KR20220018413A - Rechargebale lithium battery - Google Patents

Abstract

Provided is a lithium secondary battery. The lithium secondary battery includes: an electrolyte including a lithium salt, a non-aqueous organic solvent, and an additive containing a compound represented by chemical formula 1 below; a negative electrode including a negative electrode active material including a carbon-based material and lithium titanium oxide; and a positive electrode including a positive electrode active material, wherein the content of the additive including the compound represented by the chemical formula 1 is 0.1 wt% or more and less than 10 wt% based on the total weight of the lithium salt and the non-aqueous organic solvent, and the content of the lithium titanium oxide is 0.1 wt% or more and less than 2 wt% based on the total weight of the negative electrode active material. (In the chemical formula 1, the definition of each substituent is the same as in the detailed description).

Description

Lithium secondary battery {RECHARGEBALE LITHIUM BATTERY}

It relates to a lithium secondary battery.

Lithium secondary batteries have a high discharge voltage and high energy density, attracting attention as a power source for various electronic devices.

As a cathode active material for a lithium secondary battery, LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ (0 < x < 1) Oxides are mainly used.

Various types of carbon-based materials including artificial, natural graphite, and hard carbon capable of intercalating/deintercalating lithium are mainly used as an anode active material.

An organic solvent in which a lithium salt is dissolved is used as an electrolyte for a lithium secondary battery.

One embodiment is to provide a lithium secondary battery exhibiting improved high-temperature reliability.

According to one embodiment, a negative electrode and positive electrode active material including an electrolyte carbon-based material including an additive including a lithium salt and a non-aqueous organic solvent and an additive including a compound represented by the following Chemical Formula 1 and a negative electrode active material including lithium titanium oxide Including a positive electrode, the content of the additive including the compound represented by Formula 1 is 0.1 wt% or more and less than 10 wt% based on the total weight of the lithium salt and the non-aqueous organic solvent, and the content of the lithium titanium oxide is Provided is a lithium secondary battery in an amount of 0.1 wt% or more and less than 2 wt% based on the total weight of the negative active material.

[Formula 1]

(In Formula 1,

R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted C2 to C30 alkynyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C3 to C30 cycloalkenyl group, a substituted or unsubstituted C3 to C30 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group.)

In Formula 1, R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, It may be a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C3 to C10 cycloalkynyl group, or a substituted or unsubstituted C6 to C10 aryl group.

The carbon-based material may be crystalline carbon.

According to one embodiment, the carbon-based material may be a mixture of artificial graphite and natural graphite, and the mixing ratio of the artificial graphite and natural graphite may be 8: 2 to 5: 5 by weight.

The non-aqueous organic solvent may include a propionate-based solvent.

The lithium titanium oxide may be represented by the following formula (2).

[Formula 2]

Li _4+x Ti _y M _z O _t

(In Formula 2, 0 ≤ x ≤ 3, 1 ≤ y ≤ 5, 0 ≤ z ≤ 3, 3 ≤ t ≤ 12, M is Mg, La, Tb, Gd, Ce, Pr, Nd, Sm, Ba, Sr, Ca, or a combination thereof).

The details of other implementations are included in the detailed description below.

The additive of a lithium secondary battery according to an embodiment of the present invention can reduce battery resistance, particularly by suppressing an increase in battery resistance during high-temperature storage, thereby improving battery performance, and improving cycle life characteristics at room temperature. .

