Battery electrolyte additive, battery electrolyte and application thereof

Abstract

The invention provides a battery electrolyte additive, a battery electrolyte and application of the battery electrolyte additive, the battery electrolyte additive is an alkyl ether alkoxy silane compound, the compound has a structure shown in a formula (A), R1, R2, R3 and R4 are independently selected from one of C1-C20 alkyl groups, n is greater than or equal to 1 and less than or equal to 20, and n is an integer. The structure not only contains Si-O ether groups and C-O ether groups, but also contains a long chain consisting of the Si-O ether groups, the C-O ether groups and an alkyl chain. Under the synergistic effect of the functional groups, the viscosity of the battery electrolyte additive can be reduced, the surface tension of the battery electrolyte can be reduced, and the wettability of the battery electrolyte can be improved. In addition, the structure can also increase the dissociation degree of the lithium salt, reduce the impedance of the battery and improve the dynamic performance of the battery, so that the lithium salt cannot be separated out due to too low temperature of the battery electrolyte, and the low-temperature discharge and low-temperature cycle performance of the battery is improved. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a battery electrolyte additive, a battery electrolyte and applications thereof. Background Art

[0002] Lithium-ion batteries have become one of the important and indispensable chemical energy sources in the fields of electronic digital, electric vehicles, energy storage applications, aerospace, etc. due to their high operating voltage, high specific energy density, long cycle life, and environmental friendliness. Electrolyte is an important component of lithium-ion batteries. As the electrochemical reaction medium of lithium-ion batteries, its main function is to provide a conductive environment for the transmission and reaction of lithium ions. Its performance plays a decisive role in the energy density, safety performance and cycle life of the battery. The electrolyte is generally composed of solvents, lithium salts and additives. The solvent is the main body of the electrolyte, the lithium salt is the conductive salt of the electrolyte, and the additives can modify the conductivity, thermal stability and thermal decomposition products of the electrolyte, the conductivity of lithium ions and other properties.

[0003] The fixed size of the battery cell determines that the improvement of the energy density of the single cell needs to be designed from the material system. The use of high-capacity and high-density positive and negative electrodes is currently the most effective way to improve the energy density of the battery cell. However, the high-density electrode will cause the battery cell to absorb the electrolyte slowly during the injection, especially the electrode inside the battery cell, because the electrolyte gradually infiltrates from the outside to the inside of the winding core, resulting in uneven distribution of the electrolyte, which leads to a series of problems after the battery cell is manufactured, such as low capacity, high resistance, and short life.

[0004] At present, the problem of poor wettability of lithium-ion batteries is mostly solved by adding additives to the electrolyte to change the liquid absorption speed and wetting uniformity of the electrolyte. Commonly used additives are fluorobenzene additives. Although fluorobenzene additives can improve wettability by reducing the surface tension of the electrolyte, there are relatively strict requirements on the amount of fluorobenzene additives added. In addition, fluorobenzene additives have a relatively high acquisition cost and may decompose fluorine-containing hazardous substances in the environment, causing adverse effects on the environment. In addition, fluorobenzene additives cannot effectively prevent the precipitation of lithium salts under low temperature conditions, which seriously limits the discharge performance and cycle stability of the battery under low temperature conditions.

[0005] Therefore, developing a battery electrolyte additive that can effectively improve wettability and conductivity while also being cost-effective, environmentally friendly, and able to maintain stable performance over a wide temperature range is one of the important research directions for lithium-ion battery electrolytes. Summary of the invention

[0006] The main purpose of the present invention is to solve the problem that existing battery electrolyte additives cannot achieve both effective improvement of wettability and improvement of conductivity while also taking into account reasonable cost, environmental friendliness and maintaining stable performance over a wide temperature range.

[0007] In order to solve the above problems, the present invention provides a battery electrolyte additive, a battery electrolyte and its application. The battery electrolyte additive is an alkyl ether alkoxy silane compound, and the alkyl ether alkoxy silane compound has a structure shown in formula (A): Wherein, R1, R2, R3 and R4 are each independently selected from one of C1-C20 alkyl groups, 1≤n≤20, and n is an integer. The battery electrolyte additive having the above structure can effectively improve the surface tension of the battery electrolyte, improve the wettability and conductivity of the battery electrolyte, reduce the battery impedance, and effectively improve the low-temperature discharge and low-temperature cycle performance of the battery.

[0008] Furthermore, in the alkyl ether alkoxysilane compound, R1, R2, R3 and R4 are independently selected from one of C1-C5 alkyl groups, 1≤n≤5, and n is an integer. The above structural characteristics can make the battery electrolyte additive have better physical and chemical properties such as viscosity and system compatibility, and are more conducive to improving the surface tension and wettability of the battery electrolyte.

[0009] Furthermore, in the alkyl ether alkoxysilane compound, R1, R2, R3 and R4 are independently selected from methyl, ethyl, propyl and butyl, 3≤n≤4, and n is an integer. The above-mentioned specific branched substituent groups and alkyl chain lengths are selected so that the battery electrolyte additive has a better effect in improving the wettability and conductivity of the battery electrolyte.

