Non-aqueous electrolyte composition for lithium secondary battery with improved lifespan, and lithium secondary battery including the same

Abstract

The present invention relates to a non-aqueous electrolyte composition for a lithium secondary battery, which comprises an anhydrosugar alcohol derivative; and a lithium secondary battery comprising the non-aqueous electrolyte composition, and more specifically, to: a non-aqueous electrolyte composition, which comprises a specific amount of an anhydrosugar alcohol derivative as an additive and is capable of providing a lithium secondary battery with improved battery life performance and storage stability; and a lithium secondary battery comprising the non-aqueous electrolyte composition.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte composition for a lithium secondary battery comprising an anhydrosugar alcohol derivative and a lithium secondary battery comprising the same, and more particularly to a non-aqueous electrolyte composition comprising a specific amount of anhydrosugar alcohol derivative as an additive and capable of providing a lithium secondary battery with improved battery life performance and storage stability, and a lithium secondary battery comprising the non-aqueous electrolyte composition. Background Art

[0002] Hydrogenated sugars (also called "sugar alcohols") are compounds obtained by adding hydrogen to the reducing end groups of sugars. Their chemical formula is usually HOCH2(CHOH) n CH2OH, wherein n is an integer of 2 to 5. According to the number of carbon atoms, hydrogenated sugars are divided into tetratetrol, pentatol, hexitol and heptitol (having 4, 5, 6 and 7 carbon atoms, respectively). Among them, hexitols having 6 carbon atoms include sorbitol, mannitol, iditol, galactitol, etc., and sorbitol and mannitol are particularly useful materials.

[0003] Anhydrosugar alcohol has a diol form with two hydroxyl groups in the molecule and can be produced by using hexitol derived from starch (e.g., Korean Patent No. 10-1079518 and Korean Patent Publication No. 10-2012-0066904). Since anhydrosugar alcohol is an environmentally friendly material derived from recyclable natural resources, it has long attracted great interest, and research on its production is also continuing. Among such anhydrosugar alcohols, isosorbide produced from sorbitol currently has the widest industrial applicability.

[0004] Dehydrosugar alcohol can be used in various fields, including the treatment of heart and vascular diseases, drugs such as patches and mouthwashes, solvents for compositions in the cosmetics industry, emulsifiers in the food industry, etc. In addition, it can also increase the glass transition temperature of polymer materials such as polyester, PET, polycarbonate, polyurethane, epoxy resin, etc., and improve the strength of such materials. In addition, since dehydrosugar alcohol is an environmentally friendly material derived from natural resources, it is very useful in the plastics industry, such as bioplastics, etc. It is also known that dehydrosugar alcohol can be used as an environmentally friendly solvent for adhesives, environmentally friendly plasticizers, biodegradable polymers, and water-soluble paints.

[0005] Therefore, anhydrosugar alcohols have received a lot of attention due to their wide applicability, and the level of their practical industrial applications is constantly improving.

[0006] A lithium secondary battery is composed of a case, a cathode and an anode in the case, a membrane (separator) for separating the cathode and the anode, and an electrolyte containing lithium ions.

[0007] Since lithium secondary batteries operate under high driving voltages, non-aqueous organic solvents containing dissolved lithium salts are used to replace aqueous electrolytes that are highly reactive with lithium. As such organic solvents, carbonate solvents are mainly used because they can effectively improve ionic conductivity. Carbonate solvents are divided into cyclic and non-cyclic types. Cyclic carbonates include ethylene carbonate, propylene carbonate, ethyl propylene carbonate, etc., and non-cyclic carbonates include dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, diethyl carbonate, etc.

[0008] During the initial charge of a lithium secondary battery, an irreversible reaction occurs in which a side reaction between the anode / cathode and the electrolyte causes excessive charge usage. Due to the side reaction, a passivation layer such as a solid electrolyte interface (SEI) layer is formed on the surface of the anode, and a protective layer is formed on the surface of the cathode. During the charge / discharge of the battery, the SEI layer inhibits the decomposition of the electrolyte and acts as an ion channel.

