Electrolyte additive combination, electrolyte for electrochemical energy storage unit and application of electrolyte

Abstract

The invention provides an electrolyte additive combination, an electrolyte for an electrochemical energy storage unit and application of the electrolyte. And the electrolyte additive combination comprises a mono-cyano compound and a tricyano compound. The mono-cyano compound is selected from an additive A and / or an additive B. Cyano groups and phosphate groups in the additive A or the additive B are complexed with positive metal ions, so that the positive electrode can be effectively protected, and a phosphorus compound protective film is formed on the negative electrode. Cyano groups in the tricyanogroup compound and positive electrode metal ions have a complexing effect, so that the positive electrode can be effectively protected. The combination of the mono-cyano compound and the tricyano compound can play a synergistic role, so that the high-temperature storage performance and the high-temperature cycle performance of the battery can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolyte materials, and relates to an electrolyte additive combination, an electrolyte for an electrochemical energy storage unit, and applications thereof. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, power and energy storage. In order to meet the demand for high capacity, the development of high-voltage lithium batteries has become an effective means to improve energy density. The matching high-voltage electrolyte will use a large amount of positive electrode protection additives, among which nitrile additives are an indispensable component. Specifically, by combining dinitrile compounds and trinitrile compounds, better overall battery performance can be achieved. However, under a voltage system of 4.53V and higher, the combination of dinitrile compounds and trinitrile compounds has deficiencies in the high-temperature storage and high-temperature cycle performance of lithium batteries, and it is difficult to meet application requirements.

[0003] Therefore, it is urgent to develop an electrolyte system to solve the above problems. Summary of the invention

[0004] In view of the deficiencies in the prior art, the object of the present invention is to provide an electrolyte additive combination, an electrolyte for an electrochemical energy storage unit and applications thereof. The electrolyte additive combination is added to the electrolyte to effectively improve the high-temperature storage performance and high-temperature cycle performance of the electrochemical energy storage unit.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides an electrolyte additive combination, the electrolyte additive combination comprising a monocyano compound and a tricyano compound, the monocyano compound being selected from additive A and / or additive B, the structure of additive A being as shown in formula I, the structure of additive B being as shown in formula II,

[0007]

[0008] In formula I, R1 and R2 are each independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms;

[0009] In formula II, R3 and R4 are each independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms.

[0010] The present invention regulates the composition of the electrolyte additive combination, and the electrolyte additive combination includes a monocyano compound and a tricyano compound, and the monocyano compound is selected from additive A and / or additive B. The cyano group and the phosphate group in additive A or additive B both have a complexation with the positive electrode metal ion, which can effectively protect the positive electrode and form a phosphorus compound protective film on the negative electrode. The cyano group in the tricyano compound and the positive electrode metal ion have a complexation, which can effectively protect the positive electrode. Experiments have found that the combination of monocyano compounds and tricyano compounds, when applied to electrochemical energy storage units, can play a synergistic role and can effectively improve the high-temperature storage performance and high-temperature cycle performance of the battery.

[0011] In the present invention, the carbon number range defined by R1, R2, R3 and R4 above refers to any integer within the defined range, the carbon number is 1-6, and the carbon number can be 1, 2, 3, 4, 5 or 6; the carbon number is 3-6, and the carbon number can be 3, 4, 5 or 6; R1, R2, R3 and R4 can be the same or different. The alkyl group can be a straight chain or a branched alkyl group.

[0012] As an optional embodiment of the present invention, R1, R2, R3 and R4 are each independently selected from an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms.

[0013] As an optional embodiment of the present invention, R1 is selected from an alkyl group having 1 to 4 carbon atoms or a fluorinated alkyl group having 1 to 4 carbon atoms.

[0014] As an optional embodiment of the present invention, R2 is selected from an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms.

[0015] As an optional embodiment of the present invention, R3 is selected from an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms.

[0016] As an optional embodiment of the present invention, R4 is selected from an alkyl group having 1 to 4 carbon atoms or a fluoroalkyl group having 1 to 4 carbon atoms.

[0017] As an optional embodiment of the present invention, the alkyl group having 1 to 6 carbon atoms is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl or n-hexyl.

[0018] As an optional embodiment of the present invention, the fluorinated alkyl group having 1 to 6 carbon atoms is selected from 2-fluoroethyl, 2,2-difluoroethyl, 1,2-difluoroethyl, 2,2,2-trifluoroethyl, 1-fluoropropyl, 2-fluoropropyl, 2,2-difluoropropyl, 1,3-difluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, 4-fluorobutyl, 4,4,4-trifluorobutyl, 3,3,4,4,4-pentafluorobutyl or 2,2,3,3,tetrafluorobutyl.

[0019] As an optional embodiment of the present invention, the cycloalkyl group having 3 to 6 carbon atoms is selected from cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.

[0020] As an optional embodiment of the present invention, R1, R2, R3 and R4 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl, 2-fluoroethyl, 2,2-difluoroethyl, 1,2-difluoroethyl, 2,2,2-trifluoroethyl, 1-fluoropropyl, 2-fluoropropyl, 2,2-difluoropropyl, 1,3-difluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, 4-fluorobutyl, 4,4,4-trifluorobutyl, 3,3,4,4,4-pentafluorobutyl or 2,2,3,3,tetrafluorobutyl.

[0021] As an optional embodiment of the present invention, R1, R2, R3 and R4 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl or n-hexyl.

[0022] As an optional embodiment of the present invention, R1, R2, R3 and R4 are each independently selected from 2-fluoroethyl, 2,2-difluoroethyl, 1,2-difluoroethyl, 2,2,2-trifluoroethyl, 1-fluoropropyl, 2-fluoropropyl, 2,2-difluoropropyl, 1,3-difluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, 4-fluorobutyl, 4,4,4-trifluorobutyl, 3,3,4,4,4-pentafluorobutyl or 2,2,3,3,tetrafluorobutyl.

