Positive electrode active material, method for producing the same, and battery

Abstract

The application discloses a positive electrode active material and a preparation method and a battery thereof. The method comprises the following steps: preparing a double-metal transition metal carbide; modifying lithium manganese phosphate by using the double-metal transition metal carbide to obtain a positive electrode active material precursor; and obtaining a target positive electrode active material based on the positive electrode active material precursor. According to the embodiment of the application, the lithium manganese phosphate is modified by using the double-metal transition metal carbide, and the double metals are synergistic, so that the conductivity and the lattice stability of the lithium manganese phosphate can be improved, and the manganese dissolution can be inhibited, thereby effectively avoiding the rapid attenuation of the cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a positive electrode active material, its preparation method, and a battery. Background Technology

[0002] Lithium iron phosphate cathode materials have achieved a market share of nearly 80% in commercial power and energy storage batteries due to their excellent safety performance and long cycle life. However, their energy density is relatively low, making it difficult to meet the ever-increasing demands for driving range.

[0003] Lithium manganese phosphate and lithium iron phosphate both have an olivine structure and a theoretical specific capacity of approximately 170 mAh g. -1 However, the former has a voltage platform of up to 4.1V, which is about 0.65V higher than the latter's 3.45V. Therefore, the energy density is expected to increase by about 20%, making it one of the key technology routes for the next generation of power batteries.

[0004] However, lithium manganese phosphate has low intrinsic electronic conductivity and ion diffusion coefficient, resulting in limited practical discharge capacity and rate performance. Furthermore, Mn... 3+ The Jahn-Teller distortion causes lattice symmetry breaking, accompanied by Mn dissolution and structural degradation, resulting in a rapid decline in cycle life. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a positive electrode active material, its preparation method, and a battery, to address the problems of limited actual discharge capacity and rate performance, and rapid cycle life decay, in batteries currently prepared using lithium manganese phosphate positive electrode materials.

[0006] In a first aspect, the present invention provides a method for preparing a positive electrode active material, comprising:

[0007] Bimetallic transition metal carbides were mixed with lithium manganese phosphate, and a solvent was added. The mixture was then mechanically mixed and dried to obtain a precursor for the positive electrode active material.

[0008] The positive electrode active material precursor is subjected to heat treatment to obtain the positive electrode active material.

[0009] In some embodiments, the bimetallic transition metal carbide and the lithium manganese phosphate are mixed in a mass ratio of (4~6):(94~96).

[0010] In some embodiments, the bimetallic transition metal carbide includes at least one of Fe2MoC, Co3Mo3C, Fe2WC, and Co2WC.

[0011] In some embodiments, the particle size D50 of the bimetallic transition metal carbide is 10 nm to 500 nm.

[0012] In some embodiments, the mechanical mixing is a ball milling process;

[0013] The ball milling speed for the ball milling process is 350 rpm to 500 rpm;

[0014] The ball milling time for the ball milling process is 1 hour to 3 hours.

[0015] In some embodiments, the temperature of the heat treatment is 500°C to 600°C, and / or the time of the heat treatment is 0.5h to 2h.

[0016] In some embodiments, the drying is spray drying.

[0017] In some embodiments, the method further includes preparing bimetallic transition metal carbides via a hydrothermal process.

[0018] In a second aspect, the present invention provides a positive electrode active material, wherein the positive electrode active material is prepared by the preparation method of the positive electrode active material described in any one of the first aspects.

[0019] Thirdly, the present invention provides a battery comprising a negative electrode and a positive electrode, wherein the positive electrode comprises the positive electrode active material provided in the second aspect.

[0020] The above-described embodiments of the present invention have at least one or more of the following beneficial effects:

[0021] This invention provides a positive electrode active material, its preparation method, and a battery. It uses bimetallic transition metal carbide to modify lithium manganese phosphate. On the one hand, it can effectively improve the conductivity of lithium manganese phosphate and its ion conductivity, thereby effectively improving the capacity performance and rate performance of the battery. On the other hand, it can effectively improve the lattice stability of lithium manganese phosphate, thereby reducing the dissolution of manganese ions and improving the cycle performance of the battery.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0023] Some embodiments of the present invention are described below. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] As described in the background section, lithium manganese phosphate, which belongs to the same olivine structure as lithium iron phosphate cathode material (which accounts for nearly 80% of current batteries), has a theoretical specific capacity of approximately 170 mAh g⁻¹. -1However, its voltage platform is significantly improved compared to lithium iron phosphate, so its energy density is expected to increase by about 20%, making it one of the key technology routes for the next generation of power batteries.

[0025] However, lithium manganese phosphate has limited actual discharge capacity and rate performance, and it causes lattice symmetry breaking during battery charging and discharging, accompanied by Mn dissolution and structural degradation, resulting in rapid decay of cycle life.

