CN112018446A - Electrolyte suitable for silicon-carbon system lithium ion battery - Google Patents

Electrolyte suitable for silicon-carbon system lithium ion battery Download PDF

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CN112018446A
CN112018446A CN202011034816.8A CN202011034816A CN112018446A CN 112018446 A CN112018446 A CN 112018446A CN 202011034816 A CN202011034816 A CN 202011034816A CN 112018446 A CN112018446 A CN 112018446A
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lithium ion
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CN112018446B (en
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母英迪
王龙
王海
李素丽
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Zhuhai Cosmx Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
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Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte suitable for a silicon-carbon system lithium ion battery and the silicon-carbon system lithium ion battery comprising the electrolyte. The electrolyte combination provided by the invention can obviously improve the cycle life and the safety performance of the battery, the propenyl-1, 3-sultone in the additive and the cyclic ester group in the siloxane polymer with the structure shown in the formula 1 are subjected to ring opening in cooperation with each other in the charging and discharging processes of the battery, so that a thin-layer polycycloester can be generated on the surface of the positive electrode, a firmer CEI positive electrode protective film is formed, and the high-temperature storage and high-temperature cycle performance of the battery are effectively improved; meanwhile, Si-O bonds in the siloxane polymer with the structure shown in the formula 1 are crosslinked to generate a Si-O-Si crosslinked structure with higher rigidity, so that the toughness of an SEI film on the surface of the negative electrode can be enhanced, the cyclic expansion of the silicon-carbon negative electrode material can be obviously inhibited, and the cycle life can be prolonged.

Description

Electrolyte suitable for silicon-carbon system lithium ion battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte suitable for a silicon-carbon system lithium ion battery and the silicon-carbon system lithium ion battery comprising the electrolyte.
Background
Since commercialization, lithium ion batteries have been widely used in the fields of digital, energy storage, power, military aerospace, and communication equipment, due to their high specific energy and good cycle performance. With the wide application of lithium ion batteries, the use environment and the demand of consumers on the lithium ion batteries are continuously improved, and meanwhile, the requirement on the endurance capacity of electronic equipment is higher and higher, so that the lithium ion batteries are required to have high and low temperature performance and higher energy density.
The silicon-carbon battery is one of effective means for improving the energy density of the battery, and the electrolyte is one of main materials of the silicon-carbon lithium ion battery and plays a role in transmitting Li in the silicon-carbon lithium ion battery+The function of (1). Therefore, the research and development of the electrolyte are important for the silicon-carbon lithium ion battery, but the electrolyte which relieves the large cycle expansion of the silicon negative electrode and has high and low temperature performance is not easy to develop. At present, the use of additives in electrolytes is a highly effective weapon to solve the above problems. However, the current electrolyte additives are often difficult to form a strong and tough SEI film to resist the damage caused by the expansion of the silicon negative electrode during the cycle, and the high-temperature additives cause large impedance and seriously affect the low-temperature performance of the battery. Therefore, it is urgently required to develop an electrolyte suitable for a silicon-carbon system lithium ion battery, which can prolong the cycle life of the silicon-carbon battery and achieve both high and low temperatures.
Disclosure of Invention
The invention provides an electrolyte suitable for a silicon-carbon system lithium ion battery and the silicon-carbon system lithium ion battery comprising the electrolyte.
Specifically, the invention provides the following technical scheme:
an electrolyte comprising an organic solvent, an additive and a lithium salt, wherein the additive comprises a siloxane polymer containing a structure shown in formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate;
Figure BDA0002704841760000021
in formula 1, m is the degree of polymerization; n is an integer of 0 or more; r1Selected from alkyl or substituted alkyl; r2Selected from-O-C (═ O) -O-, -CH2-S(＝O)2-O-、-O-S(＝O)-O-、-O-S(＝O)2-O-。
Further, m is an integer greater than 1. Further, m is an integer between 10 and 50.
Further, n is an integer between 0 and 2, for example 0, 1 or 2.
Further, R1Is selected from C1-6Alkyl or fluoro substituted C1-6Alkyl groups of (a); preferably, R1Is selected from C1-3Alkyl or fluoro substituted C1-3Alkyl groups of (a); for example methyl, ethyl, propyl, fluoro-substituted methyl, fluoro-substituted ethyl, fluoro-substituted propyl, wherein the number of fluoro substitutions is 1,2 or more than 3.
