Lithium secondary battery electrolyte and lithium secondary battery with high and low temperature performance

Abstract

The application belongs to the technical field of lithium secondary batteries, and discloses a lithium secondary battery electrolyte with high and low temperature performance and a lithium secondary battery.The electrolyte comprises a non-aqueous solvent, a lithium salt, a triphenyl phosphine alkenyl compound and a compound with a carbonyl group.The electrolyte of the application is formed by the joint action of the triphenyl phosphine alkenyl compound and the compound with a carbonyl group, wherein the triphenyl phosphine alkenyl compound can be reduced in preference to the solvent, and the compound with a carbonyl group can form a thin and uniform SEI film on the positive and negative electrode surfaces of the lithium secondary battery through synergistic action, complex with positive transition metal ions, passivate the positive electrode surface, inhibit metal dissolution, improve the low-temperature rate discharge performance of the battery, and improve the normal temperature and high-temperature cycle life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium secondary batteries, and particularly relates to a lithium secondary battery electrolyte with high and low temperature performance and a lithium secondary battery. BACKGROUND

[0002] With the diversified requirements of battery performance in the fields of electric vehicles, electric tools, start-stop power sources, emergency start power sources and niche products, the performance requirements are different, and lithium ion batteries are gradually developing towards high power and high energy density. In order to meet the large current charge and discharge requirements of high-power batteries, it is usually necessary to add high-concentration lithium salt to increase the lithium ion concentration, which inevitably leads to a significant increase in the viscosity of the electrolyte system, making the wettability of the electrolyte worse, the interfacial impedance larger, the rate cycle degradation more serious, and the overall performance of the battery unable to meet the actual market demand, especially not conducive to the popularization and development of electric vehicles in high-latitude areas. Therefore, it is urgent to develop a power-type electrolyte that can meet the requirements of high and low temperature.

[0003] KR101337608B1 discloses an electrolyte for a lithium secondary battery, which can form a protective film on the surface of an active material under high pressure by adding a triphenyl phosphine olefin compound, thereby preventing side reactions between the active material and the electrolyte and prolonging the charge / discharge life of the battery. It only shows that the triphenyl phosphine olefin compound can improve the high-temperature storage and cycle performance of lithium cobaltate battery systems, and does not show its effect on improving the low-temperature rate discharge performance of lithium secondary batteries.

[0004] Patent CN111162316A discloses a non-aqueous electrolyte, which comprises a lithium salt, an organic solvent and a functional additive, and the functional additive comprises a triphenyl phosphine derivative. By adding the functional additive triphenyl phosphine derivative, the dissolution of metal ions in the positive electrode material can be well inhibited, the positive electrode can be protected, the thickness expansion of the lithium battery can be effectively reduced, and the capacity retention rate of the secondary lithium battery can be improved.

[0005] Patent CN110994029A discloses a sulfone-based high-voltage electrolyte containing a triphenyl phosphine additive, which comprises a triphenyl phosphine additive, a sulfone-based solvent and a lithium salt. The lithium battery containing the electrolyte can form a low-impedance and stable protective film on the surface of the lithium-rich manganese-based positive electrode and the graphite negative electrode during the charge and discharge process, improve the stability of the positive and negative electrode and electrolyte interface, and improve the cycle stability of the lithium ion battery under high voltage conditions. The phosphorus-oxygen double bond compound can also improve the high-temperature safety performance of the battery.

[0006] The above-mentioned patent technologies do not disclose how to improve the low-temperature rate discharge performance of lithium secondary batteries. Therefore, the technical problem to be solved by the present application is how to improve the low-temperature rate discharge performance of the battery while taking into account the high-temperature performance. SUMMARY

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the primary object of the present application is to provide a lithium secondary battery electrolyte with both high and low temperature performance. The triphenyl phosphine alkenyl compound in the electrolyte can be reduced in preference to the solvent, and can form a thin and uniform SEI film on the surface of the lithium secondary battery negative electrode by synergistic effect with the compound having a carbonyl group. The compound can also complex with the positive electrode transition metal ions, passivate the positive electrode surface, inhibit metal dissolution, and improve the low temperature rate discharge performance of the ternary and lithium iron batteries, as well as the room temperature and high temperature cycle life.