[0023] As an optional embodiment of the present invention, R1 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl or 2-fluoropropyl.

[0024] As an optional embodiment of the present invention, R2 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl, cyclobutyl, cyclopentyl, cyclohexyl or 2,2,2-trifluoroethyl.

[0025] As an optional embodiment of the present invention, R3 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclohexyl, 2-fluoroethyl, 2-fluoropropyl or 2,2-difluoropropyl.

[0026] As an optional embodiment of the present invention, R4 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl or 2-fluoropropyl.

[0027] As an optional embodiment of the present invention, the mass ratio of the monocyano compound to the tricyano compound is (0.2-3):(0.2-4). Typical but non-limiting mass ratios of the monocyano compound to the tricyano compound are 0.2:0.2, 0.2:0.5, 0.2:1, 0.2:1.5, 0.2:2, 0.2:2.5, 0.2:3, 0.2:3.5, 0.2:4, 0.5:0.2, 0.5:0.5, 0.5:1, 0.5:1.5, 0.5:2, 0.5:2.5, 0.5:3, 0.5:3.5, 0.5:4, 1:0.2, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1.5:0.2, 1.5:1 : 0.5, 1.5:1, 1.5:1.5, 1.5:2, 1.5:2.5, 1.5:3, 1.5:3.5, 1.5:4, 2:0.2, 2:0.5, 2:1, 2:1.5, 2:2, 2:2.5, 2:3, 2:3.5, 2:4, 2.5:0.2, 2.5:0.5, 2.5:1, 2.5:1.5, 2.5:2, 2.5:2.5, 2.5:3, 2.5:3.5, 2.5:4, 3:0.2, 3:0.5, 3:1, 3:1.5, 3:2, 3:2.5, 3:3, 3:3.5 or 3:4, etc. By further limiting the mass ratio of the monocyano compound to the tricyano compound, it is helpful to enhance the synergistic effect between the monocyano compound and the tricyano compound.

[0028] As an optional embodiment of the present invention, the additive A includes at least one of the compounds having the following structures:

[0029]

[0030]

[0031]

[0032] As an optional embodiment of the present invention, the additive A having a structure as shown in formula I, The preparation method is as follows:

[0033] Phosphorus oxychloride, NC-R1-OH and R2-OH are subjected to esterification reaction to obtain an intermediate After fluorination reaction, the additive A is purified to obtain the additive A. R1 and R2 are independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms.

[0034] As an optional embodiment of the present invention, additive A-1 The preparation method is as follows:

[0035] (1) Esterification reaction

[0036] Add 76.7g (0.5mol) of phosphorus oxychloride and 153.4g of 1,2-dichloroethane solvent to a 500mL three-necked flask, stir and cool to 15°C, add 23.0g (0.5mol) of ethanol dropwise, add ethanol within 30min, and continue to add 35.5g (0.5mol) of 3-hydroxypropionitrile dropwise. After the raw materials are added dropwise, heat to 25°C and continue to react for 90min to obtain a reaction solution containing a chlorinated intermediate product. Transfer the reaction solution to a 500mL single-necked flask, concentrate under reduced pressure, remove the 1,2-dichloroethane solvent, and obtain a chlorinated intermediate product.

[0037] (2) Fluorination reaction

[0038] Add the chlorinated intermediate product to a 1000mL three-necked flask, add 500mL of acetonitrile solvent and stir, control the temperature to 30°C, add 18.5g (0.5mol) of ammonium fluoride in batches, react for 3h, and obtain a fluorination reaction liquid. The fluorination reaction liquid is filtered through a Buchner funnel to remove solid salts, and the obtained filtrate is dehydrated through a 4A molecular sieve to remove water <50ppm, and then the filtrate is concentrated under reduced pressure to remove the acetonitrile solvent to obtain a crude liquid product.

[0039] (3) Purification

[0040] The crude liquid product was distilled under reduced pressure at a vacuum degree of 50 Pa, and 54.3 g of liquid with a gas chromatographic purity of 99.2% was collected.

[0041] As an optional embodiment of the present invention, additive A-2 The preparation method is as follows:

[0042] (1) Esterification reaction

[0043] Add 76.7g (0.5mol) of phosphorus oxychloride and 153.4g of 1,2-dichloroethane solvent to a 500mL three-necked flask, stir and cool to 15°C, add 30.0g (0.5mol) of n-propanol dropwise, add n-propanol within 30min, and continue to add 35.5g (0.5mol) of 3-hydroxypropionitrile dropwise. After the raw materials are added dropwise, heat to 25°C and continue to react for 90min to obtain a reaction solution containing a chlorinated intermediate product. Transfer the reaction solution to a 500mL single-necked flask, concentrate under reduced pressure, remove the 1,2-dichloroethane solvent, and obtain a chlorinated intermediate product.

[0044] (2) Fluorination reaction

[0045] Add the chlorinated intermediate product to a 1000mL three-necked flask, add 500mL of acetonitrile solvent and stir, control the temperature to 40°C, add 29.0g (0.5mol) of potassium fluoride in batches, react for 3h, and obtain a fluorination reaction liquid. The fluorination reaction liquid is filtered through a Buchner funnel to remove solid salts, and the obtained filtrate is dehydrated through a 4A molecular sieve to remove water <50ppm, and then the filtrate is concentrated under reduced pressure to remove the acetonitrile solvent to obtain a crude liquid product.

[0046] (3) Purification

[0047] The crude liquid product was distilled under reduced pressure at a vacuum degree of 50 Pa, and 87.8 g of liquid with a gas chromatographic purity of 99.4% was collected.

