An electropolymerizable ionic liquid, polymer, battery electrode and its preparation method

Abstract

This invention discloses a novel electropolymerizable ionic liquid with an X-Y structure, wherein X includes at least one of aniline, pyrrole, and thiophene, and Y includes at least one of imidazole and pyridine. This ionic liquid allows for the electrochemical polymerization of monomer materials on the cathode surface via an in-situ formation process, achieving electrochemical in-situ coating of the cathode material. This effectively transports lithium ions while avoiding the impact of the high oxidation activity of high-voltage active materials on electrolyte stability, thereby preventing battery capacity loss.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a novel electropolymerizable ionic liquid, polymer, battery electrode, and its preparation method. Background Technology

[0002] Lithium cobalt oxide, lithium manganese oxide, ternary nickel-cobalt-manganese oxide, and ternary nickel-cobalt-aluminum oxide, among others, possess advantages such as high cycle life, high tap density, high volumetric energy density, stable product performance, and good consistency, leading to their widespread application in modern electronic products. Their relatively high cost has spurred research into high-voltage materials, continuously improving their energy density and thus reducing the levelized cost of electricity (LCOE) of batteries.

[0003] The theoretical capacity of lithium cobalt oxide is 274 mAh / g, but complete delithiation requires a voltage of 5V vs. Li. Currently, the actual charging cutoff voltage of lithium cobalt oxide has reached 4.45V, and the reversible discharge specific capacity and volumetric energy density have reached 173 mAh / g. -1 and 2900Wh L -1 When the charging cutoff voltage of lithium cobalt oxide is increased to 4.6V, the discharge capacity can reach 220mAh g. -1 The volumetric energy density reaches 3700 Wh / L -1 When the charging voltage exceeds 4.5V, an unfavorable phase transformation from the O3 phase to the H1-3 phase occurs, resulting in drastic changes in cell parameters and the accumulation of significant residual stress within the material, leading to the formation of microcracks. Furthermore, due to the partial overlap between the O 2p orbitals and the Co 3d orbitals, lattice oxygen participates in redox reactions under high voltage conditions, causing oxygen release and other problems, thereby triggering structural degradation of lithium cobalt oxide.

[0004] Current technologies often involve coating active substances with inorganic solid electrolytes and polymer materials. This coating method can be complex, requiring precise control of various parameters such as temperature, humidity, and time to ensure effective and uniform coating. Secondly, the coating process may introduce impurities or defects, affecting material performance. Therefore, rigorous purification procedures are necessary to ensure material purity and quality. Furthermore, the thickness and uniformity of the coating are also crucial factors affecting material performance. Uneven coating can lead to decreased material performance or instability.

[0005] Therefore, improving the stability of lattice oxygen in cathode materials and suppressing unfavorable phase transitions are of great significance for the development of cathode materials such as 4.6V high-voltage lithium cobalt oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, and ternary lithium nickel cobalt aluminum oxide. Summary of the Invention

[0006] This invention addresses the problems in the prior art by disclosing a novel electropolymerizable ionic liquid. This ionic liquid can be used in-situ to electrochemically polymerize monomer materials on the surface of the cathode through an in-situ formation process, thereby electrochemically coating cathode materials such as lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese oxide, and ternary nickel cobalt aluminum oxide. This avoids the high oxidation activity of high-voltage active materials from affecting the stability of the electrolyte, thus preventing battery capacity loss.

[0007] This invention is achieved through the following technical solution:

[0008] A novel electropolymerizable ionic liquid for batteries, the ionic liquid having a structure of Formula I.

[0009]

[0010] X contains a structure of formula II, consisting of aniline, pyrrole, and thiophene groups.

[0011]

[0012] Wherein, R is one or more of the following: straight-chain hydrocarbon group, branched hydrocarbon group, ester group, carbonyl group, and ether group from C1 to C10;

[0013] Y contains a structure of formula III.

[0014]

[0015] Where m is selected from 1 to 10, and m is an integer; Z - It is selected from one or more of the following: halide ions, phosphate ions, perchlorate ions, sulfonamide ions, oxaloborate ions, sulfonate ions, and acetate ions.

[0016] R of X and N of Y + connect.

[0017] The X designed in this invention has good electrical conductivity, and after being grafted with an ionic liquid structure Y through molecular design, it has ion transport capabilities.

