A lithium-rich disordered rock-salt polyanion cathode material composite, and a preparation method and use thereof

Abstract

This invention discloses a lithium-rich disordered rock salt polyanion cathode material composite, its preparation method, and its applications. The composite comprises lithium-rich disordered rock salt polyanion and lithium manganese iron phosphate; the molecular formula of the lithium-rich disordered rock salt polyanion is Li. 1+ a Mn b M h O 4‑f‑4g F f (XO4) g The molecular formula of the lithium manganese iron phosphate is LiMn. 1‑x‑y Fe x M' y Both PO4 and carbon can be coated, and both can be doped with other metal elements. The composite cathode material of the present invention can leverage the complementary advantages of lithium-rich disordered rock salt cathode materials and traditional manganese iron phosphate cathode materials, while exhibiting high specific capacity and good cycle stability.

Description

Technical Field

[0001] This invention relates to a lithium-rich disordered rock salt polyanionic cathode material composite, its preparation method, and its uses. Background Technology

[0002] Among lithium-ion battery cathode materials, lithium-rich disordered rock salt materials and lithium manganese iron phosphate (LMFP) have become two novel cathode materials that have attracted much attention in recent years due to their unique structures and electrochemical properties. However, single materials often have certain limitations in practical applications. For example, lithium-rich materials are prone to structural transformation and capacity decay during cycling, which limits their performance under long-cycle conditions, while LMFP faces problems such as low electronic conductivity and slow ion diffusion rate, which limits its performance under high-rate conditions.

[0003] Lithium-rich disordered rock salt materials possess high specific capacity and high energy density, and exhibit good structural stability. However, they suffer from severe oxygen loss under high voltage, leading to poor stability. In contrast, lithium manganese iron phosphate, with its olivine structure similar to lithium iron phosphate and a higher discharge platform (approximately 4.1V), demonstrates better cycle stability. Summary of the Invention

[0004] In view of the shortcomings and deficiencies of the prior art, the present invention provides an improved composite cathode material that can simultaneously possess high specific capacity and good cycle stability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A cathode material composite comprising lithium-rich disordered rock salt polyanion and lithium manganese iron phosphate; The molecular formula of the lithium-rich disordered rock salt polyanion is Li 1+a Mn b M h O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0≤h≤1, 0.0001≤f≤1, 0.0001≤g≤1; M is selected from one or more combinations of Cr, Fe, Ni, Co, V, Mg, Zn, Cu, Al, Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; X is selected from one or more combinations of N, P, B, S, and Si. The molecular formula of the lithium manganese iron phosphate is LiMn. 1-x-y Fe x M' yPO4, where M' is one or more combinations selected from Mg, Ti, V, Cr, Co, Ni, Zn, Ga, Al, Zr, Nb, Mo, Sn, Sb, Ca, Ba, Si, B, Ru, Si, Te, and Cu, and 0.01≤x≤0.98, 0≤y≤0.1. In this invention, lithium-rich refers to a material with a relatively high lithium content. Typically, the lithium content in lithium-rich materials exceeds the conventional stoichiometry, and excess lithium helps improve the electrochemical performance of the material; disordered rock salt structure refers to an atomic arrangement of a material with a face-centered cubic oxygen sublattice. In a disordered rock salt structure, the distribution of transition metal ions and lithium ions in the lattice does not exhibit obvious long-range order, unlike in some ordered structures where atoms are arranged neatly according to specific rules. This disorder significantly impacts material performance. For example, disordered rock salt cathode materials rely on the redox reaction of oxygen ions to achieve high capacity under high voltage, but this can also lead to factors such as gas generation, causing structural instability. Polyanions are negatively charged ionic groups formed by multiple atoms bonded together by covalent bonds, such as phosphate, borate, silicate, and sulfate. In lithium-rich disordered rock salt polyanion materials, the introduction of polyanion groups is to enhance material stability. The central atom in the polyanion (such as B, P, Si, S, N, etc.) forms strong covalent bonds with oxygen atoms. When they enter the rock salt structure, they can stabilize the oxygen ions near the central atom, significantly reducing the risk of oxygen release, thereby enhancing the material's structural stability and cycle life.

[0006] Lithium-rich disordered rock salt polyanions can be doped or undoped; when h is 0, it is undoped, and when h is not 0, it is doped. Lithium manganese iron phosphate can also be doped or undoped; when y is 0, it is undoped, and when y is not 0, it is doped.

[0007] In some embodiments, the mass ratio of the lithium-rich disordered rock salt polyanion to lithium manganese iron phosphate is 1-5:5-9; preferably 1-2:8-9.

[0008] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon.

