Positive electrode material, and preparation method therefor and use thereof

Abstract

The present application provides a positive electrode material, and a preparation method therefor and a use thereof. The positive electrode material comprises an inner core and a coating layer on the surface of the inner core; the inner core comprises a lithium-rich manganese-based material, and the coating layer comprises a solid solution dielectric compound and phosphate; and the general chemical formula of the solid solution dielectric compound is BaαMβTiO3, wherein α+β=1.0, 0<β≤0.3, and M comprises a metal element. In the present application, by means of interface coating, the positive electrode material inhibits the physical contact and electrochemical side reaction between a positive electrode interface and an electrolyte, so that the battery has excellent high-temperature stability, and the problem of low interface stability of a lithium-rich manganese-based material under high-temperature conditions is effectively solved.

Description

A cathode material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411941076.4, filed on December 25, 2024, entitled "A cathode material and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery technology and relates to a cathode material, its preparation method and application. Background Technology

[0003] Lithium-ion batteries are currently the primary energy storage devices, widely used in electric vehicles and energy storage power stations. The cathode material of a lithium-ion battery largely determines its performance. Excellent cathode materials need to meet many requirements, the most important of which are high safety, low cost, and high energy density.

[0004] Currently, the mainstream cathode materials for electric vehicle lithium-ion batteries are lithium iron phosphate (LFP) and ternary cathodes. However, neither can simultaneously and effectively meet the three performance requirements of high safety, low cost, and high energy density. The safety performance of ternary cathodes needs further improvement, and their cost needs continuous reduction; while the energy density of LFP cathodes needs further enhancement. Therefore, high-capacity layered lithium-rich cathodes have become a strong contender for next-generation cathode materials, as they can simultaneously meet the above three requirements. However, due to the higher operating voltage of lithium-rich cathodes (≥4.5V vs Li / Li),... + The interfacial stability between the electrolyte and the electrolyte needs to be improved under high temperature conditions.

[0005] Based on the above research, there is a need to provide a cathode material that can meet the three performance requirements of high safety, low cost and high energy density, and has high interfacial stability with electrolyte under high temperature conditions. Summary of the Invention

[0006] The purpose of this application is to provide a cathode material, its preparation method and application. The cathode material, through interfacial coating, suppresses the physical contact and electrochemical side reactions between the cathode interface and the electrolyte, giving the battery excellent high-temperature stability and effectively solving the problem of low interfacial stability of lithium-rich manganese-based materials under high-temperature conditions.

[0007] To achieve the purpose of this application, the following technical solution is adopted:

[0008] In a first aspect, this application provides a cathode material, the cathode material comprising a core and a coating layer on the surface of the core, the core comprising a lithium-rich manganese-based material, and the coating layer comprising a solid solution dielectric compound and a phosphate;

[0009] The general chemical formula of the solid solution dielectric compound is Ba. α M β TiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

[0010] Preferably, the coating layer further includes a metal oxide.

[0011] Preferably, the metal oxide includes Al2O3 and / or Y2O3.

[0012] Preferably, the metallic element includes La and / or Sr.

[0013] Preferably, the phosphate includes Li3PO4 and / or Na3PO4.

[0014] Preferably, in the positive electrode material, the mass of the solid solution dielectric compound accounts for 0.2-2.0 wt% of the mass of the core.

[0015] Preferably, in the positive electrode material, the phosphate accounts for 0.5-2.0 wt% of the core mass.

[0016] Preferably, in the positive electrode material, the mass of the metal oxide accounts for 0.5-2.0 wt% of the mass of the core.

[0017] Preferably, the general chemical formula of the lithium-rich manganese-based material is Li. 1+y Ni t Mn u M' 1-y-t-u O 2-a N a Wherein, 0.1≤y≤0.2, 0.2≤t≤0.45, 0.5≤u≤0.7, 0.002≤a≤0.02, 0.95≤y+t+u<1.0, M' includes any one or at least two combinations of Mg, Cr, Nb, Ta or W, and N includes F and / or S;

[0018] Preferably, the particle size D50 of the positive electrode material is 3.0-12.0 μm.

[0019] Secondly, this application provides a method for preparing the cathode material as described in the first aspect, the method comprising the following steps:

[0020] The cathode material is obtained by mixing and sintering lithium-rich manganese-based materials, solid solution dielectric compounds, and phosphates.

[0021] The general chemical formula of the solid solution dielectric compound is Ba. α M βTiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

[0022] Preferably, a metal oxide is also added during the mixing process.

[0023] Preferably, the sintering temperature is 750-830℃ and the holding time is 10-15h.

[0024] Thirdly, this application provides a lithium-ion battery, which includes the positive electrode material as described in the first aspect, or the positive electrode material prepared by the preparation method described in the second aspect.