[0026] To address the aforementioned issues, this invention creatively proposes a positive electrode active material, its preparation method, and a battery. It employs bimetallic transition metal carbide-modified lithium manganese phosphate. Through bimetallic synergy, the conductivity and lattice stability of lithium manganese phosphate can be simultaneously improved, and manganese dissolution can be suppressed, thereby effectively preventing rapid degradation of battery cycle life.

[0027] The present invention will be specifically described below through specific embodiments.

[0028] This invention provides a method for preparing a positive electrode active material, comprising:

[0029] S110. A bimetallic transition metal carbide is mixed with lithium manganese phosphate, and a solvent is added. The mixture is then mechanically mixed and dried to obtain a precursor for the positive electrode active material.

[0030] In this application, the term "bimetallic transition metal carbide" refers to a ternary compound containing two different transition metal elements and carbon in its crystal structure. It is an important branch of transition metal carbides, retaining the core characteristics of single-transition metal carbides, such as high hardness, high melting point, good electrical conductivity, and thermal conductivity. Furthermore, due to the synergistic effect of the two transition metals, it exhibits performance controllability in crystal structure, electronic state density, and surface activity that is unmatched by single-component carbides. "Transition metal" refers to the d-block and ds-block elements in the periodic table (d-block elements include elements in periodic table IIIB). Elements in groups VIIB and VIII, excluding the lanthanides and actinides. The ds block includes elements in group IB of the periodic table. Group IIB elements are a series of metallic elements, also known as transition metals. Generally, this region includes elements from groups 3 to 12, a total of ten groups, but does not include the inner transition elements in the f-block (groups 58-59 in the periodic table). Element 71 is called the transition element within 4f, 90 Element number 103 is called a transition element within 5f; they all belong to the f-block elements.

[0031] Common transition metals include iron, cobalt, nickel, molybdenum, titanium, vanadium, zirconium, and tungsten.

[0032] By modifying lithium manganese phosphate with bimetallic transition metal carbides, on the one hand, the conductivity of lithium manganese phosphate can be effectively improved, thereby effectively enhancing the capacity and rate performance of the battery. On the other hand, the lattice stability of lithium manganese phosphate can be effectively improved, thereby reducing manganese ion dissolution and improving the cycle performance of the battery.

[0033] In some embodiments, bimetallic transition metal carbides are mixed with lithium manganese phosphate at a mass ratio of (4~6):(94~96).

[0034] Optionally, the mass ratio of the bimetallic transition metal carbide to lithium manganese phosphate can be 4:96, 4.5:95.5, 5:95, 5.5:94.5, 6:94, or any ratio within the above range.

[0035] In some embodiments, the solvent is any one of water, ethanol, or a water-ethanol mixture.

[0036] Ethanol can reduce the surface tension of the slurry, improve the dispersibility of bimetallic carbides on the surface of lithium manganese phosphate, and prevent agglomeration; water, as a polar solvent, can enhance the fluidity of the slurry and facilitate the uniform mixing of particles during mechanical mixing; the mixed solvent takes into account both dispersibility and environmental friendliness, and is lower in cost and easier to recycle compared to pure organic solvents.

[0037] In some embodiments, the bimetallic transition metal carbide includes any one of Fe2MoC, Co3Mo3C, Fe2WC, and Co2WC.

[0038] Fe₂MoC, Co₃Mo₃C, Fe₂WC, and Co₂WC all follow a dual-transition metal synergistic design of lattice-fitting metal + structurally stable metal. Among these, the ionic radii of Fe and Co are similar to those of Mn in lithium manganese phosphate. 2+ With high compatibility and similar chemical properties, it can be gently doped into the lithium manganese phosphate olivine lattice during high-temperature processing, replacing some Mn sites and suppressing Mn at its source. 3+ The Jan Taylor effect prevents lattice collapse; simultaneously, Fe and Co can form stable metal-oxygen and metal-phosphorus bonds with O and P on the surface of lithium manganese phosphate, strengthening interfacial bonding. Mo and W form strong covalent bonds with carbon, endowing carbides with high structural stability and excellent conductivity. They can form a protective layer resistant to electrolyte erosion on the surface of lithium manganese phosphate, preventing Mn dissolution, and simultaneously constructing a continuous conductive network, solving the problem of low intrinsic conductivity of lithium manganese phosphate. The above are merely speculative views on the possible technical solutions of this application and do not constitute a limitation on the scope of protection of this application.

[0039] In some embodiments, the particle size D50 of the bimetallic transition metal carbide is 10 nm to 500 nm.

[0040] Optionally, the particle size D50 of the bimetallic transition metal carbide can be 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or any particle size value within the above particle size range.

