CN110299561B - Non-aqueous electrolyte and lithium ion battery containing same - Google Patents
Non-aqueous electrolyte and lithium ion battery containing same Download PDFInfo
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- CN110299561B CN110299561B CN201810233231.5A CN201810233231A CN110299561B CN 110299561 B CN110299561 B CN 110299561B CN 201810233231 A CN201810233231 A CN 201810233231A CN 110299561 B CN110299561 B CN 110299561B
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- 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
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- 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
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Abstract
The invention discloses a non-aqueous electrolyte and a lithium ion battery containing the same, wherein the non-aqueous electrolyte comprises a lithium salt, an organic solvent and a cyclic phosphate additive, and the additive is added into the electrolyte, so that the non-aqueous electrolyte not only has a good flame retardant effect, but also can increase the radius of a complex formed by lithium ions and the solvent, so that the radius of the solvated lithium ions is increased, the phenomenon that the lithium ions are inserted into a negative electrode material layer in the charging and discharging processes of the battery, so that the negative electrode material layer falls off, and the cycle performance and the safety performance of the battery are improved.
Description
Technical Field
The invention relates to the field of non-aqueous electrolyte, in particular to a non-aqueous electrolyte and a lithium ion battery containing the same.
Background
The lithium ion battery has the advantages of high energy density, high open-circuit voltage, no memory effect, low self-discharge and the like, and is widely applied to consumer electronics products, military products and aviation products. However, the safety problem of lithium batteries is the first problem in large-scale application, especially in electric vehicles, hybrid vehicles and the like. At present, the accidents of electric automobile combustion often occur, and the safety problem of the lithium battery is particularly to be solved. The main problem is that the lithium battery contains volatile organic solvent with low flash point, and the leakage and further combustion explosion easily occur under the extreme conditions of overcharge, short circuit, impact and the like. In order to solve the problem, the industry makes related researches on a plurality of aspects such as a protection circuit, a control system, a ceramic diaphragm and the like. In addition, the addition of the additive into the nonaqueous electrolyte is also an important and effective way for solving the technical problem, and enterprises and scientific research institutions at home and abroad carry out a great deal of research on the technical problem; at present, the most widely researched method is that trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate and the like are used as additives to be added into the electrolyte to achieve the flame retardant effect, so that the safety performance of the battery is integrally improved; the phosphate ester is adopted as the electrolyte additive, the biggest defect is that phosphate ester molecules are co-inserted into graphite layers along with lithium ions in the charging process to cause expansion and peeling of graphite, and the performance of a lithium battery is seriously reduced when a large amount of phosphate ester molecules are used, so that the electrolyte solvent or additive with high flame retardant performance and compatible electrochemical performance needs to be searched.
Disclosure of Invention
In order to solve the above problems, the present application provides a nonaqueous electrolytic solution containing a lithium salt, an organic solvent, and an additive, characterized in that the additive has a structure represented by formula (1):
wherein R1 is selected from one of alkyl, aryl, cycloalkyl and silyl; r2 and R3 are each independently one selected from a hydrogen atom, an alkyl group, a cycloalkyl group and a silane group; r4 and R5 are independently selected from one of a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, a halogenated alkyl group and a halogenated cycloalkyl group, wherein the halogen is one of F, Cl and Br.
Preferably, R1 is selected from one of an alkyl group of 1 to 5 carbon atoms, a phenyl group, a cycloalkyl group of 1 to 5 carbon atoms, and a silyl group of 1 to 5 carbon atoms.
Preferably, R2 and R3 are each independently one selected from the group consisting of a hydrogen atom, an alkyl group of 1 to 5 carbon atoms, a cycloalkyl group of 1 to 5 carbon atoms, and a silyl group of 1 to 5 carbon atoms.
Preferably, R4 and R5 are each independently one selected from H, F, an alkyl group having 1 to 5 carbon atoms, a cycloalkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, and a fluorocycloalkyl group having 1 to 5 carbon atoms.