Further, the siloxane-based polymer contains one of the structures shown in formulas 1-1, 1-2, 1-3, 1-4 or 1-5:
Figure BDA0002704841760000031
wherein m is as defined above.
Further, the siloxane-based polymer is used in an amount of 0.1 to 10 wt%, preferably 0.2 to 5.0 wt%, and more preferably 0.2 to 2.0 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, 7.0 wt%, 8.0 wt%, 9.0 wt%, 10 wt% based on the total mass of the electrolyte.
Further, the propenyl-1, 3-sultone is used in an amount of 0.1 to 2 wt% based on the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%.
Further, the ethoxy (pentafluoro) cyclotriphosphazene is used in an amount of 0.1 to 2 wt% based on the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%.
Further, the ethylene sulfate is used in an amount of 0.1 to 2 wt% based on the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%.
Further, the additive further comprises at least one of succinonitrile, adiponitrile, 1,3, 6-hexanetricarbonitrile, 1, 2-bis (cyanoethoxy) ethane, fluoroethylene carbonate and 1, 3-propane sultone, and is used in an amount of 0 to 10 wt%, for example, 0 to 8 wt%, based on the total mass of the electrolyte.
Further, the organic solvent is selected from at least one of carbonate, carboxylic ester and fluoroether, wherein the carbonate is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and methyl propyl carbonate; the carboxylic ester is selected from one or more of ethyl propionate and propyl propionate; the fluoroether is selected from 1,1,2, 3-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether.
Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide or lithium bis (trifluoromethylsulfonyl) imide.
Further, the lithium salt is used in an amount of 10 to 20 wt%, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt% based on the total mass of the electrolyte.
The invention also provides a preparation method of the electrolyte, which comprises the following steps:
mixing an organic solvent, an additive and a lithium salt, wherein the additive comprises siloxane polymer containing a structure shown in formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate.
Illustratively, the method comprises the steps of:
preparing an organic solvent in a glove box filled with argon and qualified in water oxygen content, and then quickly adding fully dried lithium salt, siloxane polymer containing a structure shown in a formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate into the organic solvent to prepare the electrolyte.
The invention also provides a lithium ion battery which comprises the electrolyte.
Further, the lithium ion battery is a silicon-carbon system lithium ion battery.
Further, the lithium ion battery also comprises a positive plate, a negative plate and a diaphragm.
Further, the negative plate comprises a negative current collector and a negative active material layer coated on one side or two sides of the negative current collector, wherein the negative active material layer comprises a negative active material selected from nano silicon and/or SiOx(x is more than or equal to 0.8 and less than or equal to 1.3) and graphite.
Further, the nano silicon and/or SiOx1-55 wt% of the total mass of the silicon-carbon negative electrode material, such as 1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%.
Further, the anode active material layer further includes a binder, a conductive agent, and a dispersant.
Further, the mass percentage of each component in the negative electrode active material layer is as follows: 70-99.7 wt% of negative electrode active material, 0.1-10 wt% of binder, 0.1-10 wt% of dispersant and 0.1-10 wt% of conductive agent.
Preferably, the negative electrode active material layer comprises the following components in percentage by mass: 76-98.5 wt% of negative electrode active material, 0.5-8 wt% of binder, 0.5-8 wt% of dispersant and 0.5-8 wt% of conductive agent.
Still preferably, the negative electrode active material layer contains the following components in percentage by mass: 85-98.5 wt% of negative electrode active material, 0.5-5 wt% of binder, 0.5-5 wt% of dispersant and 0.5-5 wt% of conductive agent.
Further, the binder is at least one selected from among high polymer polymers such as polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Polyethyleneimine (PEI), Polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC), phenol resin, epoxy resin, and the like.
Further, the dispersant is selected from at least one of Polypropylene (PVA), cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, ethanol, N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), etc., and more preferably at least one of cetylammonium bromide, sodium dodecylbenzenesulfonate, a silane coupling agent, and ethanol.
Further, the conductive agent is selected from at least one of Carbon Nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microbeads (MCMB), graphene, Ketjen black, Super P, acetylene black, conductive carbon black or hard carbon.
