KR20170028676A - Electrolyte for lithium battery, and lithium battery including the electrolyte - Google Patents

Abstract

Disclosed are an electrolyte for a lithium battery, and a lithium battery comprising the same. The electrolyte for a lithium battery comprises: a non-aqueous organic solvent; and a silane-based compound containing at least one electron attraction group selected from a cyano group (-CN), an isothiocyanate group (-NCS) and a thiocyanate group (-SCN). The cycle characteristics of a lithium battery with a high capacity can be improved by using the electrolyte for a lithium battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a lithium battery, and a lithium battery including the electrolyte,

An electrolyte for a lithium battery, and a lithium battery including the same.

As the field of small high-tech devices such as digital cameras, mobile devices, notebook computers, and computers is developing, the demand for lithium secondary batteries, which are energy sources, is rapidly increasing. In addition, the development of high-capacity, safe lithium secondary batteries is underway through the spread of xEVs, which are collectively referred to as hybrids, plug-ins, and electric vehicles (HEV, PHEV, EV).

A new anode active material having a theoretical capacity higher than that of graphite (theoretical capacity: 372 mAh / g) which is used as an anode active material is being applied, because a lithium secondary battery is required to have a high capacity and a high energy density. Among them, silicon which is abundant in resources and capable of realizing a high capacity is widely used. However, the silicon negative electrode has a problem that lithium bulges as the lithium is inserted / removed. As the cycle progresses, cracks are generated due to the volume expansion, and generation of a thick film due to the formation of a new SEI and depletion of the electrolyte causes the life of the lithium secondary battery to deteriorate.

Therefore, in order to solve such a problem, optimization of various battery components as well as a high-capacity active material needs to be examined.

An aspect of the present invention is to provide an electrolyte for a lithium battery capable of improving cycle characteristics of a high capacity lithium battery.

Another aspect of the present invention is to provide a lithium battery including the electrolyte.

In one aspect of the invention,

Non-aqueous organic solvent; And

A silane-based compound containing at least one electron withdrawing group selected from a cyano group (-CN), an isothiocyanate group (-NCS) and a thiocyanate group (-SCN);

An electrolyte for a lithium battery is provided.

According to one embodiment, the silane-based compound may include a compound represented by the following formula (1) or (2).

[Chemical Formula 1]

(2)

In the above formulas (1) and (2)

R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group ego,

Y ₁ and Y ₂ are each independently a cyano group (-CN), an isothiocyanate group (-NCS), or a thiocyanate group (-SCN).

According to one embodiment, the content of the silane-based compound may be more than 0% by weight and less than 1% by weight based on the total weight of the electrolyte.

In another aspect of the present invention, there is provided a lithium battery employing the electrolyte.

By using the electrolyte for a lithium battery according to one aspect, the cycle characteristics of a lithium battery employing a high capacity active material can be improved.

1 is a schematic view showing a schematic structure of a lithium battery according to an embodiment.
FIG. 2 is a result of a circulating current analysis for a triode electrode manufactured according to Comparative Example 1. FIG.
FIG. 3 is a result of analysis of the circulating current method for the triode electrode fabricated according to Example 1. FIG.
4 shows the results of measurement of the capacity retention rate of each of the lithium secondary batteries of Examples 2-3 and Comparative Example 2 by cycle.

Hereinafter, an electrolyte for a lithium battery and a lithium battery employing the electrolyte according to exemplary embodiments will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The electrolyte for a lithium battery according to an embodiment includes:

Non-aqueous organic solvent; And

And a silane-based compound containing at least one electron-withdrawing group selected from a cyano group (-CN), an isothiocyanate group (-NCS) and a thiocyanate group (-SCN).

When a silane-based compound containing at least one electron withdrawing group selected from a cyano group (-CN), an isothiocyanate group (-NCS) and a thiocyanate group (-SCN) is used as an additive for an electrolyte for a lithium battery, It is possible to provide a stable protective film on the surface of the negative electrode and to realize a stable performance which prevents oxidative decomposition of the solvent and elution of metal ions even at a high voltage of 4.4 V or more, The reason why the silane-based compound exhibits the lifetime property improving effect is not clarified theoretically, but it can be estimated as follows.

