CN116364930A - Compound additive and electrochemical device using same - Google Patents

Compound additive and electrochemical device using same Download PDF

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Publication number
CN116364930A
CN116364930A CN202310329898.6A CN202310329898A CN116364930A CN 116364930 A CN116364930 A CN 116364930A CN 202310329898 A CN202310329898 A CN 202310329898A CN 116364930 A CN116364930 A CN 116364930A
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compound
further preferably
positive electrode
acid
organic
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彭军
惠康龙
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Tianmu Lake Institute of Advanced Energy Storage Technologies Co Ltd
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Tianmu Lake Institute of Advanced Energy Storage Technologies Co Ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/62Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624Electric conductive fillers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/362Composites
    • H01M4/366Composites as layered products
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/62Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M2004/026Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028Positive electrodes

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Composite Materials (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a compound additive which comprises ionic liquid, cyclic carbonate compounds, metal organic compounds and organic acid compounds, wherein the mass ratio of the ionic liquid to the cyclic carbonate compounds to the metal organic compounds to the organic acid compounds is (0.2-0.3 part) to (0.5-2 parts) to (0.5-4 parts). The compound additive can form a gel coating layer in the positive electrode plate and is coated on the surface of the positive electrode, so that the interface side reaction between the positive electrode active material and the electrolyte is reduced, and the capacity of the battery is improved. The gel-like coating layer can also reduce the contact resistance between the battery anode and the electrolyte, thereby facilitating the improvement of the electrochemical performance of the battery.

Description

Compound additive and electrochemical device using same
Technical Field
The invention relates to the technical field of materials, in particular to a compound additive and an electrochemical device using the compound additive.
Background
With the popularity of mobile phones, notebook computers, digital cameras and other electronic devices, china has become the largest consumer country in the battery industry. The electronic products bring convenience and diversity to life, and in the past few years, the market of lithium ion batteries in China keeps a trend of rapid growth. Currently, higher demands are made on the electrochemical performance of batteries.
The positive electrode of the battery is used as a source of energy density in the lithium battery and is used for electricity of the batteryThe performance has a significant impact. In the process of battery charge and discharge circulation, firstly, the positive electrode of the battery and electrolyte in the battery have certain contact internal resistance, and the wettability between the electrolyte in the battery and the positive electrode of the battery is poor, so that the rate performance of the battery can be affected to a certain extent; and secondly, certain side reactions occur after the positive electrode active material contacts with the electrolyte, so that the capacity of the battery is reduced. In the prior art, a solid electrolyte interface film (CEI film) with ion conductivity is generated in the battery charging and discharging cycle process, and the generated CEI film can isolate side reaction between a battery positive electrode active material and electrolyte on one hand, and can assist ion transmission and migration between the positive electrode and the electrolyte on the other hand, and the generation of the CEI film can be beneficial to improving the electrochemical performance of the battery to a certain extent. But during the charge and discharge cycle of the battery, a large amount of Li is often used + Thereby causing cracking of the generated CEI film, and eventually causing degradation of capacity and rate performance of the battery; when the CEI film is charged at high voltage, the generated CEI film is more prone to cracking, and the electrochemical performance of the battery is more obviously reduced.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a compound additive, which is particularly suitable for a battery charged under high voltage by preparing a compound additive capable of forming a film. The gel-like coating layer with the CEI film function can be formed on the surface of the positive electrode of the battery, on one hand, the gel-like coating layer has certain mechanical strength, and can isolate the contact between the positive electrode active material and electrolyte, so that the consumption of lithium ions by side reaction is reduced, and on the other hand, the formed gel-like coating layer has the ion conductivity equivalent to that of the electrolyte, so that the ion transmission between the positive electrode and the electrolyte can be promoted, and the contact internal resistance between the positive electrode and the electrolyte is reduced.
The invention is realized by the following technical scheme:
the invention provides a compound additive, which comprises ionic liquid, cyclic carbonate compounds, metal organic compounds and organic acid compounds, wherein the mass ratio of the ionic liquid to the cyclic carbonate compounds to the metal organic compounds to the organic acid compounds is (0.2-0.3 part) to (0.5-2 parts) to (0.5-4 parts), and the mass ratio of the compound additive in positive electrode slurry is 1.5% -8.7%.
The compound additive is particularly suitable for positive electrode slurry, the metal organic compound can be used as a catalyst to promote cyclic carbonate compounds and ionic liquid, the cyclic carbonate compounds are subjected to ring opening in the heating process to perform in-situ polymerization reaction, and in order to improve the catalytic effect of the catalyst, the compound additive is further matched with an organic acid compound to facilitate the dissolution of the metal organic compound, the metal organic compound is more favorably promoted to be uniformly dispersed in the slurry, the contact area between the metal organic compound and the cyclic carbonate compounds is increased, so that the catalytic effect is improved, and a uniform gel coating layer is formed after in-situ polymerization; in addition, the metal organic compound is also beneficial to enhancing the mechanical property of the gel-like coating layer. After ring-opening in-situ polymerization of the cyclic carbonate compound, a stable gelatinous coating layer is formed to cover the surface of the positive electrode active material, the surfaces of other substance particles in the slurry and the gaps of the particles, so that the ionic liquid is bound in the gelatinous coating layer, and the ionic liquid is prevented from losing from the electrode; the ionic liquid also has higher ionic conductivity, can improve the ionic conductivity between the coated positive electrode active material and the electrolyte, is favorable for building a bridge for lithium ion conduction 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, and the organic acid compound is favorable for removing residual alkali on the surface of the positive electrode active material so as to neutralize the pH value of the slurry. According to the invention, the relation among the binding effect of the gel coating layer, the energy density of the positive electrode and the ion transmission capacity of the gel coating layer is further balanced through the proportion of the compound additive, and on the basis that the positive electrode can obtain the maximum energy density, the compound additive is favorable for forming the gel coating layer with certain mechanical strength and stable structure in slurry, so that the gel coating layer can bind the ionic liquid, and the generated gel coating layer also has the ion conductivity equivalent to that of the electrolyte, so that the contact resistance between the positive electrode and the electrolyte is reduced, the side reaction between the positive electrode active material and the electrolyte is reduced, and the electrochemical performance of the battery is improved.
As a further scheme, the ionic liquid comprises quaternary ammonium ionic liquid, imidazole ionic liquid and pyridine ionic liquid. The imidazole ionic liquid is more suitable for being used in positive electrode slurry with higher battery working voltage, an imidazole ring in the imidazole ionic liquid structure is an electron-rich group, the imidazole structure is a five-membered heterocyclic compound, and a conjugation system with a closed large pi bond is adopted, so that the electron withdrawing capability of N is improved, the electron cloud density of nitrogen atoms in the imidazole ring is increased, and the nitrogen atoms in the electron-rich group can participate in attacking oxygen groups in the cyclic carbonate compound, so that the imidazole ionic liquid is favorable for being matched with the cyclic carbonate compound, and a gelatinous coating layer is favorable for being formed. The quaternary ammonium ionic liquid is more suitable for being used in the positive electrode slurry of a battery which works for a long time, heat can be generated at the positive electrode of the battery in the long-term circulation process of the battery, the temperature in the battery can be increased, and the quaternary ammonium ionic liquid has better thermal stability. The pyridine ionic liquid is more suitable for the general battery working environment, has better stability, can be used in most battery anodes, and has the advantage that the electrochemical performance is not easy to decay.