Preferably, the additive is selected from one or more of 2-methyl-1, 2-oxaphosphine-4-fluoro-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-5-one-2 oxide, 2-ethyl-1, 2-oxaphosphine-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoroethyl-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoromethyl-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-methyl 5-one-2 oxide.
Preferably, the electrolyte additive is contained in an amount of 0.05 to 50 parts by weight, based on the total mass of the organic solvent and the electrolyte additive.
Preferably, the electrolyte additive is contained in an amount of 0.05 to 20 parts by weight, based on the total mass of the organic solvent and the electrolyte additive.
Preferably, the electrolyte also contains an auxiliary additive, wherein the auxiliary additive comprises one or more of 1, 3-propane sultone, 1, 4-butane sultone, propenyl-1, 3-sultone, ethylene sulfate, propylene sulfate, butylene sulfite, vinylene carbonate and fluoroethylene carbonate.
Preferably, the content of the auxiliary additive is 0.05 to 20 parts by weight based on the total mass of the organic solvent and the flame retardant.
Preferably, the content of the auxiliary additive is 0.5 to 5 parts by weight based on the total mass of the organic solvent and the flame retardant.
Preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, gamma-butyrolactone, sultone, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, methyl butyrate and ethyl acetate.
Preferably, the lithium salt is selected from LiBOB and LiPF6、LiBF4、LiNSO2CF3、LiDFOB、LiSbF6、LiClO4、LiCF3SO3、Li(CF3SO2)2N、LiC4F9SO3、LiAlO4、LiAsF6、LiAlCl4One or more of LiCl, LiI and low-fatty acid lithium carbonate, wherein the concentration of the lithium salt is 0.3-3 mol/L.
The present application also provides a lithium ion battery comprising a battery case, and a cell and a nonaqueous electrolyte sealed in the battery case, wherein the cell comprises a positive electrode, a negative electrode and a separator, and the nonaqueous electrolyte is the nonaqueous electrolyte of any one of claims 1 to 11.
Compared with the prior art, the lithium ion battery negative electrode material has the advantages that the additive is added into the non-aqueous electrolyte, so that the electrolyte has a good flame retardant effect, the radius of a complex formed by lithium ions and a solvent can be increased, namely the radius of the solvated lithium ions is increased, and the solvated lithium ions cannot be embedded into the negative electrode material layer due to the steric hindrance effect, so that the expansion and peeling of the negative electrode material are inhibited.
Detailed Description
Aiming at the problems, the invention provides a non-aqueous electrolyte which contains lithium salt, organic solvent and additive, wherein the additive contains additives such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate and the like, and the molecules of the phosphate are co-inserted into the negative electrode layer along with lithium ions during charging, so that the negative electrode material expands and peels, and the performance of a lithium battery is seriously reduced when the electrolyte is used in a large amount, and the additive has the structure shown in formula (1):
in the formula, R1 is selected from one of alkyl, aryl, cycloalkyl and silyl, wherein the alkyl, alkenyl, aryl, cycloalkyl and silyl may be branched or linear, and the present application is not limited thereto, and the inventors of the present application have surprisingly found through many experiments that when R1 is selected from one of alkyl of 1 to 5 carbon atoms, phenyl, cycloalkyl of 1 to 5 carbon atoms and silyl of 1 to 5 carbon atoms, the additive has an optimal flame retardant effect.
R2 and R3 can be the same or different and are respectively and independently selected from one of a hydrogen atom, an alkyl group, a cycloalkyl group and a silane group, wherein the alkyl group, the cycloalkyl group and the silane group can be in a branched chain structure or a linear chain structure, R1 and R3 are not limited in the application, and preferably, when R2 and R3 are respectively and independently selected from one of a hydrogen atom, an alkyl group with 1 to 5 carbon atoms, a cycloalkyl group with 1 to 5 carbon atoms and a silane group with 1 to 5 carbon atoms, the additive has the optimal flame retardant effect.