[0048] As an optional embodiment of the present invention, additive A-3 The preparation method is as follows:

[0049] (1) Esterification reaction

[0050] Add 76.7g (0.5mol) of phosphorus oxychloride and 153.4g of 1,2-dichloroethane solvent to a 500mL three-necked flask, stir and cool to 15°C, add 23.0g (0.5mol) of ethanol dropwise, add ethanol within 30min, and continue to add 28.5g (0.5mol) of hydroxyacetonitrile dropwise. After the raw materials are added dropwise, heat to 25°C and continue to react for 90min to obtain a reaction solution containing a chlorinated intermediate product. Transfer the reaction solution to a 500mL single-necked flask, concentrate under reduced pressure, remove the 1,2-dichloroethane solvent, and obtain a chlorinated intermediate product.

[0051] (2) Fluorination reaction

[0052] Add the chlorinated intermediate product to a 1000mL three-necked flask, add 500mL of acetonitrile solvent and stir, control the temperature to 30°C, add 18.5g (0.5mol) of ammonium fluoride in batches, react for 3h, and obtain a fluorination reaction liquid. The fluorination reaction liquid is filtered through a Buchner funnel to remove solid salts, and the obtained filtrate is dehydrated through a 4A molecular sieve to remove water <50ppm, and then the filtrate is concentrated under reduced pressure to remove the acetonitrile solvent to obtain a crude liquid product.

[0053] (3) Purification

[0054] The crude liquid product was distilled under reduced pressure at a vacuum degree of 50 Pa, and 43.4 g of liquid with a gas chromatographic purity of 99.1% was collected.

[0055] The preparation methods of additive A with other structures can refer to the above three preparation methods and adjust the selection of R1 and R2.

[0056] As an optional embodiment of the present invention, the additive B includes at least one of the compounds having the following structures:

[0057]

[0058]

[0059]

[0060] As an optional embodiment of the present invention, the additive B with the structure shown in Formula II, The preparation method is as follows:

[0061] Esterification reaction is carried out and the additive B is obtained by purification. R3 and R4 are each independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms.

[0062] As an optional embodiment of the present invention, additive B-1 The preparation method is as follows:

[0063] (1) Esterification reaction

[0064] Add 7.1g (0.1mol) 3-hydroxypropionitrile, 10.6g (0.105mol) triethylamine (used as a base) and 100g 1,2-dichloroethane solvent to a 500mL three-necked flask and cool to 0°C; dissolve 15.0g (0.5mol, 95% content) 2-chloro-2-oxo-1,3,2-dioxaphospholane in 50g 1,2-dichloroethane solvent and add dropwise to the aforementioned three-necked flask within 2h. After the raw materials are added dropwise, the temperature is raised to 25°C and the reaction is continued for 1h to obtain an esterification reaction liquid. The esterification reaction liquid is filtered through a Buchner funnel to remove triethylamine hydrochloride, and the obtained filtrate is transferred to a 500mL single-necked flask, concentrated under reduced pressure, and the 1,2-dichloroethane solvent is removed to obtain a crude liquid product.

[0065] (2) Purification

[0066] The crude liquid product was distilled under reduced pressure with a vacuum degree of 10 Pa, and 7.1 g of liquid with a gas chromatographic purity of 99.3% was collected.

[0067] As an optional embodiment of the present invention, additive B-2 The preparation method is as follows:

[0068] (1) Esterification reaction

[0069] Add 7.1g (0.1mol) 3-hydroxypropionitrile, 10.6g (0.105mol) triethylamine (used as a base) and 100g 1,2-dichloroethane solvent to a 500mL three-necked flask and cool to 0°C; dissolve 15.7g (0.5mol) 2-chloro-2-oxo-1,3,2-dioxaphosphorinane in 50g 1,2-dichloroethane solvent and add dropwise to the aforementioned three-necked flask within 2h. After the raw materials are added dropwise, the temperature is raised to 25°C and the reaction is continued for 1h to obtain an esterification reaction liquid. The esterification reaction liquid is filtered through a Buchner funnel to remove triethylamine hydrochloride, and the obtained filtrate is transferred to a 500mL single-necked flask, concentrated under reduced pressure, and the 1,2-dichloroethane solvent is removed to obtain a crude liquid product.

[0070] (2) Purification

[0071] The crude liquid product was distilled under reduced pressure with a vacuum degree of 5 Pa, and 10.5 g of liquid with a gas chromatographic purity of 99.5% was collected.

[0072] The preparation method of additive B with other structures can refer to the above two preparation methods and adjust the selection of R3 and R4.

[0073] As an optional embodiment of the present invention, the tricyano compound includes at least one of the compounds having the following structures:

[0074]

[0075]

[0076] In a second aspect, the present invention provides an electrolyte for an electrochemical energy storage unit, comprising an electrolyte salt, an additive and an organic solvent, wherein the additive comprises the electrolyte additive combination described in the first aspect.

[0077] As an optional embodiment of the present invention, the electrochemical energy storage unit is a lithium ion battery or a sodium ion battery.

[0078] As an optional embodiment of the present invention, the electrochemical energy storage unit is a lithium-ion battery.

[0079] The present invention provides an electrolyte additive combination, including a monocyano compound and a tricyano compound, wherein the monocyano compound is selected from additive A and / or additive B. Additive A is a chain phosphate containing a cyano group, and additive B is a cyclic phosphate containing a cyano group. In terms of molecular structure design, additive A and additive B innovatively combine cyano and phosphate groups, and additive A or additive B has good oxidation stability, and both cyano and phosphate groups have complexation with positive electrode metal ions, which can effectively protect the positive electrode and reduce the dissolution of positive electrode metal ions under high temperature and high voltage. Additive A and additive B can both form a phosphorus compound protective film at the negative electrode, inhibit the impedance growth of the battery cycle process and improve the normal temperature cycle performance. The tricyano compound has excellent oxidation stability, and the cyano group and the positive electrode metal ion have complexation, which can effectively protect the positive electrode. Experiments have found that the combination of monocyano compounds and tricyano compounds can play a synergistic role, effectively improve the high temperature storage performance and high temperature cycle performance of the battery, and reduce the amount of cobalt dissolution at the negative electrode.