[0041] It is understandable that the smaller the particle size D50 of bimetallic transition metal carbides, the larger the specific surface area, the more continuous the conductive network, the better the interface contact, and the more uniform the doping. However, they are prone to agglomeration, and the introduction of too much interfacial agglomeration will seriously form a high impedance region, deteriorate the rate capability, and even aggravate local side reactions.

[0042] In some embodiments, mechanical mixing is a ball milling process.

[0043] The ball milling speed for ball milling is 350 rpm to 500 rpm.

[0044] Optionally, the ball mill speed can be 350 rpm, 370 rpm, 390 rpm, 400 rpm, 430 rpm, 450 rpm, 480 rpm, 500 rpm, or any value within the above speed range.

[0045] When the rotation speed is below 350 rpm, the grinding force of the particles is insufficient, and the bimetallic transition metal carbides cannot be uniformly attached to the surface of lithium manganese phosphate, which easily leads to local agglomeration. When the rotation speed is above 500 rpm, the excessive mechanical force may cause the lithium manganese phosphate lattice to break, resulting in capacity loss.

[0046] The ball milling time for ball milling is 1 to 3 hours. Optionally, the ball milling time can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.4 hours, 2.5 hours, 2.7 hours, 3 hours, or any value within the above range. Ball milling for 1 hour can achieve initial dispersion, and optimal mixing uniformity can be achieved within 3 hours. Beyond 3 hours, the slurry is prone to stratification, and energy consumption increases without providing any additional technical benefit.

[0047] In some embodiments, drying is spray drying.

[0048] Furthermore, by using wet ball milling and spray drying, with solvent as the dispersion medium and a dispersant, the potential agglomeration of nanoscale bimetallic transition metal carbides is first addressed through ball milling, achieving uniform dispersion and sufficient contact in the liquid phase, and improving the interfacial bonding between the two. Then, spray drying is used for rapid molding, and the carbides are tightly "anchored" to the surface of lithium manganese phosphate. The precursor has high interfacial bonding, thus obtaining a positive electrode active material precursor of lithium manganese phosphate with uniformly attached bimetallic transition metal carbides. During high-temperature processing, there is no need to overcome the gaps in loose contact first, making it easier to form a chemically bonded, controllable in-situ doping, and dense transition interface layer.

[0049] S120. Heat-treat the precursor of the positive electrode active material to obtain the positive electrode active material.

[0050] Under high temperature conditions, bimetallic transition metal carbides wet and bridge the surface of lithium manganese phosphate, forming a through conductive pathway. Electrons can quickly migrate from the bulk phase to the electrolyte interface, resulting in a significant decrease in charge transfer impedance. Moreover, trace amounts of metal elements such as Fe, Co, Mo, and W in the bimetallic carbides diffuse into the LMP olivine lattice, replacing some Mn sites, suppressing the Ginger-Taylor effect, and reducing the dissolution of manganese ions.

[0051] In some embodiments, the heat treatment is performed in an inert atmosphere. Exemplarily, the inert atmosphere is N2.

[0052] In some embodiments, the heat treatment temperature is 500°C to 600°C.

[0053] Optionally, the heat treatment temperature can be 500℃, 524℃, 535℃, 540℃, 550℃, 561℃, 573℃, 584℃, 590℃, 600℃, or any temperature value within the above temperature range.

[0054] Understandably, if the heat treatment temperature is too low, the bimetallic transition metal carbide cannot form an effective interfacial bond with lithium manganese oxide, resulting in only physical mixing. Metal ions cannot diffuse and dope, leading to poor modification. Conversely, if the heat treatment temperature is too high, it can easily cause the decomposition of the olivine phase in lithium manganese phosphate, abnormal grain growth, decomposition of the bimetallic transition metal carbide, or excessive reaction with lithium manganese phosphate, generating impurity phases and exacerbating manganese dissolution. This, in turn, degrades capacity and cycle performance. Heat treatment at 500-600℃ allows for moderate diffusion doping of metal elements, forming a stable interfacial transition layer, a continuous conductive network, and a complete structure.

[0055] In some embodiments, the heat treatment duration is 0.5-2 hours. Optionally, the heat treatment duration can be 0.5 hours, 0.7 hours, 0.9 hours, 1 hour, 1.3 hours, 1.5 hours, 1.8 hours, 2 hours, or any duration within the above range.

[0056] Insufficient heat treatment time results in incomplete thermal reaction, weak interfacial bonding, and uneven doping. Excessive heat treatment time leads to coarsening of lithium manganese phosphate grains, lengthening of lithium-ion diffusion paths, decreased rate performance, increased energy consumption, and higher costs. Heat treatment for 0.5-2 hours ensures complete interfacial reaction, uniform doping, and improved crystallinity.