R4 and R5 may be the same or different, and each is independently selected from one of a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, a haloalkyl group and a halocycloalkyl group, wherein the halogen is one of F, Cl and Br, and the alkyl group, the cycloalkyl group, the alkoxy group, the haloalkyl group and the halocycloalkyl group may be a branched chain structure or a linear chain structure. Preferably, R4 and R5 are respectively and independently selected from H, F, alkyl with 1 to 5 carbon atoms, cycloalkyl with 1 to 5 carbon atoms, alkoxy with 1 to 5 carbon atoms, haloalkyl with 1 to 5 carbon atoms and halocycloalkyl with 1 to 5 carbon atoms, when R4 and R5 are selected from the above groups, the additive has a better flame retardant effect, and further preferably, the haloalkyl and the halocycloalkyl are fluoroalkyl and fluorocycloalkyl, and the additive can further enhance the flame retardant effect and the film forming effect of the additive by introducing F-containing substituent groups on carbon atoms and utilizing the synergistic flame retardant effect of fluorine and phosphorus, and meanwhile, the additive has good compatibility with a negative electrode, can generate a stable SEI film and greatly improves the cycling stability of a battery.
Preferably, the additive is selected from one or more of 2-methyl-1, 2-oxaphosphine-4-fluoro-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-5-one-2 oxide, 2-ethyl-1, 2-oxaphosphine-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoroethyl-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoromethyl-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-methyl 5-one-2 oxide. Among them, 2-methyl-1, 2-oxa-phosphine-5-one-2 oxide (CAS number: 15171-48-9) can be obtained commercially or prepared by itself in the laboratory, and its preparation method is well known to those skilled in the art, and the preparation method of other additives is similar to that of 2-methyl-1, 2-oxa-phosphine-5-one-2 oxide.
The cyclic phosphate additive is added into the electrolyte, so that the electrolyte has the optimal effect of preventing the negative electrode material layer from falling off while the optimal flame retardant effect of the electrolyte is maintained.
According to the nonaqueous electrolytic solution of the present invention, one kind of the additive may be added alone, or a plurality of kinds of the additives may be added simultaneously. The additive can be added into the electrolyte in an amount of 0.05-50 parts by weight relative to 100 parts by weight of the non-aqueous solvent, so that a good flame-retardant effect can be achieved, and the performance of the battery cannot be greatly influenced.
According to the nonaqueous electrolytic solution of the present invention, preferably, the nonaqueous electrolytic solution further contains an auxiliary additive, and the auxiliary additive includes at least one of 1,3 propane sultone, 1,4 butane sultone, propenyl-1, 3-sultone, vinyl sulfate, propylene sulfate, butylene sulfite, vinylene carbonate, and fluoroethylene carbonate. The auxiliary additive and the cyclic phosphate additive are jointly applied to the electrolyte, so that the stability of the lithium ion battery is better.
The nonaqueous electrolytic solution provided by the invention can contain 0.05-50 parts by weight, preferably 0.5-5 parts by weight of the auxiliary additive relative to 100 parts by weight of the nonaqueous solvent, and the auxiliary additive can promote the additive to form a stable SEI film on the surface of the negative electrode, can protect the negative electrode, and further can improve the cycle performance of the battery, but the auxiliary additive is added too much to cause excessive consumption of active lithium.
According to the provided nonaqueous electrolytic solution of the present invention, the organic solvent may use a nonaqueous solvent conventionally used by those skilled in the art, and for example, may include one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, γ -butyrolactone, sultone, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, methyl butyrate, and ethyl acetate.
