Composite cathode material, preparation method thereof and lithium ion battery

Abstract

This invention relates to the field of lithium-ion batteries, and discloses a composite cathode material, its preparation method, and a lithium-ion battery. The composite cathode material comprises a multi-element material and lithium manganese iron phosphate material. The full width at half maximum (FWHM) of the (110) crystal plane and the full width at half maximum (FWHM) of the (111) crystal plane obtained by XRD testing of the composite cathode material satisfy the following conditions: 0.18 ≤ FWHM(110) ≤ 0.25, 0.2 ≤ FWHM(111) ≤ 0.26. When X-ray diffraction testing is performed, the composite cathode material exhibits a unique XRD pattern. This composite cathode material possesses suitable crystallinity, good structural stability, and high thermal stability. When used in lithium-ion batteries, this cathode material exhibits high charge / discharge capacity, high cycle rate, long cycle life, and excellent safety performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a composite cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] In recent years, new energy vehicles, as a national strategic emerging industry to address environmental pollution and the energy crisis, have shown a vigorous development trend. Lithium-ion batteries, as a high-performance new energy carrier, are widely used in electric vehicles, energy storage power stations, communications, and digital electronic products. Cathode materials, as the core and key materials of lithium-ion batteries, directly determine the battery's technical performance. Currently, the commercially available ternary cathode material NCM (LiNi)... x Co y Mn 1-x-y O2) has a high specific capacity (170-210 mAh·g). -1 While lithium iron phosphate (LiFePO4) boasts high energy density, its poor safety performance limits its market expansion, particularly for high-nickel materials (x≥0.6) or under high-voltage (≥4.4V) operating conditions, where battery stability is poor. Compared to commercially available lithium iron phosphate (LiFePO4) materials, lithium manganese iron phosphate (LiMn)... x Fe 1-x PO4 materials have higher Mn content 2+ / Mn 3+ The voltage plateau allows for higher energy density. These materials contain tetrahedral PO4 composed of strong PO bonds, which effectively stabilizes the crystal structure and exhibits high safety.

[0003] Lithium manganese iron phosphate (LMP) and ternary material systems have significant differences in electrolyte and voltage platform during use. Therefore, if conventional LMP and ternary materials are simply mixed and used, problems such as low compaction density, incompatibility of electrolytes, and overcharging of ternary material particles will occur, which will further lead to reduced battery cycle life and serious gas production, making it difficult to take into account the advantages of both LMP and ternary materials.

[0004] CN105406069A discloses a method for coating ternary materials with lithium manganese iron phosphate. When sintering lithium manganese iron phosphate and ternary materials, an argon protective atmosphere is used, which is required for lithium manganese iron phosphate. However, ternary materials require air or an oxygen-rich atmosphere for sintering. Sintering in an inert atmosphere will cause the Ni content in the ternary material to... 3+ Easily reduced to Ni 2+ Furthermore, it is easy for cations to migrate to lithium sites and cause cation mixing, which affects material properties. Therefore, the two cannot be well coordinated, and this method is not suitable for mass production.

[0005] CN108777298A discloses a method that utilizes the high energy density of ternary materials and the strong cycle stability of lithium manganese iron phosphate. By mixing the two during the slurry preparation process, the overall heat release of the cathode material can be reduced, which can improve the safety performance of the battery. However, due to the difference in density between the two, segregation is prone to occur during slurry mixing.

[0006] CN103474625A discloses an in-situ synthesis of a lithium iron phosphate layer on the surface of lithium nickel cobalt manganese oxide using a sol-gel method. The lithium iron phosphate layer formed on the surface of the cathode material can reduce the Ni content, decrease side reactions, and improve the thermal stability of the material. Nickel and manganese elements can complex with organic components in the sol to form weak chemical bonds, achieving uniform coating of the material. However, the in-situ synthesis of lithium iron phosphate on the surface is relatively complex, and the purity of the lithium iron phosphate is difficult to guarantee.

[0007] Therefore, there is an urgent need for a composite cathode material that can fully leverage the advantages of lithium manganese iron phosphate and other multi-element materials. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of existing technologies that simply mix lithium manganese iron phosphate (LFP) materials with multi-component materials, resulting in poor compatibility between the two materials, difficulty in simultaneously leveraging their advantages, overcharging of multi-component material particles, and incompatibility of electrolytes, further leading to poor battery thermal stability and reduced cycle life. To balance the advantages of LFP and multi-component materials, this invention provides a composite cathode material, its preparation method, and a lithium-ion battery. When X-ray diffraction (XRD) is performed, this composite cathode material exhibits a unique XRD pattern, demonstrating suitable crystallinity, good structural stability, and high thermal stability. When used in lithium-ion batteries, this cathode material exhibits high charge / discharge capacity, high cycle rate, long cycle life, and excellent safety performance.

