Composite-coated conversion cathode material, preparation method thereof and battery

Abstract

The composite-coated conversion positive electrode material comprises a conversion positive electrode base and a composite coating layer coated on the surface of the conversion positive electrode base, the conversion positive electrode base is M x S y , M a O, M b Z, M is at least one of Li, Fe, Cu, Ni, Mn, Co, Mo, Sn, Ti and W, Z is at least one of F, Cl and Br, the values of x, y, a and b vary according to the principle of electrical neutrality; the particle size of the conversion positive electrode base ranges from 30 nm to 25000 nm, the thickness of the composite coating layer accounts for 0.1% to 10% of the particle size of the conversion positive electrode base, the composite coating layer comprises an elastomer material and an electronic conductor material, the breaking elongation of the elastomer material is greater than or equal to 100%, and the tensile strength is greater than or equal to 5 MPa.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material chemistry, in particular to a composite coated conversion cathode material, a preparation method thereof and a battery. BACKGROUND

[0002] The popularity of new energy vehicles and the increasing demand of people put forward greater requirements for the endurance of electric vehicles and other commonly used electronic products, which undoubtedly will accelerate the development of high energy density lithium ion batteries. At present, it is urgent to find a kind of cathode material with high energy density, high specific capacity, suitable voltage platform and low cost.

[0003] Conversion electrode refers to the solid-state redox reaction during lithiation / delithiation, in which the crystal structure changes, accompanied by broken and recombined chemical bonds. FeS x The conversion cathode material represented by FeS2 has many types, good electrical conductivity, high energy density and theoretical specific capacity, and is abundant in content, many minerals exist in the form of sulfide, so its price is low, which is an ideal material for high energy density lithium secondary battery cathode. For example, FeS2 as a lithium secondary battery cathode material, its theoretical specific capacity is as high as 894mAh g -1 , the theoretical energy density is 1671Wh Kg -1 , the volume energy density is 8324Wh L -1 , the charging platform is 1.8V, 2.4V, and the discharging platform is 2.1V, 1.5V. However, this kind of conversion cathode material has a large volume expansion (generally >100%) during charging and discharging cycles, and some materials also have a shuttle effect of polysulfide during the cycle process, which leads to the loss of active material and the corrosion of lithium side, which greatly limits its large-scale commercial application. Existing technologies have tried various methods to solve these problems. For example:

[0004] 1. Using polydimethylsiloxane (PDMS) as a lithium-sulfur battery cathode framework: S-PDMS / GF porous framework provides sufficient space for sulfur loading and electrolyte penetration, and the Li-S battery made of this cathode shows high stability in bending and flattening, which indicates its application potential in flexible electronic devices. This method mainly uses the good elasticity and flexibility of PDMS, and PDMS as a supporting framework provides sufficient space for sulfur loading and electrolyte penetration.

[0005] 2. Using PDMS as a solid-state electrolyte component: improving the ionic conductivity and mechanical strength of the solid-state electrolyte; this method uses PDMS with good ionic conductivity and flexibility, and is applied to solid-state electrolyte.

[0006] 3. Using PDMS as electrolyte additive: improving the low temperature performance of the battery; this method adds PDMS protective solution to protect the liquid electrolyte composition from degradation or freezing, and takes advantage of the good chemical stability of PDMS.

[0007] 4. Using PDMS as a separator component: PVDF / PDMS blended separator for lithium batteries was prepared. Compared with pure PVDF separator, the addition of PDMS can cause a decrease in crystallinity, and can effectively improve the electrolyte absorption rate of the separator (up to 250wt%), and the ionic conductivity of the formed gel electrolyte membrane reaches 1.17×10 -3 S cm -1 .

[0008] 5. Using PDMS as a thin film to protect the metal lithium negative electrode: the PDMS thin film protective layer shows excellent stability and compatibility with electrolyte components, and the corrosion caused by dendritic metal lithium and shuttle effect and the adverse reaction of electrolyte or lithium salt in lithium-sulfur battery are effectively inhibited; this method involves Li-S battery, a layer of PDMS thin film is prepared on the metal lithium, the thin film can prevent the metal lithium dendrite from piercing the separator, and prevent the polysulfide from directly contacting the metal lithium to corrode the metal lithium; the protection is for the metal lithium negative electrode side, not for the positive S.

[0009] 6. Using PDMS as the shell of flexible battery for the preparation of flexible devices.

[0010] For example, prior art one (Chinese patent application publication CN109935779A) uses the following technical solution: a preparation method of modified iron disulfide positive electrode material includes:

[0011] (1) adding iron disulfide, conductive polymer monomer solution and oxidizing agent solution into the polymer dopant solution in sequence, stirring and then centrifuging to obtain a pre-product;

[0012] (2) mixing and grinding the pre-product with a binder, coating the obtained mixture on a current collector and then drying to obtain an electrode sheet;

[0013] (3) taking the electrode sheet as a working electrode, taking an inert electrode as a counter electrode, and putting them into a mixed solution of conductive polymer monomer solution and polymer dopant solution for electroplating to obtain a modified iron disulfide positive electrode material.

