Electrolyte solution for lithium secondary battery and lithium secondary battery including same

Abstract

An electrolyte solution for a lithium secondary battery according to the present disclosure includes a lithium salt, an ester-based solvent having a branched alkyl group, and a compound represented by chemical formula 1.

Description

Electrolyte for lithium secondary batteries and lithium secondary batteries including the same

[0001] The present disclosure provides an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same.

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and are used as power sources for small electronic devices such as mobile phones and laptop PCs.

[0003] In particular, lithium-ion batteries offer high operating voltage, energy density, and charging speed, as well as advantages in terms of weight reduction. Accordingly, lithium-ion batteries are being applied as a power source for electric vehicles as well as small electronic devices.

[0004] For example, for lithium secondary batteries to be used as a power source for electric vehicles, they must be equipped with superior output and lifespan characteristics.

[0005] Meanwhile, a lithium secondary battery may include a negative electrode comprising a negative electrode active material (e.g., graphite); a positive electrode comprising a positive electrode active material (e.g., lithium metal oxide particles); and a non-aqueous electrolyte comprising a lithium salt and an organic solvent.

[0006] For example, in a lithium secondary battery, charging and discharging can proceed as the process of lithium ions being inserted and extracted from lithium metal oxide particles and graphite is repeated.

[0007] For example, the output characteristics and lifespan characteristics of a lithium secondary battery can be improved by varying the composition of the electrolyte. For example, the output characteristics of a lithium secondary battery can be improved by enhancing the conductivity of lithium ions. In addition, the lifespan characteristics of a lithium secondary battery can be improved by firmly forming a solid electrolyte interface (SEI) on the negative electrode.

[0008] One objective of the present disclosure is to provide an electrolyte for a lithium secondary battery capable of providing improved electrochemical properties.

[0009] One objective of the present disclosure is to provide a lithium secondary battery comprising the electrolyte for the lithium secondary battery.

[0010] The electrolyte for a lithium secondary battery according to the present disclosure comprises a lithium salt, an ester-based solvent having a branched alkyl group, and a compound represented by the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012]

[0013] In Formula 1, R1 is a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted C3-C7 cycloalkyl group, a substituted or unsubstituted C3-C7 cycloalkenyl group, or -OR1; R2 to R5 are independently a halogen or a substituted or unsubstituted C1-C6 alkyl group; M is an alkali metal; and Y + is a cationic substance.

[0014] In one embodiment, R1 is a substituted or unsubstituted C1-C6 alkyl group or a substituted or unsubstituted C2-C6 alkenyl group; at least one of R2 to R5 is a halogen; M is Li, Na, or K; and Y + is N + RaRbRcRd, and at least one of Ra to Rd may be hydrogen.

[0015] In one embodiment, R1 is a substituted or unsubstituted C2-C6 alkenyl group; R2 to R5 are all halogens; M is Li; and Y + is N + RaRbRcRd, where Ra is hydrogen, and Rb to Rd can be C1-C3 alkyl groups independently of each other.

[0016] In one embodiment, the content of the compound represented by Chemical Formula 1 may be 0.01 to 10 weight percent of the total weight of the electrolyte.

[0017] In one embodiment, the ester-based solvent may include at least one selected from the group consisting of isobutyl acetate, isopropyl acetate, isoamyl acetate, and isononyl acetate.

[0018] In one embodiment, the content of the ester-based solvent may be 1 volume% to 40 volume% of the total volume of the organic solvent. In one embodiment, the electrolyte may further include an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate-based compound, a vinyl group-containing cyclic carbonate-based compound, a vinylene carbonate-based compound, a cyclic sulfate-based compound, a sulfone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, a lactone-based compound, and a sulfonylimide-based compound.

[0019] In one embodiment, the content of the auxiliary additive may be 0.01 to 10 weight percent of the total weight of the electrolyte.

[0020] In one embodiment, the ratio of the content of the auxiliary additive to the content of the compound represented by Formula 1 in the electrolyte may be 0.1 to 10.

[0021] A lithium secondary battery according to exemplary embodiments may include a positive electrode; a negative electrode facing the positive electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte for the lithium secondary battery.

[0022] The electrolyte for a lithium secondary battery according to exemplary embodiments can improve the life characteristics (e.g., repeated charge / discharge capacity retention rate) and output characteristics of the lithium secondary battery.

[0023] Figure 1 shows the three-dimensional structure of the compound of Preparation Example 1 analyzed by SC-XRD (single crystal X-ray diffraction).

[0024] FIGS. 2 and FIGS. 3 are a planar perspective view and a cross-sectional view, respectively, schematically illustrating a lithium secondary battery according to exemplary embodiments.

[0025] FIG. 4 is an external image of a graphite electrode immersed in the electrolyte of Examples 1 to 2 and Comparative Examples 1 to 4.

[0026] FIG. 5 is a graph showing the charge-discharge curves for the lithium secondary batteries of Examples 1 to 2 and Comparative Examples 1 to 4 at 45°C.