[0009] Various additives in electrolytes for forming SEI layers are disclosed (e.g., Korean Patent Publication Nos. 10-2014-0147038 A and 10-2017-0022913 A). However, as disclosed in the above publications, lithium secondary batteries including electrolytes containing phosphonate and / or sulfonate additives have a problem of insufficient life cycle retention rate during repeated charge / discharge of the battery. Summary of the invention

[0010] Problems to be solved

[0011] An object of the present invention is to provide a nonaqueous electrolyte composition that can provide a lithium secondary battery with improved life cycle performance and storage stability, and a lithium secondary battery including the nonaqueous electrolyte composition.

[0012] Technical means

[0013] In order to achieve the above-mentioned object, the present invention provides a non-aqueous electrolyte composition for a lithium secondary battery, comprising: an electrolyte solvent; a lithium salt; and an anhydrosugar alcohol derivative component, the anhydrosugar alcohol derivative component being selected from a diester of anhydrosugar alcohol, a diether of anhydrosugar alcohol or a combination thereof, wherein based on a total of 100 parts by weight of the electrolyte solvent, the composition contains greater than 0.05 parts by weight and less than 7.0 parts by weight of the anhydrosugar alcohol derivative component.

[0014] According to a preferred embodiment of the present invention, the anhydrosugar alcohol derivative component may be one or more compounds selected from the group consisting of the compounds shown in the following formulae 1-3:

[0015] [Formula 1]

[0016]

[0017] [Formula 2]

[0018]

[0019] [Formula 3]

[0020]

[0021] in:

[0022] In the above formula 1, m is an integer of 1-15, and n is an integer of 1-15;

[0023] In the above Formula 2, R is independently a hydrogen atom or a methyl group, x is an integer of 0-10, and y is an integer of 0-10.

[0024] In another aspect, the present invention provides a lithium secondary battery comprising the electrolyte composition of the present invention.

[0025] Effects of the Invention

[0026] The electrolyte composition of the present invention contains an anhydrosugar alcohol derivative selected from the diester of anhydrosugar alcohol, the diether of anhydrosugar alcohol or a combination thereof in a specific content, so when used in a lithium secondary battery, even if no separate additive is used to form the SEI layer, it will form a stable SEI layer and a protective layer on the electrode surface, thereby inhibiting the chemical reaction between the electrode and the electrolyte, thereby improving the life cycle characteristics and storage stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Graphs showing the results of a discharge capacity retention test performed at 45° C. in Examples of the present invention. DETAILED DESCRIPTION

[0028] The present invention is explained in more detail below.

[0029] The electrolyte composition of the present invention contains an electrolyte solvent.

[0030] As the electrolyte solvent, any solvent conventionally used as an electrolyte for lithium secondary batteries can be used, and more specifically, a carbonate solvent can be used.

[0031] As the carbonate solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, etc.; non-cyclic carbonates such as dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, diethyl carbonate, etc.; or combinations thereof can be used.

[0032] According to one embodiment of the present invention, the electrolyte solvent component may be selected from ethylene carbonate, ethyl methyl carbonate, or a combination thereof, and more preferably, a combination of ethylene carbonate and ethyl methyl carbonate may be used.

[0033] In one embodiment, when the electrolyte composition of the present invention comprises a combination of ethylene carbonate and ethyl methyl carbonate as the electrolyte solvent component, the amount of the ethylene carbonate solvent may be 10-50% by volume, more specifically 20-40% by volume, based on the total volume of the electrolyte solvent, and the amount of the ethyl methyl carbonate solvent may be 50-90% by volume, more specifically 60-80% by volume, based on the total volume of the electrolyte solvent.

[0034] The electrolyte composition of the present invention contains a lithium salt.

[0035] As the lithium salt, any lithium salt conventionally used for lithium secondary batteries may be used without limitation.

[0036] In one embodiment, the lithium salt may be one or more compounds selected from LiSCN, LiBr, LiI, LiPF6, LiBF4, LiSbF6, LiAsF6, LiCH3SO3, LiCF3SO3, LiClO4, LiBPh4, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SFO2)2 or LiN(CF3CF2SO2)2, but is not limited thereto. "Ph" herein refers to phenyl.

