Thiophene compound, modified positive electrode material, preparation method thereof, and lithium ion battery

Abstract

The present invention provides a thiophene compound, a modified positive electrode material, a preparation method thereof, and a lithium-ion battery. The solid electrolyte coated on the surface of the positive electrode material is modified by the thiophene compound shown in Formula I, and further carbonized to obtain a modified positive electrode composite with a core-shell-shell double layer coating. The thiophene compound can convert the residual alkali on the surface of the oxide solid electrolyte matrix into a favorable component, and the grafted functional groups containing thiophene groups can completely deactivate the metal-hydroxyl active centers on the surface. At the same time, the thiophene compounds can polymerize to form a polymer coating film, which is pyrolyzed to form a secondary coating layer, effectively blocking the side reactions between the electrolyte and the positive electrode material and the side reactions between the solid electrolyte and the solvent. According to research, the modified positive electrode composite positive electrode sheet provided by the present invention is used to prepare lithium-ion batteries, which can achieve a comprehensive improvement in high-temperature cycle and rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a thiophene compound, a modified positive electrode material, a preparation method thereof, and a lithium ion battery. Background Art

[0002] As a key material for batteries, the positive electrode material is a key component that determines the battery voltage and energy density. Currently, the mainstream positive electrode materials are mostly lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, etc. These materials have the common problem of producing side reactions with the electrolyte during the charge and discharge process, which leads to the degradation of the electrode material and a significant decrease in the battery cycle life. At the same time, due to the free HF produced by the decomposition of lithium salts in most electrolytes, the transition metal ions on the surface of the positive electrode are easily corroded in the electrolyte, resulting in the decay of the electrode material and the decay of the battery capacity, which in turn triggers strong side reactions that cause thermal runaway of the battery and explosion.

[0003] At present, it is generally believed that the use of surface coating to isolate the electrode material from the electrolyte can reduce the side reactions of the two and effectively solve the above-mentioned series of problems. Studies have shown that surface coating, as a mainstream method for stabilizing the surface of the positive electrode material, can effectively inhibit the side reactions on the positive electrode surface. There are many coating methods in the prior art. For example, the Chinese patent document with publication number CN 108682819 A discloses a process for directly coating the positive electrode with a solid electrolyte, which mainly uses carbon materials and solid electrolyte materials to perform composite coating modification on the positive electrode material.

[0004] Although this method effectively introduces solid electrolyte materials as a coating layer, solving the rate and room temperature cycle performance, it is difficult to solve the high temperature performance. Summary of the Invention

[0005] In view of this, the present invention provides a thiophene compound, a modified positive electrode material, a preparation method thereof, and a lithium ion battery. The modified positive electrode material provided by the present invention is a composite coated material, which is applied to lithium ion batteries to achieve a comprehensive improvement in high-temperature cycle and rate performance.

[0006] In order to simultaneously solve the rate and high-temperature cycle problems of ternary lithium batteries, the present invention modifies the surface of the positive electrode material by using solid electrolyte composite coating.

[0007] Solid-state electrolyte materials all have excellent structural stability and high ionic conductivity, which can effectively reduce the positive electrode interface impedance and accelerate the migration rate of lithium ions on the positive electrode surface, thereby effectively improving the battery's cycle and rate performance. However, most oxide solid electrolytes have a large amount of residual alkali on the surface, which will cause gelation in the battery. At the same time, the metal-hydroxyl active center groups on the surface of the solid electrolyte are easily oxidized and transformed at high temperatures, and then react with the solvent to capture hydrogen atoms from the solvent molecules, thereby catalyzing the decomposition of the electrolyte, resulting in poor high-temperature cycling performance.

[0008] The present invention provides a thiophene compound having a structure of Formula I:

[0009]

[0010] Wherein, X1 and X2 are independently selected from halogen elements (abbreviated as halogen), including fluorine (F), chlorine (Cl), bromine (Br), etc., preferably bromine; X1 and X2 can be the same or different, preferably both are bromine. X1 and X2 are both in the meta position of the S atom, and the thiophene ring contains α-H, so thiophene molecules can be polymerized. In addition, in formula I, (CH2) 1-2 It can represent one or two methylene groups (CH2CH2).

[0011] In a preferred embodiment of the present invention, the thiophene compound has a structure as shown in Structural Formula A, which can be referred to as Compound A.

[0012]

[0013] Furthermore, the present invention uses the compound A as an example to illustrate its preparation method, but is not limited to the preparation method provided by the present invention:

[0014] First, aluminum trichloride (AlCl3) is preferably used as a catalyst to catalyze the halogen substitution reaction of aldehyde-containing propenylthiophene to obtain an aldehyde-containing halogenated thiophene compound; the halogen substitution reaction is preferably a bromine substitution reaction, which can be carried out in a solvent such as dichloromethane (CH2Cl2) and the reaction temperature is preferably 0°C;

[0015] Then, preferably under the catalytic action of a mixed catalyst of titanium tetrachloride (TiCl4) and zinc powder (Zn powder), the aldehyde-containing halogenated thiophene compound is condensed to obtain Compound A; the halogen element is bromine, the condensation temperature can be -20°C to -10°C, and the solvent involved includes but is not limited to tetrahydrofuran (THF). The specific reaction formula is as follows:

[0016]

[0017] The thiophene compound described herein, having the general structure of Formula I, can effectively modify oxide solid electrolytes, converting residual alkali on their surfaces into beneficial components. The grafting of thiophene-containing functional groups completely deactivates surface metal-hydroxyl active centers. While maintaining the inherent properties of the oxide solid electrolyte, it effectively blocks reactions with solvents, enhancing high-temperature cycling performance. Furthermore, the elimination of residual alkali on the surface effectively avoids phenomena such as gelation caused by excessive alkalinity during homogenization.

[0018] In addition, the raw materials for the synthesis of the thiophene compound represented by Formula I of the present invention are readily available in the market, are low in cost, are highly cost-effective, and are easy to prepare.

[0019] The present invention provides a modified positive electrode material, which comprises, from the inside to the outside, a lithium-containing core, a solid electrolyte shell layer coated on the surface of the lithium-containing core, and a carbon-containing shell layer. The carbon-containing shell layer is formed by carbonization after polymerization of a monomer, and the monomer is the thiophene compound described above.