[0027] FIG. 6 is a graph showing the charge-discharge curves for the lithium secondary batteries of Examples 1 to 2 and Comparative Examples 1 to 4 at 25°C.

[0028] According to the present disclosure, a lithium-ion battery electrolyte is provided comprising a compound represented by Formula 1 and an acetate-based solvent having a branched alkyl group. Additionally, according to the present disclosure, a secondary battery comprising said electrolyte is provided.

[0029] In this specification, "X-type compound" may mean a compound containing an X unit in a parent group, a side group, or a substituent.

[0030] In this specification, "Ca-Cb" may mean "a to b number of carbon atoms." Additionally, "a 5-7 ring" may mean "a ring having 5 to 7 atoms."

[0031] An electrolyte for a secondary battery according to the present disclosure (hereinafter referred to as an electrolyte) comprises an organic solvent, and the organic solvent comprises an ester-based solvent having a branched alkyl group.

[0032] The above ester-based solvent has a relatively high boiling point, which can improve the high-temperature life performance of the battery and suppress gas generation.

[0033] According to exemplary embodiments, the ester solvent may include a branched alkyl group bonded to the oxygen of an acetate group (CH3-(C=O)-O-).

[0034] According to exemplary embodiments, the branched alkyl group may comprise an alkyl group having 3 to 10 carbon atoms. According to some embodiments, the branched alkyl group may comprise an alkyl group having 4 to 7 carbon atoms. For example, the branched alkyl group may comprise an alkyl group having 4 or 5 carbon atoms.

[0035] According to exemplary embodiments, the ester-based solvent may include isobutyl acetate, isopropyl acetate, isoamyl acetate, isononyl acetate, etc. These may be used alone or in combination of two or more.

[0036] For example, the above ester-based solvent may include isobutyl acetate.

[0037] According to exemplary embodiments, the content of the ester-based solvent may be 1 volume% to 40 volume% of the total volume of the organic solvent. According to some embodiments, the content of the ester-based solvent may be 5 volume% to 35 volume%, 10 volume% to 30 volume%, or 15 volume% to 25 volume% of the total volume of the organic solvent.

[0038] Within the above range, precipitation on the surface of the graphite-containing electrode can be suppressed, and the generation of acid during long-term storage can be reduced.

[0039] The above organic solvent may further include carbonate-based solvents, ester-based (carboxylate-based) solvents having linear alkyl groups, ether-based solvents, ketone-based solvents, alcohol-based solvents, aprotic solvents, etc.

[0040] In some embodiments, the carbonate-based solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

[0041] For example, the above linear carbonate-based solvent may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc.

[0042] For example, the above-mentioned cyclic carbonate-based solvent may include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc.

[0043] In some embodiments, the organic solvent may contain more of the linear carbonate-based solvent than the cyclic carbonate-based solvent by volume.

[0044] For example, among the organic solvents, the volume ratio of the cyclic carbonate-based solvent to the linear carbonate-based solvent may be 1:1 to 9:1, preferably 1.5:1 to 4:1.

[0045] For example, the ester-based solvent having the linear alkyl group may include methyl propionate, ethyl propionate, propyl acetate, butyl acetate, ethyl acetate, etc.

[0046] For example, the above-mentioned cyclic ester solvent may include butyrolactone, caprolactone, valerolactone, etc.

[0047] For example, the above ether-based solvent may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran.

[0048] For example, the above ketone-based solvent may include cyclohexanone, etc.

[0049] For example, the above alcohol-based solvent may include at least one of ethyl alcohol and isopropyl alcohol.

[0050] For example, the aprotic solvent may include at least one of a nitrile-based solvent, an amide-based solvent (e.g., dimethylformamide), a dioxolane-based solvent (e.g., 1,3-dioxolane), and a sulfolane-based solvent.

[0051] In some embodiments, the organic solvent may include the carbonate-based solvent, and the carbonate-based solvent may include at least one of ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC) and diethyl carbonate (DEC).

[0052] The electrolyte for a secondary battery according to the present disclosure (hereinafter abbreviated as electrolyte) comprises a compound represented by the following chemical formula 1.

[0053] [Chemical Formula 1]

[0054]

[0055] In Chemical Formula 1, R1 may be a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or -OR1.

[0056] R2 to R5 may independently be a halogen; or a substituted or unsubstituted C1-C6 alkyl group.

[0057] M is an alkali metal, and Y + It can be a cationic substance.

[0058] For example, the bond between phosphorus (P) and oxygen (O); and the bond between sulfur (S) and oxygen (O) " may indicate that some electrons are delocalized.

[0059] For example, the meaning of "substituted" may imply that a hydrogen atom is replaced by an arbitrary substituent, and that an arbitrary substituent is further bonded to that substituent.

[0060] For example, any of the above substituents may be a halogen, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a C1-C6 alkoxy group, a nitro group, a cyano group, etc. In some embodiments, any of the above substituents may be a halogen or a C1-C6 alkyl group.

[0061] In one embodiment, R1 may be a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group.