[0037] The concentration of the lithium salt may be determined in consideration of ionic conductivity, etc., and may be preferably 0.2-2.0 M, or 0.5-1.6 M, but is not limited thereto. If the lithium salt concentration in the electrolyte composition is too low, it is difficult to ensure suitable ionic conductivity for driving the battery. On the contrary, if the lithium salt concentration is too high, the viscosity of the electrolyte increases, so that the mobility of lithium ions may decrease, and the decomposition reaction of the lithium salt itself increases, so that the performance of the battery may decrease.

[0038] The electrolyte composition of the present invention comprises an anhydrosugar alcohol derivative component selected from the group consisting of diesters of anhydrosugar alcohols, diethers of anhydrosugar alcohols, or combinations thereof.

[0039] Anhydrosugar alcohol refers to any substance obtained by removing one or more water molecules from compounds generally called hydrogenated sugars or sugar alcohols, which are obtained by adding hydrogen to the reducing end group of a sugar.

[0040] The anhydrosugar alcohol may be a dianhydrohexitol which is a dehydration product of a hexitol, and more preferably, it may be selected from isosorbide (1,4:3,6-dianhydrosorbitol), isomannide (1,4:3,6-dianhydromannitol), isoidide (1,4:3,6-dianhydroiditol) or a mixture thereof, and most preferably, it may be isosorbide.

[0041] Specifically, the diester of anhydrosugar alcohol can be anhydrosugar alcohol and C1-C 15 Diesters of alkyl carboxylic acids; more specifically, anhydrosugar alcohols and C1-C 12 Diesters of alkyl carboxylic acids; more specifically, diesters of anhydrosugar alcohols and C1-C9 alkyl carboxylic acids; and more specifically, diesters of anhydrosugar alcohols and C1-C7 alkyl carboxylic acids.

[0042] Specifically, the diether of anhydrosugar alcohol can be a di(C1-C4)alkyl ether of anhydrosugar alcohol or anhydrosugar alcohol-alkylene glycol; more specifically, a di(C1-C4)alkyl ether of anhydrosugar alcohol or anhydrosugar alcohol-(C1-C3)alkylene glycol; more specifically, a di(C1-C2)alkyl ether of anhydrosugar alcohol or anhydrosugar alcohol-(C1-C3)alkylene glycol; more specifically, a di(C1)alkyl ether of anhydrosugar alcohol or anhydrosugar alcohol-(C1-C3)alkylene glycol.

[0043] Based on a total of 100 parts by weight of the electrolyte solvent, the electrolyte composition of the present invention comprises an anhydrosugar alcohol derivative component greater than 0.05 parts by weight and less than 7.0 parts by weight. Based on a total of 100 parts by weight of the electrolyte solvent, if the content of the anhydrosugar alcohol derivative is less than 0.05 parts by weight, the performance of the life retention rate and storage stability may be deteriorated. On the contrary, based on a total of 100 parts by weight of the electrolyte solvent, if the amount of the anhydrosugar alcohol derivative component is more than 7.0 parts by weight, the performance of maintaining the battery life may be deteriorated.

[0044] More specifically, based on a total of 100 parts by weight of the electrolyte solvent, the electrolyte composition of the present invention may include 0.06 parts by weight or more, 0.07 parts by weight or more, 0.08 parts by weight or more, 0.09 parts by weight or more, or 0.1 parts by weight or more, and 6.8 parts by weight or less, 6.6 parts by weight or less, 6.4 parts by weight or less, 6.2 parts by weight or less, 6 parts by weight or less, 5.8 parts by weight or less, 5.6 parts by weight or less, 5.4 parts by weight or less, 5.2 parts by weight or less, or 5 parts by weight of the anhydrosugar alcohol derivative component.

[0045] In a preferred embodiment of the present invention, the anhydrosugar alcohol derivative component may be one or more compounds selected from the group consisting of the compounds shown in the following formulae 1-3:

[0046] [Formula 1]

[0047]

[0048] [Formula 2]

[0049]

[0050] [Formula 3]

[0051]

[0052] in:

[0053] In the above formula 1, m is an integer of 1-15, and n is an integer of 1-15;

[0054] In the above Formula 2, R is independently a hydrogen atom or a methyl group, x is an integer of 0-10, and y is an integer of 0-10.

[0055] In the above formula 1, more specifically, m is an integer of 1-12, and n is an integer of 1-12; more specifically, m is an integer of 1-9, and n is an integer of 1-9; more specifically, m is an integer of 1-7, and n is an integer of 1-7.