[0009] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon at a mass percentage of 0.1%-10%. Insufficient carbon coating reduces electronic conductivity, increases material polarization, and lowers rate performance. A lack of sufficient carbon coating also makes the electrolyte more susceptible to side reactions with the active material, leading to interfacial instability and capacity decay. Excessive carbon coating reduces the content of active material, lowers the capacity of the cathode material, and an overly thick carbon coating hinders lithium-ion transport, reduces lithium-ion diffusion efficiency, and affects rate performance.

[0010] In some embodiments, the surface of the lithium manganese iron phosphate is coated with carbon.

[0011] In some embodiments, the surface of the lithium manganese iron phosphate is coated with carbon at a mass percentage of 0.1%-10%.

[0012] In some implementations, 0.4 ≤ a ≤ 0.8.

[0013] In some implementations, 1.1 ≤ b ≤ 1.6.

[0014] In some implementations, 0.1 ≤ f ≤ 0.5. Controlling the F content f within this range can further improve the overall electrochemical performance of the cathode material.

[0015] In some embodiments, 0.05 ≤ g ≤ 0.3 g. Controlling the XO4 content within this range can further improve the overall electrochemical performance of the cathode material.

[0016] In some embodiments, X is selected from P, B, or Si. Preferably, X is P.

[0017] In some embodiments, X is selected from P, B or Si, and 0.05 ≤ g ≤ 0.3.

[0018] In some embodiments, the molecular formula of the lithium-rich disordered rock salt polyanion is Li. 1+ a Mn b M1 c M2 d M3 e O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0<c+d+e≤1, 0.0001≤f≤1, 0.0001≤g≤1; M1 is selected from one or more combinations of Cr, Fe, Ni, Co, and V; M2 is selected from one or more combinations of Mg, Zn, Cu, and Al; M3 is selected from one or more combinations of Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; X is selected from one or more combinations of N, P, B, S, and Si. The doping elements of the lithium-rich disordered rock salt polyanion can be M1, M2, M3, etc.

[0019] In some embodiments, the molecular formula of the lithium-rich disordered rock salt polyanion is Li. 1+a Mn b M2 d M3 e O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0<d≤1, 0<e≤1, 0<d+e≤1, 0.0001≤f≤1, 0.0001≤g≤1; M2 is selected from one or more combinations of Mg, Zn, Cu, and Al; M3 is selected from one or more combinations of Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; X is selected from one or more combinations of N, P, B, S, and Si. The doping elements of lithium-rich disordered rock salt polyanions can be M2, M3, etc.

[0020] In some embodiments, M is selected from one or more combinations of Cr, Fe, Ni, Co, and V.

[0021] In some implementations, M is selected from one or both of Fe and V.

[0022] In some implementations, 0.001 ≤ h ≤ 0.3; preferably, 0.05 ≤ h ≤ 0.3.

[0023] In some implementations, h=0.

[0024] In some implementations, M is Fe and V, and 0.05 ≤ h ≤ 0.3.

[0025] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon accounting for 0.1%-10% of its mass, the surface of the lithium manganese iron phosphate is coated with carbon, the surface of the lithium manganese iron phosphate is coated with carbon accounting for 0.1%-10% of its mass, and M is Fe and V, 0.05≤h≤0.3.

[0026] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon accounting for 0.1%-10% of its mass, the surface of the lithium manganese iron phosphate is coated with carbon, the surface of the lithium manganese iron phosphate is coated with carbon accounting for 0.1%-10% of its mass, and h=0.

[0027] In some embodiments, M' is one or more combinations selected from Mg, Ca, Ba, and Si.

[0028] In some implementations, 10 -4 ≤y≤0.1; preferably 0.01≤y≤0.1.

[0029] In some implementations, y=0.

[0030] In some embodiments, M' is one or more combinations selected from Mg, Ca, Ba, and Si, and 0.01≤y≤0.1.

[0031] In some implementations, M' is Mg, and 0.01 ≤ y ≤ 0.1.

[0032] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon accounting for 0.1%-10% of its mass, the surface of the lithium manganese iron phosphate is coated with carbon, the surface of the lithium manganese iron phosphate is coated with carbon accounting for 0.1%-10% of its mass, and M' is Mg, and 0.01≤y≤0.1.

[0033] In some embodiments, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon, the surface of the lithium-rich disordered rock salt polyanion is coated with carbon accounting for 0.1%-10% of its mass, the surface of the lithium manganese iron phosphate is coated with carbon, the surface of the lithium manganese iron phosphate is coated with carbon accounting for 0.1%-10% of its mass, and its y=0.

[0034] The present invention also provides a method for preparing the aforementioned cathode material composite, the method comprising the step of mixing the lithium-rich disordered rock salt polyanion and lithium manganese iron phosphate.

[0035] Furthermore, the mixing is carried out in a high-speed mixer.

[0036] Furthermore, the mixing speed is 1000-2000 r / min.

[0037] Furthermore, the mixing time is 10-30 minutes.

[0038] For the preparation method of lithium-rich disordered rock salt polyanions, the method described in the prior applications CN2025106191231 and CN2025114754958 can be referred to.

