KR102375099B1 - Electrolyte and lithium secondary battery with the same - Google Patents

Abstract

The present invention relates to an electrolyte and a lithium secondary battery including the same, wherein the electrolyte contains lithium alkyl sulfate as an electrolyte additive, thereby improving battery stability and lifespan characteristics of a lithium secondary battery.

Description

Electrolyte and lithium secondary battery including same

The present invention relates to an electrolyte capable of improving battery stability and lifespan 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.

An object of the present invention is to provide an electrolyte capable of improving battery stability and lifespan 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 lithium alkyl sulfate as an electrolyte additive.

The lithium alkyl sulfate may include an alkyl group having 4 to 20 carbon atoms.

The lithium alkyl sulfate may include an alkyl group having 4 to 12 carbon atoms.

The lithium alkyl sulfate may be selected from the group consisting of lithium hexyl sulfate, lithium dodecyl sulfate, and mixtures thereof.

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 silver includes lithium alkyl sulfates.

The lithium alkyl sulfate may be selected from the group consisting of lithium hexyl sulfate, lithium dodecyl sulfate, and mixtures thereof.

The electrolyte according to the present invention can improve battery stability and lifespan 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 efficiency measured at a high temperature (45° C.) of the batteries according to Comparative Example 1 and Examples 1 to 4 of the present invention.
3 is a graph showing low resistance characteristics at high temperature (45° C.) of batteries according to Comparative Examples 1 and 1 to 4 of the present invention.
4 is a graph showing high-temperature storage characteristics at a high temperature (45° C.) of batteries according to Comparative Examples 1 and 1 to 4 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.

Unless otherwise specified herein, 'alkyl' or 'alkyl group' includes a primary alkyl group, a secondary alkyl group, and a tertiary alkyl group, and specifically may be a straight-chain or branched-chain alkyl group having 1 to 20 carbon atoms.

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 hydroxy 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, Any one selected from the group consisting of a carbonyl group, 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 meant to be replaced.

The electrolyte according to an embodiment of the present invention includes lithium alkylsulfate as an electrolyte additive.

In the lithium alkyl sulfate, the alkyl may be an alkyl having 4 to 20 carbon atoms, preferably an alkyl having 4 to 12 carbon atoms.

Specifically, lithium hexyl sulfate or lithium dodecyl sulfate of the lithium alkyl sulfate may be mentioned.

Among the lithium alkyl sulfates described above, in view of the excellent improvement effect, the alkyl is preferably an alkyl having 4 to 11 carbon atoms, more preferably an alkyl having 6 to 11 carbon atoms, and even more preferably lithium hexyl sulfate. .

In addition, the lithium alkyl sulfate 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 haloalkoxy group, a perfluoroalkoxy group, a nitrile group, an aldehyde group , an epoxy group, an ether group, an ester group, a carbonyl group, 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, and combinations thereof It may further include any one substituent selected from.

The above-described lithium alkyl sulfate may be included as an electrolyte additive either alone or as a mixture of two kinds.

The electrolyte additive including lithium alkyl sulfate 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 3% by weight based on the total weight of the electrolyte. there is.

The lithium alkyl sulfate may improve battery stability and lifespan characteristics of a lithium secondary battery, particularly, lifespan characteristics at room temperature (25°C) and high temperature (45°C).

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, 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 1 may be used.

[Formula 1]

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

(In Formula 1, 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, 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. .

( 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.

( 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 0.1 wt% of lithium hexyl sulfate as an electrolyte additive to 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.

( Example 2)

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 0.2 wt% of lithium hexyl sulfate as an electrolyte solution additive based on the total weight of the mixed solution.

( Example 3)

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 0.1 wt% of lithium dodecyl sulfate as an electrolyte additive to 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.

( Example 4)

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 0.2% by weight of lithium dodecyl sulfate as an electrolyte additive to 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.