[0008] Another object of the present application is to provide a lithium secondary battery containing the above-mentioned electrolyte.

[0009] Still another object of the present application is to provide a method for improving the high temperature performance and low temperature rate discharge performance of a lithium secondary battery using the above-mentioned electrolyte.

[0010] The objects of the present application are achieved by the following technical solutions.

[0011] A lithium secondary battery electrolyte with both high and low temperature performance, the electrolyte comprising:

[0012] a non-aqueous solvent;

[0013] a lithium salt;

[0014] a triphenyl phosphine alkenyl compound; and

[0015] a compound having a carbonyl group;

[0016] The triphenyl phosphine alkenyl compound has the following general structure formula I:

[0017]

[0018] wherein R1 and R2 are each independently any one of H or a C1-C12 hydrocarbon group, a nitrile group, an ester group, a carbonyl group, a phenyl group, or a combination of at least two of the above-mentioned groups.

[0019] Further, the compound having a carbonyl group is at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethoxyethylene carbonate, ethylene carbonate, vinyl ethylene carbonate, diethyl pyrocarbonate, 4,4'-bi-1,3-dioxolan-2,2'-dione, succinic anhydride, maleic anhydride, 2-methyl maleic anhydride, and methyl carbonic acid-2-propargyl ester.

[0020] Further preferably, the triphenyl phosphine alkenyl compound includes at least one of the following structural compounds:

[0021]

[0022]

[0023] The triphenylphosphine alkyl compound added in the present application can be used as a witting reagent, and can react with active functional groups such as carbonyl groups in compounds having carbonyl groups under the catalysis of alkyl lithium, a by-product of electrochemical reaction, to obtain compounds containing unsaturated bonds and triphenylphosphine oxide compounds. The unsaturated double bond compounds can further polymerize to form flexible SEI films, which are beneficial to improve the structure destruction of electrode active materials during the cycle process and improve the cycle stability; and the triphenylphosphine oxide compounds can participate in film formation, and the introduced heteroatoms and large conjugated systems can optimize the composition of the interface film, improve the ionic conductivity of the SEI film, reduce the internal resistance, and improve the battery power performance. At the same time, the quaternary phosphine alkyl ion generated in the reaction process can complex with transition metal ions dissolved from the positive electrode to form stable metal salts, which can relieve the promoting decomposition effect of dissolved metal ions on the electrolyte, and can also improve the structure stability of the positive electrode and improve the cycle performance of the battery. Thus, the performance is different from or better than other triphenylphosphine compounds (such as the triphenylphosphine derivatives or triphenylphosphine additives described in the background art section).

[0024] Further, the added amount of the triphenylphosphine alkyl compound is 0.03% to 0.7% of the mass of the electrolyte; preferably 0.05% to 0.5% of the mass of the electrolyte. When the triphenylphosphine alkyl compound and the compound having a carbonyl group are added in the above range, stable interface films can be formed on the positive and negative electrodes, and the corresponding effects can be produced. Because the amount of the additive is too small, the interface film formed is too thin and has poor stability, and cannot play a protective role for the positive and negative electrodes; but when the additive content is too high, the interface film formed is too thick, which can increase the overall impedance of the battery and affect the battery capacity.

[0025] Further, the added amount of the compound having a carbonyl group is 0.1% to 10% of the mass of the electrolyte.

[0026] Further, the non-aqueous solvent accounts for 50% to 92% of the total mass of the electrolyte, more preferably 52% to 90%, and more preferably 65% to 85%.

[0027] Further preferably, the nonaqueous solvent consists of a cyclic compound and a linear compound; the cyclic compound is selected from at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluorinated ethylene carbonate, fluorinated propylene carbonate, trifluoromethyl ethylene carbonate, and trifluoroethyl ethylene carbonate; and the linear compound is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, trifluoroethyl acetate, difluoroethyl acetate, trifluoroacetic acid ethyl ester, methyl acetate, propylene glycol methyl ether acetate, 2-methoxy-l-propanol acetate, n-propyl acetate, and tri(2-ethylhexyl) trimellitate.

