KR102371079B1 - Electrolyte and lithium secondary battery with the same - Google Patents

Abstract

상기 화학식 1에서, R₁, R₂, 및 X는 명세서 중에서 정의한 바와 같다. The present invention relates to an electrolyte and a lithium secondary battery including the same, wherein the electrolyte contains a phosphonate-based compound of Formula 1 as an electrolyte additive to improve battery characteristics, particularly lifespan characteristics and low resistance characteristics of a lithium secondary battery can do it
[Formula 1]

In Formula 1, R ₁ , R ₂ , and X are 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), and plug-in hybrid electric vehicles. 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 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 phosphonate-based compound of Formula 1 below as an electrolyte additive:

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms,

X is an alkylene group having 1 to 10 carbon atoms.

In addition, in Formula 1, R ₁ and R ₂ may each independently be an alkyl group having 2 to 5 carbon atoms, and X may be an alkylene group having 1 to 5 carbon atoms.

The phosphonate-based compound of Formula 1 may be diethylcyanomethyl phosphonate.

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 phosphonate-based compound represented by the following formula (1):

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms,

X is an alkylene group having 1 to 10 carbon atoms.

The phosphonate-based compound of Formula 1 may be diethyl cyanomethyl phosphonate.

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 evaluation results of the life characteristics of a lithium secondary battery according to an embodiment of the present invention.
3 is a graph showing a result of evaluation of low resistance characteristics of a lithium secondary battery according to an embodiment of the present invention.
4 is a graph showing a result of evaluation of high temperature resistance characteristics of a lithium secondary battery according to an embodiment of the present invention.

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.

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 phosphonate-based compound of Formula 1 below as an electrolyte additive:

[Formula 1]

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms,

X is an alkylene group having 1 to 10 carbon atoms.

In addition, in Formula 1, in consideration of the degree of improvement in the effect of improving battery characteristics according to the use of the electrolyte additive, R ₁ and R ₂ are each independently preferably an alkyl group having 2 to 4 carbon atoms, and an ethyl group having 2 carbon atoms It may be more preferable.

In addition, it may be more preferable that R ₁ and R ₂ are the same in terms of significant improvement effect.

In addition, in Formula 1, when considering the degree of improvement in the effect of improving battery characteristics according to the use of the electrolyte additive, X is preferably an alkylene group having 1 to 5 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms. and, among them, a methylene group having 1 carbon number may be more preferable.

Specifically, the phosphonate-based compound of Chemical 1 may be diethyl cyanomethyl phsphonate.

The electrolyte additive including the phosphonate 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. It may be included in 3 wt%.

When the phosphonate-based compound of Formula 1 is used as an electrolyte additive, it is possible to improve battery characteristics, particularly, lifespan characteristics and low resistance characteristics of a lithium secondary battery.

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 (methylpropylcarbonate, 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 capable of appropriately adjusting 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, and lithium hexafluorophosphate (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. there is.

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. there is.

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. there is.

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 2 may be used.

[Formula 2]

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

(In Formula 2, 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. there is.

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 1: electrolyte and lithium secondary battery Produce]

In the following, _{LiNi 0.6 Mn 0.2} Co _{0.2 O 4} as a positive electrode active material as a positive electrode, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, n as a solvent -Methyl-2-pyrrolidone (n-methyl-2-pyrrolidone, NMP) was mixed and prepared by coating the slurry on an aluminum (Al) substrate was used. 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 1.3M 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 0.5 wt% of diethyl cyanomethyl phosphonate (i) having the following structure 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.

(i)

(i)

( Example 2 to 4)

A battery was manufactured in the same manner as in Example 1, except that in Example 1, a compound as shown in Table 1 below was used in the amount described as an electrolyte additive instead of diethyl cyanomethyl phosphonate. prepared.

Electrolyte Additives chemical formula addition amount
(% by weight based on the total weight of the electrolyte) Example 2 Diethyl 2-cyanoethyl phosphonate
(Diethyl (2-cyanoethyl)phosphonate)

0.5 Example 3 diethyl cyanophosphonate
(Diethyl cyanophosphonate)

0.5 Example 4 Diisopropyl (cyanomethyl) phosphonate
(Diisopropyl(cyanomethyl)phosphonate)

0.5

( comparative example One)

LiPF ₆ 1.3M was added to a mixed solution of ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DEC) (volume ratio: EC/EMC/DEC = 3/5/2) to prepare an electrolyte 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.

( comparative example 2 to 4)

A battery was manufactured in the same manner as in Example 1, except that in Example 1, a compound as shown in Table 2 below was used in the amount described as an electrolyte additive instead of diethyl cyanomethyl phosphonate. prepared.