[0014] By coating conductive polymer on the surface of iron disulfide, the electrical conductivity of the material is improved, and the problems of volume expansion and active material dissolution are alleviated. However, this technology has the following disadvantages:

[0015] 1. The polymer monomer and oxidizing agent solution required are high in price and toxic and corrosive;

[0016] 2. The preparation method of the modified iron disulfide positive electrode material is generally complex and requires processes such as electroplating;

[0017] 3. The prepared modified FeS2 positive electrode material has a polymer coating layer without elasticity, which cannot effectively alleviate the volume expansion of FeS2 during the cycle process;

[0018] 4. Cannot alleviate the loss of active material and battery failure caused by the shuttle effect of polysulfide.

[0019] The prior art two (Chinese patent application publication CN109148864A) adopts the following technical solution: a preparation method of an iron disulfide composite negative electrode material, comprising:

[0020] (1) adding a certain mass ratio of iron disulfide to a specified solvent, adding a certain amount of weak acid solution to adjust the pH value to less than 7, and ultrasonic dispersion to obtain a mixed solution;

[0021] (2) adding a certain mass ratio of conductive polymer monomer and initiator to the above-mentioned mixed solution under a specified temperature and rotating speed, adding a certain amount of weak acid solution to adjust the pH value to less than 7, and stirring for a specified time to obtain a reaction product;

[0022] (3) filtering and washing the reaction product, drying by a specified drying process to obtain the iron disulfide composite negative electrode material.

[0023] The technical solution has the following disadvantages:

[0024] 1. The selected conductive polymer is limited to one of polyaniline, polypyrrole, and polythiophene, and the selection range is narrow;

[0025] 2. The preparation method of the iron disulfide composite negative electrode material requires the use of weak acid to adjust the pH value of the solution, and does not expand the preparation method in neutral and alkaline environments;

[0026] 3. The polymer monomer used has toxicity, and some polymer monomers can harm the environment. SUMMARY

[0027] The inventors of the present application realize that the conversion positive electrode material will produce serious volume expansion under deep discharge, for example, the volume expansion of FeS2 can reach 159%, which leads to the destruction of the electrode structure, and at the same time, the shuttle effect of polysulfide during the cycle process leads to the loss of active material and corrosion on the metal lithium side, resulting in battery failure. Therefore, one of the problems to be solved based on the conversion positive electrode material is the volume expansion.

[0028] To solve the above problems, an embodiment of the present application provides a composite-coated conversion positive electrode material, which comprises a conversion positive electrode matrix and a composite coating layer coated on the surface of the conversion positive electrode matrix, the conversion positive electrode matrix is M x S y , M a O, M b Z, M is at least one of Li, Fe, Cu, Ni, Mn, Co, Mo, Sn, Ti and W, Z is at least one of F, Cl and Br, wherein the values of x, y, a and b vary according to the principle of electrical neutrality; the particle size of the conversion positive electrode matrix ranges from 30 nm to 25000 nm, the thickness of the composite coating layer accounts for 0.1% to 10% of the particle size of the conversion positive electrode matrix, the composite coating layer comprises an elastomer material and an electronic conductor material, the elongation at break of the elastomer material is greater than or equal to 100%, and the tensile strength is greater than or equal to 5 MPa.

[0029] According to an embodiment of the present application, for example, the elongation at break of the elastomer material is greater than or equal to 150%, and the tensile strength is greater than or equal to 6 MPa; preferably, the elongation at break of the elastomer material is greater than or equal to 180%, and the tensile strength is greater than or equal to 6.5 MPa; preferably, the elongation at break of the elastomer material is greater than or equal to 210%, and the tensile strength is greater than or equal to 7 MPa; preferably, the elongation at break of the elastomer material is greater than or equal to 220%, and the tensile strength is greater than or equal to 7.8 MPa; preferably, the elongation at break of the elastomer material is greater than or equal to 240%, and the tensile strength is greater than or equal to 8.2 MPa.

[0030] According to an embodiment of the present application, for example, the mass ratio of the electronic conductor material to the elastomer material is 1:10-300.

[0031] According to an embodiment of the present application, for example, the electronic conductor material has an electrical conductivity of greater than or equal to 10 2 S / cm.

[0032] Preferably, the electronic conductor material is selected from at least one of amorphous carbon, conductive graphite, nano-graphite, conductive carbon black, carbon nanotube, carbon fiber, fullerene, graphene, conductive polymer, conductive polymer derivative or partially carbonized conductive polymer.

[0033] Preferably, the electronic conductor material has a linear, rod-like or sheet-like micro-morphology.

[0034] Preferably, when the electronic conductor material has a linear or rod-like micro-morphology, the aspect ratio of the electronic conductor material is 20-150:1, preferably 60-150:1, preferably 80-150:1, and further preferably 100-150:1.

[0035] According to an embodiment of the present application, for example, the elastomer material is selected from at least one of polysiloxane, polyurethane, fluorine rubber, silicone rubber, epichlorohydrin rubber, polypropylene, hydroxyl-terminated polybutadiene, polyethylene oxide.

[0036] According to an embodiment of the present application, for example, the polysiloxane is selected from at least one of dimethyl polysiloxane, cyclo-methyl polysiloxane, amino polysiloxane, methyl phenyl polysiloxane, polyether polysiloxane copolymer.