The silane-based compound substituted with one or more electron-withdrawing groups (EWG) is decomposed easily at a lower starting voltage because the self-reducing voltage is reduced as compared with the silane-based compound having an unsubstituted or electron-donating group (EDG) And exhibits high reactivity with the cathode. Therefore, by introducing a silane-based compound substituted with the electron withdrawing group (EWG), it is possible to easily form a firm and dense SEI film on the surface of the negative electrode by decomposition at the time of initial charging, thereby reducing the irreversible capacity of the lithium battery, The lifetime characteristics of the battery can be improved.

It is presumed that this reduction characteristic is mainly affected by the electronic effect. That is, when the substituent introduced has an electron donating ability, an electron effect of increasing the electron density of the additive occurs. For example, when an electron-donating group is introduced, a reduction reaction becomes difficult due to a high reduction voltage. On the other hand, when an electron withdrawing group is introduced as in the above embodiment, the reduction voltage of the silane- It can be easily done.

Also, cyano (-C≡N), isothiocyanate (-N═C═S), thiocyanate (-SC≡N), and the like introduced into the silane compound These are electron withdrawing groups with high dipole moments. These functional groups are strongly bonded to the transition metal or transition metal oxide or carbon material exposed on the surface of the electrode active material, and particularly, the surface of the electrode active material is strongly bonded to the functional group at a temperature of 45 ° C or higher, a protection layer can be formed. Therefore, when the lithium battery is initially charged, the silane-based compound introduced with the electron withdrawing group can form a more durable and dense inactive film in the state of being adsorbed on the surface of the electrode, and the formed inactive film strongly bonds with the surface of the electrode active material, The stability of the inactive film due to the progress of the discharge can be continuously maintained and the battery performance can be maintained.

The silane compound may be a silane compound including at least one electron withdrawing group (EWG) such as a cyano group (-CN), an isothiocyanate group (-NCS), and a thiocyanate group (-SCN) Available.

According to one embodiment, the silane-based compound may include a compound represented by the following formula (1) or (2).

[Chemical Formula 1]

(2)

In the above formulas (1) and (2)

R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group ego,

Y ₁ and Y ₂ are each independently a cyano group (-CN), an isothiocyanate group (-NCS), or a thiocyanate group (-SCN).

The definitions of substituents used in the formulas described herein are as follows.

The term "alkyl" refers to fully saturated branched or unbranched (or linear or linear) hydrocarbons.

Non-limiting examples of the "alkyl" include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n- pentyl, isopentyl, neopentyl, isoamyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n-heptyl and the like.

The "alkyl" at least one hydrogen atom of which is a halogen atom, an alkyl group having a halogen-substituted C1-C20: (for example, CCF _3, CHCF _2, CH ₂ F, CCl _3, etc.), an alkoxy of C1-C20, C2-C20 A carboxyl group or a salt thereof, a sulfonyl group, a sulfamoyl group, a sulfonic acid group or a salt thereof, a phosphoric acid or a salt thereof, or a C1-C18 alkyl group which may be substituted with at least one substituent selected from the group consisting of a halogen atom, a hydroxyl group, a nitro group, a cyano group, C20 alkyl group, C2-C20 alkenyl group, C2-C20 alkynyl group, C1-C20 heteroalkyl group, C6-C20 aryl group, C6-C20 arylalkyl group, C6-C20 heteroaryl group, C7- An arylalkyl group, a C6-C20 heteroaryloxy group, a C6-C20 heteroaryloxyalkyl group, or a C6-C20 heteroarylalkyl group.

The term "halogen atom" includes fluorine, bromine, chlorine, iodine and the like.

The term "C1-C20 alkyl group substituted by a halogen atom" refers to a C1-C20 alkyl group substituted by at least one halo group, and includes, but is not limited to, a monohaloalkyl, dihaloalkyl or perhaloalkyl Or a polyhaloalkyl.

Monohaloalkyl refers to the case of having one iodine, bromine, chlorine or fluorine in the alkyl group, and dihaloalkyl and polyhaloalkyl represent alkyl groups having two or more same or different halo atoms.

The term "alkoxy " used in the formula represents alkyl-O-, and the alkyl is as described above. Non-limiting examples of the alkoxy include methoxy, ethoxy, propoxy, 2-propoxy, butoxy, tert-butoxy, pentyloxy, hexyloxy, cyclopropoxy and cyclohexyloxy. At least one hydrogen atom in the alkoxy group may be substituted with the same substituent as the alkyl group described above.

The term "alkoxyalkyl" used in the formula refers to the case where the alkyl group is substituted by the alkoxy described above. At least one hydrogen atom of the alkoxyalkyl may be substituted with the same substituent as the alkyl group described above. As such, the term " alkoxyalkyl " includes substituted alkoxyalkyl moieties.