[0039] For example, its preparation method may include the following steps: 1) mechanically mixing a lithium source, a manganese source, a fluorine source, and a compound containing element X to obtain a mixture; 2) ball milling and reacting the mixture in a ball mill jar to obtain the lithium-rich disordered rock salt polyanion. When carbon coating is required, the lithium-rich disordered rock salt polyanion and carbon source can be mechanically mixed again, and then ball milled and reacted a second time in a ball mill jar to obtain the carbon-coated material.

[0040] This method does not add water; the raw materials are directly dry-milled after mixing, and a reaction occurs during the milling process to generate lithium-rich disordered rock salt polyanions. These polyanions are then milled with a carbon source and a coating reaction is carried out, which can coat the surface of the lithium-rich disordered rock salt polyanions with carbon. This process does not require solvents, drying, or long sintering steps. The precursors can be uniformly mixed through mechanical force, while refining the powder particles and improving the microstructure of the material. It can also promote the diffusion and uniform distribution of lithium ions through local pressure effects, thereby improving the electrochemical performance of the material. The rate capability and cycle performance of the material are further improved by secondary ball-and-carbon coating.

[0041] For example, its preparation method can also include the following steps: 1) mechanically mixing lithium source, manganese source, fluorine source, a compound containing element X, and water to obtain a mixture; 2) grinding the mixture to obtain a slurry with a D50 particle size less than or equal to 0.4 μm, spray-drying the slurry to obtain a powder, and sintering the powder in an oxygen atmosphere to obtain the lithium-rich disordered rock salt polyanion. When carbon coating is required, the lithium-rich disordered rock salt polyanion and carbon source can be further dispersed in an organic solvent by grinding, dried, and then solid-phase sintered to obtain the carbon-coated material. This method involves grinding the raw materials with water to obtain an aqueous slurry, then spray-drying it, and solid-phase sintering it to obtain lithium-rich disordered rock salt polyanion, which is then solid-phase sintered with a carbon source to obtain the carbon-coated target cathode material. This method is more conducive to industrialization.

[0042] The lithium source can be a conventional lithium source, such as one or a combination of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium formate, lithium oxide, lithium hydride, lithium nitride, lithium peroxide, lithium chloride, lithium nitrate, lithium sulfate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, lithium citrate, lithium laurate, and lithium ascorbate.

[0043] The manganese source can be selected from one or more combinations of manganese dioxide, manganese tetroxide, manganese trioxide, manganese monoxide, lithium hydroxide, manganese carbonate, manganese acetate, manganese sulfate, manganese nitrate, manganese chloride, potassium permanganate, manganese dihydrogen phosphate, manganese oxalate, manganese phosphate, manganese pyrophosphate, and manganese iron phosphate.

[0044] The fluorine source can be selected from one or more combinations of lithium fluoride, manganese fluoride, magnesium fluoride, sodium fluoride, potassium fluoride, hydrofluoric acid, Freon, and hexafluorophosphate.

[0045] When X is N, the compound containing element X is a nitrogen source, selected from one or more combinations of ammonium nitrate, lithium nitrate, magnesium nitrate, ferric nitrate, manganese nitrate, guanidine nitrate, cobalt nitrate, aluminum nitrate, copper nitrate, and nickel nitrate. When X is P, the compound containing element X is a phosphorus source, selected from one or more combinations of phosphorus pentoxide, phosphoric acid, pyrophosphate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, manganese dihydrogen phosphate, sodium phosphate, potassium phosphate, ferric phosphate, manganese phosphate, ferromanganese phosphate, and manganese pyrophosphate. When X is B, the compound containing element X is a boron source, selected from boron oxide, boric acid, boron nitride, boron sulfide, silicon boride, vanadium boride, titanium boride, tungsten boride, molybdenum boride, iron boride, niobium boride, chromium boride, magnesium boride, boron phosphate, lithium borate, and boron fluoride. The compound containing element X is a sulfur source when X is S, and is selected from one or more combinations of sulfuric acid, sulfurous acid, ammonium sulfate, potassium sulfate, sodium sulfate, thiourea, thiols, thioethers, sodium sulfide, boron sulfide, potassium sulfide, iron sulfide, lithium sulfide, magnesium sulfide, manganese sulfide, nickel sulfide, tin sulfide, tungsten sulfide, niobium sulfide, thioacetic acid, potassium thiocyanate, cobalt sulfide, tantalum sulfide, vanadium sulfide, and chromium sulfide. When X is Si, the compound containing element X is a silicon source, and is selected from one or more combinations of silicon oxide, silicic acid, silica gel, potassium silicate, silane, silicon nitride, vanadium silicide, tungsten silicide, titanium silicide, cobalt silicide, cobalt silicide, tantalum silicide, iron silicide, manganese silicide, niobium silicide, nickel silicide, diatomaceous earth, lithium silicate, silicon sulfide, silicon boride, silicon carbide, molybdenum silicon powder, and silicone oil.

