Electrolyte for lithium-ion capacitor and lithium-ion capacitor

Abstract

The present invention relates to the technical field of lithium-ion capacitors, and in particular to an electrolyte for a lithium-ion capacitor and a lithium-ion capacitor. The electrolyte for a lithium-ion capacitor comprises an organic solvent, a lithium salt, and additives, wherein the additives include a negative electrode film-forming additive and a water‑removal and acid‑suppression additive. By selecting the negative electrode film-forming additive and the water‑removal and acid‑suppression additive for use in reasonable combination with the organic solvent and the lithium salt, the electrolyte for a lithium-ion capacitor of the present invention enables lithium-ion capacitors to have high energy density performance and a longer cycle life.

Description

Electrolyte for lithium ion capacitor and lithium ion capacitor TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion capacitor, and in particular to an electrolyte for lithium ion capacitor and a lithium ion capacitor. BACKGROUND

[0002] As a new generation of energy storage device, lithium ion capacitor combines the advantages of lithium ion battery and super capacitor, and has high specific energy, high specific power and long service life. + The negative electrode usually uses Li

[0003] However, the current research on lithium ion capacitor is mainly focused on the application of positive and negative electrode materials and separators, and there are relatively few suitable electrolyte developments. SUMMARY

[0004] The present application provides an electrolyte for lithium ion capacitor and a lithium ion capacitor to solve the problems of limited energy density and adverse reactions such as gas production during development of existing lithium ion capacitor.

[0005] According to the first aspect of the present application, the present application provides an electrolyte for lithium ion capacitor, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a negative electrode film-forming additive and a water removal and acid suppression additive.

[0006] In the above scheme, the electrolyte for lithium ion capacitor of the present application comprises an organic solvent, a lithium salt and an additive, and the additive comprises a negative electrode film-forming additive and a water removal and acid suppression additive.

[0007] Further, the water scavenging and acid suppressing additive is added in an amount of 0.1% to 2% based on 100% of the mass of the organic solvent.

[0008] Alternatively, the water scavenging and acid suppressing additive can be added in an amount of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0% based on 100% of the mass of the organic solvent, and of course other values within the above range are also possible and are not limited herein. Preferably, the water scavenging and acid suppressing additive is added in an amount of 0.5% to 1.5%, and more preferably 0.1%.

[0009] Preferably, the water scavenging and acid suppressing additive comprises one or more of triphenyl phosphite, hexamethyldisilazane, diisopropyl carbodiimide, heptamethyldisilazane, tris(trimethylsilyl) phosphate or N'N-dicyclohexyl carbodiimide, and preferably one or more of tris(trimethylsilyl) phosphate or N'N-dicyclohexyl carbodiimide.

[0010] In the above scheme, by selecting a suitable type of water scavenging and acid suppressing additive and limiting the amount of water scavenging and acid suppressing additive to a reasonable range of values, the additive and other components can achieve better synergistic effects, thereby improving the performance of the electrolyte, and thereby improving the energy density, high and low temperature performance and long cycle life performance of the lithium ion capacitor, and improving the gas production phenomenon.

[0011] Further, the negative electrode film-forming additive is added in an amount of 1% to 5% based on 100% of the mass of the organic solvent.

[0012] Alternatively, the negative electrode film-forming additive can be added in an amount of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% based on 100% of the mass of the organic solvent, and of course other values within the above range are also possible and are not limited herein, and preferably 3.5% to 4.5%.

[0013] Preferably, the negative electrode film-forming additive comprises one or more of vinylene carbonate, fluoroethylene carbonate, vinyl vinylene carbonate, vinyl sulfite, vinyl sulfate, 1,3-propane sultone, 1,3-propene sultone or methylene methane disulfonate, and preferably one or more of vinylene carbonate, 1,3-propane sultone or fluoroethylene carbonate.

[0014] In the above scheme, by selecting a suitable type of negative electrode film-forming additive, limiting the amount of negative electrode film-forming additive within a reasonable range, the additive and other components can achieve better synergistic effect, thereby improving the performance of the electrolyte, and further improving the energy density, high and low temperature performance and long cycle life performance of the lithium ion capacitor, and improving the gas production phenomenon.