[0018] As a further embodiment, X contains a thiophene group, and Y contains an imidazole group. The thiophene group contains a polar element with more lone pairs of electrons, enabling the formation of more lithium-ion transport channels, thereby improving battery performance. Compared to imidazole groups, when the ionic liquid group is a pyridine group, it contains fewer polar groups, resulting in fewer lithium-ion transport channels and thus poorer battery performance.

[0019] As a further embodiment, when R is a straight-chain hydrocarbon group, R is C2-C6, preferably C3-C5, and most preferably C4. When the length of the side chain increases, the battery capacity retention rate initially increases and then decreases. Increasing the side chain length increases the free volume of the polymer, thus improving polymer chain segment peristalsis, which promotes lithium-ion transport and improves battery performance. However, when the side chain length increases further, the longer side chains become entangled, increasing steric hindrance and making chain segment peristalsis difficult, thereby reducing lithium-ion transport.

[0020] A second aspect of the present invention is to provide a novel electropolymerizable ionic liquid polymer formed by polymerization of an ionic liquid, said ionic liquid polymer containing a structure of formula IV.

[0021]

[0022] Wherein, R is one or more of the following: straight-chain hydrocarbon group, branched hydrocarbon group, ester group, carbonyl group, and ether group from C1 to C10;

[0023] Y contains a structure of formula III.

[0024]

[0025] Where m is selected from 1 to 10, and m is an integer; Z - It is selected from one or more of the following: halide ions, phosphate ions, perchlorate ions, sulfonamide ions, oxalate-borate ions, sulfonate ions, and acetate ions.

[0026] As a further option, the ionic liquid polymer has the following structural formula:

[0027] Wherein, R is one or more of the following: straight-chain hydrocarbon group, branched hydrocarbon group, ester group, carbonyl group, and ether group from C1 to C10;

[0028] The Y structure is as follows:

[0029] Where m is selected from 1 to 10, and m is an integer; Z - It is selected from one or more of the following: halide ions, phosphate ions, perchlorate ions, sulfonamide ions, oxalate-borate ions, sulfonate ions, and acetate ions.

[0030] As a further option, when R is a straight-chain hydrocarbon group, R is C2-C6, preferably C3-C5, and most preferably C4.

[0031] A third aspect of the present invention is to provide a novel in-situ polymerized polyionic liquid coated battery electrode, wherein the electrode is polymerized on the surface of the electrode to form a polymer coating layer or the surface of the electrode has an ionic liquid polymer.

[0032] As a further embodiment, the thickness of the polymer capping layer is 0.5 nm to 3 μm. A thinner layer cannot uniformly coat the cathode material, while a thicker layer affects the cathode reaction kinetics and reduces battery capacity. The preferred thickness of the polymer capping layer is 0.3 μm to 1 μm.

[0033] As a further embodiment, the polymer coating layer has at least one of the following characteristics:

[0034] a. The room temperature ionic conductivity of the polymer coating is 1×10⁻⁶. -5 S / cm up to 5×10 -3 S / cm;

[0035] b. The electrochemical window of the polymer capping layer is greater than 4.6V.

[0036] A fourth aspect of the present invention provides a method for preparing a battery electrode, comprising the following steps:

[0037] S1. Under a dry gas atmosphere, add the ionic liquid monomer to the electrolyte and mix evenly. Assemble the battery electrode assembly, inject the electrolyte containing the ionic liquid monomer, seal and let stand for processing.

[0038] S2. The battery undergoes a formation process, where ionic liquid monomers are uniformly formed on the electrode surface to create a battery electrode coated with polyionic liquid.

[0039] As a further embodiment, the gas in S1 can be air or an inert gas, and the ionic liquid monomer accounts for 0.05wt% to 10wt% of the total mass of the electrolyte, preferably 0.5wt% to 1wt%. When the monomer content is low, the polymer cannot completely coat the lithium cobalt oxide particles, and some of them will still contact the electrolyte, causing capacity decay; when the monomer content is too high, more monomer will remain in the electrolyte, changing the composition of the electrolyte and affecting its stability.

[0040] As a further embodiment, the formation process in S2 includes at least one of a constant current charging stage or a constant voltage charging stage. Changing the voltage and time of the constant voltage charging and the current density of the constant current charging can control the degree of polymerization and the density of the polymer.