[0046] In some embodiments, the carbon source is selected from one or more combinations of activated carbon, carbon black, carbon nanotubes, graphite, graphene, and graphene oxide.

[0047] The amount of each raw material fed is determined based on the molecular formula composition of the final target cathode material.

[0048] For the preparation of lithium manganese iron phosphate (without M' element or with M' element), conventional preparation methods in this field can be used.

[0049] The present invention also provides a lithium-ion battery, including a positive electrode material, wherein the positive electrode material includes the aforementioned positive electrode material composite.

[0050] Furthermore, the lithium-ion battery exhibits a discharge specific capacity of 160-180 mAh / g at 10 mA / g, 160-180 mAh / g at 30 mA / g, and 140-170 mAh / g at 30 mA / g. After 200 charge-discharge cycles at 150 mA / g, the capacity retention rate is 90%-99%. This demonstrates that the lithium-ion battery possesses excellent high capacity and high cycle stability.

[0051] Compared with the prior art, the present invention has the following advantages: The composite cathode material of the present invention can leverage the complementary advantages of lithium-rich disordered rock salt cathode material and traditional manganese iron phosphate cathode material, while possessing high specific capacity and good cycle stability. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the preparation process in Example 1; Figure 2 The two images are SEM images of the cathode material prepared in Example 1, with different scales. Figure 3 The image shows the XRD pattern of the cathode material prepared in Example 1. Figure 4 The charge-discharge curves of the cathode materials prepared in Example 1 and Comparative Example 1 at a current of 0.03C are shown. Figure 5 The cycling curve of the cathode material prepared in Example 1 at a current of 0.5C is shown. Detailed Implementation

[0053] In recent years, lithium-rich disordered rock salt cathode materials have attracted much attention due to their high capacity and high voltage characteristics, but they have encountered many challenges in practical applications, especially insufficient cycle stability and oxygen release issues. To address these challenges, the applicant's earlier application proposed a strategy of simultaneously introducing polyanionic groups and fluoride ions into lithium-rich disordered rock salt cathode materials, thereby improving the overall performance of the material through structural optimization.

[0054] The high capacity advantage of lithium-rich disordered rock salt cathode materials is mainly attributed to their unique "O" structure. 2- / O2 n- The redox mechanism provides an additional source of capacity. During charge and discharge, the reversible redox reaction of oxygen ions significantly improves the battery's energy density. However, under high voltage conditions, these materials are prone to oxygen release, which not only reduces cycle stability but also limits their rate performance. Furthermore, the long diffusion path of oxygen ions in the lithium-rich disordered rock salt structure further restricts performance.

[0055] To overcome these challenges, a prior art application proposed introducing polyanionic groups to enhance the structural stability and electrochemical performance of the material. Polyanionic groups are typically composed of transition metals and oxygen elements, which not only possess good electrochemical stability but also high electronic conductivity. For example, phosphate (PO4) groups... 3- The fluoride group, due to its strong covalent bond characteristics, can significantly enhance the stability of the crystal lattice. Furthermore, the fluoride ion (F...) - Due to its high electronegativity, it can more effectively bind transition metal ions, thereby improving overall stability and increasing oxygen vacancies, reducing irreversible oxygen loss. Therefore, embedding phosphate and fluoride ions into lithium-rich disordered rock salt structures can effectively reduce the instability of oxygen ions.

[0056] The prior application combines lithium-rich disordered rock salt materials (high capacity) and polyanionic materials (high stability), and uses fluorine to dope oxygen, while coating the lithium-rich disordered rock salt polyanionic material with carbon material. By using fluorine doping and carbon coating modification, the discharge specific capacity and cycle performance of the material can be further improved, enabling the lithium-rich disordered rock salt polyanionic cathode material to possess two properties that are difficult to achieve simultaneously in existing technologies.

[0057] Among these, the doping of F anions is beneficial because F anions have a lower valence state than O ions, which can improve charge compensation and increase the number of lithium ions that can be inserted or extracted. F has strong electronegativity, enabling it to form stronger covalent bonds with metal ions, thereby improving the stability of metal ions in the crystal structure and reducing metal ion dissolution. F can also increase the number of oxygen vacancies in the material, reducing irreversible oxygen loss due to reactions. For carbon coating, the material particles are uniformly coated with carbon material, or carbon material is doped between the particles. This not only improves the conductivity of the material, resulting in high-rate, high-capacity cathode materials, but also helps protect the surface structure of the material and reduces side reactions between the material interface and the electrolyte.