As still further schemes, the quaternary ammonium ionic liquid comprises one or more of tetramethyl ammonium chloride, tetramethyl ammonium bromide, tetramethyl ammonium hexafluorophosphate and tetramethyl ammonium trifluoromethane sulfonate.
As still further aspects, the imidazole ionic liquid comprises one or more of 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, 1-butyl-3-methylimidazole bis trifluoromethanesulfonyl imide salt, 1-butyl-3-methylimidazole chloride salt, 1-butyl-3-methylimidazole phosphate and 1-butyl-3-methylimidazole nitrate.
As still further aspects, the pyridine ionic liquid comprises one or more of 1-butyl-4-methylpyridine chloride, 1-hexyl-4-methylpyridine chloride and 1-ethylpyridine bromide.
As a further aspect, the cyclic carbonate compound includes a cyclic carbonate having an unsaturated ring and a cyclic carbonate having a saturated ring. In particular, the cyclic carbonate having an unsaturated ring includes vinylene carbonate. Cyclic carbonates having a saturated ring include ethylene carbonate.
As a further aspect, the cyclic carbonate having a saturated ring includes one or more of cyclic carbonates having a C2-C6 alkylene group;
As a further aspect, the cyclic carbonate having a saturated ring includes one or more of cyclic carbonates having a C2-C4 alkylene group. Specific examples thereof include ethylene carbonate, propylene carbonate, and butylene carbonate (2-ethylethylene carbonate, cis-and trans-2, 3-dimethylethylene carbonate).
As a further scheme, the cyclic carbonate compound also has one or more of unsaturated substituent groups, halogen atom substituent groups and alkyl substituent groups.
As a further aspect, the unsaturated substituent group includes one or more of c= C, C ≡c, aromatic ring.
As a further scheme, the halogen atom substituent group includes one or more of fluorine atom, chlorine atom, bromine atom, iodine atom.
As a further aspect, the alkyl substituent comprises one of C1-C4 alkyl. Specific examples thereof include methyl cyclic ethylene carbonate and ethyl cyclic ethylene carbonate.
As a further scheme, the halogen atom substituent group comprises one or more of fluorine atom and chlorine atom.
As a further aspect, the halogen atom substituent group includes a fluorine atom. Specifically, a fluorinated cyclic carbonate compound may be mentioned, and specifically, a fluorinated cyclic ethylene carbonate may be mentioned. The cyclic carbonate compound substituted by fluorine atoms is more suitable for batteries in high-voltage working environments, firstly, has lower viscosity, can be more uniformly dispersed in battery positive electrode slurry, and secondly, the fluorine substituent is beneficial to improving the oxidation stability of the cyclic carbonate compound under high pressure; the electron withdrawing effect of fluorine is beneficial to changing the electron cloud density distribution in the structure, so that the fluorine is better matched with the metal organic compound to form a uniform gel coating layer with stable structure through ring-opening polymerization in a heating environment.
As a still further aspect, the number of halogen atom substituents is 1 to 6.
As a still further aspect, the number of halogen atom substituents is 1 to 4.
As a further scheme, the organic acid compound comprises an organic carboxylic acid compound, an organic sulfonic acid compound and an organic strong binding effect, so that the shuttle effect of polysulfide is effectively inhibited, and the organic acid compound can also be used as an inhibitor of lithium dendrite. The organic sulfinic acid compound is more suitable for a battery containing metal halide in the battery positive electrode slurry, can form a complex with the metal halide, and can stabilize a gel coating layer formed by the positive electrode, and one or more of the sulfinic acid compound and the organic thiocarboxylic acid compound. The organic carboxylic acid compound is more suitable for the positive electrode slurry of the battery in a high-voltage working environment, and the carbonyl in the organic carboxylic acid compound has faster oxidation-reduction reaction power, so that the oxidation-reduction capability of the positive electrode of the battery can be improved. The organic sulfonic acid compound has rich S-O bond in structure, is more suitable for sulfur positive electrode, and has the advantage of improving oxidation resistance stability of the battery with lithium polysulfide. The organic sulfur carboxylic acid compound is more suitable for substances containing unsaturated groups in the battery anode slurry, and S-H bonds in the organic sulfur carboxylic acid compound are easier to generate dehydrogenation reaction under the action of charging voltage, so that the addition reaction of sulfur free radicals and unsaturated bonds is facilitated, and the cycle performance of the battery is improved.
As a further aspect, 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 organic dicarboxylic acid exists more stably in a high-pressure working environment, has a plurality of carbonyl groups, has higher activity, is more favorable for dissolving metal organic compounds and promoting the ionic liquid to exert better ionic conductivity, and can neutralize the alkalinity in the slurry and improve the reinforcing performance of the slurry.
As a further scheme, the organic dibasic acid comprises one or more of oxalic acid, malonic acid and succinic acid.
As a further scheme, the organic monoacid comprises one or more of formic acid, acetic acid, butyric acid and propionic acid.
As a further aspect, the monounsaturated organic carboxylic acid comprises oleic acid.
As a further aspect, the polyunsaturated organic carboxylic acid comprises butynedioic acid.
As a further scheme, the metal organic compound comprises one or more of metal isopropanol compounds, metal sulfonic acid compounds and metal alkane compounds. The metal isopropanol compound can be dissolved by the organic acid compound and then dispersed in the slurry, and a better solvent can be in the organic acid compound, so that the metal isopropanol compound is more uniformly dispersed in the anode slurry, and the gel-like coating layer is more uniformly formed; and secondly, the metal isopropanol compound dispersed in the slurry is easier to be matched with the binder than other alcohols, so that the mechanical strength of the formed coating layer is improved. As a further scheme, the metal isopropanol compound comprises aluminum isopropoxide and magnesium isopropoxide.
As a further scheme, the metal sulfonic acid compound comprises silver iso-trifluoromethane sulfonate and aluminum trifluoromethane sulfonate.
As a further scheme, the metal alkane compound comprises dibutyl tin and dibutyl zinc.
The compound additive comprises (by mass) imidazole ionic liquid, fluorinated cyclic carbonate compounds, organic dicarboxylic acid and metal isopropanol compounds, wherein the ratio of the fluorinated cyclic carbonate compounds to the organic dicarboxylic acid to the metal isopropanol compounds is (0.2-0.3 parts) (0.5-2 parts) (0.5-4 parts) (0.5-2 parts). In the prior art, the cyclic carbonate compound has stable structure at high temperature and good solubility, so the cyclic carbonate compound is commonly used as a solvent in electrolyte; in the invention, a cyclic carbonate compound is used in positive electrode slurry, then a catalyst metal organic compound is added to catalyze the cyclic carbonate compound to open a ring in the heating process, and then in-situ polymerization is carried out under the mutual coordination with imidazole ionic liquid, so that a gel-like coating layer is formed to cover the surface of a positive electrode active material. In order to promote the formation of a gel-like coating layer in the preparation process of the positive electrode and avoid side reactions between the electrolyte and the positive electrode active material in the assembled battery, the time for forming the coating layer needs to be shortened, and more matched cyclic carbonate compounds and metal organic compounds need to be selected to improve the catalytic effect. The fluorine substituent in the fluorinated cyclic carbonate has stronger electron-withdrawing effect, is beneficial to changing the electron cloud of the cyclic structure, can generate electron-withdrawing effect with electrons in the isopropanol structure in the metal isopropanol compound, enhances the catalytic effect of the metal isopropanol compound on the fluorinated cyclic carbonate compound, and is beneficial to improving 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 uniformly, the organic dicarboxylic acid is added to ensure that the metal isopropyl alcohol compound can be more uniformly dispersed around the fluorinated cyclic carbonate compound, so that the contact area between the metal isopropyl alcohol compound and the fluorinated cyclic carbonate can be increased, and the catalytic efficiency can be improved. The organic dicarboxylic acid is further selected, and the hydroxyl groups of the metal isopropyl alcohol compound and the carboxyl groups in the organic dicarboxylic acid are mutually matched, so that the influence on the structure of the metal isopropyl alcohol compound can be reduced under the mutual influence of the two carboxyl groups in the organic dicarboxylic acid, the metal isopropyl alcohol compound can be better dissolved in the organic dicarboxylic acid, and meanwhile, the catalytic activity of the metal isopropyl alcohol compound in the dissolution process is ensured.
