KR102244059B1 - Electrolyte for rechargeable lithium battery and rechargeable lithium battery - Google Patents

Abstract

상기 화학식 1 및 2에서 각 치환기 정의는 상세한 설명에 기재한 것과 동일하다.Including a non-aqueous organic solvent, a lithium salt and an additive, the additive includes a compound represented by the following formula (1) and a compound represented by the following formula (2), and the compound represented by the formula (2) is a compound represented by the formula (1) It provides an electrolyte for a lithium secondary battery containing 50 parts by weight to 300 parts by weight based on 100 parts by weight.
[Formula 1] [Formula 2]

The definition of each substituent in Formulas 1 and 2 is the same as described in the detailed description.

Description

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

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

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

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

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

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

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

One embodiment provides an electrolyte for a lithium secondary battery capable of improving battery performance by securing high temperature stability and improving resistance characteristics.

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

One embodiment of the present invention includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a compound represented by Formula 1 and a compound represented by Formula 2, and the compound represented by Formula 2 It provides an electrolyte for a lithium secondary battery containing 50 parts by weight to 300 parts by weight based on 100 parts by weight of the compound represented by Formula 1 above.

[Formula 1]

In Formula 1,

X ¹ is a fluoro group, a chloro group, a bromo group or an iodo group,

R ¹ to R ⁶ are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted A C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group,

n is an integer of 0 or 1;

[Formula 2]

In Chemical Formula 2,

X ² is a fluoro group, a chloro group, a bromo group or an iodo group,

M is Al, B or P,

m1 is one of an integer from 1 to 4,

m2 is one of an integer from 0 to 8.

The compound represented by Formula 1 may be included in an amount of 0.05% to 20% by weight based on the total amount of the electrolyte, and the compound represented by Formula 2 may be included in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte. .

The compound represented by Formula 2 may be included in an amount of 0.5% to 5% by weight based on the total amount of the electrolyte.

Formula 1 may be represented by the following Formula 1-1.

[Formula 1-1]

In Formula 1-1,

R ¹ to R ⁶ are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted A C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group,

n is an integer of 0 or 1.

Formula 1-1 may be represented by the following Formula 1-1A or Formula 1-1B.

[Formula 1-1A] [Formula 1-1B]

In Formulas 1-1A and 1-1B,

R ¹ to R ⁶ are each independently hydrogen, 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, or a substituted or unsubstituted C2 to It is a C10 alkynyl group.

n is an integer of 0 or 1.

The compound represented by Formula 2 is lithium bis (oxalato) borate (LiBOB: lithium bis (oxalato) borate), lithium difluoro (oxalato) borate (LiFOB: lithium difluoro (oxalato) borate), lithium tetrafluoro (Oxalato) phosphate (LiTFOP: lithium tetrafluoro (oxalato) phosphate), lithium difluoro bis (oxalato) phosphate (LiDFOP: lithium difluoro bis (oxlato) phosphate), and at least one selected from a combination thereof.

The additives are vinylene carbonate (VC), fluoroethylene carbonate (FEC), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF ₄ ), succinonitrile (SN), lithium di Addition of at least one of fluorophosphate (LiPO ₂ F ₂ ), 1,3,6-hexanetricarbonitrile (HTCN: 1,3,6-hexanetricarbonitrile;) and 2-fluoro biphenyl (2-FBP) It may further include additives.

The additional additive may be included in an amount of 5 to 20% by weight based on the total amount of the electrolyte for the lithium secondary battery.

The non-aqueous organic solvent may be a mixed solvent of a cyclic carbonate-based solvent and a chain ester-based solvent.

The cyclic carbonate-based solvent and the chain ester-based solvent may be included in a volume ratio of 2:8 to 5:5.

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

An interface layer including a phosphate-based polymer and an oxalate-based polymer may be further included on the surface of the negative electrode.

It is possible to implement a lithium secondary battery having excellent high-temperature storage characteristics and improved resistance characteristics.

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

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

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

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

Hereinafter, an electrolyte solution for a rechargeable lithium battery according to an embodiment will be described.

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

The additive includes a compound represented by the following formula (1) and a compound represented by the following formula (2),

The compound represented by Formula 2 is included in an amount of 50 parts by weight to 300 parts by weight based on 100 parts by weight of the compound represented by Formula 1.