[0057] In some embodiments, step S110 further includes:

[0058] Bimetallic transition metal carbides were prepared by a hydrothermal method.

[0059] Bimetallic transition metal carbide nanoparticles can be prepared by methods such as vapor deposition, molten salt / solid phase method, and liquid phase chemical method. This invention uses a hydrothermal method to prepare bimetallic transition metal carbide nanoparticles, achieving uniform alloying of bimetals and in-situ nucleation and growth of carbides in a low-temperature liquid phase environment. This allows for precise control of the particle size, morphology, and crystal phase of the nanoparticles, while avoiding the grain growth and component segregation problems of high-temperature solid phase methods. It is suitable for the requirements of nanoscale, highly dispersed, and interfacially compatible carbide powders needed for lithium manganese phosphate modification. The prepared bimetallic transition metal carbide nanoparticles have high bimetallic component uniformity, avoid segregation, and enhance synergistic effects.

[0060] In some embodiments, the preparation of bimetallic transition metal carbide nanoparticles based on a hydrothermal method includes:

[0061] A first mixture is obtained by adding a surfactant, a carbon source, and an acid to deionized water; a first transition metal hydrate and a second transition metal hydrate are added to the first mixture to obtain a second mixture; the second mixture is hydrothermally treated to obtain a target product; and the target product is heated under an inert atmosphere to obtain bimetallic transition metal carbide nanoparticles.

[0062] The surfactant is selected from at least one of hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, and citric acid; the carbon source is selected from at least one of chitosan, glucose, sucrose, and ascorbic acid; and the acid is selected from at least one of acetic acid, acetic acid, dilute hydrochloric acid, and concentrated nitric acid. The acid adjusts the pH of the first mixture to promote the dissolution of the first and second transition metal hydrated salts and prevent the hydrolysis of metal ions. The surfactant, carbon source, and acid are added to deionized water and then magnetically stirred until homogeneous to obtain the first mixture.

[0063] A second mixture is obtained by adding a first transition metal hydrated salt and a second transition metal hydrated salt to the first mixture and stirring for 25-35 minutes.

[0064] Using hydrated salts allows for complete and rapid dissolution into a homogeneous solution, which is beneficial for obtaining products with uniform composition. Furthermore, since hydrothermal reactions essentially utilize high-temperature and high-pressure water as a reaction medium and catalyst, the crystal water of hydrated salts contributes water molecules to participate in the construction of a subcritical / supercritical water environment with extremely strong dissolving power and reactivity, which is conducive to the formation and transformation of precursors.

[0065] The hydrothermal treatment of the second mixture is performed at a temperature of 170-190℃ for a reaction time of 17-19 hours. Optionally, the hydrothermal temperature can be 170℃, 173℃, 175℃, 178℃, 180℃, 186℃, 190℃, or any value within the above temperature range, and the reaction time can be 17 hours, 17.5 hours, 18 hours, 18.2 hours, 19 hours, or any value within the above time range. After obtaining the target product through hydrothermal treatment of the second mixture, the collected target product is washed and dried, and then heated at 890-910℃ for 2.5-3.2 hours under an inert atmosphere to obtain bimetallic transition metal carbide nanoparticles. The inert atmosphere refers to an argon or nitrogen atmosphere.

[0066] In some embodiments, the first transition metal hydrate is selected from at least one of ferrous hydrate, cobalt hydrate, and nickel hydrate, and the second transition metal hydrate is selected from at least one of molybdenum hydrate and tungsten hydrate.

[0067] The first transition metal hydrated salt is selected from ferrous hydrate, cobalt hydrate, and nickel hydrate, providing Fe 2+ Co 2 + Ni 2+ At least one of the ions has an ionic radius similar to that of Mn in lithium manganese phosphate (LiMnPO4). 2+ With high matching degree, it can be gently doped into the olivine lattice of lithium manganese phosphate during high-temperature processing, replacing some manganese sites and suppressing Mn. 3+ The Jahn-Teller distortion simultaneously forms stable chemical bonds with oxygen and phosphorus elements on the surface of lithium manganese phosphate, enhancing interfacial bonding; the second transition metal hydrate salt is selected from molybdenum hydrate and tungsten hydrate, providing Mo... 6+ W 6+ Ions form strong covalent bonds with carbon (Mo-C, WC), giving carbides high structural stability and conductivity. They can form a protective layer resistant to electrolyte erosion on the surface of lithium manganese phosphate, inhibiting Mn dissolution, and at the same time constructing a continuous conductive network.