1 is a diagram schematically illustrating a lithium secondary battery according to an embodiment.
2 is a graph showing a high-temperature capacity retention rate and a high-temperature storage resistance increase rate of the lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1, 2, and 4;
3 is a graph showing the high-temperature capacity retention rate and high-temperature storage resistance increase rate of the lithium secondary batteries of Examples 1, 4, and 5 and Comparative Examples 1, 3 and 5;

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

Unless otherwise defined herein, 'substitution' means that a hydrogen atom in a compound is a halogen atom (F, 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 , hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or its salt, sulfonic acid or its salt, phosphoric acid or its salt, C1 to C20 alkyl group, C2 to C20 alkenyl group, C2 to C20 Alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C4 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkyl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to C15 It means substituted with a substituent selected from a cycloalkynyl group, a C2 to C20 heterocycloalkyl group, and combinations thereof. One embodiment is an electrolyte carbon-based material comprising a non-aqueous organic solvent and an additive including a compound represented by the following formula (1) And it provides a lithium secondary battery comprising a negative electrode including a negative active material containing a lithium titanium oxide and a positive electrode including a positive electrode active material.

[Formula 1]

In Formula 1,

R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted C2 to C30 alkynyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C3 to C30 cycloalkenyl group, a substituted or unsubstituted C3 to C30 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group.

In one embodiment, R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group , a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C3 to C10 cycloalkynyl group, or a substituted or unsubstituted C6 to C10 aryl group.

In this case, the content of the additive including the compound represented by Formula 1 is based on the total weight of the lithium salt and the non-aqueous organic solvent. That is, it may be 0.1% by weight or more and less than 10% by weight based on 100% by weight of the total, according to one embodiment, 0.5% by weight or more, and less than 10% by weight, according to another embodiment, 0.5% by weight or more, 5 It may be less than or equal to weight %, and according to another embodiment, may be greater than or equal to 1% by weight and less than or equal to 5% by weight . When the content of the additive containing the compound represented by Formula 1 is included in the above range, it is appropriate because it can exhibit effects such as high-temperature reliability characteristics, for example, improvement of high-temperature capacity retention rate and reduction of high-temperature resistance increase rate.

The content of the lithium titanium oxide may be 0.1% by weight or more and less than 2% by weight based on the total weight of the negative active material, that is, based on 100% by weight of the negative active material. According to one embodiment, the content of the lithium titanium oxide may be 0.5 wt% to 1 wt% based on the total weight of the negative active material. When the content of lithium titanium oxide is included in the above range, it is possible to improve lithium ion movement, and it is suitable because it can exhibit effects such as high temperature reliability characteristics, for example, improvement of high temperature capacity retention rate and reduction of high temperature resistance increase rate.

The lithium titanium oxide may be represented by the following formula (2) .

[Formula 2]

Li _4+x Ti _y M _z O _t

In Formula 2, 0 ≤ x ≤ 3, 1 ≤ y ≤ 5, 0 ≤ z ≤3, 3 ≤ t ≤ 12, M is Mg, La, Tb, Gd, Ce, Pr, Nd, Sm, Ba, Sr , Ca, or a combination thereof. In one embodiment, the lithium titanium oxide may be Li ₄ Ti ₅ O ₁₂ .

As such, the lithium secondary battery according to an embodiment contains lithium titanium oxide in an anode in an amount of 0.1 wt% or more and less than 2 wt% based on the total weight of the anode active material, and the additive represented by Chemical Formula 1 is added to the electrolyte by the total weight of the electrolyte 0.1% by weight or more, and less than 10% by weight. By including the negative electrode and the electrolyte, high-temperature reliability of the battery may be further improved. Even if both lithium titanium oxide and the additive represented by Formula 1 are included, when each content is out of the above range, high temperature reliability is deteriorated, and thus it is not appropriate.

In addition, this high-temperature reliability effect can be obtained when a carbon-based material is used together with lithium titanium oxide for the negative electrode, but cannot be obtained when a silicon-based material is used instead of the carbon-based material. When lithium titanium oxide and a silicon-based material are used for the negative electrode, a volume change occurs severely during charging and discharging, and a side reaction with the electrolyte also occurs severely. Therefore, lithium titanium oxide and the additive represented by Formula 1 are used in the above content. The high-temperature reliability effect is hardly obtained.

