An electrochemical device and a method of manufacturing the same

Abstract

The application belongs to the technical field of batteries, and particularly relates to an electrochemical device and a preparation method thereof. The electrochemical device comprises a positive electrode, an electrolyte, a diaphragm and a negative electrode. The electrolyte comprises an isocyanate compound, a fluorine-containing sulfimide salt, a metal salt and an organic solvent. The mass percentage content a of the isocyanate compound is 0.01% to 7% based on the total mass of the electrolyte, and the mass percentage content b of the fluorine-containing sulfimide salt is 0.1% to 25%. The positive electrode comprises a positive electrode active material, a conductive material and a fluorine-containing carbon adhesive. The mass percentage content x of the fluorine-containing carbon adhesive is 0.05% to 10% based on the total mass of the positive electrode active material, and x, a and b satisfy the relationship: 0.005<=x / (a+b)<=50. The electrochemical device can simultaneously and efficiently stabilize the positive and negative electrode interfaces, prolong the cycle life of the electrochemical device, and improve the performance in terms of the rate capability, high and low temperature stability and the like.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an electrochemical device and its preparation method. Background Technology

[0002] Electrochemical devices such as lithium-ion batteries and sodium-ion batteries are widely used in various electronic devices and power systems as important energy storage devices. However, with the continuous improvement of energy density and operating voltage, the stability of their internal electrode / electrolyte interface has become a key bottleneck restricting further improvement in battery performance.

[0003] Under high-voltage operating conditions, positive electrode materials are prone to structural degradation, while the electrolyte undergoes continuous decomposition reactions at strongly oxidizing interfaces, leading to the formation of unstable interfaces, dissolution of transition metal ions, and irreversible electrolyte consumption. On the other hand, high specific surface area negative electrode materials (such as silicon-based negative electrodes and hard carbon) face significant volume changes during cycling, causing repeated rupture and reconstruction of their surface solid electrolyte interphase (SEI) film, exacerbating the loss of active materials and increasing interfacial impedance. These interfacial problems collectively contribute to the performance degradation of electrochemical devices in terms of cycle life, rate performance, and high-temperature stability, making it difficult to meet the ever-increasing demands for high performance.

[0004] Improving interfacial properties through electrolyte additives is an effective and simple strategy. Currently, various functional additives have been researched and applied, but their effects are often limited to improving a single electrode or specific properties, making it difficult to achieve synergistic stabilization of the positive and negative electrode interfaces and simultaneous improvement of overall performance. Therefore, developing novel multifunctional additive schemes that can simultaneously and efficiently stabilize the positive and negative electrode interfaces and adapt to high-voltage, high-energy-density systems has significant technical and application value. Summary of the Invention

[0005] This invention aims to provide an electrochemical device and its preparation method. The electrochemical device of this invention can simultaneously and efficiently stabilize the positive and negative electrode interfaces, adapt to high-voltage and high-energy-density systems, effectively extend the cycle life of the electrochemical device, and improve performance in terms of rate capability and high and low temperature stability, thus meeting the current high-performance requirements for batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an electrochemical device, comprising a positive electrode, an electrolyte, a diaphragm, and a negative electrode, wherein the electrolyte comprises isocyanate compounds, fluorosulfonyl imide salts, metal salts, and organic solvents; Based on the total mass of the electrolyte, the mass percentage of isocyanate compounds (a) is 0.01% to 7%, and the mass percentage of fluorosulfonyl imide salts (b) is 0.1% to 25%. Understandably, based on the total mass of the electrolyte, the mass percentage a of isocyanate compounds is, but not limited to, 0.01%, 0.05%, 0.08%, 0.1%, 0.3%, 0.7%, 0.9%, 1.2%, 2%, 3%, 4%, 5%, 6%, and 7%, and the mass percentage b of fluorosulfonyl imide salts is, but not limited to, 0.1%, 0.5%, 1%, 5%, 9%, 13%, 15%, 20%, 23%, and 25%. The positive electrode includes a positive electrode active material, a conductive material, and a fluorocarbon binder; Based on the total mass of the positive electrode active material, the mass percentage x of the fluorocarbon binder is 0.05%~10%, and x, a, and b satisfy the relationship: 0.005≤x / (a+b)≤50.

[0007] Understandably, based on the total mass of the positive electrode active material, the mass percentage x of the fluorocarbon binder includes, but is not limited to, 0.05%, 0.1%, 0.5%, 1%, 2%, 5%, 8%, and 10%, and the value of x / (a+b) includes, but is not limited to, 0.005, 0.01, 0.05, 0.1, 0.5, 0.9, 1.5, 2, 5, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45, and 50.