Further, the positive plate comprises a positive current collector and a positive active material layer coated on one side or two sides of the positive current collector, wherein the positive active material layer comprises a positive active material selected from LiCoO2、LiNiO2、LiMn2O4、LiFePO4、LixNiyM1-yO2Wherein, 0 is adopted.9≤x≤1.2，0.5≤y<1, M is selected from one or more of Co, Mn, Al, Mg, Ti, Zr, Fe, Cr, Mo, Cu and Ca.
Further, the positive electrode active material layer further includes a binder and a conductive agent.
Further, the mass percentage of each component in the positive active material layer is as follows: 80-99.8 wt% of positive active material, 0.1-10 wt% of binder and 0.1-10 wt% of conductive agent.
Preferably, the positive electrode active material layer comprises the following components in percentage by mass: 84-99 wt% of positive electrode active material, 0.5-8 wt% of binder and 0.5-8 wt% of conductive agent.
Still preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99 wt% of positive electrode active substance, 0.5-5 wt% of binder and 0.5-5 wt% of conductive agent.
Further, the binder is at least one selected from among high polymer polymers such as polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Polyethyleneimine (PEI), Polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC), phenol resin, epoxy resin, and the like.
Further, the conductive agent is selected from at least one of Carbon Nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microbeads (MCMB), graphene, Ketjen black, Super P, acetylene black, conductive carbon black or hard carbon.
Further, the separator is a separator known in the art, such as a polyethylene separator, a polypropylene separator, and the like.
The invention also provides a preparation method of the lithium ion battery, which comprises the following steps:
(1) preparing a positive plate and a negative plate, wherein the positive plate contains a positive active substance, and the negative plate contains a negative active substance;
(2) mixing an organic solvent, an additive and a lithium salt to prepare an electrolyte;
(3) winding the positive plate, the diaphragm and the negative plate to obtain a naked battery cell without liquid injection; and (3) placing the bare cell in an outer packaging foil, injecting the electrolyte in the step (2) into the dried bare cell, and preparing to obtain the lithium ion battery.
Exemplarily, the method specifically comprises the following steps:
(1) preparation of positive plate
LiCoO as positive electrode active material2Mixing polyvinylidene fluoride (PVDF) serving as a binder and acetylene black serving as a conductive agent according to a weight ratio of 96.5:2:1.5, adding N-methylpyrrolidone (NMP), and stirring under the action of a vacuum stirrer until a mixed system becomes uniform and flowable anode slurry; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 9-12 mu m; baking the coated aluminum foil in 5 sections of baking ovens with different temperature gradients, drying the aluminum foil in a baking oven at 120 ℃ for 8 hours, and rolling and cutting to obtain the required positive plate.
(2) Preparation of silicon-carbon negative plate
Preparing a silicon-carbon negative electrode material (formed by compounding SiO and graphite, wherein the SiO accounts for 5 percent by mass) with the mass ratio of 95.9 percent, a single-walled carbon nanotube (SWCNT) conductive agent with the mass ratio of 0.1 percent, a conductive carbon black (SP) conductive agent with the mass ratio of 1 percent, a sodium carboxymethylcellulose (CMC) dispersing agent with the mass ratio of 1 percent and a Styrene Butadiene Rubber (SBR) binder with the mass ratio of 2 percent into negative electrode slurry by a wet process; uniformly coating the negative electrode slurry on a copper foil with the thickness of 9-12 mu m; and baking the coated copper foil in 5 sections of baking ovens with different temperature gradients, drying the copper foil in an oven at 85 ℃ for 5 hours, and rolling and cutting to obtain the required silicon-carbon negative plate.
(3) Preparation of electrolyte
Uniformly mixing ethylene carbonate, propylene carbonate, propyl propionate and ethyl propionate according to the mass ratio of 2:1:5:2 in a glove box filled with argon and qualified in water oxygen content (the solvent needs to be normalized), and then rapidly adding 1mol/L (12.5 wt%) of fully dried lithium hexafluorophosphate (LiPF)6) And 6% by mass of fluoroethylene carbonate and other additives (including siloxane polymer containing a structure shown in formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate) to obtain the electrolyte.
(4) Preparation of the separator
Selecting a polyethylene diaphragm with the thickness of 7-9 mu m.