In an embodiment, the carbon-based material included in the negative active material may be crystalline carbon. If the carbon-based material includes amorphous carbon rather than crystalline carbon, it is not appropriate because the reversible capacity is low, the handling is difficult because the amorphous carbon is sensitive to moisture, and the battery characteristics may be adversely affected.

The crystalline carbon may be specifically a mixture of artificial graphite and natural graphite. In addition, the mixing ratio of artificial graphite and natural graphite may be 8: 2 to 5: 5 by weight. Artificial graphite can suppress volume expansion during charging and discharging, thereby preventing cracks and structural changes in the anode active material. When the mixing ratio of the artificial graphite and the natural graphite is included in the above range, it is possible to suppress the volume expansion of the negative active material during charging and discharging, thereby reducing cracking of the negative active material and side reactions with the electrolyte, while securing high capacity characteristics .

In the electrolyte according to the embodiment, the non-aqueous organic solvent may include a carbonate-based solvent, and may also include a propionate-based solvent. The propionate-based solvent may be methyl propionate, ethyl propionate, propyl propionate, or a combination thereof. When one or more of the propionate-based solvents are used, the mixing ratio may be appropriately adjusted. Since the propionate-based solvent is a low-viscosity, high-ion conductivity solvent, when the propionate-based solvent is included as the non-aqueous organic solvent, the amount of gas generated and output characteristics in a wide temperature range can be supplemented, and thus it is appropriate.

In the non-aqueous organic solvent, the content of the propionate-based solvent may be 30% by volume to 80% by volume based on the total volume of the non-aqueous organic solvent. When the content of the propionate-based solvent is included in the above range, it is appropriate because the electrolyte impregnation characteristics due to excellent ionic conductivity and low viscosity can be further improved.

The carbonate-based solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC) ), propylene carbonate (PC), butylene carbonate (BC), or a combination thereof may be used. When one or more carbonate-based solvents are used, the mixing ratio may be appropriately adjusted. In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of 1:1 to 1:9, the performance of the electrolyte may be excellent.

In one embodiment, the non-aqueous organic solvent may further include an ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methylpropionate, ethylpropionate, propylpropionate, γ-butyrolactone, decanolide, Valerolactone, mevalonolactone (mevalonolactone), caprolactone (caprolactone) and the like may be used.

Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone etc. may be used as the ketone solvent. have.

As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is T-CN (T is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, nitriles such as nitriles (which may contain double bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and the like can be used.

In addition, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 3 may be used.

[Formula 3]

(In Formula 3, R ¹⁰ to R ¹⁵ 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 organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-tri Fluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1 ,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1, 2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluoro Rottoluene, 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-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3 ,5-triiodotoluene, xylene, and combinations thereof are selected from the group consisting of.

The electrolyte for a lithium secondary battery may further include an ethylene carbonate-based compound represented by the following Chemical Formula 4 as a lifespan improving additive in order to improve battery life.

[Formula 4]

(In Formula 4, R ¹⁶ and R ¹⁷ are each independently selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ), and a fluorinated alkyl group having 1 to 5 carbon atoms, the R At least one of ¹⁶ and R ¹⁷ is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO ₂ ) and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R ¹⁶ and R ¹⁷ are not both hydrogen. .)

Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, or cyanoethylene carbonate. When such a life-enhancing additive is further used, its amount can be appropriately adjusted.

The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and serves to promote movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts include LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , Li(FSO) ₂ ) ₂ N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI and LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate: LiBOB), lithium difluoro bis(oxalato)phosphate (LiDFOP) and lithium difluoro(oxalato) borate (LiDFOB), and LiPO ₂ F ₂ (lithium difluorophosphate) contains one or two or more selected from the group consisting of a supporting electrolyte salt. The concentration of lithium salt is preferably used within the range of 0.1 M to 2.0 M. The concentration of lithium salt is within the range When included, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can migrate effectively.

In one embodiment, the negative electrode including the negative electrode active material includes a negative electrode active material layer including the negative electrode active material, and a current collector supporting the negative electrode active material layer.