[0015] Further, the organic solvent includes one or more of cyclic carbonates, chain carbonates and carboxylic acid esters;

[0016] The cyclic carbonates are one or more of ethylene carbonate, propylene carbonate, butylene carbonate or fluoroethylene carbonate, preferably one or both of ethylene carbonate or propylene carbonate;

[0017] The chain carbonates are one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate or methyl propyl carbonate, preferably one or both of dimethyl carbonate or methyl ethyl carbonate;

[0018] The carboxylic acid esters are one or more of methyl acetate, ethyl acetate, methyl propionate or ethyl propionate, preferably one or both of ethyl propionate or ethyl acetate.

[0019] Further, in the organic solvent, the content of cyclic carbonates is 10%-50% (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., of course, other values within the above range are also possible, which are not limited here), the content of chain carbonates is 30%-80% (for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., of course, other values within the above range are also possible, which are not limited here), and the content of carboxylic acid esters is 0%-40% (for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc., of course, other values within the above range are also possible, which are not limited here);

[0020] Preferably, in the organic solvent, the content of cyclic carbonates is 25%-35%, the content of chain carbonates is 55%-65%, and the content of carboxylic acid esters is 5%-15%.

[0021] It is found through experiments that adjusting the organic solvent system and adding negative electrode film-forming additives and water and acid removal additives in the electrolyte can make the capacitor have excellent energy density performance, high and low temperature performance and long cycle life performance, and the gas production phenomenon of the lithium ion capacitor is significantly improved during the cycle process.

[0022] Further, the concentration of the lithium salt in the organic solvent is 0.8-1.6 M; for example, 0.8 M, 0.9 M, 1.0 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, 1.5 M, 1.6 M, etc., and of course other values within the above range are also possible, which are not limited herein, preferably 1-1.6 M, and more preferably 1.4-1.6 M.

[0023] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, or lithium difluorophosphate, preferably one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium difluorophosphate.

[0024] In the above scheme, by selecting the appropriate type of lithium salt and limiting the amount of lithium salt within a reasonable range, the lithium salt and other components can achieve better synergistic effect, thereby improving the performance of the electrolyte, and further improving the energy density, high and low temperature performance, and long cycle life performance of the lithium ion capacitor, and improving the gas generation phenomenon.

[0025] According to a second aspect of the present application, the present application also provides a lithium ion capacitor, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the electrolyte is the above-mentioned electrolyte for lithium ion capacitors.

[0026] The lithium ion capacitor of the present application uses the above-mentioned electrolyte of the present application, which provides the anions and cations required for the adsorption and desorption of the positive electrode material and the reversible intercalation and deintercalation of the negative electrode material during the charging and discharging process, and provides the necessary environment for the migration of ions between the positive and negative electrodes; the energy storage type lithium ion capacitor using the electrolyte has excellent electrical performance, safety performance, and cycle life, stable high and low temperature performance, excellent cycle performance, long calendar life, high energy density, and other advantages, and can improve the abnormal gas generation of the lithium ion capacitor.

[0027] Further, the positive electrode sheet is formed by coating and drying a positive electrode slurry, the positive electrode slurry comprises a positive electrode active material, porous carbon, a first conductive agent, a first binder, and a first solvent, the positive electrode active material comprises one or more of lithium iron phosphate, lithium cobaltate, and lithium nickel cobalt manganese oxide, and preferably lithium iron phosphate.

[0028] Preferably, the positive electrode slurry has the following dry powder mass percentage: positive electrode active material 80-98%, porous carbon 1-20%, first conductive agent 0.1-15%, and first binder 1-10%.

[0029] The positive electrode sheet is prepared by selecting a positive electrode slurry with a specific component amount ratio, so that the obtained positive electrode sheet and the electrolyte form a better synergistic effect, further improving the overall performance of the lithium ion capacitor.

[0030] Further, the negative electrode sheet is formed by coating and drying a negative electrode slurry, the negative electrode slurry comprising a carbon material, a second conductive agent, a thickening agent, a second binder and a second solvent; the carbon material comprising hard carbon and artificial graphite;

[0031] Preferably, the negative electrode slurry comprises, in terms of dry powder mass percentage, 80-95% of the carbon material, 1-5% of the second conductive agent, 1-5% of the thickening agent, and 0.5-5% of the second binder, wherein the artificial graphite accounts for 1-45% of the total mass of the artificial graphite and the hard carbon.