The term "alkenyl" group used in the formulas refers to branched or unbranched hydrocarbons having at least one carbon-carbon double bond. Non-limiting examples of the alkenyl group include vinyl, allyl, butenyl, isopropenyl, isobutenyl and the like, and at least one hydrogen atom of the alkenyl may be substituted with the same substituent as the alkyl group described above .

The term "alkynyl" group used in the formulas refers to branched or unbranched hydrocarbons having at least one carbon-carbon triple bond. Non-limiting examples of the "alkynyl" include ethynyl, butynyl, isobutynyl, isopropynyl, and the like.

At least one hydrogen atom of the above-mentioned "alkynyl" may be substituted with the same substituent as in the above-mentioned alkyl group.

The term "aryl" groups used in the formulas, alone or in combination, means aromatic hydrocarbons containing one or more rings.

The term "aryl" also includes groups wherein an aromatic ring is fused to one or more cycloalkyl rings.

Non-limiting examples of the "aryl" include phenyl, naphthyl, tetrahydronaphthyl, and the like.

Also, at least one hydrogen atom of the above-mentioned "aryl" group may be substituted with the same substituent as in the case of the above-mentioned alkyl group.

The term "arylalkyl" means alkyl substituted with aryl. As examples of aryl alkyl benzyl or phenyl, -CH ₂ CH ₂ - it may be mentioned.

The term "aryloxy" used in the formula means -O-aryl, and examples of the aryloxy group include phenoxy and the like. At least one hydrogen atom of the above-mentioned "aryloxy" group may be substituted with the same substituent as in the case of the above-mentioned alkyl group.

The term "heteroaryl" group used in the formulas means monocyclic or bicyclic organic compounds containing at least one heteroatom selected from N, O, P or S and the remaining ring atoms carbon . The heteroaryl group may contain, for example, from 1 to 5 hetero atoms, and may include 5-10 ring members. The S or N may be oxidized to have various oxidation states.

At least one hydrogen atom of the above-mentioned " heteroaryl " can be substituted with the same substituent as in the case of the above-mentioned alkyl group.

The term "heteroarylalkyl" means alkyl substituted by heteroaryl.

The term "heteroaryloxy" means an-O-heteroaryl moiety. At least one hydrogen atom of the heteroaryloxy may be substituted with the same substituent as the alkyl group described above.

The term "heteroaryloxyalkyl" means alkyl substituted by heteroaryloxy. At least one hydrogen atom of the heteroaryloxyalkyl may be substituted with the same substituent as the alkyl group described above.

The term "cycloalkyl" refers to a saturated or partially unsaturated, non-aromatic monocyclic, bicyclic or tricyclic hydrocarbon group.

Examples of the monocyclic hydrocarbons include cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, and the like. Examples of bicyclic hydrocarbons include bornyl, decahydronaphthyl, bicyclo [2.1.1] hexyl, bicyclo [2.2. 1] heptyl, bicyclo [2.2.1] heptenyl, or bicyclo [2.2.2] octyl, and examples of tricyclic hydrocarbons include adamantly.

At least one hydrogen atom of the above-mentioned "cycloalkyl" may be substituted with the same substituent as the alkyl group described above.

The term "heterocycloalkyl" refers to a saturated or partially unsaturated non-aromatic monocyclic, bicyclic or tricyclic ring system containing one or more heteroatoms selected from N, O, P or S and the remaining ring atoms are carbon Tricyclic hydrocarbon group. At least one hydrogen atom of the above-mentioned heterocycloalkyl may be substituted with the same substituent as the above-mentioned alkyl group.

The term "sulfonyl" is R "-SO ₂ - and the meaning, R" is hydrogen, alkyl, aryl, heteroaryl, aryl-alkyl, alkoxy, aryloxy, cycloalkyl or heterocycloalkyl group-alkyl, heteroaryl.

The term "sulfamoyl" group _{H 2 NS (O 2) -} , alkyl, -NHS (O ₂₎ -, (alkyl) ₂ NS (O ₂₎ - aryl-NHS (O ₂₎ -, alkyl (aryl) -NS (O ₂₎ -, (aryl) ₂ NS (O) _2, heteroaryl, -NHS (O ₂₎ -, _{(aryl-alkyl) - NHS (O 2) -} , or (heteroaryl-alkyl) -NHS (O ₂ ) -.