The nonaqueous electrolytic solution according to the present invention, wherein the selection of the lithium salt is not particularly required, may be a lithium salt conventionally used in nonaqueous electrolytic solutions, and may include LiBOB and LiPF, for example6、LiBF4、LiSbF6、LiClO4、LiCF3SO3、Li(CF3SO2)2N、LiC4F9SO3、LiAlO4、LiAsF6、LiAlCl4One or more of LiCl, LiI and low fatty acid lithium carbonate. The concentration of the lithium salt is known to those skilled in the art and is generally 0.3 to 3mol/L, preferably 0.8 to 1.2 mol/L.
The preparation method of the non-aqueous electrolyte of the lithium ion battery provided by the invention is a method conventionally used by a person skilled in the art, namely, the components (including the lithium salt, the non-aqueous solvent and the additive) are uniformly mixed, and the mixing mode and the mixing sequence are not particularly limited in the invention. For example, the organic solvent is mixed uniformly, then the lithium salt is added and mixed uniformly, and then the electrolyte additive is added and mixed uniformly, and the auxiliary additive can be added together with the electrolyte additive.
The invention also provides a lithium ion battery which comprises a battery shell, a battery core and a non-aqueous electrolyte, wherein the battery core and the non-aqueous electrolyte are sealed in the battery shell.
The nonaqueous electrolyte solution is the nonaqueous electrolyte solution, and the battery cell comprises a positive electrode, a negative electrode and a diaphragm. The present invention relates to an improvement of a non-aqueous electrolyte of a lithium ion battery of the prior art, and therefore, other compositions and structures of the lithium ion secondary battery are not particularly limited.
For example, the positive electrode may be any one of various positive electrodes announced by those skilled in the art, and generally includes a positive electrode current collector and a positive electrode material coated and/or filled on the positive electrode current collector. The positive electrode current collector may be any of various positive electrode current collectors known to those skilled in the art, such as aluminum foil, copper foil, and nickel-plated steel strip, and the aluminum foil is selected as the positive electrode current collector in the present invention. The positive electrode material may be one known to those skilled in the artVarious known positive electrode materials generally include a mixture of a positive electrode active material, which may be selected from conventional positive electrode active materials for lithium ion batteries, such as LixNi, a conductive material, and a binder(1-y)CoO2(wherein x is more than or equal to 0.9 and less than or equal to 1.1, and y is more than or equal to 0 and less than or equal to 1.0), LimMn(2-n)BnO2(wherein B is a transition metal, m is 0.9-1.1, n is 0-1.0), Li(1+a)MbMn(2－b)O4(wherein a is more than or equal to 0.1 and less than or equal to 0.2, b is more than or equal to 0 and less than or equal to 1.0, and M is one or more of lithium, boron, magnesium, aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc, gallium, yttrium, fluorine, iodine and sulfur). Preferably, the positive electrode active material is a lithium metal phosphate having an olivine structure represented by the following formula: li(1+a)LbPO4(ii) a In the formula, a is more than or equal to-0.1 and less than or equal to 0.2, b is more than or equal to 0.9 and less than or equal to 1.1, and L is at least one of iron, aluminum, manganese, cobalt, nickel, magnesium, zinc and vanadium. The positive electrode active material is more preferably lithium iron phosphate (LiFePO)4). According to the invention, lithium metal phosphates, such as LiFePO, are used4The battery prepared by the positive active material serving as the positive electrode of the lithium ion secondary battery has more obvious improvement on high-temperature safety performance, and can normally work under lower working voltage such as 3.8-2.0 volts, so that the battery has good safety performance and good electrochemical performance such as high-current discharge performance.
The positive electrode material according to the present invention is not particularly limited to a binder, and any binder known in the art to be used for secondary lithium ion batteries may be used. May be selected from one or more of fluorine-containing resin and/or polyolefin compound, such as Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and styrene butadiene rubber. The binder is contained in an amount of 0.01 to 8 wt%, preferably 1 to 5 wt%, based on the weight of the positive electrode active material.