[0010] Furthermore, the battery electrolyte additive is selected from one or more of the following structures:

[0011]

[0012] Preferably, the battery electrolyte additive is a compound of one or more of formula I, formula II, formula III, formula IV, formula V and formula VI; further preferably, the battery electrolyte additive is a compound of formula I and formula V at a weight percentage of 2: (1-2); or, the battery electrolyte additive is a compound of formula II and formula III at a weight percentage of (3-4): 1; or, the battery electrolyte additive is a compound of formula IV and formula VI at a weight percentage of 3: (1-3). Compounding the battery electrolyte additive in the above manner can achieve the best balance of performance in terms of battery electrolyte viscosity, surface tension and dissociation degree of lithium salt, which is conducive to further improving the overall performance of the battery.

[0013] According to another aspect of the present invention, a battery electrolyte is also provided, the battery electrolyte comprising a lithium salt, an organic solvent and the above-mentioned battery electrolyte additive. The battery electrolyte additive of the present invention is applied to the battery electrolyte, which can significantly reduce the viscosity and surface tension of the battery electrolyte and improve the wettability and conductivity of the battery electrolyte.

[0014] Furthermore, by weight percentage, the lithium salt in the battery electrolyte is 8-15%, the battery electrolyte additive is 0.5-10%, and the balance is an organic solvent; preferably, by weight percentage, the lithium salt in the battery electrolyte is 9-14%, the battery electrolyte additive is 0.5-3%, and the balance is an organic solvent. Controlling the addition amount of each component in the battery electrolyte within the above ratio is conducive to further improving the wettability and conductivity of the battery electrolyte.

[0015] Further, the lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bis(oxalate)phosphate and lithium tetrafluoro(oxalate)phosphate; preferably, the lithium salt is lithium hexafluorophosphate and / or lithium hexafluoroarsenate; preferably, the organic solvent is an organic carbonate, an ionic liquid, a polyether , aromatic ether, C1-C30 alkyl ether, cyclic ether, carboxylic acid ester, sulfone, nitrile and dinitrile; preferably, the organic solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl propionate, ethyl methyl carbonate, propyl ether, butyl ether, glutaronitrile, cyclopentane sulfone, methyl propionate, ethyl propionate, butyl propionate and ethyl butyrate; further preferably, the organic solvent is one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. The above lithium salts and organic solvents are widely used and have better performance improvement effects on battery electrolytes and batteries.

[0016] Further, the battery electrolyte additive is a compound of formula I and formula V, the organic solvent is glutaronitrile, and the lithium salt is lithium perchlorate; or, the battery electrolyte additive is a compound of formula II and formula III, the organic solvent is cyclopentane sulfone, and the lithium salt is lithium difluoro (bisoxalate) phosphate; or, the battery electrolyte additive is a compound of formula IV and formula VI, the organic solvent is ethylene carbonate, and the lithium salt is lithium tetrafluoroborate; wherein the chemical structures of formula I, formula II, formula III, formula IV, formula V and formula VI are as follows:

[0017] The above-mentioned composite battery electrolyte additive can have a synergistic effect with the corresponding lithium salt and organic solvent, which is more conducive to enhancing the stability and interface characteristics of the battery electrolyte and improving the cycle stability of the battery.

[0018] According to a third aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising the above-mentioned battery electrolyte. Using the battery electrolyte containing the battery electrolyte additive proposed by the present invention can enable the lithium-ion battery to have not only good first charge characteristics, but also good capacity retention rate, and can also achieve good performance in a low temperature environment.

[0019] Furthermore, the lithium-ion battery also includes a positive electrode containing a cathode active material, a negative electrode containing an anode active material, and a battery separator; preferably, the cathode active material is a material capable of releasing lithium ions; preferably, the cathode active material is one or more of transition metal phosphates, transition metal oxide lithium salts, and metal sulfides; preferably, the anode active material is a material capable of receiving lithium ions; preferably, the anode active material is one or more of graphite material, silicon material, silicon-carbon material, graphite and silicon-carbon composite material, silicon oxide and graphite composite material, silicon carbon and silicon oxide composite material; preferably, the battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator, and a polyethylene terephthalate separator; preferably, the battery separator is a polyethylene separator or a polypropylene separator. By optimizing the crystal form of the positive electrode material, the negative electrode material, and the battery separator in the battery, the overall performance of the battery can be further improved.

[0020] The present invention provides a battery electrolyte additive, a battery electrolyte and its application. The battery electrolyte additive is an alkyl ether alkoxysilane compound, which contains not only Si-O ether groups and CO ether groups, but also a long chain structure composed of Si-O ether groups and CO ether groups and alkyl chains ((CH2)n). Under the synergistic effect of the above-mentioned functional groups, the battery electrolyte additive has a lower viscosity, which can greatly reduce the surface tension of the battery electrolyte and improve the wettability of the battery electrolyte. In addition, the oxygen atoms in the Si-O ether group and the CO ether group contain two pairs of lone pairs of electrons. Under the further effect of the electron donating effect of R1, R2, R3, R4 and the alkyl chain ((CH2)n), the electronic effect of the lone pairs of electrons around the oxygen atoms is increased. When the alkyl ether alkoxysilane battery electrolyte additive is used as one of the components in the battery electrolyte, it can more effectively react with Li in the lithium salt of the battery electrolyte. + The combination greatly increases the dissociation degree of lithium salt, thereby improving the conductivity of battery electrolyte, reducing battery impedance, and improving the dynamic performance of the battery. Alkyl ether alkoxysilane has the characteristics of low viscosity and the ability to enhance the dissociation degree of lithium salt, so that the battery electrolyte additive will not cause lithium salt precipitation due to excessively low temperature at low temperature, greatly improving the low-temperature discharge and low-temperature cycle performance of the battery, and enabling the battery to maintain stable performance over a wide temperature range. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0022] As described in the background technology section, adding battery electrolyte additives to the battery electrolyte to change the liquid absorption speed and uniformity of the battery electrolyte is currently the main method to solve the problem of poor wettability of lithium-ion batteries. Although the commonly used fluorobenzene additives can improve the wettability by reducing the surface tension of the battery electrolyte, the fluorobenzene additives not only have relatively strict requirements on the amount of addition, but also have the disadvantages of relatively high acquisition costs and easy decomposition of fluorine-containing hazardous substances. It is also impossible to effectively prevent the precipitation of lithium salts under low temperature conditions. The above shortcomings seriously limit the discharge performance and cycle stability of the battery under low temperature conditions. Therefore, it is urgent to develop a battery electrolyte additive that can effectively improve wettability and conductivity, and also take into account reasonable cost, environmental friendliness, and stable performance in a wide temperature range.