[0056] In the above formula 2, more specifically, x is an integer of 0-5, and y is an integer of 0-5; more specifically, x is an integer of 0-3, and y is an integer of 0-3.

[0057] In one embodiment, when the electrolyte composition of the present invention includes a compound represented by Formula 1 above as an anhydrosugar alcohol derivative component, its content may be 0.06 to 6.5 parts by weight, more specifically 0.06 to 5.5 parts by weight, and more specifically 0.1 to 5 parts by weight, based on a total of 100 parts by weight of the electrolyte solvent.

[0058] In another embodiment, when the electrolyte composition of the present invention includes a compound represented by Formula 2 above as an anhydrosugar alcohol derivative component, its content may be 0.06 to 6.5 parts by weight, more specifically 0.1 to 5 parts by weight, and more specifically 0.5 to 4 parts by weight, based on a total of 100 parts by weight of the electrolyte solvent.

[0059] In another embodiment, when the electrolyte composition of the present invention includes a compound represented by Formula 3 above as an anhydrosugar alcohol derivative component, its content may be 0.06 to 6.5 parts by weight, more specifically 0.1 to 6 parts by weight, and more specifically 0.5 to 5.5 parts by weight, based on a total of 100 parts by weight of the electrolyte solvent.

[0060] The anhydrosugar alcohol derivative component used in the present invention can form a solid electrolyte interface (SEI) layer on the surface of the anode material through chemical reaction, and the SEI layer improves the performance of maintaining the life cycle and storage stability of the lithium secondary battery by inhibiting the chemical reaction between the electrode and the electrolyte.

[0061] Specifically, in the case where the dehydrosugar alcohol derivative component is used in the electrolyte composition within a specific content range according to the present invention, since the SEI layer is formed on the surface of the anode material with an appropriate thickness, the expansion of the anode material caused by the migration of lithium ions as the anode material repeatedly expands and contracts during continuous charge / discharge can be suppressed, and therefore, the increase in thickness due to the increase in internal pressure can be suppressed, thereby even improving the performance of maintaining the life cycle. However, in the case where the dehydrosugar alcohol derivative component is not used or is used at a content less than the specific content according to the present invention, since the SEI layer is not formed or the SEI layer is slightly formed, the thickness increases due to the increase in internal pressure, and the phenomenon of life cycle degradation may also occur. On the contrary, in the case where the dehydrosugar alcohol derivative component is used at a content greater than the specific content according to the present invention, the SEI layer is formed too firmly, so that even the migration of lithium ions between electrodes is prevented, which may cause the phenomenon of life cycle degradation.

[0062] In addition to the above components, the electrolyte composition of the present invention may further include one or more additives conventionally used in electrolytes for lithium secondary batteries.

[0063] In one embodiment, although not limited thereto, the electrolyte composition of the present invention may further include a metal halide additive.

[0064] As the metal halide additive, metal chloride, metal bromide or metal iodide may be used. In addition, the metal halide additive may be a metal compound having a valence of two or more.

[0065] In one embodiment, the metal halide additive may be one or more compounds selected from magnesium chloride (MgCl2), magnesium bromide (MgBr2) or magnesium iodide (MgI2), but is not limited thereto.

[0066] The concentration of the metal halide additive may be 0.01-1.0 M, or 0.05-1.0 M, or 0.1-1.0 M, or 0.1-0.5 M, but is not limited thereto. If the concentration of the metal halide additive in the electrolyte composition is too low, the effect of enhancing battery performance according to its added amount cannot be fully exhibited. If the concentration of the metal halide additive is too high, the viscosity of the electrolyte increases, so that the mobility of lithium ions may decrease, and thus the battery performance may be deteriorated.

[0067] In one embodiment, although not limited thereto, the electrolyte composition of the present invention may further include inorganic fine particles.

[0068] For the inorganic particles, it is preferred to select non-conductive and electrochemically stable inorganic particles, and more preferably ion-conductive inorganic particles. Specifically, ion-conductive or non-conductive ceramic particles such as α-alumina, β-alumina, γ-alumina, silica, etc. can be used, but not limited thereto.

[0069] According to another aspect of the present invention, a lithium secondary battery comprising the electrolyte composition of the present invention is provided.