[0068] For example, ferrous salt hydrates include, but are not limited to, ferrous chloride tetrahydrate (FeCl2). 4H2O); cobalt salt hydrates include, but are not limited to, cobalt chloride hexahydrate (CoCl2). 6H2O), cobalt nitrate hexahydrate (Co(NO3)2) 6H2O); nickel salt hydrates include, but are not limited to, nickel chloride hexahydrate (NiCl2). 6H2O), nickel nitrate hexahydrate (Ni(NO3)2) (6H2O); molybdenum salt hydrates include, but are not limited to, ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O). 24 4H₂O); tungsten salt hydrates include, but are not limited to, ammonium metatungstate hydrate ((NH₄)₂O). 10 W 12 O 41 xH2O), sodium tungstate hydrate (Na2WO4) (2H2O). In addition, both the first and second transition metal hydrated salts are hydrated metal salts that are highly soluble in water, thus avoiding uneven mixing caused by sparingly soluble salts.

[0069] The molar ratio of the first transition metal hydrated salt to the second transition metal hydrated salt is consistent with the atomic ratio of the first transition metal and the second transition metal in the target bimetallic transition metal carbide nanoparticles.

[0070] This invention also provides a positive electrode active material, which is prepared by any one of the methods described in the above embodiments.

[0071] This invention also provides a battery, including a negative electrode and a positive electrode, wherein the positive electrode includes the positive electrode active material provided in any of the above embodiments.

[0072] After obtaining the positive electrode active material, the positive electrode active material, conductive agent and binder are added to an appropriate amount of NMP solvent according to a preset mass ratio, and mixed to form a uniform positive electrode slurry. Then, the slurry is coated on the positive electrode current collector, and then dried under vacuum, rolled and cut into sheets to obtain the positive electrode sheet.

[0073] The conductive agent may include any conductive material as long as it does not cause a chemical change. In some embodiments, the conductive agent includes carbon-based materials, metals and their derivatives, conductive polymers and MXenes, etc.

[0074] Among them, carbon-based materials include, but are not limited to, natural graphite, artificial graphite, graphene, carbon black, acetylene black, Ketjen black, superconducting carbon black, carbon nanotubes, carbon fibers, etc.

[0075] Metals and their derivatives include, but are not limited to, metal powders, metal fibers, metal nanowires, etc., and metals include, but are not limited to, copper, nickel, aluminum, silver, etc.

[0076] Conductive polymers include, but are not limited to, polypyrrole, PEDOT:PSS, and polyaniline.

[0077] In some embodiments, the mass of the conductive agent accounts for 0.1% to 20% of the mass of the positive electrode sheet.

[0078] The binder can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode sheet and the positive electrode current collector.

[0079] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0080] It is understood that when using a dry method to prepare the positive electrode sheet, the binder should include at least a fibrous binder, including but not limited to one or more of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

[0081] In some embodiments, the binder accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0082] In some embodiments, the positive current collector includes a metallic material that can conduct electrons, including but not limited to at least one of aluminum, nickel, tin, copper, and stainless steel.

[0083] In some embodiments, the positive current collector includes at least one of aluminum foil, carbon-coated aluminum foil, stainless steel foil, nickel foam, and porous metal.

[0084] In some embodiments, the positive electrode also includes a fast ion conductor to improve the ionic conductivity of the positive electrode. This invention does not limit the type of fast ion conductor; it can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc.

[0085] In some embodiments, the mass of the fast ion conductor accounts for 1% to 20% of the mass of the positive electrode sheet; preferably 5% to 20%.

[0086] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode layer disposed on the negative electrode current collector.

[0087] In some embodiments, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0088] In some embodiments, the battery of this application has a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the battery of this application are not particularly limited, and can be any technology disclosed in the prior art.

[0089] In some embodiments, the diaphragm comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0090] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.

[0091] In some implementations, the battery also includes an electrolyte.

[0092] In some implementations, the electrolyte includes a lithium salt and a solvent.

[0093] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0094] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0095] In some embodiments, the electrolyte also includes additives. These additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, high-temperature performance, and low-temperature performance.

[0096] In some embodiments, the aforementioned additives include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, and 4... At least one of the following: methyl vinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic acid nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

[0097] In some implementations, the battery includes a solid electrolyte layer.

[0098] In some embodiments, the solid electrolyte layer includes one of an organic solid electrolyte and an inorganic solid electrolyte; the organic solid electrolyte includes a polymer electrolyte, which includes one of a polyoxyethylene electrolyte, a polyvinylidene fluoride electrolyte, a polyacrylonitrile-based electrolyte, and a polymethyl methacrylate (PMMA)-based electrolyte.

[0099] Inorganic solid electrolytes include one or more of the following: oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, hydride solid electrolytes, boride solid electrolytes, and nitride solid electrolytes.

[0100] In some embodiments, the oxide solid electrolyte is composed of oxide solid electrolyte particles, including garnet ceramics, LISICON type oxides, NASICON type oxides, and perovskite type ceramics.