[0008] In the electrochemical device of this invention, the isocyanate compounds in the electrolyte can react with their isocyanate groups (-NCO) during battery formation and cycling, contributing to the construction of a stable interfacial film on the electrode surface. Simultaneously, fluorosulfonyl imide salts (such as LiFSI and LiTFSI) not only provide lithium ions, but their anionic portions also participate in the formation of a stable LiF-rich interface. The fluorocarbon binder in the positive electrode interacts with fluorinated species migrating from the electrolyte (from hexafluorophosphate, fluorosulfonyl imide salt decomposition derivatives), and possibly hydrogen fluoride (HF). The synergistic reaction discovered in this application originates from a unique interfacial chemical process triggered by a specific content relationship between the electrolyte and the positive electrode. The fluorocarbon binder in the positive electrode forms a strong negative electric field microenvironment on its surface, electrostatically repelling fluorinated anions in the electrolyte and inhibiting their disordered decomposition on the surface of the positive electrode active material; simultaneously, it allows electrically neutral isocyanate compounds to preferentially approach and react with the active material surface, forming a nitrogen-rich polymer organic underlayer CEI film. This organic layer has good lithium-ion conductivity and electronic insulation, thus constructing a lithium-conducting and electron-resistant composite CEI structure, which effectively improves the cycle stability, rate performance and safety of the battery.

[0009] When the positive electrode component and electrolyte component in the electrochemical device of the present invention are in a ratio that satisfies the relationship 0.005≤x / (a+b)≤50, the system can not only effectively inhibit the oxidative decomposition of the electrolyte and the dissolution of transition metals, but also significantly enhance the mechanical integrity of the electrode during the cycling process, buffer the volume change stress of the active material, prevent particle peeling and microcrack propagation, effectively extend the cycle life of the electrochemical device, and improve the performance in terms of rate performance and high temperature stability.

[0010] As one embodiment of the electrochemical device described in this invention, the chemical structural formula of the isocyanate compound is: R1 is a substituted or unsubstituted C1-C8 alkane chain, a substituted or unsubstituted C2-C8 olefin chain, a substituted or unsubstituted C2-C8 alkyne chain, a substituted or unsubstituted aromatic ring chain, or a substituted or unsubstituted C1-C8 ether-bonded alkane chain. When substituted, the substituent includes at least one of F or C1-C4 alkyl groups.

[0011] As one embodiment of the electrochemical device of the present invention, the isocyanate compound includes at least one selected from 1,6-hexanediisocyanate, 1,4-butanediisocyanate, 1,5-pentanediisocyanate, octyl 1,8-diisothiocyanate, isophorone diisocyanate, 4,4-diisocyanate dicyclohexylmethane, 4,4'-methylenebis(phenyl isocyanate), and 2,2,4-trimethylhex-1,6-dimethyldiisocyanate.

[0012] As one embodiment of the electrochemical device of the present invention, the fluorosulfonyl imide salt includes lithium fluorosulfonyl imide salt and sodium fluorosulfonyl imide salt.

[0013] In a preferred embodiment of the electrochemical device of the present invention, the fluorosulfonyl imide lithium salt includes at least one of lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI).

[0014] In a preferred embodiment of the electrochemical device of the present invention, the fluorosulfonylimide lithium sodium salt includes at least one of sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonylimide), and sodium bis(fluorosulfonylimide).

[0015] As one embodiment of the electrochemical device described in this invention, the fluorocarbon adhesive includes at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or modified derivatives thereof (such as carboxylated or sulfonated modified derivatives).

[0016] In one embodiment of the electrochemical device described in this invention, the concentration of the metal salt is 0.5~8 mol / L.

[0017] In a preferred embodiment of the electrochemical device of the present invention, the concentration of the metal salt is 1~6 mol / L.

[0018] As one embodiment of the electrochemical device of the present invention, the metal salt includes lithium salt and sodium salt.

[0019] In a preferred embodiment of the electrochemical device of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiBF2(C2O4)) (LiDFOB), lithium tetraphenylborate (LiB(C6H5)4), lithium dioxalate borate (LiB(C2O4)2) (LiBOB), lithium tetrafluorooxalate phosphate (LiPF4(C2O4)) (LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), and lithium bis(fluorosulfonylimide) (LiFSI).

[0020] In a preferred embodiment of the electrochemical device of the present invention, the sodium salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide.

[0021] As one embodiment of the electrochemical device described in this invention, the organic solvent includes one or more of the following: dimethyl ether, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, tri(ethylene glycol) dimethyl ether, 1-2-diethoxyethane, diethoxyethane, ethoxymethoxyethane, 1,3-dimethoxypropane (DMP), tetrahydrofuran, 2-methyltetrahydrofuran, and dioxolane; and carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), ethyl difluoroacetate (EDFA), ethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoropropylene carbonate (TFEC), trifluoroethyl methyl carbonate, and trifluoroethyl ethyl carbonate.

[0022] As one embodiment of the electrochemical device of the present invention, the mass percentage of the metal salt is 5-30% and the mass percentage of the organic solvent is 70-95% based on the total mass of the electrolyte.