At least one hydrogen atom of the sulfamoyl group is substitutable as in the case of the alkyl group described above.

The term "amino" group refers to the case where the nitrogen atom is covalently bonded to at least one carbon or heteroatom. The amino group includes, for example, -NH2 and substituted moieties. Alkylamino "wherein the nitrogen atom is bonded to at least one additional alkyl group," arylamino "and" diarylamino "in which at least one nitrogen or two or more are bonded to an independently selected aryl group.

According to one embodiment, the silane-based compound may include an isothiocyanate group (-NCS) -containing silane compound represented by the following formula (1a).

[Formula 1a]

In this formula,

R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be.

Specific examples of the isothiocyanate group (-NCS) -containing silane compound represented by the above formula (1a) include the following compounds.

According to one embodiment, the silane-based compound may include a silane-based compound having a cyano group (-CN) represented by the following formula (1b).

[Chemical Formula 1b]

In this formula,

R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be.

Specific examples of the cyano group (-CN) -containing silane compound represented by the above formula (1b) include the following compounds.

According to one embodiment, the silane-based compound may include a thiocyanate group (-SCN) -containing silane compound represented by the following formula (1c).

[Chemical Formula 1c]

In this formula,

R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be.

Specific examples of the thiocyanate group (-SCN) -containing silane compound represented by the above formula (1c) include the following compounds.

According to one embodiment, the content of the silane-based compound may be more than 0% by weight and less than 1% by weight based on the total weight of the electrolyte. For example, the content of the silane-based compound may be 0.1 to 0.9% by weight, 0.2 to 0.7% by weight, or 0.3 to 0.5% by weight based on the total weight of the electrolyte. Within the above range, the cycle characteristics of the lithium battery can be improved.

In addition, the electrolyte may further include other additives in addition to the fluorinated alkylene carbonate compound and the silylamide compound.

Examples of additive additives include LiBF ₄ , tris (trimethylsilyl) borate (TMSB), tris (trimethylsilyl) phosphate (TMSPa), lithium bis (oxalate) borate (LiBOB), lithium difluoroarsalate borate Such as acrylic, amino, epoxy, methoxy, ethoxy, vinyl and the like, having functional groups capable of forming siloxane bonds, such as vinylidene fluoride (LiFOB), vinyl carbonate (VC), propane sultone (PS), succinonitrile Compounds, and silazane compounds such as hexamethyldisilazane. These additives may be added singly or in combination of two or more.

The added additive may be contained in an amount of 0.01 to 10% by weight based on the total weight of the electrolyte for a more stable SEI film formation. For example, the additive may be included in an amount of 0.05 to 10 wt%, 0.1 to 5 wt%, or 0.5 to 4 wt% based on the total weight of the electrolyte. The content of the additive is not particularly limited as long as the effect of improving the capacity retention rate of the lithium battery according to the use of the electrolyte is not significantly reduced.

The nonaqueous electrolyte used in the electrolyte serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous electrolyte, a carbonate compound, an ester compound, an ether compound, a ketone compound, an alcohol compound, an aprotic solvent, or a combination thereof may be used.

As the carbonate compound, a chain type carbonate compound, a cyclic carbonate compound, or a combination thereof may be used.

Examples of the chain carbonate compound include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC) Ethylpropylcarbonate (EPC), ethylmethyl carbonate (EMC), or a combination thereof.

Examples of the cyclic carbonate compound include ethylene carbonate (EC), propylenecarbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC) .

The carbonate-based compound may be used by mixing the chain-like and cyclic carbonate compounds. The mixing ratio of the chain carbonate compound and the cyclic carbonate compound may be 85:15 to 60:40 by volume.

Examples of the ester compound include methyl acetate, acetate, n-propyl acetate, dimethylacetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, mevalonolactone mevalonolactone, caprolactone, and the like may be used. Examples of the ether compound include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. As the ketone compound, cyclohexanone and the like may be used . Examples of the alcohol-based compound include ethyl alcohol, isopropyl alcohol, and the like.

Examples of other aprotic solvents include dimethylsulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, , Dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid triester.

The nonaqueous electrolytic solution may be used alone or in combination of two or more, and when two or more of them are used in combination, the mixing ratio may be suitably adjusted according to the performance of the desired battery.

The electrolyte for a lithium battery may further include a lithium salt.