[0070] The lithium secondary battery of the present invention is characterized by comprising the electrolyte composition of the present invention, and other components of the lithium secondary battery may include a cathode, an anode, and a membrane (separator) for separating the cathode and the anode, which are generally used for lithium secondary batteries without limitation.

[0071] The lithium secondary battery of the present invention can have a conventional structure. In one embodiment, the lithium secondary battery may include an anode containing lithium metal or a lithium alloy (e.g., an alloy of Li with Si, Sn, In, etc.), a cathode as a porous current collector loaded with a composite metal oxide catalyst, and a diaphragm impregnated with an electrolyte composition between the cathode and the anode.

[0072] As the material of the anode, those materials that can be doped / undoped with lithium ions can be used. Specifically, carbonaceous compounds such as graphite, pyrolytic carbon, coke, glassy carbon, calcined organic polymers, mesophase carbon microspheres, carbon fibers, activated carbon, etc. can be used, but are not limited thereto.

[0073] The cathode may include a composite metal oxide (e.g., a metal oxide such as LiCoO2, LiMn2O4, LiNiO2, LiNiCoO2, manganese dioxide, vanadium pentoxide, chromium oxide, etc., or a metal sulfide such as titanium disulfide, molybdenum disulfide, etc.), and if necessary, a conductive agent (e.g., flake graphite, carbon black, acetylene black, etc.) or a binder (e.g., polyvinylidene fluoride, polytetrafluoroethylene, etc.) may be used. The material of the porous current collector for supporting the composite metal oxide catalyst may be aluminum, nickel, iron, titanium, etc., but is not limited thereto.

[0074] Furthermore, as for the separator placed between the cathode and the anode, a porous film or nonwoven fabric of polyethylene, polypropylene, or the like may be used, but is not limited thereto.

[0075] As for the case of the lithium secondary battery of the present invention, a case of a conventional shape, such as a coin type, a disk type, a cylindrical type, a stacked type, etc., can be used.

[0076] The present invention is explained in more detail by the following examples and comparative examples. However, the scope of the present invention is not limited in any way.

[0077] Example

[0078] <Preparation of Electrolyte Composition and Lithium Secondary Battery>

[0079] [Example 1]

[0080] Preparation of electrolyte composition

[0081] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 30:70 to prepare an electrolyte solvent. Then, based on a total of 100 parts by weight of the electrolyte solvent, 0.1 parts by weight of a compound of formula 1 (m=2, n=2) is added thereto. Then, LiPF6 is dissolved in a mixture of the electrolyte solvent and the compound of formula 1 (m=2, n=2) so that the lithium ion concentration becomes 1.0M, thereby preparing an electrolyte composition for a lithium secondary battery.

[0082] Cathode preparation

[0083] To 100 parts by weight of N-methyl-2-pyrrolidone (NMP) solvent, 40 parts by weight of cathode binder were added to prepare a cathode binder composition. The cathode binder composition was then applied to a cathode current collector (aluminum foil) having a thickness of 100 μm and dried, and then rolled to prepare a cathode. The above cathode binder was prepared by mixing a cathode active material (lithium cobalt composite oxide, LiCoO2), a conductive agent (carbon black) and a binder (polyvinylidene fluoride, PVDF) in a weight ratio of 92:4:4.

[0084] Anode preparation

[0085] To 100 parts by weight of N-methyl-2-pyrrolidone (NMP) solvent, 90 parts by weight of an anode binder was added to prepare an anode binder composition. The anode binder composition was then applied to an anode current collector (copper foil) having a thickness of 90 μm and dried, and then rolled to prepare an anode. The anode binder in the above-mentioned was prepared by mixing natural graphite, a conductive agent (carbon black), a thickener (carboxymethyl cellulose) and a binder (PVDF) in a weight ratio of 96:1:1:2.

[0086] Preparation of lithium secondary batteries

[0087] The cathode and anode prepared above were stacked with a porous polyethylene film to prepare an electrode assembly, and the electrolyte composition prepared above was injected therein to prepare a lithium secondary battery.

[0088] [Example 2]

[0089] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that the amount of the compound of Formula 1 (m=2, n=2) as an additive was changed from 0.1 parts by weight to 2.0 parts by weight during the preparation of the electrolyte composition.