[0062] In some embodiments, R1 may be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, R1 may be an unsubstituted C2-C6 alkenyl group.

[0063] In one embodiment, at least one of R2 to R5 is a halogen (e.g., F, Cl, Br, or I). In some embodiments, at least one of R2 to R5 may be F.

[0064] In one embodiment, R2 to R5 may all be halogens. In some embodiments, R2 to R5 may all be F.

[0065] In one embodiment, M may be Li, Na, or K.

[0066] In one embodiment, Y + It may be an alkali metal ion; an ammonium ion; or a primary to quaternary ammonium ion.

[0067] In some embodiments, Y + is N + RaRbRcRd or ReRfN + = It could be RgRh.

[0068] Ra to Rd may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Ra to Rd may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0069] Re to Rh may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Re to Rh may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0070] In some embodiments, Y + is N + RaRbRcRd, and at least one of Ra to Rd may be hydrogen. In some embodiments, Y + is N + RaRbRcRd, where Ra is hydrogen, and Rb to Rd can be C1-C3 alkyl groups independently of each other.

[0071] Accordingly, the cations of the above compound are adsorbed onto the surface of the graphite electrode by electrostatic attraction, thereby suppressing the precipitation of fluorine and the like during the aging process. In addition, the cations can inhibit the hydrolysis of the lithium salt, preventing the generation of hydrogen fluoride (HF), and thereby suppress the corrosion of the electrode and the decomposition of the electrolyte, which can improve long-term battery safety and performance.

[0072] According to exemplary embodiments, a compound of Formula 1 can be prepared by reacting a sulfonate-based salt or a sulfate-based salt with a phosphate-based alkali metal salt.

[0073] In one embodiment, the sulfonate-based salt or sulfate-based salt may be represented by the following chemical formula 2.

[0074] [Chemical Formula 2]

[0075]

[0076] In Formula 2, R1 may be a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkynyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or -OR1. Y + It can be a cationic substance.

[0077] In one embodiment, R1 may be a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group.

[0078] In some embodiments, R1 may be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, R1 may be an unsubstituted C2-C6 alkenyl group.

[0079] In one embodiment, Y + It may be an alkali metal ion; an ammonium ion; or a primary to quaternary ammonium ion.

[0080] In some embodiments, Y + is N + RaRbRcRd or ReRfN + = It could be RgRh.

[0081] Ra to Rd may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Ra to Rd may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0082] Re to Rh may independently be hydrogen; a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group. Additionally, at least two of Re to Rh may be bonded to each other to form a 5-7-membered heterocyclic ring.

[0083] In some embodiments, Y + is N + RaRbRcRd, and at least one of Ra to Rd may be hydrogen. In some embodiments, Y + is N + RaRbRcRd, where Ra is hydrogen, and Rb to Rd can be C1-C3 alkyl groups independently of each other.

[0084] In one embodiment, Ra may be a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group.

[0085] In some embodiments, Ra may be a substituted or unsubstituted C2-C6 alkenyl group. In some embodiments, Ra may be an unsubstituted C2-C6 alkenyl group.

[0086] In one embodiment, the phosphate-based alkali metal salt can be represented by the following chemical formula 3.

[0087] [Chemical Formula 3]

[0088]

[0089] In Chemical Formula 3, R2 and R3 may independently be a halogen (e.g., F, Cl, Br, or I); or a substituted or unsubstituted C1-C6 alkyl group.

[0090] In one embodiment, at least one of R2 and R3 may be a halogen. In some embodiments, at least one of R2 and R3 may be F.

[0091] In one embodiment, R2 and R3 may both be halogens. In some embodiments, R2 and R3 may both be F.

[0092] In one embodiment, a crystal produced by reacting the sulfonate-based salt or sulfate-based salt and the phosphate-based alkali metal salt can be filtered and dried to obtain a compound represented by the chemical formula 1.

[0093] In one embodiment, the reaction temperature may be 10 to 50°C.

[0094] In one embodiment, the molar ratio of the mixture of the sulfonate-based salt or sulfate-based salt and the phosphate-based alkali metal salt may be 1:0.9 to 1:1.1.

[0095] In one embodiment, the compound represented by the chemical formula 1 can be provided as an additive to an electrolyte for a lithium secondary battery.

[0096] A lithium secondary battery according to exemplary embodiments includes an electrolyte for the lithium secondary battery, and thus life characteristics (e.g., repeated charge / discharge capacity retention rate), output characteristics, etc., can be improved.

[0097] For example, the compound represented by Chemical Formula 1 above can be reduced and decomposed at a voltage of about 2.1 V to form a solid electrolyte interface (SEI) film on the surface of the negative electrode. The SEI film can suppress the decomposition of an organic solvent (e.g., ethylene carbonate, etc.) that occurs at a voltage of 2.9 V. Accordingly, the lifespan characteristics of the lithium secondary battery can be improved.

[0098] For example, the compound represented by the above chemical formula 1 can reduce the interface resistance of the positive electrode (100). Accordingly, the output characteristics of the lithium secondary battery can be improved.