[0032] The negative electrode sheet is prepared by selecting a specific component dosage ratio of the negative electrode slurry, so that the obtained negative electrode sheet forms a better synergistic effect with the electrolyte, further improving the overall performance of the lithium ion capacitor.

[0033] Further, the optimal working range of the lithium ion capacitor is 2.3-3.5V, and the rated working temperature is -30~+60℃. Advantages

[0034] The electrolyte for the lithium ion capacitor provided by the application can make the energy storage type lithium ion capacitor have higher energy density (≥60Wh*kg), more excellent high and low temperature performance and cycle life, and the high rate cycle at room temperature can reach 30000 times or more, and the electrolyte can effectively inhibit the gas production of the capacitor during the cycle charging and discharging process. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0036] Fig. 1 is a comparison chart of the thickness growth rate of the lithium ion capacitor during the cycle process of the lithium ion capacitor prepared by the electrolyte for the lithium ion capacitor of the application in examples 1-3, example 6, and comparative examples 1-2.

[0037] Fig. 2 is a room temperature cycle life curve of the lithium ion capacitor prepared by the electrolyte for the lithium ion capacitor of the application in examples 1, 3, 9, 10, 12, and comparative example 1. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall into the scope of the present application.

[0039] The beneficial effects of the present application will be described below in combination with specific examples and comparative examples.

[0040] Example 1

[0041] The present example provides an electrolyte for lithium ion capacitor, which comprises organic solvent, lithium salt and additive, the additive comprises negative electrode film forming additive and water removal and acid suppression additive, the organic solvent comprises dimethyl carbonate, methyl ethyl carbonate, vinyl carbonate, propylene carbonate and ethyl propionate, the lithium salt is lithium hexafluorophosphate, the negative electrode film forming additive is vinylene carbonate and 1,3-propylene sulfite, and the water removal and acid suppression additive is tris(trimethylsilyl) phosphate.

[0042] The preparation method of the electrolyte is as follows: 40% of dimethyl carbonate and 20% of methyl ethyl carbonate, 25% of vinyl carbonate and 5% of propylene carbonate, and 10% of ethyl propionate are taken according to the mass percentage content, and are fully mixed and uniformly distributed in a glove box with humidity less than 1% to prepare electrolyte solvent; 1.5 mol / L of electrolyte salt lithium hexafluorophosphate is added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% of vinylene carbonate, 1% of tris(trimethylsilyl) phosphate and 1.5% of 1,3-propylene sulfite are added to the solvent, taking the mass of the organic solvent as 100%, and the mixture is uniformly mixed by an electric mixer to obtain the energy storage type lithium ion capacitor electrolyte.

[0043] Example 2

[0044] The present example provides an electrolyte for lithium ion capacitor, which comprises organic solvent, lithium salt and additive, the additive comprises negative electrode film forming additive and water removal and acid suppression additive, the organic solvent comprises dimethyl carbonate, methyl ethyl carbonate, vinyl carbonate, propylene carbonate and ethyl propionate, the lithium salt is lithium hexafluorophosphate and lithium bis(fluorosulfonyl) imide, the negative electrode film forming additive is vinylene carbonate and 1,3-propylene sulfite, and the water removal and acid suppression additive is tris(trimethylsilyl) phosphate.

[0045] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate and 5% propylene carbonate, and 10% ethyl propionate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.5 mol / L electrolyte salt lithium bis (fluorosulfonyl) imide are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris (trimethylsilyl) phosphate and 1.5% 1, 3-propylene sulfone lactone are added to the solvent, taking the mass of the organic solvent as 100%, and the mixture is mixed uniformly by an electric mixer to obtain the energy storage type lithium ion capacitor electrolyte.

[0046] Example 3

[0047] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film forming additive and water removal acid inhibitor additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film forming additive is vinylene carbonate and 1, 3-propylene sulfone lactone, water removal acid inhibitor additive is tris (trimethylsilyl) phosphate.