[0041] As a further embodiment, the charging current density during the constant current charging phase is 0.1–20 mA / cm². 2 Preferably 5-10 mA / cm 2 When the current density is high, the polymerization rate of the monomer is fast, but the faster polymerization rate results in poor polymer consistency, making it impossible to uniformly coat the electrode surface; when the current density is low, the degree of polymerization of the monomer is low, and the resulting polymer coating layer is not dense, affecting the coating effect.

[0042] As a further embodiment, the charging voltage during the constant voltage charging stage can be any voltage value within the voltage range defined by the lower and upper limits of the charging voltage, where the upper limit is the maximum allowable charging voltage. For example, in a lithium-ion battery, lithium metal is used as the reference electrode. When the voltage range of the constant voltage charging stage is 3.0–4.2V, the charging voltage during this stage can be any value within the range of 3.0–4.2V, such as 3.0V, 3.2V, 3.4V, 3.6V, 3.8V, 4.0V, or 4.2V, with an upper limit of 4.2V. In a potassium-ion battery, potassium metal is used as the reference electrode. When the voltage range of the constant voltage charging stage is 0.01–3.0V, the upper limit of the charging voltage is 3.0V. In a sodium-ion battery, sodium metal is used as the reference electrode. When the voltage range of the constant voltage charging stage is 2.0–3.8V, the upper limit of the charging voltage is 3.8V. As a further embodiment, the constant voltage charging stage is 80%-95% of the upper limit of the charging voltage. For the aforementioned lithium-ion battery, its upper limit of charging voltage is 4.2V, and calculations show that it is preferably 3.4-4.0V; for the aforementioned potassium-ion battery, its upper limit of charging voltage is 3.0V, and calculations show that it is preferably 2.4-2.8V; for the aforementioned potassium-ion battery, its upper limit of charging voltage is 3.80V, and calculations show that it is preferably 3.0-3.6V.

[0043] As a further solution, for lithium-ion batteries, when the ionic liquid contains aniline groups, the voltage range of the constant voltage charging stage is 3.7–3.9V. When the voltage is low, the driving force for aniline polymerization is low, resulting in an uneven SEI film formed on the surface; when the voltage is too high, the driving force for aniline polymerization is fast, leading to a high degree of polymerization and a less dense SEI film, affecting battery performance. When the ionic liquid contains pyrrole groups, the voltage range of the constant voltage charging stage is 3.8–4.0V. When the ionic liquid contains thiophene groups, the voltage range of the constant voltage charging stage is 3.6–3.9V.

[0044] A fifth aspect of the invention is to provide a battery or electrochemical device having the novel electropolymerizable ionic liquid described above.

[0045] As a further embodiment, the battery is a lithium battery, sodium battery, potassium battery, zinc battery, or magnesium battery, etc. The battery includes a positive electrode, a negative electrode, a separator, and the novel electropolymerizable ionic liquid, etc. The positive electrode material is selected from lithium cobalt oxide, lithium manganese oxide, ternary nickel-cobalt-manganese oxide, ternary nickel-cobalt-aluminum oxide, etc. The negative electrode contains alkali metals, alkaline earth metals, carbon materials with carbon as a constituent element, silicon materials with silicon as a constituent element, tin materials with tin as a constituent element, carbon-silicon composite materials with carbon as a constituent element, lithium-containing transition metal nitrides, etc. The separator is selected from polyethylene, polypropylene, PP / PE, PP / PE / PP separators, ceramic separators, coated separators, etc.

[0046] As a further embodiment, the electrochemical device can be used in end-consumer products, including but not limited to mobile phones, laptops, pen input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, and portable printers.

[0047] As a further embodiment, the electrochemical device can be used in electrical equipment, including large and small electrical equipment. Small electrical equipment includes consumer products, wearable electronic devices, or portable electronic devices; large electrical equipment includes transportation equipment. Transportation equipment includes, but is not limited to, vehicles such as automobiles, motorcycles, electric bicycles, buses, subways, high-speed trains, airplanes, and ships. Wearable electronic devices or portable electronic devices include, but are not limited to, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, drones, motors, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0048] The features and beneficial effects of this invention are as follows:

[0049] (1) The ionic liquid of the present invention can electrochemically polymerize the monomer material on the surface of the positive electrode through the in-situ formation process, and electrochemically coat the positive electrode material in situ. It can effectively transport lithium ions, while avoiding the high oxidation activity of high voltage active materials from affecting the stability of the electrolyte, thereby avoiding battery capacity loss.