[0009] To achieve the above objectives, the first aspect of the present invention provides a composite cathode material, characterized in that the composite cathode material comprises a multi-element material and a lithium manganese iron phosphate material;

[0010] The full width at half maximum (FWHM) of the (110) crystal plane of the cathode material obtained by XRD testing (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0011] 0.18≤FWHM (110) ≤0.25, 0.2≤FWHM (111) ≤0.26.

[0012] A second aspect of the present invention provides a method for preparing a composite cathode material, characterized in that the preparation method includes the following steps:

[0013] Step 1: Preparation of multi-component materials

[0014] (1) Mix the multi-material precursor, the first lithium source, and optionally the additive N1, and perform a first calcination to obtain the first calcined material;

[0015] (2) The first calcined material is coated with optional additive N2 and then subjected to a first heat treatment to obtain the multi-element material;

[0016] Step 2: Preparation of lithium manganese iron phosphate materials

[0017] (3) Mix and homogenize the lithium manganese iron phosphate material precursor, the second lithium source, the first carbon source, and the additive L1, dry them, and perform a second calcination to obtain the lithium manganese iron phosphate material.

[0018] Step 3: Preparation of composite cathode material

[0019] (4) The composite cathode material is obtained by mixing the multi-element material with the lithium manganese iron phosphate material, performing a second heat treatment, and sieving.

[0020] In step (4), the conditions for the second heat treatment include: a heat treatment temperature of 100-400℃ and a heat treatment time of 1-6h in an oxygen-containing atmosphere, with an oxygen concentration ≥8 vol%.

[0021] A third aspect of the present invention provides a composite cathode material prepared by the above-described preparation method.

[0022] A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned composite cathode material.

[0023] Through the above technical solutions, the composite cathode material, its preparation method, and the lithium-ion battery provided by this invention achieve the following beneficial effects:

[0024] (1) When the composite cathode material provided by the present invention is subjected to X-ray diffraction testing, it has a specific (110) crystal plane full width at half maximum (FWHM). (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) Within a given numerical range, composite cathode materials with this specific crystal structure exhibit suitable crystallinity and good structural stability.

[0025] (2) Furthermore, the composite cathode material provided by this invention provides a convenient electron transport path through the carbon coating layer of lithium manganese iron phosphate on the surface of the multi-element material particles, enhancing the conductivity of the conductive carbon black in the cathode sheet, which is beneficial to Li +The electron migration during the intercalation / deintercalation reaction avoids side reactions that occur when multi-component material particles come into contact with the electrolyte, reduces the resistance of charge migration, and decreases battery polarization.

[0026] (3) The composite cathode material provided by the present invention, after heat treatment under specific conditions, allows the lithium manganese iron phosphate material to react only with the residual alkali on the surface of the multi-element material, without further entering the crystal lattice and forming an internal crystal structure that blocks lithium ion shuttle. It forms only a thin coating layer on the surface of the multi-element material, effectively improving the cycle performance without reducing the capacity of the multi-element material.

[0027] (4) The preparation method provided by the present invention is simple and pollution-free; the method of introducing doping elements is simple and the process is controllable, which is very suitable for industrial production.

[0028] (5) When the composite cathode material provided by this invention is used in lithium-ion batteries, it exhibits good structural stability during charging and discharging, with a discharge specific capacity exceeding the theoretical value and excellent cycle performance. It ensures both high charge / discharge capacity and safety performance. The structurally stable lithium manganese iron phosphate coating delays the thermal decomposition temperature of the composite cathode material, reduces the heat released during thermal runaway, improves battery safety, and extends the cycle life of the lithium-ion battery. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the composite cathode material prepared in Comparative Example 1, magnified 10K times.

[0030] Figure 2 This is a scanning electron microscope image of the composite cathode material prepared in Comparative Example 4, magnified 10K times.

[0031] Figure 3 This is a scanning electron microscope image of the composite cathode material prepared in Comparative Example 5, magnified 10K times.

[0032] Figure 4 This is a scanning electron microscope image of the composite cathode material prepared in Comparative Example 7, magnified 10K times.

[0033] Figure 5 This is a scanning electron microscope image of the composite cathode material prepared in Comparative Example 8, magnified 10K times.

[0034] Figure 6 This is a scanning electron microscope image of the composite cathode material prepared in Example 1, magnified 10K times;

[0035] Figure 7 The X-ray diffraction patterns of the composite cathode materials prepared in Comparative Examples 1, 4, 5 and 1 are shown.