[0048] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate and 5% propylene carbonate, and 10% ethyl propionate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.5 mol / L electrolyte salt lithium bis (fluorosulfonyl) imide are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris (trimethylsilyl) phosphate and 1.5% 1, 3-propylene sulfone lactone are added to the solvent, taking the mass of the organic solvent as 100%, and the mixture is mixed uniformly by an electric mixer to obtain the energy storage type lithium ion capacitor electrolyte.

[0049] Example 4

[0050] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film forming additive and water removal acid inhibitor additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film forming additive is vinylene carbonate and 1, 3-propylene sulfone lactone, water removal acid inhibitor additive is tris (trimethylsilyl) phosphate.

[0051] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate, and 5% propylene carbonate, and 10% ethyl acetate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure an electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.4 mol / L electrolyte salt lithium bis(fluorosulfonyl)imide, and 0.1 mol / L electrolyte salt lithium difluorophosphate are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris(trimethylsilyl) phosphate, and 1.5% 1,3-propylene sultone are added to the solvent, taking the mass of the organic solvent as 100%, and the electrolyte for energy storage type lithium ion capacitors is obtained after uniform mixing by using an electric mixer.

[0052] Example 5

[0053] The embodiment provides an electrolyte for lithium ion capacitors, which comprises an organic solvent, a lithium salt, and an additive, the additive comprises a negative electrode film-forming additive and a water removal and acid suppression additive, the organic solvent comprises dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate, and ethyl acetate, the lithium salt is lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate, the negative electrode film-forming additive is vinylene carbonate and 1,3-propylene sultone, and the water removal and acid suppression additive is tris(trimethylsilyl) phosphate.

[0054] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate, and 5% propylene carbonate, and 5% ethyl propionate, and 5% ethyl acetate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure an electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.4 mol / L electrolyte salt lithium bis(fluorosulfonyl)imide, and 0.1 mol / L electrolyte salt lithium difluorophosphate are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris(trimethylsilyl) phosphate, and 1.5% 1,3-propylene sultone are added to the solvent, taking the mass of the organic solvent as 100%, and the electrolyte for energy storage type lithium ion capacitors is obtained after uniform mixing by using an electric mixer.

[0055] Example 6

[0056] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film forming additive and water removal acid suppression additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, vinyl carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film forming additive is vinylene carbonate and 1,3-propylene sulfone lactone, water removal acid suppression additive is N'N-dicyclohexyl carbodiimide.

[0057] The preparation method of the electrolyte is as follows: 40% of dimethyl carbonate and 20% of methyl ethyl carbonate, 25% of vinyl carbonate and 5% of propylene carbonate, 10% of ethyl propionate are taken according to mass percentage content, are fully mixed uniformly in the humidity less than 1% glove box, and are configured into electrolyte solvent;1.0 mol / L of electrolyte salt lithium hexafluorophosphate, 0.4 mol / L of electrolyte salt lithium bis (fluorosulfonyl) imide, 0.1 mol / L of electrolyte salt lithium difluorophosphate are added to the solvent;After lithium hexafluorophosphate is dissolved, 2.5% of vinylene carbonate, 1% of N'N-dicyclohexyl carbodiimide and 1.5% of 1,3-propylene sulfone lactone are added to the solvent, taking the mass of organic solvent as 100%, and the energy storage type lithium ion capacitor electrolyte is obtained after being mixed uniformly by electric mixer.

[0058] Example 7

[0059] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film forming additive and water removal acid suppression additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, vinyl carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film forming additive is vinylene carbonate and 1,3-propylene sulfone lactone, water removal acid suppression additive is N'N-dicyclohexyl carbodiimide.