(5) Preparation of lithium ion battery
Winding the prepared positive plate, the diaphragm and the prepared negative plate to obtain a naked battery cell without liquid injection; placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping, sorting and other processes to obtain the required lithium ion battery.
The invention has the beneficial effects that:
the electrolyte combination provided by the invention can obviously improve the cycle life and the safety performance of the battery, the propenyl-1, 3-sultone in the additive and the cyclic ester group in the siloxane polymer with the structure shown in the formula 1 are subjected to synergistic ring opening in the charging and discharging processes of the battery to generate a thin-layer polycylic ester on the surface of the positive electrode, so that a firmer CEI positive electrode protective film is formed, and the high-temperature storage and high-temperature cycle performance of the battery are effectively improved; meanwhile, Si-O bonds in the siloxane polymer with the structure shown in the formula 1 are crosslinked to generate a Si-O-Si crosslinked structure with higher rigidity, so that the toughness of an SEI (solid electrolyte interphase) film on the surface of the negative electrode can be enhanced, the cyclic expansion of the silicon-carbon negative electrode material can be obviously inhibited, and the cycle life can be prolonged; the ethylene sulfate is subjected to a reductive decomposition reaction at the interface of the silicon-carbon negative electrode material to generate a layer of passivation film, the reductive decomposition of an organic solvent in the electrolyte is inhibited, the impedance of the formed passivation film is low, the chemical and dynamic properties of the negative electrode interface are remarkably improved, the rapid intercalation and deintercalation effects of lithium ions are greatly improved, the internal resistance of the battery is effectively reduced, and the low-temperature performance is improved; the ethoxy (pentafluoro) cyclotriphosphazene is gasified and decomposed when the battery is heated at high temperature, and releases flame-retardant free radical phosphorus free radical (P), so that hydrogen free radical (H) in an electrolyte system can be effectively captured, chain reaction of combustion or explosion of hydrocarbon is prevented, and the safety performance of the battery cell is effectively improved.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
The polymer A, B, C, D, E used in the following examples is shown below, where the end capping group is methyl:
Figure BDA0002704841760000091
a compound A: wherein the degree of polymerization m is 22.
Figure BDA0002704841760000092
Compound B: wherein the degree of polymerization m is 10.
Figure BDA0002704841760000101
Compound C: wherein the degree of polymerization m is 41.
Figure BDA0002704841760000102
Compound D: wherein the degree of polymerization m is 50.
Figure BDA0002704841760000103
Compound E: wherein the degree of polymerization m is 32.
Comparative examples 1 to 4 and examples 1 to 8
The lithium ion batteries of comparative examples 1 to 4 and examples 1 to 8 were each prepared according to the following preparation method, differing only in the selection and addition amount of each component in the electrolyte, and the specific differences are shown in table 1.
(1) Preparation of positive plate
LiCoO as positive electrode active material2Polyvinylidene fluoride (PVDF) as binder and acetylene black as conductive agentMixing according to the weight ratio of 96.5:2:1.5, adding N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until a mixed system becomes uniform and fluid anode slurry; uniformly coating the positive electrode slurry on an aluminum foil with the thickness of 9-12 mu m; baking the coated aluminum foil in 5 sections of baking ovens with different temperature gradients, drying the aluminum foil in a baking oven at 120 ℃ for 8 hours, and rolling and cutting to obtain the required positive plate.
(2) Preparation of silicon-carbon negative plate
Preparing a silicon-carbon negative electrode material (formed by compounding SiO and graphite, wherein the SiO accounts for 5 percent by mass) with the mass ratio of 95.9 percent, a single-walled carbon nanotube (SWCNT) conductive agent with the mass ratio of 0.1 percent, a conductive carbon black (SP) conductive agent with the mass ratio of 1 percent, a sodium carboxymethylcellulose (CMC) dispersing agent with the mass ratio of 1 percent and a Styrene Butadiene Rubber (SBR) binder with the mass ratio of 2 percent into negative electrode slurry by a wet process; uniformly coating the negative electrode slurry on a copper foil with the thickness of 9-12 mu m; and baking the coated copper foil in 5 sections of baking ovens with different temperature gradients, drying the copper foil in an oven at 85 ℃ for 5 hours, and rolling and cutting to obtain the required silicon-carbon negative plate.
