KR102414682B1 - Electrolyte and lithium secondary battery with the same - Google Patents

Abstract

상기 화학식 1에서, X, Y, n 및 a는 명세서 중에서 정의한 바와 같다.The present invention relates to an electrolyte and a lithium secondary battery including the same, wherein the electrolyte includes a lithium borate-based compound or a lithium phosphate-based compound represented by the following Chemical Formula 1 as an electrolyte additive, so that the battery characteristics of the lithium secondary battery, particularly the lifespan characteristics and low Resistance characteristics can be improved.
[Formula 1]

In Formula 1, X, Y, n and a is as defined in the specification.

Description

Electrolyte and lithium secondary battery including same

The present invention relates to an electrolyte capable of improving battery characteristics, particularly, lifespan characteristics and low resistance characteristics of a lithium secondary battery, and a lithium secondary battery including the same.

Lithium secondary batteries are used not only as portable power sources for mobile phones, notebook computers, digital cameras, and camcorders, but also as power tools, electric bicycles, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles, etc. Its application is rapidly expanding to medium and large power sources such as HEV and PHEV). The external shape and size of the battery are also changing in various ways according to the expansion of the application field and the increase in demand, and better performance and stability than the characteristics required for the existing small battery are required. In order to meet these demands, the battery components must stably realize the performance of the battery under the condition that a large current flows.

A lithium secondary battery is manufactured by using a material capable of inserting and deintercalating lithium ions as an anode and a cathode, installing a porous separator between the two electrodes, and then injecting a liquid electrolyte, and inserting and deintercalating lithium ions in the anode and cathode Electricity is generated or consumed by redox reactions following desorption.

In order to improve battery characteristics such as output characteristics, cycle characteristics, and storage characteristics of lithium ion batteries, various studies have been made on non-aqueous solvents and additives as electrolyte-equipped components. In addition, even when a specific compound is added to the electrolyte as an additive to improve battery performance, performance improvement of some items of most battery performance can be expected, but there is a problem in that the performance of other items is rather reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrolyte capable of improving battery characteristics, particularly, lifespan characteristics and low resistance characteristics of a lithium secondary battery.

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

In order to achieve the above object, the electrolyte according to an embodiment of the present invention includes a lithium borate compound or a lithium phosphate compound represented by the following Chemical Formula 1 as an electrolyte additive:

[Formula 1]

In Formula 1,

A is B (boron) or P (phosphorus),

X and Y are each independently selected from the group consisting of a hydrogen atom, an alkyl group, a halogen group, and a haloalkyl group,

n is 2 when A is B, and 4 when A is P. and

a represents a single bond or a double bond.

Specifically, in Formula 1, X and Y may each independently be selected from the group consisting of a hydrogen atom, a methyl group, a fluoro group, and a trifluoromethyl group.

The lithium borate compound of Formula 1 may be a compound of Formula 2a or 2b below:

[Formula 2a]

[Formula 2b]

The lithium phosphate-based chemical of Formula 1 may be of Formula 3a or 3b:

[Formula 3a]

[Formula 3b]

The electrolyte may further include an organic solvent and a lithium salt.

A lithium secondary battery according to another embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode disposed opposite to the positive electrode, a negative electrode including a negative electrode active material, and an electrolyte interposed between the positive electrode and the negative electrode, the electrolyte includes a lithium borate compound or a lithium phosphate compound of Formula 1 below as an electrolyte additive:

[Formula 1]

In Formula 1,

A is B (boron) or P (phosphorus),

X and Y are each independently selected from the group consisting of a hydrogen atom, an alkyl group, a halogen group, and a haloalkyl group,

n is 2 when A is B, and 4 when A is P. and

a represents a single bond or a double bond.

Specifically, in Formula 1, X and Y may each independently be selected from the group consisting of a hydrogen atom, a methyl group, a fluoro group, and a trifluoromethyl group.

The lithium borate compound of Formula 1 may be a compound of Formula 2a or 2b below:

[Formula 2a]

[Formula 2b]

The lithium phosphate-based chemical of Formula 1 may be of Formula 3a or 3b:

[Formula 3a]

[Formula 3b]

The electrolyte according to the present invention can improve battery characteristics, particularly, lifespan characteristics and low resistance characteristics of a lithium secondary battery.