[0020] The embodiment of the present invention aims to modify the solid electrolyte coating layer coated on the surface of the positive electrode material through the above-mentioned functional compound A with a thiophene structure, and the molecules of compound A can be polymerized to form a polymer coating film. Finally, the outermost polymer coating film is pyrolyzed and a secondary coating is performed to finally prepare a modified positive electrode composite (modified positive electrode material) with a core-shell-shell double-layer coating, that is, the solid electrolyte composite coating effectively improves the problems of structural instability, poor rate performance, and poor high-temperature cycle performance of the positive electrode material.

[0021] Accordingly, the present invention provides a method for preparing a modified positive electrode material, comprising the following steps:

[0022] Providing a lithium-containing positive electrode material coated with a solid electrolyte shell;

[0023] reacting the lithium-containing positive electrode material coated with the solid electrolyte shell with a functional compound, wherein the functional compound is the thiophene compound described above, so that the thiophene compound is grafted onto the surface of the solid electrolyte shell and polymerized into a coating film to obtain an intermediate;

[0024] The intermediate is subjected to pyrolysis treatment under a protective atmosphere to obtain a modified positive electrode material with a double-layer coating structure.

[0025] In the embodiment of the present invention, a lithium-containing positive electrode material coated with a solid electrolyte shell is first prepared, wherein the thickness of the solid electrolyte shell is preferably 200 to 400 nm, and can be 210 to 350 nm. The preparation of the lithium-containing positive electrode material coated with the solid electrolyte shell comprises: dry mixing the lithium-containing positive electrode material raw material and the solid electrolyte, and then sintering at a high temperature to obtain the obtained material.

[0026] The lithium-containing cathode material raw materials described in the present invention correspondingly form a lithium-containing core structure at the innermost part of the material. Further, its composition is selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese oxide. Further still, the present invention preferably selects lithium nickel cobalt manganese oxide, etc.

[0027] In the embodiment of the present invention, the solid electrolyte and the lithium-containing cathode material raw materials are added to a high-speed mixer in proportion for dry mixing for physical mixing, and then through high-temperature sintering, the first coating is completed to form a cathode precursor with a solid electrolyte shell layer. This step cleverly coats the solid electrolyte material evenly on the surface of the cathode material to form a coating shell layer (i.e., the solid electrolyte shell layer coated on the surface of the lithium-containing core), which can directly isolate the cathode material and the electrolyte, while improving the conductivity and enhancing the rate performance. The preparation of the cathode precursor described in the embodiment of the present invention adopts a dry coating method, which not only effectively avoids the problems of complex interface between the cathode material and the electrolyte in wet coating and low process efficiency, but also has a simple process and is easy to industrialize.

[0028] Further, the composition of the solid electrolyte and the shell layer is a NASICON-type oxide solid electrolyte. The chemical formula of the NASICON-type oxide solid electrolyte is Li 1+x A x E 2-x (PO4)3; where the A-site element is one or several of aluminum (Al), lanthanum (La), gallium (Ga), iron (Fe), scandium (Sc), lutetium (Lu), and yttrium (Y); the E-site element is one or several of titanium (Ti), germanium (Ge), zirconium (Zr), hafnium (Hf), and tin (Sn); where 0 ≤ x ≤ 0.5. The solid electrolyte is more preferably lithium aluminum titanium phosphate, with aluminum at the A-site and titanium at the E-site; the chemical formula is: Li 1+y Al y Ti 2-y P3O 12 , where 0.3 < y < 0.6, and it can be 0.35, 0.4, 0.45, or 0.5, etc., which is simply referred to as LATP.

[0029] Preferably, during the preparation of the lithium-containing positive electrode material coated with the solid electrolyte shell, the mass ratio of the lithium-containing positive electrode material raw material to the solid electrolyte is (1-m):m, 0<m≤0.1. Furthermore, the high-temperature sintering temperature is 0.2 to 0.5 times the melting point of the solid electrolyte, for example, the high-temperature sintering temperature is 90 to 300°C, and further 100 to 250°C. In an embodiment of the present invention, the above-mentioned positive electrode material raw material and the coating material can be added to a high-speed mixer according to a mass ratio of (1-m):m, 0<m≤0.1, and preferably mixed at a speed of 800~1000 rpm for 15~25 minutes to obtain a premix; the premix is ​​then put into a fusion coating machine, and the blade speed range can be 2000~4000 rpm. The coating is carried out for 15~30 minutes under a protective environment such as nitrogen, and the coated positive electrode material is subjected to a high temperature treatment in the range of (0.2~0.5)Ta (Ta is the melting point of the coating material), thereby obtaining a positive electrode precursor coated with a solid electrolyte once, which is a lithium-containing positive electrode material coated with a solid electrolyte shell.

[0030] After preparing a lithium-containing positive electrode material coated with a solid electrolyte shell, the embodiment of the present invention reacts it with a functional compound (the thiophene compound described above) to graft the thiophene compound onto the surface of the solid electrolyte shell and polymerize into a coating film; the obtained intermediate is pyrolyzed under a protective atmosphere to obtain a modified positive electrode material with a double-layer coating structure.

[0031] An embodiment of the present invention provides a method for modifying a composite coated positive electrode material with a solid electrolyte, specifically comprising: reacting a synthesized functional compound A, etc., with the solid electrolyte on the surface of the above-mentioned positive electrode precursor to form a chemical bond, so that compound A can be grafted onto the surface of the solid electrolyte. At the same time, the functional group in compound A is polymerizable, and it can evenly form a dense polymer coating layer outside the solid electrolyte coating layer on the surface of the positive electrode particles. Finally, the outermost polymer coating layer is pyrolyzed to obtain a final product having a double-layer coated modified positive electrode composite with a core-shell-shell structure, which is the modified positive electrode material.

[0032] In some embodiments of the present invention, the reaction between the lithium-containing cathode material coated with a solid electrolyte shell and the functional compound is carried out with stirring in the presence of an alkaline solution; the molar ratio of the lithium-containing cathode material to the functional compound is (0.4-0.6):1, further preferably 0.5:1; the alkaline solution is preferably a carbonate aqueous solution with a molar concentration of 0.1-0.2 mol / L. Furthermore, the reaction temperature is 100-120°C, for example, 105-115°C, and the reaction time can be 24-30 hours, specifically 24 hours of stirring reaction.

[0033] Specifically, Compound A and a cathode precursor coated with 200-400nm thick LATP can be combined under a protective atmosphere such as nitrogen. Potassium carbonate (K2CO3) catalyzes the reaction of hydroxyl groups (-OH) on the surface of the solid electrolyte with bromine to form ether bonds, resulting in a surface-grafted modified material. The reaction formula involved is as follows (R-Br is the abbreviation of Compound A, where R contains a polymerizable thiophene structure). Continuing to stir under alkaline conditions (sodium carbonate and potassium carbonate solutions) allows polymerization between the surface-grafted Compound A molecules to form a dense polymer coating, which is an intermediate with a core-shell structure.

