery.

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