[0023] As one embodiment of the electrochemical device of the present invention, the electrolyte further includes a linear carboxylic acid ester compound and a sulfur-containing substance; the mass ratio of the linear carboxylic acid ester compound to the sulfur-containing substance is (0.5-10):1. It can be understood that the mass ratio of the linear carboxylic acid ester compound to the sulfur-containing substance includes, but is not limited to, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1.

[0024] As one embodiment of the electrochemical device of the present invention, the linear carboxylic acid ester compound includes at least one selected from methyl acetate, ethyl acetate, ethyl propionate, ethyl butyrate, methyl formate, and methyl butyrate.

[0025] As one embodiment of the electrochemical device of the present invention, the sulfur-containing substance includes at least one of 1,3-propane sulfonyl lactone (PS), methylene disulfonate (MMDS), vinyl sulfate (DTD), 1,3-propene sulfonate lactone (PST), 1,4-butane sulfonyl lactone, ethyl methanesulfonate, butyl methanesulfonate, vinyl sulfite (ES), and 1,3-dithiaane.

[0026] As one embodiment of the electrochemical device of the present invention, the preparation process of the electrolyte includes the following steps: S1: Solvent premixing: The organic solvent and the linear carboxylic acid ester compound are mixed and stirred to obtain a mixed solvent, which is then cooled and kept warm for later use. S2: Preparation and dissolution of metal salts: Metal salts are added to the reaction vessel in multiple portions, along with a portion of fluorosulfonamide salts. The mixture is stirred, and sulfur-containing substances are added while stirring. Isocyanate compounds are added in multiple portions. S3: Addition and ripening of fluorosulfonamide salt: The remaining fluorosulfonamide salt was added to the system and stirred continuously to obtain the electrolyte.

[0027] As one embodiment of the electrochemical device described in this invention, the cooling in step S1 is to reduce the temperature to 10-20°C.

[0028] As one embodiment of the electrochemical device described in this invention, the step S2 of adding the metal salt to the reactor in multiple stages is as follows: 60%-70% of the total lithium salt feed amount is injected into the reactor through a closed pipe under a nitrogen atmosphere using a vacuum conveying system, so that the powder is instantly entrained and dispersed by the high-speed rotating solvent, and the temperature rise rate is controlled to be less than 3℃ / min; 20%-35% of the total metal salt feed amount is added at a rate of 200-400g / min, and stirring is continued for 30-60 minutes, controlling the temperature to be below 30℃ and the temperature rise rate to be below 2℃ / min; 5%-10% of the total metal salt feed amount is pulsed and circulated, with each feeding time being 10s and the feeding amount being 20g, and stirring is carried out to control the solution temperature at 25-30℃, then the feeding is paused for 20s, and the cycle is repeated until the solution is completely clear and transparent, at which point the feeding is finished.

[0029] As one embodiment of the electrochemical device of the present invention, the portion of fluorosulfonyl imide salt in step S2 is 60%-70% of the total fluorosulfonyl imide salt.

[0030] As one embodiment of the electrochemical device of the present invention, the addition of the isocyanate compound in step S2 is as follows: first add 70% of the total amount of diisocyanate diluent, stir rapidly for 30 minutes; after standing for 15 minutes, add the remaining 30%.

[0031] In this invention, isocyanate compounds are added in two stages during the preparation of the electrolyte, which helps to ensure their uniform distribution under different polarity environments and avoids excessively high local concentrations that could lead to gelation or side reactions.

[0032] As one embodiment of the electrochemical device described in this invention, the continuous stirring time in step S3 is 4-8 hours.

[0033] In this invention, the fluorosulfonamide salt is added in two stages during the preparation of the electrolyte, which can effectively avoid violent reactions during the preparation process. In subsequent cycles, the high concentration of fluorosulfonamide salt can not only increase the metal ion transport number, but also generate more inorganic fluorides through decomposition on the basis of the already formed SEI / CEI, filling the pores of the interfacial film and making the film more compact without sacrificing ionic conductivity.

[0034] As one embodiment of the electrochemical device of the present invention, the mass ratio of the positive electrode active material, conductive material and fluorocarbon binder in the positive electrode is (95~98):(0.5~2):(1~3).

[0035] As one embodiment of the electrochemical device of the present invention, the positive electrode active material includes at least one of ternary materials, high-nickel ternary materials, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese oxide; or, the positive electrode active material includes at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

[0036] In a preferred embodiment of the electrochemical device of the present invention, the layered transition metal oxide compound has the chemical formula Na. s L y O z 0 < s ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and L can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0037] In a preferred embodiment of the electrochemical device of the present invention, the chemical formula of the Prussian compound is Na. c M[M′(CN)6] d ·eH₂O, M is a transition metal, M′ is a transition metal, 0 <c≤2,0<d≤1,0<e≤20。

[0038] In a preferred embodiment of the electrochemical device of the present invention, the chemical formula of the phosphate compound is Na3(RO). 1-f PO4)2F 1+2f Or Na2R′PO4F, where 0≤f≤1, R is selected from at least one of Al, V, Ge, Fe, and Ga, and R′ is selected from at least one of Fe and Mn.