[0034]

[0035] Finally, the intermediate with a core-shell structure is pyrolyzed under a protective environment such as nitrogen for 20 to 30 minutes. The pyrolysis temperature range is preferably 200 to 300°C, further 210 to 290°C. After cooling, a positive electrode composite with a core-shell-shell double-layer coating structure is obtained, which is a modified positive electrode material with a double-layer coating structure.

[0036] The positive electrode composite prepared by the embodiment of the present invention adopts a composite coating method, which not only ensures the structural stability of the positive electrode material, but also directly isolates the positive electrode material and the electrolyte, effectively reducing the side reactions of the positive electrode and the electrolyte; at the same time, after the functional compound shown in the synthetic formula I modifies the solid electrolyte in the positive electrode precursor, the polymer coating formed is further pyrolyzed into a carbon-containing shell, which not only improves the electronic conductivity while maintaining the original excellent properties, but also cooperates with the inherent fast ion conductivity of the solid electrolyte to improve both electronic conductivity and ion conductivity, thereby significantly alleviating the polarization phenomenon under rapid charge and discharge and enhancing the rate performance of the battery. Furthermore, the residual alkali in the solid electrolyte is converted into a favorable component, which blocks the high-temperature side reaction of the solid electrolyte and the solvent from the source, inhibits the dissolution of transition metal elements, and thus improves the high-temperature cycle performance of the lithium battery.

[0037] The present invention provides a positive electrode sheet, wherein the modified positive electrode material described above, or the modified positive electrode material obtained by the preparation method described above, is used as the active material. Specifically, the positive electrode sheet comprises an active material, a conductive agent, a binder, and a current collector, wherein the active material is the positive electrode composite described above.

[0038] Furthermore, the conductive agent is selected from one or more of carbon black, acetylene black, Ketjen black, graphene, and carbon nanotubes; in the present invention, carbon black and carbon nanotubes are preferred.

[0039] Furthermore, the binder is selected from one or more of polyvinylidene fluoride, polyethylene oxide, and polyacrylic acid; polyvinylidene fluoride is preferred in the present invention.

[0040] Furthermore, the current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and composite current collector; carbon-coated aluminum foil is preferred in the present invention.

[0041] Preferably, in an embodiment of the present invention, the active material, conductive agent, and binder of the positive electrode are mixed in a mass ratio of 95-97:1-3:1-2, and the solid content is adjusted to 65-69% by adding N-methylpyrrolidone. After homogenization, coating, drying, rolling, slitting, and die-cutting, a positive electrode sheet containing a positive electrode composite can be obtained.

[0042] The present invention provides a lithium-ion battery comprising the aforementioned positive electrode sheet. The lithium-ion battery is specifically a solid-liquid hybrid lithium-ion battery, which includes, in addition to the aforementioned positive electrode sheet containing the positive electrode composite, a negative electrode, a separator, and a non-aqueous electrolyte.

[0043] Furthermore, the active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, metallic lithium, a silicon-carbon composite material, and silicon monoxide. These materials may be used alone or in combination in the present invention, with artificial graphite being preferred. The present invention does not particularly limit the materials for the negative electrode; those commonly used in the art may be used.

[0044] Furthermore, the diaphragm is selected from polypropylene (PP) and polyethylene (PE) diaphragms; the present invention prefers PE diaphragms.

[0045] Furthermore, the non-aqueous electrolyte is a standard non-aqueous electrolyte comprising an organic solvent, a lithium salt, and an additive. The solid-liquid hybrid lithium-ion battery has good compatibility between its positive and negative electrodes and the electrolyte.

[0046] Furthermore, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiODFB) and lithium difluorodioxalatophosphate (LiDODFP).

[0047] Furthermore, the organic solvent is at least two of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate and ethyl butyrate;

[0048] Furthermore, the additive is any one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, vinyl sulfate or tris(trimethylsilyl)phosphate.

[0049] Furthermore, the mass fraction of the organic solvent in the non-aqueous electrolyte is 82.5-85.5%; the mass fraction of the lithium salt in the non-aqueous electrolyte is 12-14.5%; and the mass fraction of the additive in the non-aqueous electrolyte is 0.1-5.5%.

[0050] In some embodiments of the present invention, button batteries can be manufactured in a glove box. The negative electrode, diaphragm, positive electrode sheet, stainless steel gasket, and spring are stacked in order, injected with a non-aqueous electrolyte, sealed with a hydraulic crimping machine, left to stand, and aged to obtain a solid-liquid hybrid battery sample.

[0051] In summary, the embodiment of the present invention is to coat the solid electrolyte on the surface of the positive electrode material once by physically mixing and sintering the solid electrolyte with the positive electrode material to form a positive electrode precursor; then the solid electrolyte is modified according to the synthesized functional compound, and the thiophene compound shown in Formula I is grafted onto the solid electrolyte on the surface of the positive electrode precursor. The polymerizable group in the thiophene compound can form a dense polymer conductive coating layer on the outermost layer of the solid electrolyte coating layer on the surface of the positive electrode material. Finally, the outermost polymer coating layer is used as a carbon source, and after heat treatment, a dense coating layer is formed on the outermost layer, thereby forming a modified positive electrode material (positive electrode composite) with a core-shell-shell double-layer coating structure. This positive electrode composite has a double-layer coating structure and has higher electronic conductivity and ionic conductivity. It can give the charge a rapid transfer capability between the interface and the bulk phase, while isolating the side reactions between the positive electrode material and the electrolyte, the solid electrolyte and the solvent.

[0052] After testing, it was found that the solid-liquid hybrid lithium-ion battery prepared using a positive electrode composite can exhibit better electrochemical performance and better safety performance compared to conventional systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a SEM image of the positive electrode composite 1 in Example 1;

[0054] Figure 2 1 is a capacity-voltage comparison curve of Example 1 and Comparative Example 1;

[0055] Figure 3 The figure is a comparison chart of the discharge performance at different rates of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings and other figures in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0057] In order to better illustrate the present invention, the following examples are further illustrated. Unless otherwise specified, the various reagents and raw materials used in the present invention are all commercially available products or products that can be prepared by recognized methods. Unless otherwise specified, the ratios involved are all weight ratios.