[0080] As an optional embodiment of the present invention, the mass fraction of the additive A in the electrolyte is 0.2%-3%. If the mass fraction of the additive A is too high (higher than 3%), it is easy to cause the degradation of the dynamic performance, such as the accelerated decay of the normal temperature cycle performance. If the mass fraction of the additive A is too low (lower than 0.2%), it is easy to cause the addition to be ineffective. Therefore, the typical but non-limiting mass fraction of the additive A is 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.3%, 2.5%, 2.6%, 2.8% or 3.0%, etc. and the numerical range between any two points.

[0081] As an optional embodiment of the present invention, the mass fraction of the additive B in the electrolyte is 0.2%-3%. If the mass fraction of the additive B is too high (higher than 3%), it is easy to cause the degradation of the dynamic performance, such as the accelerated decay of the normal temperature cycle performance. If the mass fraction of the additive B is too low (lower than 0.2%), it is easy to cause the addition to be ineffective. Therefore, the typical but non-limiting mass fraction of the additive B is 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.3%, 2.5%, 2.6%, 2.8% or 3.0%, etc. and the numerical range between any two points.

[0082] As an optional embodiment of the present invention, the additive also includes additive C, and the main function of additive C is to improve the stability of the electrolyte and electrode interface, and improve the storage performance and cycle performance of the battery. The additive C includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, methylene disulfonate, 1,3-propane sultone, 1,3-propylene sultone, butene glycol derivatives, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, vinyl sulfate, propylene sulfate, vinyl sulfite or tetravinylsilane.

[0083] As a preferred embodiment of the present invention, the additive C includes fluoroethylene carbonate and 1,3-propane sultone, and the mass ratio of fluoroethylene carbonate to 1,3-propane sultone is 10:3.

[0084] As a preferred embodiment of the present invention, the additive C includes fluoroethylene carbonate, 1,3-propane sultone and lithium difluorooxalate borate, and the mass ratio of fluoroethylene carbonate, 1,3-propane sultone and lithium difluorooxalate borate is 10:3:0.5.

[0085] As a preferred embodiment of the present invention, the additive C is fluoroethylene carbonate.

[0086] As a preferred embodiment of the present invention, the additive C is 1,3-propane sultone.

[0087] As a preferred embodiment of the present invention, the additive C is methylene methanedisulfonate.

[0088] As an optional embodiment of the present invention, the mass fraction of the additive C in the electrolyte is 1%-15%. Typical but non-limiting mass fractions are 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., and the numerical range between any two points.

[0089] As an optional embodiment of the present invention, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, sodium hexafluorophosphate, sodium bisfluorosulfonyl imide or sodium bistrifluoromethanesulfonyl imide.

[0090] As an optional embodiment of the present invention, the concentration of the electrolyte salt in the electrolyte is 0.6mol / L-1.8mol / L, and a typical but non-limiting concentration is 0.6mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L or 1.8mol / L and a numerical range between any two points.

[0091] As an optional embodiment of the present invention, the organic solvent includes at least three of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, propyl propionate, propyl acetate, ethyl propionate, ethyl acetate or 2,2-difluoroethyl acetate.

[0092] As an optional embodiment of the present invention, the organic solvent includes ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate, and the mass ratio of ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate is 15:15:20:50.

[0093] In a third aspect, the present invention provides an electrochemical energy storage unit, comprising the electrolyte additive combination described in the first aspect or the electrolyte for the electrochemical energy storage unit described in the second aspect.

[0094] As an optional embodiment of the present invention, the electrochemical energy storage unit is a lithium ion battery or a sodium ion battery.

[0095] As an optional embodiment of the present invention, the electrochemical energy storage unit is a lithium-ion battery, and the lithium-ion battery further includes a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode.

[0096] As an optional embodiment of the present invention, the positive electrode active material of the positive electrode includes at least one of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material or lithium cobalt oxide.

[0097] As an optional embodiment of the present invention, the negative electrode active material of the negative electrode includes at least one of natural graphite, artificial graphite, silicon, silicon alloy, silicon carbon or silicon oxygen.

[0098] In a fourth aspect, the present invention provides a power device comprising the electrolyte additive combination described in the first aspect, the electrolyte for the electrochemical energy storage unit described in the second aspect, or the electrochemical energy storage unit described in the third aspect.

[0099] As an optional embodiment of the present invention, the power device includes at least one of an electric vehicle, an electric ship, an electric aircraft or an electric tool. Electric vehicles include electric cars, electric buses, electric trams, electric bicycles, electric motorcycles, electric scooters, electric golf carts and electric trucks. Electric vehicles include pure electric vehicles or hybrid electric vehicles, and hybrid electric vehicles can be plug-in hybrid electric vehicles. Electric ships include ferries, passenger ships, tugboats and sightseeing boats. Electric aircraft include electric airplanes, electric helicopters, electric gliders and electric drones. Electric tools include electric drills, impact drills, electric hammers, electric saws, electric cutters, electric lawn mowers, electric vacuum cleaners and electric mixers.

[0100] In a fifth aspect, the present invention provides an energy storage device, comprising the electrolyte additive combination described in the first aspect, the electrolyte for the electrochemical energy storage unit described in the second aspect, or the electrochemical energy storage unit described in the third aspect.

[0101] As an optional implementation manner of the present invention, the energy storage device is a communication base station or power grid energy storage, etc.