[0039] In a preferred embodiment of the electrochemical device of the present invention, the chemical formula of the sulfate compound is Na2A(SO4)2·2H2O, where A is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0040] As one embodiment of the electrochemical device of the present invention, the conductive material of the positive electrode includes at least one of conductive carbon black and carbon nanotubes.

[0041] As one embodiment of the electrochemical device of the present invention, the negative electrode includes a negative electrode active material and a conductive material.

[0042] As one embodiment of the electrochemical device of the present invention, the mass ratio of the negative electrode active material to the conductive material in the negative electrode is (95~98):(0.5~3).

[0043] As one embodiment of the electrochemical device of the present invention, the negative electrode active material includes one or more of carbonaceous materials, alloy materials, and lithium metal composite materials.

[0044] As one embodiment of the electrochemical device of the present invention, the negative electrode active material includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon alloy, and silicon-oxygen alloy.

[0045] As one embodiment of the electrochemical device of the present invention, the conductive material of the negative electrode includes at least one of conductive carbon black and carbon nanotubes.

[0046] As one embodiment of the electrochemical device described in this invention, the negative electrode further includes a binder and a thickener.

[0047] In one embodiment of the electrochemical device described in this invention, the adhesive may be styrene-butadiene rubber (SBR).

[0048] In one embodiment of the electrochemical device described in this invention, the thickener may be sodium carboxymethyl cellulose (CMC).

[0049] This invention also claims a method for preparing the electrochemical device, comprising assembling a positive electrode, a negative electrode, an electrolyte, and a separator to obtain the electrochemical device. The method for preparing the electrochemical device in this invention is performed according to conventional methods in the art.

[0050] Compared with the prior art, the present invention has the following beneficial effects: (1) To address the problems of rapid cycle performance degradation, poor rate performance, and severe high-temperature expansion caused by the instability of the cathode-electrolyte interface in high-energy-density electrochemical devices, this invention precisely controls the ratio of the fluorinated carbon binder in the cathode to the branched diisocyanate and fluorosulfonyl imide salt in the electrolyte. This enables the in-situ construction of a dense, stable, and highly functional solid electrolyte interphase (CEI) film on the cathode surface. This interphase film possesses both high alkali metal ion conductivity and good electronic insulation, effectively promoting alkali metal ion transport and preventing direct contact between the electrolyte and the highly active cathode material, significantly reducing interfacial impedance and improving battery rate performance. Simultaneously, the stable chemical structure provided by the fluorinated components in the interphase film effectively inhibits the oxidative decomposition of the electrolyte under high voltage, reducing the dissolution of transition metal ions and the irreversible consumption of active alkali metal ions. More importantly, the tight bond formed between the interface film and the fluorocarbon binder enhances the mechanical stability of the overall electrode structure, buffers the volume change stress during cycling, prevents the pulverization and detachment of active material particles, thereby significantly improving the cycle life of the battery and effectively suppressing electrode expansion at high temperatures.

[0051] (2) By optimizing the ratio of the three components in the electrochemical device (0.005≤x / (a+b)≤50), the present invention achieves directional control of interface performance, enabling the electrochemical device to maintain high energy density while obtaining excellent comprehensive electrochemical performance and environmental stability. Attached Figure Description

[0052] Figure 1 The figures show the high and low temperature discharge test results of batteries in some embodiments and comparative examples of the present invention. Detailed Implementation

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0054] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0055] Example 1: An electrochemical device Positive electrode: Positive electrode active material, conductive material, fluorocarbon binder; Among them, the positive electrode active material is the high-nickel ternary material LiNi. 0.8 Co 0.1 Mn 0.1 O2(NCM811) Conductive material: Super P conductive carbon black Fluorocarbon adhesive: Polyvinylidene fluoride (PVDF) Based on the total mass of the positive electrode active material, the mass percentage x of the fluorocarbon binder is 1.5%.

[0056] Preparation of the positive electrode sheet: The positive electrode active material, conductive material, and fluorocarbon binder are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a mass ratio of 96.5:1.5:2.0 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated onto the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained. The areal density of the positive electrode active material is 20 mg / cm³. 2 The compacted density is 3.45 g / cm³. 3 .