(3) Preparation of electrolyte
Uniformly mixing ethylene carbonate, propylene carbonate, propyl propionate and ethyl propionate according to the mass ratio of 2:1:5:2 in a glove box filled with argon and qualified in water oxygen content (the solvent needs to be normalized), and then rapidly adding 1mol/L (12.5 wt%) of fully dried lithium hexafluorophosphate (LiPF)6) And 6 wt% of fluoroethylene carbonate and other additives (comprising siloxane polymer containing a structure shown in formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate, wherein the specific dosage and selection are shown in table 1) to obtain the electrolyte.
(4) Preparation of the separator
Selecting a polyethylene diaphragm with the thickness of 7-9 mu m.
(5) Preparation of lithium ion battery
Winding the prepared positive plate, the diaphragm and the prepared negative plate to obtain a naked battery cell without liquid injection; placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping, sorting and other processes to obtain the required lithium ion battery.
TABLE 1 compositions of lithium ion batteries prepared in comparative examples 1-4 and examples 1-8
Figure BDA0002704841760000121
The cells obtained in the above comparative examples and examples were subjected to electrochemical performance tests, as described below:
(1)45 ℃ cycling experiment: placing the batteries obtained in the above examples and comparative examples in an environment of (45 +/-2) DEG C, standing for 2-3 hours, when the battery body reaches (45 +/-2) DEG C, keeping the cut-off current of the battery at 0.05C according to 1C constant current charging, standing for 5min after the battery is fully charged, then discharging to the cut-off voltage of 3.0V at 0.7C constant current, recording the highest discharge capacity of the previous 3 cycles as the initial capacity Q, recording the initial thickness T of the battery cell, and when the cycles reach the required times, recording the last discharge capacity Q of the battery1And battery thickness T1The results are reported in Table 2.
The calculation formula used therein is as follows:
capacity retention (%) ═ Q1(ii)/Q × 100%; thickness change rate (%) - (T)1-T)/T×100％
(2) High temperature storage at 60 ℃ for 30 days experiment: the cells obtained in the above examples and comparative examples were subjected to a charge-discharge cycle test at a charge-discharge rate of 0.5C for 3 times at room temperature, and then charged to a full charge state at a rate of 0.5C, and the maximum discharge capacity Q of the previous 0.5C cycles was recorded2And battery thickness T2. The fully charged battery was stored at 60 ℃ for 30 days, and the battery thickness T after 30 days was recorded3And 0.5C discharge capacity Q3And calculating to obtain experimental data such as the thickness change rate, the capacity retention rate and the like of the battery stored at high temperature, and recording the results as shown in table 1.
The calculation formula used therein is as follows:
capacity retention (%) ═ Q3/Q2X is 100%; thickness change rate (%) - (T)3-T2)/T2×100％
(3) Thermal shock test at 130 ℃: the cells obtained in the above examples and comparative examples were heated at an initial temperature of 25. + -. 3 ℃ by convection or a circulating hot air oven at a temperature change rate of 5. + -. 2 ℃/min to 130. + -. 2 ℃ for 60min, and the test was terminated, and the results of the cell conditions were recorded as shown in Table 2.
(4) Low-temperature discharge experiment: discharging the batteries obtained in the above examples and comparative examples to 3.0V at ambient temperature of 25 + -3 deg.C at 0.2C, and standing for 5 min; charging at 0.7C, changing to constant voltage charging when the voltage at the cell terminal reaches the charging limit voltage, stopping charging until the charging current is less than or equal to the cut-off current, standing for 5 minutes, discharging to 3.0V at 0.2C, and recording the discharge capacity as the normal temperature capacity Q4. Then the battery cell is charged at 0.7C, when the voltage of the battery cell terminal reaches the charging limiting voltage, constant voltage charging is changed, and charging is stopped until the charging current is less than or equal to the cut-off current; standing the fully charged battery at-10 +/-2 ℃ for 4h, discharging to cut-off voltage of 3.0V at 0.2C, and recording discharge capacity Q5The low-temperature discharge capacity retention rate was calculated and reported in table 2.