[0058] However, single materials often have certain limitations in practical applications. For example, lithium-rich materials are prone to structural transformation and capacity decay during cycling, limiting their performance under long-term cycling conditions. Lithium manganese iron phosphate, on the other hand, faces problems such as low electronic conductivity and slow ion diffusion rate, limiting its performance under high-rate conditions. This application, based on the previously developed lithium-rich disordered rock salt polyanionic cathode material, combines it with traditional lithium manganese iron phosphate cathode material. The resulting composite material can achieve complementary advantages of the two materials, improving the overall electrochemical performance of the composite.

[0059] Lithium-rich disordered rock salt materials possess high specific capacity and high energy density, and exhibit good structural stability. However, they suffer from severe oxygen loss under high voltage, leading to poor stability. In contrast, lithium manganese iron phosphate, with its olivine structure similar to lithium iron phosphate and a higher discharge platform (approximately 4.1V), demonstrates better cycle stability. Therefore, by leveraging the complementary advantages of both materials, the composite material proposed in this application can simultaneously achieve high specific capacity and good cycle stability.

[0060] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0061] Example 1 This embodiment provides a composite cathode material, the preparation process of which is as follows: it is LiMn 0.595 Mg 0.005 Fe 0.4 PO4 and Li 1.68 Mn 1.27 Fe 0.1 V 0.05 (PO4) 0.2 O 3.0 F 0.2 @C complex: (1) Preparation of LiMn 0.595 Mg 0.005 Fe 0.4 PO4: Add 2.0 kg of deionized water to the feed tank of the sand mill, turn on the sand mill and add 172.35 g of lithium carbonate, 657.77 g of manganese iron phosphate precursor, 56.66 g of glucose monohydrate, 12.59 g of polyethylene glycol, 0.922 g of magnesium oxide and 2.611 g of concentrated phosphoric acid in sequence. Sand mill until the particle size D50 of the slurry is ≤0.5 μm. Set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 110℃. Spray dry the slurry after sand milling into powder. Sinter the powder in a tube furnace under a nitrogen atmosphere. The sintering temperature is 350℃ for 2 hours, and then the temperature is raised to 750℃ and sintered for 10 hours to obtain magnesium-doped manganese iron phosphate with the above molecular formula. Its surface is coated with 2% by mass of carbon.

[0062] (2) Preparation of Li 1.68 Mn 1.27 Fe 0.1 V 0.05 (PO4) 0.2 O 3.0 F 0.2@C: Weigh the following raw materials: 13.195g Li₂O, 39.470g Mn₂O₃, 66.663g MnO₂, 23.159g Li₃PO₄, 7.985g Fe₂O₃, 5.188g LiF, and 4.547g V₂O₅. Place them in a high-speed mixer and disperse for 5 minutes at 1200 rpm. Then place the mixture in a ball mill jar, add a certain amount of zirconium beads (bead-to-material weight ratio 20:1), seal well, and perform a high-energy ball milling reaction (800 rpm, 10 hours). Weigh 100.0g of the ball-milled material and 1.010g of carbon nanotubes, mix them mechanically until homogeneous, and then place them in a ball mill jar for ball milling reaction (400 rpm, 5 hours). Finally, obtain the carbon-coated lithium-rich disordered rock salt polyanionic material with the aforementioned molecular formula.

[0063] (3) The magnesium-doped lithium manganese iron phosphate prepared in step (1) and the carbon-coated lithium-rich disordered rock salt polyanionic material prepared in step (2) are stirred in a high-speed mixer at a speed of 1200 r / min for 15 min at a mass ratio of 9:1 to obtain the composite cathode material.

[0064] A schematic diagram of the preparation process of the composite cathode material is shown below. Figure 1 As shown. The SEM image of this cathode material is as follows. Figure 2 As shown. Its XRD pattern is as follows. Figure 3 As shown, the primary particle size of the lithium manganese iron phosphate before compositing is around 150-200 nm, while that of the lithium-rich rock salt polyanionic material before compositing is around 150-400 nm. The average primary particle size of the composite material is around 200 nm. The lithium-rich material and lithium manganese iron phosphate are uniformly composited together, and the two are combined in a synergistic manner at the nano / micro scale, rather than a simple physical mixture. The main peak of the XRD diffraction of the composite material is consistent with that of lithium manganese iron phosphate. Compared with lithium manganese iron phosphate, the peak of the lithium-rich material is weaker. Among them, 19°, 36°, 44° and 65° are the main peaks of the lithium-rich material, and there are no other impurity peaks, indicating that the material is a two-phase composite material.