[Formula 1]

In Formula 1,

X ¹ is a fluoro group, a chloro group, a bromo group or an iodo group,

R ¹ to R ⁶ are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted A C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group,

n is an integer of 0 or 1;

[Formula 2]

In Chemical Formula 2,

X ² is a fluoro group, a chloro group, a bromo group or an iodo group,

M is Al, B or P,

m1 is one of an integer from 1 to 4,

m2 is one of an integer from 0 to 8.

According to an embodiment of the present invention, when an additive containing a compound represented by Formula 1 is used, an SEI film (solid electrolyte interface) having high high temperature stability and excellent ion conductivity is formed on the surface of the negative electrode, and -PO ₂ F _{By suppressing the side reaction of LiPF 6} due to the functional group, it is possible to reduce gas generation due to the decomposition reaction of the electrolyte during high temperature storage.

In addition, by including the compound represented by Formula 2 together with the compound represented by Formula 1, an SEI film and/or a protective layer having low resistance may be formed, and accordingly, internal resistance of the battery may be reduced.

Specifically, the compound represented by Formula 1 _{may form a complex by coordinating with a thermal decomposition product of a lithium salt such as LiPF 6} or an anion dissociated from a lithium salt, and due to the formation of these complexes, Since the negative ions are stabilized, unwanted side reactions between them and the electrolyte can be suppressed, thus improving the cycle life characteristics of the lithium secondary battery and preventing gas from being generated inside the lithium secondary battery, significantly reducing the rate of defects. have.

In particular, the compound represented by Formula 2 has a higher reduction potential than the compound represented by Formula 1, and thus participates in the formation of the SEI film first, thereby preventing overdecomposition of the compound represented by Formula 1, and thus the electrolyte solution The SEI film and/or the protective layer having low resistance may be formed by suppressing side reactions with.

In an embodiment, the compound represented by Formula 2 may be included in an amount of 50 parts by weight to 300 parts by weight based on 100 parts by weight of the compound represented by Formula 1.

When the compounds represented by Chemical Formulas 1 and 2 are included in the content ratio, an SEI film having low resistance and excellent thermal stability may be formed to suppress an electrolyte solution decomposition reaction.

For example, the compound represented by Formula 1 may be included in an amount of 0.05% to 20% by weight based on the total amount of the electrolyte, and the compound represented by Formula 2 may be included in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte. have.

For example, the compound represented by Formula 1 may be included in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte, and the compound represented by Formula 2 may be included in an amount of 0.5% to 10% by weight based on the total amount of the electrolyte. have.

When the content of the compound represented by Formula 1 is less than 0.05% by weight, there is a problem that the high temperature storage and swelling improvement effect is deteriorated, and when it exceeds 20% by weight, there is a problem that the lifespan is decreased due to an increase in interface resistance.

In addition, when the content of the compound represented by Formula 2 is less than 0.1% by weight, the effect of inhibiting the increase of the interface resistance is insignificant, and when it exceeds 10% by weight, the viscosity increases and the interface resistance increases, thereby improving battery performance such as capacity and lifespan. There is a problem in securing.

In a specific embodiment, the compound represented by Formula 2 may be included in an amount of 0.5% to 5% by weight based on the total amount of the electrolyte.

When the compound represented by Formula 2 is included in the above content, reduction decomposition proceeds first at a relatively high reduction potential, such as 2.0 V to 2.4 V, thereby forming an SEI film having excellent ^{Li + ion transfer properties on the surface of the negative electrode.}

For example, Chemical Formula 1 may be represented by Chemical Formula 1-1 below.

[Formula 1-1]

In Formula 1-1, R ¹ to R ⁶ and n are as described above.

The compound represented by Formula 1-1 has an electron-accepting fluorine substituent directly bonded to the central atom, phosphorus (P(III)), so that the stability of the SEI film present on the anode can be improved.

For example, Chemical Formula 1-1 may be represented by Chemical Formula 1-1A or Chemical Formula 1-1B.

[Formula 1-1A] [Formula 1-1B]

In Formulas 1-1A and 1-1B,

R ¹ to R ⁶ are each independently hydrogen, 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, or a substituted or unsubstituted C2 to It is a C10 alkynyl group.

Specifically, R ¹ to R ⁶ may each independently be hydrogen or a substituted or unsubstituted C1 to C10 alkyl group, and more specifically, R ¹ to R ⁶ may each be hydrogen.

For example, the compound represented by Formula 1 may be 2-fluoro-1,3,2-dioxaphospholane.