[0058] Regarding the preparation of compound A, the specific steps are as follows:

[0059]

[0060] Under a nitrogen atmosphere, 2-formaldehyde-3-propenylthiophene (13.68 g, 0.09 mol) and 200 mL of ultra-dry dichloromethane were added to a 500 mL three-necked flask equipped with a magnetic rotor. The reaction mixture was then transferred to a low-temperature reactor and stirred, cooled to 0°C. Aluminum trichloride (26.88 g, 0.20 mol) was then gradually added to the solution in multiple portions, while maintaining the temperature of the reaction mixture at 0°C. Liquid bromine (5.00 mL, 0.1 mol) was then added, and the mixture was stirred and reacted. After 3 h, the low-temperature reactor was removed, and the mixed solution was poured into 300 mL of ice together with 100 mL of 1 M aqueous hydrochloric acid solution and stirred for 30 min.

[0061] The organic layer was then separated, and the solvent removed under reduced pressure. The residue was purified by silica gel short column chromatography using n-hexane as the eluent. The solvent was removed by rotary evaporation to obtain the intermediate brominated monomer, 2-formaldehyde-3-propenyl-4-bromothiophene, in a 92.3% yield. GC-MS (m / z): calcd. for C8H7BrOS[M+1]+, 229.94, found 229.97.

[0062] Under a nitrogen atmosphere, 2-formaldehyde-3-propenyl-4-bromothiophene (11.50 g, 50.00 mmol) and 100 mL of ultra-dry tetrahydrofuran were added to a 250 mL three-necked flask equipped with a magnetic rotor. The flask was then transferred to a low-temperature reactor and stirred. After the system temperature dropped to the preset temperature of -18°C, titanium tetrachloride (6.5 mL) was slowly added dropwise and allowed to stand for 30 minutes. After the addition was complete, stirring was continued for 30 minutes. Zinc powder (7.8 g) was then added in small portions over 30 minutes. The mixture was stirred and reacted at -18°C for 1 hour. The low-temperature reactor was then removed and the reaction continued at room temperature for 3 hours.

[0063] The reaction was quenched by adding 100 mL of ice water, and the resulting solid was collected by filtration and dissolved in 80 mL of dichloromethane. Insoluble inorganic matter was removed by a second filtration. The filtrate was evaporated, and the residue was recrystallized from n-hexane to obtain compound A with a yield of 94.7%. GC-MS (m / z): calculated for C 16 H 14 Br2S2[M+1]+,427.89, found 427.92.

[0064] Compound B was prepared in the following steps:

[0065]

[0066] Under a nitrogen atmosphere, 2-formaldehyde-3-butenylthiophene (14.94 g, 0.09 mol) and 200 mL of ultra-dry dichloromethane were added to a 500 mL three-necked flask equipped with a magnetic rotor. The reaction mixture was then transferred to a low-temperature reactor and stirred, cooled to 0°C. Aluminum trichloride (26.88 g, 0.20 mol) was then gradually added to the solution in multiple portions, while maintaining the temperature of the reaction mixture at 0°C. Liquid bromine (5.00 mL, 0.1 mol) was then added, and the mixture was stirred for reaction. After 3 h, the low-temperature reactor was removed, and the mixed solution was poured into 300 mL of ice together with 100 mL of 1 M aqueous hydrochloric acid solution and stirred for 30 min.

[0067] The organic layer was then separated, and the solvent removed under reduced pressure. The residue was purified by silica gel short column chromatography using n-hexane as the eluent. After removing the solvent by rotary evaporation, the intermediate brominated monomer, 2-formaldehyde-3-butenyl-4-bromothiophene, was obtained in a 90.9% yield. GC-MS (m / z): calcd. for C9H9BrOS, 243.96, found 243.86.

[0068] Under a nitrogen atmosphere, 2-formaldehyde-3-butenyl-4-bromothiophene (12.20 g, 50.00 mmol) and 100 mL of ultra-dry tetrahydrofuran were added to a 250 mL three-necked flask equipped with a magnetic rotor. The flask was then transferred to a low-temperature reactor and stirred. After the system temperature dropped to the preset temperature of -18°C, titanium tetrachloride (6.5 mL) was slowly added dropwise and allowed to stand for 30 minutes. After the addition was complete, stirring was continued for 30 minutes. Zinc powder (7.8 g) was then added in small portions over 30 minutes. The mixture was stirred and reacted at -18°C for 1 hour. The low-temperature reactor was then removed and the reaction continued at room temperature for 3 hours.

[0069] The reaction was quenched by adding 100 mL of ice water, and the resulting solid was collected by filtration and dissolved in 80 mL of dichloromethane. Insoluble inorganic matter was removed by a second filtration. The filtrate was evaporated, and the residue was recrystallized from n-hexane to obtain compound B with a yield of 91.8%. GC-MS (m / z): calculated for C 18 H 18 Br2S2,455.92,found 456.12.

[0070] Example 1

[0071] The preparation of the positive electrode precursor 1 is as follows:

[0072] The positive electrode material 8 series nickel cobalt manganese oxide (NCM811) 90.0, LATP (Li 1.4 Al 0.4 Ti 1.6 10.0 g of (PO4)3) was placed in a high-speed mixer and premixed at 1000 rpm for 20 minutes. The resulting premix was placed in a fusion coating machine and operated at 2000 rpm for 30 minutes. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 hours under a nitrogen blanket to obtain positive electrode precursor 1 (the thickness of the primary coating shell was between 200 and 400 nm).

[0073] The preparation of intermediate 1 is as follows:

[0074] To a DMF (1000 mL) solution at room temperature, cathode precursor 1 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and potassium carbonate (13.8 g, 0.1 mol) were added. Stirring was started, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, it was cooled to room temperature, poured into ice water (3000 mL), filtered, and washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain a modified cathode precursor 1. This was then added to alkaline conditions, stirred evenly for 30 min, filtered, and dried to obtain intermediate 1.

[0075] The preparation steps of the positive electrode composite 1 are as follows:

[0076] 10.0 g of intermediate 1 was placed in a fusion coating machine and operated at 2000 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 200°C for 3 h under a nitrogen blanket to obtain cathode composite 1.

[0077] The positive electrode composite 1 in Example 1 was subjected to SEM testing, and the results are shown in Figure 1 .

[0078] Figure 1 is a scanning electron microscope SEM image of the positive electrode composite 1, such as Figure 1 As shown, it can be clearly seen that the surface of the positive electrode composite 1 is covered with a dense coating layer, which is uniform and dense, and the size is at the micron level.