[0102] Compared with the prior art, the present invention has the following beneficial effects:

[0103] The present invention provides an electrolyte additive combination, including a monocyano compound and a tricyano compound, wherein the monocyano compound is selected from additive A and / or additive B. Additive A is a chain phosphate containing a cyano group, and additive B is a cyclic phosphate containing a cyano group. In terms of molecular structure design, additive A and additive B innovatively combine cyano and phosphate groups, and additive A or additive B has good oxidation stability. When applied to electrochemical energy storage units, cyano and phosphate groups both have complexation with positive electrode metal ions, which can effectively protect the positive electrode and reduce the dissolution of positive electrode metal ions under high temperature and high voltage. Additive A and additive B can both form a phosphorus compound protective film at the negative electrode, inhibit the impedance growth of the cycle process and improve the normal temperature cycle performance. Tricyano compounds have excellent oxidation stability and are applied to electrochemical energy storage units. There is a complexation between cyano and positive electrode metal ions, which can effectively protect the positive electrode. Experiments have found that the combination of monocyano compounds and tricyano compounds can play a synergistic role and can effectively improve the high temperature storage performance and high temperature cycle performance of the battery. DETAILED DESCRIPTION

[0104] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0105] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0106] The present invention is further described in detail below in conjunction with specific examples and comparative examples. Those skilled in the art should understand that the examples are only to help understand the present invention and should not be regarded as specific limitations of the present invention. In addition to preparing additives A and additives B according to the above preparation method, other raw materials used in the present invention can be obtained from commercially available products. Among them, the specific structures of additives A and additives B in the following examples and comparative examples are shown in Table 1:

[0107] Table 1

[0108]

[0109] Example 1

[0110] The present embodiment provides a lithium ion battery electrolyte, including an electrolyte additive combination, wherein the electrolyte additive combination includes an additive A and a tricyano compound; the lithium ion battery electrolyte specifically includes the following components in mass fractions: 15% electrolyte salt, 2% additive A, 2% tricyano compound, 13% additive C, and the balance is an organic solvent;

[0111] Wherein, the electrolyte salt is lithium hexafluorophosphate, and its concentration in the electrolyte is 1.2 mol / L;

[0112] Additive A is additive A-1, and the specific structure is shown in Table 1;

[0113] The tricyano compound is 1,3,6-hexanetrinitrile (HTCN for short);

[0114] Additive C includes fluoroethylene carbonate and 1,3-propane sultone, and the mass ratio of fluoroethylene carbonate to 1,3-propane sultone is 10:3;

[0115] The organic solvent includes ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate. Based on the total mass of the organic solvent as 100%, the mass ratio of ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate is 15:15:20:50.

[0116] The method for preparing the lithium ion battery electrolyte of this embodiment comprises the following steps:

[0117] Ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate are proportioned to form an organic solvent, and then a formulated amount of electrolyte salt (lithium hexafluorophosphate) is added to the organic solvent, and then a formulated amount of additive C (fluoroethylene carbonate and 1,3-propane sultone) is added respectively, and then additive A and a tricyano compound are added, and mixed evenly to prepare a lithium-ion battery electrolyte.

[0118] Example 2

[0119] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 is replaced by the additive A-2, and the other raw materials and amounts are the same as those in Embodiment 1.

[0120] The structural formula of additive A-2 is shown in Table 1.

[0121] Example 3

[0122] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 is replaced by the additive A-3, and the other raw materials and amounts are the same as those in Embodiment 1.

[0123] The structural formula of additive A-3 is shown in Table 1.

[0124] Example 4

[0125] This embodiment provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 0.2%, the remaining raw materials and amounts are the same as those in Embodiment 1.

[0126] Example 5

[0127] This embodiment provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 1%, the other raw materials and amounts are the same as those in Embodiment 1.

[0128] Example 6

[0129] This embodiment provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 3%, the other raw materials and amounts are the same as those in Embodiment 1.

[0130] Example 7

[0131] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 is replaced by the additive B-1, and the other raw materials and amounts are the same as those in Embodiment 1.

[0132] The structural formula of additive B-1 is shown in Table 1.

[0133] Example 8

[0134] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 with a mass fraction of 2% is replaced by the additive B-1 with a mass fraction of 1%, and the other raw materials and amounts are the same as those in Example 1.

[0135] Example 9

[0136] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 with a mass fraction of 2% is replaced by the additive B-1 with a mass fraction of 3%, and the other raw materials and amounts are the same as those in Example 1.

[0137] Example 10

[0138] This embodiment provides a lithium ion battery electrolyte, except that the additive A-1 is replaced by the additive B-2, and the other raw materials and amounts are the same as those in Embodiment 1.

[0139] The structural formula of additive B-2 is shown in Table 1.

[0140] Embodiment 11

[0141] This embodiment provides a lithium-ion battery electrolyte, except that 2% by mass of additive A-1 is replaced by 1% by mass of additive A-1 and 1% by mass of additive B-1, and the other raw materials and amounts are the same as those in Example 1.

[0142] Example 12

[0143] This embodiment provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 3%, and the mass fraction of tricyano compound HTCN is adjusted from 2% to 3%, the other raw materials and amounts are the same as those in Embodiment 1.

[0144] Embodiment 13

[0145] This embodiment provides a lithium-ion battery electrolyte, except that 2% by mass of the tricyano compound HTCN is replaced by 3% by mass of 1,2,3-tris(2-cyanoethoxy)propane, and the remaining raw materials and amounts are the same as those in Example 1.

[0146] Embodiment 14

[0147] This embodiment provides a lithium-ion battery electrolyte, except that 2% by mass of the tricyano compound HTCN is replaced by 3% by mass of 1,3,5-cyclohexanetricarbonitrile, and the remaining raw materials and amounts are the same as those in Example 1.