[0036] Figure 8The charge-discharge curves of lithium-ion batteries assembled from the composite cathode materials of Comparative Example 1, Comparative Example 4 and Example 1 at 0.1C are shown.

[0037] Figure 9 The graph shows the cycle performance of lithium-ion batteries assembled from the composite cathode materials of Comparative Example 1, Comparative Example 4 and Example 1 at 0.1C.

[0038] Figure 10 This is a differential scanning calorimetry (DSC) graph of the composite cathode material of Comparative Example 1 and Example 1. Detailed Implementation

[0039] 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.

[0040] The first aspect of the present invention provides a composite cathode material, characterized in that the composite cathode material comprises a multi-element material and a lithium manganese iron phosphate material;

[0041] The full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material was obtained by XRD testing. (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0042] 0.18≤FWHM (110) ≤0.25, 0.2≤FWHM (111) ≤0.26.

[0043] According to the present invention, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material obtained by XRD testing (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0044] 0.2≤FWHM (110) ≤0.24, 0.22≤FWHM (111) ≤0.25.

[0045] In this invention, when the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material is... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111)When the ratio meets the above range, the ternary material and the lithium manganese iron phosphate material are tightly bonded, and the small particles are uniformly attached to the surface of the large particles, so that the composite cathode material containing the above ternary material and lithium manganese iron phosphate material has suitable crystallinity and good structural stability.

[0046] In this invention, further XRD spectrum analysis of the composite cathode material revealed that, in this invention, when the composite cathode material has a full width at half maximum (FWHM) of the (110) crystal plane... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) When the above range is met, the composite cathode material, when used in a lithium-ion battery, results in a battery with high charge / discharge capacity, high cycle rate, long cycle life, and excellent safety performance.

[0047] Specifically, XRD testing of the composite cathode material revealed that when the position of the characteristic diffraction peaks of the composite cathode material did not shift and no other new diffraction peaks were observed, the resulting composite cathode material exhibited suitable crystallinity and good structural stability.

[0048] Furthermore, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material, as obtained by XRD testing, is... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0049] 0.6≤FWHM (110) / FWHM (111) ≤1.1.

[0050] In this invention, the lithium manganese iron phosphate material has an olivine-type crystal structure, and the ternary material has an α-NaFePO2 layered crystal structure belonging to the R3m space.

[0051] Furthermore, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material obtained by XRD testing... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0052] 0.7≤FWHM (110) / FWHM (111) ≤1.

[0053] According to the present invention, the multi-element material has the composition shown in Formula I:

[0054] Li e (Ni 1-x-y-z-m Co x M y G z R m )Oq (PO4) n Formula I;

[0055] Wherein, 0.9≤e≤1.3, x≤(1-xyzm), y≤(1-xyzm), 0.5≤1-xyzm<1, 0<y≤0.25, 0≤z<0.05, 0≤m<0.05, 0<n≤0.01, q=(4-3n) / 2; M is selected from Al and / or Mn, G is selected from at least one element in Groups IIA-IIIA of Periods 2-5, and R is selected from at least one element in B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

[0056] In this invention, according to O 2- and PO4 3- The valence calculation requires that 2*q+3*n=4.

[0057] In this invention, the multi-element material uses specific types of doping elements G and R, which allows different bonds to be formed between the transition metal and different doping elements in the multi-element material, thereby enabling the battery made from this cathode material to have high initial charge-discharge capacity and excellent cycle performance.

[0058] Further, 0.95≤e≤1.2, x≤(1-xyzm), y≤(1-xyzm), 0.6≤1-xyzm<0.9, 0.05≤y≤0.2, 0.01≤z≤0.03, 0.01≤m<0.03, 0<n≤0.007, q=(4-3n) / 2; G is selected from at least one element from Al, Mg, Ca, Sr, Zr, Nb and Mo.

[0059] According to the present invention, the lithium manganese iron phosphate material has the composition shown in Formula II:

[0060] Li i Mn 1-h-k-j Fe h D k D′ j (PO4) / C Formula II;

[0061] Wherein, 0.1 < h ≤ 0.4, 0 < k ≤ 0.04, 0 < j ≤ 0.04, 0.9 < i ≤ 1.2; D is selected from at least one element from Mg, Co, Ni, Cu, Zn and Ti, and D' is selected from at least one element from Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm, with carbon accounting for 5% to 12% of the total weight of the lithium manganese iron phosphate material.

[0062] In this invention, doping elements D and D' can stabilize the material structure, weaken the interaction of Li-O bonds, and improve the ion diffusion coefficient, thereby improving the battery capacity, rate, and cycle performance. Furthermore, the carbon coating of lithium manganese iron phosphate material enhances the overall conductivity of the material, provides a convenient electron transport path, facilitates charge transport and lithium ion diffusion, and is beneficial to the utilization of the capacity of multi-element materials.