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

The batteries prepared in Comparative Example 1 and Examples 1 to 4 were respectively charged at 910 mA under CC/CV (1.0C-0.05C) conditions, and discharged under CC (1.0C, 2.7V-4.2V) conditions.

This process was repeated 50 times at a high temperature (45° C.) to measure the efficiency (efficiency, %), and the results are shown in Tables 1 and 2, respectively.

Electrolyte 1 cycle discharge capacity (mAh) 500cycle discharge capacity (mAh) efficiency(%) Comparative Example 1 1053.9 741.8 70.4 Example 1 1039.2 839.3 80.8 Example 2 1039.8 807.8 77.7 Example 3 1046.2 772.9 73.9 Example 4 1045.7 753.3 72.0

Referring to Table 1 and FIG. 2, the batteries of Examples 1 to 4 using the lithium alkyl sulfate additive exhibited excellent lifespan characteristics at high temperature (45° C.) compared to Comparative Example 1, and in particular, using lithium hexyl sulfate. It was confirmed that the batteries of Examples 1 and 2 exhibited better efficiency than Examples 2 and 3 using lithium dodecyl sulfate.

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

After charging the batteries prepared in Comparative Examples 1 and 1 to 4 at 910mA to 4.2V, leaving them at 60°C for 1 week, DC-IR was measured for each parking using a charger/discharger, and after measurement until the 5th week , the results are shown in Table 2 and Figure 3 below.

by parking Comparative Example 1 Example 1 Example 2 Example 3 Example 4 0 parking 48.9 51.8 52.4 51.4 47.4 1 week 82.0 70.0 69.8 83.7 75.7 2nd week 96.6 77.9 77.8 96.6 91.1 3 weeks 85.4 73.6 76.1 84.2 80.2 4 weeks 98.4 86.2 85.5 94.9 92.4 5 weeks 102.7 91.4 91.1 98.4 96.4

(Unit: mΩ)

Referring to Table 2 and FIG. 3 , the DC-IR values of Week 0 were similar to Comparative Examples and Examples, or Examples 1 and 2 showed somewhat higher values. However, in the 1st to 5th weeks, Examples 1 to 4 showed a lower value compared to Comparative Example 1, confirming that the low resistance characteristic was remarkably excellent.

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

After charging the batteries prepared in Comparative Examples 1 and 1 to 4 with a current of 455 mA (0.5 C) to 4.2 V, and leaving them at 60° C. for 1 week, a current of 455 mA (0.5 C) using a charger/discharger After discharging to 3V with a furnace, it was charged again to 4.2V with a current of 455mA (0.5C) to measure the recovery capacity. After the measurement until the 5th week, the results are shown in Tables 3 and 4.

by parking Comparative Example 1 Example 1 Example 2 Example 3 Example 4 0 parking 928.0 921.3 929.7 925.4 932.8 1 week 873.6 894.2 901.7 888.4 903.8 2nd week 850.6 884.5 889.5 873.6 884.1 3 weeks 826.3 867.2 878.7 859.2 862.7 4 weeks 805.6 854.6 868.4 847.6 852.1 5 weeks 786.1 841.1 857.9 829.7 821.9

(Unit: mAh)

Referring to Table 3 and FIG. 4, it was confirmed that the high-temperature storage characteristics of Comparative Examples and Examples 1 to 4 were similar at week 0, but showed a significant difference of 50 or more at week 5. Therefore, it can be seen that the lithium secondary batteries according to Examples 1 to 4 according to the present invention have improved battery stability and lifespan characteristics compared to Comparative Example 1.

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 (7)

lithium alkyl sulfate;
The lithium alkyl sulfate is an electrolyte comprising an alkyl group having 4 to 6 carbon atoms. delete delete The method of claim 1,
wherein the lithium alkyl sulfate is lithium hexyl sulfate. 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 includes lithium alkyl sulfate, and the lithium alkyl sulfate includes an alkyl group having 4 to 6 carbon atoms. 7. The method of claim 6,
wherein the lithium alkyl sulfate is lithium hexyl sulfate.

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