[0101] Garnet ceramics include, but are not limited to, Li 6.5 La 24 Zr 1.75 Te 0.25 O 12 、Li7La 24 Zr2O 12 Li 6.2 Ga 0.24 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La 24 Zr2O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 Li 6.75 La 24 Zr 1.75 Nb0.25 O 12 And their combinations.

[0102] LISICON type oxides include, but are not limited to, Li 14 Zn(GeO4)4, Li 24+x (P 1-x Si x O4 (where 0 < x < 1), Li 24+x Ge x V 1-x O4 (where 0 < x < 1) and their combinations.

[0103] NASICON-type oxides can be produced from LiMM′(PO4). 24 Defined where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. NASICON-type oxides include, but are not limited to, Li. 1+x Al x Ge 2-x (PO4) 24 (LAGP) (where 0 ≤ x ≤ 2), Li 1+ x Al x Ti 2-x (PO4) 24 (LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr 2-x (PO4) 24 (LYZP) (where 0≤x≤2), Li 1.24 Al 0.24 Ti 1.7 (PO4) 24 LiTi2(PO4) 24 LiGeTi(PO4) 24 LiGe2(PO4) 24 LiHf2(PO4) 24 And their combinations.

[0104] Perovskite ceramics include, but are not limited to, Li 24.24 La 0.524 TiO 24 LiSr 1.65 Zr 1.24 Ta 1.7 O9、Li 2x-y Sr 1- x Ta y Zr 1-y O 24 (where x = 0.75y and 0.60 < y < 0.75), Li24 / 8 Sr 7 / 16 Nb 24 / 4 Zr 1 / 4 O 24 Li 24x La (2 / 24-x) TiO 24 (where 0 < x < 0.25) and their combinations.

[0105] In some embodiments, the ionic conductivity of the oxide solid electrolyte is 10. -5 S / cm~10 -1 S / cm.

[0106] In some embodiments, the sulfide solid electrolyte is composed of sulfide solid electrolyte particles, including but not limited to Li2S-P2S5 and Li2S-P2S5-MS. x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 24.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.24 Li 9.6 P 24 S 12 Li7P 24 S 11 Li9P 24 S9O 24 Li 10.245 Si 1.245 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li (Ge 0.5 Sn 0.5 P2S 12 Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br, or I), Li7P2S8I, Li 10.245 Ge 1.245 P 1.65 S 12 Li 24.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.24 , (1-x)P2S5-xLi2S (where 0.5≤x≤0.7) and their combinations.

[0107] In some embodiments, the ionic conductivity of the sulfide solid electrolyte is 10. -7 S / cm ~ 1S / cm.

[0108] In some embodiments, the halide solid electrolyte layer includes halide solid electrolyte particles, and the halide solid electrolyte particles include Li a M b X c N d M includes one or more of the basic metal elements, such as Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. M also includes doped metal elements, used in conjunction with the aforementioned basic metal elements, such as one or more of Nb, Ta, Al, La, Mg, Ca, Ba, and Ag. X includes one or more of F, Cl, Br, and I. N includes one or more of O and S, and satisfies a+mb=c+nd, where m and n are the weighted valences of M and N, respectively, 1≤a≤4, b>0, c>0, and d≥0.

[0109] For example, the halide solid electrolyte particles can be Li₂ZrCl₆, Li₂ZrCl₅F, or Li₂ZrCl₆. 5.5 O 0.25 At least one of Li3InCl6, Li3YCl6, Li2HfCl6, LiInBr4, Li3InBr6, Li3LaI6, Li3LuCl6, and Li3ErCl6.

[0110] In some embodiments, the ionic conductivity of the halide solid electrolyte is 10. -8 S / cm~10 -1 S / cm.

[0111] In some embodiments, the hydride solid electrolyte is composed of hydride solid electrolyte particles, including but not limited to Li 24 AlH6, LiBH4, LiBH4-LiX (where X is one of Cl, Br and I), LiNH2, Li2NH, LiBH4-LiNH2 and combinations thereof.

[0112] In some embodiments, the ionic conductivity of the hydride solid electrolyte is 10. -7 S / cm~10 -2 S / cm.

[0113] In some embodiments, the boride solid electrolyte is composed of borate solid electrolyte particles, including but not limited to Li₂B₄O₇ and Li₂O-(B₂O₃)₂O₃. 24 )-(P2O5) and their combinations.

[0114] In some embodiments, the ionic conductivity of the boride solid electrolyte is 10. -7 S / cm~10 -2 S / cm.

[0115] In some embodiments, the nitride solid electrolyte comprises nitride solid electrolyte particles, including Li 24 N, Li7PN4, LiSi2N 24 LiPON and their combinations.

[0116] In some embodiments, the ionic conductivity of the nitride solid electrolyte is 10. -9 S / cm ~ 1S / cm.