[0023] In order to solve the above problems, the present invention provides a battery electrolyte additive, which is an alkyl ether alkoxy silane compound, and the alkyl ether alkoxy silane compound has a structure shown in the following formula (A):

[0024] Wherein, R1, R2, R3 and R4 are each independently selected from one of C1 to C20 alkyl groups, 1≤n≤20, and n is an integer.

[0025] The alkyl ether alkoxysilane structure in the above-mentioned battery electrolyte additive contains not only Si-O ether group and CO ether group, but also an alkyl chain ((CH2)n) connecting the Si-O ether group and the CO ether group. The above-mentioned group structural characteristics make the alkyl ether alkoxysilane have a long-chain structure. Under the synergistic effect of the functional groups and groups in the structure, the battery electrolyte additive has a lower viscosity, which can greatly reduce the surface tension of the battery electrolyte and improve the wettability of the battery electrolyte. In addition, the two pairs of lone pairs of electrons contained in the oxygen atoms in the Si-O ether group and the CO ether group in the structure can greatly enhance the electronic effect of the lone pairs of electrons around the oxygen atoms under the further effect of the electron donating effect of R1, R2, R3, R4 and the alkyl chain ((CH2)n), so that it can more effectively interact with Li in the battery electrolyte. +Combined with, it increases the dissociation degree of lithium salt, improves the conductivity of battery electrolyte, and can also reduce battery impedance, thereby effectively improving the dynamic performance of the battery. Furthermore, R1, R2, R3 and R4 in the alkyl ether alkoxysilane structure are each independently selected from one of the C1~C20 alkyl groups, 1≤n≤20, and n is an integer. The battery electrolyte additive proposed in the present invention is mainly used to improve the wettability of the battery electrolyte. By controlling the length of the side chain and the alkyl chain within the above range, the obtained battery electrolyte additive can have a suitable viscosity and system compatibility, which is beneficial to improve the wettability and conductivity of the battery electrolyte, thereby playing a better role in improving the overall performance of the battery.

[0026] In summary, the alkyl ether alkoxysilane battery electrolyte additive with the above structure proposed by the present invention has a unique structural feature, so that the battery electrolyte additive composed of the alkyl ether alkoxysilane battery electrolyte additive not only has a lower viscosity, but also has the characteristic of enhancing the dissociation degree of lithium salt, and has a significant effect on reducing the surface tension of the battery electrolyte, improving the wettability and conductivity of the battery electrolyte, and reducing the battery impedance. In addition, the above battery electrolyte additive prevents the battery electrolyte from causing lithium salt precipitation due to excessively low temperature, greatly improving the low-temperature discharge and low-temperature cycle performance of the battery.

[0027] In a preferred embodiment, R1, R2, R3 and R4 in the alkyl ether alkoxysilane compound are independently selected from one of C1 to C5 alkyl groups, 1≤n≤5, and n is an integer. Further controlling the length of the R1, R2, R3 and R4 side chains and alkyl chains in the alkyl ether alkoxysilane structure within the above range can make the battery electrolyte additive have better physical and chemical properties such as viscosity and system compatibility.

[0028] In a preferred embodiment, R1, R2, R3 and R4 in the alkyl ether alkoxysilane compound are independently selected from methyl, ethyl, propyl and butyl, 3≤n≤4, and n is an integer. The above-mentioned specific branched substituent groups and alkyl chain lengths are selected, and the prepared battery electrolyte additive plays a better role in improving the wettability and conductivity of the battery electrolyte and improving the overall performance of the battery. In addition, the selection of the above-mentioned branched and alkyl chains with lower carbon numbers can make the preparation cost relatively low, the preparation process is also simpler, and it is more conducive to large-scale production after promotion.