Electrolyte Additives chemical formula addition amount
(% by weight based on the total weight of the electrolyte) Comparative Example 2 diethyl methylphosphonate
(Diethyl methylphosphonate)

0.5 Comparative Example 3 diethyl ethylphosphonate
(Diethyl ethylphosphonate)

0.5 Comparative Example 4 Diethyl-cyano-fluoro-methylphosphonate
(diethyl-cyanofluoro-methyl-phosphonate)

0.5

[ Experimental example : Evaluation of lifespan characteristics of lithium secondary batteries]

The batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were respectively charged at 925 mAh under CC/CV (1.5C-0.05C) conditions and discharged under CC (1.5C, 2.7V-4.2V) conditions. .

This process was repeated 500 times at room temperature (25° C.) to measure the efficiency (efficiency, %), and the results are shown in Table 3 and FIG. 2 below.

Furtherance 1 cycle discharge capacity (mAh) 500cycle discharge capacity (mAh) efficiency(%) Comparative Example 1 913.9 685.4 75.0 Comparative Example 2 905.4 674.4 74.5 Comparative Example 3 927.0 682.2 73.6 Comparative Example 4 925.1 723.1 78.2 Example 1 925.3 772.5 83.5 Example 2 924.9 769.7 83.2 Example 3 923.7 741.4 80.3 Example 4 923.6 761.1 82.4

Referring to Table 3, it was confirmed that the 500 cycle discharge capacity and efficiency of Examples 1 to 4 containing the phosphonate-based compound as an electrolyte additive were superior to those of Comparative Examples 1 to 4.

[ Experimental example 2: Lithium secondary battery low resistance Characteristic evaluation]

The batteries prepared in Comparative Examples 1 to 4 and Examples 1 to 4 were charged at 925 mAh under CC/CV (0.5C-0.05C) conditions, left at 60°C for 5 weeks, and then discharged DC-IR changes for each week were observed. measured. The results are shown in Table 4 and FIG. 3 .

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Example 1 Example 2 Example 3 Example 4 0 parking 32.1 47.9 46.8 42.0 38.8 39.6 42.1 43.1 1 week 100.3 89.2 115.5 88.7 64.5 76.7 99.1 93.1 2nd week 141.6 176.9 167.0 144.9 106.7 119.6 163.0 166.2 3 weeks 160.8 177.9 178.4 170.2 130.9 131.3 171.6 174.6 4 weeks 189.9 173.3 174.1 178.2 144.9 141.3 161.7 162.1 5 weeks 181.4 163.9 162.6 165.9 142.9 138.1 155.0 153.3

(Unit: mΩ)

Referring to Table 4, as a result of DCIR evaluation after high temperature resistance, it was confirmed that the values of Examples 1 to 4 were lower than those of Comparative Examples 1 to 4. Therefore, it was found that Examples 1 to 4 including the phosphonate-based compound as an electrolyte additive exhibit excellent low resistance properties.

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

The batteries prepared in Comparative Examples 1 to 4 and Examples 1 to 4 were charged at 925 mAh under CC/CV (0.5C-0.05C) conditions, left at 60°C for 5 weeks, and then again using a charger/discharger for each week. The 925 mAh was discharged under CC (0.5C, 2.7V-4.2V) conditions, and was charged under CC/CV (0.5C-0.05C) conditions to measure the change in recovery capacity. The results are shown in Table 5 and FIG. 4 .

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Example 1 Example 2 Example 3 Example 4 0 parking 859.6 874.5 867.1 873.5 882.2 876.5 872.2 872.8 1 week 635.1 744.2 678.4 668.8 718.0 764.1 656.4 626.5 2nd week 604.5 635.2 641.2 587.4 643.6 675.7 576.2 579.1 3 weeks 648.8 662.4 650.8 580.9 700.9 702.5 573.0 638.5 4 weeks 663.8 671.2 670.1 665.8 736.1 713.5 653.4 704.1 5 weeks 679.0 690.1 686.8 712.5 756.4 736.6 712.0 726.1

(Unit: mAh)

As a result, the batteries of Examples 1 to 4 showed improved characteristics even in high-temperature storage evaluation compared to the batteries of Comparative Examples 1 to 4.

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: cathode 5: anode
7: separator 9: electrode assembly
10, 13: lead member 15: case

Claims (6)

It consists of an organic solvent, a lithium salt, and a phosphonate-based compound represented by the following formula (1),
The phosphonate-based compound represented by Formula 1 is diethylcyanomethyl phosphonate, and the electrolyte is included in an amount of 0.1 to 0.5% by weight based on the total weight of the electrolyte:
[Formula 1]

In Formula 1,
R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms,
X is an alkylene group having 1 to 10 carbon atoms. delete delete delete 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 composed of an organic solvent, a lithium salt, and a phosphonate-based compound represented by the following Chemical Formula 1, wherein the phosphonate-based compound represented by Chemical Formula 1 is diethylcyanomethyl phosphonate (diethylcyanomethyl phosphonate). phosphonate), which is included in 0.1 to 0.5% by weight based on the total weight of the electrolyte, a lithium secondary battery:
[Formula 1]

In Formula 1,
R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms,
X is an alkylene group having 1 to 10 carbon atoms. delete

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