[0079] Prepare the electrolyte 1 sample as follows:

[0080] In an argon glove box with a water and oxygen content of ≤0.1ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed in a volume ratio of 10:15:65:10 to obtain an organic solvent. Subsequently, lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiPO2F2) were slowly added to the organic solvent. After complete dissolution, vinylene carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), and vinyl sulfate (DTD) were added and stirred evenly to obtain an electrolyte sample. The amounts of LiPF6, LiPO2F2, organic solvent, VC, PS, FEC, and DTD used were 11%, 1%, 82.5%, 0.5%, 1.5%, 2.5%, and 1% of the total mass of the electrolyte, respectively.

[0081] Prepare the experimental battery 1 sample, the specific steps are as follows:

[0082] The positive electrode composite 1, conductive agent carbon black (Super P), conductive agent carbon nanotubes (CNT, NMP solution with a content of 4% by mass), and binder polyvinylidene fluoride (PVDF, NMP solution with a content of 5% by mass) were weighed and mixed in a mass ratio of 97:1.2:0.8:1. After mixing, an appropriate amount of NMP was added to control the theoretical solid content to 65%. A planetary homogenizer was used to homogenize the mixture to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of a 17 μm thick carbon-coated aluminum foil by transfer coating. After drying, rolling, and cutting, a positive electrode disc with a diameter of 12 mm was obtained.

[0083] The negative electrode material, artificial graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC, 1.5% by mass in deionized water), and the binder styrene-butadiene rubber (SBR, 48% by mass in deionized water) were mixed in a mass ratio of 95:1:1.5:2.5. After mixing, deionized water was added to control the theoretical solid content to 52%. The negative electrode slurry was homogenized using a planetary homogenizer and evenly coated on both sides of a 17μm-thick carbon-coated copper foil by transfer coating. After drying, roller pressing, and cutting, negative electrode discs with a diameter of 14mm were obtained. The N / P ratio of the positive and negative electrodes was 1.1.

[0084] A button cell was prepared in a glove box with a water and oxygen value of ≤0.1 ppm. The negative electrode sheet, separator, positive electrode sheet, stainless steel gasket, and spring were stacked in order, 80 μL of electrolyte was injected, and the battery was sealed using a hydraulic crimping machine. The battery was allowed to stand for 12 h and aged to obtain experimental cell 1.

[0085] Example 2

[0086] The preparation of the positive electrode precursor 2 is as follows:

[0087] 91.0 g of lithium nickel cobalt manganese oxide (811) and 9.0 g of LATP were placed in a high-speed mixer and premixed at 900 rpm for 25 min. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 25 min. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 h under a nitrogen blanket to obtain positive electrode material precursor 2.

[0088] The preparation of intermediate 2 is as follows:

[0089] To a DMF (1000 mL) solution at room temperature, cathode material precursor 2 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol) and sodium carbonate (10.6 g, 0.1 mol) were added, stirring was started, and the mixture was stirred at 120 ° C for 24 h. After the reaction was completed, it was cooled to room temperature and the reaction mixture was poured into ice water (3000 mL). After filtering, it was washed three times with 300 mL of chloroform and ethanol respectively, and dried to obtain the modified cathode precursor 2. It was then added to alkaline conditions, stirred evenly for 30 minutes, filtered, and dried to obtain intermediate 2.

[0090] The preparation steps of the positive electrode composite 2 are as follows:

[0091] 10.0 g of intermediate 2 was placed in a fusion coating machine and operated at 2000 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 250°C for 3 h under a nitrogen blanket to obtain cathode composite 2.

[0092] The same operation as in Example 1 was followed to prepare electrolyte sample 2, except that the amounts of LiPF6, LiPO2F2, organic solvent, VC, PS, and FEC used were 12.5%, 1%, 83.5%, 0.5%, 0.5%, and 2% of the total mass of the electrolyte, respectively.

[0093] The same operation as in Example 1 was followed to prepare an experimental battery 2, except that the positive electrode sheet prepared from the positive electrode composite 2 was used.

[0094] Example 3

[0095] The preparation of the positive electrode precursor 3 is as follows:

[0096] 92.0 g of lithium nickel cobalt manganese oxide (811) and 8.0 g of LATP were placed in a high-speed mixer and premixed at 1800 rpm for 30 min. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 25 min. The coated cathode material was placed in a tubular furnace and treated at 100°C for 2 h under a nitrogen blanket to obtain cathode precursor 3.

[0097] The preparation of intermediate 3 is as follows:

[0098] To a DMF (1000 mL) solution at room temperature, cathode precursor 3 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was started, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, it was cooled to room temperature, poured into ice water (3000 mL), filtered, and washed three times with 300 mL of chloroform and ethanol, respectively. After drying, the modified cathode precursor 3 was obtained, which was then added to alkaline conditions, stirred evenly for 30 min, and filtered and dried to obtain intermediate 3.

[0099] The preparation steps of the positive electrode composite 3 are as follows:

[0100] 10.0 g of intermediate 3 was placed in a fusion coating machine and operated at 2000 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 200°C for 3 h under a nitrogen blanket to obtain cathode composite 3.

[0101] The same operation as in Example 1 was followed to prepare electrolyte sample 3, except that the amounts of LiPF6, LiPO2F2, organic solvent, VC, PS, and FEC used were 11.5%, 0.5%, 85.5%, 1%, 0.5%, and 1% of the total mass of the electrolyte, respectively.

[0102] The same operation as in Example 1 was followed to prepare an experimental battery 3, except that the positive electrode sheet prepared from the positive electrode composite 3 was used.

[0103] Example 4

[0104] The preparation of the positive electrode precursor 4 is as follows:

[0105] 93.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 7.0 g of LATP were placed in a high-speed mixer and premixed at 2000 rpm for 30 min. The resulting premix was placed in a fusion coating machine and operated at 3000 rpm for 25 min. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 h under a nitrogen blanket to obtain positive electrode precursor 4.

[0106] The preparation of intermediate 4 is as follows:

[0107] To a DMF (1000 mL) solution at room temperature, cathode precursor 4 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was initiated, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature and poured into ice water (3000 mL). After filtration, the mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 4. This was then added to alkaline conditions, stirred evenly for 30 min, and filtered to dryness to obtain intermediate 4.

[0108] The preparation steps of the positive electrode composite 4 are as follows:

[0109] 10.0 g of intermediate 4 was placed in a fusion coating machine and operated at 2500 rpm for 25 min. The coated cathode material was placed in a tube furnace and treated at 200°C for 3 h under a nitrogen blanket to obtain cathode composite 4.