[0029] By way of example but not limitation, the battery electrolyte additive is selected from one or more of the structures shown below:

[0030]

[0031]

[0032] Preferably, the battery electrolyte additive is a compound of one or more of Formula I, Formula II, Formula III, Formula IV, Formula V and Formula VI. The above-mentioned battery electrolyte additives having an alkyl ether alkoxysilane structure all show a good effect of improving the overall performance of the battery when applied to the battery. In addition, after a large number of experiments, the inventors creatively discovered that when the battery electrolyte additive is a compound of one or more of Formula I, Formula II, Formula III, Formula IV, Formula V and Formula VI, the effect of improving the battery performance is better. This may be because when one or more battery electrolyte additives are compounded, the properties of different additives can be complementary, so that the viscosity, surface tension and dissociation degree of lithium salts can achieve the best balance of performance, thereby achieving the purpose of further improving the overall performance of the battery. Preferably, the battery electrolyte additive is a compound of Formula I and Formula V at a weight percentage of 2: (1-2); or, the battery electrolyte additive is a compound of Formula II and Formula III at a weight percentage of (3-4): 1; or, the battery electrolyte additive is a compound of Formula IV and Formula VI at a weight percentage of 3: (1-3). The above improvement effect will be better when the battery electrolyte additive is compounded and used in the above ratio.

[0033] The present invention adopts the method of preparing the battery electrolyte additive by selecting alkenyl ether and alkoxysilane corresponding to the target product in a molar ratio of 1: (8-20) and adding them to anhydrous ethanol, using CuCl as a reaction catalyst, reacting the mixed system at 45-75° C. for 5-16 hours, and after the reaction is completed, removing the anhydrous ethanol and unreacted alkoxysilane by vacuum rotary evaporation to obtain the corresponding battery electrolyte additive. The method is simple to operate and highly efficient, and is a preferred preparation method.

[0034] According to another aspect of the present invention, a battery electrolyte is also provided, which includes a lithium salt, an organic solvent and the above-mentioned battery electrolyte additive. Applying the battery electrolyte additive of the present invention to the battery electrolyte can significantly reduce the viscosity and surface tension of the battery electrolyte, and improve the wettability and conductivity of the battery electrolyte. In addition, the battery electrolyte containing the above-mentioned battery electrolyte additive is less susceptible to low temperature, and lithium salts will not precipitate due to excessively low temperature. It can greatly improve the low-temperature discharge performance and low-temperature cycle performance of the battery, so that the battery maintains an efficient and stable working state in a wider temperature range, and has significant economic benefits and application prospects.

[0035] In a preferred embodiment, the lithium salt in the battery electrolyte is 8-15%, the battery electrolyte additive is 0.5-10%, and the balance is an organic solvent. By controlling the relative proportions of the lithium salt, the battery electrolyte additive and the organic solvent in the battery electrolyte, the battery performance can be optimized. By controlling the proportions of each component in the battery electrolyte within the above range, the obtained battery electrolyte can have better performance during use, which is beneficial to improving the comprehensive performance of the battery. Preferably, by weight percentage, the lithium salt in the battery electrolyte is 9-14%, the battery electrolyte additive is 0.5-3%, and the balance is an organic solvent. Controlling the relative proportions of the lithium salt, the battery electrolyte additive and the organic solvent within the above preferred range has a better effect on improving the battery electrolyte and battery performance.

[0036] By way of example but not limitation, the lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bisoxalate)phosphate and lithium tetrafluoro(oxalate)phosphate; preferably, the lithium salt is lithium hexafluorophosphate and / or lithium hexafluoroarsenate; preferably, the organic solvent is an organic carbonate, an ionic liquid, One or more of polyether, aromatic ether, C1-C30 alkyl ether, cyclic ether, carboxylate, sulfone, nitrile and dinitrile; preferably, the organic solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl propionate, ethyl methyl carbonate, propyl ether, butyl ether, glutaronitrile, cyclopentane sulfone, methyl propionate, ethyl propionate, butyl propionate and ethyl butyrate; further preferably, the organic solvent is one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. The battery electrolyte provided by the present invention has many properties such as improving the wettability of the battery electrolyte, increasing the dissociation degree of the lithium salt, and improving the stability of the battery electrolyte in a wide temperature range. There is no strict restriction on the specific types of lithium salts and organic solvents. The above types of lithium salts and organic solvents are all widely used types, and the performance improvement effect on the battery electrolyte and the battery is better.

[0037] In a preferred embodiment, the battery electrolyte additive is a compound of formula I and formula V, the organic solvent is glutaronitrile, and the lithium salt is lithium perchlorate; or, the battery electrolyte additive is a compound of formula II and formula III, the organic solvent is cyclopentane sulfone, and the lithium salt is lithium difluoro (bisoxalate) phosphate; or, the battery electrolyte additive is a compound of formula IV and formula VI, the organic solvent is ethylene carbonate, and the lithium salt is lithium tetrafluoroborate; wherein the chemical structures of formula I, formula II, formula III, formula IV, formula V and formula VI are as follows:

[0038] The inventors have found in a large number of experiments that in the process of preparing the battery electrolyte, when the battery electrolyte additive, lithium salt and organic solvent are used in combination in the above manner, the comprehensive use effect of the obtained battery electrolyte is better. This may be because the above-mentioned composite battery electrolyte additive can synergize with the corresponding lithium salt and organic solvent, which is more conducive to enhancing the stability and interface characteristics of the battery electrolyte and improving the cycle stability of the battery.

[0039] According to the third aspect of the present invention, a lithium-ion battery is also provided, the lithium-ion battery comprising the above-mentioned battery electrolyte. Using the battery electrolyte containing the battery electrolyte additive proposed by the present invention can make the obtained lithium-ion battery not only have good first charge characteristics, but also have good capacity retention rate, excellent performance in cycle stability and safety, and can also achieve good performance in low temperature environment, which provides a new idea for the development of lithium-ion batteries suitable for cold environment.