The anode active material layer includes an anode active material and a binder, and may optionally further include a conductive material.

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

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

Examples of the water-insoluble binder include ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyepichloro hydrin, polyphosphazene, ethylene propylene diene copolymer pole, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included as a thickener. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used. The amount of the thickener used may be 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative active material.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, denka black, and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

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

In one embodiment, the positive electrode including the positive electrode active material includes a positive electrode active material layer including the positive electrode active material, and a current collector supporting the positive electrode active material layer.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used, and specifically, selected from cobalt, manganese, nickel, and combinations thereof. At least one of a complex oxide of a metal and lithium may be used. As a more specific example, a compound represented by any one of the following formulas may be used. Li _a A _1-b X _b D ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li _a A _1-b X _b O _2-c 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-bc Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤2); Li _a Ni _1-bc Co _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α <2); Li _a Ni _1-bc Co _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α <2); Li _a Ni _1-bc Mn _b X _c D _α (0.90 ≤ a ≤1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤2); Li _a Ni _1-bc Mn _b X _c O _2-α T _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 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 ≤0.5, 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, a compound 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 may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. can The compound constituting these coating layers may be amorphous or crystalline. As the 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. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, immersion method, etc.). Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

In the positive electrode, the content of the positive active material may be 90 wt% to 98 wt% based on the total weight of the positive active material layer.

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

The binder serves to adhere the positive active material particles well to each other and also to the positive active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the configured battery, any electronically conductive material may be used without causing a chemical change. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof.

The current collector may be an aluminum foil, a nickel foil, or a combination thereof, but is not limited thereto.

The positive active material layer and the negative active material layer are formed by preparing an active material composition by mixing an active material, a binder, and optionally a conductive material in a solvent, and applying the active material composition to a current collector. Since such a method for forming an active material layer is widely known in the art, a detailed description thereof will be omitted herein. The solvent may include, but is not limited to, N-methylpyrrolidone. In addition, when a water-soluble binder is used for the anode active material layer, water may be used as a solvent used in preparing the anode active material composition.

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

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. Although the lithium secondary battery according to the embodiment has been described by taking the pouch-type battery as an example, the present invention is not limited thereto, and may be applied to various types of batteries, such as cylindrical and prismatic batteries.

Referring to FIG. 1 , a lithium secondary pouch battery 100 according to an embodiment includes an electrode assembly 110 wound with a separator 30 interposed between a positive electrode 10 and a negative electrode 20 , the electrode assembly 110 . ) may include a case 120 therein, and an electrode tab 130 serving as an electrical path for inducing a current formed in the electrode assembly 110 to the outside. The two surfaces of the case 120 overlap and seal the surfaces facing each other. In addition, the electrolyte is injected into the case 120 containing the electrode assembly 110, and the positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with the electrolyte (not shown). .

Hereinafter, Examples and Comparative Examples of the present invention will be described. However, the following examples are only examples of the present invention, and the present invention is not limited thereto.

(Example 1)

1.3M LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed at 10:15:30:45 volume %, and sulfolane of the following formula 1a was added, An electrolyte for a lithium secondary battery was prepared. In this case, the content of sulfolane in Formula 1a was 5% by weight based on 100% by weight of the total amount of the lithium salt and the non-aqueous organic solvent.

[Formula 1a]

A carbon-based material mixed with artificial graphite and natural graphite in a weight ratio of 8: 2, a negative electrode active material of Li ₄ Ti ₅ O ₁₂ , a styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed in a weight ratio of 98:1:1, respectively, and distilled water to prepare a negative electrode active material slurry. At this time, the content of the Li ₄ Ti ₅ O ₁₂ was 1 wt% based on 100 wt% of the total negative active material. The negative electrode active material slurry was coated on a copper foil, dried and rolled to prepare a negative electrode.