1 is an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention.
2 is a graph showing the high temperature life evaluation results of the lithium secondary battery.
3 is a graph showing the results of resistance during evaluation of high-temperature storage characteristics of a lithium secondary battery.
4 is a graph showing the results of the recovery capacity during the evaluation of high-temperature storage characteristics of the lithium secondary battery.

Since the present invention can apply various transformations and can have various embodiments, specific embodiments are illustrated and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, the terms include or have is intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features, number, step , it should be understood that it does not preclude in advance the possibility of the presence or addition of an operation, component, part, or combination thereof.

In the present specification, unless otherwise specified, an alkyl group means a straight-chain or branched alkyl group having 1 to 10 carbon atoms.

In addition, unless otherwise specified in the present specification, a halogen group means a fluoro group, a chloro group, a bromo group, or an iodo group.

In addition, unless otherwise specified in the present specification, the haloalkyl group means an alkyl group having 1 to 20 carbon atoms substituted with a halogen group.

All compounds or substituents may be substituted or unsubstituted unless otherwise specified in the present specification. Here, substituted means that hydrogen is a halogen atom, a hydroxyl group, a carboxy group, a cyano group, a nitro group, an amino group, a thio group, a methylthio group, an alkoxy group, a nitrile group, an aldehyde group, an epoxy group, an ether group, an ester group, a carbonyl group, Substituted with any one selected from the group consisting of an acetal group, a ketone group, an alkyl group, a perfluoroalkyl group, a cycloalkyl group, a heterocycloalkyl group, an allyl group, a benzyl group, an aryl group, a heteroaryl group, derivatives thereof, and combinations thereof means that

The electrolyte according to an embodiment of the present invention includes a lithium borate compound or a lithium phosphate compound represented by Formula 1 below as an electrolyte additive:

[Formula 1]

In Formula 1,

A is B (boron) or P (phosphorus),

X and Y are each independently selected from the group consisting of a hydrogen atom, an alkyl group, a halogen group, and a haloalkyl group,

n is 2 when A is B, and 4 when A is P. and

a represents a single bond or a double bond.

When the lithium borate-based compound and the lithium phosphate-based compound of Formula 1 are used as electrolyte additives, battery characteristics, particularly, lifespan characteristics and low resistance characteristics of a lithium secondary battery can be improved.

Specifically, in Formula 1, X and Y may each independently be selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a halogen group, and a haloalkyl group having 1 to 4 carbon atoms, and Considering the degree of improvement in the effect of improving battery characteristics according to use, in Formula 1, X and Y may each independently be selected from the group consisting of a hydrogen atom, a methyl group, a fluoro group, and a trifluoromethyl group, among which Also, it may be more preferable that X and Y are each independently a fluoro group or a trifluoromethyl group in terms of the remarkable effect of improving battery characteristics.

More specifically, the lithium borate compound of Formula 1 may be a compound of Formula 2a or 2b below:

[Formula 2a]

[Formula 2b]

The lithium phosphate-based compound of Formula 1 may be a compound of Formula 3a or 3b below:

[Formula 3a]

[Formula 3b]

In addition, the lithium borate-based compound and lithium phosphate-based compound of Formula 1 may be included in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, and more preferably 0.1 to 10% by weight based on the total weight of the electrolyte. to 3% by weight.

The electrolyte may further include an organic solvent and a lithium salt in addition to the electrolyte additive described above.

The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, an ester solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an alkoxyalkane solvent, a carbonate solvent, etc. may be used, and among these solvents, one type alone or two or more types may be mixed.

Specific examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, and ethyl propionate. Cypionate (ethyl propionate), γ-butyrolactone (γ-butyrolactone), decanolide (decanolide), γ-valerolactone (γ-valerolactone), mevalonolactone (mevalonolactone), γ-caprolactone (γ -caprolactone), δ-valerolactone, or ε-caprolactone (ε-caprolactone).

Specific examples of the ether-based solvent include dibutyl ether, tetraglyme, 2-methyltetrahydrofuran, or tetrahydrofuran.

Specific examples of the ketone-based solvent include cyclohexanone and the like. Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, chlorobenzene, iodobenzene, toluene, fluorotoluene, or xylene. (xylene) and the like. Examples of the alkoxyalkane solvent include dimethoxy ethane or diethoxy ethane.