[0025] Compared with the prior art, this application has the following advantages:

[0026] This application, by coating the surface of lithium-rich manganese-based materials with solid solution dielectric compounds and phosphates, not only effectively suppresses the side reactions at the interface between the cathode and the electrolyte under high-temperature conditions, reduces the surface oxidation of the lithium-rich manganese-based materials, effectively improves the interfacial stability of the cathode material, and inhibits the decomposition and failure of the electrolyte, but also effectively inhibits the dissolution and migration of transition metal ions at the cathode material interface, blocks direct contact between the electrolyte and the cathode material or core, slows down acid corrosion and O release, and significantly improves the high-temperature stability of the cathode material. Attached Figure Description

[0027] Figure 1 is a schematic diagram of the structure of the positive electrode material described in Embodiment 1 of this application;

[0028] Figure 2 is a SEM image of the kernel described in Embodiment 1 of this application;

[0029] Figure 3 is a SEM image of the cathode material described in Embodiment 1 of this application.

[0030] Among them, 101 is the core, 102 is the cladding layer, and 103 is the metal oxide. Detailed Implementation

[0031] High-capacity layered lithium-rich cathodes, due to their high operating voltage window (≥4.5V vs graphite), exhibit significant interfacial stability issues at high temperatures. This is primarily manifested in a substantial decrease in high-temperature cycling performance compared to room-temperature cycling, sometimes even leading to a dramatic drop in capacity. Current technologies employ ternary cathode material coating to address this problem, utilizing inert oxide coatings and the formation of in-situ fast ion conductors. However, these methods do not effectively resolve the interfacial side reactions in lithium-rich cathodes.

[0032] Due to the strong oxidation properties of high-valence nickel and manganese metal elements on the surface of lithium-rich manganese-based materials under high temperature and high voltage conditions, they inevitably undergo slow oxidation and decomposition of the electrolyte on the positive electrode side during long-term use. This oxidation and decomposition of the electrolyte is accompanied by a decrease in the valence state of the transition metals on the surface of the positive electrode material. This manifests as a decrease in the average discharge voltage of the battery system containing the lithium-rich positive electrode, as well as the release of lattice oxygen. The released lattice oxygen combines with the organic groups in the oxidized electrolyte to form oxygen-containing functional groups, which ionize in the electrolyte and continuously consume active lithium ions, leading to the loss of active lithium. This loss of active lithium manifests as a continuous decrease in the battery system capacity, and in severe cases, even a significant capacity drop and battery failure. Therefore, simple oxide coating alone is unlikely to significantly improve the high-temperature stability of lithium-rich manganese-based materials.

[0033] The ideal coating for lithium-rich manganese-based materials is one with a certain dielectric constant to form a reverse electric field on the surface, low resistance at room temperature, and a significantly increased resistivity as the temperature rises, especially when the temperature reaches 40°C and above. This resistivity can block interfacial side reactions to a certain extent, thereby protecting the various components of the battery and ensuring system stability. Therefore, in order to solve the problem of high-temperature stability of lithium-rich manganese-based materials, this application provides a composite coated cathode material. The coating of the cathode material includes a resistance-adjustable solid solution dielectric compound with positive temperature coefficient characteristics and a phosphate-based fast ion conductor. The coating can achieve the effect of the aforementioned ideal coating, enabling the battery system to maintain excellent stability under high voltage and high temperature conditions.

[0034] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0036] In a first specific embodiment, this application provides a positive electrode material, the positive electrode material comprising a core and a coating layer on the surface of the core, the core comprising a lithium-rich manganese-based material, and the coating layer comprising a solid solution dielectric compound and a phosphate;

[0037] The general chemical formula of the solid solution dielectric compound is Ba. α M β TiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

[0038] The solid solution dielectric compound specified in this application has a positive temperature coefficient of resistance, and the resistance can be adaptively adjusted so that the resistance of the coating layer increases with the increase of the temperature of the battery system in which the cathode material is located. Thus, under high temperature conditions, it can effectively suppress the interfacial electron conduction of the cathode material. At the same time, by utilizing its dielectric properties, it forms a reverse electric field inside the coating layer, reducing the surface oxidation of lithium-rich manganese-based materials. This effectively reduces the oxidation of the electrolyte by high-valence, strongly oxidizing transition metal ions on the surface of lithium-rich cathode materials, improves the interfacial stability of the cathode material, and inhibits the decomposition and failure of the electrolyte.

[0039] Therefore, the solid solution dielectric compound described in this application exhibits exponentially increasing resistance at high temperatures, effectively suppressing side reactions at the cathode-electrolyte interface, effectively blocking the electron conduction required for side reactions, and maintaining extremely high system health, thereby improving the high-temperature cycle performance of the battery system. Furthermore, although the resistance of the solid solution dielectric compound increases at high temperatures, the electronic and ionic conductivity of the lithium-rich manganese-based material also increases significantly under high-temperature conditions. Therefore, the addition of the solid solution dielectric compound does not lead to a significant increase in the internal resistance of the system.