[0117] The present application will be further described in detail below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection claimed in this application.

[0118] Example 1: Preparation of Fe2MoC nanoparticles using a hydrothermal method: Hexadecyltrimethylammonium bromide, chitosan, and acetic acid were added to 100 mL of deionized water and magnetically stirred. Then, FeCl2·4H2O was added until completely dissolved, followed by the addition of 52.8 mg (NH4)6Mo7O. 24 Add 4H2O and continue stirring for 30 min. Then perform hydrothermal treatment at 180℃ for 18 h. After collecting the product, wash and dry it, and then react it at 900℃ for 3 h under Ar protective atmosphere to obtain Fe2MoC nanoparticles. The D50 of the prepared Fe2MoC nanoparticles is 50 nm.

[0119] Preparation of Fe2MoC-modified LiMnPO4 cathode: The above-mentioned Fe2MoC nanoparticles and commercial LiMnPO4 cathode were added to an ethanol / water mixed solvent at a mass ratio of 5:95, ball-milled at 400 rpm for 2 h, and spray-dried to obtain the cathode active material precursor. The cathode active material precursor was heat-treated in N2 at 550℃ for 1 h to obtain the cathode active material.

[0120] Positive electrode homogenization: The positive electrode active material, conductive agent and binder are added to an appropriate amount of NMP solvent at a mass ratio of 8:1:1 and mixed to form a uniform positive electrode slurry. The slurry is then coated onto the positive electrode current collector and transferred to a vacuum oven to dry at 100°C for 12 hours. After drying, the positive electrode sheet is obtained by rolling and cutting.

[0121] Battery assembly: The positive electrode, separator and negative electrode are sequentially installed into the CR2032 coin cell, and 1M LiPF6 (EC:DMC:EMC=1:1:1) electrolyte is added. Let it stand for 12 hours to fully wet the electrolyte.

[0122] Example 2: The difference between this example and Example 1 is that the mass ratio of Fe2MoC nanoparticles to commercial LiMnPO4 cathode is 4:96.

[0123] Example 3: The difference between this example and Example 1 is that the mass ratio of Fe2MoC nanoparticles to commercial LiMnPO4 cathode is 6:94.

[0124] Example 4: The difference between this example and Example 1 is that the mass ratio of Fe2MoC nanoparticles to commercial LiMnPO4 cathode is 2:98.

[0125] Example 5: The difference between this example and Example 1 is that the mass ratio of Fe2MoC nanoparticles to commercial LiMnPO4 cathode is 10:90.

[0126] Example 6: The difference between this example and Example 1 is that the bimetallic transition metal carbide used is Co3Mo3C.

[0127] Example 7: The difference between this example and Example 1 is that the bimetallic transition metal carbide used is Fe2WC.

[0128] Example 8: The difference between this example and Example 1 is that the bimetallic transition metal carbide used is Ni2WC.

[0129] Example 9: The difference between this example and Example 1 is that the D50 of the Fe2MoC nanoparticles is 10 nm.

[0130] Example 10: The difference between this example and Example 1 is that the D50 of the Fe2MoC nanoparticles is 500 nm.

[0131] Comparative Example 1: The difference between this comparative example and Example 1 is that only lithium manganese phosphate is used as the positive electrode active material, and bimetallic transition metal carbide modification is not used.

[0132] Comparative Example 2: The difference between this comparative example and Example 1 is that the positive electrode active material includes lithium manganese phosphate and Mo2C.

[0133] The batteries provided in the above embodiments and comparative examples were subjected to performance tests. The batteries prepared in the above embodiments and comparative examples were charged at a constant current of 0.1C to the charging cutoff voltage of 4.4V, and then charged at a constant voltage until the charging cutoff current was 0.05C, which was considered as fully charged.

[0134] 1) Discharge capacity test:

[0135] At room temperature (25℃±3℃), a fully charged battery is discharged at a constant current of 0.1C until the cutoff voltage of 2.0V. Calculate the discharge capacity of the battery.

[0136] 2) Ratio performance test:

[0137] The batteries prepared in the above embodiments and comparative examples were fully charged. They were then discharged at a constant current of 0.1C and 1C to a discharge cutoff voltage of 2.0V, respectively, and the discharge capacity was recorded. The rate performance was calculated as: 1C discharge capacity / 0.1C discharge capacity.

[0138] 3) Cyclic performance test:

[0139] At room temperature (25℃±3℃), charge at a current of 1C to the charging cutoff voltage of 4.4V, then switch to constant voltage charging to the cutoff current of 0.05C, let stand for 0.5h, then discharge at a current of 1C to the cutoff voltage of 2.0V, let stand for 0.5h, and begin the next charge-discharge cycle. Repeat this process for 300 cycles. Record the battery capacity. Cycle retention rate = discharge capacity on the 300th cycle / initial discharge capacity.

