A positive electrode sheet and electrochemical device thereof

Abstract

The present invention discloses a positive electrode plate comprising a gel-like coating layer coated on the surface of a positive electrode active material, wherein an ionic liquid is bound in the coating layer. The coating layer in the positive electrode plate of the present invention not only helps reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the battery capacity, but also reduces the contact resistance between the battery's positive electrode and the electrolyte, thereby improving the battery's electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode plate and an electrochemical device thereof. Background Art

[0002] With the widespread adoption of mobile phones, laptops, digital cameras, and other electronic devices, my country has become the largest consumer of batteries. The convenience and diversity brought by electronic products have driven rapid growth in my country's lithium-ion battery market over the past few years. This is driven by the increasing demand for higher electrochemical performance in batteries.

[0003] As the source of energy density in lithium batteries, the positive electrode of the battery has a significant impact on the electrical performance of the battery. During the battery charge and discharge cycle, first, there is a certain contact internal resistance between the positive electrode of the battery and the electrolyte in the battery, and the wettability between the electrolyte in the battery and the positive electrode of the battery is poor, which will affect the rate performance of the battery to a certain extent; secondly, certain side reactions will occur after the positive electrode active material in the positive electrode sheet contacts the electrolyte, which will cause the capacity of the battery to decrease. In the prior art, a solid electrolyte interface film (CEI film) with ionic conductivity will be generated during the battery charge and discharge cycle. The generated CEI film can, on the one hand, isolate the side reactions between the positive electrode of the battery and the electrolyte, and on the other hand, assist in the ion transport and migration between the positive electrode and the electrolyte. The generation of the CEI film can, to a certain extent, help improve the electrochemical performance of the battery. However, during the battery charge and discharge cycle, it is often due to a large amount of Li + The embedding and extraction of CEI membranes lead to cracking, which ultimately leads to a decrease in the capacity and rate performance of the battery. When charged at a high voltage, the CEI membrane is more likely to crack, and the electrochemical performance of the battery decreases more significantly. Summary of the Invention

[0004] The present invention addresses the problems of the prior art. The positive electrode sheet of the present invention comprises a gel-like coating layer, which also functions as a CEI membrane. First, the gel-like coating layer coats the surface of the positive electrode active material, isolating the positive electrode active material from the electrolyte in the positive electrode sheet, thereby reducing the consumption of lithium ions by side reactions. Second, the gel-like coating layer contains ionic liquid and dispersed metal oxide, which imparts mechanical strength to the gel-like coating layer. It also ensures that the formed gel-like coating layer has an ionic conductivity comparable to that of the electrolyte, promoting ion transport between the positive electrode and the electrolyte, thereby reducing the contact internal resistance between the positive electrode and the electrolyte. Furthermore, the positive electrode sheet of the present invention is particularly suitable for use in high-voltage rechargeable batteries. The entire conceptual process of this solution will be described in further detail.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a compound additive, which includes an ionic liquid, a cyclic carbonate compound, a metal organic compound, and an organic acid compound. By mass, the ratio of the ionic liquid: the cyclic carbonate compound: the metal organic compound: the organic acid compound is (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-2 parts): (0.5 parts-4 parts), and the mass proportion of the compound additive in the positive electrode slurry is 1.5%-8.7%.

[0007] The above-mentioned design of the present invention, the compound additive of the present invention is particularly suitable for positive electrode slurry, the metal organic compound can be used as a catalyst to promote cyclic carbonate compounds and ionic liquids, and the cyclic carbonate compounds undergo ring opening during the heating process to carry out in-situ polymerization reaction. In order to improve the catalytic effect of the catalyst, we have further added organic acid compounds, which are beneficial to promote the dissolution of the metal organic compound, and are more beneficial to promote the uniform dispersion of the metal organic compound in the slurry, increase the contact area between the metal organic compound and the cyclic carbonate compound, thereby improving the catalytic effect, and forming a uniform gel coating layer after in-situ polymerization; in addition, the metal organic compound is also beneficial to enhance the mechanical properties of the gel coating layer. After the ring-opening in-situ polymerization of the cyclic carbonate compounds, a stable gel-like coating layer is formed, which is coated on the surface of the positive electrode active material, the surface of other material particles in the slurry, and the gaps between the particles, which is beneficial to bind the ionic liquid in the gel-like coating layer and prevent the ionic liquid from being lost from the electrode; among them, the ionic liquid also has a high ionic conductivity, which can improve the ion conduction ability between the coated positive electrode active material and the electrolyte, and is beneficial to build a lithium ion conduction bridge between the positive electrode active material and the electrolyte, thereby promoting the transmission and migration of lithium ions in the positive electrode of the battery. The organic acid compound is beneficial to remove the residual alkali on the surface of the positive electrode active material and thus neutralize the pH of the slurry. In the present invention, we further balance the relationship among the binding effect of the gel coating, the energy density of the positive electrode and the ion transmission capacity of the gel coating by adjusting the ratio of the compound additives. Under the ratio of the compound additives of the present invention, the positive electrode of the present invention can obtain the maximum energy density. The compound additives are conducive to forming a gel coating with certain mechanical strength and structural stability in the slurry, so that the gel coating can bind the ionic liquid, and the generated gel coating also has an ionic conductivity equivalent to that of the electrolyte, which is not only conducive to reducing the contact resistance between the positive electrode and the electrolyte and improving the ion transmission capacity between the positive electrode and the electrolyte, but also can reduce the side reactions between the positive electrode active material and the electrolyte, thereby helping to improve the electrochemical performance of the battery.

[0008] As a further solution, the ionic liquid includes quaternary ammonium ionic liquid, imidazole ionic liquid, pyridine ionic liquid. Imidazole ionic liquid is more suitable for the higher positive electrode slurry of battery operating voltage. In the structure of imidazole ionic liquid, the imidazole ring is an electron-rich group. The imidazole structure is a five-membered heterocyclic compound with a conjugated system of a closed large π bond, so that the electron-withdrawing ability of N increases. The electron cloud density of the nitrogen atom in the imidazole ring increases. The nitrogen atom in the electron-rich group will participate in attacking the oxygen group in the cyclic carbonate compound, thereby facilitating the mutual coordination between the cyclic carbonate compound and facilitating the formation of a gel-like coating layer. Quaternary ammonium ionic liquid is more suitable for the positive electrode slurry of long-term working batteries. During the long-term cycle process of the battery, heat will be generated in the battery positive electrode, and the temperature inside the battery will increase, while quaternary ammonium ionic liquid has better thermal stability. Pyridine ionic liquid is more suitable for general battery operating environment. Pyridine ionic liquid has better stability and can be used in most battery positive electrodes. Its electrochemical performance is not easy to decay.

[0009] As a further embodiment, the quaternary ammonium ionic liquid includes one or more of tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium hexafluorophosphate, and tetramethylammonium trifluoromethanesulfonate.

[0010] As a further embodiment, the imidazolium ionic liquid includes one or more of 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium phosphate, and 1-butyl-3-methylimidazolium nitrate.

[0011] As a further embodiment, the pyridinium ionic liquid includes one or more of 1-butyl-4-methylpyridinium chloride, 1-hexyl-4-methylpyridinium chloride, and 1-ethylpyridinium bromide.

[0012] As a further embodiment, the cyclic carbonate compound includes a cyclic carbonate having an unsaturated ring and a cyclic carbonate having a saturated ring. Specifically, the cyclic carbonate having an unsaturated ring includes vinylene carbonate. The cyclic carbonate having a saturated ring includes ethylene carbonate.