96 wt% of LiCoO ₂ cathode active material, 2 wt% of Ketjen black conductive material, and 2 wt% of polyvinylidene fluoride were mixed in N-methylpyrrolidone solvent to prepare a cathode active material slurry. The positive electrode active material slurry was coated on an aluminum foil, dried and rolled to prepare a positive electrode.

Using the electrolyte, the positive electrode and the negative electrode, a 4.4V class pouch-type lithium secondary battery was prepared by a conventional method.

(Example 2)

A negative electrode was prepared in the same manner as in Example 1, except that the content of Li ₄ Ti ₅ O ₁₂ was changed to 0.1% by weight based on 100% by weight of the total negative electrode active material, and the negative electrode and Example 1 A pouch-type lithium secondary battery was prepared in the same manner as in Example 1 using the electrolyte and positive electrode of

(Example 3)

A negative electrode was prepared in the same manner as in Example 1, except that the content of Li ₄ Ti ₅ O ₁₂ was changed to 0.5% by weight based on 100% by weight of the total negative electrode active material, and the negative electrode and Example 1 A pouch-type lithium secondary battery was prepared in the same manner as in Example 1 using the electrolyte and positive electrode of

(Example 4)

An electrolyte was prepared in the same manner as in Example 1 by changing the sulfolane content of Formula 1a to 1 wt%, and the same as in Example 1 using this electrolyte and the negative electrode and positive electrode of Example 1 Thus, a pouch-type lithium secondary battery was prepared.

(Example 5)

An electrolyte was prepared in the same manner as in Example 1 by changing the sulfolane content of Formula 1a to 3 wt%, and the same as in Example 1 using this electrolyte and the negative electrode and the positive electrode of Example 1 Thus, a pouch-type lithium secondary battery was prepared.

(Example 6)

A negative electrode was prepared in the same manner as in Example 1, except that the mixing ratio of artificial graphite and natural graphite was changed to a weight ratio of 7: 3, and the negative electrode, the electrolyte and the positive electrode of Example 1 were used. A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1.

(Example 7)

A negative electrode was prepared in the same manner as in Example 1, except that the mixing ratio of artificial graphite and natural graphite was changed to a weight ratio of 6: 4, and the negative electrode, the electrolyte and the positive electrode of Example 1 were used. A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1.

(Example 8)

A negative electrode was prepared in the same manner as in Example 1, except that the mixing ratio of artificial graphite and natural graphite was changed to a weight ratio of 5: 5, and the negative electrode, the electrolyte and the positive electrode of Example 1 were used. A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1.

(Comparative Example 1)

An electrolyte for a lithium secondary battery was prepared by dissolving 1.3M LiPF ₆ in a non-aqueous organic solvent in which ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed at 10:15:30:45 volume %.

The carbon-based negative active material, styrene-butadiene rubber binder, and carboxymethyl cellulose in which artificial graphite and natural graphite were mixed in an 8:2 weight ratio were mixed in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative electrode active material slurry . The negative electrode active material slurry was coated on a copper foil, dried and rolled to prepare a negative electrode.

96 wt% of LiCoO ₂ cathode active material, 2 wt% of Ketjen black conductive material, and 2 wt% of polyvinylidene fluoride were mixed in N-methylpyrrolidone solvent to prepare a cathode active material slurry. The positive electrode active material slurry was coated on an aluminum foil, dried and rolled to prepare a positive electrode.

Using the electrolyte, the positive electrode and the negative electrode, a 4.4V class pouch-type lithium secondary battery was prepared by a conventional method.

(Comparative Example 2)

1.3M LiPF ₆ was dissolved in a non-aqueous organic solvent in which ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed at 10:15:30:45% by volume, and sulfolane of the following formula 1a was added , an electrolyte for a lithium secondary battery was prepared. In this case, the sulfolane content of the following formula (1a) was 5 wt% based on 100 wt% of the total content of the lithium salt and the non-aqueous organic solvent.