[0028] The above description of the nonaqueous solvent does not mean that the above solvent system cannot contain other types of solvents, and as an electrolyte, commonly used solvents such as cyclic carboxylic acid esters, chain carboxylic acid esters, ether compounds, and sulfone compounds can be added.

[0029] Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone, γ-hexalactone, ε-hexalactone, and the like. The cyclic carboxylic acid ester can prevent a decrease in conductivity, inhibit an increase in negative electrode resistance, and easily achieve a good range of large-current discharge characteristics of the nonaqueous electrolyte secondary battery.

[0030] The chain carboxylic acid ester is preferably a chain carboxylic acid ester having 3 to 7 carbon atoms. Specific examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, isopropyl isobutyrate, and the like. The chain carboxylic acid ester can inhibit an increase in negative electrode resistance, and easily achieve a good range of large-current discharge characteristics and cycle characteristics of the nonaqueous electrolyte battery.

[0031] The ether compound is preferably a linear ether having 3 to 10 carbon atoms, in which part of the hydrogen is optionally replaced with fluorine, and a cyclic ether having 3 to 6 carbon atoms. As the linear ether having 3 to 10 carbon atoms, there are mentioned diethyl ether, di(2-fluoroethyl) ether, di(2,2-difluoroethyl) ether, di(2,2,2-trifluoroethyl) ether, ethyl(2-fluoroethyl) ether, ethyl(2,2,2-trifluoroethyl) ether, ethyl(l,l,2,2-tetrafluoroethyl) ether, (2-fluoroethyl)(2,2,2-trifluoroethyl) ether, (2-fluoroethyl)(l,l,2,2-tetrafluoroethyl) ether, (2,2,2-trifluoroethyl)(l,l,2,2-tetrafluoroethyl) ether, ethyl-n-propyl ether, ethyl(3-fluoro-n-propyl) ether, ethyl(3,3,3-trifluoro-n-propyl) ether, ethyl(2,2,3,3-tetrafluoro-n-propyl) ether, ethyl(2,2,3,3,3-pentafluoro-n-propyl) ether, 2-fluoroethyl-n-propyl ether, (2-fluoroethyl)(3-fluoro-n-propyl) ether, (2-fluoroethyl)(3,3,3-trifluoro-n-propyl) ether, (2-fluoroethyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (2-fluoroethyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, 2,2,2-trifluoroethyl-n-propyl ether, (2,2,2-trifluoroethyl)(3-fluoro-n-propyl) ether, (2,2,2-trifluoroethyl)(3,3,3-trifluoro-n-propyl) ether, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (2,2,2-trifluoroethyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, l,l,2,2-tetrafluoroethyl-n-propyl ether, (l,l,2,2-tetrafluoroethyl)(3-fluoro-n-propyl) ether, (l,l,2,2-tetrafluoroethyl)(3,3,3-trifluoro-n-propyl) ether, (l,l,2,2-tetrafluoroethyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (l,l,2,2-tetrafluoroethyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, di-n-propyl ether, (n-propyl)(3-fluoro-n-propyl) ether, (n-propyl)(3,3,3-trifluoro-n-propyl) ether, (n-propyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (n-propyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, di(3-fluoro-n-propyl) ether, (3-fluoro-n-propyl)(3,3,3-trifluoro-n-propyl) ether, (3-fluoro-n-propyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (3-fluoro-n-propyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, di(3,3,3-trifluoro-n-propyl) ether, (3,3,3-trifluoro-n-propyl)(2,2,3,3-tetrafluoro-n-propyl) ether, (3,3,3-trifluoro-n-propyl)(2,2,3,3,3-pentafluoro-n-propyl) ether, di(2,2,3,3-tetrafluoro-n-propyl) ether, (2,2,3,3-tetrafluoro-n-propyl)(2,2,3,3,3-pentafluoro-n-propyl) ether,3-pentafluoro-n-propyl) ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, methoxy(2-fluoroethoxy)methane, methoxy(2,2,2-trifluoroethoxy)methane, methoxy(l, 1,2,2-tetrafluoroethoxy)methane, diethoxymethane, ethoxy(2-fluoroethoxy)methane, ethoxy(2,2,2-trifluoroethoxy)methane, ethoxy(l, 1,2,2-tetrafluoroethoxy)methane, di(2-fluoroethoxy)methane, (2-fluoroethoxy)(2,2,2-trifluoroethoxy)methane, (2-fluoroethoxy)(l, 1,2,2-tetrafluoroethoxy)methane, di(2,2,2-trifluoroethoxy)methane, (2,2,2-trifluoroethoxy)(l, 1,2,2-tetrafluoroethoxy)methane, di(l, 1,2,2-tetrafluoroethoxy)methane, dimethoxyethane, methoxyethoxyethane, methoxy(2-fluoroethoxy)ethane, methoxy(2,2,2-trifluoroethoxy)ethane, methoxy(l, 1,2,2-tetrafluoroethoxy)ethane, diethoxyethane, ethoxy(2-fluoroethoxy)ethane, ethoxy(2,2,2-trifluoroethoxy)ethane, ethoxy(l, 1,2,2-tetrafluoroethoxy)ethane, di(2-fluoroethoxy)ethane, (2-fluoroethoxy)(2,2,2-trifluoroethoxy)ethane, (2-fluoroethoxy)(l, 1,2,2-tetrafluoroethoxy)ethane, di(2,2,2-trifluoroethoxy)ethane, (2,2,2-trifluoroethoxy)(l, 1,2,2-tetrafluoroethoxy)ethane, di(l, 1,2,2-tetrafluoroethoxy)ethane, ethyleneglycol di-n-propyl ether, ethyleneglycol di-n-butyl ether, diethyleneglycol dimethyl ether, and the like; as the cyclic ether having 3 to 6 carbon atoms, there can be mentioned tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-l,3-dioxolane, 4-methyl-l,3-dioxolane, 1,4-dioxolane, and the like, and fluorinated compounds thereof; in the case where the negative electrode active material is a carbonaceous material, the ether compound is apt to be co-intercalated with lithium ions, resulting in a capacity decrease, but the problem can be avoided in the presence of the auxiliary solvent.