[0037] The embodiments of the present application also provide a preparation method of the composite-coated conversion cathode material, which comprises the following steps:

[0038] (1) adding an electronic conductor material into a solvent, mixing to obtain a uniformly dispersed dispersion I;

[0039] (2) adding an elastomer precursor 1 into the dispersion I, continuing to mix to obtain a uniformly dispersed dispersion II;

[0040] (3) adding a conversion cathode matrix material into the dispersion II, and continuing to mix at a temperature T1 to obtain a uniformly dispersed dispersion III;

[0041] (4) adding an elastomer precursor 2 into the dispersion III, and continuing to mix at a temperature T2, and then performing a heat treatment in a vacuum environment or an inert atmosphere, cooling, and crushing to obtain the composite-coated conversion cathode material.

[0042] According to an embodiment of the present application, for example, in the method, the solvent in the step (1) is selected from at least one of N-methyl pyrrolidone, N,N-dimethyl formamide, N,N-dimethyl acetamide, N,N-diethyl formamide, dimethyl sulfoxide, tetrahydrofuran, acetone, acetonitrile, dimethyl carbonate, propylene carbonate, methanol, ethanol, propanol, isopropanol, ethylene glycol, benzyl alcohol, benzene, toluene, xylene, methyl ether, ethyl ether and glycol dimethyl ether, cyclohexane, cyclohexanone, toluene cyclohexanone, pentane, hexane, octane, chlorobenzene, dichlorobenzene, dichloromethane, methyl acetate, ethyl acetate, propyl acetate, methyl butanone, methyl isobutyl ketone, acetonitrile, pyridine, phenol.

[0043] According to an embodiment of the present application, for example, in the method, the elastomer precursor 1 is selected from at least one of alkenylized silicon dioxide, alkylized silicon dioxide, polymeric diol, diisocyanate, difluoroethylene, dimethyl cyclosiloxane, epichlorohydrin, ethylene oxide, allyl glycidyl ether, propylene, butadiene.

[0044] Preferably, the elastomer precursor 2 is selected from at least one of octamethylcyclotetrasiloxane, polytetrahydrofuran ether glycol, 4,4-dicyclohexyl methane diisocyanate, isoprene, butyl acrylate, methyl methacrylate.

[0045] According to an embodiment of the present application, for example, in the method, the step (4) adds a crosslinking agent; the crosslinking agent is selected from at least one of an amine crosslinking agent, an acid anhydride crosslinking agent or modified silica, the amine crosslinking agent is selected from at least one of a polyamide, an aliphatic amine, an aromatic amine, a cycloaliphatic amine, a polyether amine, an imidazole, the acid anhydride crosslinking agent is selected from at least one of an aromatic acid anhydride, an aliphatic acid anhydride, a cycloaliphatic acid anhydride;

[0046] Preferably, the crosslinking agent is selected from at least one of diethylene triamine (DTA), 2-ethyl-4-methyl imidazole, 2-phenyl imidazole, 2-isopropyl imidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylene tetramine, dimethyl aminopropyl amine, diethyl aminopropyl amine, dimethyl vinylated silica, trimethylated silica, tetraethyl orthosilicate, vinyl trimethoxysilane or phenyl triethoxysilane;

[0047] Preferably, the step (4) adds an additive, the additive is selected from at least one of 1,4-butanediol, diisopropyl percarbonate, methyl vinyl cyclosiloxane, tetramethyl divinyl siloxane, triisobutyl aluminum, TiCl3-Al(C2H5)3, peroxide, azo compound, tetrabutyl ammonium bromide;

[0048] Preferably, the electronic conductor material of the step (1) accounts for 0.1-20wt% of the solvent;

[0049] Preferably, the elastomer precursor 1 of the step (2) accounts for 1-50wt% of the dispersion I;

[0050] Preferably, the mass ratio of the conversion positive electrode material to the electronic conductor added in the step (3) is 100:0.1-10;

[0051] Preferably, the mass ratio of the conversion positive electrode material to the elastomer precursor added in the step (3) is 100:1-30;

[0052] Preferably, the temperature T1 in the step (3) is 70-150℃;

[0053] Preferably, the mass ratio of the elastomer precursor 2 to the crosslinking agent in the step (4) is 100:0.1-20;

[0054] Preferably, the temperature T2 in the step (3) is 30-90℃;

[0055] Preferably, the heat treatment temperature in step (4) is 60-350℃, and the calcination time is 0.5-20h.

[0056] The beneficial effects of the present application include:

[0057] (1) By coating the surface of the conversion cathode base material with the elastomer and electronic conductor composite material, the volume expansion of the conversion cathode base material during charging and discharging is effectively alleviated, greatly improving the battery performance of the conversion cathode base material including FeS2.(2) The FeS2 conversion cathode material coated with the electronic conductor material and the elastomer material exhibits more excellent electrochemical cycling effect and lower volume expansion rate, which is due to the synergistic effect between the electronic conductor material and the elastomer material. Experimental results prove that the expansion rate of the base material is greatly reduced.(3) By optimizing the thickness of the coating layer and using electronic conductor materials with appropriate length-diameter ratio, the battery performance can be further optimized, and the expansion rate of the base material can be further reduced, and the battery cycle performance can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 The first cycle charge-discharge curve diagram of the cathode material of Example 1 and Comparative Example 1.