The lithium salt acts as a source of lithium ions in the battery, thereby enabling operation of a basic lithium battery. Examples of the lithium salt include LiCl, LiBr, LiI, LiClO ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , and LiBF ₆ , which are soluble in the non-aqueous electrolyte. _{CF 3 SO 3 Li, CH 3} SO 3 Li, C 4 F 3 SO 3 Li, (CF 3 SO 2) 2 NLi, LiN (C x F 2x + 1 SO 2) (C y F 2 + y SO 2) (Where x and y are natural numbers), CF ₃ CO ₂ Li, LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlF ₄ , Lithium chloroborate, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, and the like can be used.

The lithium salt may be used in the range of about 0.1 M to about 2.0 M, for example, in order to ensure practical performance of the lithium battery. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that it can exhibit excellent electrolyte performance and can effectively transfer lithium ions.

The electrolyte for a lithium battery may further include other additives to improve the electrochemical characteristics such as a cyclic characteristic by helping to form a stable SEI or a film on the electrode surface.

Examples of the additive include tris (trimethylsilyl) phosphate (TMSPa), lithium difluorooxalate borate (LiFOB), vinylene carbonate (VC), propane sultone (PS), succinonitrile , LiBF ₄ , a silane compound having a functional group capable of forming a siloxane bond such as acrylic, amino, epoxy, methoxy, ethoxy, vinyl and the like, and a silazane compound such as hexamethyldisilazane. These additives may be added singly or in combination of two or more.

The additive may be contained in an amount of 0.01 to 10% by weight based on the total weight of the non-aqueous organic solvent. For example, the additive may be contained in an amount of 0.05 to 10% by weight, 0.1 to 5% by weight, or 0.5 to 4% by weight based on the total weight of the non-aqueous organic solvent. However, the content of the additive is not particularly limited as long as the effect of improving the capacity retention rate of the lithium battery according to the use of the electrolyte is not significantly reduced.

The electrolyte according to one embodiment of the present invention can be applied to a lithium battery operating at a high voltage of 4.3 V or more to improve cell performance and stability. For example, the electrolyte can be used in high voltage batteries operating in the 4.3V to 4.6V voltage range.

A lithium battery according to another embodiment includes a positive electrode, a negative electrode, and an electrolyte for the lithium battery disposed between the positive electrode and the negative electrode. The lithium battery can be manufactured by a manufacturing method well known in the art.

FIG. 1 schematically shows a typical structure of a lithium battery according to an embodiment.

1, the lithium battery 30 includes a positive electrode 23, a negative electrode 22, and a separator 24 disposed between the positive electrode 23 and the negative electrode 22. The positive electrode 23, the negative electrode 22 and the separator 24 described above are wound or folded and accommodated in the battery container 25. Then, an electrolyte is injected into the battery container 25 and sealed with a sealing member 26, thereby completing the lithium battery 30. The battery container 25 may have a cylindrical shape, a rectangular shape, a thin film shape, or the like. The lithium battery may be a lithium ion battery.

The anode 23 includes a cathode current collector and a cathode active material layer formed on the cathode current collector.

The positive electrode collector is generally made to a thickness of 3 to 500 mu m. The positive electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the positive electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. Further, fine unevenness may be formed on the surface to enhance the bonding force of the cathode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material layer includes a cathode active material, a binder, and optionally a conductive agent.

As the cathode active material, lithium-containing metal oxide may be used as long as it is commonly used in the art. For example, at least one of complex oxides of metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used. Specific examples thereof include Li _a A _1-b B _b D ₂ 0.90? A? 1, and 0? B? 0.5); Li _a E _1-b B _b O _{2 -c} D _{c where} 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05; LiE (in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05) 2-b B b O 4-c D c; Li _a Ni _{1 -bc} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _{2 -?} F _? Wherein? 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1- b c} Co _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c D _{? Where} 0.90? A? 1, 0? B? 0.5, 0? C? 0.05, 0 <?? 2; Li _a Ni _1-bc Mn _b B _c O _2-α F _α wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2; Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1, and 0.001? B? 0.1); Li _a CoG _b O ₂ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ (in the above formula, 0.90? A? 1, 0.001? B? 0.1); QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0? F? 2); In the formula of LiFePO ₄ may be used a compound represented by any one:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x = 1, 2), LiNi _1-x Mn _x O _2x (0 <x <1), LiNi _1-xy Co _x Mn _y O ₂ 0.5, 0? Y? 0.5), FePO _4, and the like.