[0032] The sulfone compound can be selected from dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl n-butyl sulfone, trifluoroethyl t-butyl sulfone, trifluoromethyl n-butyl sulfone, trifluoromethyl t-butyl sulfone, and the like. In the presence of the sulfone compound as an auxiliary solvent, the cycle performance and cycle retention performance of the battery can be improved, the solution viscosity can be reduced, and the electrochemical performance can be improved.

[0033] Further, the lithium salt is preferably at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiTDI, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, LiPF4C2O4, and lithium perfluorobutylsulfonate.

[0034] As the lithium salt in the nonaqueous electrolyte of the present application, there is no particular limitation as long as it is a publicly known lithium salt used in this use, and any of the following lithium salts can be arbitrarily used:

[0035] Inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, and the like; lithium tungstate such as LiWOF5;

[0036] Carboxylic acid lithium salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li, and the like;

[0037] Sulfonic acid lithium salts such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, and the like;

[0038] LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethane disulfonimide, lithium cyclic 1,3-perfluoropropane disulfonimide, LiN(CF3SO2)(C4F9SO2), and the like imide lithium salts;

[0039] LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, and the like methylated lithium salts;

[0040] lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, and the like lithium oxalato borate salts;

[0041] lithium difluoro bis(oxalato)phosphate, lithium tris(oxalato)phosphate, and the like lithium oxalato phosphate salts;

[0042] LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, and the like fluorine-containing organic lithium salts; and the like.

[0043] The above lithium salts can be used alone or in combination of two or more.