[0065] Example 2 This embodiment provides a composite cathode material, the preparation process of which is as follows: it is LiMn 0.6 Fe 0.4 PO4 and Li 1.68 Mn 1.27 Fe 0.1 V 0.05 (PO4) 0.2 O 3.0 F 0.2 @C complex: (1) Preparation of LiMn 0.6 Fe 0.4PO4: Add 2.0 kg of deionized water to the hopper of the sand mill, turn on the sand mill and add 172.35 g of lithium carbonate, 661.00 g of manganese iron phosphate precursor, 56.66 g of glucose monohydrate and 12.59 g of polyethylene glycol in sequence. Sand mill until the particle size D50 of the slurry is ≤0.5 μm. Set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 110℃. Spray dry the slurry after sand milling into powder. Sinter the powder in a tube furnace under a nitrogen atmosphere. The sintering temperature is 350℃ for 2 hours, and then the temperature is raised to 750℃ and sintered for 10 hours to obtain lithium manganese iron phosphate with the above molecular formula.

[0066] (2) Preparation of Li 1.68 Mn 1.27 Fe 0.1 V 0.05 (PO4) 0.2 O 3.0 F 0.2 @C: Weigh the following raw materials: 13.195g Li₂O, 39.470g Mn₂O₃, 66.663g MnO₂, 23.159g Li₃PO₄, 7.985g Fe₂O₃, 5.188g LiF, and 4.547g V₂O₅. Place them in a high-speed mixer and disperse for 5 minutes at 1200 rpm. Then place the mixture in a ball mill jar, add a certain amount of zirconium beads (bead-to-material weight ratio 20:1), seal well, and perform a high-energy ball milling reaction (800 rpm, 10 hours). Weigh 100.0g of the ball-milled material and 1.010g of carbon nanotubes, mix them mechanically until homogeneous, and then place them in a ball mill jar for ball milling reaction (400 rpm, 5 hours). Finally, obtain the carbon-coated lithium-rich disordered rock salt polyanionic material with the aforementioned molecular formula.

[0067] (3) The lithium manganese iron phosphate prepared in step (1) and the carbon-coated lithium-rich disordered rock salt polyanionic material prepared in step (2) are stirred in a high-speed mixer at a speed of 1200 r / min for 15 min at a mass ratio of 9:1 to obtain the composite cathode material.

[0068] Example 3 This embodiment provides a composite cathode material, the preparation process of which is as follows: it is LiMn 0.595 Mg 0.005 Fe 0.4 PO4 and Li 170 Mn 1.4 (PO4) 0.2 O 3.0 F 0.2 @C complex: (1) Preparation of LiMn 0.595 Mg 0.005 Fe0.4 PO4: Add 2.0 kg of deionized water to the feed tank of the sand mill, turn on the sand mill and add 172.35 g of lithium carbonate, 657.77 g of manganese iron phosphate precursor, 56.66 g of glucose monohydrate, 12.59 g of polyethylene glycol, 0.922 g of magnesium oxide and 2.611 g of concentrated phosphoric acid in sequence. Sand mill until the particle size D50 of the slurry is ≤0.5 μm. Set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 110℃. Spray dry the slurry after sand milling into powder. Sinter the powder in a tube furnace under a nitrogen atmosphere. The sintering temperature is 350℃ for 2 hours, and then the temperature is raised to 750℃ and sintered for 10 hours to obtain magnesium-doped manganese iron phosphate with the above molecular formula.

[0069] (2) Preparation of Li 170 Mn 1.4 (PO4) 0.2 O 3.0 F 0.2 @C: Weigh the following raw materials: 13.446g Li2O, 39.470g Mn2O3, 78.243g MnO2, 23.159g Li3PO4, and 5.188g LiF. Place them in a high-speed mixer and disperse for 5 minutes at 1200 rpm. Then place the mixture in a ball mill jar, add a certain amount of zirconium beads (bead-to-material weight ratio 20:1), seal well, and perform a high-energy ball milling reaction (800 rpm, 10 hours). Weigh 100.0g of the ball-milled material and 1.010g of carbon nanotubes, mix them mechanically until homogeneous, and then place them in a ball mill jar for ball milling reaction (400 rpm, 5 hours). Finally, obtain the carbon-coated lithium-rich disordered rock salt polyanionic material with the aforementioned molecular formula.

[0070] (3) The magnesium-doped lithium manganese iron phosphate prepared in step (1) and the carbon-coated lithium-rich disordered rock salt polyanionic material prepared in step (2) are stirred in a high-speed mixer at a speed of 1200 r / min for 15 min at a mass ratio of 9:1 to obtain the composite cathode material.

[0071] Example 4 This embodiment provides a composite cathode material, the preparation process of which is as follows: it is LiMn 0.6 Fe 0.4 PO4 and Li 1.70 Mn 1.4 (PO4) 0.2 O 3.0 F 0.2 @C complex: (1) Preparation of LiMn 0.6 Fe 0.4PO4: Add 2.0 kg of deionized water to the hopper of the sand mill, turn on the sand mill and add 172.35 g of lithium carbonate, 661.00 g of manganese iron phosphate precursor, 56.66 g of glucose monohydrate and 12.59 g of polyethylene glycol in sequence. Sand mill until the particle size D50 of the slurry is ≤0.5 μm. Set the inlet air temperature of the spray dryer to 240℃ and the outlet air temperature to 110℃. Spray dry the slurry after sand milling into powder. Sinter the powder in a tube furnace under a nitrogen atmosphere. The sintering temperature is 350℃ for 2 hours, and then the temperature is raised to 750℃ and sintered for 10 hours to obtain lithium manganese iron phosphate with the above molecular formula.