Specific examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) , methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenes carbonate (BC), or fluoro and ethylene carbonate (FEC).

Among them, it is preferable to use a carbonate-based solvent as the organic solvent, and more preferably among the carbonate-based solvents, a carbonate-based organic solvent having high ionic conductivity capable of increasing the charge/discharge performance of a battery, and the intrinsic It may be preferable to use a mixture of a carbonate-based organic solvent having a low viscosity that can appropriately adjust the viscosity of the organic solvent of the totality. Specifically, an organic solvent of high dielectric constant selected from the group consisting of ethylene carbonate, propylene carbonate, and mixtures thereof, and an organic solvent of low viscosity selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, and mixtures thereof. It can be used by mixing. More preferably, the high dielectric constant organic solvent and the low viscosity organic solvent are mixed in a volume ratio of 2:8 to 8:2, and more specifically, ethylene carbonate or propylene carbonate; ethyl methyl carbonate; And dimethyl carbonate or diethyl carbonate may be mixed in a volume ratio of 5:1:1 to 2:5:3, and preferably mixed in a volume ratio of 3:5:2.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as the lithium salt, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C _a F _{2a +1} SO ₂ )(C _b F _{2b +1} SO ₂ ), provided that a and b are natural numbers , preferably 1≤a≤20, and 1≤b≤20), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ and mixtures thereof may be used, preferably lithium hexa Fluorophosphate (LiPF ₆ ) is preferably used.

When the lithium salt is dissolved in the electrolyte, the lithium salt functions as a source of lithium ions in the lithium secondary battery, and may promote movement of lithium ions between the positive electrode and the negative electrode. Accordingly, the lithium salt is preferably contained in the electrolyte in a concentration of about 0.6 mol% to 2 mol%. If the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte may be lowered, and thus electrolyte performance may be deteriorated. Considering the conductivity of the electrolyte and the mobility of lithium ions, it may be more preferable that the lithium salt be adjusted to approximately 0.7 mol% to 1.6 mol% in the electrolyte.

In addition to the electrolyte components, the electrolyte may further include additives (hereinafter referred to as other additives) that can be generally used in the electrolyte for the purpose of improving battery life characteristics, suppressing reduction in battery capacity, and improving battery discharge capacity. have.

Specific examples of the other additives include vinylene carbonate (VC), metal fluoride (eg, LiF, RbF, TiF, AgF, AgF ₂ , BaF ₂ , CaF ₂ , CdF ₂ , FeF ₂ , HgF ₂ , Hg ₂ F ₂ , MnF ₂ , NiF ₂ , PbF ₂ , SnF ₂ , SrF ₂ , XeF ₂ , ZnF ₂ , AlF ₃ , BF ₃ , BiF ₃ , CeF ₃ , CrF ₃ , DyF ₃ , EuF ₃ , GaF ₃ , GdF ₃ , FeF ₃ , HoF ₃ , InF ₃ , LaF _{3 , LuF 3 , MnF 3 , NdF 3 , PrF 3 , SbF 3 , ScF 3} , SmF ₃ , TbF ₃ , TiF ₃ , TmF ₃ , YF ₃ , YbF ₃ , TIF ₃ , CeF ₄ , GeF ₄ , HfF ₄ , SiF ₄ , SnF ₄ , TiF ₄ , VF ₄ , ZrF4 ₄ , NbF ₅ , SbF ₅ , TaF ₅ , BiF ₅ , MoF ₆ , ReF ₆ , SF ₆ , WF ₆ , CoF ₂ , CoF ₃ , CrF ₂ , CsF, ErF ₃ , PF ₃ , PbF ₃ , PbF ₄ , ThF ₄ , TaF ₅ , SeF ₆ , etc.), glutaronitrile (GN), Succinonitrile (SN), adiponitrile (AN), 4-tolunitrile (4-tolunitrile), 1,3,6-hexane tricarbonitrile (1,3,6-hexanetricarbonitrile) , propylene sulfide (PS), 3,3'-thiodipropionitrile (TPN), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC) ), difluoroethylene carbonate (difluoroethylenecarbo nate), fluorodimethylcarbonate, fluoroethylmethylcarbonate, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium tetrafluoroborate (lithium) tetrafluoroborate, LiBF ₄ ), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium (malonato oxalato)borate (lithium ( malonato oxalato) borate, LiMOB), lithium difluorophosphate (LiPO ₂ F ₂ ), LiPF ₂ C ₄ O ₈ , LiSO ₃ CF ₃ , LiPF ₄ (C ₂ O ₄ ), LiP(C ₂ O ₄ ) ) ₃ , LiC(SO ₂ CF ₃ ) ₃ , LiBF ₃ (CF ₃ CF ₂ ), LiPF ₃ (CF ₃ CF ₂ ) ₃ , Li ₂ B ₁₂ F ₁₂ , 1,3-propanesultone(1,3-propane sultone), 1,3-propene sultone, biphenayl, cyclohexyl benzene, 4-fluorotoluene, succinoanhydride ( succinic anhydride), ethylene sulfate anhydride, tris(trimethylsilyl)borate, and the like, and may include one type alone or a mixture of two or more thereof. have.