[0090] [Example 3]

[0091] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that the amount of the compound of Formula 1 (m=2, n=2) as an additive was changed from 0.1 parts by weight to 5.0 parts by weight during the preparation of the electrolyte composition.

[0092] [Example 4]

[0093] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that 2.0 parts by weight of the compound of Formula 3 was used instead of 0.1 parts by weight of the compound of Formula 1 (m=2, n=2) as an additive during the preparation of the electrolyte composition.

[0094] [Example 5]

[0095] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that 5.0 parts by weight of the compound of Formula 3 was used instead of 0.1 parts by weight of the compound of Formula 1 (m=2, n=2) as an additive during the preparation of the electrolyte composition.

[0096] [Example 6]

[0097] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that 2.0 parts by weight of the compound of Formula 2 (x=2, y=3, R=H) were used instead of 0.1 parts by weight of the compound of Formula 1 (m=2, n=2) as an additive during the preparation of the electrolyte composition.

[0098] [Example 7]

[0099] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that 1.0 parts by weight of a compound of Formula 2 (x=4, y=5, R=CH3) was used instead of 0.1 parts by weight of a compound of Formula 1 (m=2, n=2) as an additive during the preparation of the electrolyte composition.

[0100] [Comparative Example 1]

[0101] An electrolyte composition and a lithium secondary battery including the electrolyte composition were prepared in the same manner as in Example 1, except that the compound of Formula 1 (m=2, n=2) was not used as an additive during the preparation of the electrolyte composition.

[0102] [Comparative Example 2]

[0103] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that the amount of the compound of Formula 1 (m=2, n=2) as an additive was changed from 0.1 parts by weight to 0.05 parts by weight during the preparation of the electrolyte composition.

[0104] [Comparative Example 3]

[0105] An electrolyte composition and a lithium secondary battery comprising the electrolyte composition were prepared in the same manner as in Example 1, except that the amount of the compound of Formula 1 (m=2, n=2) as an additive was changed from 0.1 parts by weight to 7.0 parts by weight during the preparation of the electrolyte composition.

[0106] The components and their contents in the electrolyte compositions prepared in Examples 1 to 7 and Comparative Examples 1 to 3 above are provided in Table 1 below.

[0107] [Table 1]

[0108]

[0109] -EC: Ethylene carbonate

[0110] -EMC: Ethyl Methyl Carbonate

[0111] -Amount of electrolyte solvent: Based on the total volume of electrolyte solvent

[0112] -Amount of anhydrosugar alcohol derivative: based on 100 parts by weight of the electrolyte solvent in total

[0113] <Performance Evaluation of Lithium Secondary Batteries>

[0114] The performance of the lithium secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 above was evaluated according to the following method, and the results are provided in Table 2 below. In addition, the results of the discharge capacity retention test at 45° C. are shown in Table 2. Figure 1 middle.

[0115] (1) Discharge capacity retention test at 45°C: The lithium secondary batteries prepared in the above Examples 1 to 7 and Comparative Examples 1 to 3 were tested for discharge capacity at 45°C. Specifically, the prepared lithium secondary battery was charged at 500mAh in a constant current-constant voltage mode at 45°C until 4.2V, and the charging was completed when the charging capacity dropped to 50mAh. Ten minutes after the end of charging, the battery was discharged at 500mAh in a constant current mode until 3.0V. The above-mentioned process of charging and discharging once was defined as one cycle, and 200 charge and discharge cycles were performed simultaneously to determine the charge capacity retention rate (life cycle retention rate) relative to the initial charge capacity at 45°C.

[0116] (2) Storage stability at 55° C.: The lithium secondary batteries prepared in the above Examples 1 to 7 and Comparative Examples 1 to 3 were tested for storage stability at 55° C. Specifically, the prepared lithium secondary batteries were stored under a temperature condition of 55° C. for two (2) weeks, and then the thickness increase rate was measured.

[0117] [Table 2]

[0118]

[0119] As described in Table 2 above, in Examples 1 to 7 in which anhydrosugar alcohol derivative compounds are used as additives within the content range specified according to the present invention, the lithium secondary batteries show good charge capacity retention (life cycle retention) relative to the initial charge capacity after 200 cycles (above 96%), and good thickness increase rate after storage at 55°C for two weeks (below 127%).