[0040] In a preferred embodiment, the lithium-ion battery further comprises a positive electrode containing a cathode active material, a negative electrode containing an anode active material and a battery separator; preferably, the cathode active material is a material capable of releasing lithium ions; by way of example but not limitation, the cathode active material is one or more of transition metal phosphates, transition metal oxide lithium salts and metal sulfides; preferably, the anode active material is a material capable of receiving lithium ions; preferably, the anode active material is one or more of a graphite material, a silicon material, a silicon-carbon material, a graphite and silicon-carbon composite material, a silicon oxide and graphite composite material, a silicon carbon and silicon oxide composite material; preferably, the battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator and a polyethylene terephthalate separator; preferably, the battery separator is a polyethylene separator or a polypropylene separator. By optimizing the crystal form of the positive electrode material, the negative electrode material and the battery separator in the battery, the overall performance of the battery can be further improved, so that it can reach the best state in terms of high energy density, high power density, long cycle life and wide temperature operating range, and the above materials have a significant effect on further improving the comprehensive performance of the battery.

[0041] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0042] Example 1

[0043] (1) Preparation of battery electrolyte additives

[0044] Vinyl n-butyl ether and ethyl trimethoxy silane were added to anhydrous ethanol in a molar ratio of 1:8, and CuCl was used as a reaction catalyst. After the reaction was allowed to react at 50°C for 12 hours, the anhydrous ethanol and unreacted ethyl trimethoxy silane were removed by vacuum rotary evaporation of the reaction mixture to obtain a battery electrolyte additive A1 as shown in Formula I. The reaction formula of the above reaction is:

[0045]

[0046] (2) Preparation of battery electrolyte

[0047] In a glove box filled with argon, ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:5:2, wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1ppm, and then lithium hexafluorophosphate (LiPF6) is added thereto, and after the lithium salt is completely dissolved, the battery electrolyte additive shown in formula I is added thereto, and the battery electrolyte is obtained after being mixed evenly. In the battery electrolyte, by weight percentage, the lithium salt is 12%, the battery electrolyte additive is 1%, and the organic solvent is 87%.

[0048] (3) Preparation of batteries

[0049] Positive electrode sheet: According to weight percentage, 95% NCM811, 2% acetylene black and 3% PVDF binder are added to N-methylpyrrolidone to prepare slurry, and the obtained slurry is coated on 12 micron thick aluminum foil, and then rolled after drying to obtain the positive electrode sheet.

[0050] Negative electrode sheet: According to the weight percentage, 91% of artificial graphite, 4% of acetylene black and 5% of SBR binder are added with deionized water to prepare a mixed slurry, and the obtained slurry is coated on an 8-micron copper foil, and then rolled after drying to obtain a negative electrode sheet.

[0051] Lithium-ion battery: In a dry environment with a leakage point below -50°C, stack the positive electrode, battery separator, and negative electrode in sequence to make a battery cell. The stacking process must ensure that the separator completely separates the positive electrode and the negative electrode completely covers the positive electrode. Then use the glue-attached pole ear to encapsulate it in an aluminum-plastic film of a fixed size to form a soft-pack battery to be filled with liquid. Then inject the battery electrolyte prepared above into the soft-pack battery, and then perform sealing, formation, aging, and secondary sealing and capacity division operations in sequence to obtain a lithium-ion battery.

[0052] Example 2

[0053] The difference between Example 2 and Example 1 is that the prepared battery electrolyte additives are different, and the addition ratios of the battery electrolyte additives, lithium salt and organic solvent are different during the process of preparing the battery electrolyte.

[0054] (1) Preparation of battery electrolyte additives

[0055] Propylene n-butyl ether and methyltripropoxysilane were added to anhydrous ethanol in a molar ratio of 1:10, and CuCl was used as a reaction catalyst. After reacting at 60°C for 8 hours, the reaction mixture was subjected to reduced pressure rotary evaporation to remove anhydrous ethanol and unreacted methyltripropoxysilane, to obtain a battery electrolyte additive A2 as shown in Formula II. The reaction formula of the above reaction is:

[0056]

[0057] (2) Preparation of battery electrolyte

[0058] The battery electrolyte preparation process is the same as the battery electrolyte preparation process in Example 1, but in the battery electrolyte prepared in this example, the lithium salt is 12%, the battery electrolyte additive is 0.5%, and the organic solvent is 87.5% by weight.

[0059] Example 3

[0060] The difference between Example 3 and Example 1 is that the prepared battery electrolyte additives are different, and the addition ratios of the battery electrolyte additives, lithium salt and organic solvent are different during the process of preparing the battery electrolyte.

[0061] (1) Preparation of battery electrolyte additives

[0062] Vinyl ethyl ether and methyltrimethoxysilane were added to anhydrous ethanol at a molar ratio of 1:15, and CuCl was used as a reaction catalyst. After reacting at 45°C for 7 hours, the reaction mixture was subjected to reduced pressure rotary evaporation to remove anhydrous ethanol and unreacted methyltrimethoxysilane, to obtain a battery electrolyte additive A3 as shown in Formula III. The reaction formula of the above reaction is:

[0063]

[0064] (2) Preparation of battery electrolyte

[0065] The battery electrolyte preparation process is the same as the battery electrolyte preparation process in Example 1, but in the battery electrolyte prepared in this example, the lithium salt is 12%, the battery electrolyte additive is 3%, and the organic solvent is 85%, by weight percentage.