The positive electrode material provided by the invention can also selectively contain a conductive agent which is usually contained in the positive electrode material in the prior art. Since the conductive agent serves to increase the conductivity of the electrode and to reduce the internal resistance of the battery, the present invention preferably contains the conductive agent. The content and kind of the conductive agent are well known to those skilled in the art, and for example, the content of the conductive agent is generally 0 to 15% by weight, preferably 0 to 10% by weight, based on the positive electrode material. The conductive agent can be one or more selected from conductive carbon black, acetylene black, nickel powder, copper powder and conductive graphite.
The composition of the negative electrode is well known to those skilled in the art, and generally, the negative electrode includes a negative electrode current collector and a negative electrode material coated and/or filled on the negative electrode current collector. The negative electrode current collector is well known to those skilled in the art, and may be selected from one or more of aluminum foil, copper foil, nickel-plated steel strip, and punched steel strip, for example. The negative active material is well known to those skilled in the art, and comprises a negative active material and a binder, wherein the negative active material can be selected from one or more of conventional negative active materials of lithium ion batteries, such as natural graphite, artificial graphite, petroleum coke, organic pyrolysis carbon, mesocarbon microbeads, carbon fibers, tin alloy and silicon alloy. The binder can be selected from one or more of conventional binders of lithium ion batteries, such as polyvinyl alcohol, polytetrafluoroethylene, hydroxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR). Generally, the binder is contained in an amount of 0.5 to 8% by weight, preferably 2 to 5% by weight, of the negative electrode active material.
The negative electrode of the present invention may further include an adsorption layer on the surface of the negative electrode material.
According to the lithium ion battery, the additive is added into the non-aqueous electrolyte, so that the additive is partially reduced and adsorbed on the negative electrode of the battery in the use process of the battery, a uniform film is formed on the surface of the negative electrode, the film can effectively prevent solvent molecules from passing through, but lithium ions can be freely inserted and extracted through the film, and the cycle performance of the battery can be improved on the premise of improving the safety performance of the battery.
The solvent used for preparing the positive electrode slurry and the negative electrode slurry according to the present invention may be selected from conventional solvents, such as one or more selected from N-methylpyrrolidone (NMP), Dimethylformamide (DMF), Diethylformamide (DEF), Dimethylsulfoxide (DMSO), Tetrahydrofuran (THF), and water and alcohols. The solvent may be used in an amount such that the slurry can be applied to the current collector. In general, the solvent is used in an amount such that the concentration of the positive electrode active material or the negative electrode active material in the slurry is 40 to 90% by weight, preferably 50 to 85% by weight.
The separator has an electrical insulating property and a liquid retaining property, is disposed between the positive electrode and the negative electrode, and is sealed in a battery case together with the positive electrode, the negative electrode, and the electrolytic solution. The membrane can be various membranes commonly used in the field, such as modified polyethylene felt, modified polypropylene felt, superfine glass fiber felt, vinylon felt or nylon felt of various production brands produced by various manufacturers known to the field and a composite membrane formed by welding or bonding the wettable polyolefin microporous membrane and the membrane.
The preparation method of the secondary lithium ion battery comprises the steps of preparing an anode, a cathode and a diaphragm into an electrode group, and sealing the obtained electrode group and electrolyte in a battery shell to obtain the secondary lithium ion battery, wherein the electrolyte is the electrolyte provided by the invention. The injection amount of the electrolyte is generally 1.5 to 4.9g/Ah, and the concentration of the electrolyte is generally 0.5 to 2.9 mol/L.
The preparation method of the positive electrode comprises the steps of coating slurry containing a positive electrode active substance, a binding agent and a selective conductive agent on a positive electrode current collector, drying, rolling and slicing to obtain the positive electrode. The drying is generally carried out at from 50 to 160 ℃ and preferably from 80 to 150 ℃.
The negative electrode is prepared in the same manner as the positive electrode except that the slurry containing the positive electrode active material, the binder and the conductive agent is replaced with a slurry containing the negative electrode active material and the binder.