As a further scheme, the compound additive comprises fluorinated cyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt and oxalic acid, wherein the ratio of the fluorinated cyclic ethylene carbonate to the aluminum isopropoxide to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to the oxalic acid is (0.5-2 parts) to (0.2-0.3 parts) to (0.5-4 parts) by mass. The fluorinated cyclic ethylene carbonate can partially replace the use amount of the solvent, and is beneficial to improving the addition amount of the positive electrode active material. On the basis, the unsaturated group in the fluorinated cyclic ethylene carbonate can improve the electron-withdrawing capability of the fluorinated group, then forms an electron-withdrawing effect with 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, and can open the ring and polymerize the fluorinated cyclic ethylene carbonate to form a gelatinous coating layer in the thermal process better under the catalysis of aluminum isopropoxide as a catalyst. Oxalic acid can realize the separation of aluminum ions and isopropanol organic anions in aluminum isopropoxide, so that the aluminum isopropoxide is more uniformly dispersed in the slurry while the catalytic activity of the aluminum isopropoxide is more favorably released; the aluminum isopropoxide can react with residual alkali on the surface of the positive electrode active material to form a layer of lithium ion conductor, so that the lithium removal and lithium intercalation speed of the positive electrode active material can be further promoted; in addition, aluminum isopropoxide is favorable for better matching with the binder, so that the mechanical strength of the coating layer is improved. When the dispersed aluminum isopropoxide is dispersed around the fluorinated cyclic ethylene carbonate, the aluminum isopropoxide has more contact area with the fluorinated cyclic ethylene carbonate, which is more beneficial to promoting the rapid progress of the catalytic action; and aluminum ions in the aluminum isopropoxide structure can have more coordination, so that the interaction with fluoride ions in the fluorinated cyclic ethylene carbonate is facilitated, and the catalytic efficiency of aluminum isopropoxide on the fluorinated cyclic ethylene carbonate ring-opening polymerization is also directly promoted.
The invention also provides application of the compound additive in positive electrode slurry.
As a further proposal, the compound additive exists on the surface of the positive electrode active material in the form of a gel coating layer; the gel-like coating layer is bound with an ionic liquid.
The raw materials of the positive electrode slurry further comprise positive electrode active materials, binding agents and conductive agents, wherein the ratio of (90-95 parts) of ionic liquid to annular carbonic ester compounds to metal organic compounds to organic acid compounds to binding agents to conductive agents is (0.2-0.3 parts) of (0.5-2 parts) of (0.5-4 parts) of (1.5-2.5 parts) of (2.5-3.5 parts) of (0.5-2 parts) of (0.5 parts) of (1.5) of (0.2) of (1.5). The adhesive can be matched with the metal organic compound on the basis of bonding all substances, so that the mechanical strength of the gel-like coating layer can be improved; the ionic liquid can be matched with the conductive agent, so that the transmission balance of electrons and ions in the anode can be balanced; the proportion of each substance in the positive electrode slurry further balances the relation among the binding effect of the gel coating layer, the energy density of the positive electrode and the ion transmission capacity of the gel coating layer, and on the basis that the positive electrode can obtain the maximum energy density under the proportion of the positive electrode slurry, the compound additive is favorable for forming the gel coating layer with certain mechanical strength and stable structure in the slurry, so that the gel coating layer can bind the ionic liquid, and the generated gel coating layer also has the ion conductivity equivalent to that of the electrolyte, thereby not only being favorable for 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 being favorable for reducing the side reaction of the positive electrode active material and the electrolyte, thereby being favorable for improving the electrochemical performance of the battery
As a further aspect, the raw material of the positive electrode slurry further includes a solvent. The amount of solvent added can be added by the skilled person depending on the actual viscosity of the slurry.
As a further aspect, the positive electrode active material includes one or more of a metal oxide, a polyanion salt, and a nonmetallic compound.
As a still further aspect, the metal oxide includes one or more of a layered structure metal oxide and a spinel type metal oxide.
As still further aspects, the layered structure metal oxide comprises one or more of lithium cobaltate, lithium nickelate, nickel cobalt manganese ternary material, nickel cobalt lithium aluminate, and lithium-rich manganese-based material.
As still further aspects, the spinel-type metal oxide includes one or more of lithium manganate, lithium nickel manganate, ferric oxide, and lithium vanadate.
As a still further aspect, the polyanionic salt includes one or more of phosphate, silicate, sulfate, borate, titanate.
As still further aspects, the phosphate comprises one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium cobalt phosphate, and lithium nickel phosphate.
As still further aspects, the silicate comprises lithium iron silicate.
As still further alternatives, the sulfate comprises lithium iron fluoride sulfate.
As still further aspects, the borate comprises lithium iron borate.
As still further aspects, the titanate comprises lithium iron titanate.
As a still further aspect, the nonmetallic compound includes one or more of fluoride, sulfide, selenide.
As still further aspects, the fluoride comprises one or more of iron trifluoride, cobalt trifluoride, nickel trifluoride.
As still further aspects, the sulfide comprises one or more of titanium disulfide, iron disulfide, and di-fluidized molybdenum.
As yet a further aspect, the selenide comprises niobium triselenide.
As a further aspect, the binder comprises one or more of a fluoropolymer, a nitrile-containing polymer, an amine-containing polymer, and a carboxymethylated derivative.
As a still further aspect, the fluoropolymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene.
As a still further aspect, the nitrile containing polymer comprises polyacrylonitrile.
As a still further aspect, the amine-containing polymer comprises a polyamide.
As a still further aspect, the carboxymethylated derivative comprises sodium carboxymethyl cellulose.
As a further scheme, the conductive agent comprises one or more of acetylene black, ketjen black, graphite, conductive carbon black (Super P), carbon Nanotubes (CNT), carbon fibers, graphene, multi-wall carbon nanotubes, single-wall carbon nanotubes.
As a further aspect, the solvent comprises N-methylpyrrolidone (NMP).