[0050] (2) The battery electrode sheet is prepared by in-situ formation process in this invention. The preparation method is simple, efficient and conducive to large-scale production. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 The equations are for the preparation of aniline-based ionic liquids in Examples 1-10 of this invention.

[0053] Figure 2 The structural formulas of the polyaniline-based ionic liquids in Examples 1-10 of this invention are shown.

[0054] Figure 3 The equation for the preparation of the pyrrole-based ionic liquid in Example 11 of this invention is shown.

[0055] Figure 4 The structural formula of the polypyrrole-based ionic liquid in Example 11 of this invention is shown.

[0056] Figure 5 The equation for the preparation of the pyrrole-based ionic liquid in Example 12 of this invention is shown.

[0057] Figure 6 The structural formula of the polypyrrole-based ionic liquid in Example 12 of this invention is shown.

[0058] Figure 7 The equation for the preparation of the pyrrole-based ionic liquid in Example 13 of this invention is shown.

[0059] Figure 8 The structural formula of the polypyrrole-based ionic liquid in Example 13 of this invention is shown.

[0060] Figure 9 The equation for the preparation of the thiophene-based ionic liquid in Example 14 of this invention is shown.

[0061] Figure 10 The structural formula of the polythiophene-based ionic liquid in Example 14 of this invention is shown.

[0062] Figure 11 The equation for the preparation of the aniline-pyridyl ionic liquid in Example 15 of this invention is shown.

[0063] Figure 12 The structural formula of the polyaniline-pyridyl ionic liquid in Example 15 of this invention is shown.

[0064] Figure 13 The equation for the preparation of the pyrrole-pyridyl ionic liquid in Example 16 of this invention is shown.

[0065] Figure 14The structural formula of the polypyrrole-pyridyl ionic liquid in Example 16 of this invention is shown.

[0066] Figure 15 The equation for the preparation of the thiophene-pyridyl ionic liquid in Example 17 of this invention is shown.

[0067] Figure 16 The structural formula of the polythiophene-pyridyl ionic liquid in Example 17 of this invention is shown.

[0068] Figure 17 The equation for the preparation of the quaternary amino ionic liquid in Comparative Example 2 of this invention is shown below.

[0069] Figure 18 The structural formula of the polyquaternary amino ionic liquid in Comparative Example 2 of this invention is shown.

[0070] Figure 19 The above are the 1H NMR spectra of the aniline-based ionic liquids in Examples 1-10 of this invention.

[0071] Figure 20 The surface morphology of the positive electrode electrolyte interface formed by in-situ polymerization of polyaniline-based ionic liquid (left) in Example 3 of the present invention and commercial electrolyte (right) in Comparative Example 1 is shown.

[0072] Figure 21 This is a graph showing the capacity retention rate of Embodiment 3 and Comparative Example 1 after 200 cycles.

[0073] Figure 22 This is a cyclic voltammetry (CV) curve of the lithium cobalt oxide-lithium battery prepared in Example 3 of the present invention. Detailed Implementation

[0074] To facilitate understanding of the positive electrode sheet of the present invention, a more comprehensive description of the positive electrode sheet of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0075] Example 1

[0076] (1) Preparation of aniline-based ionic liquids

[0077] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0078] (2) Preparation of electrolyte

[0079] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.2wt%.

[0080] (3) Battery assembly

[0081] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 8:1:1) as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. The assembled battery was a lithium cobalt oxide-lithium half-cell, with a lithium sheet (lithium metal) as the reference electrode. After assembly and 5 hours of resting, the formation process involved charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0082] Example 2

[0083] (1) Preparation of aniline-based ionic liquids

[0084] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0085] (2) Preparation of electrolyte

[0086] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.5wt%.

[0087] (3) Battery assembly

[0088] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0089] Example 3

[0090] (1) Preparation of aniline-based ionic liquids

[0091] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0092] (2) Preparation of electrolyte

[0093] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0094] (3) Battery assembly

[0095] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0096] Example 4

[0097] (1) Preparation of aniline-based ionic liquids

[0098] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0099] (2) Preparation of electrolyte

[0100] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 1wt%.

[0101] (3) Battery assembly

[0102] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0103] Example 5

[0104] (1) Preparation of aniline-based ionic liquids

[0105] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0106] (2) Preparation of electrolyte

[0107] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 2wt%.