For example, Chemical Formula 2 may be represented by Chemical Formula 2-1 below.

[Formula 2-1]

In Formula 2, X ² , m1 and m2 are as described above.

As a specific example, the compound represented by Formula 2 is lithium bis (oxalato) borate (LiBOB: lithium bis (oxalato) borate), lithium difluoro (oxalato) borate (LiFOB: lithium difluoro (oxalato) borate), lithium Tetrafluoro (oxalato) phosphate (LiTFOP: lithium tetrafluoro (oxalato) phosphate), lithium difluoro bis (oxalato) phosphate (LiDFOP: lithium difluoro bis (oxlato) phosphate) and at least one selected from a combination thereof I can.

For example, lithium bis (oxalato) borate (LiBOB: lithium bis (oxalato) borate), lithium difluoro (oxalato) borate (LiFOB: lithium difluoro (oxalato) borate), and a combination thereof, but It is not limited.

The additives are vinylene carbonate (VC), fluoroethylene carbonate (FEC), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF ₄ ), succinonitrile (SN), lithium di Addition of at least one of fluorophosphate (LiPO ₂ F ₂ ), 1,3,6-hexanetricarbonitrile (HTCN: 1,3,6-hexanetricarbonitrile;) and 2-fluoro biphenyl (2-FBP) It may further include additives.

The additional additive may be included in an amount of 5% to 20% by weight, for example, 5% to 15% by weight based on the total amount of the electrolyte for the lithium secondary battery.

In addition, the additional additive and the compound represented by Formula 1 may be included in a weight ratio of 9: 1 to 1: 1, for example, in a weight ratio of 9: 1 to 8: 2.

When the content range of the additional additive is as described above, it is possible to more effectively suppress battery resistance and implement a lithium secondary battery having further improved cycle life characteristics.

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

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent may be used.

As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), and the like may be used. As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, Caprolactone or the like may be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like may be used. In addition, cyclohexanone or the like may be used as the ketone-based solvent. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms) as the aprotic solvent. , A double bonded aromatic ring or an ether bond), such as nitriles, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. .

The organic solvent may be used alone or as a mixture of one or more, and the mixing ratio in the case of using one or more mixtures may be appropriately adjusted according to the desired battery performance, which may be widely understood by those engaged in the field. have.

The organic solvent may further include an aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed in a volume ratio of 1:1 to 30:1.

As the aromatic hydrocarbon-based solvent, an aromatic hydrocarbon-based compound represented by the following formula (A) may be used.

[Formula A]

(In Formula A, R ⁷ to R ¹² are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.

Specific examples of the aromatic hydrocarbon-based solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluoro Lobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1, 2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diaiodobenzene, 1,4-diaiodobenzene, 1,2,3-triiodobenzene, 1,2 ,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Toluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3 ,5-trichlorotoluene, iodotoluene, 2,3-diaiodotoluene, 2,4-diaiodotoluene, 2,5-diaiodotoluene, 2,3,4-triiodotoluene, 2,3, It is selected from the group consisting of 5-triiodotoluene, xylene, and combinations thereof.

In order to improve the battery life, the electrolyte may further include an ethylene-based carbonate-based compound of Formula B below as a life-improving additive in addition to vinylene carbonate.

[Formula B]

(In Formula 3, R ¹³ and R ¹⁴ are the same as or different from each other, and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms. , ^{At least one of R 13} and R ¹⁴ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated C 1 to C 5 alkyl group, provided that both ^{R 13} and R ^{14 are} It is not hydrogen.)

Representative examples of the ethylene-based carbonate-based compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate or fluoroethylene carbonate. Can be lifted. In the case of further use of such a life-improving additive, the amount of the additive may be appropriately adjusted.

The non-aqueous organic solvent according to an embodiment of the present invention may be a mixed solvent of a cyclic carbonate-based solvent and a chain ester-based solvent.

The cyclic carbonate-based solvent may be a two/three-component solvent based on ethylene carbonate (EC).

For example, it may be a binary solvent of ethylene carbonate (EC) and propylene carbonate (PC). In this case, the electrolyte can be used in a wide temperature range without deteriorating battery performance.

In particular, by including a chain-type ester-based solvent together with a cyclic carbonate-based solvent, the mobility of ions in the solvent may increase, thereby improving ionic conductivity.

For example, the chain ester solvent may be a binary organic solvent of ethyl propionate (EP) and propyl propionate (PP).