[0060] The preparation method of the electrolyte is as follows: 40% of dimethyl carbonate and 20% of methyl ethyl carbonate, 25% of vinyl carbonate and 5% of propylene carbonate, 10% of ethyl propionate are taken according to mass percentage content, are fully mixed uniformly in the humidity less than 1% glove box, and are configured into electrolyte solvent;1.0 mol / L of electrolyte salt lithium hexafluorophosphate, 0.4 mol / L of electrolyte salt lithium bis (fluorosulfonyl) imide, 0.1 mol / L of electrolyte salt lithium difluorophosphate are added to the solvent;After lithium hexafluorophosphate is dissolved, 2.5% of vinylene carbonate, 1% of N'N-dicyclohexyl carbodiimide and 1.5% of 1,3-propylene sulfone lactone are added to the solvent, taking the mass of organic solvent as 100%, and the energy storage type lithium ion capacitor electrolyte is obtained after being mixed uniformly by electric mixer.

[0061] Example 8

[0062] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film-forming additive and water removal acid inhibitor additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film-forming additive is vinylene carbonate, 1,3-propylene sulfone lactone and methane methylene disulfonate, water removal acid inhibitor additive is tris (trimethylsilyl) phosphate.

[0063] The preparation method of the electrolyte is as follows: 40% of dimethyl carbonate and 20% of methyl ethyl carbonate, 25% of ethylene carbonate and 5% of propylene carbonate, 10% of ethyl propionate are taken according to mass percentage content, are fully mixed uniformly in glove box with humidity less than 1%, and are configured into electrolyte solvent; 1.0 mol / L of electrolyte salt lithium hexafluorophosphate, 0.4 mol / L of electrolyte salt lithium bis (fluorosulfonyl) imide, 0.1 mol / L of electrolyte salt lithium difluorophosphate are added to the solvent; after lithium hexafluorophosphate is dissolved, 2.5% of vinylene carbonate, 1% of tris (trimethylsilyl) phosphate, 1.0% of 1,3-propylene sulfone lactone and 0.5% of methane methylene disulfonate are added to the solvent, taking the mass of organic solvent as 100%, and the energy storage type lithium ion capacitor electrolyte is obtained after being mixed uniformly by electric mixer.

[0064] Example 9

[0065] The embodiment provides a kind of electrolyte for lithium ion capacitor, including organic solvent, lithium salt and additive, additive includes negative electrode film-forming additive and water removal acid inhibitor additive, organic solvent includes dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, negative electrode film-forming additive is vinylene carbonate, 1,3-propylene sulfone lactone and fluorinated ethylene carbonate, water removal acid inhibitor additive is tris (trimethylsilyl) phosphate.

[0066] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate and 5% propylene carbonate and 10% ethyl propionate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.4 mol / L electrolyte salt lithium bis (fluorosulfonyl) imide and 0.1 mol / L electrolyte salt lithium difluorophosphate are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris (trimethylsilyl) phosphate, 1.0% 1, 3-propylene sulfone and 0.5% fluoroethylene carbonate are added to the solvent, taking the mass of the organic solvent as 100%, and the electrolyte for energy storage type lithium ion capacitor is obtained after the mixture is mixed uniformly by an electric mixer.

[0067] Example 10

[0068] The embodiment provides an electrolyte for lithium ion capacitor, which comprises an organic solvent, a lithium salt and an additive, the additive comprises a negative electrode film forming additive and a water removal and acid suppression additive, the organic solvent comprises dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, the lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, the negative electrode film forming additive is vinylene carbonate, 1, 3-propylene sulfone and ethylene sulfate, and the water removal and acid suppression additive is tris (trimethylsilyl) phosphate.

[0069] The preparation method of the electrolyte is as follows: 40% dimethyl carbonate, 20% methyl ethyl carbonate, 25% ethylene carbonate and 5% propylene carbonate and 10% ethyl propionate are taken respectively according to the mass percentage content, and are fully mixed uniformly in a glove box with humidity less than 1% to configure electrolyte solvent; 1.0 mol / L electrolyte salt lithium hexafluorophosphate, 0.4 mol / L electrolyte salt lithium bis (fluorosulfonyl) imide and 0.1 mol / L electrolyte salt lithium difluorophosphate are added to the solvent; after the lithium hexafluorophosphate is dissolved, 2.5% vinylene carbonate, 1% tris (trimethylsilyl) phosphate, 1.0% 1, 3-propylene sulfone and 0.5% ethylene sulfate are added to the solvent, taking the mass of the organic solvent as 100%, and the electrolyte for energy storage type lithium ion capacitor is obtained after the mixture is mixed uniformly by an electric mixer.