[0013] As a further embodiment, the cyclic carbonate having a saturated ring includes one or more cyclic carbonates having a C2-C6 alkylene group;

[0014] As a further embodiment, the cyclic carbonate having a saturated ring includes one or more cyclic carbonates having a C2-C4 alkylene group, specifically ethylene carbonate, propylene carbonate, butylene carbonate (2-ethylethylene carbonate, cis- and trans-2,3-dimethylethylene carbonate).

[0015] As a further embodiment, the cyclic carbonate compound further has one or more of an unsaturated substituent group, a halogen atom substituent group, and an alkyl substituent group.

[0016] As a further embodiment, the unsaturated substituent group includes one or more of C=C, C≡C, and an aromatic ring.

[0017] As a further embodiment, the halogen atom substituent group includes one or more of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0018] As a further embodiment, the alkyl substituent group includes one of C1-C4 alkyl groups, specifically methyl cyclic ethylene carbonate and ethyl cyclic ethylene carbonate.

[0019] As a further embodiment, the halogen atom substituent group includes one or more of fluorine atoms and chlorine atoms.

[0020] As a further solution, the halogen atom substituent group includes a fluorine atom. Specifically, it can be a fluorinated cyclic carbonate compound, and specifically, fluorinated cyclic ethylene carbonate can be mentioned. Fluorine-substituted cyclic carbonate compounds are more suitable for batteries operating in high-voltage environments. First, they have lower viscosity and can be more evenly dispersed in the battery positive electrode slurry. Second, the fluorine substituent helps improve its oxidative stability under high pressure. The electron-withdrawing effect of fluorine helps to change the electron cloud density distribution in the structure, thereby better cooperating with the metal organic compound to form a uniform and structurally stable gel-like coating layer through ring-opening polymerization in a heated environment.

[0021] As a further embodiment, the number of the halogen atom substituent groups is 1-6.

[0022] As a further embodiment, the number of the halogen atom substituent groups is 1-4.

[0023] As a further solution, the organic acid compounds include organic carboxylic acid compounds, organic sulfonic acid compounds, and organic strong binding effects, which effectively inhibit the shuttle effect of polysulfides and can also serve as inhibitors of lithium dendrites. Organic sulfinic acid compounds are more suitable for batteries containing metal halides in the battery positive electrode slurry. Organic sulfinic acid compounds can form complexes with metal halides and can stabilize the gel-like coating formed on the positive electrode, including one or more of sulfinic acid compounds and organic sulfur carboxylic acid compounds. Organic carboxylic acid compounds are more suitable for the positive electrode slurry of batteries with high voltage working environments. The carbonyl group in the organic carboxylic acid compound has a faster redox reaction kinetics, which can improve the redox ability of the battery positive electrode. The organic sulfonic acid compound has abundant SO bonds in its structure, which is more suitable for sulfur positive electrodes. It not only has a strong bond with lithium polysulfide, but also helps to improve the oxidation stability of the battery. Organic sulfur carboxylic acid compounds are more suitable for substances containing unsaturated groups in the battery positive electrode slurry. When the battery is under the action of the charging voltage, the SH bonds in the organic sulfur carboxylic acid compound are more likely to undergo dehydrogenation reactions, which is conducive to the addition reaction of sulfur free radicals with unsaturated bonds, thereby helping to improve the cycle performance of the battery.

[0024] As a further embodiment, the organic carboxylic acid compound includes one or more of an organic dicarboxylic acid, an organic monocarboxylic acid, a monounsaturated organic carboxylic acid, and a polyunsaturated organic carboxylic acid. Organic dicarboxylic acids are more stable under high-voltage working environments and have multiple carbonyl groups, resulting in higher activity. These compounds are more conducive to dissolving metal organic compounds and promoting the ionic liquid to exhibit better ionic conductivity. Furthermore, organic dicarboxylic acids can neutralize alkalinity in the slurry, improving the slurry's reinforcement properties.

[0025] As a further embodiment, the organic dibasic acid includes one or more of oxalic acid, malonic acid, and succinic acid.

[0026] As a further embodiment, the organic monoacid includes one or more of formic acid, acetic acid, butyric acid, and propionic acid.

[0027] As a further embodiment, the monounsaturated organic carboxylic acid includes oleic acid.

[0028] As a further embodiment, the polyunsaturated organic carboxylic acid comprises butynedioic acid.

[0029] As a further embodiment, the metal organic compound includes one or more of a metal isopropyl alcohol compound, a metal sulfonic acid compound, and a metal alkane compound. First, the metal isopropyl alcohol compound can be dissolved by the organic acid compound and then dispersed in the slurry. This allows for better solubility in the organic acid compound, resulting in a more uniform dispersion in the positive electrode slurry, thereby promoting a more uniform formation of the gel-like coating layer. Second, the metal isopropyl alcohol compound dispersed in the slurry is more easily combined with a binder than other alcohols, thereby improving the mechanical strength of the formed coating layer. As a further embodiment, the metal isopropyl alcohol compound includes aluminum isopropylate or magnesium isopropylate.

[0030] As a further embodiment, the metal sulfonate compound includes silver isotrifluoromethanesulfonate and aluminum trifluoromethanesulfonate.

[0031] As a further embodiment, the metal alkane compound includes dibutyltin and dibutylzinc.

[0032] As a further solution, the compound additive includes an imidazole ionic liquid, a fluorinated cyclic carbonate compound, an organic dicarboxylic acid, and a metal isopropyl alcohol compound. The ratio of the imidazole ionic liquid: the fluorinated cyclic carbonate compound: the organic dicarboxylic acid: the metal isopropyl alcohol compound is (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (0.5 parts-2 parts) in mass. In the prior art, cyclic carbonate compounds are often used as solvents in electrolytes because of their stable structure at high temperatures and good solubility. In the present invention, the cyclic carbonate compound is used in the positive electrode slurry, and then a catalyst metal organic compound is added to catalyze the ring opening of the cyclic carbonate compound during the heating process, and then in situ polymerization occurs under the mutual cooperation with the imidazole ionic liquid to form a gel-like coating layer coated on the surface of the positive electrode active material. In order to promote the formation of a gel-like coating during the preparation of the positive electrode and avoid side reactions between the electrolyte and the positive electrode active material in the assembled battery, we need to shorten the time for the coating to form. We need to select more compatible cyclic carbonate compounds and metal organic compounds to improve the catalytic effect. The fluorine substituent in the fluorinated cyclic carbonate has a stronger electron-withdrawing effect, which is conducive to changing the changes in the electron cloud of the cyclic structure. It can also produce an electron-withdrawing effect with the electrons in the isopropyl alcohol structure of the metal isopropyl alcohol compound, thereby strengthening the catalytic effect of the metal isopropyl alcohol compound on the fluorinated cyclic carbonate compound and helping to improve the catalytic efficiency of the fluorinated cyclic carbonate. In order to promote the metal isopropyl alcohol compound to be better dissolved in the slurry and better dispersed, an organic dicarboxylic acid is added so that the metal isopropyl alcohol compound can be more evenly dispersed around the fluorinated cyclic carbonate compound, which can increase the contact area between the metal isopropyl alcohol compound and the fluorinated cyclic carbonate and also improve the catalytic efficiency. We further selected organic dicarboxylic acids, the mutual coordination of the hydroxyl group of metal isopropyl alcohol compounds and the carboxyl group in the organic dicarboxylic acid. Due to the mutual influence of the two carboxyl groups in the organic dicarboxylic acid, the influence on the structure of the metal isopropyl alcohol compounds can be reduced, thereby achieving better dissolution of the metal isopropyl alcohol compounds in the organic dicarboxylic acid while ensuring the catalytic activity of the metal isopropyl alcohol compounds during dissolution.