[0072] (2) Preparation of Li 1.70 Mn 1.4 (PO4) 0.2 O 3.0 F 0.2 @C: Weigh the following raw materials: 13.446g Li2O, 39.470g Mn2O3, 78.243g MnO2, 23.159g Li3PO4, and 5.188g LiF. Place them in a high-speed mixer and disperse for 5 minutes at 1200 rpm. Then place the mixture in a ball mill jar, add a certain amount of zirconium beads (bead-to-material weight ratio 20:1), seal well, and perform a high-energy ball milling reaction (800 rpm, 10 hours). Weigh 100.0g of the ball-milled material and 1.010g of carbon nanotubes, mix them mechanically until homogeneous, and then place them in a ball mill jar for ball milling reaction (400 rpm, 5 hours). Finally, obtain the carbon-coated lithium-rich disordered rock salt polyanionic material with the aforementioned molecular formula.

[0073] (3) The magnesium-doped lithium manganese iron phosphate prepared in step (1) and the carbon-coated lithium-rich disordered rock salt polyanionic material prepared in step (2) are stirred in a high-speed mixer at a speed of 1200 r / min for 15 min at a mass ratio of 9:1 to obtain the composite cathode material.

[0074] Comparative Example 1 This comparative example provides a carbon-coated lithium-rich disordered rock salt polyanionic material with the molecular formula Li. 1.70 Mn 1.4 (PO4) 0.2 O 3.0 F 0.2@C, the preparation process is as follows: Weigh the raw materials: 13.446g Li2O, 39.470g Mn2O3, 78.243g MnO2, 23.159g Li3PO4 and 5.188g LiF, place them in a high-speed mixer, adjust the speed to 1200 rpm and disperse for 5 min; then place the above mixture in a ball mill jar, add a certain amount of zirconium beads (bead-to-material weight ratio 20:1), seal well, and carry out high-energy ball milling reaction (speed 800 r / min, time 10 h). Weigh 100.0g of the ball-milled material and 1.010g of carbon nanotubes, mix them evenly by mechanical mixing; then place them in a ball mill jar for ball milling reaction (speed 400 r / min, time 5 h), and finally obtain the carbon-coated lithium-rich disordered rock salt polyanionic material with the aforementioned molecular formula.

[0075] Comparative Example 2 This comparative example provides a comparative lithium iron phosphate cathode material with the molecular formula LiMn. 0.6 Fe 0.4 The preparation process of PO4 is as follows: 2.0 kg of deionized water is added to the hopper of a sand mill. The sand mill is then turned on and 172.35 g of lithium carbonate, 661.00 g of manganese iron phosphate precursor, 56.66 g of glucose monohydrate, and 12.59 g of polyethylene glycol are added sequentially. The sand mill is then milled until the particle size D50 of the slurry is ≤0.5 μm. The spray dryer is set with an inlet air temperature of 240℃ and an outlet air temperature of 110℃. The milled slurry is spray-dried into powder. The powder is sintered in a tube furnace under a nitrogen atmosphere. The sintering temperature is 350℃ for 2 hours, and then the temperature is raised to 750℃ for 10 hours to obtain lithium manganese iron phosphate with the aforementioned molecular formula.

[0076] The above-mentioned positive electrode materials were combined with conductive carbon nanotubes, conductive carbon black, polyvinylidene fluoride (PVDF) binder, and N-methylpyrrolidone (N-Methylpyrrolidone) solvent to form a positive electrode slurry, wherein the mass ratio of the positive electrode material, conductive carbon black, and PVDF binder was 70:20:10. The positive electrode slurry was coated onto aluminum foil, then vacuum baked, punched, and finally formed into a positive electrode sheet. Using this positive electrode sheet as the positive electrode, lithium foil as the negative electrode, and a 1 mol / L LiPF6 DEC / EC / EMC solution as the electrolyte, a button cell battery was assembled, and charge-discharge tests were performed on the battery (charge-discharge window 1.5V~4.8V) to obtain the electrical performance of the lithium-rich disordered rock salt polyanion. The results are shown in Table 1 below (discharge specific capacity at 0.03 / 0.1 / 0.5C and capacity retention after 200 cycles at 0.5C). At 0.03C, the charge-discharge curves of Example 1 are shown below. Figure 4 As shown, the cyclic curve at 0.5C is as follows: Figure 5 As shown. The charge-discharge curve of Comparative Example 2 at 0.03C is shown in the figure. Figure 4 As shown. As can be seen, this application combines lithium-rich disordered rock salt polyanionic cathode material with traditional manganese iron phosphate cathode material to obtain a composite cathode material that has both high specific capacity and good cycle stability, thus achieving the complementary advantages of the two materials.