Of course, a compound having a coating layer on the surface of the compound may be used, or a compound having a coating layer may be mixed with the compound. The coating layer may comprise an oxide, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a coating element compound of the hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. The coating layer may contain Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer forming step may be any coating method as long as it can coat the above compound by a method which does not adversely affect the physical properties of the cathode active material (for example, spray coating, dipping, etc.) by using these elements, It will be understood by those skilled in the art that a detailed description will be omitted.

The binder serves to adhere the positive electrode active material particles to each other well and adhere the positive electrode active material to the positive electrode current collector. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, , Polymers containing carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene Rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, but not limited thereto.

The conductive agent is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive agent include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as Ketjen black, carbon fiber, copper, nickel, aluminum and silver, metal fibers, and the like, and conductive materials such as polyphenylene derivatives may be used singly or in combination.

The cathode 22 includes a negative electrode collector and a negative electrode active material layer formed on the negative collector.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness may be formed on the surface to enhance the bonding force of the negative electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode active material layer includes a negative electrode active material, a binder, and optionally a conductive agent.

The negative electrode active material may be used without limitation as long as it is commonly used in the art. For example, a lithium metal, a metal capable of alloying with lithium, a transition metal oxide, a material capable of doping and dedoping lithium, a material capable of reversibly intercalating and deintercalating lithium ions, and the like can be used. Or in a combined form.

As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used.

Non-limiting examples of the transition metal oxide may be tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, and the like.

The materials capable of doping and dedoping lithium include, for example, Si, Sn, Al, Ge, Pb, Bi, Sb SiO _x (0 <x <2) (Where 0 < x < x &_lt; 1), SnO _x (0 &lt; x &lt; 2), a Sn-Y alloy (Y is an alkali metal, an alkaline earth metal, a Group 11 element, a Group 12 element, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, Element, not Sn), and the like. The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Se, Te, Po, or a combination thereof.

As the material capable of reversibly intercalating and deintercalating lithium ions, any carbonaceous anode active material commonly used in lithium batteries can be used as the carbonaceous material. For example, crystalline carbon, amorphous carbon, or mixtures thereof. Non-limiting examples of the crystalline carbon include natural graphite, artificial graphite, expanded graphite, graphene, fullerene soot, carbon nanotube, carbon fiber and the like. Non-limiting examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, baked coke and the like. The carbonaceous anode active material may be used in the form of spheres, plates, fibers, tubes, or powders.

According to one embodiment, the negative electrode active material includes a silicon-based negative active material, and may be selected from the group consisting of Si, SiO _x (0 <x <2), Si-Z alloy (where Z is an alkali metal, Element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element or a combination element thereof, but not Si), and combinations thereof. The element Z is at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Wherein the first electrode layer is selected from the group consisting of Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Ge, P, As, Sb, Bi, S, Se, Te, . In addition, such a silicon-based negative electrode active material such as Si, SiO _x , Si-Z alloy and the like may substantially comprise crystalline (including single crystal, polycrystalline), amorphous, or mixed form thereof.

The binder serves to adhere the anode active material particles to each other and to adhere the anode active material to the current collector. Examples of the binder include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinyl chloride, Such as polyvinyl chloride, polyvinyl fluoride, polymers comprising ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but the present invention is not limited thereto.

The conductive agent is used for imparting conductivity to the electrode. Any conductive material can be used without causing any chemical change in the battery. Examples of the conductive agent include natural graphite, artificial graphite, carbon black, acetylene black, Carbon-based materials such as Ketjen black and carbon fiber; Metal powders such as copper, nickel, aluminum, and silver, or metal-based materials such as metal fibers; Conductive polymers such as polyphenylene derivatives; Or a mixture thereof may be used.

The positive electrode 23 and the negative electrode 22 are each prepared by mixing an active material, a conductive agent and a binder in a solvent to prepare an active material composition and applying the composition to a current collector.

The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein. As the solvent, N-methylpyrrolidone (NMP), acetone, water and the like can be used, but it is not limited thereto.

The positive electrode 23 and the negative electrode 22 may be separated by a separator 24 and the separator 24 may be any of those conventionally used in a lithium battery. Particularly, it is preferable to have a low resistance against the ion movement of the electrolyte and an excellent ability to impregnate the electrolyte. The separator 24 may be a single film or a multilayer film and may be made of a material selected from, for example, glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE) It may be in woven form. The separator has a pore diameter of 0.01 to 10 mu m and a thickness of 3 to 100 mu m.