The electrolyte provided by the invention can be applied to various lithium ion secondary batteries, and is particularly suitable for being used for anode active material of lithium phosphate metal salt such as LiFePO4The obtained lithium ion secondary battery was prepared.
The following examples further illustrate the invention.
Example 1
Preparing an electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, taking 30g of ethylene carbonate, 30g of diethyl carbonate and 30g of methyl ethyl carbonate, mixing, adding 30g of lithium hexafluorophosphate and 90g of 2-methyl-1, 2 oxa-phosphine-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare a non-aqueous electrolyte, wherein the non-aqueous electrolyte is recorded as C1. 2-methyl-1, 2-oxaphospho-4-fluoro-5-one-2 oxide has the following structural formula:
LiNi0.5Co0.2Mn0.3O2, acetylene black and polyvinylidene fluoride are mixed according to the weight ratio of 85: 10: 5, uniformly mixing the mixture with an anode solvent N-methyl pyrrolidone to prepare anode slurry, coating the anode slurry on an aluminum foil, drying and rolling to prepare an anode plate; mixing graphite (P15B), styrene butadiene rubber and sodium cellulose carboxylate according to the weight ratio of 100: 3: 2, uniformly mixing the mixture with a negative solvent water to prepare a negative slurry, coating the negative slurry on a copper foil, drying and rolling to prepare a negative plate; assembling the prepared positive plate, the prepared negative plate and the Celgard2300 type microporous diaphragm into a soft package battery; and (3) injecting the nonaqueous electrolytic solution prepared in the step (1) into an argon glove box, and sealing to prepare the lithium ion battery S1.
Example 2
Preparing electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of methyl ethyl carbonate and 0.056g of Vinylene Carbonate (VC), adding 19g of lithium hexafluorophosphate and 22.5g of 2-methyl-1, 2-oxa-phospho-5-ketone-2 oxide, and uniformly mixing to prepare non-aqueous electrolyte, wherein the non-aqueous electrolyte is marked as C2; the lithium ion battery obtained in reference example 1 was designated as S2. The 2-methyl-1, 2-oxaphospho-5-one-2 oxide has the following structural formula:
example 3
Preparing electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of ethyl methyl carbonate and 0.075g of Vinylene Carbonate (VC), adding 25g of lithium hexafluorophosphate, 30g of 2-ethyl-1, 2-oxaphosphorin-5-one-2 oxide and 30g of 2-methyl-1, 2-oxaphosphorin-4-fluoro-5-one-2 oxide to prepare nonaqueous electrolyte, and marking as C3; the lithium ion battery obtained in reference example 1 was designated as S3. The 2-ethyl-1, 2-oxaphospho-5-one-2 oxide has the following structural formula:
example 4
Preparing an electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of methyl ethyl carbonate, 0.88g of fluoroethylene carbonate (FEC) and 0.88g of Vinylene Carbonate (VC), adding 25g of lithium hexafluorophosphate, 30g of 2-methyl-1, 2 oxaphosphorus-4-trifluoroethyl-5-ketone-2 oxide and 30g of 2-methyl-1, 2 oxaphosphorus-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare a non-aqueous electrolyte, which is marked as C4; the lithium ion battery obtained in reference example 1 was designated as S4. 2-methyl-1, 2-oxaphospho-4-trifluoroethyl-5-one-2 oxide has the following structural formula:
example 5
Preparing electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, taking 30g of ethylene carbonate, 30g of diethyl carbonate and 30g of methyl ethyl carbonate, mixing, adding 19g of lithium hexafluorophosphate, 11.25g of 2-methyl-1, 2-oxaphosphorin-4-trifluoromethyl-5-ketone-2 oxide and 11.25g of 2-methyl-1, 2-oxaphosphorin-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare a non-aqueous electrolyte, wherein the non-aqueous electrolyte is marked as C5; the lithium ion battery obtained in reference example 1 was designated as S5. 2-methyl-1, 2-oxaphospho-4-trifluoromethyl-5-one-2 oxide has the following structural formula:
example 6
Preparing an electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of methyl ethyl carbonate and 4.5g of Vinylene Carbonate (VC), adding 19g of lithium hexafluorophosphate, 11.25g of 2-methyl-1, 2-oxaphosphorin-4-methyl 5-ketone-2 oxide and 11.25g of 2-methyl-1, 2-oxaphosphorin-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare a non-aqueous electrolyte, wherein the non-aqueous electrolyte is marked as C6; the lithium ion battery obtained in reference example 1 was designated as S6. 2-methyl-1, 2-oxaphospho-4-methyl-5-one-2 oxide has the following structural formula:
example 7
Preparing electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of dimethyl carbonate and 4.5g of Vinylene Carbonate (VC), adding 19g of lithium hexafluorophosphate and 22.5g of 2-methyl-1, 2-oxaphosphorin-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare non-aqueous electrolyte, wherein the non-aqueous electrolyte is recorded as C7; the lithium ion battery obtained in reference example 1 was designated as S7.