For example, the cyclic carbonate-based solvent and the chain ester-based solvent may be included in a volume ratio of 2:8 to 5:5, and specifically, may be included in a volume ratio of 2:8 to 4:6, for example, 3:7. It can be included in a volume ratio.

The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery, enables basic operation of a lithium secondary battery, and promotes the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _{2x + 1} SO ₂ )(C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers, for example It is an integer of 1 to 20), LiCl, LiI, and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB). The concentration of the lithium salt is preferably within the range of 0.1M to 2.0 M. If the concentration of the lithium salt falls within the above range, the electrolyte has an appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited, and lithium ions can move effectively. have.

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

An interface layer including a phosphate-based polymer and an oxalate-based polymer may be further included on the surface of the negative electrode.

By further including an interface layer on the surface of the negative electrode, high-temperature storage characteristics and resistance resistance characteristics may be further improved.

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.

As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (reitiated intercalation compound) may be used.

Specifically, at least one of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

An example of the positive electrode active material may be a compound represented by any one of the following formulas.

_{Li a A 1 - b X b} D 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); _{Li a A 1 - b X b} O 2 - c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); _{Li a E 1 - b X b} O 2 - c D c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); _{Li a E 2 - b X b} O 4 - c D c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _{1 -b- c} Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2); _{Li a Ni 1 -b- c Co b} X c O 2 - α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); _{Li a Ni 1 -b- c Co b} X c O 2 - α T 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); _{Li a Ni 1 -b- c Mn b} X c O 2 - α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -bc} Mn _b X _c O _2-α T ₂ (0.90 <a <1.8, 0 <b <0.5, 0 <c <0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a CoG _b O ₂ (0.90≦a≦1.8, 0.001≦b≦0.1); _{Li a Mn 1 - b G b} O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (0.90≦a≦1.8, 0.001≦b≦0.1); Li _a Mn _{1 -g} G _g PO ₄ (0.90≦a≦1.8, 0≦g≦0.5); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); Li _a FePO ₄ (0.90 ≤ a ≤ 1.8)

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer contains at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. I can. The compound constituting these coating layers may be amorphous or crystalline. As a coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. The coating layer forming process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g., spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted.

The positive electrode active material according to an embodiment of the present invention may be lithium cobalt oxide.

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

In one embodiment of the present invention, the positive active material layer may include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

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

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

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

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

The negative active material includes a material capable of reversibly intercalating/deintercalating lithium ions, a lithium metal, an alloy of a lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

As a material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used as a carbon material, and a representative example thereof is crystalline carbon. , Amorphous carbon, or they may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon ( hard carbon), mesophase pitch carbide, and fired coke.

As the lithium metal alloy, in the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn The alloy of the metal of choice can be used.

The lithium-doped and undoped materials include Si, Si-C composite, SiO _x (0 <x <2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, It is an element selected from the group consisting of a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, but not Si), Sn, SnO2, Sn-R (wherein R is an alkali metal, alkaline earth metal, group 13 An element selected from the group consisting of an element, a group 14 element, a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof, and not Sn), and the like, and at least one of them and SiO ₂ You can also mix and use. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, What is selected from the group consisting of S, Se, Te, Po, and combinations thereof may be used.

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

The content of the negative active material in the negative active material layer may be 95% to 99% by weight based on the total weight of the negative active material layer.

In one embodiment of the present invention, the negative active material layer includes a binder, and may optionally further include a conductive material. The content of the binder in the negative active material layer may be 1% to 5% by weight based on the total weight of the negative active material layer. In addition, when a conductive material is further included, the negative active material may be used in an amount of 90% to 98% by weight, a binder may be used in an amount of 1% to 5% by weight, and a conductive material may be used in an amount of 1% to 5% by weight.

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

As the water-insoluble binder, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluorine rubber, and combinations thereof. The polymeric resin binder is polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, Ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K or Li may be used as the alkali metal. The content of the thickener may be 0.1 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 constituted, any material can be used as long as it does not cause chemical change and is an electron conductive material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen Carbon-based materials such as black and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

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

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

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

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment is disposed between a negative electrode 112, a positive electrode 114 positioned opposite to the negative electrode 112, and between the negative electrode 112 and the positive electrode 114. A battery cell including an electrolyte (not shown) impregnating the separator 113 and the negative electrode 112, the positive electrode 114 and the separator 113, and a battery container 120 and the battery containing the battery cell And a sealing member 140 for sealing the container 120.