[0044] Further, the lithium salt is 8% to 25% of the total mass of the electrolyte. Generally, the concentration of the lithium salt used in the art is 0.5 to 3 M; preferably, the concentration of the lithium salt is 0.8 to 2.5 M; preferably, the concentration of the lithium salt is 1 to 2 M; preferably, the concentration of the lithium salt is 1 to 1.5 M. In practical applications, the amount of lithium salt can be more, such as up to 35%, which is also potentially possible.

[0045] Further, in the above electrolyte, in addition to the above-mentioned solvent, lithium salt, triphenylphosphine alkyl compound, and compound having a carbonyl group, an additive can be further included; the additive includes at least one of vinyl sulfate, propylene carbonate, 1,3-propane sulfite, 1,3-propylene sulfite, 1,4-butane sulfite, 2,4-butane sulfite, tetraethylenesilane, divinyltetramethyldisilazane, divinyltetramethyldisiloxane, triallylisocyanurate, hexamethylenediisocyanate, o-phenanthroline, p-phenylenediisocyanate, 2,4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, bisvinyl sulfate, methylsulfate, bispropylene sulfite, hydroquinone difluorosulfonate, triallyl phosphate, tripropargyl phosphate, 2,4-butane sulfite, isocyanatoethyl methacrylate, methanedi sulfite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(vinyl dimethylsilyl)phosphate, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate, (2-allylphenoxy)trimethylsilane, 1-p-tolylsulfonylimidazole, tetramethylenemethylene diphosphate, isocyanatoethyl methacrylate, 2-fluoropyridine, ethoxy pentafluorocyclophosphazene, trifluoroethoxy pentafluorocyclophosphazene, 2-phenyl-1-yl 1H-imidazole-1-sulfonate.

[0046] The additive is 0.1% to 10% of the total mass of the electrolyte.

[0047] Meanwhile, the present application also discloses a lithium secondary battery containing the above-mentioned electrolyte, the lithium secondary battery comprising:

[0048] a positive electrode;

[0049] a negative electrode;

[0050] a separator disposed between the positive electrode and the negative electrode; and

[0051] The lithium secondary battery electrolyte as described in any one of the above.

[0052] Further, the lithium secondary battery has a charge cut-off voltage of not less than 4.2V.

[0053] Further, the positive electrode includes, but is not limited to, Li 1+a (Ni x Co y M 1-x-y )O2, Li(Ni p Mn q Co 2-p-q )O4, and LiM h (PO4) mone or more of the following: wherein 0≤a≤0.3, 0≤x≤1, 0≤y≤1, 0

[0054] The negative electrode is preferably at least one of graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-carbon composite. However, the negative electrode material can be any of various conventionally known materials that can be used as an active material of a negative electrode of an electrochemical device, without being limited thereto.

[0055] The separator is a separator film that is conventionally known in the art and that can be used in an electrochemical device and is stable to the electrolyte used, such as, but not limited to, a resin, glass fiber, ceramic, and the like. For example, the separator film includes at least one of a polyolefin, an aromatic polyamide, polytetrafluoroethylene, a polyether sulfone. Preferably, the polyolefin includes at least one of polyethylene, polypropylene. Preferably, the polyolefin includes polypropylene. Preferably, the separator film is laminated with a plurality of material layers, such as, for example, a three-layer separator film that is laminated in the order of polypropylene, polyethylene, polypropylene, or an inorganic material separator film coated with a film of the above-mentioned organic material, and the like.

[0056] Finally, the present application also provides a method for improving the high-temperature performance and the low-temperature rate discharge performance of a lithium secondary battery using the above-mentioned electrolyte; the method includes: adding the electrolyte as claimed in any one of the above to a lithium secondary battery.

[0057] Compared with the prior art, the present application has the following advantages:

[0058] (1) The electrolyte of the present application can improve the low-temperature rate discharge performance of a lithium ion battery, and improve the normal-temperature and high-temperature rate cycle life, through the synergistic effect of the triphenylphosphine alkenyl compound additive and the compound having a carbonyl group.