[0066] Example 4

[0067] The difference between Example 4 and Example 1 is that the prepared battery electrolyte additives are different, and the addition ratios of the battery electrolyte additives, lithium salt and organic solvent are different during the process of preparing the battery electrolyte.

[0068] (1) Preparation of battery electrolyte additives

[0069] Vinyl propyl ether and methyl triethoxysilane were added to anhydrous ethanol at a molar ratio of 1:20, and CuCl was used as a reaction catalyst. After reacting at 70°C for 5 hours, the reaction mixture was subjected to reduced pressure rotary evaporation to remove anhydrous ethanol and unreacted methyl triethoxysilane, to obtain a battery electrolyte additive A4 as shown in Formula IV. The reaction formula of the above reaction is:

[0070]

[0071] (2) Preparation of battery electrolyte

[0072] The battery electrolyte preparation process is the same as the battery electrolyte preparation process in Example 1, but in the battery electrolyte prepared in this example, the lithium salt is 12%, the battery electrolyte additive is 1.5%, and the organic solvent is 86.5% by weight.

[0073] Example 5

[0074] The difference between Example 5 and Example 1 is that the prepared battery electrolyte additives are different, and the addition ratios of the battery electrolyte additives, lithium salt and organic solvent are different during the process of preparing the battery electrolyte.

[0075] (1) Preparation of battery electrolyte additives

[0076] Propylene n-butyl ether and methyltributoxysilane are added to anhydrous ethanol in a molar ratio of 1:18, and CuCl is used as a reaction catalyst. After reacting at 65°C for 14 hours, the reaction mixture is subjected to reduced pressure rotary evaporation to remove anhydrous ethanol and unreacted methyltributoxysilane, to obtain a battery electrolyte additive A5 as shown in Formula V. The reaction formula of the above reaction is:

[0077]

[0078] (2) Preparation of battery electrolyte

[0079] The battery electrolyte preparation process is the same as the battery electrolyte preparation process in Example 1, but in the battery electrolyte prepared in this example, the lithium salt is 12%, the battery electrolyte additive is 2.5%, and the organic solvent is 85.5% by weight.

[0080] Example 6

[0081] The difference between Example 6 and Example 1 is that the prepared battery electrolyte additives are different, and the addition ratios of the battery electrolyte additives, lithium salt and organic solvent are different during the process of preparing the battery electrolyte.

[0082] (1) Preparation of battery electrolyte additives

[0083] Vinyl methyl ether and methyl triethoxysilane were added to anhydrous ethanol in a molar ratio of 1:11, and CuCl was used as a reaction catalyst. After the reaction was reacted at 75°C for 16 hours, the anhydrous ethanol and unreacted methyl triethoxysilane were removed by vacuum rotary evaporation of the reaction mixture to obtain a battery electrolyte additive A6 as shown in Formula VI. The reaction formula of the above reaction is:

[0084]

[0085] (2) Preparation of battery electrolyte

[0086] The battery electrolyte preparation process is the same as the battery electrolyte preparation process in Example 1, but in the battery electrolyte prepared in this example, the lithium salt is 12%, the battery electrolyte additive is 2%, and the organic solvent is 86%, by weight percentage.

[0087] Example 7

[0088] The difference between Example 7 and Example 1 is that, in the battery electrolyte, by weight percentage, the lithium salt accounts for 8%, the battery electrolyte additive accounts for 0.5%, and the organic solvent accounts for 91.5%.

[0089] Example 8

[0090] The difference between Example 8 and Example 1 is that, in the battery electrolyte, by weight percentage, the lithium salt accounts for 15%, the battery electrolyte additive accounts for 10%, and the organic solvent accounts for 75%.

[0091] Example 9

[0092] The difference between Example 9 and Example 1 is that, in the battery electrolyte, by weight percentage, the lithium salt accounts for 9%, the battery electrolyte additive accounts for 0.5%, and the organic solvent accounts for 90.5%.

[0093] Example 10

[0094] The difference between Example 10 and Example 1 is that, in the battery electrolyte, by weight percentage, the lithium salt accounts for 14%, the battery electrolyte additive accounts for 3%, and the organic solvent accounts for 83%.

[0095] Embodiment 11

[0096] The difference between Example 11 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A1 and a battery electrolyte additive A5 compounded in a weight ratio of 2:1, the lithium salt is lithium perchlorate (LiClO4), and the organic solvent is glutaronitrile.

[0097] Example 12

[0098] The difference between Example 12 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A1 and a battery electrolyte additive A5 compounded in a weight ratio of 1:1, the lithium salt is lithium perchlorate, and the organic solvent is glutaronitrile.

[0099] Embodiment 13

[0100] The difference between Example 13 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A2 and a battery electrolyte additive A3 compounded in a weight ratio of 3:1, the lithium salt is lithium difluoro(bisoxalate)phosphate (Li2PF2(C2O4)), and the organic solvent is cyclopentane sulfone.

[0101] Embodiment 14

[0102] The difference between Example 14 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A2 and a battery electrolyte additive A3 compounded in a weight ratio of 4:1, the lithium salt is lithium difluoro(bisoxalate)phosphate, and the organic solvent is cyclopentane sulfone.