[0099] TEA-H of the compound represented by the above chemical formula 1 + Cations are adsorbed onto the surface of the graphite electrode (anode) by electrostatic attraction, and PO2F on the electrode surface 2- , PO2 3- It inhibits the precipitation of component compounds. Also, TEA-H + Cations can improve the safety of the battery and electrolyte by removing or deactivating protic impurities such as water, alcohol, and peroxides in the electrolyte.

[0100] In one embodiment, the content of the compound represented by Formula 1 may be 0.01 to 10 weight%, preferably 0.1 to 7.5 weight%, and more preferably 0.3 to 5 weight% of the total weight of the electrolyte. Within this range, the life characteristics and output characteristics of the lithium secondary battery may be further improved.

[0101] For example, the compound represented by Chemical Formula 1 above may exist as a single unit in the electrolyte, or may exist in the form of a dimer (e.g., see Chemical Formula 4 below, description of substituents omitted), a trimer, a tetramer or more, or a polymer.

[0102] [Chemical Formula 4]

[0103]

[0104] In one embodiment, the electrolyte for the lithium secondary battery may further include an auxiliary additive to further improve the lifespan characteristics and output characteristics of the lithium secondary battery, or to improve high-temperature storage characteristics, etc.

[0105] For example, the above auxiliary additive may include a fluorine-containing cyclic carbonate compound, a vinyl group-containing cyclic carbonate compound, a vinylene carbonate compound, a cyclic sulfate compound, a sulfone compound, a fluorine-containing lithium phosphate compound, a lithium borate compound, a lactone compound, a sulfonylimide compound, etc.

[0106] In some embodiments, the content of the auxiliary additive may be 0.01 to 10 weight%, 0.1 to 7.5 weight%, or 0.3 to 5 weight% of the total weight of the electrolyte. Within this range, the life characteristics, output characteristics, high-temperature storage characteristics, etc., of the lithium secondary battery may be further improved.

[0107] In some embodiments, the ratio of the content of the auxiliary additive to the content of the compound represented by Formula 1 in the total weight of the electrolyte may be 0.1 to 10, preferably 0.1 to 7, more preferably 0.5 to 5.

[0108] For example, the above fluorine-containing cyclic carbonate compound may have a cyclic structure of 5 to 7 members. For example, the above fluorine-containing cyclic carbonate compound may have a fluorine atom directly bonded to a carbon atom, or a fluorine-substituted alkyl group (e.g., -CF3, etc.) bonded thereto.

[0109] In some embodiments, the fluorine-containing cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0110] In some embodiments, the content of the fluorine-containing cyclic carbonate compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0111] In some embodiments, the vinyl group-containing cyclic carbonate compound may include vinyl ethylene carbonate (VEC), etc. Additionally, the vinylene carbonate compound may include vinylene carbonate (VC), etc.

[0112] In some embodiments, the content of the vinyl group-containing cyclic carbonate compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte. Additionally, the content of the vinylene carbonate compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0113] For example, the cyclic sulfate compound may have a 5- to 7-membered cyclic structure. In some embodiments, the cyclic sulfate compound may include ethylene sulfate (ESA), trimethylene sulfate (TMS), methyltrimethylene sulfate (MTMS), 1,3-propanediol cyclic sulfate, etc.

[0114] In some embodiments, the cyclic sulfate compound may include a non-cyclic sulfate compound. In some embodiments, the non-cyclic sulfate compound may include 2,4,8,10-tetraoxa-3,9-dithiaspiro[5.5]undecane 3,3,9,9-tetraoxide, 4,4'-bi(1,3,2-dioxathiolan)] 2,2,2',2'-tetraoxide, etc.

[0115] In some embodiments, the content of the cyclic sulfate compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0116] For example, the sulfonate compound may have a cyclic structure of 5 to 7 members. In some embodiments, the sulfonate compound may include at least one of an alkyl sulfonate compound and an alkenyl sulfonate compound. For example, the alkyl sulfonate compound may have only saturated bonds within the ring, and the alkenyl sulfonate compound may include double bonds within the ring.

[0117] In some embodiments, the alkyl sulfone compound may include 1,3-propane sulfone (PS), 1,4-butane sulfone, etc. Additionally, the alkenyl sulfone compound may include ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, 1-methyl-1,3-propene sulfone, etc.

[0118] In some embodiments, the content of the sulfonate compound may be 0.01 to 2 weight% or 0.1 to 1 weight% with respect to the total weight of the electrolyte.

[0119] For example, the above fluorine-containing lithium phosphate compound may have a fluorine atom directly bonded to a phosphorus atom, or a fluorine-substituted alkyl group (e.g., -CF3) bonded to it.

[0120] In some embodiments, the fluorine-containing lithium phosphate-based compound may include lithium difluorophosphate, lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalato)phosphate (LiPO2F2, LiDFOP), etc.

[0121] In some embodiments, the content of the fluorine-containing lithium phosphate-based compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0122] In some embodiments, the lithium borate-based compound may include lithium tetraphenylborate, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), etc.