[0033] As a further scheme, the composite additive comprises fluorocyclic ethylene carbonate, aluminum isopropylate, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, oxalic acid, by mass, the fluorocyclic ethylene carbonate: aluminum isopropylate: 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt: the ratio of oxalic acid is (0.5 part-2 part): (0.5 part-2 part): (0.2 part-0.3 part): (0.5 part-4 part). Fluorocyclic ethylene carbonate can partially replace the usage amount of solvent, is conducive to carrying the addition amount of positive electrode active material. On this basis, the unsaturated group in fluorocyclic ethylene carbonate can improve the electron-withdrawing ability of fluorine group, then forms electron-withdrawing effect with 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, can better under the catalysis of catalyst aluminum isopropylate, in thermal process, fluorocyclic ethylene carbonate open ring, polymerization forms gel-like coating. Oxalic acid can separate the aluminum ions and organic anions in aluminum isopropoxide, thereby facilitating the release of its catalytic activity while allowing aluminum isopropoxide to be more evenly dispersed in the slurry. Furthermore, aluminum isopropoxide can react with residual alkali on the surface of the positive electrode active material to form a layer of lithium ion conductor, which can further promote the rate of lithium removal and insertion of the positive electrode active material. Furthermore, aluminum isopropoxide facilitates better coordination with the binder, thereby enhancing the mechanical strength of the coating layer. When the dispersed aluminum isopropoxide is dispersed around the fluorocyclic ethylene carbonate, it has more contact area with the fluorocyclic ethylene carbonate, which is more conducive to the rapid progress of the catalytic reaction. Furthermore, the aluminum ions in the aluminum isopropoxide structure can have more coordination, which is conducive to the interaction with the fluoride ions in the fluorocyclic ethylene carbonate, and directly promotes the catalytic efficiency of aluminum isopropoxide in the ring-opening polymerization of fluorocyclic ethylene carbonate.

[0034] The present invention also provides application of the compound additive in positive electrode slurry.

[0035] As a further solution, the compound additive exists on the surface of the positive electrode active material in the form of a gel-like coating layer; the gel-like coating layer contains ionic liquid.

[0036] As a further solution, the raw materials of the positive electrode slurry also include positive electrode active material, binder, and conductive agent. The ratio of the positive electrode active material: ionic liquid: cyclic carbonate compound: metal organic compound: organic acid compound: binder: conductive agent is (90 parts-95 parts): (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts) by mass. On the basis of bonding the various substances, the binder can cooperate with the metal organic compound to improve the mechanical strength of the gel coating; the ionic liquid can cooperate with the conductive agent to balance the transmission balance of electrons and ions in the positive electrode; the ratio between the various substances in the positive electrode slurry further balances the relationship between the binding effect of the gel coating, the energy density of the positive electrode and the ion transmission capacity of the gel coating. Under the ratio of the positive electrode slurry of the present invention, the positive electrode of the present invention can obtain the maximum energy density. The compound additives are conducive to forming a gel coating with certain mechanical strength and structural stability in the slurry, so that the gel coating can bind the ionic liquid, and the generated gel coating also has an ionic conductivity equivalent to that of the electrolyte, which is not only conducive to reducing the contact resistance between the positive electrode and the electrolyte and improving the ion transmission capacity between the positive electrode and the electrolyte, but also can reduce the side reactions of the positive electrode active material and the electrolyte, thereby helping to improve the electrochemical performance of the battery.

[0037] As a further solution, the raw materials of the positive electrode slurry further include a solvent, and the amount of solvent added can be determined by technicians based on the actual viscosity of the slurry.

[0038] As a further embodiment, the positive electrode active material includes one or more of metal oxides, polyanion salts, and non-metallic compounds.

[0039] As a further solution, the metal oxide includes one or more of layered metal oxides and spinel metal oxides.

[0040] As a further solution, the layered structure metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, nickel-cobalt-manganese ternary material, lithium nickel-cobalt-aluminum oxide, and lithium-rich manganese-based material.

[0041] As a further solution, the spinel metal oxide includes one or more of lithium manganese oxide, lithium nickel manganese oxide, ferrosoferric oxide, and lithium vanadate.

[0042] As a further embodiment, the polyanion salt includes one or more of phosphate, silicate, sulfate, borate, and titanate.

[0043] As a further embodiment, the phosphate includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0044] As yet a further aspect, the silicate comprises lithium iron silicate.

[0045] As a further aspect, the sulfate comprises lithium ferrous fluorosulfate.

[0046] As yet a further aspect, the borate comprises lithium iron borate.

[0047] As a further aspect, the titanate includes lithium iron titanate.

[0048] As a further solution, the non-metallic compound includes one or more of fluoride, sulfide, and selenide.

[0049] As a further embodiment, the fluoride includes one or more of iron trifluoride, cobalt trifluoride, and nickel trifluoride.

[0050] As a further embodiment, the sulfide includes one or more of titanium disulfide, iron disulfide, and molybdenum disulfide.

[0051] As yet a further aspect, the selenide comprises niobium triselenide.

[0052] As a further embodiment, the binder includes one or more of fluorine-containing polymers, nitrile-containing polymers, amine-containing polymers, and carboxymethylated derivatives.

[0053] As a further embodiment, the fluorine-containing polymer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene.

[0054] As a further embodiment, the nitrile-containing polymer comprises polyacrylonitrile.

[0055] As a further aspect, the amine-containing polymer comprises a polyamide.

[0056] As a further embodiment, the carboxymethylated derivative comprises sodium carboxymethylcellulose.

[0057] As a further embodiment, the conductive agent includes one or more of acetylene black, Ketjen black, graphite, conductive carbon black (Super P), carbon nanotubes (CNT), carbon fibers, graphene, multi-walled carbon nanotubes, and single-walled carbon nanotubes.

[0058] As a further embodiment, the solvent comprises N-methylpyrrolidone (NMP).

[0059] As a further embodiment, the raw materials of the positive electrode slurry include a layered metal oxide, an imidazole ionic liquid, a fluorinated cyclic carbonate compound, a metal isopropyl alcohol compound, an organic dicarboxylic acid, a fluoropolymer, and a conductive agent. The ratio of the layered metal oxide: imidazole ionic liquid: fluorinated cyclic carbonate compound: metal isopropyl alcohol compound: organic dicarboxylic acid: fluoropolymer: conductive agent is (90 parts-95 parts): (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts). In order to improve the mechanical strength of the formed coating layer, we also use a fluoropolymer with better flexibility, which has a better surface for coating the material in the slurry; and the fluoropolymer and the metal isopropyl alcohol compound can produce an electron-withdrawing effect, which is beneficial for cooperating with the metal isopropyl alcohol compound to form a coating layer with a certain mechanical strength. To increase the energy density of the positive electrode, fluorinated cyclic carbonate compounds in the slurry can replace part of the solvent, which helps increase the mass ratio of the positive electrode active material in the slurry and ensure the energy density of the battery. Conductive agents facilitate the conduction of electrons and, in conjunction with imidazole ionic liquids, balance the migration of electrons and ions in the positive electrode. Metal isopropanol compounds can remove residual alkali from the surface of layered metal oxides and, when charged at a high voltage, help increase the rate of lithium ion insertion and extraction from the layered metal oxides.