[0040] The specific chemical formula of the solid solution dielectric compound described in this application is Ba. α M β TiO3, wherein α+β=1.0, 0<β≤0.3, for example, can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3, and M includes a metallic element, which refers to a metallic element other than Ba ​​and Ti, exemplarily such as any one or at least two combinations of Sr, Zr, Ca or La; and in this application Ba α M β TiO3 is a one-time solid solution, and the Curie temperature can be adjusted by adjusting the β coefficient to obtain a cathode material with low resistance at room temperature and significantly increased resistance at high temperature within the battery operating temperature range of 25-60℃. This ensures the capacity and kinetic performance of the cathode material at room temperature, while significantly improving high-temperature stability, blocking high-temperature interface side reactions to a certain extent, avoiding overcharging, and improving high-temperature long-cycle stability.

[0041] The coating layer described in this application also includes phosphate, which, as a fast ion conductor, can effectively inhibit the dissolution and migration of transition metal ions at the cathode material interface, and prevent direct contact between the electrolyte and the cathode material or core. Simultaneously, phosphate possesses excellent lithium-ion conductivity, acting as a physical membrane for transition metal ions. Therefore, the phosphate fast ion conductor can significantly reduce the dissolution of transition metals on the cathode material surface, improve the integrity of the cathode surface structure during long-cycle processes, prevent the acidic electrolyte from corroding the cathode material interface, and slow down structural reconstruction and degradation. Furthermore, the high PO bond energy in phosphate and the high structural stability of the O anion can stabilize the O lattice at high voltage and full charge, preventing the release of O from the cathode lattice due to the nucleophilic properties of organic groups in the electrolyte. Therefore, phosphate plays multiple roles, including slowing acid corrosion, inhibiting metal ion dissolution and O release, thereby further improving the stability of the cathode material.

[0042] The phosphate and solid solution dielectric compound in the coating layer described in this application also play a synergistic role. Since interfacial side reactions are intensified at high temperatures compared to room temperature, the significantly increased resistance of the solid solution dielectric compound effectively suppresses these side reactions. The ionic conductivity provided by the phosphate ensures good ion migration during charging and discharging, mitigating the increased polarization caused by higher electronic conductivity. Furthermore, the phosphate can improve ionic conductivity, reduce oxygen release, and inhibit transition metal dissolution at room temperature, exhibiting excellent stability and power performance. The solid solution dielectric compound provides good physical barrier properties. Therefore, the combination of these two components provides excellent and balanced high-temperature performance.

[0043] Preferably, the coating layer further includes a metal oxide; the metal oxide exemplarily includes any one or a combination of at least two of Al2O3, Y2O3, ZnO, MgO, TiO2 or ZrO2.

[0044] The metal oxide described in this application, combined with the solid solution dielectric compound and phosphate to form a coating layer, can better spread and melt onto the surface of the cathode material, improve the surface coating effect, better protect the bulk material, and prevent direct contact between high-valence Ni and Mn ions and the electrolyte when fully charged.

[0045] Preferably, the metal oxide includes Al2O3 and / or Y2O3.

[0046] The metal oxides selected in this application are low-oxidizing metal ion oxides. On the one hand, they can lower the melting point and melt, making the coating layer dense and uniform. On the other hand, low-oxidizing metal oxides have extremely high chemical stability, and their metal ions have weak electron-acquiring ability, resulting in good acid corrosion resistance. Therefore, the interface between the cathode material and the electrolyte has high stability, which can effectively enhance the durability of the coating layer. In addition, the metal ions in the low-oxidizing metal ion oxides have low valence states and low O content in the structure itself, so there will be no significant structural decomposition and O release, thus exhibiting good inertness.

[0047] Preferably, the metallic element includes La and / or Sr.

[0048] The solid solution dielectric compound Ba described in this application α M β The preferred form of M in TiO3 is La and / or Sr, which effectively lowers the temperature point at which its resistance increases significantly, i.e., the Curie temperature. This allows the battery to maintain a low resistance below this temperature and provide a significantly increased resistance above it, thereby significantly reducing interfacial side reactions under high-temperature conditions and improving the battery's high-temperature lifespan. Furthermore, the La / Sr elements possess good electrochemical inertness, which can improve the dielectric properties of the solid solution dielectric compound Ba. α M β Durability of TiO3.

[0049] Preferably, the phosphate includes Li3PO4 and / or Na3PO4.

[0050] The phosphates selected in this application, namely Li3PO4 and / or Na3PO4, can provide excellent ionic conductivity and effectively suppress the dissolution of transition metal ions, thereby improving the stability of the material interface structure, suppressing gas release, enabling the cathode material to have excellent power performance, and extending the service life of the cathode material at room temperature.

[0051] Preferably, in the positive electrode material, the mass of the solid solution dielectric compound accounts for 0.2-2.0 wt% of the mass of the core, for example, it can be 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, or 2 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] The mass of the solid solution dielectric compound described in this application accounts for the mass of the core = the mass of the solid solution dielectric compound / the mass of the core.