[0123] In some embodiments, the content of the lithium borate-based compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0124] In some embodiments, the lactone compound may include at least one of a bicyclolactone compound and a lactone compound containing a double bond within a ring. In some embodiments, the lactone compound may include a muconic lactone, etc.

[0125] In some embodiments, the content of the lactone-based compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0126] In some embodiments, the sulfonyl imide compound may include lithium bis(fluorosulfonyl)imide, etc.

[0127] In some embodiments, the content of the sulfonyl imide compound may be 0.01 to 2 weight% or 0.1 to 1 weight% of the total weight of the electrolyte.

[0128] The electrolyte for a lithium secondary battery according to exemplary embodiments comprises a lithium salt. For example, the lithium salt is Li + X - It can be expressed as.

[0129] In one embodiment, the anion (X) of the lithium salt - ) is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P -, CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It could be the back.

[0130] In some embodiments, the lithium salt may be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, LiN(CF3SO2)2, CF3SO3Li, LiC(CF3SO2)3, etc.

[0131] In one embodiment, the lithium salt may be included in the organic solvent at a concentration of 0.01 to 5 M, preferably 0.01 to 2 M. Within the concentration range, lithium ions and / or electrons can be smoothly transported during charging and discharging of the battery. According to exemplary embodiments of the present disclosure, a lithium secondary battery comprising the electrolyte for the lithium secondary battery is provided.

[0132] Hereinafter, a lithium secondary battery according to exemplary embodiments will be described in more detail with reference to the drawings. FIGS. 2 and 3 are a schematic plan perspective view and a cross-sectional view, respectively, showing a lithium secondary battery according to exemplary embodiments.

[0133] Referring to FIGS. 2 and 3, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) facing the positive electrode (100).

[0134] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) on the positive electrode current collector (105).

[0135] For example, the positive active material layer (110) may include a positive active material, a positive binder and a conductive material as needed.

[0136] For example, the anode (100) can be manufactured by mixing and stirring an anode active material, an anode binder, a conductive material, a dispersion medium, etc. to produce an anode slurry, and then applying, drying, and rolling the anode slurry onto an anode current collector (105).

[0137] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0138] For example, the positive electrode active material may include lithium metal oxide particles capable of reversible insertion and extraction of lithium ions.

[0139] In one embodiment, the lithium metal oxide particles can resist nickel, cobalt, manganese, aluminum, etc.

[0140] In some embodiments, the lithium metal oxide particles contain nickel, and the nickel content in the lithium metal oxide particles may be 80 mol% or more of the total elements excluding lithium and oxygen.

[0141] In some embodiments, the lithium metal oxide particles may be represented by LiNiO2, LiCoO2, LiMnO2, LiMn2O4, or the following chemical formula 5.

[0142] [Chemical Formula 5]

[0143] Li x Ni (1-a-b) Co a M b O y

[0144] In Chemical Formula 5, M is at least one of Al, Zr, Ti, Cr, B, Mg, Mn, Ba, Si, Y, W, and Sr, and 0.9≤x≤1.2, 1.9≤y≤2.1, and 0≤a+b≤0.5.

[0145] In some embodiments, in Formula 5, a and b are 0 <a+b≤0.4, 0<a+b≤0.3, 0<a+b≤0.2 또는 0<a+b≤0.1을 만족할 수 있다.

[0146] For example, the anode binder may include organic binders such as polyvinylidenefluoride (PVDF), vinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, and polymethylmethacrylate; and water-based binders such as styrene-butadiene rubber (SBR). Additionally, for example, the anode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0147] For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; and metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0148] The cathode (130) may include a cathode current collector (125) and a cathode active material layer (120) on the cathode current collector (125).

[0149] For example, the negative electrode active material layer (120) may include a negative electrode active material, a negative electrode binder and a conductive material as needed.

[0150] For example, the cathode (130) can be manufactured by mixing and stirring a cathode active material, a cathode binder, a conductive material, a solvent, etc. to produce a cathode slurry, and then applying, drying, and rolling the cathode slurry onto a cathode current collector (125).

[0151] For example, the negative current collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably may include copper or a copper alloy.

[0152] For example, the above-mentioned negative electrode active material may be a material capable of absorbing and extracting lithium ions. For example, the above-mentioned negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, etc.

[0153] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0154] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0155] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, mesophase pitch-based carbon fiber (MPCF), etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0156] In one embodiment, the negative electrode active material may include a silicon-based active material. For example, the silicon-based active material may be Si, SiO x (0 <x<2), Si / C, SiO / C, Si-Metal 등을 포함할 수 있다.

[0157] The above-described cathode binder and conductive material may be materials substantially identical or similar to the anode binder and conductive material described above. For example, the cathode binder may be a water-based binder such as styrene-butadiene rubber (SBR). Additionally, for example, the cathode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0158] In one embodiment, a separator (140) may be interposed between the anode (100) and the cathode (130).