[0108] (3) Battery assembly

[0109] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0110] Example 6

[0111] (1) Preparation of aniline-based ionic liquids

[0112] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0113] (2) Preparation of electrolyte

[0114] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0115] (3) Battery assembly

[0116] A coin cell was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the cells were allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.4V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0117] Example 7

[0118] (1) Preparation of aniline-based ionic liquids

[0119] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0120] (2) Preparation of electrolyte

[0121] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0122] (3) Battery assembly

[0123] A coin cell was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the cells were allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.6V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0124] Example 8

[0125] (1) Preparation of aniline-based ionic liquids

[0126] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0127] (2) Preparation of electrolyte

[0128] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0129] (3) Battery assembly

[0130] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 4.0V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention rate after 200 cycles was calculated.

[0131] Example 9

[0132] (1) Preparation of aniline-based ionic liquids

[0133] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0134] (2) Preparation of electrolyte

[0135] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0136] (3) Battery assembly

[0137] A coin cell battery was assembled using a lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 8:1:1) as the positive electrode material, a 25μm thick PP separator, a lithium sheet as the negative electrode, and 60μL of electrolyte. After assembly and 5 hours of resting, the formation process involved charging at a constant voltage of 4.2V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0138] Example 10

[0139] (1) Preparation of aniline-based ionic liquids

[0140] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N-methylimidazolium and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 33g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 20g of black liquid product.

[0141] (2) Preparation of electrolyte

[0142] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-based ionic liquid added is 0.75wt%.

[0143] (3) Battery assembly

[0144] A coin cell was assembled using a lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 8:1:1) as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly and standing for 5 hours, the formation process showed an A / cm² voltage of 6.5 mA. -2 Constant current charging. Constant current charge-discharge tests were conducted at 25°C and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention rate after 200 cycles was calculated.

[0145] Example 11

[0146] (1) Preparation of pyrrole ionic liquids

[0147] Take 30g of 1-(2-chloroethyl)-pyrrole and 27g of N-ethylimidazole and dissolve them in 50g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 50g of LiDFOB (lithium difluorooxalate borate) and stir for 1h. Separate the solution three times with 50mL of deionized water and rotary evaporate to obtain 40g of liquid product.

[0148] (2) Preparation of electrolyte

[0149] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of pyrrole ionic liquid added is 0.75wt%.

[0150] (3) Battery assembly

[0151] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0152] Example 12

[0153] (1) Preparation of pyrrole ionic liquids

[0154] Take 30g of 1-(2-chlorobutyl)-pyrrole and 27g of N-ethylimidazole and dissolve them in 50g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 50g of LiDFOB (lithium difluorooxalate borate) and stir for 1h. Separate the solution three times with 50mL of deionized water and rotary evaporate to obtain 42g of liquid product.

[0155] (2) Preparation of electrolyte

[0156] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of pyrrole ionic liquid added is 0.75wt%.

[0157] (3) Battery assembly

[0158] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0159] Example 13

[0160] (1) Preparation of pyrrole ionic liquids

[0161] Take 30g of 1-(2-chlorohexyl)-pyrrole and 27g of N-ethylimidazol and dissolve them in 50g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 50g of LiDFOB (lithium difluorooxalate borate) and stir for 1h. Separate the solution three times with 50mL of deionized water and rotary evaporate to obtain 48g of liquid product.

[0162] (2) Preparation of electrolyte

[0163] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of pyrrole ionic liquid added is 0.75wt%.

[0164] (3) Battery assembly

[0165] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0166] Example 14

[0167] (1) Preparation of thiophene-based ionic liquids

[0168] Take 20g of 3-(2-chloroethyl)thiophene and 16g of N-ethylimidazole and dissolve them in 30g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 30mL of ethyl acetate. Add 30g of deionized water to the upper layer solution, add 30g of LiFSI (lithium bisfluorosulfonylimide) and stir for 1h. Separate the solution three times with 30mL of deionized water and rotary evaporate to obtain 30g of liquid product.

[0169] (2) Preparation of electrolyte

[0170] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of thiophene-based ionic liquid added is 0.75wt%.

[0171] (3) Battery assembly

[0172] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0173] Example 15

[0174] (1) Preparation of aniline-pyridyl ionic liquid

[0175] Take 24g of 2-bromo-3-nitroacetophenone and 10g of 4-methylpyridine and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution and add 35g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)). Stir for 1h and then separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid and add 10g of iron powder. Stir at 80℃ for 4h and then dissolve in anhydrous ethanol. Filter and rotary evaporate to obtain 19g of black liquid product.