[0070] Example 11

[0071] The embodiment provides an electrolyte for lithium ion capacitor, which comprises an organic solvent, a lithium salt and an additive, the additive comprises a negative electrode film forming additive and a water removal and acid suppression additive, the organic solvent comprises dimethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate, the lithium salt is lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium difluorophosphate, the negative electrode film forming additive is vinylene carbonate, 1, 3-propylene sulfone and ethylene sulfate, and the water removal and acid suppression additive is tris (trimethylsilyl) phosphate.

[0072] Example 12

[0073] The embodiment provides a lithium ion capacitor electrolyte, and a preparation method thereof is as follows: 45% of dimethyl carbonate and 25% of methyl ethyl carbonate, 25% of ethylene carbonate and 5% of propylene carbonate are taken respectively according to mass percentage content, are uniformly mixed in a glove box with humidity less than 1%, and are configured into electrolyte solvents; 1.5 mol / L of electrolyte salt lithium hexafluorophosphate is added into the solvents; after the lithium hexafluorophosphate is dissolved, 2.5% of vinylene carbonate, 1% of tris(trimethylsilyl) phosphate and 1.5% of 1,3-propylene sultone are added into the solvents, taking the mass of the organic solvents as 100%, and the energy storage type lithium ion capacitor electrolyte is obtained after uniform mixing by using an electric mixer.

[0074] Embodiment 13

[0075] The embodiment provides a lithium ion capacitor electrolyte, and the difference from the embodiment 1 is only that the lithium salt lithium hexafluorophosphate has a concentration of 1.0 M, and the rest of components, component allocation ratios and the preparation method are the same as those of the embodiment 1.

[0076] Embodiment 14

[0077] The embodiment provides a lithium ion capacitor electrolyte, and the difference from the embodiment 1 is only that the lithium salt lithium hexafluorophosphate has a concentration of 1.3 M, and the rest of components, component allocation ratios and the preparation method are the same as those of the embodiment 1.

[0078] Embodiment 15

[0079] The embodiment provides a lithium ion capacitor electrolyte, and the difference from the embodiment 1 is only that the vinylene carbonate has an addition amount of 3.0%, and the rest of components, component allocation ratios and the preparation method are the same as those of the embodiment 1.

[0080] Embodiment 16

[0081] The embodiment provides a lithium ion capacitor electrolyte, and the difference from the embodiment 1 is only that the vinylene carbonate has an addition amount of 0.5%, and the rest of components, component allocation ratios and the preparation method are the same as those of the embodiment 1.

[0082] Embodiment 17

[0083] The embodiment provides a lithium ion capacitor electrolyte, and the difference from the embodiment 1 is only that the tris(trimethylsilyl) phosphate has an addition amount of 0.2%, and the rest of components, component allocation ratios and the preparation method are the same as those of the embodiment 1.

[0084] Comparative embodiment 1

[0085] The comparative example 1 provides an electrolyte for a lithium ion capacitor, which is different from example 1 only in that no tris(trimethylsilyl) phosphate is added, and the rest of the components, component ratio and preparation method are the same as example 1.

[0086] Comparative example 2:

[0087] The comparative example 1 provides an electrolyte for a lithium ion capacitor, which is different from example 1 only in that no tris(trimethylsilyl) phosphate is added, and the rest of the components, component ratio and preparation method are the same as example 1.

[0088] Example 18

[0089] The electrolyte prepared by examples 1-17 and comparative examples 1-2 is used to prepare a lithium ion capacitor, which includes a positive electrode sheet, a negative electrode sheet, a separator film and an electrolyte.

[0090] The positive electrode material is composed of lithium iron phosphate (or lithium cobaltate, lithium nickel cobalt manganese oxide), porous carbon, conductive agent, PVDF binder, and the mass ratio of its components is 85%, 5%, 5%, 5%. Then each material is added in a certain order and mixed with NMP (N-methyl pyrrolidone) solvent, and the viscosity is adjusted after high-speed stirring and dispersion to prepare a positive electrode slurry.