[0148] Embodiment 15

[0149] This embodiment provides a lithium-ion battery electrolyte, except that 2% by mass of the tricyano compound HTCN is replaced by 4% by mass of 1,3,5-pentanetricarbonitrile, and the remaining raw materials and amounts are the same as those in Example 1.

[0150] Example 16

[0151] This embodiment provides a lithium ion battery electrolyte, except that the mass fraction of additive C is adjusted from 13% to 13.5%, the composition of additive C is adjusted as follows: additive C includes fluoroethylene carbonate, 1,3-propane sultone and lithium difluorooxalatoborate, and the mass ratio of fluoroethylene carbonate, 1,3-propane sultone and lithium difluorooxalatoborate is 10:3:0.5; the remaining raw materials and amounts are the same as those in Example 1.

[0152] Embodiment 17

[0153] This embodiment provides a lithium ion battery electrolyte. In addition to adjusting the mass fraction of additive C from 13% to 10%, the composition of additive C is adjusted as follows: additive C includes fluoroethylene carbonate; the remaining raw materials and amounts are the same as those in embodiment 1.

[0154] Embodiment 18

[0155] This embodiment provides a lithium ion battery electrolyte. In addition to adjusting the mass fraction of additive C from 13% to 3%, the composition of additive C is adjusted as follows: additive C includes 1,3-propane sultone, and the remaining raw materials and amounts are the same as those in embodiment 1.

[0156] Embodiment 19

[0157] This embodiment provides a lithium ion battery electrolyte. In addition to adjusting the mass fraction of additive C from 13% to 1%, the composition of additive C is adjusted as follows: additive C includes methylene disulfonate, and the remaining raw materials and amounts are the same as those in embodiment 1.

[0158] Embodiment 20

[0159] This embodiment provides a lithium ion battery electrolyte, which does not contain additive C, and the other raw materials and amounts are the same as those in embodiment 1.

[0160] Comparative Example 1

[0161] This comparative example provides a lithium ion battery electrolyte, except that the additive A-1 and the tricyano compound HTCN are not added, and the remaining raw materials and amounts are the same as those in Example 1.

[0162] Comparative Example 2

[0163] This comparative example provides a lithium ion battery electrolyte, except that the tricyano compound HTCN is not added, and the other raw materials and amounts are the same as those in Example 1.

[0164] Comparative Example 3

[0165] This comparative example provides a lithium ion battery electrolyte, except that the additive A-1 is not added, the other raw materials and amounts are the same as those in Example 1.

[0166] Comparative Example 4

[0167] This comparative example provides a lithium ion battery electrolyte, except that the additive A-1 is replaced by succinonitrile SN, and the other raw materials and amounts are the same as those in Example 1.

[0168] Comparative Example 5

[0169] This comparative example provides a lithium ion battery electrolyte, except that 2% by mass of additive A-1 is replaced by 1% by mass of succinonitrile SN and 2% by mass of adiponitrile ADN, and the remaining raw materials and amounts are the same as those in Example 1.

[0170] Comparative Example 6

[0171] This comparative example provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 0.05%, the other raw materials and amounts are the same as those in Example 1.

[0172] Comparative Example 7

[0173] This comparative example provides a lithium ion battery electrolyte. Except that the mass fraction of additive A-1 is adjusted from 2% to 3.5%, the remaining raw materials and amounts are the same as those in Example 1.

[0174] Comparative Example 8

[0175] This comparative example provides a lithium ion battery electrolyte. Except that the mass fraction of the tricyano compound HTCN is adjusted from 2% to 4.5%, the remaining raw materials and amounts are the same as those in Example 1.

[0176] Application Examples 1-20 and Comparative Application Examples 1-8

[0177] The lithium ion battery electrolytes prepared in Examples 1-20 and Comparative Examples 1-8 are made into lithium ion battery application examples 1-20 and comparative application examples 1-8 (i.e., the lithium ion battery electrolyte in Example 1 is made into lithium ion battery application example 1, the lithium ion battery electrolyte in Example 2 is made into lithium ion battery application example 2, the lithium ion battery electrolyte in Comparative Example 1 is made into lithium ion battery comparative application example 1, the lithium ion battery electrolyte in Comparative Example 4 is made into lithium ion battery comparative application example 4, and so on). The specific preparation method is as follows:

[0178] Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide LB08 (Xiamen Xiatung New Energy Materials Co., Ltd.), conductive agent carbon black (SP), conductive agent carbon nanotube (CNT) and binder polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.075:1.0:0.625:1.3 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector aluminum foil, dried, and cold pressed. The double-sided surface density is 355g / m 2 , compacted density 4.0g / cm 3 , the designed gram capacity is 195mAh / g, and the positive electrode sheet is obtained.

[0179] Preparation of negative electrode sheet: The negative electrode active material artificial graphite QCG-H2 (Shanghai Shanshan Technology Co., Ltd.), silicon carbon CONE-LSC-2 (Zhejiang Lichen New Material Technology Co., Ltd.), conductive agent carbon black (SP), thickener sodium carboxymethyl cellulose (CMC) and binder styrene butadiene rubber are fully stirred and mixed in deionized water solvent at a mass ratio of 91.5:5:0.5:1.4:1.6 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector copper foil, dried, and cold pressed. The double-sided surface density is 160g / m 2 , compacted density 1.6g / cm 3 , the designed gram capacity is 420mAh / g, and the negative electrode sheet is obtained.

[0180] The positive electrode sheet, PE separator (Shenzhen Xingyuan Material Technology Co., Ltd.) and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role. Then the bare battery cell is wound. The bare battery cell is placed in an outer packaging bag, and the electrolyte is injected into the dried battery. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery with a nominal capacity of 1500mAh is obtained.