[0176] (2) Preparation of electrolyte

[0177] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of aniline-pyridyl ionic liquid added is 0.75wt%.

[0178] (3) Battery assembly

[0179] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0180] Example 16

[0181] (1) Preparation of pyrrole-pyridyl ionic liquids

[0182] Take 30g of 1-(2-chloroethyl)-pyrrole and 23g of 4-ethylpyridine and dissolve them in 50g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 50g of LiDFOB (lithium difluorooxalate borate) and stir for 1h. Separate the solution three times with 50mL of deionized water and rotary evaporate to obtain 35g of liquid product.

[0183] (2) Preparation of electrolyte

[0184] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of pyrrole-pyridyl ionic liquid added is 0.75wt%.

[0185] (3) Battery assembly

[0186] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0187] Example 17

[0188] (1) Preparation of thiophene-pyridyl ionic liquids

[0189] Take 20g of 3-(2-chloroethyl)thiophene and 18g of 4-ethylpyridine and dissolve them in 30g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 30mL of ethyl acetate. Add 30g of deionized water to the upper layer solution, add 30g of LiFSI (lithium bisfluorosulfonylimide) and stir for 1h. Separate the solution three times with 30mL of deionized water and rotary evaporate to obtain 28g of liquid product.

[0190] (2) Preparation of electrolyte

[0191] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of thiophene-pyridyl ionic liquid added is 0.75wt%.

[0192] (3) Battery assembly

[0193] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0194] Comparative Example 1

[0195] A coin cell was assembled using lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 8:1:1) as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. The electrolyte was 1M LiPF6 EC:EMC:DMC (1:1:1), with 60μL of electrolyte added. After assembly, the cells were allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0196] Comparative Example 2

[0197] (1) Preparation of quaternary amino ionic liquids

[0198] Take 24g of 2-bromo-3-nitroacetophenone and 10g of N,N-diethylmethylamine and dissolve them in 200g of ethyl acetate solution. Heat and stir at 70℃ for 24h. After stirring, separate the solution three times with 50mL of ethyl acetate. Add 50g of deionized water to the upper layer solution, add 35g of LiTFSI (lithium bis(trifluoromethanesulfonylimide)) and stir for 1h. Separate the solution three times with 50mL of deionized water. Dissolve the product in 20g of concentrated hydrochloric acid, add 10g of iron powder, stir at 80℃ for 4h, dissolve in anhydrous ethanol, filter, and rotary evaporate to obtain 15g of yellow liquid product.

[0199] (2) Preparation of electrolyte

[0200] The base electrolyte is 1M LiPF6 EC:EMC:DMC (1:1:1), and the amount of quaternary amino ionic liquid added is 0.75wt%.

[0201] (3) Battery assembly

[0202] A coin cell battery was assembled using lithium cobalt oxide (LiCoO2), carbon black (SP), and polyvinylidene fluoride (HSV900) in a mass ratio of 8:1:1 as the positive electrode material, a 25μm thick PP separator, and a lithium sheet as the negative electrode. 60μL of electrolyte was added. After assembly, the battery was allowed to stand for 5 hours, followed by a formation process of charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a voltage range of 3V-4.6V at a 0.5C rate, and the capacity retention after 200 cycles was calculated.

[0203] Comparative Example 3

[0204] A commercial alumina-coated lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 8:1:1) was used as the positive electrode material, with a 25μm thick PP separator and lithium foil as the negative electrode. The electrolyte was 1M LiPF6 EC:EMC:DMC (1:1:1), with 60μL of electrolyte added. A coin cell was assembled. After assembly and 5 hours of resting, the formation process involved charging at a constant voltage of 3.8V for 24 hours. Constant current charge-discharge tests were conducted at 25℃ and a 0.5C rate within a voltage range of 3V-4.6V, and the capacity retention after 200 cycles was calculated.

[0205] Table 1. Constant current charge-discharge test data for the examples and comparative examples.

[0206]

[0207] The polymer layer thickness was obtained by scanning electron microscopy analysis of the cross-section of the polymer-coated electrode. The polymer layer ionic conductivity was calculated by preparing a polymer film, assembling a stainless steel-stainless steel symmetric cell, testing its impedance (R), and then using the formula σ = d / (RS), where d is the polymer thickness and S is the effective area of ​​the polymer in the middle of the electrode.