[0091] The negative electrode material is composed of hard carbon, artificial graphite, conductive agent, thickening agent, SBR (styrene-butadiene rubber) binder, and the mass ratio of its components is 90% of hard carbon and artificial graphite, 4% of conductive agent, 3% of thickening agent, and 3% of SBR binder. Then each material is added in a certain order and mixed with deionized water solvent, and the viscosity is adjusted after high-speed stirring and dispersion to prepare a negative electrode slurry.

[0092] The positive electrode sheet, the negative electrode sheet and the cellulose separator film are assembled into a soft package and an aluminum shell cell of a lithium ion capacitor in a Z-type stacking manner, and the electrolyte prepared by examples 1-17 and comparative examples 1-2 is injected, and after a series of measures such as formation, aging, vacuum sealing and capacity, the final lithium ion capacitor is obtained.

[0093] According to the test methods of QC / T 741-2014 supercapacitor for vehicle, DL / T 2080-2020 supercapacitor for power energy storage and DL / T+2081-2020 supercapacitor for power energy storage test procedures, the capacity, internal resistance, 5C calibration, high and low temperature performance, cyclic charge and discharge and other series tests of the capacitor prepared above are carried out in the voltage range of 2.2-3.65V, and the test results are shown in Table 1:

[0094] Table 1

[0095] The thickness of the square aluminum-cased capacitor prepared above was tested during cyclic charging and discharging, and the increase in thickness with the number of cycles was calculated. The test results are shown in Table 2.

[0096] Table 2

[0097] Based on the test results above, it can be seen that the electrolyte for lithium-ion capacitors of the present invention, by adjusting the organic solvent system and adding negative electrode film-forming additives and dehydration and acid-suppressing additives to the electrolyte, can enable the capacitor to have excellent energy density performance, high and low temperature performance and long life cycle performance. Moreover, the gas generation phenomenon of lithium-ion capacitors during cycling is significantly improved. Among them, the electrolyte for lithium-ion capacitors in Example 3 has the best performance, with a cell thickness growth rate of only 5.11% after 20,000 cycles at 5C.

[0098] As can be seen from the energy density data in Table 1, at a 5C rate, the energy density of the lithium-ion capacitors prepared using the embodiments of the present invention is increased by 6-8.5 Wh*kg, and the energy density is significantly improved compared with Examples 1, 2, 3, 4, 5, 6, 10 and Comparative Examples 1 and 2.

[0099] As can be seen from the low-temperature performance data at -20℃ in Table 1, at a 5C rate, the experimental results of Examples 2, 3, 4, 5, 6, 9 and Example 12 show that the low-temperature performance of lithium-ion capacitors prepared using the electrolyte of the present invention is significantly improved. Adjusting the low-temperature organic solvent system and matching the negative electrode film-forming additives in the lithium-ion capacitor electrolyte results in a significant low-temperature effect.

[0100] As can be seen from the high-temperature performance data at 55℃ in Table 1, at a 5C rate, the lithium-ion capacitors prepared using the electrolyte of the present invention showed a thickness increase of ≤5% after 10,000 cycles, which is much lower than the data of the comparative examples. The electrolyte production line performance was significantly improved after adding water-removing and acid-suppressing additives.

[0101] As can be seen from the 25°C room temperature cycle life curve in Figure 2, the comparison between Examples 3, 9, 10, 12 and Comparative Example 1 shows that the lithium-ion capacitors prepared using the electrolyte of the present invention still retain 83% or more of the capacity after 20,000 cycles of 5C high-rate charge-discharge testing, and have a cycle life of ≥30,000 cycles. In contrast, Example 12, which did not add carboxylic acid ester, stopped at 15,719 cycles, indicating that adjusting the organic solvent system affects the cycle performance of the capacitor. Comparative Example 1, which did not add tris(trimethylsilyl)phosphate and 1,3-propenesulfonyl lactone, stopped at 12,606 cycles, indicating that the reasonable combination of the negative electrode film-forming additive and the dehydration and acid-suppressing additive of the present invention affects the cycle performance of the capacitor.

[0102] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features therein can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrolyte solution for a lithium-ion capacitor, characterized by comprising: The organic solvent, the lithium salt and the additive, wherein the additive comprises a negative electrode film-forming additive and a water and acid removal additive.