[0060] As a further embodiment, the raw materials of the positive electrode slurry include fluorocyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, oxalic acid, polyvinylidene fluoride, carbon black + multi-walled carbon nanotubes, and lithium cobaltate active material (lithium cobaltate active material). The ratio of the fluorocyclic ethylene carbonate: aluminum isopropoxide: 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide: oxalic acid: polyvinylidene fluoride: carbon black + multi-walled carbon nanotubes: lithium cobaltate active material (lithium cobaltate active material) is (0.5 parts-2 parts): (0.5 parts-2 parts): (0.2 parts-0.3 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts): (90 parts-95 parts). Fluorinated cyclic vinyl carbonate can react with 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to form a gel coating layer under the catalysis of aluminum isopropoxide. Polyvinylidene fluoride facilitates the better binding of 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt within the coating layer, thereby increasing the ionic conductivity of the coating layer. Carbon black and multi-walled carbon nanotubes form an electron transport network, and the hollow tubular structure of the multi-walled carbon nanotubes also provides a channel for ion transport. 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt can balance the electron and ion balance in the positive electrode with the carbon black and multi-walled carbon nanotubes. Polyvinylidene fluoride also has good flexibility, allowing it to be better coated in the gel coating layer. Although fluoropolymers can produce an electron-withdrawing effect with aluminum isopropoxide, thereby facilitating interaction with the aluminum isopropoxide and improving the mechanical strength of the gel-like coating, the excessive number of fluorine substituents in the fluoropolymers, while potentially further enhancing the mechanical strength of the coating, also somewhat compromises the flexibility of the gel-like coating. Therefore, we chose polyvinylidene fluoride. With the coordination of various substances in the positive electrode slurry, it was found that the slurry of the present invention is more suitable for lithium cobalt oxide active materials, significantly improving the electrochemical performance of batteries containing lithium cobalt oxide active materials.

[0061] The present invention also provides a method for preparing the positive electrode slurry, which comprises:

[0062] The positive electrode active material, conductive agent, binder, cyclic carbonate compound, organic acid compound, ionic liquid, and metal organic compound are weighed in a mass ratio, then a solvent is added and mixed uniformly, and filtered to obtain a positive electrode slurry. The method of the present invention does not limit the order of adding and mixing the materials; furthermore, the amount of solvent used is not limited and can be adjusted by those skilled in the art based on the actual slurry viscosity.

[0063] As a further embodiment, the ratio of the positive electrode active material: ionic liquid: cyclic carbonate compound: metal organic compound: organic acid compound: binder: conductive agent is (90 parts-95 parts): (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts) by mass.

[0064] As a further solution, the condition for uniform mixing is to stir in a vacuum environment with a dew point below -40°C until the viscosity of the slurry reaches 4000 MPa·s-8000 MPa·s.

[0065] As a further solution, the present invention provides a preferred embodiment of positive electrode slurry preparation, which can further improve the dispersion of various substances in the slurry. First, in a vacuum environment with a dew point below -40°C, the positive electrode active material, conductive agent, and binder are uniformly mixed. An appropriate amount of NMP is added and kneaded. The CNT conductive agent is added and mixed uniformly. The ionic liquid and cyclic carbonate compound are added and mixed uniformly. The metal organic compound and NMP are added in batches until the slurry viscosity reaches 4000-8000 MPa·s.

[0066] The present invention also provides a method for preparing a battery having the positive electrode slurry, the method comprising:

[0067] The positive electrode slurry is coated on the surface of the current collector, dried and cut at a temperature of 70°C-130°C to form positive electrode sheets. The positive electrode sheets are prepared into battery cells, which are then baked. The obtained battery cells are then subjected to the liquid injection process, chemical process, and sealing process to obtain a battery. Generally, cyclic carbonate compounds undergo ring-opening polymerization at a temperature of not less than 150°C. In the present invention, a metal organic compound is added as a catalyst to promote the ring-opening polymerization of the cyclic carbonate compounds during the baking process of the electrode sheets. At least a portion of the metal organic compound plays a catalytic role and is heated to decompose to form metal oxides and volatile substances, thereby preventing the metal organic compound in the gel-like coating from penetrating into the electrolyte and causing the electrolyte to polymerize. In addition, the generated metal oxide after thermal decomposition is diffusely dispersed in the coating layer, which also helps to improve the mechanical strength of the coating layer.

[0068] As a further solution, the electrode is dried at a temperature of 95° C. to 110° C. A drying temperature within this range not only ensures the ring-opening polymerization of the cyclic carbonate compound, but also facilitates the complete thermal decomposition of the metal organic compound, thereby ensuring the electrical performance of the battery cell.

[0069] As a best example of the present invention, baking is the best way to dry the electrode.

[0070] The present invention also provides a positive electrode sheet having the positive electrode slurry. The positive electrode sheet comprises a gel-like coating layer coated on the surface of the positive electrode active material, wherein the coating layer binds an ionic liquid.

[0071] As a further solution, the coating layer further comprises dispersed metal oxides. The metal oxides are diffusely dispersed in the coating layer, which is beneficial to improving the ionic conductivity of the coating layer.

[0072] As a further embodiment, at least a part of the metal oxide is derived from a metal organic compound.

[0073] As a further solution, the raw materials of the slurry of the positive electrode plate include positive electrode active material, ionic liquid, cyclic carbonate compound, metal organic compound, organic acid compound, binder, and conductive agent; the cyclic carbonate compound is cross-linked and polymerized to form a gel-like coating layer; the surface of the positive electrode active material is coated with the gel-like coating layer; the binder and conductive agent are dispersed between the positive electrode active materials in the coating layer.

[0074] The present invention also provides an electrochemical device having the positive electrode plate, which can be used in terminal consumer products. The terminal consumer products applied for include but are not limited to mobile phones, laptops, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, and portable printers.

[0075] The present invention also provides an electrochemical device having the positive electrode sheet, which can be used in electrical equipment, including large portable electrical equipment and small portable electrical equipment, wherein small portable electrical equipment includes terminal consumer products, wearable electronic devices, or portable electronic devices; large portable electrical equipment includes transportation electrical equipment. Transportation electrical equipment includes, but is not limited to, automobiles, motorcycles, power-assisted bicycles, bicycles, buses, subways, high-speed trains, airplanes, and ships; wearable electronic devices or portable electronic devices include, but are not limited to, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, 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. The battery positive electrode plate of the present invention is used in an electrochemical device, which can be accommodated in an electrical equipment in the form of an electrochemical device. Generally, the electrochemical device includes a battery pack or / multiple battery modules or / single battery module or / single battery cell and a management system for controlling them.

[0076] The characteristics and beneficial effects of the present invention are:

[0077] (1) The compound additive of the present invention is particularly suitable for use in positive electrode sheets.

[0078] (2) The slurry of the present invention can form a gel-like coating layer in the positive electrode sheet, coating the surface of the positive electrode active material, which is beneficial to reducing the interface side reaction between the positive electrode active material and the electrolyte, thereby facilitating the improvement of the battery capacity.

[0079] (3) The gel-like coating can also reduce the contact resistance between the battery positive electrode and the electrolyte, thereby improving the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0081] Figure 1 This is an SEM image of the positive electrode provided by an embodiment of the present invention.

[0082] Figure 2 This is the XRD pattern of the positive electrode slurry provided in an embodiment of the present invention.

[0083] Figure 3 The cycle performance of the batteries of the embodiments of the present invention and the comparative example at 25°C is shown.

[0084] Figure 4 The figures show the cycle performance of the batteries of the embodiments of the present invention and the comparative example at 45°C.

[0085] Figure 5 It is the capacity retention rate of the present invention and the traditional battery.

[0086] Figure 6 This is the test result of the metal oxide in the electrode of the present invention.