[0059] Figure 2 The cycle performance comparison diagram of the cathode material of Example 1 and Comparative Example 1.

[0060] Figure 3 The SEM image of the uncoated FeS2 conversion cathode in Comparative Example 1, from which it can be seen that the particle size distribution is 5-25 microns.

[0061] Figure 4 The SEM image of the FeS2 conversion cathode after coating in Example 1, from which it can be seen that the surface of the cathode material is coated with CNTs and PDMS. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. However, those skilled in the art will appreciate that the present application is not limited to the drawings and the following embodiments.

[0063] Example 1

[0064] (1) CNTs were added to the NMP solution and stirred to obtain a uniform dispersion of 0.1% wt dispersion I;

[0065] (2) The elastomer precursor 1 dimethyl vinylated silica was added to the uniform dispersion I of step (1) and stirred to obtain a uniform dispersion of 1% wt dispersion II;

[0066] (3) Add FeS2-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of FeS2-based powder to CNTs in solution is 50: 1, continue stirring, and heat the mixed solution until NMP is completely volatilized to obtain a homogeneous dispersion III;

[0067] (4) Add octamethylcyclotetrasiloxane, an elastomer precursor 2, to the homogeneous dispersion III of step (3) such that the mass ratio of FeS2-based powder to PDMS in solution is 10:2, stir the mixture, and then calcine in a vacuum environment at a temperature- increasing rate of 2°C / min to 120°C for 8 hours, and then cool down to obtain a composite-coated conversion cathode material.

[0068] Example 2

[0069] (1) Add CNTs to a NMP solution, stir the mixture to obtain a 0.2%wt homogeneous dispersion I;

[0070] (2) Add dimethylvinylated silica to the homogeneous dispersion I of step (1), stir the mixture to obtain a 1.5%wt homogeneous dispersion II;

[0071] (3) Add FeS2-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of FeS2-based powder to CNTs in solution is 25: 1, continue stirring, and heat the mixed solution until NMP is completely volatilized to obtain a homogeneous dispersion III;

[0072] (4) Add octamethylcyclotetrasiloxane to the homogeneous dispersion III of step (3) such that the mass ratio of FeS2-based powder to PDMS in solution is 10:3, stir the mixture, and then calcine in a vacuum environment at a temperature- increasing rate of 5°C / min to 140°C for 10 hours, and then cool down to obtain a composite-coated conversion cathode material.

[0073] Example 3

[0074] (1) Add graphene to a NMP solution, stir the mixture to obtain a 0.1%wt homogeneous dispersion I;

[0075] (2) Add polytetrahydrofuran ether glycol, 4,4-dicyclohexyl methane diisocyanate to the homogeneous dispersion I of step (1), stir the mixture to obtain a 1%wt homogeneous dispersion II;

[0076] (3) Add TiS2-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of TiS2-based powder to graphene in solution is 10: 1, continue stirring, and heat the mixed solution until NMP is completely volatilized to obtain a homogeneous dispersion III;

[0077] (4) Add 1,4-butanediol to the homogeneous dispersion III of step (3) such that the mass ratio of TiS2-based powder to polyurethane in solution is 10:2, mix by stirring, and then calcine in a vacuum environment at a ramp rate of 5 °C / min to 60 °C for 20 hours, cool down, and obtain.

[0078] Example 4

[0079] (1) Add graphene to NMP solution, mix by stirring, and obtain a homogeneous dispersion I of 0.2% wt;

[0080] (2) Add 1,1-difluoroethylene to the homogeneous dispersion I of step (1), mix by stirring, and obtain a homogeneous dispersion II of 1.5% wt;

[0081] (3) Add MoS2-based powder to the homogeneous dispersion II of step (2) while ensuring that the mass ratio of MoS2-based powder to graphene in solution is 25:1, continue stirring, and heat the mixed solution until NMP is completely volatilized to obtain a homogeneous dispersion III;

[0082] (4) Add diisopropyl peroxydicarbonate to the homogeneous dispersion III of step (3) such that the mass ratio of MoS2-based powder to polyvinylidene fluoride in solution is 10:2, mix by stirring, and then calcine in a vacuum environment at a ramp rate of 5 °C / min to 180 °C for 20 hours, cool down, and obtain.

[0083] Example 5

[0084] (1) Add CNTs to NMP solution, mix by stirring, and obtain a homogeneous dispersion I of 0.1% wt;

[0085] (2) Add dimethylcyclosiloxane to the homogeneous dispersion I of step (1), mix by stirring, and obtain a homogeneous dispersion II of 1% wt;

[0086] (3) Add CuS-based powder to the homogeneous dispersion II of step (2) while ensuring that the mass ratio of CuS-based powder to CNTs in solution is 50:1, continue stirring, and heat the mixed solution until NMP is completely volatilized to obtain a homogeneous dispersion III;

[0087] (4) Add methylvinylcyclosiloxane and tetramethyldivinylsiloxane to the homogeneous dispersion III of step (3) such that the mass ratio of CuS-based powder to silicone rubber in solution is 10:3, mix by stirring, and then calcine in a vacuum environment at a ramp rate of 5 °C / min to 350 °C for 10 hours, cool down, and obtain.