[0053] Preferably, in the positive electrode material, the phosphate accounts for 0.5-2.0 wt% of the core mass, for example, 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, or 2 wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0054] Similarly, the mass of the phosphate relative to the mass of the kernel is equal to the mass of the phosphate divided by the mass of the kernel.

[0055] Preferably, in the positive electrode material, the mass of the metal oxide accounts for 0.5-2.0 wt% of the mass of the core, for example, it can be 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, or 2 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] By rationally selecting the amount of each component added in the coating layer of this application, the coating effect can be further improved and the role of the components can be promoted. In particular, the use of an appropriate amount of solid solution dielectric compound will not lead to a significant increase in the internal resistance of the system. Moreover, by rationally controlling the amount of coating, the electronic conductivity of the interface between the cathode material and the electrolyte can be kept at a level close to or slightly lower than that at room temperature, thereby significantly reducing the degree of side reaction and enabling the battery to achieve cycle performance close to that at room temperature at high temperatures.

[0057] Similarly, the mass of the metal oxide accounts for the mass of the core = the mass of the metal oxide / the mass of the core.

[0058] Preferably, the general chemical formula of the lithium-rich manganese-based material is Li. 1+y Ni t Mn u M' 1-y-t-u O 2-a N a Wherein, 0.1≤y≤0.2, for example, can be 0.1, 0.15 or 0.2; 0.2≤t≤0.45, for example, can be 0.2, 0.3, 0.4 or 0.45; 0.5≤u≤0.7, for example, can be 0.5, 0.6 or 0.7; 0.002≤a≤0.02, for example, can be 0.002, 0.005, 0.01, 0.015 or 0.02; 0.95≤y+t+u<1.0, for example, can be 0.95, 0.96, 0.97, 0.98 or 0.99; M' includes any one or at least two combinations of Mg, Cr, Nb, Ta or W; and N includes F and / or S.

[0059] The lithium-rich manganese-based material in the core of this application also contains a specific amount of doping elements, which can further improve the cycle stability of the cathode material.

[0060] Preferably, the particle size D50 of the positive electrode material is 3.0-12.0 μm, for example, it can be 3.0 μm, 5.0 μm, 7.0 μm, 9.0 μm, 11.0 μm or 12.0 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] The particle size D50 mentioned in this application represents the particle size at which the material particles reach 50% of the total volume in a volume-based particle size distribution, measured from the smallest particle size.

[0062] The cathode material described in this application has a particle size D50 within a suitable range, which can ensure its comprehensive properties such as good ion transport characteristics and good capacity utilization.

[0063] In a second embodiment, this application provides a method for preparing the cathode material as described in the first embodiment, the method comprising the following steps:

[0064] The cathode material is obtained by mixing and sintering lithium-rich manganese-based materials, solid solution dielectric compounds, and phosphates.

[0065] The general chemical formula of the solid solution dielectric compound is Ba. α M β TiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

[0066] The cathode material described in this application can be obtained by directly mixing and sintering the core material and the coating material, and the preparation method is simple and convenient.

[0067] Preferably, the sintering temperature is 750-830℃, for example, 750℃, 800℃ or 830℃, and the holding time is 10-15h, for example, 10h, 12h, 14h or 15h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] The solid solution dielectric compound described in this application is a high-temperature, one-time molding solid solution of Ba. α M β TiO3, not the product of low-temperature sintering of a mixture of BaTiO3 and SrTiO3, therefore, solid solution type Ba α M β The Curie temperature of TiO3 can be adjusted by adjusting the β coefficient to obtain a cathode material with low resistance at room temperature and significantly increased resistance at high temperature within the battery operating temperature range of 25 to 60°C.

[0069] For example, the Ba α M β The preparation method of TiO3 includes the following steps:

[0070] According to the formula, barium carbonate, carbonate of metallic M, and titanium oxide are mixed and sintered to obtain the Ba. α M β TiO3.

[0071] As a preparation of Ba α M β The preferred technical solution for TiO3 includes the following steps: using barium carbonate, carbonate of metallic M, and titanium oxide as raw materials, the materials are proportioned according to a stoichiometric ratio, thoroughly mixed, and then the mixture is subjected to air jet milling to ensure the average particle size D based on the volume of the raw materials. 50 <3.0μm (e.g., 2.9μm, 2.5μm, 2.0μm, or 1.5μm), the mixed raw materials are then dispersed in water, milled, dried, and sieved to obtain the volume-based average particle size D. 50 The mixture system with a particle size <1.0 μm was then sintered at a high temperature of 1300-1500℃ (e.g., 1300℃, 1400℃, or 1500℃) for 4-6 hours (e.g., 4 hours, 5 hours, or 6 hours). The sintered solid was then subjected to air jet milling and sieve to obtain a solid solution dielectric compound Ba with a particle size <3 μm. α M β The chemical formula for the sintering process of TiO3 can be represented as: BaCO3=BaO+CO2↑ MCO3=MO+CO2↑ αBaO+βMO+TiO2=Ba α M β TiO3

[0072] Preferably, the cathode material is obtained by naturally cooling to room temperature after sintering and then sieving.