[0059] (2) Since the triphenylphosphine alkenyl compound additive can undergo a reduction reaction preferentially over the solvent, and the compound having a carbonyl group can form a thin and uniform SEI film with flexibility on the surface of the negative electrode of a lithium secondary battery through synergistic effect, while passivating the surface of the positive electrode, so that the above-mentioned lithium secondary battery has good low-temperature rate discharge performance and rate cycle life. DETAILED DESCRIPTION

[0060] The present application will be further described in detail below with reference to the examples, but the embodiments of the present application are not limited thereto.

[0061] The following abbreviations are used for the materials used in the examples and comparative examples: succinic anhydride (SA), fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO2F2), vinyl sulfonate (DTD), 4,4'-bisoxyvalerolactone-2,2'-dione (bis-EC), tris(dimethylvinylsilyl)phosphate (DMVSP), trifluoroethoxyethylene carbonate (TFEEC), 2-methylmaleic anhydride (CA), ethylene carbonate (VC), trispirosulfonate propylene (TDS), vinyl ethylene carbonate (VEC), maleic anhydride (MA), hexamethylene diisocyanate (HDI), succinonitrile (SN), tris(trimethylsilyl)borate (TMSB).

[0062] Example 1

[0063] In this example, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a glove box in a mass ratio of 3:7. Then, 85.5 g of the mixed solution was taken, and 12.5 g of LiPF6, 1.5 g of vinyl sulfonate (DTD), and 0.5 g of lithium difluorophosphate (LiPO2F2) were sequentially added to prepare 100 g of a base electrolyte. Then, 0.2 g of the triphenylphosphine alkene compound of compound 4, 0.3 g of succinic anhydride (SA), and 2.0 g of fluoroethylene carbonate (FEC) were added to obtain a power-type lithium secondary battery electrolyte.

[0064] The obtained power-type lithium secondary battery electrolyte was combined with a lithium ion battery positive electrode material LiNi 0.33 Co 0.33 Mn 0.33 O2, an artificial graphite negative electrode material, and a polyethylene film coated ceramic separator to assemble a soft pack laminate lithium secondary battery by a conventional method after liquid injection.

[0065] Examples 2 to 13 and Comparative Examples 1 to 13

[0066] The electrolytes were prepared according to the component compositions in Table 1, and soft pack laminate lithium secondary batteries were assembled according to the method of Example 1.

[0067] Table 1: Composition of electrolytes for examples and comparative examples

[0068]

[0069]

[0070] The lithium secondary batteries obtained in Examples 1 to 13 and Comparative Examples 1 to 13 were tested for normal temperature cycle, high temperature cycle, and low temperature discharge performance, and the test method was as follows:

[0071] 1. Room temperature cycle performance: the lithium secondary battery was placed in a room temperature condition, charged to 4.2V at a current of 3C, then discharged to 2.7V at a current of 3C, cycled for 500 times, and the capacity retention rate of the lithium secondary battery was determined.

[0072] Capacity retention rate = (500th discharge capacity / first discharge capacity) x 100%.

[0073] 2. High temperature cycle performance: the lithium secondary battery was placed in a constant temperature oven at 45°C, charged to 4.2V at a current of 3C, then discharged to 2.7V at a current of 3C, cycled for 500 times, and the capacity retention rate of the lithium secondary battery was determined.

[0074] Capacity retention rate = (500th discharge capacity / first discharge capacity) x 100%.

[0075] 3. Low temperature storage performance: the lithium secondary battery was charged to a voltage of 4.2V at a constant current of 1C at room temperature, then the battery was placed in a -20°C low temperature cabinet, and the storage time was >4h, until the battery temperature dropped to -20°C, and then discharged to 2.7V at 0.2C.

[0076] After the discharge was completed, the battery was placed at room temperature again, and after the battery temperature returned to room temperature, the lithium secondary battery was charged to a voltage of 4.2V at a constant current of 1C, then the battery was placed in a -20°C low temperature cabinet, and the storage time was >4h, until the battery temperature dropped to -20°C, and then discharged to 2.7V at 0.5C.