[0088] Example 6

[0089] (1) CNTs were added to NMP solution, mixed by stirring, to obtain a 0.2%wt uniformly dispersed dispersion I;

[0090] (2) Propylene was added to the uniformly dispersed dispersion I of step (1), mixed by stirring, to obtain a 1.5%wt uniformly dispersed dispersion II;

[0091] (3) Li2S-based powder was added to the uniformly dispersed dispersion II of step (2), while ensuring that the mass ratio of Li2S-based powder to CNTs in solution was 25:1, continued to be stirred, and the mixed solution was heated to complete volatilization of NMP, to obtain a uniform dispersion III;

[0092] (4) TiCl3-Al(C2H5)3 was added to the uniformly dispersed dispersion III of step (3), so that the mass ratio of Li2S-based powder to polypropylene in solution was 10:3, mixed by stirring, and then placed in a vacuum environment to be calcined at a temperature increasing rate of 5°C / min to 140°C for 12 hours, and then cooled to obtain.

[0093] Example 7

[0094] (1) Graphene was added to a tetrahydrofuran solution, mixed by stirring, to obtain a 0.2%wt uniformly dispersed dispersion I;

[0095] (2) 1,3-butadiene was added to the uniformly dispersed dispersion I of step (1), mixed by stirring, to obtain a 1%wt uniformly dispersed dispersion II;

[0096] (3) CuO-based powder was added to the uniformly dispersed dispersion II of step (2), while ensuring that the mass ratio of CuO-based powder to graphene in solution was 50:1, continued to be stirred, and the mixed solution was heated to complete volatilization of tetrahydrofuran, to obtain a uniform dispersion III;

[0097] (4) An azo compound was added to the uniformly dispersed dispersion III of step (3), so that the mass ratio of CuO-based powder to hydroxyl-terminated polybutadiene in solution was 10:3, mixed by stirring, and then placed in a vacuum environment to be calcined at a temperature increasing rate of 5°C / min to 140°C for 10 hours, and then cooled to obtain.

[0098] Example 8

[0099] (1) Graphene was added to an acetone solution, mixed by stirring, to obtain a 0.1%wt uniformly dispersed dispersion I;

[0100] (2) 1,3-butadiene was added to the uniformly dispersed dispersion I of step (1), mixed by stirring, to obtain a 1.5%wt uniformly dispersed dispersion II;

[0101] (3) Add NiO-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of NiO-based powder to graphene in solution is 10:1, continue stirring, and heat the mixed solution until the acetone is completely volatilized to obtain a homogeneous dispersion III;

[0102] (4) Add peroxide to the homogeneous dispersion III of step (3) so that the mass ratio of NiO-based powder to hydroxyl-terminated polybutadiene in solution is 10:3, stir the mixture, and then calcine in a vacuum environment at a temperature- increasing rate of 5°C / min to 120°C for 20 hours, and then cool down to obtain.

[0103] Example 9

[0104] (1) Add CNTs to an NMP solution, stir the mixture to obtain a 10% wt homogeneous dispersion I;

[0105] (2) Add ethylene oxide to the homogeneous dispersion I of step (1), stir the mixture to obtain a 25% wt homogeneous dispersion II;

[0106] (3) Add LiCl-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of LiCl-based powder to CNTs in solution is 25:1, continue stirring, and heat the mixed solution until the NMP is completely volatilized to obtain a homogeneous dispersion III;

[0107] (4) Add tetraoctylammonium bromide and triisobutylaluminum to the homogeneous dispersion III of step (3) so that the mass ratio of LiCl-based powder to polyethylene oxide in solution is 10:3, stir the mixture, and then calcine in a vacuum environment at a temperature- increasing rate of 5°C / min to 100°C for 1 hour, and then cool down to obtain.

[0108] Example 10

[0109] (1) Add CNTs to an acetone solution, stir the mixture to obtain a 20% wt homogeneous dispersion I;

[0110] (2) Add ethylene oxide to the homogeneous dispersion I of step (1), stir the mixture to obtain a 50% wt homogeneous dispersion II;

[0111] (3) Add LiCl-based powder to the homogeneous dispersion II of step (2) while ensuring the mass ratio of LiCl-based powder to CNTs in solution is 50:1, continue stirring, and heat the mixed solution until the acetone is completely volatilized to obtain a homogeneous dispersion III;

[0112] (4) Add tetraoctylammonium bromide and triisobutylaluminum to the homogeneous dispersion III of step (3) so that the mass ratio of LiCl-based powder to polypropylene in solution is 10:2, stir the mixture, and then place it in a vacuum environment to be calcined at a temperature- increasing rate of 5°C / min to 140°C for 1 hour, and then cool it down to obtain.

[0113] Example 11

[0114] The main difference from Example 1 is that PDMS is replaced by butyl rubber.

[0115] Example 12

[0116] The main difference from Example 1 is that PDMS is replaced by butyl nitrile rubber.

[0117] Example 13

[0118] The main difference from Example 1 is that CNTs are replaced by carbon fibers and PDMS is replaced by isoprene rubber.

[0119] Example 14

[0120] The main difference from Example 1 is that CNTs are replaced by fullerenes and PDMS is replaced by acrylate rubber.

[0121] Comparative Example 1

[0122] Comparative Example 1 selects FeS2 without using CNTs and PDMS coating as the matrix material. Other conditions are the same as in Example 1.