[0208] Figure 19 The figures show the 1H NMR spectra of the aniline-based ionic liquids from Examples 1-10. As can be seen from the figures, the hydrogen atoms at different positions in the ionic liquid correspond one-to-one with the chemical shifts and peak areas in the spectra, indicating the successful preparation of the aniline-based ionic liquids described in Examples 1-10. Polyaniline has good conductivity, and after molecular design and grafting the ionic liquid structure, it can effectively transport lithium ions. Furthermore, the in-situ prepared artificial positive electrode electrolyte interface can protect the positive electrode material from electrolyte corrosion, thereby extending battery life and improving battery cycle performance. Through observation... Figure 1From the surface morphology of the SEI formed in Example 3 and Comparative Example 1, the in-situ polyaniline-based artificial positive electrode electrolyte interface is denser, while the SEI formed by the commercial electrolyte exhibits obvious cracks and fissures, failing to achieve a good coating effect. Furthermore, analysis of the results from Examples 1-5 shows that controlling the content of aniline monomers can improve the coating effect on lithium cobalt oxide. With increasing addition amount, the battery capacity initially increases and then decreases. As the addition amount increases, the thickness of the formed SEI gradually increases, resulting in a better coating effect. However, excessive thickness can affect the lithium insertion / extraction kinetics of the positive electrode material, impacting its reactivity and consequently affecting the battery's cycle performance.

[0209] Analysis of the results from Examples 3 and 6-9 shows that the polymerization of aniline can be affected by adjusting the constant voltage during battery formation. As the constant voltage increases, the battery capacity retention rate initially increases and then decreases. At lower voltages, the driving force for aniline polymerization is lower, resulting in an unevenly formed SEI film on the lithium cobalt oxide surface. At higher voltages, the driving force for aniline polymerization is faster, leading to a higher degree of polymerization and a less dense SEI film, thus affecting battery performance. Furthermore, by controlling the formation process, changing the voltage and time of constant voltage charging and the current density of constant current charging can control the degree of polymerization and density of the polymer. The results from Examples 3 and 10 demonstrate that under appropriate constant voltage or constant current charging parameters, a better degree of polymerization and coating effect can be obtained, improving the battery's charge-discharge performance.

[0210] Through extensive research, the inventors discovered that lithium ions are transported within polymers by coordinating with polar molecules and transferring them via the peristalsis of polymer molecular chain segments. Therefore, the polymer chain structure can influence the lithium ion transport rate, thereby altering the battery's electrochemical performance. When X contains a thiophene group and Y contains an imidazole group, the battery performance is better: Analysis of the results from Examples 3, 11, and 14 shows that when the polar elements in the main chain have more lone pairs of electrons, more lithium ion transport channels can be formed, thus improving battery performance. The sulfur in the thiophene group contains more lone pairs of electrons, resulting in a higher capacity retention rate. Comparing the results of Examples 3 and 15, 11 and 16, and 14 and 17, compared to imidazole groups, when the ionic liquid group is a pyridine group, it contains fewer polar groups, resulting in fewer lithium ion transport channels and thus poorer battery performance.

[0211] Changing the type of ionic liquid can also change the performance of the battery. Comparing Example 3 and Comparative Example 2, the molecular size of the imidazole-based ionic liquid is significantly different from that of the conventional quaternary ammonium-based ionic liquid. The imidazole-based ionic liquid has a five-membered ring, which has a larger volume. Therefore, the free volume of the polymer after electropolymerization will be larger, the molecular chain segment peristalsis will be easier, the lithium ion transport speed will be faster, and the performance of the prepared battery will be better.

[0212] Through extensive research, the inventors also discovered that altering the side chain length affects battery performance. Increasing the side chain length increases the free volume of the polymer, thus enhancing polymer chain segment peristalsis and promoting lithium-ion transport, thereby improving battery performance. However, as the side chain length increases further, the longer side chains become entangled, increasing steric hindrance and making chain segment peristalsis more difficult, thus reducing lithium-ion transport. The results from Examples 11-13 show that batteries with side chain lengths of 2-6 exhibit high capacity retention, especially those with a side chain length of 4.