[0110] The same operation as in Example 1 was followed to prepare electrolyte sample 4, except that the amounts of LiPF6, LiPO2F2, organic solvent, VC, PS, and FEC used were 12%, 1%, 84%, 1%, 0.5%, and 1.5% of the total mass of the electrolyte, respectively.

[0111] An experimental battery 4 was prepared by the same operation as in Example 1, except that the positive electrode sheet prepared from the positive electrode composite 4 was used.

[0112] Example 5

[0113] The preparation of the positive electrode precursor 5 is as follows:

[0114] 94.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 6.0 g of LATP were placed in a high-speed mixer and premixed at 2000 rpm for 30 minutes. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 25 minutes. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 hours under a nitrogen blanket to obtain positive electrode precursor 5.

[0115] The preparation of intermediate 5 is as follows:

[0116] To a DMF (1000 mL) solution at room temperature, cathode precursor 5 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was initiated, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature and poured into ice water (3000 mL). After filtration, the mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 5. This was then added to alkaline conditions, stirred evenly for 30 min, and filtered to dryness to obtain intermediate 5.

[0117] The preparation steps of the positive electrode composite 5 are as follows:

[0118] 10.0 g of intermediate 5 was placed in a fusion coating machine and operated at 2800 rpm for 25 min. The coated cathode material was placed in a tube furnace and treated at 300°C for 2 h under a nitrogen blanket to obtain cathode composite 5.

[0119] The same operation as in Example 1 was followed to prepare electrolyte sample 5, except that the amounts of LiPF6, LiPO2F2, organic solvent, VC, PS, and FEC used were 13.5%, 1%, 82.5%, 1%, 1%, and 1% of the total mass of the electrolyte, respectively.

[0120] The same operation as in Example 1 was followed to prepare an experimental battery 5, except that a different compound was used, and the positive electrode sheet prepared from the positive electrode composite 5 was used.

[0121] Example 6

[0122] The preparation of the positive electrode precursor 6 is as follows:

[0123] 95.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 5.0 g of LATP were placed in a high-speed mixer and premixed at 2000 rpm for 30 minutes. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 25 minutes. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2.5 hours under a nitrogen blanket to obtain positive electrode precursor 6.

[0124] The preparation of intermediate 6 is as follows:

[0125] To a DMF (1000 mL) solution at room temperature, cathode material precursor 6 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was started, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, it was cooled to room temperature and poured into ice water (3000 mL). After filtering, it was washed three times with 300 mL of chloroform and ethanol respectively. After drying, the modified cathode precursor 6 was obtained. It was then added to alkaline conditions, stirred evenly for 30 min, and filtered and dried to obtain intermediate 6.

[0126] The preparation steps of the positive electrode composite 6 are as follows:

[0127] 10.0 g of intermediate 6 was placed in a fusion coating machine and operated at 2500 rpm for 25 min. The coated cathode material was placed in a tube furnace and treated at 300°C for 2 h under a nitrogen blanket to obtain cathode composite 6.

[0128] The same operation as in Example 1 was followed to prepare electrolyte sample 1. This example uses electrolyte sample 1.

[0129] The same operation as in Example 1 was followed to prepare an experimental battery 6, except that a different compound was used, and a positive electrode sheet prepared from the positive electrode composite 6 was used.

[0130] Example 7

[0131] The preparation of the positive electrode precursor 7 is as follows:

[0132] 96.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 4.0 g of LATP were placed in a high-speed mixer and premixed at 2000 rpm for 30 minutes. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 30 minutes. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 hours under a nitrogen blanket to obtain positive electrode precursor 7.

[0133] The preparation of intermediate 7 is as follows:

[0134] To a DMF (1000 mL) solution at room temperature, cathode precursor 7 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was started, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, it was cooled to room temperature and poured into ice water (3000 mL). After filtering, the reaction mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 7. This was then added to alkaline conditions, stirred evenly for 30 min, and filtered and dried to obtain intermediate 7.

[0135] The preparation of the positive electrode composite 7 is carried out in the following steps:

[0136] 10.0 g of intermediate 7 was placed in a fusion coating machine and operated at 2500 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 300°C for 2 h under a nitrogen blanket to obtain cathode composite 7.

[0137] The same operation as in Example 1 was followed to prepare electrolyte sample 2. This example uses electrolyte sample 2.

[0138] The same operation as in Example 1 was followed to prepare an experimental battery 7, except that a different compound was used, and a positive electrode sheet prepared from the positive electrode composite 7 was used.

[0139] Example 8

[0140] The preparation of the positive electrode precursor 8 is as follows:

[0141] 97.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 3.0 g of LATP were placed in a high-speed mixer and premixed at 2000 rpm for 30 min. The resulting premix was then placed in a fusion coating machine and operated at 3000 rpm for 20 min. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 h under a nitrogen blanket to obtain positive electrode precursor 8.

[0142] The preparation of intermediate 8 is as follows:

[0143] To a DMF (1000 mL) solution at room temperature, cathode material precursor 8 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was initiated, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature and poured into ice water (3000 mL). After filtration, the mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 8. This was then added to alkaline conditions, stirred uniformly for 30 min, and filtered and dried to obtain intermediate 8.

[0144] The preparation steps of the positive electrode composite 8 are as follows:

[0145] 10.0 g of intermediate 8 was placed in a fusion coating machine and operated at 2500 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 250°C for 2 h under a nitrogen blanket to obtain cathode composite 8.

[0146] The same operation as in Example 1 was followed to prepare electrolyte sample 3. This example uses electrolyte sample 3.

[0147] The same operation as in Example 1 was followed to prepare an experimental battery 8, except that a different compound was used, and a positive electrode sheet prepared from the positive electrode composite 8 was used.

[0148] Example 9

[0149] The preparation of the positive electrode precursor 9 is as follows:

[0150] 98.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 2.0 g of LATP were placed in a high-speed mixer and premixed at 2500 rpm for 25 min. The resulting premix was then placed in a fusion coating machine and operated at 2500 rpm for 25 min. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 h under a nitrogen blanket to obtain positive electrode precursor 9.

[0151] The preparation of intermediate 9 is as follows:

[0152] To a DMF (1000 mL) solution at room temperature, cathode precursor 9 (19.1 g, 0.05 mol), compound A (42.8 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was initiated, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature and poured into ice water (3000 mL). After filtration, the mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 9. This was then added to alkaline conditions, stirred evenly for 30 min, and filtered to dryness to obtain intermediate 9.