Example 8
Preparing electrolyte in a glove box, controlling the oxygen content in the glove box to be less than 2ppm, filling the glove box with nitrogen and controlling the purity of the nitrogen in the glove box to be 99.999%, mixing 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of methyl ethyl carbonate and 4.5g of Vinylene Carbonate (VC), adding 11.72g of lithium tetrafluoroborate and 22.5g of 2-methyl-1, 2-oxaphosphorin-4-fluoro-5-ketone-2 oxide, and uniformly mixing to prepare non-aqueous electrolyte, wherein the non-aqueous electrolyte is recorded as C8; the lithium ion battery obtained in reference example 1 was designated as S8.
Comparative example 1
An electrolyte was placed in a glove box, the oxygen content in the glove box was controlled to be <2ppm, the glove box was filled with nitrogen gas, the purity of the nitrogen gas in the glove box was controlled to be 99.999%, 30g of ethylene carbonate, 30g of diethyl carbonate, 30g of ethyl methyl carbonate, 4.5g of Vinylene Carbonate (VC) were mixed, 19g of lithium hexafluorophosphate and 22.5g of trimethyl phosphate were added thereto and mixed uniformly, and a nonaqueous electrolyte solution was prepared and recorded as DS1, and the lithium ion battery prepared in example 1 was recorded as DS 1.
Performance testing
(1) Cycle performance test
The experimental batteries S1 to S8 and DS1 were charged to 4.35V at a temperature of 25 ℃ with a constant current of 100mA, then charged at a constant voltage of 4.35V until the current value was 20mA, and then discharged to 3V with a constant current of 100mA as one cycle; recording the first charge capacity and discharge capacity and calculating the first coulombic efficiency (%); after the charge and discharge cycles were repeated 200 times in this manner, the discharge capacity at the 200 th cycle was recorded, and the capacity retention (%) after the cycles was calculated as discharge capacity at the 200 cycles/first discharge capacity × 100%; the test results are shown in table 1.
(2) Test for flame retardancy
Taking a plurality of small disks with the diameter of 1cm from a glass fiber filter membrane, weighing the weight of each small disk, clamping each small disk by using tweezers, soaking each small disk in electrolyte C1-C8 and DC1 for 1min, wiping off redundant liquid on the surface, weighing the weight of each small disk after the electrolyte is absorbed, wherein the weight of each small disk after the electrolyte is absorbed, namely the weight of the electrolyte absorbed by each small disk before the electrolyte is absorbed, igniting the electrolyte by using an ignition device, recording the time from the moment the ignition device is removed to the moment the electrolyte is extinguished, and calculating the self-extinguishing time of the electrolyte in unit mass, wherein the test result is shown in Table 2.