[0181] Test conditions

[0182] The lithium ion batteries prepared in Application Examples 1-20 and Comparative Application Examples 1-8 were tested for electrochemical performance, and the test method was as follows:

[0183] 1. Stored at 85℃ for 8h, 100% SOC (100% SOC means fully charged)

[0184] (1) The battery is discharged at 0.2C to 3.0V and left to stand for 10 minutes;

[0185] (2) 0.5C CC-CV (constant current constant voltage) charging to 4.53V, cut-off current 1 / 20C, and rest for 10 minutes;

[0186] (3) 0.5C discharge to 3.0V, let stand for 10min;

[0187] Cycle (2)-(3) twice and record the second discharge capacity Q1;

[0188] (4) 0.5C CC-CV (constant current constant voltage) charging to 4.53V, cut-off current 1 / 20C, measure internal resistance (denoted as R5), voltage (denoted as U1), volume (denoted as V1), and thickness (denoted as H1);

[0189] (5) Stand at 85°C for 8 h;

[0190] (6) Measure the internal resistance (denoted as R6), voltage (denoted as U2), volume (denoted as V2), and thickness (denoted as H2) in the hot state;

[0191] (7) At 25°C, let stand for 2 hours, and the thickness measured at room temperature is recorded as H3;

[0192] (8) Discharge at 0.5C to 3.0V, let stand for 10 min, and record the capacity Q2;

[0193] (9) 0.5C CC-CV (constant current constant voltage) charging to 4.53V, cut-off current 1 / 20C, stand for 10 min;

[0194] (10) 0.5C discharge to 3.0V, let stand for 10min;

[0195] (11) Repeat steps (9)-(10) twice and record capacities Q3 and Q4;

[0196] Capacity retention rate = Q2 / Q1; Capacity recovery rate = max(Q3:Q4) / Q1, where max(Q3:Q4) refers to the maximum value between the capacities Q3 and Q4;

[0197] Volume change rate = V2 / V1; Voltage change rate = U2 / U1; Internal resistance change rate = R6 / R5;

[0198] The test data are shown in Table 2.

[0199] 2. Negative electrode cobalt dissolution test

[0200] Discharge the battery that has completed the 85℃ high temperature storage test to 3.0V and perform the test as follows:

[0201] (1) Disassemble the battery in the glove box and cut a certain area of ​​the negative electrode sheet;

[0202] (2) Place the above negative electrode sheet into a PFA digestion tank, weigh it with an analytical balance, and record the sample mass;

[0203] (3) Add 5 mL of ultrapure water to the PFA digestion tank containing the weighed sample, then add 7 mL of nitric acid, tighten the lid, place the PFA digestion tank in a graphite digestion furnace, and digest at 150 °C for 3 h;

[0204] (4) After digestion is completed, the PFA digestion tank is removed from the graphite furnace digestion instrument and cooled. The cooled digestion solution is then filtered into a 50 mL plastic volumetric flask using a glass funnel equipped with quantitative filter paper. The inner wall of the PFA digestion tank also needs to be rinsed with ultrapure water into the glass funnel equipped with quantitative filter paper, and then fixed to volume with ultrapure water, shaken well, and then diluted 10 times for testing;

[0205] (5) Dilute the mixed standard containing elements such as Ni, Co, and Mn with 2% by volume nitric acid to a gradient of 0 mg / L, 0.05 mg / L, 0.10 mg / L, 0.20 mg / L, 0.50 mg / L, and 1.00 mg / L, and test it using an ICP-OES machine;

[0206] (6) The cobalt content in the sample, that is, the amount of cobalt dissolved from the negative electrode, is calculated by reading the test results. Two negative electrode sheets are tested in parallel each time and the average value is taken.

[0207] The test data are shown in Table 2.

[0208] 3. 45℃ cycle test

[0209] (1) Stand at 45°C for 2 hours;

[0210] (2) 0.5C discharge to 3.0V, let stand for 10min;

[0211] (3) 0.5C CC-CV (constant current constant voltage) charging to 4.53V, cut-off current 1 / 20C, and rest for 10 minutes;

[0212] (4) 0.7C discharge to 3.0V, let stand for 10min;

[0213] (5) Repeat steps (3)-(4) for 300 cycles.

[0214] The 300-week capacity retention rate was calculated using the 300-week capacity and the initial capacity. The test data are shown in Table 3.

[0215] 4. 25℃ cycle test

[0216] (1) Let stand at 25°C for 2 hours;

[0217] (2) 0.5C discharge to 3.0V, let stand for 10min;

[0218] (3) 0.7C CC-CV (constant current constant voltage) charging to 4.53V, cut-off current 1 / 20C, and rest for 10 minutes;

[0219] (4) 1C discharge to 3.0V, let stand for 10min;

[0220] (5) Repeat steps (3)-(4) for 500 cycles.

[0221] The 500-week capacity retention rate was calculated using the 500-week capacity and the initial capacity. The test data are shown in Table 3.

[0222] Table 2

[0223]

[0224]

[0225] Table 3

[0226]

[0227]

[0228] It can be seen from the data in Table 2 and Table 3 that the electrochemical performance of the lithium ion batteries (Application Examples 1-20) prepared using the lithium ion battery electrolytes provided by the embodiments of the present invention is significantly higher than the electrochemical performance of the lithium ion batteries (Comparative Application Examples 1-8) prepared using the comparative lithium ion battery electrolytes.