The anode slurry comprises layered structure metal oxide, imidazole ionic liquid, fluorinated cyclic carbonate compounds, metal isopropyl alcohol compounds, organic dicarboxylic acid, fluorine-containing polymers and conductive agents, wherein the ratio of the imidazole ionic liquid to the fluorinated cyclic carbonate compounds to the metal isopropyl alcohol compounds to the organic dicarboxylic acid to the fluorine-containing polymers to the conductive agents is (90-95 parts) 0.2-0.3 parts (0.5-2 parts) (0.5-4 parts) (1.5-2.5 parts) (2.5-3.5 parts). In order to improve the mechanical strength of the formed coating layer, the coating layer is matched with a fluorine-containing polymer with better flexibility, so that the surface of the material coated in the slurry is better; in addition, the fluorine-containing polymer and the metal isopropyl alcohol compound can generate an electron-withdrawing effect, so that the metal isopropyl alcohol compound can be matched, and a coating layer with certain mechanical strength is formed. In order to improve the energy density of the positive electrode, the fluoro-cyclic carbonate compound in the slurry can replace part of the solvent, so that the mass ratio of the positive electrode active material in the slurry is improved, and the energy density of the battery is ensured. The conductive agent is favorable for conducting electrons, and can balance the migration balance of electrons and ions in the anode under the mutual coordination with the imidazole ionic liquid. The metal isopropanol compound can remove residual alkali on the surface of the layered structure metal oxide, and is beneficial to improving the speed of intercalation and deintercalation of lithium ions by the layered structure metal oxide under high-voltage charging voltage.
As a further scheme, the cathode slurry comprises raw materials of fluorinated cyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, oxalic acid, polyvinylidene fluoride, carbon black and multi-wall carbon nano tube, and lithium cobaltate active material (lithium cobaltate active material), wherein the ratio of the fluorinated cyclic ethylene carbonate to the aluminum isopropoxide to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to the oxalic acid to the polyvinylidene fluoride to the carbon black and multi-wall carbon nano tube to the lithium cobaltate active material (lithium cobaltate active material) is (0.5-2 parts) to (0.2-0.3 parts) to (0.5-4 parts) to (1.5-2.5 parts) to (2.5-3.5 parts) to (90-95 parts). The fluorocyclic carbonate vinyl ester and 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt form a gel coating layer under the catalysis of aluminum isopropoxide; the polyvinylidene fluoride is favorable for the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to be well bound in the coating layer, so that the ionic conductivity of the coating layer is favorable to be increased. The carbon black and the multi-wall carbon nano tube form an electron transmission network in cooperation, and the hollow tubular structure of the multi-wall carbon nano tube can also provide a channel for ion transmission, and the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt can balance electrons and ions in the anode with the carbon black and the multi-wall carbon nano tube. The polyvinylidene fluoride also has better flexibility and can be better coated in a gel coating layer. Although the fluorine-containing polymer can generate electron-withdrawing effect with the aluminum isopropoxide, so that the fluorine-containing polymer is favorable for being matched with the aluminum isopropoxide to improve the mechanical strength of the gel-like coating layer, the fluorine substituent groups in the fluorine-containing polymer are too many, and the mechanical strength of the coating layer can be possibly further improved, but the flexibility of the gel-like coating layer can be influenced to a certain extent, so that the polyvinylidene fluoride is selected. In the case of the mixing of the substances in the positive electrode slurry, the slurry of the invention is more suitable for lithium cobalt oxide active materials, and the electrochemical performance of the battery with the lithium cobalt oxide active materials is improved remarkably.
The invention also provides a preparation method of the positive electrode slurry, which comprises the following steps:
and respectively weighing the positive electrode active material, the conductive agent, the binder, the cyclic carbonate compound, the organic acid compound, the ionic liquid and the metal organic compound according to the mass ratio, adding a solvent, uniformly mixing, and filtering to obtain the positive electrode slurry. The method of the present invention does not limit the order of adding and mixing the substances; the amount of the solvent used is not limited, and may be adjusted by those skilled in the art according to the actual viscosity of the slurry.
The positive electrode active material comprises, by mass, an ionic liquid, a cyclic carbonate compound, a metal organic compound, an organic acid compound and a binder, wherein the ratio of the ionic liquid to the metal organic compound to the organic acid compound to the binder to the conductive agent is (90-95 parts), 0.2-0.3 parts, 0.5-2 parts, 0.5-4 parts, 1.5-2.5 parts and 2.5 parts.
As a further scheme, the condition of uniform mixing is that stirring is carried out under the vacuum environment with the dew point lower than-40 ℃ until the viscosity of the slurry reaches 4000 mpa.s to 8000 mpa.s.
As a further aspect, the present invention provides an optimal example of preparation of the positive electrode slurry, and can further improve the dispersibility of each substance in the slurry. Under the vacuum environment with the dew point lower than-40 ℃, firstly, uniformly mixing the positive electrode active material, the conductive agent and the binder, adding a proper amount of NMP for kneading, adding the CNT conductive agent, uniformly mixing, adding the ionic liquid and uniformly mixing the cyclic carbonate compound. The metal organic compound is added in portions and NMP is added in portions until the viscosity of the slurry reaches 4000 mpa.s to 8000 mpa.s.
The invention also provides a preparation method of the battery with the positive electrode slurry, which comprises the following steps:
and (3) coating positive electrode slurry on the surface of a current collector, drying and cutting at the temperature of 70-130 ℃ to prepare a positive electrode plate, preparing the positive electrode plate into a battery core, baking the battery core, and then carrying out a liquid injection process, a chemical process and a sealing process on the obtained battery core to obtain the battery. In general, the cyclic carbonate compound is ring-opening polymerized at a temperature of not lower than 150 ℃, and in the invention, a metal organic compound is added as a catalyst to promote the cyclic carbonate compound to be ring-opening polymerized in the pole piece baking process. At least a part of the metal organic compounds are heated and decomposed to generate metal oxides and volatile substances after the catalytic action, so that the electrolyte is prevented from being polymerized due to the fact that the metal organic compounds in the gel-like coating layer penetrate into the electrolyte. And the generated metal oxide after thermal decomposition is diffusely dispersed in the coating layer, which is also beneficial to improving the mechanical strength of the coating layer.
As a further scheme, the drying temperature of the pole piece is 95-110 ℃. The drying temperature in the range is favorable for complete heating decomposition of metal organic matters on the basis of ensuring the ring-opening polymerization of the cyclic carbonate compounds, so that the electrical property of the battery cell can be ensured.
As a best example of the invention, the pole piece is dried in a baking best way.
The invention also provides a positive electrode plate with the positive electrode slurry, which comprises a gel-like coating layer coated on the surface of a positive electrode active material, wherein the coating layer is bound with ionic liquid.
As a further proposal, the coating layer also comprises dispersed metal oxide. The metal oxide is diffusely dispersed in the coating layer, which is beneficial to improving the ion conductivity of the coating layer.
As a further aspect, at least a portion of the metal oxide source is derived from a metal organic compound.
As a further scheme, the raw materials of the slurry of the positive electrode plate comprise positive electrode active materials, ionic liquid, cyclic carbonate compounds, metal organic compounds, organic acid compounds, binders and conductive agents; the cyclic carbonate compound is crosslinked and polymerized to form a gel-like coating layer; the surface of the positive electrode active material is coated with a gel coating layer; the binder and the conductive agent are dispersed between the positive electrode active materials in the coating layer.
The invention also provides an electrochemical device with the positive electrode sheet, which can be used for end consumer products, including, but not limited to, mobile phones, notebook computers, pen-input computers, mobile computers, electronic book players, portable phones, portable fax machines, portable copiers, and portable printers.