[0073] Preferably, a metal oxide is also added during the mixing process.

[0074] Preferably, the method for preparing the lithium-rich manganese-based material includes the following steps:

[0075] The precursor material, lithium salt, M'-containing compound and N-containing compound are mixed and calcined, then naturally cooled to room temperature and sieved to obtain the lithium-rich manganese-based material.

[0076] Preferably, the calcination is carried out in a box furnace or roller kiln at a temperature of 850-950°C, such as 850°C, 900°C or 950°C, and the holding time is 10-15 hours, such as 10 hours, 12 hours, 14 hours or 15 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] Preferably, the lithium salt comprises lithium carbonate and / or lithium hydroxide.

[0078] Preferably, the M'-containing compound includes any one or a combination of at least two of Nb2O5, WO3, Ta2O5, MgO, or Cr2O3.

[0079] Preferably, the nitrogen-containing compound includes LiF and / or Li2S.

[0080] Preferably, the method for preparing the precursor material includes the following steps:

[0081] In a protective gas atmosphere, a metal salt solution, a precipitant solution, and a complexing agent solution are subjected to a co-precipitation reaction. Once the particle size reaches the target size, the feed is stopped and the slurry is collected. The collected slurry is then aged, washed, centrifuged, and dried to obtain the precursor material.

[0082] Preferably, the metal salt solution includes nickel salt and manganese salt.

[0083] In a third embodiment, this application provides a lithium-ion battery, which includes a positive electrode material as described in the first embodiment, or a positive electrode material prepared by the preparation method described in the second embodiment.

[0084] The lithium-ion battery provided in this application includes a positive electrode sheet containing the positive electrode material, a negative electrode sheet, an electrolyte, and a separator, wherein the separator is optional.

[0085] Preferably, the positive electrode sheet includes a positive current collector and an active material layer coated on at least one side of the positive current collector, wherein the active material layer includes the positive electrode material, positive electrode binder and positive electrode conductive agent as described in the first specific embodiment.

[0086] Preferably, the positive electrode binder includes any one or a combination of at least two of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, or polyacrylate. Those skilled in the art can select according to their needs, and no specific limitation is made here.

[0087] Preferably, the positive electrode conductive agent includes any one or a combination of at least two of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. Those skilled in the art can select according to their needs, and no specific limitation is made here.

[0088] Preferably, the negative electrode sheet includes a negative current collector and a layer of negative active material covering the surface of the negative current collector.

[0089] Preferably, the negative electrode active material layer includes a negative electrode binder, a negative electrode active substance, and a negative electrode conductive agent.

[0090] Preferably, the negative electrode binder includes any one or a combination of at least two of polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, nitrile rubber, styrene-ethylene-butene-styrene copolymer, styrene-butadiene-styrene copolymer, lithium polyacrylate, sodium polyacrylate, sodium alginate, or lithium alginate. Those skilled in the art can select according to their needs, and no specific limitation is made here.

[0091] Preferably, the negative electrode active material includes any one or a combination of at least two of graphite, soft carbon, hard carbon, silicon oxide, or silicon carbon. Those skilled in the art can choose according to their needs, and no specific limitation is made here.

[0092] Preferably, the negative electrode conductive agent includes any one or a combination of at least two of conductive carbon black, carbon nanotubes, vapor-grown carbon nanotubes, or carbon nanofibers. Those skilled in the art can choose according to their needs, and no specific limitation is made here.

[0093] Preferably, this application does not particularly limit the type of electrolyte; any known electrolyte material can be used in this application without departing from the concept of this application. As an illustrative example, the electrolyte can be a liquid electrolyte, a solid electrolyte, or a mixture of solid and liquid electrolytes.

[0094] In addition, the electrolyte used in this application may be an organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte or molten inorganic electrolyte, etc., which can be used to manufacture secondary batteries, but is not limited to these.

[0095] Preferably, the electrolyte can be a solid electrolyte. The solid electrolyte particles may contain one or more polymer components, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, borate solid electrolytes, nitride solid electrolytes, or hydride solid electrolytes, or any combination of at least two of these. Those skilled in the art can choose according to their needs, and no specific limitation is made here.

[0096] Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0097] Preferably, the organic solvent can be an ester solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, and E-caprolactone; an ether solvent, such as dibutyl ether or tetrahydrofuran; a ketone solvent, such as cyclohexanone; an aromatic hydrocarbon solvent, such as benzene and fluorobenzene; a carbonate solvent, such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate; an alcohol solvent, such as ethanol and isopropanol; a nitrile, such as R-CN (where R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, and may contain a double-bonded aromatic ring or ether bond); an amide, such as dimethylformamide; a dioxolane, such as 1,3-dioxolane; or sulfolane.