[0123] Comparative Example 2

[0124] The difference from Example 1 is that Comparative Example 2 does not add PDMS.

[0125] Comparative Example 3

[0126] The difference from Example 1 is that Comparative Example 3 does not add CNTs.

[0127] Comparative Example 4

[0128] The difference from Comparative Example 2 is that CNTs are replaced by conductive graphite.

[0129] Comparative Example 5

[0130] The difference from Comparative Example 3 is that PDMS is replaced by polyhexafluoropropylene.

[0131] Comparative Example 6

[0132] The difference from Example 1 is that PDMS is replaced by polysulfide rubber.

[0133] Test Characterization:

[0134] Elastomer performance characterization

[0135] The tensile properties of the elastomer were tested by GB / T 1040.1-2018, GB / T 1040.2-2022 and GB / T 1040.3-2006. The specific test method was as follows: the elastomer was cut into a sample with a length of 100 mm and a width of 15 mm, and was tested in the longitudinal and transverse directions respectively. A universal testing machine was used, the sample was first fixed with the lower clamp, the machine was zeroed, then the sample was clamped with the upper clamp, the sample length and width were input, the tensile speed was set to 200 mm / min, and the maximum tensile strength (MPa) and elongation at break (%) were recorded. The above test was repeated 5 times, and the data was averaged. The data is shown in Table 1 below.

[0136] Electrical performance characterization:

[0137] The positive electrode materials prepared in the above examples and comparative examples were made into electrode sheets as positive electrode sheets, and the thickness of the electrode sheets was tested to obtain thickness 1. The negative electrode used metal lithium, and a conventional commercial ether electrolyte was used to assemble lithium ion batteries, which were then subjected to charge and discharge tests. The voltage range of examples 1 and comparative example 1 was 1-3V, and the first discharge specific capacity and the first coulombic efficiency were tested at 0.1C / 0.1C, and the 100 cycle capacity retention rate was tested at 1C / 1C. The test results are shown in Table 1. After cycling, the battery was disassembled, and the thickness of the positive electrode sheet was tested to obtain thickness 2. The volume expansion rate = (thickness 2-thickness 1) / thickness 1*100%.

[0138] The test results are shown in Table 1 below:

[0139]

[0140]

[0141] Results and discussion:

[0142] (1) The scheme of the present application is suitable for solving the volume expansion problem of various transformed positive electrode matrix materials. Examples 1-14 were tested on 8 different matrix materials including FeS2, TiS2, MoS2, CuS, Li2S, CuO, NiO and LiCl, and the volume expansion was well inhibited. This shows that the scheme of the present application is suitable for solving the expansion problem of various transformed positive electrode matrix materials.

[0143] (2) About the elongation at break and tensile strength of the elastomer. In the technical solution of the present application, the elastomer is the key coating component. The present application wraps the elastomer material onto the surface of the substrate material particles. When the substrate material expands in volume during the charging and discharging process, the shrinkage elastic force of the elastomer material can inhibit the excessive expansion of the substrate material, thereby achieving the technical effect of reducing the expansion rate. The elongation at break of the elastomer material is the percentage of the increase in the length of the sample when it breaks during the tensile test, which is used to measure the extension capacity. The tensile strength refers to the maximum tensile stress that the elastomer material can withstand until it breaks during the tensile test. Therefore, the larger the two parameters of elongation at break and tensile strength, the stronger the ability of the elastomer material to resist volume expansion, and ultimately the volume expansion problem of the coated substrate material is solved. The results of Comparative Examples 1-2, 11-14 and Comparative Examples 1-5 can confirm the above theoretical speculation. The elastomer materials in Examples 1, 2 and 14, which have the best solution to the volume expansion problem, have larger elongation at break and tensile strength; while the elastomer materials in Examples 11 and 13, which have less satisfactory solution to the volume expansion problem, have smaller elongation at break and tensile strength, and the elastomer material in Example 12, which has the worst technical effect, has the smallest elongation at break and tensile strength.

[0144] (3) Synergistic effect of the elastomer material and the electronic conductor material. Comparing Example 1 with Comparative Example 1, the other experimental conditions of Comparative Example 1 are the same as those of Example 1, the difference is that the surface of the matrix material of Comparative Example 1 is not wrapped with any material. The volume expansion rate of Comparative Example 1 is significantly higher than that of Example 1, which proves that the technical solution of the present application can effectively solve the volume expansion problem of the matrix material. Then, comparing Example 1 with Comparative Examples 2 and 3, the surface of the matrix material of Comparative Example 2 is only wrapped with the electronic conductor material, and the surface of the matrix material of Comparative Example 3 is only wrapped with the elastomer material. The volume expansion problem of Comparative Example 2 is more serious than that of Example 1, which is due to the lack of the key elastomer material in Comparative Example 2. However, the volume expansion problem of Example 1 is better solved than that of Comparative Example 3. In theory, the electronic conductor material mixed in the elastomer material of Example 1 will reduce the elongation at break and tensile strength of the elastomer material to some extent. It is speculated that the volume expansion rate of Comparative Example 3 should be smaller than that of Example 1. A reasonable explanation is that compared with the matrix material coated with the electronic conductor material or the elastomer material alone, the FeS2 conversion cathode material coated with the electronic conductor material and the elastomer material exhibits more excellent electrochemical cycling effect and lower volume expansion rate, which is probably due to the fact that the electronic conductor material can effectively promote the interface dynamics transmission of electrons in the cycling process, thereby inhibiting the structural change of the cathode material (the accumulation of electric charge in the lattice will cause the strain of the matrix material to increase), and the elastomer has a high elongation at break and tensile strength, which can alleviate the volume expansion of the cathode matrix during the charging and discharging process. The electronic conductor material timely transmits the electric charge of the matrix material from the inside, and the elastomer material suppresses the expansion of the matrix material from the outside. Through the synergistic effect of the inside and the outside, the expansion rate of the matrix material is greatly reduced. In order to prove that this synergistic effect is universal and does not depend on a specific electronic conductor material and elastomer material, Comparative Examples 4 and 5 change the electronic conductor material and the elastomer material, and in comparison, Example 1 still shows obvious synergistic effect. It can be seen that this synergistic effect is universal.