[0057] Electrolytes: isocyanate compounds, fluorosulfonyl imide salts, lithium salts, organic solvents, linear carboxylic acid ester compounds, sulfur-containing substances; Among them, isocyanate compounds include: 1,6-hexanediisocyanate; Fluorosulfonyl imide salt: lithium difluorosulfonyl imide; Lithium salt: Lithium hexafluorophosphate (LiPF6), concentration 1.0 mol / L; Organic solvents: ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate; Linear carboxylic acid ester compounds: methyl acetate; Sulfur-containing substance: 1,3-propanesulfonyl lactone; The mass ratio of linear carboxylic acid esters to sulfur-containing substances is 4:1; Based on the total mass of the electrolyte, the mass percentage of isocyanate compounds (a) is 2%, and the mass percentage of fluorosulfonyl imide salt (b) is 5%. Electrolyte preparation: S1: Solvent premixing; Ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and linear carboxylic acid esters were purified by distillation, with the water content strictly controlled to be below 10 ppm and the free acid (calculated as HF) below 20 ppm. In a reaction vessel at room temperature (25±5℃) and protected by dry nitrogen or argon, EC was added first, followed by DEC, and stirred evenly (0.5-1 hour). Finally, EMC and linear carboxylic acid esters were added to obtain a mixed solvent. The mixed solvent was cooled to 10-20℃ and kept at that temperature.

[0058] S2: The preparation and dissolution of lithium salt; The total LiPF6 feed amount is divided into three parts: Part 1, Part 2, and Part 3. Part 1 accounts for 60%-70% of the total LiPF6 feed amount, Part 2 accounts for 20%-35%, and Part 3 accounts for 5%-10%. The first part of LiPF6 is injected into the reactor through a closed pipe under a nitrogen atmosphere using a vacuum conveying system, so that the powder is instantly entrained and dispersed by the high-speed rotating solvent, and the temperature rise rate is controlled to be less than 3℃ / min. The second part of LiPF6 is added at a rate of 200-400g / min and stirred continuously for 30-60 minutes, with the temperature controlled to be below 30% and the temperature rise rate below 2℃ / min. The third part of LiPF6 is then added in a pulse cycle, with each addition of 20g for 10 seconds and stirring to control the solution temperature at 25-30℃, followed by a 20-second pause in addition. This cycle is repeated until the solution is completely clear and transparent. Finally, 60%-70% of the total amount of lithium fluorosulfonyl imide salt is added and stirred evenly. The sulfur-containing substance was diluted with EMC solvent at a ratio of 1:5 and then slowly dripped into the reaction vessel while stirring until the sulfur-containing substance was evenly dispersed. The isocyanate compound was diluted with carboxylic acid ester solvent at a ratio of 1:4 to obtain a diluted isocyanate compound solution. 70% of the total amount of the diluted isocyanate compound solution was added first and stirred rapidly for 30 minutes. After standing for 15 minutes, the remaining 30% was added.

[0059] S3: Addition and ripening of lithium fluorosulfonyl imide salt Slowly add the 30-40% fluorinated sulfonamide lithium salt reserved in the second step to the system and stir continuously at low speed for 4-8 hours to fully solubilize the components and obtain the electrolyte.

[0060] Negative electrode: Negative electrode active material (artificial graphite), conductive material (conductive carbon black), binder (styrene-butadiene rubber), thickener (sodium carboxymethyl cellulose) Preparation of negative electrode sheet: The negative electrode active material, conductive carbon black, binder, and thickener were thoroughly mixed in an appropriate amount of deionized water solvent at a mass ratio of 96.2:1.0:1.5:1.3 to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly coated onto the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained. The areal density of the negative electrode active material was 10.5 mg / cm³. 2 The compacted density is 1.65 g / cm³. 3 .

[0061] Separator: A single-layer porous polyethylene (PE) membrane with a thickness of 9 μm and a porosity of 42% is selected as the separator. At least one surface of the separator is coated with a heat-resistant coating composed of inorganic alumina (Al2O3) particles and polyvinylidene fluoride (PVDF) binder.

[0062] Preparation method of electrochemical device: The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes, and then wound to form a battery cell. The battery cell is placed in an aluminum-plastic film outer packaging bag and vacuum-baked at 80°C for 24 hours, after which a measured amount of the above-mentioned electrolyte is injected. After vacuum sealing, settling, formation (0.02C constant current charging to 3.6V), and shaping processes, the electrochemical device is obtained.

[0063] In this embodiment, the positive electrode active material may also be at least one of ternary materials, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese oxide; Conductive materials can also be selected from commonly used conductive components in this field, such as carbon nanotubes; The lithium salt may also be selected from at least one of lithium perchlorate, lithium tetrachloroaluminate, lithium iodide, lithium bromide, lithium thiocyanate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium tetraphenylborate, lithium dioxalate borate, lithium tetrafluorooxalate phosphate, lithium nitrate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide. The organic solvent may also be selected from one or more of the following: ethers such as dimethyl ether, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, tri(ethylene glycol) dimethyl ether, 1-2-diethoxyethane, diethoxyethane, ethoxymethoxyethane, 1,3-dimethoxypropane, tetrahydrofuran, 2-methyltetrahydrofuran, and dioxolane; and carbonates such as ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl difluoroacetate, ethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, trifluoroethyl methyl carbonate, and trifluoroethyl ethyl carbonate. The binder and thickener in the negative electrode can also be selected from commonly used components in the field, and can ultimately achieve the effect of this embodiment.