[0098] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in lithium secondary batteries. For example, the lithium salt source includes, but is not limited to, any one or at least a combination of two of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4 or LiCF3SO3.

[0099] The primary function of the separator described in this application is to separate the negative and positive electrode plates and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a separator commonly used in secondary batteries. In particular, a separator with excellent electrolyte wettability and low resistance to ion movement in the electrolyte is preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers: ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, for example, nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. In addition, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0100] The technical solution of this application is further illustrated below through specific embodiments.

[0101] Example 1

[0102] This embodiment provides a positive electrode material. The structural schematic diagram of the positive electrode material is shown in Figure 1. It includes a core 101 and a coating layer 102 on the surface of the core 101. The surface of the coating layer 102 also contains metal oxides 103 that have not completely melted and are coated in an island-like manner.

[0103] The core 101 includes a lithium-rich manganese-based material, which is Li. 1.145 Ni 0.295 Mn 0.55 Nb 0.005 Mg 0.005 O 1.995 S 0.005 ;

[0104] The coating layer 102 comprises a solid solution dielectric compound, a phosphate, and a metal oxide, wherein the solid solution dielectric compound is Ba. 0.75 Sr 0.25 TiO3, wherein the phosphate is Li3PO4, and the metal oxide is Al2O3;

[0105] The particle size D50 of the positive electrode material is 10.2 μm; in the positive electrode material, the mass of the solid solution dielectric compound accounts for 1.0 wt% of the core mass, the mass of the phosphate accounts for 1 wt% of the core mass, and the mass of the metal oxide accounts for 1 wt% of the core mass.

[0106] The method for preparing the cathode material includes the following steps:

[0107] (1) Prepare a nickel and manganese salt solution with a concentration of 2.5 mol / L as a metal salt solution, wherein the nickel and manganese sources are nickel sulfate and manganese sulfate, respectively, and the molar ratio of nickel ions to manganese ions is 35:65; prepare a 10 mol / L sodium hydroxide solution and a 10 wt% ammonia complexing agent solution.

[0108] (2) Fill the 50L reactor with clean water, set the stirring speed of the reactor to 800rpm and the temperature to 55℃, and introduce nitrogen gas. After exhausting the gas for 2 hours, introduce the metal salt solution described in step (1) into the reactor at a flow rate of 2L / min, introduce the sodium hydroxide solution described in step (1) at a flow rate of 0.5L / min, introduce the ammonia complexing agent solution described in step (1) at a flow rate of 0.05L / min, and maintain the pH of the reaction system at 9.8.

[0109] (3) When the particle size in the system of step (2) grows to D 50 When the particle size reaches 10.0 μm, stop feeding and collect the slurry in the reactor;

[0110] (4) The slurry collected in step (3) is aged, washed, centrifuged and dried to obtain the precursor material Ni. 0.35 Mn 0.65 (OH)2;

[0111] (5) The precursor material described in step (4) is mixed with lithium carbonate at a metal ion molar ratio of 1:1.34, and the formulated amounts of Nb2O5, MgO and Li2S are added. The mixture is thoroughly mixed and sintered in a box furnace at a heating rate of 2℃ / min and a sintering temperature of 950℃. After holding at the temperature for 12h, the mixture is allowed to cool naturally to room temperature and then sieved to obtain the lithium-rich manganese-based material.

[0112] (6) According to the formula, the lithium-rich manganese-based material, solid solution dielectric compound, phosphate and metal oxide described in step (5) are fully mixed and sintered in a box furnace. The sintering heating rate is 2℃ / min, the sintering temperature is 780℃, and after holding for 10h, it is naturally cooled to room temperature and sieved to obtain the positive electrode material.

[0113] Among them, the solid solution dielectric compound Ba 0.75 Sr 0.25 The preparation method of TiO3 includes the following steps: using barium carbonate, strontium carbonate, and titanium oxide as raw materials, the ingredients are weighed according to the stoichiometric ratio, thoroughly mixed, and then the mixture is subjected to air jet milling to obtain a particle size D. 50 The raw materials were mixed with a particle size of 2 μm. The mixture was then dispersed in water, milled, dried, and sieved to obtain a particle size D. 50 The mixed powder was 0.5 μm thick. The powder was then sintered at 1400℃ for 5 hours. The sintered solid was then subjected to air jet milling and sieved to obtain D. 50 A solid solution dielectric compound with a diameter of 1 μm;

[0114] The SEM image of the core described in this embodiment is shown in Figure 2. The grain boundaries are clear and distinct, and the surface is smooth without any adhering substances. The SEM image of the cathode material is shown in Figure 3. The grain boundaries on the surface of the cathode material are covered by a molten coating layer, and the number and size of the voids between primary particles are significantly reduced. At the same time, there are some island-shaped metal oxides on the surface that have not completely melted due to their high thermal stability.