The calculation formula used therein is as follows: low-temperature discharge capacity retention (%) ═ Q5/Q4×100％。
TABLE 2 results of experimental tests of comparative examples 1-4 and examples 1-8
Figure BDA0002704841760000131
As can be seen from the results of table 2:
as can be seen from comparative examples 1,2 and 3, the additive propenyl-1, 3-sultone and the siloxane polymer act synergistically to effectively improve the high-temperature storage and high-temperature cycle performance of the battery; comparing comparative examples 3 and 4, it can be seen that the ethylene sulfate effectively reduces the internal resistance of the battery and improves the low-temperature performance; further, by comparing each example with comparative example 4, it can be found that ethoxy (pentafluoro) cyclotriphosphazene is effective in improving cell safety performance.
In summary, the electrolyte for the silicon-carbon system lithium ion battery provided by the invention contains the additive combination of siloxane polymer, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate, and the silicon-carbon system lithium ion battery has excellent high-temperature cycle, high-temperature storage and low-temperature discharge performance and high safety through the synergistic effect of the additives.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. An electrolyte, wherein the electrolyte comprises an organic solvent, an additive and a lithium salt, wherein the additive comprises siloxane polymer containing a structure shown in formula 1, propenyl-1, 3-sultone, ethoxy (pentafluoro) cyclotriphosphazene and ethylene sulfate;
Figure FDA0002704841750000011
in formula 1, m is the degree of polymerization; n is an integer of 0 or more; r1Selected from alkyl or substituted alkyl; r2Selected from-O-C (═ O) -O-, -CH2-S(＝O)2-O-、-O-S(＝O)-O-、-O-S(＝O)2-O-。
2. The electrolyte of claim 1, wherein m is an integer greater than 1; and/or the presence of a gas in the gas,
m is an integer between 10 and 50; and/or the presence of a gas in the gas,
n is an integer between 0 and 2.
3. The lithium ion battery of claim 1 or 2, wherein R1Is selected from C1-6Alkyl or fluoro substituted C1-6Alkyl groups of (a); preferably, R1Is selected from C1-3Alkyl or fluoro substituted C1-3Alkyl groups of (a); for example methyl, ethyl, propyl, fluoro-substituted methyl, fluoro-substituted ethyl, fluoro-substituted propyl, wherein the number of fluoro substitutions is 1,2 or more than 3.
4. A lithium ion battery according to any of claims 1-3, wherein the siloxane-based polymer comprises one of the structures shown by formulas 1-1, 1-2, 1-3, 1-4, or 1-5:
Figure FDA0002704841750000021
wherein m is as defined above.
5. The lithium ion battery according to any of claims 1 to 4, wherein the siloxane-based polymer is used in an amount of 0.1 to 10 wt%, preferably 0.2 to 5.0 wt%, and more preferably 0.2 to 2.0 wt% based on the total mass of the electrolyte; and/or the presence of a gas in the gas,
the using amount of the propenyl-1, 3-sultone accounts for 0.1 to 2 weight percent of the total mass of the electrolyte; and/or the presence of a gas in the gas,
the usage amount of the ethoxy (pentafluoro) cyclotriphosphazene accounts for 0.1-2 wt% of the total mass of the electrolyte; and/or the presence of a gas in the gas,
the usage amount of the ethylene sulfate accounts for 0.1-2 wt% of the total mass of the electrolyte.
6. The lithium ion battery of any of claims 1-5, wherein the additive further comprises at least one of succinonitrile, adiponitrile, 1,3, 6-hexanetricarbonitrile, 1, 2-bis (cyanoethoxy) ethane, fluoroethylene carbonate, and 1, 3-propane sultone, used in an amount of 0-10 wt% based on the total mass of the electrolyte.
7. The lithium ion battery of any of claims 1-6, wherein the organic solvent is selected from at least one of carbonate, carboxylic ester, and fluoroether, wherein the carbonate is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl propyl carbonate; the carboxylic ester is selected from one or more of ethyl propionate and propyl propionate; the fluoroether is selected from 1,1,2, 3-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether.
8. The lithium ion battery of any of claims 1-7, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis-fluorosulfonylimide, or lithium bis (trifluoromethylsulfonyl) imide; and/or the presence of a gas in the gas,
the usage amount of the lithium salt accounts for 10-20 wt% of the total mass of the electrolyte.
9. A lithium-ion battery comprising the electrolyte of any of claims 1-8.
10. The lithium ion battery of claim 9, wherein the lithium ion battery is a silicon carbon system lithium ion battery.
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