The other additives may be included in an amount of 0.1 to 20% by weight, preferably 0.2 to 5% by weight, based on the total weight of the electrolyte.

According to another embodiment of the present invention, there is provided a lithium secondary battery including the electrolyte. A lithium secondary battery according to an embodiment of the present invention may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the type of separator and electrolyte used, and may be cylindrical, prismatic, coin-type, or pouch-type according to the shape. and the like, and may be divided into a bulk type and a thin film type according to the size. The electrolyte according to the embodiment of the present invention may be particularly excellent for application to a lithium ion battery, an aluminum laminate battery, and a lithium polymer battery.

In detail, the lithium secondary battery includes a positive electrode including a positive electrode active material disposed opposite to each other, a negative electrode including a negative electrode active material, and the electrolyte interposed between the positive electrode and the negative electrode.

1 is an exploded perspective view of a lithium secondary battery 1 according to an embodiment of the present invention. Referring to FIG. 1 , a lithium secondary battery 1 according to another embodiment of the present invention includes a negative electrode 3 , a positive electrode 5 , and a separator 7 between the negative electrode 3 and the positive electrode 5 . to prepare an electrode assembly 9 by placing it, placing it in a case 15, and injecting a non-aqueous electrolyte so that the negative electrode 3, the positive electrode 5 and the separator 7 are impregnated with the electrolyte. have.

Conductive lead members 10 and 13 for collecting current generated during battery operation may be attached to the negative electrode 3 and the positive electrode 5, respectively, and the lead members 10 and 13 are respectively the positive electrode 5 And it is possible to induce the current generated in the negative electrode 3 to the positive and negative terminals.

The positive electrode 5 is manufactured by mixing a positive electrode active material, a conductive agent and a binder to prepare a composition for forming a positive electrode active material layer, applying the composition for forming a positive electrode active material layer on a positive electrode current collector such as aluminum foil, and then rolling can do.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used. Specifically, an olivine-type lithium metal compound represented by the following Chemical Formula 4 may be used.

[Formula 4]

Li _x M _y M' _z XO _{4 - w} Y _w

(In Formula 4, M and M' are each independently Fe, Ni, Co, Mn, Cr, Zr, Nb, Cu, V, Mo, Ti, Zn, Al, Ga, Mg, B, and combinations thereof. is an element selected from the group consisting of, X is an element selected from the group consisting of P, As, Bi, Sb, Mo, and combinations thereof, and Y is selected from the group consisting of F, S, and combinations thereof. element, 0<x≤1, 0<y≤1, 0<z≤1, 0<x+y+z≤2, 0≤w≤0.5)

Among the above compounds, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Mn _(1-x) O ₂ (provided that 0<x<1), LiM _lx M _2y O ₂ (provided that 0≤x≤1, 0≤y≤1, 0≤x+y≤1, M ₁ and M ₂ are each independently selected from the group consisting of Al, Sr, Mg and La one) and mixtures thereof may be preferably used.

The negative electrode 3 is prepared by mixing a negative electrode active material, a binder and optionally a conductive agent in the same manner as the positive electrode 5 to prepare a composition for forming a negative electrode active material layer, and then coating it on a negative electrode current collector such as copper foil. can

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the anode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon. In addition to the carbonaceous material, a metal compound capable of alloying with lithium or a composite including the metal compound and the carbonaceous material may be used as the negative electrode active material.