[0087] Figure 7 These are the test results of the ionic liquid in the electrode of the present invention. DETAILED DESCRIPTION

[0088] In order to facilitate understanding of a positive electrode plate of the present invention, the application of the composite additive of the present invention in the positive electrode slurry and obtaining the positive electrode plate of the present invention will be described in more detail below, and an embodiment of the present invention is given, but the scope of the present invention is not limited thereby.

[0089] In the present invention, a method for preparing a positive electrode slurry, taking Example 1 as an example, comprises the following steps:

[0090] 96 g of positive electrode active material, 0.5 g of conductive agent, 2 g of binder, 0.5 g of cyclic carbonate compound, 0.25 g of organic acid compound, 0.5 g of ionic liquid, and 0.5 g of metal organic compound were weighed respectively, then mixed evenly with the solvent and filtered to obtain positive electrode slurry.

[0091] The condition for uniform mixing is to stir in a vacuum environment with a dew point below -40°C until the viscosity of the slurry reaches 4000mPa·s-8000mPa·s.

[0092] We also coat the obtained positive electrode slurry on the current collector to obtain a battery. The main steps include:

[0093] We will coat the obtained positive electrode slurry on aluminum foil, and then dry, roll and die-cut it to make the positive electrode sheet. It is then assembled with the graphite main material negative electrode sheet, separator, commercial liquid electrolyte and battery casing. After charge and discharge activation, a lithium cobalt oxide soft-pack battery with a charge cut-off voltage of 4.50V and a capacity of 4Ah is produced.

[0094] We also tested the electrochemical performance of the obtained batteries:

[0095] (1) Test method for nominal battery capacity: Charge to 4.5V at 0.2C, constant voltage to current 0.05C, let stand for 10 minutes, discharge to 3.0V at 0.2C, repeat 2 cycles, and take the discharge capacity of the last cycle as the nominal capacity of the battery.

[0096] (2) Test method for 45℃ cycle performance (80% SOH cycles): Place the battery on the test fixture and keep it moisturized in a constant temperature box for 0.5h. The first cycle capacity is 0.2C, followed by 1C cycle. The voltage range is 3.0V-4.5V, and 1C is the constant capacity.

[0097] Verification result analysis:

[0098] Table 1 Formula of battery positive electrode slurry of embodiment and comparative example

[0099] positive electrode active material Cyclic carbonate compounds Organic acid compounds organometallic compounds Ionic liquids binder Conductive agent solvent Example 1 LCO Fluorinated cyclic carbonate oxalic acid Aluminum isopropylate 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 2 LC Cyclic vinylene carbonate oxalic acid Aluminum isopropylate -Allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PvDF Carbon black + multi-walled carbon nanotubes OP Example 3 LCO Cyclic ethylene carbonate oxalic acid Aluminum isopropylate 1-allyl-3-methylimidazolium bis(difluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 4 LCO Methyl cyclic ethylene carbonate oxalic acid Aluminum isopropylate -Allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes Example 5 LCO Ethyl cyclic ethylene carbonate oxalic acid Aluminum isopropylate -Allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 6 LCO Fluorinated cyclic carbonate Formic acid Aluminum isopropylate -Allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 7 LCO Fluorinated cyclic carbonate Oleic acid Aluminum isopropylate 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 8 LCO Fluorinated cyclic carbonate Butynedioic acid Aluminum isopropylate 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 9 LCO Fluorinated cyclic carbonates oxalic acid Silver trifluoromethanesulfonate 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 10 LCO Fluorinated cyclic carbonates oxalic acid Dibutyltin 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide PvDF Carbon black + multi-walled carbon nanotubes NMP Example 11 LCO Fluorinated cyclic carbonates oxalic acid Aluminum isopropylate Tetramethylammonium bromide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 12 LCO Fluorinated cyclic carbonate oxalic acid Aluminum isopropylate 1-Ethylpyridinium bromide PvDF Carbon black + multi-walled carbon nanotubes NMP Example 13 LCO Cyclic vinylene carbonate Formic acid Silver trifluoromethanesulfonate -Allyl-3-methylimidazolium bis(difluoromethanesulfonyl)imide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 14 L(CO Cyclic ethylene carbonate oxalic acid Aluminum isopropylate Tetramethylammonium bromide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 15 LCO Fluorinated cyclic carbonates Acetic acid Magnesium isopropoxide -Ethylpyridinium bromide PVDF Carbon black + multi-walled carbon nanotubes NMP Example 16 LCO Fluorinated cyclic carbonates Malonic acid Magnesium isopropoxide -Butyl-3-methylimidazolium chloride PVDF Carbon black + multi-walled carbon nanotubes NMP Comparative Example 1 LCO - - - - PVDF Carbon black + multi-walled carbon nanotubes NMP

[0100] Table 2 Performance index results of examples and comparative examples

[0101]

[0102]

[0103] Table 3 Performance of batteries with different positive electrode active materials

[0104] — High temperature storage 45 degree cycle positive electrode active material Example 17 85 degrees 12h retention rate 95% 2C / 1C, 350 weeks, 80% retention rate lithium cobalt oxide Example 18 45 degrees 30 days retention rate 96% 2C / 1C, 450 weeks, retention rate 80% Lithium nickel cobalt manganese oxide 811 type Example 19 85 degrees 12h retention rate 94% 2C / 1C, 340 weeks, 80% retention rate lithium cobalt oxide Example 20 45 degrees 30 days retention rate 95% 0.7C / 0.7C, 700 weeks, retention rate 80% lithium iron phosphate Comparative Example 1 85 degrees 12 retention rate 85% 2C / 1C, circle, retention rate 80% lithium cobalt oxide Comparative Example 2 45 degrees 30 days retention rate 90% 2C / 1C, 400 weeks, 80% retention rate Lithium nickel cobalt manganese oxide 811 type Comparative Example 3 45 degrees 30 days retention rate 94% 0.7C / 0.7C, 720 weeks, retention rate 80% lithium iron phosphate

[0105] We successfully obtained the positive electrode sheet through the formula in Table 1, such as Figure 1As shown. We applied the obtained positive electrode sheet in a battery and compared it with a battery obtained by a traditional method. As shown in Table 2, we found that the electrochemical performance of all Examples 1 to 16 in Table 2 was better than that of Comparative Example 1. We believe that in the present invention, cyclic carbonate compounds, ionic liquids and metal organic compounds are added to the positive electrode slurry. Under the catalytic action of the metal organic compound, during the thermal process, the cyclic carbonate compound is promoted to open its ring, and then in situ polymerizes with the ionic liquid to form a gel-like coating layer, which is coated on the surface of the positive electrode active material and between the pores of the particles of each substance in the positive electrode slurry. Finally, a gel-like coating layer with a stable structure having ion-conducting properties is formed on the positive electrode sheet, and the gel-like coating layer also has certain mechanical properties. In order to promote the rapid ring-opening polymerization of cyclic carbonate compounds, we further added organic acid compounds, which are beneficial to promote the dissolution of metal organic compounds, promote the metal organic compounds to be more evenly dispersed in the positive electrode slurry, increase the contact area between metal organic compounds and cyclic carbonate compounds, and further enhance the catalytic effect of metal organic compounds on cyclic carbonate compounds. In addition, organic acid compounds can also remove residual alkali on the surface of the positive electrode active material, thereby neutralizing the pH value in the slurry. The gel-like coating layer formed can bind ionic liquids and organic acid compounds. Ionic liquids have the ability to conduct ions and can serve as ion transmission channels between the positive electrode active material and the electrolyte in the coating layer. Organic acid compounds can also enhance the ion conductivity of the coated ionic liquid. It can be seen that the gel-like coating layer formed by the positive electrode slurry of the present invention is coated on the positive electrode and has an ionic conductivity equivalent to that of the electrolyte. It can not only promote the transmission of lithium ions between the positive electrode and the electrolyte, but also further isolate the side reactions between the positive electrode active material and the electrolyte, thereby improving the electrochemical performance of the battery. We can also further from Figure 2 It was verified that after adding the compound additive, the characteristic peak of the positive electrode active material in the slurry did not change, which shows that the gel-like coating layer of the present invention is beneficial to protecting the positive electrode active material and isolating the side reaction between the positive electrode active material and the electrolyte; and Figure 5 It can be seen that the technical solution of the present invention has a better capacity retention rate than the traditional method (i.e. no compound additives are added to the positive electrode of the battery and no electrode solidification occurs).