[0077] After the discharge was completed, the battery was placed at room temperature again, and after the battery temperature returned to room temperature, the lithium secondary battery was charged to a voltage of 4.2V at a constant current of 1C, then the battery was placed in a -20°C low temperature cabinet, and the storage time was >4h, until the battery temperature dropped to -20°C, and then discharged to 2.7V at 1C.

[0078] The test results are shown in Table 2 below:

[0079] Table 2 Test results of lithium secondary battery cycle performance and low temperature performance

[0080]

[0081]

[0082] As can be seen from the results in Table 2, the room temperature and high temperature rate cycle performance and low temperature discharge performance of the lithium ion batteries in Examples 1-13 are better than those of Comparative Examples 1-13, indicating that the electrolyte additives in Examples 1-13 can effectively improve the rate cycle and low temperature rate discharge performance of the lithium secondary battery.

[0083] Specifically:

[0084] 1. It can be seen from Examples 1-13 and Comparative Examples 1-4 that the addition of neither triphenylphosphine alkenyl compound additive nor compound having carbonyl group, nor the use of triphenylphosphine alkenyl compound additive alone, nor the use of compound having carbonyl group alone can achieve satisfactory electrochemical effect. The use of triphenylphosphine alkenyl compound additive alone can improve low-temperature performance to some extent but affect high-temperature performance; the use of compound having carbonyl group alone can improve high-temperature performance but reduce low-temperature performance; and the use of triphenylphosphine alkenyl compound additive in combination with compound having carbonyl group can improve both high-temperature performance and low-temperature performance, and the improvement of high-temperature cycle performance is more significant than that of compound having carbonyl group alone, and the improvement of low-temperature discharge performance is more significant than that of triphenylphosphine alkenyl compound additive alone, indicating that the combination of the two achieves good synergistic effect.

[0085] 2. It can be seen from Examples 1-13 and Comparative Examples 5-8 that when used in combination with compound having carbonyl group, too high or too low content of triphenylphosphine alkenyl compound cannot achieve satisfactory electrochemical effect. It can be seen from the comparison of Examples 1-4 and Comparative Examples 5-6 that when the content of triphenylphosphine alkenyl compound 4 is reduced to 0.01% or increased to 1.5%, the cycle performance and low-temperature discharge performance of lithium secondary battery are obviously reduced. When the content of triphenylphosphine alkenyl compound 4 is within the range of 0.05%-0.7%, satisfactory electrochemical effect can be achieved. It can be seen from the comparison of Examples 5-8 and Comparative Examples 7-8 that when the content of triphenylphosphine alkenyl compound 5 is reduced to 0.01% or increased to 1.5%, the cycle performance and low-temperature discharge performance of lithium secondary battery are obviously reduced. When the content of triphenylphosphine alkenyl compound 5 is within the range of 0.1%-0.7%, satisfactory electrochemical effect can be achieved.

[0086] 3. It can be seen from Examples 1-13 and Comparative Examples 9-10 that when used in combination with triphenylphosphine alkenyl compound, compound having carbonyl group with too high content (20.3%) or too low content (0.06%) cannot achieve satisfactory electrochemical effect, and the cycle performance and low-temperature discharge performance of lithium secondary battery are reduced to some extent. When the addition amount of compound having carbonyl group is within the range of 0.1%-10% of the mass of electrolyte, satisfactory electrochemical effect can be achieved.

[0087] 4. It can be seen from Examples 1-13 and Comparative Example 11 that the functional group connected with triphenylphosphine alkenyl group has particularity, and non-limited structure cannot achieve satisfactory electrochemical effect.

[0088] 5. It can be seen from Examples 1-13 and Comparative Examples 12-13 that when the additives in Comparative Examples 12 and 13 are used in combination with triphenylphosphine alkenyl compound, satisfactory electrochemical effect cannot be achieved.

[0089] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application should be equivalent replacement manners and should be included in the protection scope of the present application.