[0103] Embodiment 15

[0104] The difference between Example 15 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A4 and a battery electrolyte additive A6 compounded in a weight ratio of 3:1, the lithium salt is lithium tetrafluoroborate (LiBF4), and the organic solvent is ethylene carbonate (EC).

[0105] Example 16

[0106] The difference between Example 16 and Example 1 is that in the battery electrolyte, the battery electrolyte additive is a battery electrolyte additive A4 and a battery electrolyte additive A6 compounded in a weight ratio of 1:1, the lithium salt is lithium tetrafluoroborate, and the organic solvent is ethylene carbonate.

[0107] Embodiment 17

[0108] The difference between Example 17 and Example 3 is that, in the battery electrolyte, by weight percentage, the battery electrolyte additive is 0.2%, the lithium salt is 12%, and the organic solvent is 87.8%.

[0109] Embodiment 18

[0110] The difference between Example 18 and Example 3 is that in the battery electrolyte, by weight percentage, the battery electrolyte additive accounts for 12%, the lithium salt accounts for 12%, and the organic solvent accounts for 76%.

[0111] Comparative Example 1

[0112] The difference between Comparative Example 1 and Example 1 is that, in the prepared battery electrolyte, by weight percentage, the lithium salt is 12%, the battery electrolyte additive is 0.5%, the organic solvent is 87.5%, and the battery electrolyte additive is fluorobenzene.

[0113] Comparative Example 2

[0114] The difference between Comparative Example 1 and Example 1 is that, in the prepared battery electrolyte, by weight percentage, the lithium salt is 12%, the battery electrolyte additive is 1%, the organic solvent is 87%, and the battery electrolyte additive is fluorobenzene.

[0115] Comparative Example 3

[0116] The difference between Comparative Example 1 and Example 1 is that, in the prepared battery electrolyte, by weight percentage, the lithium salt is 12%, the battery electrolyte additive is 3%, the organic solvent is 85%, and the battery electrolyte additive is fluorobenzene.

[0117] Comparative Example 4

[0118] The difference between Comparative Example 1 and Example 1 is that, in the prepared battery electrolyte, by weight percentage, the lithium salt accounts for 12%, the organic solvent accounts for 88%, and no battery electrolyte additives are added.

[0119] The components and weight percentage contents of the battery electrolytes in the examples and comparative examples are summarized in Table 1. The proportions of the organic solvents and battery electrolyte additives involved in the table are all mass proportions.

[0120] Table 1

[0121]

[0122]

[0123] The battery electrolytes and batteries prepared in the examples and comparative examples were tested for relevant performances, and the results are shown in Table 2. The testing methods for the relevant data in the table are as follows:

[0124] Battery electrolyte surface tension test: The battery electrolyte prepared in the above examples and comparative examples was tested for surface tension using a fully automatic surface tension tester, and the test environment was 25±2°C;

[0125] Battery electrolyte viscosity test: The battery electrolyte prepared in the above embodiment and comparative example was tested for viscosity using a rotational viscometer at 25°C and -40°C, respectively, with a rotor measuring range of 0.01-25 mPa / s and a measuring speed of 60 rpm;

[0126] Conductivity test of battery electrolyte: Conductivity test of the battery electrolyte prepared in the above embodiment and comparative example was performed using a benchtop conductivity tester at test temperatures of 25°C and -40°C, respectively. The test result was the average of three measurements.

[0127] Battery performance test: The batteries prepared in the above examples and comparative examples are placed in a -40°C ultra-low temperature constant temperature box and connected to a charge and discharge tester. First, charge to 4.2V with a 1C constant current and constant voltage, and set the cut-off current to 0.05C; after standing for 10 minutes, discharge to 2.8V with a 1C constant current, and perform a cyclic charge and discharge test in this way, and record the discharge capacity each time. According to the recorded data, the battery cell capacity retention rate of the 100th, 150th and 300th weeks of the battery cycle is calculated respectively, where the battery cell capacity retention rate of the Nth week of the battery cycle (%) = Nth week discharge capacity / first week discharge capacity × 100%. -40°C discharge capacity retention rate (%) = -40°C constant capacity / normal temperature constant capacity × 100%.

[0128] Table 2

[0129]

[0130]

[0131] From the above description, it can be seen that in Examples 1 to 18, the addition of the alkyl ether alkoxysilane battery electrolyte additive provided by the present invention to the battery electrolyte can achieve the purpose of reducing the surface tension of the battery electrolyte and reducing the viscosity of the battery electrolyte, and can also significantly improve the conductivity of the battery, especially at a low temperature of -40°C, it can also have a good improvement effect on the viscosity and conductivity of the battery electrolyte, indicating that the addition of the alkyl ether alkoxysilane battery electrolyte additive of the present invention can effectively improve the wettability of the battery electrolyte. The above-mentioned battery electrolyte is applied to the battery, and it still has a good discharge capacity retention rate and cycle capacity retention rate under a low temperature of -40°C. In addition, controlling the addition amount of the battery electrolyte additive within the preferred range will have a better improvement effect on the above-mentioned improvement effect on the battery electrolyte and the battery. The battery prepared under the preferred conditions has a capacity retention rate of more than 80% after 100 cycles under a low temperature of -40°C, which greatly improves the low temperature cycle performance.