2. The electrolyte solution for a lithium-ion capacitor according to claim 1, characterized by, The water and acid removal additive is added in an amount of 0.1%-2%, preferably 0.5%-1.5%, based on 100% of the mass of the organic solvent; Preferably, the water and acid removal additive comprises one or more of triphenyl phosphite, hexamethyldisilazane, diisopropyl carbodiimide, heptamethyldisilazane, tris(trimethylsilyl) phosphate or N'N-dicyclohexyl carbodiimide, preferably one or more of tris(trimethylsilyl) phosphate or N'N-dicyclohexyl carbodiimide.

3. The electrolyte solution for a lithium-ion capacitor according to claim 1, characterized by, The negative electrode film-forming additive is added in an amount of 1%-5%, preferably 3.5%-4.5%, based on 100% of the mass of the organic solvent; Preferably, the negative electrode film-forming additive comprises one or more of vinylene carbonate, fluoroethylene carbonate, vinyl vinylene carbonate, vinyl sulfite, vinyl sulfate, 1,3-propane sultone, 1,3-propene sultone or methylene methane disulfonate, preferably one or more of vinylene carbonate, 1,3-propane sultone or fluoroethylene carbonate.

4. The electrolyte solution for a lithium-ion capacitor according to claim 1, characterized by The organic solvent comprises one or more of a cyclic carbonate, a chain carbonate and a carboxylic acid ester; The cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, butylene carbonate or fluoroethylene carbonate, preferably one or both of ethylene carbonate or propylene carbonate; The chain carbonate is one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate or methyl propyl carbonate, preferably one or both of dimethyl carbonate or methyl ethyl carbonate; The carboxylic acid ester is one or more of methyl acetate, ethyl acetate, methyl propionate or ethyl propionate, preferably one or both of ethyl propionate or ethyl acetate.

5. The electrolyte solution for a lithium-ion capacitor according to claim 4, characterized by In the organic solvent, the content of the cyclic carbonate is 10%-50%, the content of the chain carbonate is 30%-80% and the content of the carboxylic acid ester is 0%-40%; Preferably, in the organic solvent, the content of the cyclic carbonate is 25%-35%, the content of the chain carbonate is 55%-65% and the content of the carboxylic acid ester is 5%-15%.

6. The electrolyte solution for a lithium-ion capacitor according to claim 1, wherein The concentration of the lithium salt in the organic solvent is 0.8-1.6 M, preferably 1-1.6 M; Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide or lithium difluorophosphate, preferably one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide or lithium difluorophosphate.

7. A lithium-ion capacitor characterized by comprising: The lithium ion capacitor comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte is the electrolyte for lithium ion capacitors according to any one of claims 1-6.

8. The lithium-ion capacitor of claim 7, wherein, The positive electrode sheet is formed by coating and drying a positive electrode slurry, wherein the positive electrode slurry comprises a positive electrode active material, porous carbon, a first conductive agent, a first binder and a first solvent, and the positive electrode active material comprises one or more of lithium iron phosphate, lithium cobaltate and lithium nickel cobalt manganese oxide, preferably lithium iron phosphate; Preferably, the positive electrode slurry is in the following dry powder mass percentage: positive electrode active material 80-98%, porous carbon 1-20%, first conductive agent 0.1-15%, and first binder 1-10%.

9. The lithium-ion capacitor of claim 7, wherein, The negative electrode sheet is formed by coating and drying a negative electrode slurry, the negative electrode slurry comprising a carbon material, a second conductive agent, a thickening agent, a second binder, and a second solvent; the carbon material comprising hard carbon and artificial graphite; Preferably, the negative electrode slurry is in the following dry powder mass percentage: carbon material 80-95%, second conductive agent 1-5%, thickening agent 1-5%, and second binder 0.5-5%, wherein the artificial graphite accounts for 1-45% of the total mass of the artificial graphite and the hard carbon.

10. The lithium-ion capacitor of any one of claims 7-9, wherein, The optimal working range of the lithium ion capacitor is 2.3-3.5V, and the rated working temperature is -30~+60℃.

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