The invention also provides an electrochemical device with the positive electrode plate, the electrochemical device can be used for electric equipment, the electric equipment comprises large movable electric equipment and small movable electric equipment, and the small movable electric equipment comprises terminal consumer products, wearable electronic equipment or movable electronic equipment; the large movable electric equipment comprises traffic and transportation electric equipment. Traffic and transportation consumers include, but are not limited to, for example, automobiles, motorcycles, mopeds, bicycles, buses, subways, high-speed rails, airplanes, boats; wearable or removable electronic devices include, but are not limited to, devices such as headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-compact discs, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, standby power supplies, drones, motors, lighting fixtures, toys, gaming machines, watches, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors. The battery positive electrode sheet is applied to an electrochemical device, and can be accommodated in electric equipment in the form of the electrochemical device, and generally, the electrochemical device comprises a battery pack or/and a plurality of battery modules or/and a single battery module or/and a single battery, a management system for managing the battery modules or/and the single battery, and the like.
The invention has the characteristics and beneficial effects that:
(1) The compound additive is particularly suitable for being used in positive pole pieces.
(2) The slurry can form a gel coating layer in the positive electrode plate and is coated on the surface of the positive electrode active material, so that the interfacial side reaction between the positive electrode active material and the electrolyte is reduced, and the capacity of the battery is improved.
(3) The gel-like coating layer can also reduce the contact resistance between the battery anode and the electrolyte, thereby facilitating the improvement of the electrochemical performance of the battery.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is an SEM image of a positive electrode sheet according to an embodiment of the present invention.
Fig. 2 is an XRD pattern in the positive electrode slurry provided in the embodiment of the present invention.
Fig. 3 is a graph showing the cycle performance of the batteries of the examples and comparative examples of the present invention at 25 ℃.
Fig. 4 shows the cycle performance of the cells at 45 c for the inventive and comparative examples.
Fig. 5 shows the capacity retention ratio of the present invention and the conventional battery.
FIG. 6 shows the results of a test of metal oxides in a pole piece of the present invention.
Fig. 7 is a test result of ionic liquid in a pole piece of the present invention.
Detailed Description
In order to facilitate an understanding of one of the present invention, the application of one of the present invention to a positive electrode slurry will be more fully described below, and examples of the present invention are given, but the scope of the present invention is not limited thereto.
In the invention, taking example 1 as an example, a preparation method of positive electrode slurry comprises the following steps:
96g of positive electrode active material, 0.5g of conductive agent, 2g of binder, 0.5g of cyclic carbonate compound, 0.25g of organic acid compound, 0.5g of ionic liquid and 0.5g of metal organic compound are respectively weighed, then evenly mixed with a solvent, and filtered to obtain positive electrode slurry.
The condition of uniform mixing is that stirring is carried out under the vacuum environment with the dew point lower than-40 ℃ until the viscosity and viscosity of the slurry reach 4000 mpa.s to 8000 mpa.s.
We also coated the obtained positive electrode slurry on a current collector to obtain a battery, the main steps comprising:
The obtained positive electrode slurry is coated on aluminum foil, then dried, rolled and die-cut to prepare a positive electrode plate, and then assembled with a graphite main material negative electrode plate, a diaphragm, commercial liquid electrolyte and a battery shell, and the lithium cobalt oxide soft-package battery with the charge cut-off voltage of 4.50V and the capacity of 4Ah is prepared after charge-discharge activation.
We also performed electrochemical performance tests on the obtained cells:
(1) The method for testing the nominal capacity of the battery comprises the following steps: charging 0.2C to 4.5V, constant voltage to current 0.05C, standing for 10min, discharging 0.2C to 3.0V, circulating for 2 circles, and taking the discharge capacity of the last circle as the nominal capacity of the battery.
(2) Test method of 45℃cycle performance (80% SOH turns): and (3) a test fixture is arranged on the battery, the incubator is moisturized for 0.5h, the initial circle capacity at the side of 0.2C, the circulation is carried out at the back 1C, and the voltage interval is 3.0V-4.5V, and 1C is the constant volume capacity.
And (3) verification result analysis:
table 1 formulation of battery positive electrode slurry of examples and comparative examples
Figure BDA0004154599950000121
Table 2 results of performance indicators for examples and comparative examples
Figure BDA0004154599950000122
Figure BDA0004154599950000131
TABLE 3 Battery Performance of different cathode active materials
High temperature storage 45 degree cycle Positive electrode active material
Example 17 85 DEG 12h retention 95% 2C/1C for 350 weeks with a retention of 80% Lithium cobalt oxide
Example 18 45 degree 30 days retention 96% 2C/1C for 450 weeks, the retention rate is 80% Nickel cobalt lithium manganate 811
Example 19 85 DEG 12h retention 94% 2C/1C for 340 weeks, retention rate 80% Lithium cobalt oxide
Example 20 45 degree 30 days retention rate 95% 0.7C/0.7C for 700 weeks, retention 80% Lithium iron phosphate
Comparative example 1 85 DEG 12 retention 85% 2C/1C, circle, retention 80% Lithium cobalt oxide
Comparative example 2 45 degree 30 day retention 90% 2C/1C for 400 weeks with a retention of 80% Nickel cobalt lithium manganate 811
Comparative example 3 45 degree 30 day retention 94% 0.7C/0.7C for 720 weeks, retention 80% Lithium iron phosphate
We succeeded in obtaining positive electrode sheets by the formulation in table 1, as shown in fig. 1. We have found that the electrochemical properties of all examples 1-16 in table 2 are superior to those of comparative example 1, as shown in table 2, when we have applied the obtained positive electrode sheet to a battery, compared to a battery having a conventional method for obtaining a positive electrode sheet. According to the invention, the cyclic carbonate compound, the ionic liquid and the metal organic compound are added into the positive electrode slurry, under the catalysis of the metal organic compound, the cyclic carbonate compound is promoted to open a ring in a thermal process, then in-situ polymerization is carried out on the cyclic carbonate compound and the ionic liquid to form a gel coating layer, the gel coating layer is coated on the surface of a positive electrode active material and between pores of each substance particle in the positive electrode slurry, and finally the gel coating layer with a stable structure and ion conducting performance is formed on a positive electrode plate, and the gel coating layer also has certain mechanical properties. In order to promote the rapid ring-opening polymerization of the cyclic carbonate compound, an organic acid compound is further added, so that the dissolution of the metal organic compound is promoted, the metal organic compound is promoted to be more uniformly dispersed in the positive electrode slurry, the contact area between the metal organic compound and the cyclic carbonate compound is increased, the catalytic effect of the metal organic compound on the cyclic carbonate compound is further improved, and the residual alkali on the surface of the positive electrode active material can be removed by the organic acid compound, so that the pH value in the slurry is neutralized. The formed gel coating layer can bind the ionic liquid and the organic acid compound, the ionic liquid has ion conducting capacity, the ionic liquid can be used as an ion transmission channel between the positive electrode active material and the electrolyte in the coating layer, and the organic acid compound can also improve the ion conducting capacity of the coated ionic liquid. The gel-like coating layer formed by the positive electrode slurry is coated on the positive electrode, has ion conductivity equivalent to that of the electrolyte, can promote the transmission of lithium ions between the positive electrode and the electrolyte, and can further isolate side reactions between the positive electrode active material and the electrolyte, so that the electrochemical performance of the battery is improved. We can further verify from fig. 2 that after the compound additive is added, the characteristic peak of the positive electrode active material in the slurry is not changed, so that the gel-like coating layer of the 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 as can be seen from fig. 5, the technical scheme of the invention has better capacity retention rate compared with the battery obtained in the traditional mode (i.e. no compound additive is added in the positive electrode of the battery and no pole piece solidification occurs).