[0229] Specifically, comparative application examples 1-3 are comparative experiments of application example 1, which mainly investigate the effect of the addition of monocyano compounds and / or tricyano compounds on battery performance. From the experimental data of application example 1 and comparative application examples 1-3 in Table 2-3, it can be seen that the simultaneous addition of monocyano compounds and tricyano compounds can significantly improve the high-temperature storage performance and high-temperature cycle performance of the battery, and reduce the amount of cobalt dissolution from the negative electrode. In addition, the battery's room temperature cycle performance is slightly better or equivalent, while the single addition of monocyano compounds or tricyano compounds cannot achieve such an obvious effect.

[0230] Comparative Application Examples 4-5 are also comparative experiments of Application Example 1, which mainly investigate the effect of the combination of dicyano compounds and tricyano compounds on battery performance. From the data in Tables 2-3, it can be seen that the addition of the combination of dicyano compounds and tricyano compounds significantly reduces the performance of the battery in all aspects. It can be seen that there is a certain synergistic relationship between the monocyano compound and the tricyano compound in the present invention. Only through the joint action of the two can the high-temperature storage performance and high-temperature cycle performance of the battery be significantly improved, and the amount of cobalt dissolution of the negative electrode be reduced. In addition, the battery room temperature cycle performance is slightly better or equivalent.

[0231] Comparative Application Examples 6-8 are also comparative experiments of Application Example 1, which mainly examine the effect of the amount of monocyano compound or tricyano compound. It can be seen from the relevant experimental data in Tables 2-3 that when the amount of monocyano compound or tricyano compound added is too much, the battery performance is affected, and when the amount added is too little, no effect is achieved.

[0232] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. An electrolyte additive combination, characterized in that: The electrolyte additive combination includes a monocyano compound and a tricyano compound, wherein the monocyano compound is selected from additive A and / or additive B, wherein the structure of additive A is shown in formula I, and the structure of additive B is shown in formula II. In formula I, R1 and R2 are each independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms; In formula II, R3 and R4 are each independently selected from an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms or a cycloalkyl group having 3 to 6 carbon atoms.

2. The electrolyte additive combination according to claim 1, characterized in that: The R1 is selected from an alkyl group having 1 to 4 carbon atoms or a fluoroalkyl group having 1 to 4 carbon atoms; Preferably, R2 is selected from an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms; Preferably, R3 is selected from an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms; Preferably, R4 is selected from an alkyl group having 1 to 4 carbon atoms or a fluoroalkyl group having 1 to 4 carbon atoms; Preferably, R1, R2, R3 and R4 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, n-hexyl, 2-fluoroethyl, 2,2-difluoroethyl, 1,2-difluoroethyl, 2,2,2-trifluoroethyl, 1-fluoropropyl, 2-fluoropropyl, 2,2-difluoropropyl, 1,3-difluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, 4-fluorobutyl, 4,4,4-trifluorobutyl, 3,3,4,4,4-pentafluorobutyl or 2,2,3,3,tetrafluorobutyl; Preferably, the mass ratio of the monocyano compound to the tricyano compound is (0.2-3):(0.2-4).

3. The electrolyte additive combination according to claim 1 or 2, characterized in that: The additive A includes at least one of the compounds having the following structures:

4. The electrolyte additive combination according to claim 1 or 2, characterized in that: The additive B includes at least one of the compounds having the following structures:

5. The electrolyte additive combination according to claim 1 or 2, characterized in that: The tricyano compound includes at least one of the compounds having the following structures:

6. An electrolyte for an electrochemical energy storage unit, characterized in that: comprising an electrolyte salt, an additive and an organic solvent, wherein the additive comprises the electrolyte additive combination according to any one of claims 1 to 5; Preferably, the electrochemical energy storage unit is a lithium ion battery or a sodium ion battery; Preferably, the mass fraction of the additive A in the electrolyte is 0.2%-3%; Preferably, the mass fraction of the additive B in the electrolyte is 0.2%-3%.

7. The electrolyte for electrochemical energy storage unit according to claim 6, characterized in that: The additive further includes an additive C, and the additive C includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, methylene disulfonate, 1,3-propane sultone, 1,3-propylene sultone, butene glycol derivatives, tris(trimethylsilane)phosphate, tris(trimethylsilane)borate, vinyl sulfate, propylene sulfate, vinyl sulfite, or tetravinylsilane; Preferably, the mass fraction of the additive C in the electrolyte is 1%-15%; Preferably, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethanesulfonyl)imide; Preferably, the concentration of the electrolyte salt in the electrolyte is 0.6 mol / L-1.8 mol / L; Preferably, the organic solvent includes at least three of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, propyl propionate, propyl acetate, ethyl propionate, ethyl acetate or 2,2-difluoroethyl acetate.

8. An electrochemical energy storage unit, characterized in that: An electrolyte additive combination according to any one of claims 1 to 5 or an electrolyte for an electrochemical energy storage unit according to claim 6 or 7; Preferably, the electrochemical energy storage unit is a lithium ion battery or a sodium ion battery; Preferably, the electrochemical energy storage unit is a lithium-ion battery, and the lithium-ion battery further comprises a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode; Preferably, the positive electrode active material of the positive electrode includes at least one of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material or lithium cobalt oxide; Preferably, the negative electrode active material of the negative electrode includes at least one of natural graphite, artificial graphite, silicon, silicon alloy, silicon carbon or silicon oxygen.

9. A power device, characterized in that: The electrolyte additive combination according to any one of claims 1 to 5, the electrolyte for the electrochemical energy storage unit according to any one of claims 6 or 7, or the electrochemical energy storage unit according to claim 8; Preferably, the power device includes at least one of an electric vehicle, an electric ship, an electric aircraft or an electric tool.

10. An energy storage device, characterized in that: The electrolyte additive combination according to any one of claims 1 to 5, the electrolyte for the electrochemical energy storage unit according to any one of claims 6 or 7, or the electrochemical energy storage unit according to claim 8; Preferably, the energy storage device is a communication base station or a power grid energy storage.

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