[0064] Examples 2-27 and Comparative Examples 1-7 The electrochemical devices of Examples 2-26 and Comparative Examples 1-5 are based on the components of Example 1, and the components that differ from those of Example 1 are shown in Tables 1-3.

[0065] The preparation methods of the corresponding positive electrode, electrolyte, diaphragm, and negative electrode in the electrochemical devices of Examples 2-21 and Comparative Examples 1-5, as well as the assembly methods of the electrochemical devices, are the same as in Example 1.

[0066] The electrochemical devices prepared in Examples 22-26 have the same composition as those in Example 1, with the only difference being the preparation method of the electrolyte, as detailed below: Example 22

[0067] Compared with Example 1, the only difference in this example is that EC, DEC, EMC and linear carboxylic acid ester compounds are added simultaneously in step S1 during the preparation of the electrolyte.

[0068] Apart from the differences mentioned above, the preparation process of the electrochemical device in this embodiment is strictly consistent with that in Example 1. Example 23

[0069] Compared with Example 1, the only difference in this example is that the lithium salt in step S2 of the electrolyte preparation process is added in a single batch.

[0070] Apart from the differences mentioned above, the preparation process of the electrochemical device in this embodiment is strictly consistent with that in Example 1. Example 24

[0071] Compared with Example 1, the only difference in this example is that in the electrolyte preparation process, the first part of lithium salt in step S2 is 20%-35%, the second part of lithium salt is 60%-70%, and the third part of lithium salt is 5%-10%.

[0072] Apart from the differences mentioned above, the preparation process of the electrochemical device in this embodiment is strictly consistent with that in Example 1. Example 25

[0073] Compared with Example 1, the only difference in this example is that in the electrolyte preparation process, the first part of lithium salt in step S2 is 5%-10%, the second part of lithium salt is 20%-35%, and the third part of lithium salt is 60%-70%.

[0074] Apart from the differences mentioned above, the preparation process of the electrochemical device in this embodiment is strictly consistent with that in Example 1. Example 26

[0075] Compared with Example 1, the only difference in this example is that 100% of the total amount of fluorosulfonylimide lithium salt is added in step S2 during the preparation of the electrolyte.

[0076] Apart from the differences mentioned above, the preparation process of the electrochemical device in this embodiment is strictly consistent with that in Example 1. Example 27

[0077] Compared with Example 1, the only difference in this example is that an equal amount of sodium salt (sodium hexafluorophosphate) is used to replace the lithium salt in the electrolyte, sodium difluorosulfonamide salt is used as the fluorosulfonamide salt, and layered transition metal oxide (NaNiO2) is used as the positive electrode active material.

[0078] The preparation method is the same as in Example 1.

[0079] Comparative Example 6 Compared with Example 27, the only difference in this comparative example is that the content of isocyanate compound a (%) is 5, the content of fluorosulfonyl imide salt b (%) is 20, the content of fluorocarbon adhesive x (%) is 0.1, and x / (a+b) is 0.004.

[0080] The preparation method is described in Example 27.

[0081] Comparative Example 7 Compared with Example 27, the only difference in this comparative example is that the content of isocyanate compound a (%) is 0.1, the content of fluorosulfonamide salt b (%) is 0.1, the content of fluorocarbon adhesive x (%) is 15, and x / (a+b) is 75.

[0082] The preparation method is described in Example 27.

[0083] Table 1 Table 2 Table 3 I. Performance Testing The electrochemical devices fabricated in the above embodiments and comparative examples were subjected to corresponding performance tests according to the following methods.

[0084] (1) 25℃ cycle test: The test method is as follows: In a constant temperature chamber at 25℃±2℃, the electrochemical device is charged to 4.4V at a constant current and voltage of 1C, with a cutoff current of 0.05C, and then discharged to 3V at 1C. Multiple charge-discharge cycles are performed under the above conditions. The capacity retention rate of each battery after 800 cycles is calculated.

[0085] Calculation formula: Capacity retention rate (%) = Discharge capacity (mAh) of the corresponding cycle number / Discharge capacity of the third cycle (mAh) * 100%.

[0086] Each example and comparative example used 5 batteries for testing. The average capacity retention rate of each group of 5 batteries after different cycles is recorded in Table 4.

[0087] Table 4. Cyclic performance test results for each group The experimental results in Table 4 show that when the content of isocyanate compounds, fluorosulfonamide salts, and fluorocarbon binders in the electrochemical device prepared in the embodiments of the present invention meets the condition 0.005≤x / (a+b)≤50, high cycle performance can be achieved. The cycle performance is also affected by the selected components of isocyanate compounds, fluorosulfonamide salts, and fluorocarbon binders, as well as the mass ratio of linear carboxylic acid ester compounds to sulfur-containing substances.