The cycle performance of the battery anode prepared by the invention and the battery anode prepared by the traditional method at different temperatures is also studied, as shown in fig. 3 and 4. We have conducted experiments on the cycle performance of the battery using example 1 and comparative example 1, and in fig. 3, the capacity retention rate is 90% after the battery of the present invention can be cycled at 1C rate for about 780 cycles in an environment of 25 ℃; while the capacity retention rate of the battery of comparative example 1 was 87% after approximately 500 cycles at a 1C rate. In fig. 4, when the capacity of the battery is reduced from 100% to 80% in an environment of 45 ℃, the battery of the present invention can be cycled about 350 turns, whereas the battery of comparative example 1 can be cycled about 220 turns, which is much lower than the cycle number of the present invention at high temperature. It is considered that the present invention is possible because the gel-like coating layer obtained by the present invention can well isolate the side reaction between the positive electrode active material and the electrolyte, thereby improving the capacity of the battery. And the materials in the gel coating layer are matched and balanced to balance the transmission balance of electrons and ions in the anode, so that the electrochemical reaction unbalance of the battery can be reduced when the battery circulates at high temperature.
We also matched slurries with the built additives with different types of positive electrode active materials as shown in table 3. The built-up additive of the present invention can be applied to different positive electrode active materials as shown in example 17-example 20. We further compare examples 17-20 with comparative examples 1-3, wherein examples 17 and 19 are better than comparative example 1, example 18 is better than comparative example 2, and example 20 is better than comparative example 3. Therefore, the compound additive is more suitable for being used in the positive electrode active material of lithium cobaltate, and the electrochemical performance of the battery is further improved by taking the positive electrode active material of lithium cobaltate as an example through further researching the formed gel-like coating of different types of cyclic carbonate compounds, metal organic compounds, organic acid compounds and ionic liquid.
We first studied the coating uniformity of the gel coating layer that the dispersibility of the cyclic carbonate compound can directly affect. We can see from examples 1-5 that the cycling performance and nominal capacity of example 1 are highest and the resistance is very small. It is thought that the fluorine substituent group can change the electron cloud density of the cyclic structure, so that the fluoro cyclic carbonate compound can need less energy for ring opening and can actively participate in the formation process of the gel-like coating layer; and the second is that the fluoro cyclic carbonate compound has lower viscosity and is easier to disperse in the positive electrode slurry, so that the generated coating layer is more uniform and stable. The fluoro-cyclic carbonate compound can be more easily coated on the gel-like coating layer of the surface of the positive electrode active material, thereby reducing side reactions between the positive electrode active material and the electrolyte and being beneficial to improving the electrochemical performance of the battery. Further preferred are fluorinated cyclic carbonates among cyclic carbonates.
We have further studied the optimization of the electrochemical performance of the battery by the selection of the metal organic compound, which plays an important role in the ring-opening polymerization of the cyclic carbonate compound in the process of forming the gel-like coating layer. We can compare the results of examples 1, 9-10, and find that example 1 has the least resistance and the best cycle performance and capacity. The reason why the metal isopropyl alcohol compound is easier to catalyze the ring-opening polymerization of the cyclic carbonate compound is considered to be that firstly, the metal isopropyl alcohol compound is easier to dissolve in the organic acid compound, so that the metal isopropyl alcohol compound is more uniformly dispersed in the slurry, the contact area with the cyclic carbonate compound is promoted to be increased, and the ring-opening polymerization of the cyclic carbonate compound is easier to catalyze; in addition, the metal isopropanol compound can also remove residual alkali on the surface of the positive electrode active material, which is beneficial to improving the speed of the positive electrode active material for inserting and extracting lithium ions. We further prefer metallo-isopropyl alcohols in the metal organic compounds.
In the slurry, under the action of heat, the ionic liquid and the cyclic carbonic compound are subjected to ring opening under the action of a catalyst, then are polymerized to form a gelatinous coating layer, ions are bound in the coating structure by the coating layer, and a bridge for transmitting lithium ions between the positive electrode active material and the electrolyte is built in the gelatinous coating layer by the ionic liquid. When the battery is in a circulating process, the ionic liquid can be matched with the conductive agent in the slurry, so that the transmission of electrons and ions in the anode is balanced, the balance of chemical reaction in the battery is more facilitated under the high-pressure high-temperature environment of the battery, and the electrochemical performance of the battery is maintained. Comparing example 1 with examples 11-12, the electrochemical performance of example 1 is best, and it is considered that the imidazole ring in the imidazole ionic liquid structure is an electron-rich group, the imidazole structure is a five-membered heterocyclic compound, and a conjugated system with a closed large pi bond is adopted, so that the electron withdrawing capability of N is improved, the electron cloud density of nitrogen atoms in the imidazole ring is increased, and the nitrogen atoms in the electron-rich group can participate in attacking oxygen groups in the cyclic carbonate compound, so that the imidazole ring is beneficial to the mutual coordination with the cyclic carbonate compound, the formation of a gel-like coating layer is beneficial, and meanwhile, an ion transmission channel can be built. We further prefer an imidazole-based ionic liquid in the ionic liquid.
Finally, the optimization of the organic acid compound on the formation of the gel-like coating layer is studied, and the organic dicarboxylic acid can promote the dissolution and dispersion of the metal organic compound, so that the coating layer with a more stable and uniform structure is formed; the ionic liquid can be promoted to exert more ionic conductivity, so that the ionic conduction between the positive electrode active material and the electrolyte is promoted. We have found from a comparison of examples 1, 6-8 that the electrochemical performance of the cell of example 1 is optimal, presumably because of the interaction of the carboxylic acid groups in the organic dicarboxylic acid, which promotes dispersion of the metal organic compound while better maintaining the structural characteristics of the ionic liquid and the metal organic compound. We further prefer organic dicarboxylic acids in the organic acid-based compounds.
On the basis, the method has the advantages that under the cooperation of adding the fluorinated cyclic carbonate compound substance and the imidazole ionic liquid into the positive electrode slurry, the fluorinated cyclic carbonate compound substance is subjected to ring opening and then in-situ polymerization to form a gel coating layer to be coated on the surface of the positive electrode active material, and the fluorinated substituent group of the fluorinated cyclic carbonate compound substance can change the electron cloud density of the cyclic structure, so that the method is beneficial to reducing ring opening energy, has lower viscosity, is beneficial to being uniformly dispersed in the positive electrode slurry, and lays a foundation for forming a uniform ion conducting coating layer; the imidazole structure in the imidazole ionic liquid structure is a five-membered heterocyclic compound and has a closed conjugated system with a large pi bond, so that the electron withdrawing capability of N is improved, the fluoro cyclic carbonate compound structure also contains electron withdrawing groups such as carbonyl and fluoro substituents, and lone pair electrons are arranged on oxygen atoms in organic anions in aluminum isopropoxide, so that aluminum isopropoxide is promoted to catalyze the interaction between the imidazole ionic liquid and fluoro cyclic carbonate compound substances, a gel coating layer is formed, and the imidazole ionic liquid has specific ion conducting capability and can transfer ions between an anode active material and an electrolyte. In order to improve the rapid ring-opening polymerization of the fluorinated cyclic carbonate compound, the metal isopropyl alcohol compound and the organic dicarboxylic acid are further selected, and the carboxyl group in the organic dicarboxylic acid and the hydroxyl group in the metal alcohol compound are matched, so that the metal isopropyl alcohol compound is better dissolved in the slurry, and is further uniformly dispersed, the close contact between the metal isopropyl alcohol compound and the fluorinated cyclic carbonate compound and the increase of the contact area are realized, the catalytic activity of the metal isopropyl alcohol compound is not damaged by the organic dicarboxylic acid, and the efficiency of forming a gel coating layer uniformly coated by the fluorinated cyclic carbonate compound through ring-opening polymerization can be further improved. The strong electron-withdrawing effect in the fluorinated cyclic carbonate and electrons in the isopropanol structure in the metal isopropanol compound generate electron-withdrawing effect, so that the catalytic effect of the metal isopropanol compound on the fluorinated cyclic carbonate compound is enhanced. The conductive agent in the slurry can also realize balance of electron and ion transmission in the anode with imidazole ionic liquid, so that balance of electrochemical reaction of the battery is improved, and comparison of example 1 and examples 13-16 proves that the example 1 and the example 16 are better than other examples. The imidazole ionic liquid, the fluorinated cyclic carbonate compound, the organic dicarboxylic acid and the metal isopropanol compound are further preferred, and the ratio of the fluorinated cyclic carbonate compound to the organic dicarboxylic acid to the metal isopropanol compound is (0.2-0.3 part) 0.5-2 parts 0.5-4 parts 0.5-2 parts by mass.