[0145] (4) Thickness of the coating layer. The thickness of the coating layer should meet certain requirements. If the thickness is too large, it will affect the charge transfer, and if the thickness is too small, it cannot effectively suppress the volume expansion of the matrix material. Since the thickness of the coating layer is related to the particle size of the matrix, the larger the particle size of the matrix, the more serious the volume expansion phenomenon, and a thicker coating layer is needed to suppress the volume expansion. Therefore, in the examples, the thickness is expressed as a percentage of the particle size of the matrix. From the experimental results of the examples, a relatively wide range of this percentage from 0.2% (Example 11) to 10% (Example 7) has achieved good results, effectively suppressing the volume expansion of the matrix material while obtaining excellent battery performance.

[0146] (5) Aspect ratio of the electronic conductor material. The carbon nanotubes (CNTs) used in some embodiments have a one-dimensional tubular microstructure. In theory, CNTs have high electronic conductivity and their one-dimensional tubular microstructure enables the electronic conductor material to make more intimate contact with the matrix material, thus improving the electronic conductivity, which is more pronounced when the coating layer is thicker. Comparing Example 1 and Example 2, it can be found that the initial discharge capacity performance and the 100-cycle capacity retention rate of Example 1 are both more excellent than those of Example 2, and this can be attributed in part to the more suitable aspect ratio of the CNTs used in Example 1 than in Example 2.

[0147] (6) Discussion of the comprehensive test results. Figure 1 The initial charge-discharge curves of the positive electrode materials of Example 1 and Comparative Example 1. As can be seen from the figure, the specific capacity of Example 1 is significantly greater than that of Comparative Example 1, which indicates that the scheme provided in the embodiments of the present application can significantly improve the battery performance. Figure 2 The cycle performance of the positive electrode materials of Example 1 and Comparative Example 1. As can be seen from the figure, the specific capacity of Example 1 is significantly better than that of Comparative Example 1, and this advantage becomes more and more obvious as the cycle number increases, which is because the volume expansion problem of Comparative Example 1 becomes more and more serious as the cycle number increases, while the scheme of the present application used in Example 1 solves the problem of volume expansion very well. Figure 3 The SEM image of the uncoated FeS2 conversion positive electrode in Comparative Example 1, from which it can be seen that the particle size distribution is 5-25 microns. Figure 4 The SEM image of the coated FeS2 conversion positive electrode in Example 1, from which it can be seen that the positive electrode material surface is coated with CNTs and PDMS.

Claims

1. A composite-coated conversion cathode material, characterized in that, The composite-coated conversion anode material comprises a conversion anode base and a composite coating layer coated on the surface of the conversion anode base, the conversion anode base is M x S y , M a O, M b Z, M is at least one of Li, Fe, Cu, Ni, Mn, Co, Mo, Sn, Ti and W, Z is at least one of F, Cl and Br, wherein the values of x, y, a and b vary according to the principle of electrical neutrality; the particle size of the conversion anode base ranges from 30 nm to 25000 nm, the thickness of the composite coating layer accounts for 0.1% to 10% of the particle size of the conversion anode base, the composite coating layer comprises an elastomer material and an electronic conductor material, the breaking elongation of the elastomer material is greater than or equal to 100%, and the tensile strength is greater than or equal to 5 MPa. The electronic conductor material is selected from at least one of carbon nanotubes, carbon fibers and graphene; the mass ratio of the transformed positive electrode matrix to the electronic conductor material is 100:2-10.

2. The composite-coated conversion cathode material of claim 1, wherein, The breaking elongation of the elastomer material is greater than or equal to 150%, and the tensile strength is greater than or equal to 6 MPa.

3. The composite-coated conversion cathode material of claim 2, wherein, The breaking elongation of the elastomer material is greater than or equal to 180%, and the tensile strength is greater than or equal to 6.5 MPa.

4. The composite-coated conversion cathode material of claim 3, wherein, The breaking elongation of the elastomer material is greater than or equal to 210%, and the tensile strength is greater than or equal to 7 MPa.

5. The composite-coated conversion cathode material of claim 4, wherein, The breaking elongation of the elastomer material is greater than or equal to 220%, and the tensile strength is greater than or equal to 7.8 MPa.