[0159] In some embodiments, the area of ​​the negative electrode (130) may be larger than the area of ​​the positive electrode (100). In this case, lithium ions generated from the positive electrode (100) can move smoothly to the negative electrode (130) without precipitating in the middle.

[0160] For example, the separator (140) may include a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. Additionally, for example, the separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0161] For example, an electrode cell may be formed including an anode (100), a cathode (130), and a separator (140).

[0162] For example, a plurality of electrode cells may be stacked to form an electrode assembly (150) (however, for convenience, only one electrode cell is shown in FIG. 3).

[0163] For example, an electrode assembly (150) can be formed by winding, lamination, zigzag-folding, etc. of a separator (140).

[0164] A lithium secondary battery according to exemplary embodiments may include a positive electrode lead (107) connected to a positive electrode (100) and protruding outside of a case (160); and a negative electrode lead (127) connected to a negative electrode (130) and protruding outside of a case (160).

[0165] For example, the positive electrode (100) and the positive electrode lead (107) may be electrically connected. Likewise, the negative electrode (130) and the negative electrode lead (127) may be electrically connected.

[0166] For example, the positive lead (107) can be electrically connected to the positive current collector (105). Additionally, the negative lead (130) can be electrically connected to the negative current collector (125).

[0167] For example, the positive current collector (105) may include a protrusion (positive tab, 106) on one side. A positive active material layer (110) may not be formed on the positive tab (106). The positive tab (106) may be integral with the positive current collector (105) or connected by welding or the like. The positive current collector (105) and the positive lead (107) may be electrically connected through the positive tab (106).

[0168] Likewise, the negative current collector (125) may include a protrusion (negative tab, 126) on one side. A negative active material layer (120) may not be formed on the negative tab. The negative tab (126) may be integral with the negative current collector (125) or connected by welding or the like. The negative current collector (125) and the negative lead (127) may be electrically connected through the negative tab (126).

[0169] In one embodiment, the electrode assembly (150) may include a plurality of positive electrodes and a plurality of negative electrodes. For example, the plurality of positive electrodes and the plurality of negative electrodes may be arranged alternately with respect to each other, and a separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). Accordingly, a lithium secondary battery according to one embodiment of the present disclosure may include a plurality of positive electrode tabs and a plurality of negative electrode tabs protruding from each of the plurality of positive electrodes and the plurality of negative electrodes.

[0170] In one embodiment, the positive tabs (or negative tabs) may be laminated, pressed, and welded to form a positive tab laminate (or negative tab laminate). The positive tab laminate may be electrically connected to a positive lead (107). Additionally, the negative tab laminate may be electrically connected to a negative lead (127).

[0171] For example, the electrode assembly (150) and the above-described electrolyte can be housed together in a case (160) to form a lithium secondary battery.

[0172] The above lithium secondary battery can be manufactured in, for example, cylindrical, prismatic, pouch, or coin types.

[0173] Preferred embodiments and comparative examples of the present disclosure are described below. However, the following examples are merely preferred embodiments of the present disclosure, and the present disclosure is not limited to the following examples.

[0174] Preparation Example

[0175] 1,000 g of a solvent mixed with ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7 and 50 g of lithium difluorophosphate (LiPO2F2) were added to a reactor and stirred, and 97 g of triethylammonium ethenesulfonate was added.

[0176] The mixture in the reactor was stirred at room temperature for about 7 hours to carry out the reaction. After the reaction was finished, the resulting crystals were filtered, washed with DMC, and vacuum dried to obtain a white target product (yield about 90%).

[0177] A three-dimensional structural analysis using SC-XRD was performed on the above object and is shown in FIG. 1. The SC-XRD analysis data is shown in Table 1 below.

[0178] Through SC-XRD analysis, it was confirmed that the above target product has the desired structure (chemical formula 6 below).

[0179] [Chemical Formula 6]

[0180]

[0181] Empirical formula C8H 19 F4Li2NO7P2S Chemical formula Weight 425.12 Temperature 223(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P21 / c Unit lattice Dimensions a = 13.4915(13)Å b = 12.5771(13)Å c = 11.0764(11)Å α = 90° β = 96.338(3)° γ = 90° Volume 1868.0(3) Å 3 Z4 density (theoretical value) 1.512 mg / m² 3 Absorption coefficient 0.410 mm -1 F(000)872 Crystal size 0.413 x 0.207 x 0.144 mm 3Data acquisition Theta range 2.220 to 28.389° Exponent range -18<=h<=15, -16<=k<=16, -14<=l<=14 Collected reflections 25372 Independent reflections 4581 [R(int) = 0.0655] Completeness to theta = 25.242° 98.10% Absorption correction Semi-empirical from equivalents Maximum and minimum transmission 0.7457 and 0.5236 Separation method Pre-matrix least-squares data / suppression / variables for F2 4581 / 0 / 233 Goodness of fit for F2 1.078 Final R-index [I>2 sigma(I)] R1 = 0.0587, w R2 = 0.1633 R-index (all data) R1 = 0.0762, w R2 = 0.1797 Absorption Coefficient n / a maximum diffraction peak and hole 1.097 and -0.660 e.Å -3

[0182] Examples and Comparative Examples

[0183] (1) Preparation of electrolyte

[0184] A 1.0 M LiPF6 solution was prepared using a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and isobutyl acetate (IBAc) mixed according to Table 2 below.