[0140] 4) Mn on the negative electrode side 2+ Content testing:

[0141] After the batteries underwent cycle performance testing, they were disassembled. Two portions of approximately 0.1g of negative electrode powder (accurate to ±0.0003g) from each example and comparative example were weighed and placed in a 100ml beaker. A small amount of distilled water was added to moisten the bottom of the beaker, followed by the addition of 5ml of 12mol / L HCl (Shandong-made, GR) to dissolve the powder. The solution was heated on an electric heating plate for 20 minutes, then removed and cooled. After dilution, the solution was ready for testing. The prepared series of standard solutions were introduced into an ICAP7000 inductively coupled plasma optical transilluminator (ICP) instrument (made in the USA). The intensity of each element in the standard solution was measured at the wavelength of the element to be tested (manganese). When the linear correlation coefficient r of the working curve was ≥0.9995, the measurement could be performed.

[0142] The test results are shown in the table below:

[0143]

[0144] As shown in the table above, compared with Comparative Example 1, which uses lithium manganese phosphate as the positive electrode active material, the discharge capacity, rate performance, and cycle performance of the batteries provided by Examples 1-10 are significantly improved, and the Mn on the negative electrode side is also significantly improved. 2+ The significant decrease in content is due to the following: the first transition metal ion in the bimetallic transition metal carbide is mildly doped with lithium manganese phosphate in situ, which adapts to Mn sites, stabilizes the lattice, and hardly loses capacity; the second transition metal ion strengthens the structure, inhibits Mn dissolution, and the two transition metals form a continuous conductive phase with high conductivity and uniform network. The first transition metal element bonds with the surface of lithium manganese phosphate, and the second transition metal element forms a corrosion-resistant layer, resulting in strong interfacial bonding and stable CEI.

[0145] As can be seen from Comparative Examples 1 and 2 and the Examples, single-metal Mo2C doping modification does not significantly improve the battery discharge capacity, rate performance, and cycle performance. This is because: only Mo can be doped in trace amounts, making doping difficult and prone to introducing impurities; it lacks the lattice compatibility gain of Fe; the Mo-C system is singular in its conductive network, resulting in lower electron transport efficiency than bimetallic systems; Mo2C only provides structural stabilization and lacks a transition metal that matches the lattice of lithium manganese phosphate, leading to low capacity and limited cycle performance improvement after modification. In contrast, Fe2MoC solves the lattice compatibility issue with Fe and the manganese dissolution issue with Mo. Single-metal carbides have weak bonding with the LMP interface, mostly physical adhesion, and are easily oxidized and detached under long-term cycling at 4.1V, failing to continuously suppress electrolyte side reactions and leaving the continuous consumption of active lithium unresolved. They lack metals like Fe / Co, which are highly compatible with the LMP lattice, making it impossible to achieve mild and effective lattice doping to suppress Mn. 3+ Despite the Jahn-Teller distortion, manganese leaching remains significant. The above is merely a possible mechanistic speculation and does not constitute a limitation on the scope of protection of this application.

[0146] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0147] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0148] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for producing a positive electrode active material, characterized by, include: A bimetallic transition metal carbide is mixed with lithium manganese phosphate, and a solvent is added. The mixture is then mechanically mixed and dried to obtain a positive electrode active material precursor. The bimetallic transition metal carbide and the lithium manganese phosphate are mixed at a mass ratio of (4~6):(94~96). The bimetallic transition metal carbide includes at least one of Fe2MoC, Co3Mo3C, Fe2WC, and Co2WC. The positive electrode active material precursor is subjected to heat treatment to obtain the positive electrode active material.

2. The method for producing a positive electrode active material according to claim 1, characterized by, The particle size D50 of the bimetallic transition metal carbide is 10 nm to 500 nm.

3. The method for producing a positive electrode active material according to claim 1, characterized by, The mechanical mixing is a ball milling process; The ball milling speed for the ball milling process is 350 rpm to 500 rpm; The ball milling time for the ball milling process is 1 hour to 3 hours.

4. The method for producing a positive electrode active material according to claim 1, characterized by, The heat treatment temperature is 500℃~600℃, and / or the heat treatment time is 0.5h~2h.

5. The method of producing a positive electrode active material according to claim 1, characterized by, The drying process is spray drying.

6. The method for producing a positive electrode active material according to claim 1, characterized by, It also includes the preparation of bimetallic transition metal carbides via hydrothermal methods.

7. A positive electrode active material, characterized by, The positive electrode active material is prepared by the method for preparing the positive electrode active material according to any one of claims 1-6.

8. A battery, characterized by It includes a negative electrode and a positive electrode, wherein the positive electrode includes the positive electrode active material as described in claim 7.

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