On the basis, the fluoro-cyclic ethylene carbonate is further selected in the positive electrode slurry, the fluoro-cyclic ethylene carbonate is substituted to form a stronger electron-withdrawing effect, and the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt has more lone pair electrons and can form better interaction. In order to realize the formation of the coating layer, aluminum isopropoxide is further selected, and the oxalic acid is considered to realize the separation of aluminum ions and organic anions of the aluminum isopropoxide under the coordination of the oxalic acid, so that the aluminum isopropoxide is more uniformly dispersed in the slurry while the catalytic activity of the aluminum isopropoxide is more favorably released; and the catalyzed aluminum isopropoxide can react with residual alkali on the surface of the positive electrode active material to form a layer of lithium ion conductor, so that the lithium removal and lithium intercalation speed of the positive electrode active material can be further promoted, and in addition, the aluminum isopropoxide is favorable for better matching with a binder, so that the mechanical strength of a coating layer is improved. When the dispersed aluminum isopropoxide is dispersed around the fluorinated cyclic ethylene carbonate, the aluminum isopropoxide has more contact area with the fluorinated cyclic ethylene carbonate, which is more beneficial to promoting the rapid progress of the catalytic action; and aluminum ions in the aluminum isopropoxide structure can have more coordination, so that the interaction with fluoride ions in the fluorinated cyclic ethylene carbonate is facilitated, and the catalytic efficiency between the fluorinated cyclic ethylene carbonate and aluminum isopropoxide is also directly promoted. The sulfonate in the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt can improve the ionic conductivity of imidazole ionic liquid, so that when the battery is charged at high voltage by adding the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt and a conductive agent, the electron migration in the positive electrode and the ion transmission balance between the positive electrode active material and the electrolyte are realized, and the balance of chemical reaction in the battery at high temperature is maintained; in addition, more carbonyl in oxalic acid can improve the oxidation-reduction reaction power of the anode, and meanwhile, the ionic conductivity of the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt in the coating layer can also be improved, so that the contact resistance between the gel coating layer and the electrolyte is further reduced. We have verified by comparing example 1 with example 16 that example 1 has better electrochemical performance than example 16. It is further preferable that the positive electrode slurry contains fluorinated cyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt and oxalic acid, wherein the ratio of the fluorinated cyclic ethylene carbonate to the aluminum isopropoxide to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to the oxalic acid is (0.5-2 parts) to (0.2-0.3 parts) to (0.5-4 parts) by mass.
On this basis, we have further studied the better coordination of the compounding additive with other substances in the positive electrode slurry.
In order to improve the mechanical strength of the formed coating layer, the fluoropolymer is matched, and firstly, the fluoropolymer has better flexibility and can fully coat the surfaces of other particles in the slurry, so that the substances in the slurry are better bonded; and secondly, fluorine substituent groups in the fluorine-containing polymer can generate electron-withdrawing effect with electrons in an isopropanol structure in the metal isopropanol compound, so that the metal isopropanol compound can be bonded, and a coating layer with certain mechanical strength is formed. In order to improve the energy density of the positive electrode, the fluoro-cyclic carbonate compound in the slurry can replace part of the solvent, so that the addition amount of the solvent in the positive electrode is reduced, the mass ratio of the positive electrode active material is improved, and the energy density of the battery is ensured. The conductive agent can be matched with imidazole ionic liquid in the slurry, so that the capacity of transporting electrons and ions in the anode is balanced, and the balance of electrochemical reaction in the charge-discharge cycle process of the battery is facilitated. The metal isopropanol compound can remove residual alkali on the surface of the layered structure metal oxide, and is beneficial to improving the speed of intercalation and deintercalation of lithium ions by the layered structure metal oxide under high-voltage charging voltage. The anode slurry is prepared from the following raw materials of layered structure metal oxide, imidazole ionic liquid, fluorinated cyclic carbonate compound, metal isopropyl alcohol compound, organic dicarboxylic acid, fluorine-containing polymer and conductive agent, wherein the ratio of the imidazole ionic liquid to the fluorinated cyclic carbonate compound to the metal isopropyl alcohol compound to the organic dicarboxylic acid to the fluorine-containing polymer to the conductive agent is (90-95 parts) 0.2-0.3 parts (0.5-2 parts) 0.5-2 parts (0.5-4 parts) 1.5-2.5 parts (2.5-3.5 parts).
On the basis, we further find that the fluorinated cyclic ethylene carbonate can partially replace the use amount of the solvent, which is beneficial to improving the addition amount of the lithium cobaltate active material; on the basis, fluoro cyclic ethylene carbonate, polyvinylidene fluoride and 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt form an electron-withdrawing effect, and fluoro cyclic ethylene carbonate and 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt form a gel coating layer under the catalysis of aluminum isopropoxide; the polyvinylidene fluoride is beneficial to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to be well bound in the coating layer, so that the ionic conductivity of the coating layer is beneficial to the increase. In addition, the coating layer is provided with dot carbon black and hollow tubular multi-wall carbon nano tubes, the dot carbon black is connected with the hollow tubular multi-wall carbon nano tubes to form an electron transmission network, the hollow tubular multi-wall carbon nano tubes can also provide ion transmission channels, and the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt can balance electrons and ions in the anode with the carbon black and the multi-wall carbon nano tubes. The polyvinylidene fluoride also has better flexibility and can be better coated in a gel coating layer. Although the fluorine-containing polymer can generate electron-withdrawing effect with the aluminum isopropoxide, so that the fluorine-containing polymer is favorable for being matched with the aluminum isopropoxide to improve the mechanical strength of the gel-like coating layer, the fluorine substituent groups in the fluorine-containing polymer are too many, and the mechanical strength of the coating layer can be possibly further improved, but the flexibility of the gel-like coating layer can be influenced to a certain extent, so that the polyvinylidene fluoride is selected. In the case of the mixing of the substances in the positive electrode slurry, the slurry of the invention is more suitable for lithium cobalt oxide active materials, and the electrochemical performance of the battery with the lithium cobalt oxide active materials is improved remarkably. It is further preferable that the positive electrode slurry comprises fluorinated cyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, oxalic acid, polyvinylidene fluoride, carbon black+multi-wall carbon nanotubes and lithium cobaltate active material (LCO active material), wherein the ratio of the fluorinated cyclic ethylene carbonate to the aluminum isopropoxide to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to the oxalic acid to the polyvinylidene fluoride to the carbon black+multi-wall carbon nanotubes to the lithium cobaltate active material (LCO active material) is (0.5-2 parts) (0.2-0.3 parts) (0.5-4 parts) (1.5-2.5 parts) (2.5-3.5 parts) (90-95 parts).