As the metal capable of alloying with lithium, at least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, and Al alloy may be used. In addition, a metal lithium thin film may be used as the negative electrode active material.

As the negative active material, any one selected from the group consisting of crystalline carbon, amorphous carbon, carbon composite material, lithium metal, lithium-containing alloy, and mixtures thereof in view of high stability may be used.

On the other hand, since the electrolyte is the same as described in the section related to the electrolyte, the description thereof is omitted. Since the lithium secondary battery may be manufactured by a conventional method, a detailed description thereof will be omitted herein. In this embodiment, a pouch-type lithium secondary battery has been described as an example, but the technology of the present invention is not limited to a pouch-type lithium secondary battery, and any shape may be possible as long as it can operate as a battery.

As described above, the lithium secondary battery including the electrolyte according to the embodiment of the present invention can exhibit low DC-IR characteristics, high temperature storage characteristics, and improved output characteristics, so that a fast charging speed is required for mobile phones and notebook computers. It can be useful in portable devices such as computers, digital cameras, and camcorders, in the field of electric vehicles such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), and medium and large energy storage systems. have.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

[ production example : electrolyte and lithium secondary battery Produce]

In the following, LiCoO ₂ as a positive electrode active material as a positive electrode, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, n-methyl-2-pyrrolidone (n-methyl) as a solvent A slurry prepared by mixing -2-pyrrolidone, NMP) was used by coating it on an aluminum (Al) substrate. In addition, a slurry prepared by mixing artificial graphite (mesocarbon microbead) (MCMB) and carbon black as an anode, PVDF as a binder, and NMP as a solvent was coated on a copper (Cu) base material. .

( Example One)

After adding LiPF ₆ to 1.15M to a mixed solution of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DEC) (volume ratio: EC/EMC/DEC = 3/5/2), the obtained An electrolyte solution was prepared by adding 0.25 wt% of lithium borate of the following Chemical Formula 2a as an electrolyte solution additive based on the total weight of the mixed solution. A lithium secondary battery of an aluminum pouch type (Al-pouch type) was prepared using the prepared electrolyte solution and the positive and negative electrodes prepared above.

[Formula 2a]

Product Name: SSB05A

Manufacturer: Suyang Chemtech

( Example 2)

A lithium secondary battery in the form of an aluminum pouch was prepared in the same manner as in Example 1, except that lithium borate of Formula 2b was used instead of the lithium borate compound of Formula 1a in Example 1.

[Formula 2b]

Product Name: SSB05E

Manufacturer: Suyang Chemtech

( comparative example One)

An electrolyte solution was prepared by adding LiPF ₆ to 1.15M to a mixed solution of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DEC) (volume ratio: EC/EMC/DEC = 3/5/2). . A lithium secondary battery in the form of an aluminum pouch was prepared using the prepared electrolyte solution and the positive and negative electrodes prepared above.

( comparative example 2)

Example 1 was carried out in the same manner as in Example 1, except that lithium bis(oxalato)borate of Formula 5 below was used instead of the lithium borate compound of Formula 2a. Thus, a lithium secondary battery in the form of an aluminum pouch was prepared.

[Formula 5]

( comparative example 3)

The same method as in Example 1, except that in Example 1, lithium difluoro(oxalato) borate of Formula 6 below was used instead of the lithium borate compound of Formula 1a was carried out to prepare a lithium secondary battery in the form of an aluminum pouch.

[Formula 6]

[ Experimental example : Capacity evaluation of lithium secondary batteries by additives]

The batteries prepared in Comparative Examples 1 and 2 and Examples 1 and 2 were charged under 910mA/4.35V (CC/CV) conditions, respectively, until the current reached 45mA, and the voltage was 2.7 at a constant current of 910mA (CC). It was discharged until it became V. This process was carried out at room temperature (25° C.) and the results are shown in Table 1 below.

Electrolyte composition discharge capacity
( mAh ) Comparative Example 1 1039.2 Comparative Example 2 955.1 Example 1 1053.9 Example 2 1045.7

As a result, the batteries of Examples 1 and 2 containing lithium borate showed improved discharge capacity compared to the batteries of Comparative Examples 1 and 2.