The electrolyte is an electrolyte for a lithium battery comprising lithium nitrate (LiNO ₃ ) in an amount of 0.1 to 1% by weight based on the total weight of the non-aqueous organic solvent. The electrolyte is injected between the anode 23 and the cathode 22 separated by the separator 24.

The lithium battery is suitable for applications requiring high-voltage, high-output, and high-temperature driving such as an electric vehicle in addition to the use of conventional mobile phones and portable computers. In addition, the lithium battery can be used in a hybrid vehicle or the like in combination with a conventional internal combustion engine, a fuel cell, and a supercapacitor, and can be used for electric bicycles, power tools and all other uses requiring high output, high voltage, Can be used.

EXAMPLES The following examples and comparative examples illustrate exemplary embodiments in more detail. It should be noted, however, that the embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example  One

LiPF ₆ was added to a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) at a ratio of 30:50:20 by volume. 1% by weight of trimethylsilyl isothiocyanate as an additive was added to the mixed solvent to prepare an electrolyte.

A mixture of a Si-Fe-based Si alloy and graphite as a negative electrode active material, a poly amide imide as a binder and a ketjen black as a conductive agent in a weight ratio of 80: 10: 8: 2, respectively, Methylpyrrolidone was added so as to have a solid content of 60 wt% to prepare an anode slurry.

A 10 mu m thick copper foil current collector was coated with the negative electrode slurry to a thickness of about 40 mu m. This was dried at room temperature, dried again at 120 ° C, and rolled to produce a negative electrode.

A three electrode beaker cell was prepared by injecting the electrolyte using a Li metal as a counter electrode and a reference electrode.

Comparative Example  One

A three electrode cell was fabricated in the same manner as in Example 1 except that trimethylsilyl isothiocyanate, which is an additive, was not added to the electrolyte.

Evaluation example  One: Cyclic current method ( cyclovoltametry ) analysis

A three-electrode cell manufactured according to Comparative Example 1 and Example 1 was subjected to a circulating current method using a M273A constant current / constant current (EG & G) at a scanning speed of about 2 mV / s.

The cyclic current method used Biologicals, an impedance measuring instrument, and the analysis conditions were 5 cycles at 0V ~ 3V and 1mV / s scan rate. The measurement principle is to observe the voltage change while flowing a constant current.

The results of the analysis of the cyclic current method for the triode electrode manufactured according to Comparative Example 1 and Example 1 are shown in FIG. 2 and FIG. 3, respectively.

As shown in FIG. 2, the three-electrode cell of Comparative Example 1 shows a phenomenon in which the discharge capacity according to the cycle is continuously decreased and the lifetime is lowered, and the peak area responding at the same time becomes smaller, .

On the other hand, in Example 1, as shown in Fig. 3, the cycle became sharp compared to the CV cycle of Comparative Example 1. [ This means that the resistance of the triode electrode of Example 1 is lower than that of the triode electrode of Comparative Example 1. Also, the discharge capacity according to the cycle was maintained. From this, it can be indirectly confirmed that the output and lifetime characteristics of the triode electrode of Example 1 can be improved as compared with the case of Comparative Example 1 in which trimethylsilyl isothiocyanate is not added.

Example  2

LiPF ₆ was added to a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) at a ratio of 20:10:70 by volume. 0.5% by weight of trimethylsilyl isothiocyanate as an additive was added to the mixed solvent to prepare an electrolyte.

As an evaluation cell using the above electrolyte, a coin pull cell was prepared as follows.

To adjust the viscosity of a mixture of LiNi _0.85 Co _0.1 Al _0.05 O ₂ powder, Super-P (Timcal Ltd.) and PVDF (polyvinylidene fluoride) binder as a cathode active material at a weight ratio of 90: 5: 5 The solvent N-methylpyrrolidone (NMP) was added so as to have a solid content of 60% by weight to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil having a thickness of 15 mu m to a thickness of about 40 mu m. This was dried at room temperature, dried again at 120 ° C, and rolled to prepare a positive electrode.

A 2016 type coin type lithium secondary battery was produced using the prepared positive electrode, negative electrode, electrolyte, and porous polyethylene (PE) separator.

Example  3

A lithium secondary battery was produced in the same manner as in Example 2 except that 1 wt% of trimethylsilyl isothiocyanate as an additive was added to the electrolyte.

Comparative Example  2

A lithium secondary battery was produced in the same manner as in Example 2 except that trimethylsilyl isothiocyanate, which is an additive, was not added to the electrolyte.