[0115] Examples 2-20 provide a positive electrode material. The difference between the positive electrode material and Example 1 is that the selection of the core, solid solution dielectric compound, phosphate and metal oxide, the mass ratio of the solid solution dielectric compound, phosphate and metal oxide to the core, and the particle size D50 of the positive electrode material are different. All other aspects are the same as Example 1.

[0116] Comparative Examples 1-11 provide a cathode material that differs from Example 1 in the selection of the core, solid solution dielectric compound, phosphate, and metal oxide; the mass ratio of the solid solution dielectric compound, phosphate, and metal oxide to the core; and the particle size D50 of the cathode material. All other aspects are the same as in Example 1. In Comparative Example 10, Ba... 0.7 Sr 0.2 La 0.1 TiO3 was replaced with 0.7BaTiO3·0.2SrTiO3·0.1LaTiO3. The preparation method of 0.7BaTiO3·0.2SrTiO3·0.1LaTiO3 includes: mixing BaTiO3, SrTiO3 and LaTiO3 in a molar ratio of 0.7:0.2:0.1 and sintering at 1400℃ for 5h, followed by air jet milling and sieving.

[0117] The composition of the core, solid solution dielectric compound, phosphate and metal oxide of the above embodiments and comparative examples, the mass ratio of solid solution dielectric compound, phosphate and metal oxide to the core, and the particle size D50 of the cathode material are shown in Table 1. The particle size D50 was measured using a laser particle size analyzer.

[0118] Table 1

[0119] The cathode materials obtained in the above examples and comparative examples were subjected to ICP-AES analysis to determine their actual chemical composition. The test results are shown in Table 2.

[0120] Table 2

[0121] As shown in Table 2, the trace element results measured by ICP-AES generally correspond to the experimental design values. Each sample exhibits small fluctuations or errors to varying degrees, with differences from the theoretical values ​​not exceeding 20%. Therefore, the experiment proves that the design of this application is consistent with reality.

[0122] The positive electrode materials described in the above embodiments and comparative examples are assembled into liquid coin cell half-cells. The assembly method is as follows: the obtained positive electrode material, Super-P (conductive carbon black) and PVDF (polyvinylidene fluoride) are added to NMP (N-methylpyrrolidone) in a mass ratio of 94:3:3 and mixed evenly to obtain a slurry. The obtained slurry is then coated, dried, stamped and rolled to obtain a positive electrode sheet. The stainless steel shell, positive electrode sheet, PP separator and lithium sheet of the coin cell are stacked in sequence, a certain amount of electrolyte is added, and then the cells are sealed and left to stand to obtain a liquid coin cell half-cell.

[0123] The liquid coin cell was subjected to the following electrochemical performance tests:

[0124] (1) 0.2C discharge capacity test

[0125] Test method: After the assembled battery has been left to stand for 5 hours at 25℃, it is charged to 4.55V at a constant current of 0.2C, then charged to 0.05C at a constant voltage of 4.55V. After standing for 5 minutes, it is discharged to 2.5V at a constant current of 0.2C. The resulting discharge capacity is the 0.2C discharge capacity.

[0126] (2) First Coulomb efficiency

[0127] Test method: After the assembled battery is left to stand for 5 hours at 25℃, it is charged to 4.55V at a constant current of 0.2C, then charged to 0.05C at a constant voltage of 4.55V. After standing for 5 minutes, it is discharged to 2.5V at a constant current of 0.2C. The resulting discharge capacity / charge capacity is the initial coulombic efficiency.

[0128] (3) Capacity retention rate after 300 cycles at 1.0°C

[0129] Test method: After testing the first discharge capacity of the battery at 25℃, the battery was transferred to a 45℃ constant temperature insulation box and charged at a constant current of 1.0C to 4.55V. Then, it was charged at a constant voltage of 4.55V until the cutoff current was equal to 0.05C. After resting for 5 minutes, it was discharged at a constant current of 1.0C to 2.5V. This process was repeated 300 times, that is, 300 charge-discharge cycles at a charge-discharge rate of 1.0C / 1.0C. The discharge capacity of the 300th cycle / the discharge capacity of the 1st cycle is the capacity retention rate of the battery after 300 cycles at 1.0C / 1.0C.

[0130] The electrochemical performance test results are shown in Table 3: r

[0131] Table 3

[0132] As can be seen from Table 3:

[0133] (1) As can be seen from Examples 1-20 and Comparative Example 1, the present application uses a specific coating layer, which can improve the high-temperature cycling performance of the cathode material, and the cathode material also has a high specific capacity. As can be seen from Examples 1 and Comparative Examples 2-4, when only solid solution dielectric compounds, phosphates or metal oxides are used for coating, it is not possible to effectively improve the high-temperature long-cycle stability of the cathode material. Since a single coating layer can only improve one aspect of performance under high temperature conditions, the final high-temperature performance depends on the weak link of the material performance. It is necessary to improve the "shortcomings" in a coordinated manner to raise the lower limit of the "shortcomings" in order to finally obtain a cathode material with excellent high-temperature performance. The composite coating of the present application can play a synergistic role and obtain a cathode material with excellent high-temperature performance. As can be seen from Examples 1 and Comparative Examples 5-6, when the coating layer lacks phosphates or solid solution dielectric compounds, the high-temperature performance of the cathode material will decrease, and the lack of solid solution dielectric compounds has a more obvious impact on the high-temperature performance.