[0106] We also studied the cycle performance of the battery positive electrode prepared by the present invention and the battery positive electrode prepared by the traditional method at different temperatures, such as Figure 3 and Figure 4 We used Example 1 and Comparative Example 1 to test the cycle performance of the battery. Figure 3In the case of the battery of the present invention, when it is kept at 25°C for about 780 cycles at a rate of 1C, the capacity retention rate is 90%; while the capacity retention rate of the battery of comparative example 1 is 87% after about 500 cycles at a rate of 1C. Figure 4 In a 45°C environment, when the battery capacity decreased from 100% to 80%, the battery of the present invention could cycle approximately 350 times, while the battery in Comparative Example 1 could cycle approximately 220 times, far fewer than the number of cycles achieved at high temperatures. We believe this may be because the gel-like coating of the present invention effectively isolates side reactions between the positive electrode active material and the electrolyte, thereby increasing the battery capacity. Furthermore, the coordination between the various substances in the gel-like coating of the present invention balances the transport of electrons and ions in the positive electrode, thereby reducing electrochemical reaction imbalances during high-temperature cycling.

[0107] We also matched the slurry with the compound additive with different types of positive electrode active materials, as shown in Table 3. The compound additive of the present invention can be applied to different positive electrode active materials, as shown in Examples 17 to 20. We further compared Examples 17 to 20 with Comparative Examples 1 to 3, among which Example 17 and Example 19 were better than Comparative Example 1, Example 18 was better than Comparative Example 2, and Example 20 was better than Comparative Example 3. It can be seen that the compound additive of the present invention is more suitable for use in the positive electrode active material of lithium cobalt oxide. Taking lithium cobalt oxide positive electrode active material as an example, we further studied the improvement of the electrochemical performance of the battery by the gel-like coating formed by different types of cyclic carbonate compounds, metal organic compounds, organic acid compounds, and ionic liquids.

[0108] We first studied cyclic carbonic acid compounds. The dispersibility of cyclic carbonate compounds can directly affect the coating uniformity of the gel coating layer. We can see from Examples 1 to 5 that the cycle performance and nominal capacity of Example 1 are the highest, and the resistance is very small. We believe that this may be because the fluorine-substituted group can change the electron cloud density of the cyclic structure, so the fluorinated cyclic carbonate compounds may require less energy for ring opening and can actively participate in the formation of the gel coating layer; secondly, the fluorinated cyclic carbonate compounds have lower viscosity and are easier to disperse in the positive electrode slurry, making the generated coating more uniform and stable. Therefore, fluorinated cyclic carbonate compounds are more likely to achieve a gel coating layer uniformly coated on the surface of the positive electrode active material, thereby reducing the side reactions between the positive electrode active material and the electrolyte, which is beneficial to improving the electrochemical performance of the battery. We further prefer fluorinated cyclic carbonate compounds among cyclic carbonate compounds.

[0109] We further studied the effect of the selection of metal organic compounds on the optimization of the electrochemical performance of the battery. Metal organic compounds play an important role in the ring-opening polymerization of cyclic carbonate compounds in the process of forming a gel-like coating. Through comparison of Example 1 and Examples 9-10, we found that Example 1 has the lowest resistance and the best cycle performance and capacity. We believe that this may be because metal isopropanol compounds are more likely to catalyze the ring-opening polymerization of cyclic carbonate compounds. First, metal isopropanol compounds are more easily dissolved in organic acid compounds, thereby being more evenly dispersed in the slurry, which increases the contact area with the cyclic carbonate compounds, making it easier to catalyze the ring-opening polymerization of cyclic carbonate compounds; in addition, metal isopropanol compounds can also remove residual alkali on the surface of the positive active material, which is beneficial to increase the rate of insertion and extraction of lithium ions by the positive active material. We further prefer metal isopropanol compounds among the metal organic compounds.

[0110] We also studied ionic liquids. In a slurry, under the influence of heat, the ionic liquid and cyclic carbonate compounds undergo ring opening under the action of a catalyst, and then polymerize to form a gel-like coating. This coating binds ions within the structure, while the ionic liquid within the gel-like coating bridges the lithium ion transport between the cathode active material and the electrolyte. During the battery cycle, the ionic liquid also interacts with the conductive agent in the slurry to balance the transmission of electrons and ions in the cathode. This facilitates the balance of chemical reactions within the battery under high-voltage and high-temperature environments, maintaining the battery's electrochemical performance. We compared Example 1 and Example 11-Example 12 and found that the electrochemical performance of Example 1 was the best. We believe that this may be because the imidazole ring in the imidazole ionic liquid structure is an electron-rich group. The imidazole structure is a five-membered heterocyclic compound with a closed large π bond conjugated system, which increases the electron-withdrawing ability of N and increases the electron cloud density of the nitrogen atom in the imidazole ring. The nitrogen atom in the electron-rich group will participate in attacking the oxygen group in the cyclic carbonate compound, thereby facilitating the mutual cooperation with the cyclic carbonate compound, facilitating the formation of a gel-like coating layer, and also building an ion transmission channel. We further prefer imidazole ionic liquids among ionic liquids.

[0111] Finally, we investigated the optimization of organic acid compounds for the formation of a gel-like coating. Organic dicarboxylic acids can promote the dissolution and dispersion of metal organic compounds, facilitating the formation of a more stable and uniform coating. They can also promote the ionic liquid to exert greater ionic conductivity, thereby promoting ionic conduction between the positive electrode active material and the electrolyte. By comparing Example 1 with Examples 6-8, we found that the battery of Example 1 exhibited the best electrochemical performance. We believe this may be due to the interaction between the carboxylic acid groups in the organic dicarboxylic acid, which promotes the dispersion of the metal organic compound while better maintaining the structural characteristics of the ionic liquid and the metal organic compound. We further preferred organic dicarboxylic acids among the organic acid compounds.