Hereinafter, examples and comparative examples of the present invention will be described. The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

Fabrication of lithium secondary battery

Example One

_{LiCoO 2} as a positive electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed at a weight ratio of 92:4:4, respectively, and dispersed in N-methyl pyrrolidone to prepare a positive electrode active material slurry.

The positive electrode active material slurry was coated on an Al foil having a thickness of 15 μm, dried at 100° C., and then rolled to prepare a positive electrode.

Artificial graphite as a negative electrode active material and polyvinylidene fluoride as a binder were mixed in a weight ratio of 98:2, respectively, and dispersed in N-methyl pyrrolidone to prepare a negative electrode active material slurry.

The negative active material slurry was coated on a Cu foil having a thickness of 10 μm, dried at 100° C., and then rolled to prepare a negative electrode.

A lithium secondary battery was manufactured using the prepared positive and negative electrodes, a separator made of polyethylene having a thickness of 25 μm, and an electrolyte.

The composition of the electrolyte solution is as follows.

(Electrolyte composition)

Salt: LiPF ₆ 1.15 M

Solvent: ethylene carbonate: propylene carbonate: ethyl propionate: propyl propionate (EC:EP=30:70 by volume)

Additives: 2-fluoro-1,3,2-dioxaphosphoran 1% by weight, LiFOB 0.5% by weight, FEC 5% by weight, VC 1% by weight

(However, "% by weight" in the composition of the electrolyte is based on the total content of the electrolyte.)

Example 2 to 4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the contents of LiFOB were changed to 1% by weight, 2% by weight, and 3% by weight, respectively.

Example 5

A lithium secondary battery was manufactured in the same manner as in Example 2, except that LiBOB was added instead of LiFOB.

Comparative example One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiFOB was not added as an additive.

Battery characteristic evaluation

Evaluation 1: Low and room temperature resistance characteristics evaluation

Each lithium secondary battery manufactured according to Examples 1 to 5 and Comparative Example 1 was discharged at a constant current of 0.1C in a 100% charge state at 0°C and 25°C, respectively, and a charge state of 70%, 20%, and 10%, respectively. Discharged at a constant current of 1C for 10 seconds

The direct current resistance (DC-IR) was calculated by the formula ΔR =ΔV/ΔI from the data of 1C and 0.1C, and the results are shown in Table 1 below.

25℃ DC-IR (1C/0.1C)
(mOhm) 0℃ DC-IR (1C/0.1C)
(mOhm) SOC70 SOC20 SOC10 SOC70 SOC20 SOC10 Example 1 46.21 50.65 55.10 139.92 168.08 174.79 Example 2 43.84 47.97 52.10 138.12 165.98 172.25 Example 3 44.21 48.65 52.00 138.23 166.00 172.20 Example 4 44.19 48.43 51.87 138.20 165.80 171.98 Example 5 43.95 48.03 52.35 139.20 167.80 173.20 Comparative Example 1 52.54 56.98 61.91 152.71 174.40 181.10

Referring to Table 1, it can be seen that in the case of the lithium secondary battery according to Examples 1 to 5 using the additive according to an embodiment, room temperature and low temperature DC-resistance are reduced compared to the lithium secondary battery according to Comparative Example 1. Therefore, it can be seen that the resistance resistance of the charged-state battery is improved when the compound according to the embodiment is used as an additive.

Evaluation 2: rate of thickness change

The lithium secondary batteries manufactured according to Examples 1 to 5 and Comparative Example 1 were fully charged at 25°C at 0.5C, and then the initial thickness was measured and left at 60°C for 4 weeks, and then the thickness of the battery was measured. The thickness change rate (%) of the thickness increase value (thickness-initial thickness after being left at 60° C. for 4 weeks) was calculated.

In addition, the thickness of the battery was measured after allowing it to stand at 85° C. for 8 hours, and the thickness change rate (%) of the thickness increase value (thickness after leaving at 85° C. for 8 hours – initial thickness) with respect to the initial thickness was calculated.

The calculated thickness change rate (%) is shown in Table 2 below.

