KR102449845B1 - Electrolyte for rechargeable lithium battery and rechargeable lithium battery - Google Patents

Abstract

One embodiment is a non-aqueous organic solvent; lithium salt; and an additive, wherein the additive includes at least one of (A) a compound represented by Formula 1, and (B) a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound, an electrolyte solution for a lithium secondary battery and the same A lithium secondary battery is provided.

Description

Electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same

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

Lithium secondary batteries can be recharged, and compared to conventional lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, etc., the energy density per unit weight is three times higher and fast charging is possible. , are being commercialized for electric bicycles, and research and development for further energy density improvement is being actively conducted.

Such a lithium secondary battery includes a positive electrode including a positive active material capable of intercalation and deintercalation of lithium, and a negative electrode including a negative electrode active material capable of intercalating and deintercalating lithium. It is used by injecting an electrolyte 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 often used as a lithium salt of an electrolyte, reacts with an electrolyte solvent to accelerate the depletion of the solvent and generate a large amount of gas. When LiPF ₆ decomposes, LiF and PF ₅ are generated, which causes electrolyte depletion in the battery and leads to deterioration of high-temperature performance and poor safety.

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

One embodiment provides an electrolyte for a lithium secondary battery having improved initial resistance, resistance increase rate, and gas generation amount of the battery.

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

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 Chemical 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 —O—, —S—, —S(=O)—, —S(=O) ₂ —, —C in the main chain (=O)—, —OC(=O)— and —C(=O)O—C1 to C10 alkylene group including at least one functional group selected from the group consisting of.

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 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 - 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.

[Formula 3-1] [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 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 wt% to 10 wt% based on the total amount of the electrolyte for a 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 wt% to 3 wt% based on the total amount of the electrolyte for a 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 phosphate (LiPO ₂ F ₂ ) or a combination thereof.

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

Another embodiment is a positive electrode; 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 active material is lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium cobalt It may include at least one active material selected from the group consisting of oxide (LiCoO ₂ ), lithium manganese oxide (LiMnO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium iron phosphate (LiFePO ₄ ).

The electrolyte solution including the additive composition of the present invention can suppress the initial resistance and resistance increase rate and gas generation of the battery, and it is possible to obtain a lithium secondary battery with improved cycle life characteristics.

1 is a schematic diagram illustrating 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 thereto, and the present invention is only defined by the scope of the claims to be described later.

Unless otherwise defined herein, 'substitution' means that a hydrogen atom in a 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 its salt, sulfonic acid group or its salt, phosphoric acid or its salt, 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 herein, 'hetero' means containing 1 to 3 heteroatoms selected from N, O, S and P.

The electrolyte solution 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 of the secondary battery can move, for example, by controlling the dissociation degree of dissolution of an electrolyte to promote smooth movement of lithium ions.

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.

Examples of the carbonate-based solvent 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. Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, propylpropionate, decanolide, mevalonolactone, Caprolactone and the like may be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used. Cyclohexanone and the like may be used as the ketone-based solvent. As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms, a linear, branched, or ring structure, 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 may be used alone or in a mixture of one or more, and when one or more are mixed and used, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those in the art. can be

The lithium salt is actually a means of 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), one or two or more selected from the group consisting of LiCl and LiI.

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 appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

The additive controls the viscosity of the electrolyte, forms a Solid Electrolyte Interface (SEI) film at the interface between the electrode active material and the separator, prevents side reactions with the electrolyte, and suppresses gas generation. It helps to move smoothly.

The additive includes a cathodic protection additive that forms an SEI film on the surface of the anode to suppress the side reaction between the electrolyte by-product and the negative electrode, a positive electrode protection additive that forms an SEI film on the surface of the positive electrode to suppress the side reaction between the electrolyte by-product and the positive electrode, and lithium in the positive electrode and the negative electrode. and an amphoteric lithium salt additive that aids in replenishment and absorption, and promotes lithium insertion/removal of positive and negative active materials to improve charge/discharge characteristics of batteries.

The additive according to an embodiment includes (A) a compound represented by the following Chemical Formula 1, and (B) at least one of 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 group a heteroaryl group,

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

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

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

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 group a heteroaryl group,

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

When (A) the compound represented by Formula 1 is included in the additive, as the compound represented by Formula 1 (A) includes a sultam group, the effect of inhibiting resistance increase through formation of a strong positive/negative electrode film is And, as it contains a silyl group, there is a bulk electrolyte stabilization effect through HF/H ₂ O capturing, and at the same time there is a resistance reduction function. In addition, by including the sulfamyl group and the silyl group at the same time, a stable film formation 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 Formula 1 is, for example, -O-, -S--, -S(=O)-, -S(=O) in the main chain. ₂ It may be a C2 to C5 alkylene group including at least one functional group selected from 2 —, —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 group 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 - 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 Formulas 3-1, 3-2, or a combination thereof.