[0213] In addition, through analysis Figure 22 The cyclic voltammetry (CV) curves of the lithium cobalt oxide-lithium battery prepared in Example 3 show that the prepared battery only exhibits oxidation and reduction peaks during lithium intercalation / deintercalation of lithium cobalt oxide material at voltages of 3V-4.6V. This indicates that the artificial CEI prepared by the in-situ formation process has excellent high-voltage stability. Combined with the capacity retention data of the examples, the artificial CEI prepared by the in-situ method avoids the impact of the high oxidation activity of high-voltage active materials on the stability of the electrolyte, thereby reducing the capacity loss of the battery.

[0214] Compared with Comparative Example 3, the battery prepared by the in-situ formation process of lithium cobalt oxide has better performance than conventional commercially available alumina-coated lithium cobalt oxide.

[0215] It should be noted that 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 should be included within the protection scope of the present invention.

Claims

1. A battery-grade electropolymerizable ionic liquid, characterized in that, The ionic liquid has a structure of Formula I. (Equation I) X represents the structure of Equation II. (Formula II) Wherein, R is a C2-C6 straight-chain hydrocarbon group; Y represents the structure of Equation III. (Formula III) wherein m is selected from 1-10, m is an integer; Z - is selected from one of a sulfonamide ion, an oxalate borate ion; R of X and N of Y + Connection.

2. An electropolymerizable ionic liquid polymer, characterized in that, The ionic liquid polymer has the following structural formula: ； Wherein, R is a C2-C6 straight-chain hydrocarbon group; The Y structure is as follows: ; Where m is selected from 1 to 10, and m is an integer; Z - Selected from one of sulfonamide ions and oxalate-borate ions, wherein R and Y have N + connect.

3. A battery electrode, characterized in that, The electrode is polymerized on the surface of the electrode using the ionic liquid of claim 1 to form a polymer coating layer, or the surface of the electrode has the electropolymerized ionic liquid polymer of claim 2.

4. The battery electrode according to claim 3, characterized in that, The thickness of the polymer coating is 0.5 nm to 3 μm.

5. The battery electrode according to claim 3, characterized in that, The thickness of the polymer coating layer is 0.3 μm to 1 μm; The polymer coating layer has at least one of the following characteristics: a. The room temperature ionic conductivity of the polymer coating is 1×10⁻⁶. -5 S / cm up to 5×10 -3 S / cm; b. The electrochemical window of the polymer capping layer is greater than 4.6V.

6. The method for preparing the battery electrode according to claim 5, characterized in that, Includes the following steps: S1. Under a dry gas atmosphere, the ionic liquid described in claim 1 is added to the electrolyte as a monomer and mixed evenly. The battery electrode assembly is assembled, and the electrolyte containing the ionic liquid monomer is injected. After sealing, it is left to stand for further processing. S2. The battery undergoes a formation process, where ionic liquid monomers are uniformly formed on the electrode surface to create a battery electrode coated with polyionic liquid.

7. The method for preparing battery electrode sheets according to claim 6, characterized in that, The ionic liquid monomer in S1 accounts for 0.05wt% to 10wt% of the total mass of the electrolyte.

8. The method for preparing battery electrode sheets according to claim 6, characterized in that, The ionic liquid monomer in S1 accounts for 0.5wt% to 1wt% of the total mass of the electrolyte.

9. The method for preparing battery electrode sheets according to claim 6, characterized in that, The formation in S2 includes at least one of a constant current charging stage or a constant voltage charging stage. The charging current density during the constant current charging phase is 0.1~20 mA / cm². 2 ; The charging voltage during the constant voltage charging phase is any voltage value within the voltage range formed by the lower limit and upper limit of the battery charging voltage.

10. The method for preparing the battery electrode according to claim 9, characterized in that, The charging current density during the constant current charging phase is 5~10 mA / cm². 2 .

11. The method for preparing the battery electrode according to claim 9, characterized in that, The charging voltage during the constant voltage charging phase is 80%-95% of the upper limit of the charging voltage.

12. A battery having an electropolymerizable ionic liquid as described in claim 1, or an electropolymerizable ionic liquid polymer as described in claim 2, a battery electrode as described in any one of claims 3-5, or a battery electrode obtained by any one of claims 6-11.

13. An electrochemical device comprising the electropolymerizable ionic liquid of claim 1 or the electropolymerizable ionic liquid polymer of claim 2, the battery electrode of any one of claims 3-5 or the battery electrode obtained by the preparation method of any one of claims 6-11.

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