[0112] On this basis, we found that when fluorinated cyclic carbonate compounds and imidazole ionic liquids are added to the positive electrode slurry, the fluorinated cyclic carbonate compounds undergo ring opening and then undergo in-situ polymerization to form a gel-like coating layer coated on the surface of the positive electrode active material. The fluorine substituents of the fluorinated cyclic carbonate compounds can change the electron cloud density of the ring structure, which is beneficial to reducing the ring opening energy, and also have lower viscosity, which is beneficial to uniform dispersion in the positive electrode slurry, laying the foundation for the formation of a uniform ion-conducting coating layer; the imidazole ion The imidazole structure in the liquid structure is a five-membered heterocyclic compound with a conjugated system of a closed large π bond, which increases the electron-withdrawing ability of N. The fluorinated cyclic carbonate compound structure also contains electron-withdrawing groups such as carbonyl and fluorine substituents. The lone pair of electrons on the oxygen atom in the organic anion in the metal isopropoxide aluminum promotes the metal isopropoxide to catalyze the mutual cooperation between the imidazole ionic liquid and the fluorinated cyclic carbonate compound, thereby forming a gel-like coating layer. In addition, the specific ion-conducting ability of the imidazole ionic liquid can transfer ions between the positive electrode active material and the electrolyte. To accelerate the ring-opening polymerization of fluorinated cyclic carbonates, we further selected metal isopropanols and organic dicarboxylic acids. By combining the carboxyl groups in the organic dicarboxylic acids with the hydroxyl groups in the metal alcohols, we achieved better dissolution of the metal isopropanols in the slurry and further uniform dispersion, thereby achieving close contact and increased contact area between the metal isopropanols and the fluorinated cyclic carbonates. Furthermore, the organic dicarboxylic acids did not destroy the catalytic activity of the metal isopropanols, further enhancing the efficiency of the ring-opening polymerization of the fluorinated cyclic carbonates to form a uniformly coated gel-like coating. The strong electron-withdrawing effect of the fluorinated cyclic carbonates interacts with the electrons in the isopropanol structure of the metal isopropanols, thereby enhancing the catalytic effect of the metal isopropanols on the fluorinated cyclic carbonates. The conductive agent in the slurry can also achieve a balance between electron and ion transport in the positive electrode with the imidazole ionic liquid, which is beneficial to improving the balance of the electrochemical reaction of the battery. We compare and verify through Example 1, Example 13-Example 16, wherein Example 1 and Example 16 are better than other embodiments. We further prefer imidazole ionic liquids, fluorinated cyclic carbonate compounds, organic dicarboxylic acids, and metal isopropanol compounds. By mass, the ratio of the imidazole ionic liquid: fluorinated cyclic carbonate compound: organic dicarboxylic acid: metal isopropanol compound is (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (0.5 parts-2 parts).

[0113] On this basis, we further selected fluorinated cyclic ethylene carbonate in the positive electrode slurry. The fluorine substitution forms a stronger electron-withdrawing effect, while 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt has more lone pairs of electrons, which can form a better mutual coordination effect. In order to achieve the formation of the coating layer, we further selected aluminum isopropoxide. We believe that with the cooperation of oxalic acid, oxalic acid can separate the aluminum ions and isopropanol organic anions in aluminum isopropoxide, thereby being more conducive to releasing its catalytic activity while aluminum isopropoxide is more evenly dispersed in the slurry; and the catalyzed aluminum isopropoxide can react with the residual alkali on the surface of the positive electrode active material to form a layer of lithium ion conductor, which can further promote the rate of lithium removal and lithium insertion of the positive electrode active material. In addition, aluminum isopropoxide is conducive to better coordination with the binder, thereby improving the mechanical strength of the coating layer. When the dispersed aluminum isopropoxide is dispersed around the fluorocyclic ethylene carbonate, it has more contact area with the fluorocyclic ethylene carbonate, which is more conducive to promoting the rapid progress of the catalytic action; and the aluminum ions in the aluminum isopropoxide structure can have more coordination, which is conducive to the interaction with the fluoride ions in the fluorocyclic ethylene carbonate, and also directly promotes the catalytic efficiency between the fluorocyclic ethylene carbonate and the aluminum isopropoxide. The sulfonate in 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide can improve the ionic conductivity of the imidazole ionic liquid, thereby achieving a balance between electron migration in the positive electrode and ion transport between the positive electrode active material and the electrolyte when the battery is charged at high voltage by adding 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and the conductive agent, thereby facilitating the maintenance of a balance in the chemical reaction in the battery at high temperature. In addition, the greater number of carbonyl groups in oxalic acid can further improve the redox reaction kinetics of the positive electrode and, at the same time, increase the ionic conductivity of 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide in the coating layer, thereby further reducing the contact resistance between the gel-like coating layer and the electrolyte. By comparing Example 1 and Example 16, we found that Example 1 had better electrochemical performance than Example 16. We further prefer that the positive electrode slurry includes fluorocyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and oxalic acid, and the ratio of the fluorocyclic ethylene carbonate: aluminum isopropoxide: 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide: oxalic acid is (0.5 parts-2 parts): (0.5 parts-2 parts): (0.2 parts-0.3 parts): (0.5 parts-4 parts) by mass.

[0114] On this basis, we further studied the better coordination between the compound additive and other substances in the positive electrode slurry.

[0115] To enhance the mechanical strength of the resulting coating, we incorporate a fluoropolymer. Firstly, the fluoropolymer exhibits enhanced flexibility, allowing it to coat the surfaces of other particles in the slurry, thereby enhancing adhesion. Secondly, the fluorinated groups in the fluoropolymer can interact with the electrons in the isopropyl alcohol structure of the metal isopropyl alcohol compound through electron-withdrawing, thereby facilitating bonding and forming a mechanically strong coating. To improve the energy density of the positive electrode, the fluorinated cyclic carbonate compound in the slurry partially replaces the solvent, reducing the amount of solvent required in the positive electrode and increasing the mass fraction of the positive electrode active material, thereby ensuring the battery's energy density. The conductive agent, in conjunction with the imidazolium ionic liquid in the slurry, balances the electron and ion transport capabilities in the positive electrode, facilitating electrochemical reaction equilibrium during the battery's charge and discharge cycles. The metal isopropyl alcohol compound removes residual alkali from the surface of the layered metal oxide and, under high charging voltages, enhances the rate of lithium ion insertion and extraction from the layered metal oxide. We further selected that the raw materials of the positive electrode slurry include layered metal oxide, imidazole ionic liquid, fluorinated cyclic carbonate compound, metal isopropyl alcohol compound, organic dicarboxylic acid, fluorinated polymer, and conductive agent, and the ratio of the layered metal oxide: imidazole ionic liquid: fluorinated cyclic carbonate compound: metal isopropyl alcohol compound: organic dicarboxylic acid: fluorinated polymer: conductive agent is (90 parts-95 parts): (0.2 parts-0.3 parts): (0.5 parts-2 parts): (0.5 parts-2 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts).

[0116] On this basis, we further found that fluorocyclic vinyl carbonate can partially replace the amount of solvent used, which is beneficial to increase the amount of lithium cobalt oxide active material added; on this basis, fluorocyclic vinyl carbonate, polyvinylidene fluoride can form an electron-withdrawing effect with 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and fluorocyclic vinyl carbonate can form a gel coating layer with 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt under the catalysis of aluminum isopropoxide; polyvinylidene fluoride is beneficial to better confine 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt in the coating layer, thereby facilitating an increase in the ionic conductivity of the coating layer. In addition, the coating layer also has point-like carbon black and hollow tubular multi-walled carbon nanotubes, point-like carbon black connects the hollow tubular multi-walled carbon nanotubes to form an electron transport network, and the hollow tubular multi-walled carbon nanotubes can also provide the channel for ion transmission, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt can balance the balance of electrons and ions in the positive electrode with carbon black and multi-walled carbon nanotubes. Polyvinylidene fluoride also has good flexibility, can better be coated in the gel-like coating layer. Although fluoropolymer can produce electron-withdrawing effect with aluminum isopropylate, thereby is conducive to mutual coordination with aluminum isopropylate, improves the mechanical strength of gel-like coating layer, but the fluorine substituent in fluoropolymer is too many, although the mechanical strength of coating layer may be further promoted, the flexibility of gel-like coating layer may also be affected to a certain extent, so we select polyvinylidene fluoride. With the coordination of various substances in the positive electrode slurry, it is found that the slurry of the present invention is more suitable for lithium cobalt oxide active materials and has a more significant improvement on the electrochemical performance of batteries having lithium cobalt oxide active materials. We further prefer that the positive electrode slurry includes fluorocyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, oxalic acid, polyvinylidene fluoride, carbon black + multi-walled carbon nanotubes, and lithium cobalt oxide active material (LCO active material). The ratio of the fluorocyclic ethylene carbonate: aluminum isopropoxide: 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide: oxalic acid: polyvinylidene fluoride: carbon black + multi-walled carbon nanotubes: lithium cobalt oxide active material (LCO active material) is (0.5 parts-2 parts): (0.5 parts-2 parts): (0.2 parts-0.3 parts): (0.5 parts-4 parts): (1.5 parts-2.5 parts): (2.5 parts-3.5 parts): (90 parts-95 parts) in mass.