[ Experimental Example 2 : Evaluation of lifespan characteristics of lithium secondary batteries]

The batteries prepared in Comparative Examples 1 and 2 and Examples 1 and 2 were respectively charged under 910mA/4.35V (CC/CV) conditions until the current reached 45mA, and the voltage was 2.7 at a constant current of 910mA (CC). It was discharged until it became V. This process was repeated 500 times at a high temperature (45° C.) to measure the efficiency (efficiency, %), and the results are shown in Table 2 and FIG. 2 below.

Electrolyte composition 1 cycle discharge capacity
(mAh) 500 cycle discharge capacity
(mAh) efficiency
(%) Comparative Example 1 990.4 55.3 5.6 Comparative Example 2 1009.8 332.5 32.9 Example 1 999.8 622.4 62.3 Example 2 1000.8 568.5 56.8

Referring to Table 2, it was confirmed that the 500-cycle discharge capacity of the batteries of Examples 1 and 2 containing lithium borate was improved by 30 times compared to Comparative Example 1 and 2 times compared to Comparative Example 2, and the efficiency was also improved.

[ Experimental Example 3 : Evaluation of high-temperature storage characteristics of lithium secondary batteries]

The batteries prepared in Comparative Examples 1 to 3 and Examples 1 and 2 were charged to 4.2V under 455mA (CC/CV) conditions, and then left at 60°C for 1 week. After one week, the battery was discharged to 2.7V under the condition of 455mA (CC) and then charged again to 4.2V under the condition of 455mA (CC/CV) to measure the recovery capacity and resistance. The results for the resistance are shown in Table 3 and FIG. 3, and the results for the recovery capacity are shown in Tables 4 and 4.

by parking Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 0 parking 37.1 47.6 38.0 37.1 38.9 1 week 65.9 69.8 64.8 64.6 62.6 2nd week 74.9 76.3 67.7 66.8 69.9 3 weeks 110.0 117.6 102.2 98.8 104.6 4 weeks 128.9 134.9 121.5 116.3 119.5

(Unit: mΩ)

by parking Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 0 parking 908.322 899.165 926.799 920.151 918.678 1 week 850.433 837.411 869.77 854.707 862.011 2nd week 841.265 830.136 852.82 839.213 856.981 3 weeks 767.526 752.634 772.197 771.46 780.992 4 weeks 709.681 721.25 719.9 729.4 742.395

(Unit: mAh)

As a result, Examples 1 and 2 containing lithium borate showed lower resistance properties and excellent recovery capacity compared to Comparative Examples 1 to 3.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

1: lithium secondary battery
3: negative electrode 5: positive electrode
7: separator 9: electrode assembly
10, 13: lead member 15: case

Claims (6)

An electrolyte comprising a lithium borate compound of Formula 1 below:
[Formula 1]

In Formula 1,
A is B (boron),
X and Y are each independently selected from the group consisting of a hydrogen atom, an alkyl group, a halogen group, and a haloalkyl group,
n is 2,
a represents a single bond or a double bond. The method of claim 1,
said X and Y is each independently selected from the group consisting of a hydrogen atom, a methyl group, a fluoro group, and a trifluoromethyl group. According to claim 1,
The lithium borate compound of Formula 1 is an electrolyte which is a compound of Formula 2a or 2b:
[Formula 2a]

[Formula 2b]

The method of claim 1,
The electrolyte further comprises an organic solvent and a lithium salt. A positive electrode comprising a positive electrode active material;
a negative electrode disposed opposite to the positive electrode and including an anode active material; and
It includes an electrolyte interposed between the positive electrode and the negative electrode,
The electrolyte is a lithium secondary battery comprising a lithium borate-based compound of Formula 1:
[Formula 1]

In Formula 1,
A is B (boron),
X and Y are each independently selected from the group consisting of a hydrogen atom, an alkyl group, a halogen group, and a haloalkyl group,
n is 2,
a represents a single bond or a double bond. 6. The method of claim 5,
The lithium borate compound of Formula 1 is a lithium secondary battery that is a compound of Formula 2a or 2b:
[Formula 2a]

[Formula 2b]

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