[0132] In Comparative Examples 1 to 3, conventional fluorobenzene battery electrolyte additives are added to the battery electrolyte, and in Comparative Example 4, no conventional additives are added during the preparation of the battery electrolyte. When the mass percentage of fluorobenzene added to the battery electrolyte in Comparative Examples 1 to 3 is 0.5%, 1%, and 3%, the improvements in the viscosity, surface tension, and conductivity of the battery electrolyte are not ideal, and may even reduce the viscosity and surface tension of the battery electrolyte, and have an adverse effect on the conductivity of the battery electrolyte. Similarly, when the corresponding battery electrolyte in the comparative example is applied to the battery, the improvement effect of the discharge capacity retention rate and cycle capacity retention rate of the battery at a low temperature of -40°C is significantly different from that of the present invention, and may even have an adverse effect, making it impossible to continue the cycle process.

[0133] In summary, the application of the alkyl ether alkoxysilane battery electrolyte additive proposed by the present invention in the battery electrolyte has a significant effect on reducing the surface tension and viscosity of the battery electrolyte, improving the wettability and conductivity of the battery electrolyte, and reducing the battery impedance. In addition, it can also greatly improve the low-temperature discharge and low-temperature cycle performance of the battery.

[0134] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A battery electrolyte additive, characterized in that: The battery electrolyte additive is an alkyl ether alkoxy silane compound, and the alkyl ether alkoxy silane compound has a structure shown in formula (A): Wherein, R1, R2, R3 and R4 are each independently selected from one of C1-C20 alkyl groups, 1≤n≤20, and n is an integer.

2. The battery electrolyte additive according to claim 1, characterized in that: In the alkyl ether alkoxysilane compound, the R1, the R2, the R3 and the R4 are independently selected from one of C1 to C5 alkyl groups, 1≤n≤5, and n is an integer.

3. The battery electrolyte additive according to claim 1, characterized in that: In the alkyl ether alkoxysilane compound, R1, R2, R3 and R4 are independently selected from methyl, ethyl, propyl and butyl, 3≤n≤4, and n is an integer.

4. The battery electrolyte additive according to any one of claims 1 to 3, characterized in that: The battery electrolyte additive is selected from one or more of the following structures: Preferably, the battery electrolyte additive is a combination of one or more of the formula I, the formula II, the formula III, the formula IV, the formula V and the formula VI; Further preferably, the battery electrolyte additive is a compound of the formula I and the formula V in a weight percentage of 2:(1-2); or, the battery electrolyte additive is a compound of the formula II and the formula III in a weight percentage of (3-4):1; or, the battery electrolyte additive is a compound of the formula IV and the formula VI in a weight percentage of 3:(1-3).

5. A battery electrolyte, characterized in that: The battery electrolyte comprises a lithium salt, an organic solvent and the battery electrolyte additive according to any one of claims 1 to 4.

6. The battery electrolyte according to claim 5, characterized in that In terms of weight percentage, the lithium salt in the battery electrolyte is 8-15%, the battery electrolyte additive is 0.5-10%, and the balance is the organic solvent; Preferably, by weight percentage, the lithium salt in the battery electrolyte is 9-14%, the battery electrolyte additive is 0.5-3%, and the balance is the organic solvent.

7. The battery electrolyte according to claim 5 or 6, characterized in that: The lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bis(oxalato)phosphate and lithium tetrafluoro(oxalato)phosphate; Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium hexafluoroarsenate; Preferably, the organic solvent is one or more of organic carbonate, ionic liquid, polyether, aromatic ether, C1-C30 alkyl ether, cyclic ether, carboxylate, sulfone, nitrile and dinitrile; Preferably, the organic solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl propionate, ethyl methyl carbonate, propyl ether, butyl ether, glutaronitrile, cyclopentane sulfone, methyl propionate, ethyl propionate, butyl propionate and ethyl butyrate; Further preferably, the organic solvent is one or more of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

8. The battery electrolyte according to claim 7, characterized in that: The battery electrolyte additive is a compound of the formula I and the formula V, the organic solvent is glutaronitrile, and the lithium salt is lithium perchlorate; or, The battery electrolyte additive is a compound of the formula II and the formula III, the organic solvent is sulfolane, and the lithium salt is lithium difluoro(bisoxalate)phosphate; or, The battery electrolyte additive is a compound of the formula IV and the formula VI, the organic solvent is ethylene carbonate, and the lithium salt is lithium tetrafluoroborate; Wherein, the chemical structures of Formula I, Formula II, Formula III, Formula IV, Formula V and Formula VI are as follows:

9. A lithium ion battery, characterized in that: The lithium ion battery comprises the battery electrolyte according to any one of claims 5 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery also includes a positive electrode containing a cathode active material, a negative electrode containing an anode active material, and a battery separator; Preferably, the cathode active material is a material capable of releasing lithium ions; preferably, the cathode active material is one or more of transition metal phosphates, transition metal oxide lithium salts and metal sulfides; Preferably, the anode active material is a material capable of receiving lithium ions; preferably, the anode active material is one or more of a graphite material, a silicon material, a silicon-carbon material, a graphite and silicon-carbon composite material, a silicon oxide and graphite composite material, a silicon-carbon and silicon oxide composite material; Preferably, the battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator and a polyethylene terephthalate separator; preferably, the battery separator is a polyethylene separator or a polypropylene separator.

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