[0185] The electrolytes of the examples and comparative examples were prepared by adding additives according to Table 2 below to the above LiPF6 solution based on the total weight of the electrolyte (100 wt%).

[0186] (2) Manufacturing of lithium secondary batteries

[0187] Li(Ni) 0.6 Co 0.2 Mn 0.2 An anode slurry was prepared by dispersing O2, polyvinylidene fluoride (PVdF), and carbon black in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 92:4:4.

[0188] The above anode slurry was applied onto an aluminum foil (thickness: 20 μm) having a protrusion on one side (hereinafter, anode tab) (excluding the protrusion portion), and an anode was manufactured by drying and rolling.

[0189] A cathode slurry was prepared by dispersing crystalline artificial graphite, acetylene black, and PVDF in NMP in a weight ratio of 92:1:7.

[0190] The above cathode slurry was applied onto a copper foil (thickness: 15 μm) having a protrusion on one side (hereinafter, cathode tab) (excluding the protrusion portion), and the cathode was manufactured by drying and rolling.

[0191] A cell was formed by interposing a polyethylene separator (thickness: 20 μm) between the anode and the cathode. An anode lead and a cathode lead were welded and connected to the anode tab and the cathode tab, respectively.

[0192] The cell was housed inside a pouch such that a portion of the positive lead and the negative lead were exposed to the outside.

[0193] A lithium secondary battery was manufactured by injecting an electrolyte into the pouch and sealing the pouch.

[0194] Organic Solvent Additive Type Content (Volume Ratio) Type Content (Weight%) Example 1 EC / EMC / IBAC 20 / 60 / 20 PA 8000 0.5 Example 2 EC / EMC / IBAC 20 / 70 / 10 PA 8000 0.5 Comparative Example 1 EC / EMC 20 / 80 -- Comparative Example 2 EC / EMC / IBAC 20 / 60 / 20 -- Comparative Example 3 EC / EMC / IBAC 20 / 60 / 20 LiDFOP 0.5 Comparative Example 4 EC / EMC / PAC 20 / 60 / 20 PA 8000 0.5

[0195] In Table 2 above, PAC is propylene acetate, and PA800 is a compound represented by Chemical Formula 6 prepared in the above preparation example.

[0196] Experimental Example

[0197] The physical properties of the electrolyte and battery of the examples and comparative examples were evaluated in the following manner, and the results are shown in Tables 3 and 4.

[0198] (1) Electrode immersion evaluation

[0199] Graphite anodes were immersed in the electrolytes of the examples and comparative examples for 3 days, and surface precipitates were examined visually and by scanning electron microscope (SEM).

[0200] FIG. 4 is an external image of a graphite electrode immersed in the electrolyte of Examples 1 to 2 and Comparative Examples 1 to 4.

[0201] (2) Electrolyte time evaluation

[0202] The electrolytes of the examples and comparative examples were left at room temperature (25°C) for 6 days, and the acidity of each electrolyte on day 1, day 3, and day 6 was measured by potentiometric titration.

[0203] Based on the measurement value of Comparative Example 3, the remaining measurements were expressed as percentages.

[0204] (3) Room temperature / high temperature lifespan evaluation

[0205] The batteries of the examples and comparative examples were charged and discharged at a rate of 1C in a voltage range of 3 V to 4.2 V as one cycle, and the discharge capacity was measured after repeating 1000 cycles at room temperature (25℃) or high temperature (45℃).

[0206] Based on the measurement value of Comparative Example 3, the remaining measurements were expressed as percentages.

[0207] Figures 5 and 6 are charge-discharge curves of the example and comparative example at room temperature or high temperature for 1,000 cycles, respectively.

[0208] (4) High-temperature storage evaluation

[0209] 1) Evaluation of thickness and rate of change of open circuit voltage (Open Circuit Voltage; OCV)

[0210] After charging the batteries of the examples and comparative examples to 4.2 V, they were stored at a high temperature (60°C) for one week, and the battery thickness and rate of change were indicated.

[0211] 2) DC Internal Resistance (DCIR)

[0212] The batteries of the examples and comparative examples were charged to 4.2 V at 1C, discharged to SOC 50, and discharged for 10 seconds each at four C-Rates to measure the initial DC resistance. Then, they were charged again to 4.2 V to SOC 100 and stored at a high temperature (60℃) for one week. Afterward, the DC resistance was measured in the same way as the initial DC resistance measurement method.