[Formula 3-1] [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, or a substituted or unsubstituted C2 to C10 an 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 wt% to 10 wt% based on the total amount of the electrolyte for a lithium secondary battery, for example, 0.1 wt% to 5 wt%, 0.1 wt% to 2.5 wt%, 0.2 wt% 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 included in an amount of 10% by weight or less with respect to the total amount of the electrolyte for a lithium secondary battery, an increase in gas generation due to excessive film formation and generation of decomposition gas can be suppressed, and when included in an amount of 0.1% by weight or more, the initial The resistance and resistance increase rate may 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, an effect of improving the initial resistance and the long-term resistance increase rate can be obtained through the formation of an appropriate anode film.

The cyclic carbonate-based compound (B) may be included in an amount of 0.1 to 3 wt%, for example, 0.5 to 2.0 wt% or 0.5 to 1.5 wt%, based on the total amount of the electrolyte for a lithium secondary battery. When the cyclic carbonate-based compound (B) is included in an amount of 0.1 wt % or more based on the total amount of the electrolyte for a lithium secondary battery, the 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 wt % or less with respect to 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, it is possible to prevent the problem that the cyclic carbonate-based compound remaining undecomposed is oxidatively decomposed when left at a high temperature to cause positive electrode self-discharge or to lower 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 wt%, for example, 0.5 to 2.0 wt% or 0.5 to 1.5 wt%, based on the total amount of the electrolyte for a lithium secondary battery. When the amphoteric lithium salt compound (C) 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, the 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 first reduced and decomposed among the compounds included in the electrolyte to form a film, excessive formation of the film is prevented when included in an amount of 3% by weight or less based on the total amount of the electrolyte for a lithium secondary battery It is possible to prevent a sudden increase in initial resistance.

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 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 cathode active material may be 90 wt% to 98 wt% based on the total weight of the cathode active material layer.

In one embodiment of the present invention, the positive electrode 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 wt% to 5 wt%, respectively, based on the total weight of the positive electrode active material layer.

The binder serves to adhere the positive active material particles well to each other and also to the positive active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers including 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 configured, any electronic conductive material can be used as long as it does not cause chemical change, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen carbon-based materials such as black and carbon fiber; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including 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 an anode 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, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating lithium ions is a carbon material, and any carbon-based negative active material generally used in lithium ion secondary batteries may be used, and a representative example thereof is crystalline carbon. , amorphous carbon or these 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.

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

Examples of the material capable of doping and dedoping lithium include Si, Si-C composite, SiO _x (0 < x ≤ 2), Si-Q alloy (wherein Q is alkali metal, alkaline earth metal, group 13 element, group 14 element, 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, and not Si), Sn, SnO ₂ , a Sn-R alloy (wherein R is an alkali metal, an alkaline earth metal, 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 a combination thereof (not Sn); You may mix and use SiO2 _. 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, One selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide or lithium titanium oxide.

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

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

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

The water-soluble binder may include a rubber-based binder or a polymer resin binder. The rubber binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder is polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepicrohydrin, 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 of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. 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 active material.

The conductive material is used to impart conductivity to the electrode, and in the battery configured, any electronic conductive material can be used as long as it does not cause chemical change, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen carbon-based materials such as black and carbon fiber; metal-based substances such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

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 conductive metal, and combinations thereof.

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

1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Although the lithium secondary battery according to an embodiment is described as having a cylindrical shape as an example, 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 to face the negative electrode 112 , and a negative electrode 112 and a positive electrode 114 , A battery cell including a separator 113 and a negative electrode 112, a positive electrode 114 and an electrolyte (not shown) impregnated with the separator 113, a battery container 120 containing the battery cell, and the battery container and a sealing member 140 sealing the 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.

Production of lithium secondary batteries

Preparation Example 1: Synthesis of the 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 ammonium chloride, 0.2 g ) and mixed with After stirring at 100 °C for 2 hours, the mixture was further stirred at 130 °C for 1 hour. Purification by vacuum distillation gave a colorless and transparent liquid (7.5 g, yield: 75%).

[Formula 1a]

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

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 and 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 (N-hydroxy-N-methylmethanesulfonamide)

After dissolving N-methylhydroxylamine hydrochloride (N-methylhydroxylamine hydrochloride, 10.0 g, 120 mmol) in water (12 mL), the temperature was reduced to 0°C. To the prepared reaction mixture, 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 while maintaining the temperature, and the mixture was stirred for 10 minutes. At 0° C., methanesulfonyl chloride (6.85 g, 59.8 mmol) was slowly added and stirred for 30 minutes. After that, the reaction was raised to room temperature and stirred for 4 hours more. Water was added until all of the white precipitated solid was dissolved, and then extracted using diethyl ether. The extracted organic layer was dried over MgSO ₄ , filtered, and the resulting 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 under a nitrogen atmosphere was dissolved in tetrahydrofuran (THF, 50 mL). 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]

Preparation 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 cathode 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 slurry the cathode active material was prepared. The cathode active material slurry was coated on Al foil having a thickness of 15 μm, dried at 100° C., and then pressed to prepare a cathode.