[Formula 1a]

A pouch-type lithium secondary battery was manufactured in the same manner as in Comparative Example 1 using the electrolyte and the negative electrode and positive electrode of Comparative Example 1.

(Comparative Example 3)

A carbon-based material mixed with artificial graphite and natural graphite in a weight ratio of 8: 2, a negative electrode active material of Li ₄ Ti ₅ O ₁₂ , a styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed in a weight ratio of 98:1:1, respectively, and distilled water to prepare a negative electrode active material slurry. In this case, the content of Li ₄ Ti ₅ O ₁₂ was 1 wt% based on 100 wt% of the negative active material. The negative electrode active material slurry was coated on a copper foil, dried and rolled to prepare a negative electrode.

A pouch-type lithium secondary battery was prepared in the same manner as in Comparative Example 1 using the negative electrode, the electrolyte and the positive electrode of Comparative Example 1.

(Comparative Example 4)

A negative electrode was prepared in the same manner as in Comparative Example 3 by changing the content of Li ₄ Ti ₅ O ₁₂ to 2% by weight based on 100% by weight of the total negative electrode active material, and using the electrolyte and positive electrode of Comparative Example 2 A pouch-type lithium secondary battery was manufactured in the same manner as in Comparative Example 1.

(Comparative Example 5)

An electrolyte was prepared by changing the sulfolane content of Formula 1a to 10% by weight based on 100% by weight of the total content of the lithium salt and non-aqueous organic solvent, and using this electrolyte and the negative electrode and positive electrode of 3 for comparison A lithium secondary battery was manufactured in the same manner as in Comparative Example 1.

(Reference Example 1)

A negative electrode was prepared in the same manner as in Example 1, except that the mixing ratio of artificial graphite and natural graphite was changed to a weight ratio of 9: 1, and the negative electrode, the electrolyte and the positive electrode of Example 1 were used. A lithium secondary battery was manufactured in the same manner as in Example 1.

(Reference Example 2)

A negative electrode was prepared in the same manner as in Example 1, except that the mixing ratio of artificial graphite and natural graphite was changed to a weight ratio of 4: 6, and the negative electrode, the electrolyte and the positive electrode of Example 1 were used A lithium secondary battery was manufactured in the same manner as in Example 1.

The content of Li ₄ Ti ₅ O ₁₂ and the sulfolane content of Formula 1 in Examples 1 to 5 and Comparative Examples 1 to 5 are summarized in Table 1 below, and Examples 1, 6 to 8 and the above reference The mixing ratio of the artificial graphite and natural graphite of Examples 1 and 2 and the sulfolane content of Chemical Formula 1 are summarized in Table 2 below.

Li ₄ Ti ₅ O ₁₂ content (wt%) Sulfolane content of Formula 1 (wt%) Comparative Example 1 0 0 Comparative Example 2 0 5 Comparative Example 3 One 0 Comparative Example 4 2 5 Comparative Example 5 One 10 Example 1 One 5 Example 2 0.1 5 Example 3 0.5 5 Example 4 One One Example 5 One 3

Artificial graphite: natural graphite (wt%) Sulfolane content of Formula 1 (wt%) Reference Example 1 9:1 5 Reference Example 2 4:6 5 Example 1 8:2 5 Example 6 7:3 5 Example 7 6:4 5 Example 8 5:5 5

* Direct current internal resistance (DC-IR) evaluation

The lithium secondary batteries prepared in Examples 1 to 8, Comparative Examples 1 to 5, and Reference Examples 1 to 2 were subjected to SOC100 (state of charge, full charge state, total battery charge capacity of 100% at 60°C). When the battery is charged to 100% charging capacity), discharge with a constant current of 10A for 10 seconds, discharge a constant current of 1A for 10 seconds, discharge a constant current of 10A for 4 seconds, and measure the voltage and current values just before storage. , and the battery was stored at 60° C. for 30 days, and voltage and current values were measured.