Evaluation example  2: Evaluation of life characteristics

Each of the lithium secondary batteries prepared in Example 2-3 and Comparative Example 2 was charged with a constant current until the voltage reached 4.2 V at a current of 0.2 C rate at 25 캜 and then 0.2 C at a constant current, which was performed twice.

The lithium secondary battery having been subjected to the conversion step was charged with constant current until the voltage reached 4.2 V at a current of 0.7 C rate at 25 DEG C, and was charged at a constant voltage until the current became 0.05 C while maintaining 4.2 V. Subsequently, a cycle of discharging at a constant current of 0.5 C until the voltage reached 2.5 V at the time of discharging was repeated 100 times.

The discharge capacity of the discharge capacity in each cycle was measured for each lithium secondary battery, and the capacity retention ratio (%) of the following formula (1) was calculated from the discharge capacity.

&Quot; (1) &quot;

Capacity retention rate [%] = [Discharge capacity in each cycle / Discharge capacity in 1st cycle] × 100

The results of measurement of the capacity retention rate of each of the lithium secondary batteries of Examples 2-3 and Comparative Example 2 are shown in Fig. 4, and the capacity retention ratios at the 100th cycle are shown in Table 1 below.

additive In the 100 ^th cycle
Capacity retention rate (%) Example 2 TMSNCS 0.5 wt% 73% Example 3 TMSNCS 1wt% 73% Comparative Example 2 none 67%

As shown in FIG. 4 and Table 1, in Comparative Example 2 in which trimethylsilyl isothiocyanate was not added, the capacity retention ratio was 67%, whereas in Example 2-3 in which trimethylsilyl isothiocyanate was added, The retention ratio was 73%, indicating that the lifetime characteristics were improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, . Accordingly, the scope of protection of the present invention should be determined by the appended claims.

30: Lithium battery
22: cathode
23: anode
24: Separator
25: Battery container
26:

Claims (12)

Non-aqueous organic solvent; And
A silane-based compound containing at least one electron withdrawing group selected from a cyano group (-CN), an isothiocyanate group (-NCS) and a thiocyanate group (-SCN);
And an electrolyte solution for a lithium battery. The method according to claim 1,
Wherein the silane-based compound comprises a compound represented by the following formula (1) or (2):
[Chemical Formula 1]

(2)

In the above formulas (1) and (2)
R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group ego,
Y ₁ and Y ₂ are each independently a cyano group (-CN), an isothiocyanate group (-NCS), or a thiocyanate group (-SCN). The method according to claim 1,
Wherein the silane-based compound comprises an isothiocyanate group (-NCS) -containing silane compound represented by the following formula (1a):
[Formula 1a]

In this formula,
R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be. The method of claim 3,
The isothiocyanate group (-NCS) -containing silane-based compound includes at least one of the following compounds:

The method according to claim 1,
The silane-based compound includes a silane-based compound having a cyano group (-CN) represented by the following formula (1b): &lt; EMI ID =
[Chemical Formula 1b]

In this formula,
R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be. 6. The method of claim 5,
The silane-based compound containing a cyano group (-CN) includes at least one of the following compounds:

The method according to claim 1,
Wherein the silane-based compound comprises a silane-based compound containing a thiocyanate group (-SCN) represented by the following Chemical Formula 1c:
[Chemical Formula 1c]

In this formula,
R ₁ , R ₂ and R ₃ are each independently a hydrogen atom, an unsubstituted or substituted C 1 -C 30 alkyl group, an unsubstituted or substituted C 2 -C 30 alkenyl group, an unsubstituted or substituted C 2 -C 30 alkynyl group, An unsubstituted or substituted C6-C30 aryl group, an unsubstituted or substituted C3-C30 heteroaryl group, an unsubstituted or substituted C4-C30 cycloalkyl group, or an unsubstituted or substituted C3-C30 heterocycloalkyl group to be. 8. The method of claim 7,
The thiocyanate group (-SCN) -containing silane-based compound includes at least one of the following compounds:

The method according to claim 1,
The content of the silane-based compound is more than 0 wt% and not more than 1 wt% based on the total weight of the electrolyte. The method according to claim 1,
An electrolyte for a lithium battery further comprising a lithium salt. anode;
cathode; And
The lithium battery according to any one of claims 1 to 10, which is disposed between the positive electrode and the negative electrode. 12. The method of claim 11,
Wherein the negative electrode comprises a silicon-based negative active material.

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