[0117] We also tested the substances in the coating layer of the positive electrode obtained in Example 1 after cycling. The test results are as follows: Figure 6 and Figure 7 As shown. We can Figure 6In the figure, we can see that the coating layer of the positive electrode sheet contains ionic liquid (1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)), and the CF bond, S=O bond, and C=C bond can be detected to verify this result. Figure 7 It can be verified that the metal oxide (Al2O3) is dispersed in the coating layer. It can be seen that in the present invention, the surface of the positive electrode active material is coated with a gel-like coating layer, and the coating layer contains ionic liquid and dispersed metal oxide.

[0118] In summary, the compound additive of the present invention is used in the positive electrode slurry to form a gel-like coating layer to isolate the side reactions between the positive electrode active material and the electrolyte, thereby improving the electrochemical performance of the battery. In addition, the formed gel-like coating layer has an ionic conductivity equivalent to that of the electrolyte, which can reduce the contact resistance between the electrolyte and the positive electrode.

[0119] 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 in the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that: The positive electrode plate includes a gel-like coating layer coated on the surface of the positive electrode active material, wherein the coating layer contains an ionic liquid; the coating layer also includes a dispersed metal oxide; at least a portion of the metal oxide is derived from a metal organic compound, and the metal organic compound includes one or more of a metal isopropyl alcohol compound, a metal sulfonic acid compound, and a metal alkane compound; the gel-like coating layer is formed by ring-opening polymerization of a cyclic carbonate compound.

2. A positive electrode sheet according to claim 1, characterized in that: The raw materials of the positive electrode plate include positive electrode active material, ionic liquid, cyclic carbonate compound, metal organic compound, organic acid compound, binder, and conductive agent; the binder and conductive agent are also dispersed in the coating layer.

3. The positive electrode sheet according to claim 1, characterized in that: The ionic liquid includes one or more of quaternary ammonium ionic liquids, imidazole ionic liquids, and pyridine ionic liquids.

4. The positive electrode sheet according to claim 3, characterized in that: The quaternary ammonium ionic liquid includes one or more of tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium hexafluorophosphate, and tetramethylammonium trifluoromethanesulfonate; The imidazole ionic liquid includes one or more of 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium phosphate, and 1-butyl-3-methylimidazolium nitrate; The pyridinium ionic liquid includes one or more of 1-butyl-4-methylpyridinium chloride, 1-hexyl-4-methylpyridinium chloride, and 1-ethylpyridinium bromide.

5. The positive electrode sheet according to claim 1, characterized in that: The metal isopropyl alcohol compound includes one or more of aluminum isopropyl alcohol and magnesium isopropyl alcohol; The metal sulfonate compound includes one or more of silver isotrifluoromethanesulfonate and aluminum trifluoromethanesulfonate; The metal alkane compound includes one or more of dibutyltin and dibutylzinc.

6. The positive electrode sheet according to claim 2, characterized in that: The positive electrode active material includes one or more of metal oxides, polyanion salts, and non-metallic compounds; the cyclic carbonate compound includes one or more of cyclic carbonates with unsaturated rings and cyclic carbonates with saturated rings; the organic acid compound includes one or more of organic carboxylic acid compounds, organic sulfonic acid compounds, organic sulfinic acid compounds, and organic sulfur carboxylic acid compounds; the binder includes one or more of fluorine-containing polymers, nitrile-containing polymers, amine-containing polymers, and carboxymethylated derivatives; and the conductive agent includes one or more of graphite, conductive carbon black, carbon nanotubes, carbon fibers, and graphene.

7. The positive electrode sheet according to claim 6, characterized in that: In the conductive agent, the conductive carbon black includes one or more of acetylene black and Ketjen black, and the carbon nanotubes include one or more of multi-walled carbon nanotubes and single-walled carbon nanotubes.

8. The positive electrode sheet according to claim 6, characterized in that: The fluorine-containing polymer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene; The nitrile-containing polymer includes polyacrylonitrile; The amine-containing polymer comprises a polyamide; The carboxymethylated derivatives include sodium carboxymethyl cellulose; The organic carboxylic acid compound includes one or more of an organic dicarboxylic acid, an organic monocarboxylic acid, a monounsaturated organic carboxylic acid, and a polyunsaturated organic carboxylic acid; The cyclic carbonate having a saturated ring includes one or more of one or more cyclic carbonates having a C2-C6 alkylene group; The metal oxide includes one or more of layered metal oxides and spinel metal oxides.

9. The positive electrode sheet according to claim 8, characterized in that: The organic dicarboxylic acid includes one or more of oxalic acid, malonic acid, and succinic acid; The organic monocarboxylic acid includes one or more of formic acid, acetic acid, butyric acid, and propionic acid; The monounsaturated organic carboxylic acid includes oleic acid; The polyunsaturated organic carboxylic acid includes butynedioic acid.

10. The positive electrode sheet according to claim 8, characterized in that: The cyclic carbonate having a saturated ring includes one or more cyclic carbonates having a C2-C4 alkylene group.

11. The positive electrode sheet according to claim 8, characterized in that: The cyclic carbonate compound further has one or more of an unsaturated substituent group, a halogen atom substituent group, and an alkyl substituent group; The unsaturated substituent group includes one or more of C=C, C≡C, and aromatic ring; The halogen atom substituent group includes one or more of fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms; The alkyl substituent group includes one of C1-C4 alkyl groups; The number of the halogen atom substituent groups is 1-6.

12. The positive electrode sheet according to claim 8, characterized in that: The layered structure metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, nickel-cobalt-manganese ternary material, lithium nickel-cobalt-aluminum oxide, and lithium-rich manganese-based material.

13. A method for preparing a positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode active material, conductive agent, binder, cyclic carbonate compound, organic acid compound, ionic liquid, metal organic compound and solvent are weighed respectively, mixed evenly, and filtered to obtain positive electrode slurry; the positive electrode slurry is coated on the surface of the current collector, dried at a temperature of 70°C-130°C, and cut into positive electrode sheets.

14. The method for preparing a positive electrode sheet according to claim 13, characterized in that: The drying temperature is 95°C-110°C.

15. The method for preparing a positive electrode sheet according to claim 13, wherein: In terms of mass, the mass ratio of the positive electrode active material: ionic liquid: cyclic carbonate compound: metal organic compound: organic acid compound: binder: conductive agent is (90-95): (0.2-0.3): (0.5-2): (0.5-2): (0.5-4): (1.5-2.5): (2.5-3.5).

16. The method for preparing a positive electrode sheet according to claim 13, wherein: The condition for uniform mixing is to stir the slurry in a vacuum environment with a dew point below -40°C until the viscosity of the slurry reaches 4000 mPa·s to 8000 mPa·s.

17. An electrochemical device, characterized in that The electrochemical device comprises the positive electrode sheet according to any one of claims 1 to 12.

18. An electrical product, characterized in that: The electrical product comprises the electrochemical device according to claim 17 .

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