The DC resistance value was calculated from the data of 18 seconds and 23 seconds by the formula ΔR =ΔV/ΔI. That is, (measured voltage value after 10A 10 sec discharge, 1A 10 sec discharge and 10A 4 sec discharge)-10A 10 sec discharge and 1A 8 sec discharge after 10 sec discharge)/10A current value after 10 sec discharge, 8 sec discharge, saved

The DC resistance value just before storage and the DC resistance value measured after 30 days were calculated by the following formula (1) and obtained.

[Equation 1]

DCIR increase rate = [DCIR(30d.)]/DCIR(0d.) X 100%

In Equation 1, DCIR (30d.) represents DCIR after 30 days, and DCIR (0d.) represents DCIR just before storage.

Among the results, the results of Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Table 3 below, and the results of Examples 6 to 8 and Reference Examples 1 and 2 are shown in Table 4 below. indicated as

* Evaluation of high temperature capacity retention rate

The lithium secondary batteries prepared in Examples 1 to 8, Comparative Examples 1 to 5, and Reference Examples 1 and 2 were CC-CV 0.7C 4.4V 0.05C cut-off charging at 60°C, CC 0.5C 3.0V Charge-discharge was performed 300 times under discharge conditions as a cut-off. A ratio of the 300 discharge capacity to the single discharge capacity was obtained. Among the results, the results of Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Table 3 below, and the results of Examples 6 to 8 and Reference Examples 1 and 2 are shown in Table 4 below. indicated as

High temperature capacity retention rate (%) Resistance increase rate after high temperature storage (%) Comparative Example 1 88.0 136 Comparative Example 2 89.0 133 Comparative Example 3 88.0 134 Comparative Example 4 86.0 140 Comparative Example 5 87.0 138 Example 1 92.0 118 Example 2 90.0 130 Example 3 90.5 127 Example 4 90.5 129 Example 5 91.0 125

High temperature capacity retention rate (%) Resistance increase rate after high temperature storage (%) Reference Example 1 85.0 151 Reference Example 2 86.1 144 Example 1 92.0 118 Example 6 91.0 124 Example 7 89.2 127 Example 8 87.9 129

As shown in Table 3, an electrolyte containing sulfolane of Formula 1 in an amount of 0.1 wt% or more and less than 10 wt% and a negative electrode containing Li ₄ Ti ₅ O ₁₂ in an amount of 0.1 wt% or more and less than 2 wt% was used. It can be seen that the lithium secondary batteries of Examples 1 to 5 exhibited very excellent capacity retention and a low resistance increase rate after high-temperature storage.

On the other hand, the battery of Comparative Example 1 using the electrolyte not containing sulfolane of Formula 1 and the negative electrode not containing Li ₄ Ti ₅ O ₁₂ had a low high-temperature capacity retention rate and a high resistance increase rate after high-temperature storage. In Comparative Examples 2 and 3 containing sulfolane of Formula 1 or Li ₄ Ti ₅ O ₁₂ , the high temperature capacity retention rate was low and the resistance increase rate after high temperature storage was high. In addition, even when an electrolyte containing sulfolane of Formula 1 and a negative electrode containing Li ₄ Ti ₅ O ₁₂ are used, Li ₄ Ti ₅ O ₁₂ is included in an excess of 2 wt% (Comparative Example 4), or Even in the case of including an excess of 10% by weight of eggs (Comparative Example 5), the high temperature capacity retention rate was low and the resistance increase rate after high temperature storage was high.