[0088] Compared with Example 1, Comparative Examples 1-3 lacked one or both of the isocyanate compound and fluorosulfonyl imide salt components, resulting in significantly worse cycle performance of the electrochemical devices. In Comparative Examples 4-5, the content relationship of isocyanate compound, fluorosulfonyl imide salt and fluorocarbon binder did not meet the condition 0.005≤x / (a+b)≤50, resulting in significantly worse cycle performance than the Examples.

[0089] Compared with Example 27, the content relationship of isocyanate compounds, fluorosulfonamide salts and fluorocarbon adhesives in Comparative Examples 6-7 does not meet the condition 0.005≤x / (a+b)≤50, resulting in significantly worse cycle performance than in the Example.

[0090] (2) Battery high and low temperature discharge test The discharge performance of the electrochemical devices in Examples 1, 27, and Comparative Examples 1-7 was tested at -20°C, -10°C, 0°C, 5°C, 45°C, and 60°C. The results are shown in Table 5. Figure 1 The test data in the middle.

[0091] Taking a -20℃ battery discharge test as an example: Under 25℃ environmental conditions, discharge the capacity-sorted battery at 0.2C to 3V and let it rest for 5 minutes; then charge it at 0.2C to 4.4V. When the cell voltage reaches 4.4V, switch to constant voltage charging at 4.4V until the charging current is less than or equal to the given cutoff current of 0.05C, and let it rest for 5 minutes. Transfer the fully charged battery to a high and low temperature chamber, set it to -20℃, and let it rest in the chamber for 120 minutes after the temperature is reached. Remove the battery, then discharge it at 0.2C to the cutoff voltage of 3V and let it rest for 5 minutes; then adjust the high and low temperature chamber temperature to 25℃±3℃, and let it rest in the chamber for 60 minutes after the temperature is reached. Remove the battery and charge it at 0.2C to 4.4V. When the cell voltage reaches 4.4V, switch to constant voltage charging at 4.4V until the charging current is less than or equal to the given cutoff current of 0.05C, and let it rest for 5 minutes. Calculate the capacity retention rate of the battery after discharging at -20℃ for 3V.

[0092] Calculation formula: -20℃ discharge 3V capacity retention rate (%) = (-20℃ discharge to 3V discharge capacity / 25℃ discharge to 3V discharge capacity) × 100%.

[0093] Table 5 Discharge Capacity Retention Rate As can be seen from the experimental data in Table 5, the electrochemical device prepared in Example 1 of this invention can maintain a high capacity retention rate and has good environmental stability, whether in a high-temperature environment of 45°C or a low-temperature environment of -20°C.

[0094] Compared with Example 1, Comparative Examples 1-3 lacked one or both of the isocyanate compound and fluorosulfonyl imide salt components, resulting in a significant decrease in the discharge capacity retention rate of the prepared electrochemical devices at low temperature (-20°C) and at room temperature; in Comparative Examples 4-5, the content relationship of isocyanate compound, fluorosulfonyl imide salt and fluorocarbon binder did not meet 0.005≤x / (a+b)≤50, and the final discharge capacity retention rate was significantly worse than that of Example 1.

[0095] Compared with Example 27, the content relationship of isocyanate compounds, fluorosulfonamide salts and fluorocarbon adhesives in Comparative Examples 6-7 did not meet the condition 0.005≤x / (a+b)≤50, and the final discharge capacity retention rate was significantly worse than that of Example 27.

[0096] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electrochemical device comprising a positive electrode, an electrolyte, a diaphragm, and a negative electrode, characterized in that, The electrolyte includes isocyanate compounds, fluorosulfonyl imide salts, metal salts, and organic solvents; Based on the total mass of the electrolyte, the mass percentage of isocyanate compounds (a) is 0.01% to 7%, and the mass percentage of fluorosulfonyl imide salts (b) is 0.1% to 25%. The positive electrode includes a positive electrode active material, a conductive material, and a fluorocarbon binder; Based on the total mass of the positive electrode active material, the mass percentage x of the fluorocarbon binder is 0.05%~10%, and x, a, and b satisfy the relationship: 0.005≤x / (a+b)≤50.

2. The electrochemical device as described in claim 1, characterized in that, The chemical structural formula of the isocyanate compound is: R1 is a substituted or unsubstituted C1-C8 alkane chain, a substituted or unsubstituted C2-C8 olefin chain, a substituted or unsubstituted C2-C8 alkyne chain, a substituted or unsubstituted aromatic ring chain, or a substituted or unsubstituted C1-C8 ether-bonded alkane chain. When substituted, the substituent includes at least one of F or C1-C4 alkyl groups.