[0213] Classification Precipitation Presence Time Evaluation (ppm) Life Characteristic Evaluation (mAh) Storage 1 Day Storage 3 Days Storage 6 Days 25℃ 45℃ Example 1 X 27.8 36.2 41.1 715795 Example 2 X 27.0 36.4 42.2 714793 Comparative Example 1 X 26.0 35.9 39.5 709758 Comparative Example 2 X 28.4 40.1 45.2 692770 Comparative Example 3 O 37.0 56.8 68.6 692772 Comparative Example 4 X 29.7 38.8 44.6 700798

[0214] Classification Before High-Temperature Storage After High-Temperature Storage (60℃ for 1 week) Battery Thickness (mm) OCV (V) DCIR (mΩ) Battery Thickness (mm) OCV (V) DCIR (mΩ) Example 15.1 34.1 735 2.3 6.5 34.1 26 6 3.5 Example 25.1 14.1 735 1.6 6.5 74.1 25 6 5.2 Comparative Example 15.0 94.1 735 2.9 6.6 14.1 19 70.7 Comparative Example 25.0 84.1 735 3.8 6.5 74.1 20 6 8.4 Comparative Example 35.1 24.1 735 3.5 6.6 44.1 24 6 7.8 Comparative Example 45.1 04.1 735 5.8 6.5 14.1 25 6 4.3

[0215] Referring to FIGS. 4 to 6 and Tables 2 and 3 above, in the examples, fluorine, copper, etc. were not deposited on the electrode surface due to side reactions between the electrode and the electrolyte.

[0216] In the batteries of the examples, the decrease in battery performance due to transition metal leaching and electrolyte decomposition by acid was suppressed.

[0217] In the examples, the rate of degradation of battery performance was reduced even when stored at high temperatures for a long time.

[0218] On the other hand, in the battery of Comparative Example 3 containing LiDFOP without containing the compound represented by Chemical Formula 1, fluorine, copper, etc. were precipitated due to the degradation of the electrode.

[0219] In the batteries of Comparative Examples 1 to 3 having an electrolyte that does not contain a compound represented by Chemical Formula 1, the effect of battery performance was degraded due to the leaching of transition metals by acid and the decomposition of the electrolyte, and the battery performance was also degraded when stored at high temperatures for a long time.

[0220] In addition, in the battery of Comparative Example 4 having an electrolyte that uses an acetate-based solvent not having a branched alkyl group, the effect of battery performance was degraded due to the leaching of transition metals by acid and the decomposition of the electrolyte, and the DCIR value was particularly degraded during high-temperature storage.

Claims

Lithium salt; An organic solvent comprising an ester-based solvent having a branched alkyl group; and Electrolyte for a lithium secondary battery comprising a compound represented by the following chemical formula 1: [Chemical Formula 1] (In Chemical Formula 1, R1 is a substituted or unsubstituted C1-C6 alkyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C2-C6 alkenyl group; a substituted or unsubstituted C3-C7 cycloalkyl group; a substituted or unsubstituted C3-C7 cycloalkenyl group; or -OR1, and R2 to R5 are independently a halogen; or a substituted or unsubstituted C1-C6 alkyl group, and M is an alkali metal, and Y + is a cationic substance). In claim 1, R1 is a substituted or unsubstituted C1-C6 alkyl group; or a substituted or unsubstituted C2-C6 alkenyl group, and At least one of R2 to R5 is a halogen, and M is Li, Na, or K, and Y + is N + Electrolyte for a lithium secondary battery, wherein RaRbRcRd and at least one of Ra to Rd is hydrogen. In claim 1, R1 is a substituted or unsubstituted C2-C6 alkenyl group, and R2 to R5 are all halogens, and M is Li, and Y + An electrolyte for a lithium secondary battery, wherein N+RaRbRcRd, Ra is hydrogen, and Rb to Rd are independently C1-C3 alkyl groups. An electrolyte for a lithium secondary battery according to claim 1, wherein the content of the compound represented by Chemical Formula 1 is 0.01 to 10 weight% of the total weight of the electrolyte. An electrolyte for a secondary battery according to claim 1, wherein the ester-based solvent comprises at least one selected from the group consisting of isobutyl acetate, isopropyl acetate, isoamyl acetate, and isononyl acetate. An electrolyte for a lithium secondary battery according to claim 1, wherein the content of the ester-based solvent is 1 volume% to 40 volume% of the total volume of the organic solvent. An electrolyte for a lithium secondary battery according to claim 1, further comprising an auxiliary additive comprising at least one of a fluorine-containing cyclic carbonate-based compound, a vinyl group-containing cyclic carbonate-based compound, a vinylene carbonate-based compound, a cyclic sulfate-based compound, a sulfone-based compound, a fluorine-containing lithium phosphate-based compound, a lithium borate-based compound, a lactone-based compound, and a sulfonyl imide-based compound. An electrolyte for a lithium secondary battery according to claim 7, wherein the content of the auxiliary additive is 0.01 to 10 weight% of the total weight of the electrolyte. An electrolyte for a lithium secondary battery according to claim 8, wherein the ratio of the content of the auxiliary additive to the content of the compound represented by Formula 1 in the electrolyte is 0.1 to 10. anode; A negative electrode facing the above positive electrode; A separator interposed between the anode and the cathode; and A lithium secondary battery comprising an electrolyte for a lithium secondary battery according to claim 1.

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