Thickness increase rate @ 60℃ 4 weeks (%) Thickness increase rate @ 85℃ 8hr (%) Example 1 7.12 6.51 Example 2 6.55 5.15 Example 3 6.31 5.13 Example 4 8.69 8.07 Example 5 6.23 5.11 Comparative Example 1 10.42 8.13

As shown in Table 2, the lithium secondary batteries of Examples 1 to 5 using an electrolyte containing an additive according to an embodiment of the present invention are compared to the lithium secondary battery of Comparative Example 1 after standing at 60°C for 4 weeks. It can be seen that both the thickness increase rate of and the thickness increase rate of the battery after leaving for 8 hours at 85°C can be effectively suppressed.

In other words, it was found that both the swelling characteristics when left to stand at high temperature for a long term and the swelling characteristics when left at high temperature for a short term were excellent.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this is also the present invention. It is natural to fall within the scope of the invention.

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

Claims (12)

Including a non-aqueous organic solvent, a lithium salt and an additive,
The additive includes a compound represented by the following formula (1) and a compound represented by the following formula (2),
The compound represented by Formula 2 is an electrolyte for a lithium secondary battery contained in an amount of 50 to 300 parts by weight based on 100 parts by weight of the compound represented by Formula 1:
[Formula 1]

In Formula 1,
X ¹ is a fluoro group, a chloro group, a bromo group or an iodo group,
R ¹ to R ⁶ are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted A C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group,
n is an integer of 0 or 1;
[Formula 2]

In Chemical Formula 2,
X ² is a fluoro group, a chloro group, a bromo group or an iodo group,
M is Al, B or P,
m1 is one of an integer from 1 to 4,
m2 is one of an integer from 0 to 8. In claim 1,
The compound represented by Formula 1 is contained in an amount of 0.05% to 20% by weight based on the total amount of the electrolyte,
The compound represented by Formula 2 is an electrolyte for a lithium secondary battery contained in an amount of 0.1% to 10% by weight based on the total amount of the electrolyte. In paragraph 2,
The compound represented by Formula 2 is an electrolyte for a lithium secondary battery contained in an amount of 0.5% to 5% by weight based on the total amount of the electrolyte. In claim 1,
Formula 1 is an electrolyte for a lithium secondary battery represented by the following Formula 1-1:
[Formula 1-1]

In Formula 1-1,
R ¹ to R ⁶ are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted A C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group,
n is an integer of 0 or 1. In claim 4,
Formula 1-1 is an electrolyte for a lithium secondary battery represented by the following Formula 1-1A or Formula 1-1B:
[Formula 1-1A] [Formula 1-1B]

In Formulas 1-1A and 1-1B,
R ¹ to R ⁶ are each independently hydrogen, 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, or a substituted or unsubstituted C2 to It is a C10 alkynyl group.
n is an integer of 0 or 1. In claim 1,
The compound represented by Formula 2 is lithium bis (oxalato) borate (LiBOB: lithium bis (oxalato) borate), lithium difluoro (oxalato) borate (LiFOB: lithium difluoro (oxalato) borate), lithium tetrafluoro (Oxalato) phosphate (LiTFOP: lithium tetrafluoro (oxalato) phosphate), lithium difluoro bis (oxalato) phosphate (LiDFOP: lithium difluoro bis (oxlato) phosphate) and at least one selected from a combination thereof, for a lithium secondary battery Electrolyte. In claim 1,
The additives are vinylene carbonate (VC), fluoroethylene carbonate (FEC), propene sultone (PST), propane sultone (PS), lithium tetrafluoroborate (LiBF ₄ ), succinonitrile (SN), lithium di Addition of at least one of fluorophosphate (LiPO ₂ F ₂ ), 1,3,6-hexanetricarbonitrile (HTCN: 1,3,6-hexanetricarbonitrile;) and 2-fluoro biphenyl (2-FBP) An electrolyte for a lithium secondary battery further comprising an additive. In clause 7,
The additional additive is an electrolyte for a lithium secondary battery contained in an amount of 5% to 20% by weight based on the total amount of the electrolyte for a lithium secondary battery. In claim 1,
The non-aqueous organic solvent is an electrolyte for a lithium secondary battery, which is a mixed solvent of a cyclic carbonate-based solvent and a chain ester-based solvent. In claim 9,
The cyclic carbonate-based solvent and the chain-type ester-based solvent are contained in a volume ratio of 2:8 to 5:5 for a lithium secondary battery electrolyte. anode;
cathode; And
The electrolyte according to any one of claims 1 to 10
Lithium secondary battery comprising a. In clause 11,
A lithium secondary battery further comprising an interface layer including a phosphate-based polymer and an oxalate-based polymer on the surface of the negative electrode.

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