3. The electrochemical device as described in claim 2, characterized in that, The isocyanate compounds include at least one of 1,6-hexanediisocyanate, 1,4-butanediisocyanate, 1,5-pentanediisocyanate, octyl 1,8-diisothiocyanate, isophorone diisocyanate, 4,4-diisocyanate dicyclohexylmethane, 4,4'-methylenebis(phenyl isocyanate), and 2,2,4-trimethylhex-1,6-dimethyldiisocyanate.

4. The electrochemical device as described in claim 1, characterized in that, The fluorosulfonyl imide salts include lithium fluorosulfonyl imide salts and sodium fluorosulfonyl imide salts; Fluorocarbon adhesives include at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, and polyvinyl fluoride; The concentration of the metal salt is 0.5~8 mol / L; The metal salts include lithium salts and sodium salts; The organic solvents include one or more of the following: ethers such as dimethyl ether, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, tri(ethylene glycol) dimethyl ether, 1-2-diethoxyethane, diethoxyethane, ethoxymethoxyethane, 1,3-dimethoxypropane, tetrahydrofuran, 2-methyltetrahydrofuran, and dioxolane; and carbonates such as ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl difluoroacetate, ethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, trifluoroethyl methyl carbonate, and trifluoroethyl ethyl carbonate.

5. The electrochemical device as described in claim 1, characterized in that, The electrolyte also includes a linear carboxylic acid ester compound and a sulfur-containing substance; the mass ratio of the linear carboxylic acid ester compound to the sulfur-containing substance is (3-5):

1.

6. The electrochemical device as described in claim 5, characterized in that, The linear carboxylic acid ester compound includes at least one of methyl acetate, ethyl acetate, ethyl propionate, ethyl butyrate, methyl formate, and methyl butyrate. The sulfur-containing substances include at least one of 1,3-propane sulfonyl lactone, methylene disulfonate, vinyl sulfate, 1,3-propene sulfonate lactone, 1,4-butane sulfonyl lactone, ethyl methanesulfonate, butyl methanesulfonate, vinyl sulfite, and 1,3-dithiaane.

7. The electrochemical device as described in claim 6, characterized in that, The preparation process of the electrolyte includes the following steps: S1: Solvent premixing: The organic solvent and the linear carboxylic acid ester compound are mixed and stirred to obtain a mixed solvent, which is then cooled and kept warm for later use. S2: Preparation and dissolution of metal salts: Metal salts are added to the reaction vessel in multiple portions, along with a portion of fluorosulfonamide salts. The mixture is stirred, and sulfur-containing substances are added while stirring. Isocyanate compounds are added in multiple portions. S3: Addition and ripening of fluorosulfonyl imide salts: The remaining fluorosulfonamide salt was added to the system and stirred continuously to obtain the electrolyte.

8. The electrochemical device as described in claim 7, characterized in that, The cooling described in step S1 refers to reducing the temperature to 10-20℃; The step S2, which involves adding the metal salt to the reactor in multiple stages, is as follows: Using a vacuum conveying system under a nitrogen atmosphere, 60%-70% of the total metal salt feed amount is injected through a closed pipe from the powder inlet of the reactor, controlling the temperature rise rate to be less than 3℃ / min; 20%-35% of the total metal salt feed amount is added at a rate of 200-400g / min, with continuous stirring for 30-60 minutes, controlling the temperature to be below 30℃ and the temperature rise rate to be below 2℃ / min; 5%-10% of the total metal salt feed amount is added in a pulsed cyclic feeding process, with each feeding lasting 10 seconds and adding 20g of metal salt while stirring to control the solution temperature at 25-30℃, then pausing the feeding for 20 seconds, and repeating the cycle until the solution is completely clear and transparent, thus completing the feeding process. The portion of fluorosulfonyl imide salt mentioned in step S2 constitutes 60%-70% of the total fluorosulfonyl imide salt; The step S2, which involves adding the isocyanate compound in multiple portions, is as follows: first, add 70% of the total amount of the diisocyanate diluent and stir rapidly for 30 minutes; then, after standing for 15 minutes, add the remaining 30%. The continuous stirring time in step S3 is 4-8 hours.

9. The electrochemical device as described in claim 1, characterized in that, The positive electrode active material includes at least one of ternary materials, high-nickel ternary materials, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese oxide. Alternatively, the positive electrode active material may include at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds; The conductive material of the positive electrode includes at least one of conductive carbon black and carbon nanotubes. The negative electrode includes a negative electrode active material and a conductive material; The negative electrode active material includes one or more of carbonaceous materials, alloy materials, and lithium metal composite materials; The conductive material of the negative electrode includes at least one of conductive carbon black and carbon nanotubes.

10. A method for preparing an electrochemical device as described in any one of claims 1 to 9, characterized in that, The electrochemical device is obtained by assembling the positive electrode, negative electrode, electrolyte, and separator.

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