[0134] (2) As can be seen from Examples 11 and Comparative Examples 7-9, simply replacing the solid solution dielectric compound of this application with BaTiO3, SrTiO3, or LaTiO3 cannot effectively guarantee the room temperature and high temperature performance of the cathode material. Since pure phase BaTiO3 has low resistance at room temperature, its resistance increases exponentially at around Curie temperature of 120°C. Pure phase SrTiO3 has a Curie temperature close to absolute zero and has extremely high resistivity at room temperature. Therefore, although the BaTiO3 coating component has a high dielectric constant in the battery operating temperature range of 25-60°C, its resistance is low at high temperature, which has a limited effect on improving the long-term cycling stability at high temperature. SrTiO3 can easily cause the cathode material to have excessive resistance at room temperature, making it difficult to achieve its capacity. While the abundant oxygen vacancies in LaTiO3 can buffer oxygen loss to some extent, its high conductivity exacerbates interfacial side reactions. As shown in Example 11 and Comparative Example 10, the solid solution dielectric compound described in this application is a solid solution type material. In Comparative Example 10, the solid solution type material of this application was replaced with a non-solid solution material. The product of physical mixing and high-temperature calcination of BaTiO3, SrTiO3, and LaTiO3 in Comparative Example 10 is not a solid solution. This is because the perovskite finished product (BaTiO3, SrTiO3, LaTiO3) has high structural stability, and simple high-temperature sintering makes it difficult for them to fully react and dissolve to form a solid solution, thus failing to effectively improve the high-temperature performance of the cathode material. As shown in Example 1 and Comparative Example 11, Ba... α M β In TiO3, the β value cannot be too large, otherwise it will affect its performance and fail to effectively improve the high-temperature cycling performance of the cathode material.

[0135] In summary, this application provides a cathode material, its preparation method, and its application. The cathode material, through interfacial coating, suppresses the physical contact and electrochemical side reactions between the cathode interface and the electrolyte, thereby giving the battery excellent high-temperature stability and effectively solving the problem of low interfacial stability of lithium-rich manganese-based materials under high-temperature conditions.

[0136] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A cathode material, wherein, The cathode material includes a core and a coating layer on the surface of the core. The core includes a lithium-rich manganese-based material, and the coating layer includes a solid solution dielectric compound and a phosphate. The general chemical formula of the solid solution dielectric compound is Ba. α M β TiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

2. The cathode material according to claim 1, wherein, The coating layer also includes metal oxides.

3. The cathode material according to claim 2, wherein, The metal oxides include Al2O3 and / or Y2O3.

4. The cathode material according to any one of claims 1-3, wherein, The metallic elements include La and / or Sr.

5. The cathode material according to any one of claims 1-4, wherein, The phosphate includes Li3PO4 and / or Na3PO4.

6. The cathode material according to claim 2 or 3, wherein, In the positive electrode material, the mass of the solid solution dielectric compound accounts for 0.2-2.0 wt% of the mass of the core; And / or, in the positive electrode material, the mass of the phosphate accounts for 0.5-2.0 wt% of the mass of the core; And / or, in the cathode material, the mass of the metal oxide accounts for 0.5-2.0 wt% of the mass of the core.

7. The cathode material according to any one of claims 1-6, wherein, The general chemical formula of the lithium-rich manganese-based material is Li. 1+y Ni t Mn u M' 1-y-t-u O 2-a N a Wherein, 0.1≤y≤0.2, 0.2≤t≤0.45, 0.5≤u≤0.7, 0.002≤a≤0.02, 0.95≤y+t+u<1.0, M' includes any one or at least two combinations of Mg, Cr, Nb, Ta or W, and N includes F and / or S; And / or, the particle size D50 of the positive electrode material is 3.0-12.0 μm.

8. A method for preparing the cathode material according to any one of claims 1-7, wherein, The preparation method includes the following steps: The cathode material is obtained by mixing and sintering lithium-rich manganese-based materials, solid solution dielectric compounds, and phosphates. The general chemical formula of the solid solution dielectric compound is Ba. α M β TiO3, where α+β=1.0, 0<β≤0.3, and M includes metallic elements.

9. The preparation method according to claim 8, wherein, Metal oxides were also added during the mixing process.

10. The preparation method according to claim 8 or 9, wherein, The sintering temperature is 750-830℃, and the holding time is 10-15h.

11. A lithium-ion battery, wherein, The lithium-ion battery includes the cathode material as described in any one of claims 1-7, or the cathode material prepared by the preparation method as described in any one of claims 8-10.

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