We also tested the positive electrode sheet obtained in example 1 for the substance in the coating layer after cycling, and the test results are shown in fig. 6 and 7. As can be seen from fig. 6, ionic liquid (1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl)) is bound in the coating layer of the positive electrode sheet, and the results can be verified by detecting the C-F bond, the s=o bond and the c=c bond energy. In FIG. 7, it can be confirmed that the metal oxide (Al 2 O 3 ). 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 is bound with an ionic liquid and a dispersed metal oxide.
In summary, the compound additive provided by the invention is used in the positive electrode slurry, and can form a gel coating layer to isolate side reactions between the positive electrode active material and the electrolyte, so that the electrochemical performance of the battery is improved, and the formed gel coating layer has ion conductivity equivalent to that of the electrolyte, so that the contact resistance between the electrolyte and the positive electrode can be reduced.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The compound additive is characterized by comprising ionic liquid, cyclic carbonate compounds, metal organic compounds and organic acid compounds, wherein the ratio of the ionic liquid to the cyclic carbonate compounds to the metal organic compounds to the organic acid compounds is (0.2-0.3 part) to (0.5-2 parts) to (0.5-4 parts) by mass.
2. A compounding additive according to claim 1, wherein the ionic liquid comprises one or more of quaternary ammonium ionic liquids, imidazole ionic liquids, pyridine ionic liquids;
further preferably, the quaternary ammonium ionic liquid comprises one or more of tetramethyl ammonium chloride, tetramethyl ammonium bromide, tetramethyl ammonium hexafluorophosphate and tetramethyl ammonium trifluoromethane sulfonate;
further preferably, the imidazole ionic liquid comprises one or more of 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, 1-butyl-3-methylimidazole bis trifluoromethanesulfonyl imide salt, 1-butyl-3-methylimidazole chloride salt, 1-butyl-3-methylimidazole phosphate and 1-butyl-3-methylimidazole nitrate;
further preferably, the pyridine ionic liquid comprises one or more of 1-butyl-4-methylpyridine chloride, 1-hexyl-4-methylpyridine chloride and 1-ethylpyridine bromide.
3. The compound additive according to claim 1, wherein the cyclic carbonate compound comprises one or more of a cyclic carbonate having an unsaturated ring and a cyclic carbonate having a saturated ring;
further preferably, the cyclic carbonates having a saturated ring include one or more of cyclic carbonates having a C2-C6 alkylene group;
further preferably, the cyclic carbonate having a saturated ring includes one or more of cyclic carbonates having a C2-C4 alkylene group;
further preferably, the cyclic carbonate compound further has one or more of an unsaturated substituent group, a halogen atom substituent group, and an alkyl substituent group;
further preferably, the unsaturated substituent group comprises one or more of c= C, C ≡c, aromatic ring;
further preferably, the halogen atom substituent group includes one or more of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom;
further preferably, the alkyl substituent comprises one of C1-C4 alkyl;
further preferably, the halogen atom substituent group includes one or more of a fluorine atom and a chlorine atom;
further preferably, the halogen atom substituent group includes a fluorine atom;
Further preferably, the number of the halogen atom substituent groups is 1 to 6;
more preferably, the number of the halogen atom substituent groups is 1 to 4.
4. The compound additive according to claim 1, wherein the organic acid compound comprises one or more of an organic carboxylic acid compound, an organic sulfonic acid compound, an organic sulfinic acid compound, and an organic thiocarboxylic acid compound;
further preferably, the organic carboxylic acid compound comprises one or more of organic dicarboxylic acid, organic monocarboxylic acid, monounsaturated organic carboxylic acid, polyunsaturated organic carboxylic acid;
further preferably, the organic dibasic acid comprises one or more of oxalic acid, malonic acid and succinic acid;
further preferably, the organic monoacid comprises one or more of formic acid, acetic acid, butyric acid and propionic acid;
further preferably, the monounsaturated organic carboxylic acid comprises oleic acid;
further preferably, the polyunsaturated organic carboxylic acid comprises butynedioic acid.
5. The compound additive according to claim 1, wherein the metal organic compound comprises one or more of a metal isopropanol compound, a metal sulfonic acid compound, and a metal alkane compound;
Further preferably, the metal isopropanol compound comprises one or more of aluminum isopropoxide and magnesium isopropoxide;
further preferably, the metal sulfonic acid compound comprises one or more of silver iso-trifluoromethane sulfonate and aluminum trifluoromethane sulfonate;
further preferably, the metal alkane compound comprises one or more of dibutyl tin and dibutyl zinc.
6. The compound additive according to claim 1, wherein the compound additive comprises (by mass) imidazole ionic liquid, (0.2-0.3 parts) 0.5-2 parts, 0.5-4 parts, and 0.5-2 parts of fluorinated cyclic carbonate compound, and metal isopropanol compound.
7. The compound additive according to claim 1, wherein the compound additive comprises fluorinated cyclic ethylene carbonate, aluminum isopropoxide, 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt and oxalic acid, and the ratio of the fluorinated cyclic ethylene carbonate to the aluminum isopropoxide to the 1-allyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt to the oxalic acid is (0.5-2 parts) to (0.2-0.3 parts) to (0.5-4 parts) by mass.
8. A positive electrode slurry comprising the formulated additive of any one of claims 1-7;
further preferably, the ratio of the compound additive in the positive electrode slurry is 1.5-8.7% by mass;
further preferably, the positive electrode slurry further comprises a positive electrode active material, a binder and a conductive agent;
further preferably, the positive electrode active material includes one or more of a metal oxide, a polyanion salt, and a nonmetallic compound;
further preferably, the metal oxide comprises one or more of a layered structure metal oxide and a spinel type metal oxide;
further preferably, the layered structure metal oxide comprises one or more of lithium cobaltate, lithium nickelate, nickel cobalt manganese ternary material, nickel cobalt lithium aluminate and lithium-rich manganese base material;
further preferably, the binder comprises one or more of a fluoropolymer, a nitrile-containing polymer, an amine-containing polymer, a carboxymethylated derivative;
further preferably, the fluoropolymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene;
further preferably, the nitrile-containing polymer comprises polyacrylonitrile;
Further preferably, the amine-containing polymer comprises a polyamide;
further preferably, the carboxymethylated derivative comprises sodium carboxymethyl cellulose;
further preferably, the conductive agent comprises one or more of acetylene black, ketjen black, graphite, conductive carbon black, carbon nanotubes, carbon fibers, graphene, multi-walled carbon nanotubes, single-walled carbon nanotubes.
9. An electrochemical device comprising the positive electrode sheet made of the positive electrode slurry according to claim 8.
10. An electrical device, characterized in that it comprises the electrochemical device of claim 9.
CN202310329898.6A 2023-03-30 2023-03-30 Compound additive and electrochemical device using same Pending CN116364930A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116613321A (en) * 2023-07-18 2023-08-18 宁德时代新能源科技股份有限公司 Composite cathode material, additive, cathode plate, secondary battery and electricity utilization device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116613321A (en) * 2023-07-18 2023-08-18 宁德时代新能源科技股份有限公司 Composite cathode material, additive, cathode plate, secondary battery and electricity utilization device

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