In addition, as shown in Table 4, an electrolyte containing sulfolane of Formula 1 in an amount of 5% by weight and Li ₄ Ti ₅ O ₁₂ in an amount of 1% by weight, artificial graphite and natural graphite, which are carbon-based materials 8: In the case of Examples 1 and 6 to 8, which were included in a weight ratio of 2 to 5:5, a high capacity retention rate and a low resistance increase rate effect after high temperature storage were obtained. On the other hand, even if the electrolyte containing the sulfolane of Formula 1 and Li ₄ Ti ₅ O ₁₂ at 1 wt % is 1 wt %, artificial graphite and natural graphite, which are carbon-based materials, are mixed in a 9:1 weight ratio or 4:6 weight ratio. In the case of Reference Examples 1 and 2, which includes

In addition, among the obtained results, in order to find out the results for each content of Li ₄ Ti ₅ O ₁₂ (in FIGS. 2 and 3, denoted as LTO), Comparative Examples 1, 2 and 4 and Examples 1 to 3 The capacity retention rate and resistance increase rate results are shown in FIG. 2 . In order to examine the results for each sulfolane content of Formula 1, the measured results of Comparative Examples 1, 3, and 5 and Examples 1, 4 and 5 are shown in FIG. 3 .

As shown in FIG. 2 , as the Li ₄ Ti ₅ O ₁₂ content increased to 1% by weight, the capacity retention rate increased and the resistance increase rate decreased (Examples 2, 3 and 1), while the excess amount was 2% by weight. It can be seen that (Comparative Example 4), the capacity increase rate and the resistance increase rate were significantly deteriorated compared to the case in which the Li ₄ Ti ₅ O ₁₂ content was not included (Comparative Examples 1 and 2) regardless of the presence or absence of sulfolane of Formula 1 (Comparative Examples 1 and 2).

In addition, as shown in FIG. 3 , as the sulfolane content of Formula 1 increases to 5% by weight, the capacity retention rate increases and the resistance increase rate decreases (Examples 4, 5 and 1), whereas in the case of 10% by weight, (Comparative Example 5) It can be seen that the capacity increase rate and resistance increase rate were significantly deteriorated compared to the case in which the sulfolane content of Formula 1 was not included (Comparative Examples 1 and 3) regardless of the presence or absence of Li ₄ Ti ₅ O ₁₂ .

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (7)

An electrolyte comprising a lithium salt, a non-aqueous organic solvent, and an additive comprising a compound represented by the following formula (1);
a negative electrode including a negative active material including a carbon-based material and lithium titanium oxide; and
A positive electrode comprising a positive electrode active material,
The content of the additive including the compound represented by Formula 1 is 0.1 wt% or more and less than 10 wt% based on the total weight of the lithium salt and the non-aqueous organic solvent,
The content of the lithium titanium oxide is 0.1 wt% or more and less than 2 wt% based on the total weight of the negative active material.
[Formula 1]

(In Formula 1,
R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted C2 to C30 alkynyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C3 to C30 cycloalkenyl group, a substituted or unsubstituted C3 to C30 cycloalkynyl group, or a substituted or unsubstituted C6 to C30 aryl group.) According to claim 1,
wherein R ¹ to R ⁸ are each independently a hydrogen atom, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted A lithium secondary battery comprising a C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C3 to C10 cycloalkynyl group, or a substituted or unsubstituted C6 to C10 aryl group. The method of claim 1,
The carbon-based material is a lithium secondary battery of crystalline carbon. The method of claim 1,
The carbon-based material is a lithium secondary battery that is a mixture of artificial graphite and natural graphite. 5. The method of claim 4,
The mixing ratio of the artificial graphite and natural graphite is 8: 2 to 5: 5 weight ratio of a lithium secondary battery. The method of claim 1,
The non-aqueous organic solvent is a lithium secondary battery comprising a propionate-based solvent. According to claim 1,
The lithium titanium oxide is a lithium secondary battery represented by the following formula (2).
[Formula 2]
Li _4+x Ti _y M _z O _t
(In Formula 2, 0 ≤ x ≤ 3, 1 ≤ y ≤ 5, 0 ≤ z ≤ 3, 3 ≤ t ≤ 12, M is Mg, La, Tb, Gd, Ce, Pr, Nd, Sm, Ba, It is an element selected from Sr, Ca, or a combination thereof)

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