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

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

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

Preparation Example 1
(weight%) Preparation 2
(weight%) Preparation 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 formed by the following process. In the first cycle, a constant current was charged to 3.6V at 0.2C and then discharged to 2.6V, and in the second cycle, CC was charged to 4.2V at 0.2C and then discharged to 2.5V.

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

DC resistance is calculated from the difference in current and voltage when different currents are applied, and in the initial full charge state, constant current discharge at 10 A for 10 seconds, constant current discharge at 1 A for 10 seconds, and constant current discharge at 10 A for 4 seconds. , from the data of 18 s and 23 s, DC resistance was calculated using the equation ΔR =ΔV/ΔI.

The resistance increase rate (ΔDC-IR) was calculated as the ratio of DC-IR after 30 days storage to 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 the additive according to one embodiment, compared to Comparative Examples 1 to 6, the initial resistance, the resistance after 30 days of standing, and the resistance increase rate when left at a high temperature (60 ° C) are improved. could check

*Evaluation 2: Capacity retention and recovery rate at 60°C

For the lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6, initial formation and SOC 100% charging were performed in the same manner as in Evaluation 1.

Subsequently, the lithium secondary battery charged with initial chemical conversion and SOC 100% was stored at 60° C. for 10 days, 20 days, and 30 days, and then discharged at 0.2C, 2.5V cut-off, the discharge capacity ratio after storage to the one-time discharge capacity (0 days) is shown as the capacity retention rate in Table 3 below.

On the other hand, after preserving the lithium secondary battery 100% charged with initial chemical conversion and SOC 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 after 0.2C, 2.5V charging The discharge capacity was measured by performing cut-off discharge, and the ratio of the discharge capacity to the initial capacity before storage is shown as the 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

For the lithium secondary batteries prepared in Example 1, Examples 3 to 5, and Comparative Examples 1, 2, 4 and 5, initial formation and SOC 100% charging were performed in the same manner as in Evaluation 1.

A lithium secondary battery that was initially chemically charged and 100% SOC was charged at 25°C with 0.2C, 4.2V cutoff constant current, 4.2V, 0.05C cutoff constant voltage charge, and then 0.2C, 2.5V cutoff constant current discharge was performed as one cycle. , a total of 200 cycles were performed. The ratio of the 200-cycle discharge capacity to the 1-cycle discharge capacity is shown in Table 4 below as cycle life characteristics (0.2C).

A lithium secondary battery that was initially chemically charged and 100% SOC was charged with 1C, 4.2V cutoff constant current at 25°C, charged with 4.2V, 0.05C cutoff constant voltage, and then discharged with 1C, 2.5V cutoff constant current as one cycle, total 200 cycles were performed. The ratio of the 200-cycle discharge capacity to the 1-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 1C current for 10 seconds and measuring the voltage drop, and obtaining the 200-cycle DC resistance increase rate (ΔDC-IR) for the initial DC resistance, Table 4 shows 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 had initial discharge capacity, cycle life characteristics, direct current resistance (DC-IR) and charge compared to Comparative Examples 1, 2, 4 and 5. 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 initialized in the same manner as in Evaluation 1. Then, after degassing the initially chemically formed lithium secondary battery, it was placed in a pouch and stored in an oven at 60° C. for 30 days. Thereafter, the change in the volume of the pouch was measured, and this was converted into a change in mass using the Archimedes method, and is shown as the amount of gas generated in Table 5 below.

Gas generation (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 gas generation amount is reduced due to the increase in thermal stability by the strong SEI film. On the other hand, it was confirmed that Comparative Examples 1, 2, 4 and 5 had a higher amount of gas generation than in Examples.

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and it is possible to carry out various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings. It goes without saying that it falls within the scope of the invention.

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

Claims (12)

non-aqueous organic solvents; lithium salt; and additives,
The additive is (A) a compound represented by the following Chemical Formula 3-1, Chemical Formula 3-2, or a combination thereof, and
(B) comprising at least one of a cyclic carbonate-based compound and (C) an amphoteric lithium salt compound,
Electrolyte for lithium secondary batteries:
[Formula 3-1] [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 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,
Wherein 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,
Wherein R ¹ To R ⁵ are each independently a substituted or unsubstituted C1 to C5 alkyl group,
Electrolyte for lithium secondary batteries. delete delete In claim 1,
The compound (A) is included in an amount of 0.1 wt% to 10 wt% with respect to the total amount of the electrolyte for a 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 included in an amount of 0.1 wt% to 3 wt% with respect to the total amount of the electrolyte for a 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 included in an amount of 0.1% to 3% by weight based on the total amount of the electrolyte for a lithium secondary battery,
Electrolyte for lithium secondary batteries. anode; cathode; And any one of claims 1 to 3 and 6 to 10 comprising the electrolyte solution,
lithium secondary battery. In claim 11,
The positive electrode includes a current collector and a positive electrode active material layer comprising a positive electrode active material formed on the current collector,
The positive active material includes 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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