[0153] The preparation of the positive electrode composite 9 is as follows:

[0154] 10.0 g of intermediate 9 was placed in a fusion coating machine and operated at 2500 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 250°C for 3 h under a nitrogen blanket to obtain cathode composite 9.

[0155] The same operation as in Example 1 was followed to prepare electrolyte sample 4. This example uses electrolyte sample 4.

[0156] The same operation as in Example 1 was followed to prepare an experimental battery 9, except that a different compound was used, and a positive electrode sheet prepared from the positive electrode composite 9 was used.

[0157] Example 10

[0158] The preparation of the positive electrode precursor 10 is carried out in the following specific steps:

[0159] 99.0 g of positive electrode lithium nickel cobalt manganese oxide (811) and 1.0 g of LATP were placed in a high-speed mixer and premixed at 2500 rpm for 30 minutes. The resulting premix was then placed in a fusion coating machine and operated at 2500 rpm for 25 minutes. The coated positive electrode material was placed in a tubular furnace and treated at 100°C for 2 hours under a nitrogen blanket to obtain positive electrode precursor 10.

[0160] The preparation of intermediate 10 is as follows:

[0161] To a DMF (1000 mL) solution at room temperature, cathode precursor 10 (19.1 g, 0.05 mol), compound B (45.6 g, 0.1 mol), and sodium carbonate (10.6 g, 0.1 mol) were added. Stirring was initiated, and the mixture was stirred at 120°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature and poured into ice water (3000 mL). After filtering, the mixture was washed three times with 300 mL of chloroform and ethanol, respectively, and dried to obtain the modified cathode precursor 10. This was then added to alkaline conditions, stirred uniformly for 30 min, and filtered and dried to obtain intermediate 10.

[0162] The preparation steps of the positive electrode composite 10 are as follows:

[0163] 10 g of the intermediate 10 was placed in a fusion coating machine and operated at 3000 rpm for 30 min. The coated cathode material was placed in a tube furnace and treated at 300°C for 2 h under a nitrogen blanket to obtain the cathode composite 10.

[0164] The same operation as in Example 1 was followed to prepare electrolyte sample 5. This example uses electrolyte sample 5.

[0165] The same operation as in Example 1 was followed to prepare an experimental battery 10 , except that a different compound was used, and a positive electrode sheet prepared from the positive electrode composite 10 was used.

[0166] Comparative Example 1

[0167] The same operation as in Example 1 was followed to prepare a sample of electrolyte 1, which was used in this comparative example.

[0168] The experimental battery 11 was prepared by the same operation as in Example 1, except that the positive electrode material used was uncoated lithium nickel cobalt manganese oxide (811).

[0169] Comparative Example 2

[0170] The same operation as in Example 1 was followed to prepare a sample of electrolyte 1, which was used in this comparative example.

[0171] The experimental battery 12 was prepared by the same operation as in Example 1, except that the positive electrode material used was a once-coated lithium nickel cobalt manganese oxide precursor (811).

[0172] Comparative Example 3

[0173] The same operation as in Example 1 was followed to prepare a sample of electrolyte 1, which was used in this comparative example.

[0174] The experimental battery 13 was prepared by the same operation as in Example 1, except that the positive electrode material used was a mixture of a once-coated lithium nickel cobalt manganese oxide precursor (811) and compound A.

[0175] The lithium ion batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3 were subjected to cycle performance tests and electrochemical tests, and the test contents are as follows:

[0176] Specific capacity test:

[0177] The prepared lithium-ion battery was placed in a constant temperature room at an ambient temperature of 25°C and a current of 0.1C for the first charge and discharge curve test. Figure 2 Capacity-voltage curves of Example 1 and Comparative Example 1.

[0178] Battery room temperature cycle test

[0179] The prepared lithium-ion battery was placed in a constant temperature room at an ambient temperature of 25°C, with a current of 1C and a voltage of 4.2V, and constant current and constant voltage charging to a cutoff current of 0.05C. It was then discharged at a constant current of 1C to a voltage of 3V (the value of b depends on the positive electrode material) and cycled for 100 cycles. The capacity retention rate was recorded, and the nth cycle capacity retention rate (%) = (nth cycle discharge specific capacity / first cycle discharge specific capacity) * 100%.

[0180] Battery high temperature cycle test

[0181] The prepared lithium-ion battery was placed in a thermostat at 45°C or 60°C with a constant current and constant voltage charge at a current of 1C and a voltage of 4.2V to a cutoff current of 0.05C. It was then discharged at a constant current of 1C to a voltage of 3V. The cycle was repeated for 80 or 50 cycles, and the capacity retention rate was recorded. The capacity retention rate at the nth cycle (%) = (discharge capacity at the nth cycle / discharge capacity at the first cycle) * 100%.

[0182] Battery rate discharge test

[0183] The prepared lithium-ion battery was charged at a constant current and constant voltage of 1C and 4.2V in a constant temperature room at 25°C to a cutoff current of 0.05C. It was then discharged at constant currents of 0.2C / 0.5C / 1C / 2C / 3 / C / 0.2C to a voltage of 3V. The capacity retention was recorded: capacity retention at different rates (%) = (discharge capacity at different rates / discharge capacity at 0.2C) * 100%.

[0184] Figure 2 The first charge and discharge curves of Example 1 and Comparative Example 1 at 0.1C. At a charge and discharge current density of 0.1C, the first discharge capacity of Example 1 is 206.0 mAh·g -1 The first coulombic efficiency is as high as 91.38%; the first discharge capacity of comparative example 1 is 204mAh·g -1 The first coulombic efficiency reached 89.12%, indicating that this composite coating can improve the electrochemical performance of the positive electrode material.

[0185] Solid-liquid hybrid lithium batteries were prepared using the positive electrode active materials in Examples 1 to 10 and Comparative Examples 1 to 3. The battery performance test results are shown in Table 1.

[0186] Table 1. Performance test results of lithium ion batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3

[0187]

[0188] As can be seen from Table 1, the positive electrode composites prepared in Examples 1 to 10 are used in solid-liquid hybrid lithium batteries, and at different cycle test temperatures, they all show better capacity retention than those of Comparative Examples 1 to 3, proving that the present invention significantly improves the electrical performance of lithium batteries by using a solid electrolyte composite to coat the positive electrode material.