TABLE 1
TABLE 2
As can be seen from tables 1 and 2, by adopting the phosphate compound with the structure as the electrolyte additive, the cycle performance of the battery is not affected, and meanwhile, the electrolyte has good flame retardant property, and the safety performance of the battery is greatly improved.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (13)
1. A nonaqueous electrolytic solution containing a lithium salt, an organic solvent, and an additive, characterized in that the additive has a structure represented by formula (1):
formula (1)
Wherein R1 is selected from one of alkyl, aryl, cycloalkyl and silyl; r2 and R3 are each independently one selected from a hydrogen atom, an alkyl group, a cycloalkyl group and a silane group; r4 and R5 are independently selected from one of hydrogen atom, halogen, alkyl, cycloalkyl, alkoxy, haloalkyl and halocycloalkyl, wherein the halogen is one of F, Cl and Br.
2. The nonaqueous electrolytic solution of claim 1, wherein R1 is one selected from an alkyl group having 1 to 5 carbon atoms, a phenyl group, a cycloalkyl group having 1 to 5 carbon atoms, and a silane group having 1 to 5 carbon atoms.
3. The nonaqueous electrolytic solution of claim 1, wherein R2 and R3 are each independently one selected from a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a cycloalkyl group having 1 to 5 carbon atoms, and a silane group having 1 to 5 carbon atoms.
4. The nonaqueous electrolytic solution of claim 1, wherein R4 and R5 are each independently one selected from H, F, an alkyl group having 1 to 5 carbon atoms, a cycloalkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, and a halocycloalkyl group having 1 to 5 carbon atoms.
5. The nonaqueous electrolytic solution of claim 1, wherein the additive is selected from one or more of 2-methyl-1, 2-oxaphosphine-4-fluoro-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-5-one-2 oxide, 2-ethyl-1, 2-oxaphosphine-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoroethyl-5-one-2 oxide, 2-methyl-1, 2-oxaphosphine-4-trifluoromethyl-5-one-2 oxide, and 2-methyl-1, 2-oxaphosphine-4-methyl-5-one-2 oxide.
6. The nonaqueous electrolytic solution of claim 1, wherein the additive is contained in an amount of 0.05 to 50 parts by weight based on the total mass of the organic solvent and the additive.
7. The nonaqueous electrolytic solution of claim 6, wherein the additive is contained in an amount of 0.05 to 20 parts by weight based on the total mass of the organic solvent and the additive.
8. The nonaqueous electrolytic solution of claim 1, wherein the electrolytic solution further comprises an auxiliary additive, and the auxiliary additive comprises one or more of 1,3 propane sultone, 1,4 butane sultone, propenyl-1, 3-sultone, vinyl sulfate, propylene sulfate, butylene sulfite, vinylene carbonate and fluoroethylene carbonate.
9. The nonaqueous electrolytic solution of claim 8, wherein the content of the auxiliary additive is 0.05 to 20 parts by weight based on the total mass of the organic solvent and the additive.
10. The nonaqueous electrolytic solution of claim 9, wherein the content of the auxiliary additive is 0.5 to 5 parts by weight based on the total mass of the organic solvent and the additive.
11. The nonaqueous electrolytic solution of claim 1, wherein the organic solvent is one or more selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, gamma-butyrolactone, sultone, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, methyl butyrate, and ethyl acetate.
12. The nonaqueous electrolytic solution of claim 1, wherein the lithium salt is selected from the group consisting of LiBOB and LiPF6、LiBF4、LiNSO2CF3、LiDFOB、LiSbF6、LiClO4、LiCF3SO3、Li(CF3SO2)2N、LiC4F9SO3、LiAlO4、LiAsF6、LiAlCl4One or more of LiCl, LiI and low-fatty acid lithium carbonate, wherein the concentration of the lithium salt is 0.3-3 mol/L.
13. A lithium ion battery comprising a battery case, and a cell and a nonaqueous electrolytic solution sealed in the battery case, the cell comprising a positive electrode, a negative electrode and a separator, characterized in that the nonaqueous electrolytic solution is the nonaqueous electrolytic solution according to any one of claims 1 to 12.
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