[0120] On the contrary, when the dehydrated sugar alcohol derivative compound is not used as an additive (Comparative Example 1), or when it is used in an amount less than that specified in the present invention (Comparative Example 2), the lithium secondary battery shows a significantly reduced charge capacity retention rate (life cycle retention rate) relative to the initial charge capacity after 200 cycles, and a poor thickness increase rate (more than 148%) after storage at 55°C for two weeks. In addition, when the dehydrated sugar alcohol derivative compound is used as an additive in an amount greater than that specified in the present invention (Comparative Example 3), the lithium secondary battery shows a lower charge capacity retention rate (life cycle retention rate) relative to the initial charge capacity after 200 cycles compared to this embodiment.

[0121] That is, in the case of using anhydrosugar alcohol derivative compounds as additives within the specific content range according to the present invention, SEI layers are formed by chemical reactions, so that the volume expansion of the lithium secondary battery caused by repeated expansion and contraction during continuous charge / discharge can be suppressed, so that the thickness increase is relatively small, and the life cycle retention rate is improved. However, in the case of not using anhydrosugar alcohol derivative compounds as additives or using less than the specific content according to the present invention, the SEI layer is not formed or slightly formed, so due to the increase in the internal pressure of the battery, the volume of the lithium secondary battery expands, resulting in a significant increase in thickness, and a poor life cycle retention rate. In addition, in the case of using anhydrosugar alcohol derivative compounds as additives with a content greater than the specific content according to the present invention, the SEI layer is formed too firmly, resulting in a decrease in the mobility of lithium ions and a decrease in the life cycle retention rate.

Claims

1. An electrolyte composition for a lithium secondary battery, comprising Electrolyte solvent; lithium salts; and Anhydrosugar alcohol derivative component, wherein the anhydrosugar alcohol derivative component is selected from the diester of anhydrosugar alcohol shown in the following formula 1, the diether of anhydrosugar alcohol shown in the following formula 2, the diether of anhydrosugar alcohol shown in the following formula 3, or a combination thereof, wherein the composition comprises greater than 0.05 parts by weight and less than 7.0 parts by weight of the anhydrosugar alcohol derivative component based on a total of 100 parts by weight of the electrolyte solvent, [Formula 1] [Formula 2] [Formula 3] in, In the above formula 1, m is an integer of 1-15, and n is an integer of 1-15; In the above formula 2, R is independently a hydrogen atom or a methyl group, x is an integer of 0-10, and y is an integer of 0-10, provided that at least one of x and y is not zero. 2 . The electrolyte composition for a lithium secondary battery according to claim 1 , wherein the electrolyte solvent is a carbonate solvent. 3 . The electrolyte composition for a lithium secondary battery according to claim 2 , wherein the carbonate solvent is selected from ethylene carbonate, ethyl methyl carbonate or a combination thereof.

4. The electrolyte composition for a lithium secondary battery according to claim 1, wherein the lithium salt is one or more selected from LiSCN, LiBr, LiI, LiPF6, LiBF4, LiSbF6, LiAsF6, LiCH3SO3, LiCF3SO3, LiClO4, LiBPh4, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(C2F5SO2)2 and LiN(SFO2)2.

5. The electrolyte composition for lithium secondary battery according to claim 1, wherein: The electrolyte composition includes 0.06 parts by weight to 6.5 parts by weight of the compound represented by Formula 1 as the anhydrosugar alcohol derivative component, based on 100 parts by weight of the electrolyte solvent in total.

6. The electrolyte composition for lithium secondary battery according to claim 1, wherein: The electrolyte composition includes 0.06 parts by weight to 6.5 parts by weight of the compound represented by Formula 2 as the anhydrosugar alcohol derivative component, based on 100 parts by weight of the total electrolyte solvent.

7. The electrolyte composition for lithium secondary battery according to claim 1, wherein: The electrolyte composition includes 0.06 parts by weight to 6.5 parts by weight of the compound represented by Formula 3 as the anhydrosugar alcohol derivative component, based on a total of 100 parts by weight of the electrolyte solvent.

8. A lithium secondary battery comprising the electrolyte composition according to any one of claims 1 to 7.

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