[0077] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0078] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A positive electrode material composite, characterized by, The composite comprises lithium-rich disordered rock salt polyanions and lithium manganese iron phosphate. The molecular formula of the lithium-rich disordered rock salt polyanion is Li 1+a Mn b M h O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0≤h≤1, 0.0001≤f≤1, 0.0001≤g≤1; M is selected from one or more combinations of Cr, Fe, Ni, Co, V, Mg, Zn, Cu, Al, Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; X is selected from one or more combinations of N, P, B, S, and Si. The molecular formula of the lithium manganese iron phosphate is LiMn. 1-x-y Fe x M' y PO4, wherein M' is one or more combinations selected from Mg, Ti, V, Cr, Co, Ni, Zn, Ga, Al, Zr, Nb, Mo, Sn, Sb, Ca, Ba, Si, B, Ru, Si, Te, Cu, and 0.01≤x≤0.98, 0≤y≤0.

1.

2. The positive electrode material composite according to claim 1, characterized in that The mass ratio of the lithium-rich disordered rock salt polyanion and lithium manganese iron phosphate is 1-5:5-9; preferably 1-2:8-9.

3. The cathode material composite of claim 1, wherein, The surface of the lithium-rich disordered rock salt polyanion is coated with carbon; and / or, the surface of the lithium manganese iron phosphate is coated with carbon.

4. The cathode material composite of claim 3, wherein: The surface of the lithium-rich disordered rock salt polyanion is coated with carbon at a mass percentage of 0.1%-10%; and / or, the surface of the lithium manganese iron phosphate is coated with carbon at a mass percentage of 0.1%-10%.

5. The cathode material composite of claim 1, wherein, 0.4≤a≤0.8; and / or, 1.1≤b≤1.6; and / or, 0.1≤f≤0.5; and / or, 0.05≤g≤0.

3.

6. The cathode material composite according to claim 1 or 2, characterized in that: The X is selected from P, B or Si, and 0.05 ≤ g ≤ 0.

3.

7. The positive electrode material composite according to claim 1 or 2, characterized in that: The molecular formula of the lithium-rich disordered rock salt polyanion is Li 1+a Mn b M1 c M2 d M3 e O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0<c+d+e≤1, 0.0001≤f≤1, 0.0001≤g≤1; M1 is selected from one or more combinations of Cr, Fe, Ni, Co, and V; M2 is selected from one or more combinations of Mg, Zn, Cu, and Al; M3 is selected from one or more combinations of Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; and X is selected from one or more combinations of N, P, B, S, and Si.

8. The positive electrode material composite according to claim 1 or 2, characterized in that: The molecular formula of the lithium-rich disordered rock salt polyanion is Li 1+a Mn b M2 d M3 e O 4-f-4g F f (XO4) g Wherein, 0.1≤a≤2, 1≤b≤2, 0<d≤1, 0<e≤1, 0<d+e≤1, 0.0001≤f≤1, 0.0001≤g≤1; M2 is selected from one or more combinations of Mg, Zn, Cu, and Al; M3 is selected from one or more combinations of Nb, Ti, Mo, Ru, W, Ta, Sn, Zr, Ru, Sb, Te, Re, and Si; X is selected from one or more combinations of N, P, B, S, and Si.

9. The positive electrode material composite according to claim 1 or 2, characterized in that: The M is selected from one or more combinations of Cr, Fe, Ni, Co, and V; preferably, the M is selected from one or two of Fe and V; and / or, 0.001≤h≤0.3; preferably, 0.05≤h≤0.

3.

10. The positive electrode material composite according to claim 1 or 2, characterized in that: h=0; or, M is Fe and V, and 0.05≤h≤0.

3.

11. The positive electrode material composite according to claim 1 or 2, characterized in that: M' is a combination of one or more selected from the group consisting of Mg, Ca, Ba, Si; and / or,10 -4 y < 0.1 ; preferably 0.01 < y < 0.

1.

12. The positive electrode material composite according to claim 1 or 2, characterized in that: y=0, or M' is one or more combinations selected from Mg, Ca, Ba, Si, and 0.01≤y≤0.

1.

13. A lithium-ion battery comprising a cathode material, characterized in that: The cathode material includes the cathode material composite according to any one of claims 1-12.

14. The lithium-ion battery of claim 13, wherein: The lithium-ion battery has a discharge specific capacity of 160-180 mAh / g at a current of 10 mA / g, a discharge specific capacity of 160-180 mAh / g at a current of 30 mA / g, a discharge specific capacity of 140-170 mAh / g at a current of 30 mA / g, and a capacity retention rate of 90%-99% after 200 charge-discharge cycles at a current of 150 mA / g.

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