6. The composite-coated conversion cathode material of claim 5, wherein, The breaking elongation of the elastomer material is greater than or equal to 240%, and the tensile strength is greater than or equal to 8.2 MPa.

7. The composite-coated conversion cathode material of claim 1, wherein, The mass ratio of the electronic conductor material to the elastomer material is 1:10-300.

8. The composite-coated conversion cathode material of claim 1, wherein, The electronic conductor material has an electrical conductivity ≥ 10 2 S / cm; And / or, the electronic conductor material has a linear, rod-like or sheet-like micro-morphology; When the electronic conductor material has a linear or rod-like micro-morphology, the aspect ratio of the electronic conductor material is 20-150:

1.

9. The composite-coated conversion cathode material of claim 8, wherein, When the electronic conductor material has a linear or rod-like micro-morphology, the aspect ratio of the electronic conductor material is 60-150:

1.

10. The composite-coated conversion cathode material of claim 9, wherein, When the electronic conductor material has a linear or rod-like micro-morphology, the aspect ratio of the electronic conductor material is 80-150:

1.

11. The composite-coated conversion cathode material of claim 10, wherein, When the electronic conductor material has a linear or rod-like micro-morphology, the aspect ratio of the electronic conductor material is 100-150:

1.

12. The composite-coated conversion cathode material of any one of claims 1-11, wherein, The elastomer material is selected from at least one of polysiloxane, polyurethane, fluororubber, silicone rubber, chloroether rubber, polypropylene, hydroxyl-terminated polybutadiene, and polyethylene oxide.

13. The composite coated conversion cathode material of claim 12, wherein, The polysiloxane is selected from at least one of polydimethylsiloxane, polymethylphenylsiloxane, and polyether polysiloxane copolymer.

14. The method of producing a composite-coated conversion cathode material according to any one of claims 1 to 13, characterized in that, The preparation method comprises the following steps: (1) adding the electronic conductor material into a solvent, mixing to obtain dispersion I; (2) adding elastomer precursor 1 into dispersion I, continuing to mix to obtain dispersion II; (3) adding the transformed positive electrode matrix material into dispersion II, and continuing to mix at temperature T1 to obtain dispersion III; (4) adding elastomer precursor 2 into dispersion III, and continuing to mix at temperature T2, and then heat treating in a vacuum environment or inert atmosphere, cooling, and crushing to obtain the composite-coated transformed positive electrode material.

15. The method of claim 14, wherein, The solvent in step (1) is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetone, acetonitrile, dimethyl carbonate, propylene carbonate, methanol, ethanol, propanol, isopropanol, ethylene glycol, benzyl alcohol, benzene, toluene, xylene, methyl ether, ethyl ether and glycol dimethyl ether, cyclohexane, cyclohexanone, toluene cyclohexanone, pentane, hexane, octane, chlorobenzene, dichlorobenzene, dichloromethane, methyl acetate, ethyl acetate, propyl acetate, methyl butanone, methyl isobutyl ketone, acetonitrile, pyridine, and phenol.

16. The method of claim 14, wherein, The elastomer precursor 1 is selected from at least one of vinylated silica, alkylated silica, polymeric glycol, diisocyanate, difluoroethylene, dimethylcyclosiloxane, epichlorohydrin, oxirane, allyl glycidyl ether, propylene, butadiene; And / or, the elastomer precursor 2 is selected from at least one of octamethylcyclotetrasiloxane, polytetrahydrofuran ether glycol, 4,4-dicyclohexylmethane diisocyanate, isoprene, butyl acrylate, methyl methacrylate.

17. The method of making according to any one of claims 14-16, wherein, The crosslinking agent added in step (4) is selected from at least one of amine crosslinking agent, acid anhydride crosslinking agent or modified silica; the amine crosslinking agent is selected from at least one of polyamide, aliphatic amine, aromatic amine, alicyclic amine, polyether amine, imidazole; the acid anhydride crosslinking agent is selected from at least one of aromatic acid anhydride, aliphatic acid anhydride, alicyclic acid anhydride; The percentage of the electronic conductor material of step (1) in the solvent is 0.1-20wt%; The percentage of the elastomer precursor 1 of step (2) in the dispersion I is 1-50wt%; The mass ratio of the conversion positive electrode matrix material added in step (3) to the electronic conductor material is 100:2-10; The mass ratio of the conversion positive electrode matrix material added in step (3) to the elastomer precursor 1 is 100:1-30; The temperature T1 in step (3) is 70-150℃; The mass ratio of the elastomer precursor 2 to the crosslinking agent in step (4) is 100:0.1-20; The temperature T2 in step (4) is 30-90℃; The heat treatment temperature in step (4) is 60-350℃, and the calcination time is 0.5-20h; And / or, the additive added in step (4) is selected from at least one of 1,4-butanediol, diisopropyl percarbonate, methylvinylcyclosiloxane, tetramethyldivinylsiloxane, triisobutylaluminum, TiCl3-Al(C2H5)3, peroxide, azo compound, tetrabutylammonium bromide.

18. The method of claim 17, wherein, The crosslinking agent is selected from at least one of diethylenetriamine (DTA), 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, diethylaminopropylamine, dimethylvinylated silica, trimethylated silica, tetraethyl orthosilicate, vinyltrimethoxysilane or phenyltriethoxysilane.

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