[0189] It is particularly noteworthy that, compared with Example 1, the untreated lithium nickel cobalt manganese oxide (811) used in Comparative Example 1 exhibits cycle performance far lower than that of Example 1, while Comparative Example 2 is a lithium nickel cobalt manganese oxide precursor that has only been coated with a solid electrolyte once. Compared with Comparative Example 1, although the room temperature cycle performance is improved, the high temperature (45-60°C) cycle performance is still poor; Comparative Example 3 adds compound A on the basis of Comparative Example 2, but the high temperature cycle performance is less improved and the effect is not significant.

[0190] The above test results can be attributed to the ingenious coating of the oxide solid electrolyte on the positive electrode material in the present invention, forming a core-shell-shell double-layer coating structure, which can directly isolate the contact between the positive electrode material and the electrolyte, effectively preventing the side reactions between the two. At the same time, the present invention innovatively introduces a functional compound with formula I structure to modify the solid electrolyte on the coating layer, converting the residual alkali in the solid electrolyte into beneficial components, blocking the high-temperature side reaction of the solid electrolyte and the solvent from the source, alleviating the side reaction between the electrolyte and the positive electrode as a whole, inhibiting the dissolution of transition metal elements, and thereby improving the high-temperature cycle performance of the lithium battery.

[0191] The solid-liquid hybrid lithium battery was prepared by using Example 1 and Comparative Example 1, and the rate discharge performance test results are as follows: Figure 3 As shown, it can be seen that the solid-liquid hybrid lithium battery prepared in Example 1 exhibits a better capacity retention rate than that of Comparative Example 1, proving that the nickel cobalt manganese oxide positive electrode material of the present invention, which is composite-coated with an oxide solid electrolyte, has a significant effect on improving the rate discharge performance of the nickel cobalt manganese oxide battery. This test result is mainly due to the presence of an oxide solid electrolyte layer and an outermost coating layer in the modified positive electrode composite with a double-layer coating structure obtained by the composite coating method, which can form a conductive network during the battery charge and discharge process, thereby improving the electron conduction capacity and coordinating the inherent fast ion conduction capacity of the oxide solid electrolyte. It can take into account the improvement of both electronic conductivity and ion conductivity, thereby significantly alleviating the polarization phenomenon during rapid charge and discharge, so as to achieve the purpose of enhancing the battery rate capacity.

[0192] The present invention adopts a composite coating method to complete the primary coating of the positive electrode material and the solid electrolyte through physical mixing and high-temperature sintering, and then uses a method of modifying the solid electrolyte by synthesizing a functional compound. Compound A can be grafted onto the positive electrode material containing a solid electrolyte coating layer on the surface, and a dense polymer coating layer is formed on the outside of the solid electrolyte coating layer by utilizing the reaction between compound A and residual alkali and the polymerizable groups contained in the compound A. Finally, the polymer coating layer is heat-treated to complete the secondary coating, and finally a stable positive electrode composite with a double-layer core-shell-shell structure is formed. The composite composite has higher electronic conductivity and ionic conductivity, can provide a fast charge transfer capability between the interface and the bulk phase, and simultaneously blocks side reactions between the positive electrode material and the electrolyte, and between the solid electrolyte and the solvent. Finally, a solid-liquid hybrid lithium ion battery prepared using the positive electrode composite exhibits more excellent electrochemical performance and better safety performance.

[0193] At the same time, the synthesis method and route of the thiophene compound represented by Formula I of the present invention are relatively simple, the raw materials are readily available, the cost is low, and it can simultaneously solve the problems of rate and high-temperature cycle performance, which is a very cost-effective method.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A thiophene compound, characterized in that Having the structure of formula I: Wherein, X1 and X2 are independently selected from halogen elements.

2. A modified positive electrode material, characterized in that From the inside to the outside, it includes a lithium-containing core, a solid electrolyte shell layer coated on the surface of the lithium-containing core, and a carbon-containing shell layer. The carbon-containing shell layer is formed by carbonization after polymerization of a monomer, and the monomer is the thiophene compound according to claim 1.

3. The modified positive electrode material according to claim 2, characterized in that The composition of the lithium-containing core is selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel manganese oxide and lithium-rich lithium manganese oxide.

4. The modified positive electrode material according to claim 2, characterized in that The solid electrolyte shell layer is composed of a NASICON type oxide solid electrolyte.

5. A method for preparing a modified positive electrode material, characterized in that: The following steps are involved: Providing a lithium-containing positive electrode material coated with a solid electrolyte shell; reacting the lithium-containing positive electrode material coated with the solid electrolyte shell with a functional compound, wherein the functional compound is the thiophene compound according to claim 1, so that the thiophene compound is grafted onto the surface of the solid electrolyte shell and polymerized into a coating film to obtain an intermediate; The intermediate is subjected to pyrolysis treatment under a protective atmosphere to obtain a modified positive electrode material with a double-layer coating structure.

6. The preparation method according to claim 5, characterized in that In the lithium-containing positive electrode material coated with a solid electrolyte shell layer, the thickness of the solid electrolyte shell layer is 200 to 400 nm; The preparation of the lithium-containing positive electrode material coated with the solid electrolyte shell layer comprises: dry-mixing the lithium-containing positive electrode material raw material and the solid electrolyte, and then sintering them at 90-300° C.

7. The preparation method according to claim 6, characterized in that During the preparation of the lithium-containing positive electrode material coated with the solid electrolyte shell, the mass ratio of the lithium-containing positive electrode material raw material to the solid electrolyte is (1-m):m, 0<m≤0.1; the composition of the solid electrolyte shell is a NASICON type oxide solid electrolyte; The temperature of high-temperature sintering is 0.2 to 0.5 times the melting point of the solid electrolyte.

8. The preparation method according to any one of claims 5 to 7, characterized in that The reaction between the lithium-containing positive electrode material coated with a solid electrolyte shell and the functional compound is carried out by stirring in the presence of an alkaline solution; the molar ratio of the lithium-containing positive electrode material to the functional compound is (0.4-0.6):1; the alkaline solution is a carbonate aqueous solution with a molar concentration of 0.1-0.2 mol / L, the reaction temperature is 100-120°C, and the reaction time is 24-30 hours.

9. The preparation method according to claim 8, characterized in that The temperature of the pyrolysis treatment is 200-300° C., and the time is 20-30 minutes.

10. A positive electrode sheet, characterized in that: The modified positive electrode material according to any one of claims 2 to 4, or the modified positive electrode material obtained by the preparation method according to any one of claims 5 to 9 is used as the active material.

11. A lithium-ion battery, characterized in that: Including the positive electrode sheet according to claim 10.

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