Claims

1. A lithium secondary battery electrolyte with both high and low temperature performance, characterized by comprising: a lithium salt; a cyclic carbonate; a linear carbonate; and a cyclic ether. The electrolyte comprises: a non-aqueous solvent; a lithium salt; a triphenylphosphine alkenyl compound; and a compound having a carbonyl group; The triphenylphosphine alkenyl compound comprises at least one of the following structural compounds: ； The triphenylphosphine alkenyl compound is added in an amount of 0.03% to 0.7% of the mass of the electrolyte; The compound having a carbonyl group is at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethoxyethylene carbonate, ethylene carbonate, vinyl ethylene carbonate, diethyl pyrocarbonate, 4,4'-bi-1,3-dioxolan-2,2'-dione, succinic anhydride, maleic anhydride, 2-methyl maleic anhydride, and methyl carbonic acid-2-propynyl ester; The compound having a carbonyl group is added in an amount of 0.1% to 10% of the mass of the electrolyte.

2. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 1, characterized by, The triphenylphosphine alkenyl compound is added in an amount of 0.05% to 0.5% of the mass of the electrolyte.

3. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 1, characterized by, The non-aqueous solvent accounts for 50% to 92% of the total mass of the electrolyte; The non-aqueous solvent is composed of a cyclic compound and a linear compound; The cyclic compound is at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, butanediol sulfone, trifluoroethoxyethylene carbonate, fluoro propylene carbonate, trifluoromethyl ethylene carbonate, and trifluoroethyl ethylene carbonate; The linear compound is at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, trifluoroethyl acetate, difluoroethyl acetate, trifluoroacetic acid ethyl ester, methyl acetate, propylene glycol methyl ether acetate, 2-methoxy-1-propanol acetate, n-propyl acetate, and tri(2-ethylhexyl) trimellitate.

4. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 3, characterized by, The non-aqueous solvent accounts for 52% to 90% of the total mass of the electrolyte.

5. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 4, characterized by, The non-aqueous solvent accounts for 65% to 85% of the total mass of the electrolyte.

6. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 1, characterized by, The lithium salt is at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiTDI, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, LiPF4C2O4, and lithium perfluorobutylsulfonate; The lithium salt accounts for 8% to 25% of the total mass of the electrolyte.

7. The high and low temperature performance compatible lithium secondary battery electrolyte according to claim 1, characterized in that, The electrolyte further comprises an additive. The additive includes at least one of vinyl sulfate, propylene carbonate, 1,3-propane sulfite, 1,3-propylene sulfite, 1,4-butane sulfite, 2,4-butane sulfite, tetraethenesilane, diethenyltetramethyldisilazane, diethenyltetramethyldisiloxane, triallylisocyanurate, hexamethylenediisocyanate, o-phenanthroline, p-phenylenediisocyanate, 2,4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, bisvinyl sulfate, methylsulfate, bispropylene sulfite, hydroquinone difluorosulfonate, triallyl phosphate, tripropargyl phosphate, 2,4-butane sulfite, isocyanatoethyl methacrylate, methanedi sulfite, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(vinyldimethylsilyl)phosphate, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate, (2-allylphenoxy)trimethylsilane, 1-p-tolylsulfonylimidazole, tetramethyl methylene diphosphate, isocyanatoethyl methacrylate, 2-fluoropyridine, ethoxy pentafluorocyclotriphosphazene, trifluoroethoxy pentafluorocyclotriphosphazene, 2-phenyl-1-yl 1H-imidazole-1-sulfonate; The additive accounts for 0.1% to 10% of the total mass of the electrolyte.

8. A lithium secondary battery, characterized by comprising: The lithium secondary battery includes: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and The electrolyte of the lithium secondary battery according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, wherein The positive electrode is Li 1+a (Ni x Co y M 1-x-y O2, Li(Ni) p Mn q Co 2-p-q O4 and LiM h (PO4) m One or more of them; wherein 0≤a≤0.3, 0≤x≤1, 0≤y≤1, 0 The negative electrode is at least one of graphite, soft carbon, hard carbon, silicon, silicon oxide compound, and silicon-carbon composite. The separator is at least one of resin, glass fiber, and ceramic membrane.

Images