[0063] Further, 0.15<h≤0.35, 0.01≤k≤0.03, 0.01≤j≤0.03, 1<i≤1.1; D is selected from at least one element selected from Mg, Cu and Ti; D' is selected from at least one element selected from Ti, Nb and B, based on the total weight of the lithium manganese iron phosphate material, wherein the weight percentage of carbon element is 8% to 10%.

[0064] According to the present invention, the average particle size D of the composite cathode material is... 50 The size is 1-20 μm, preferably D. 50 It is 2-10μm.

[0065] According to the present invention, the composite cathode material is a composite cathode material with a multi-element material as the core and lithium manganese iron phosphate as the coating layer.

[0066] In this invention, the inventors discovered through XRD testing that the lithium manganese iron phosphate material used as a coating layer in the composite cathode material does not penetrate into the crystal lattice of the multi-element material, ensuring that the structure of the multi-element material remains unchanged. This improves the stability and safety of the composite cathode material during cycling without affecting the capacity of the multi-element material. Furthermore, the lithium manganese iron phosphate coating material in this invention can prevent direct contact between the multi-element material and the organic electrolyte, reducing the probability of side reactions and enhancing the stability and safety of the composite cathode material during cycling.

[0067] According to the present invention, the average particle size D of the multi-element material 50 The size is 1-20 μm, preferably 2-10 μm.

[0068] According to the present invention, the average thickness of the lithium manganese iron phosphate material coating layer is 10-400 nm, preferably 50-300 nm.

[0069] According to the present invention, based on the total weight of the composite cathode material, the weight ratio of the multi-element material to the lithium manganese iron phosphate material is 1-9:1, preferably 1.5-4:1.

[0070] A second aspect of the present invention provides a method for preparing a composite cathode material, characterized in that the preparation method includes the following steps:

[0071] Step 1: Preparation of multi-component materials

[0072] (1) Mix the multi-component precursor, the first lithium source, and optionally the additive N1, and perform a first calcination to obtain the first calcined material;

[0073] (2) The first calcined material is coated with optional additive N2 and then subjected to a first heat treatment to obtain the multi-element material;

[0074] Step 2: Preparation of lithium manganese iron phosphate materials

[0075] (3) Mix and homogenize the lithium manganese iron phosphate material precursor, the second lithium source, the first carbon source, and the additive L1, dry them, and perform a second calcination to obtain the lithium manganese iron phosphate material.

[0076] Step 3: Preparation of composite cathode material

[0077] (4) The composite cathode material is obtained by mixing the multi-element material with the lithium manganese iron phosphate material, performing a second heat treatment, and sieving.

[0078] In step (4), the conditions for the second heat treatment include: a heat treatment temperature of 100-400℃ and a heat treatment time of 1-6h in an oxygen-containing atmosphere, with an oxygen concentration ≥8 vol%.

[0079] The inventors of this invention have discovered that mixing multi-component materials and lithium manganese iron phosphate materials using conventional methods cannot fully combine the advantages of the two materials, resulting in problems such as low compaction density, incompatibility with electrolytes, and overcharging of multi-component material particles.

[0080] After heat treatment under specific conditions, the lithium manganese iron phosphate material reacts only with the residual alkali on the surface of the multi-element material, without further entering the crystal lattice and forming an internal crystal structure that blocks lithium ion shuttle. Instead, it forms a thin coating layer on the surface of the multi-element material, effectively improving cycle performance without reducing the capacity of the multi-element material.

[0081] More importantly, the method provided by this invention can produce the composite cathode material described in the first aspect of this invention. Specifically, when the composite cathode material is tested by XRD, the full width at half maximum (FWHM) of the (110) crystal plane is... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) When this composite cathode material is used in lithium-ion batteries within a specific range, the batteries exhibit high charge / discharge capacity, high cycle rate, long cycle life, and excellent safety performance.

[0082] In this invention, during the preparation of the composite cathode material, a second heat treatment is performed on the mixture comprising multi-component materials and lithium manganese iron phosphate material. The specific conditions of this second heat treatment are beneficial for improving the reactivity of the cathode material, facilitating close contact between the multi-component materials and lithium manganese iron phosphate material, optimizing the particle size distribution of secondary particles, and effectively improving rate performance and cycle performance. Performing the second heat treatment in an oxygen-containing atmosphere can prevent Ni from forming during the heat treatment process. 3+ Reduced to Ni 2+ The cations migrate to the lithium site and undergo cation mixing, affecting the material's properties.

[0083] Furthermore, the preparation method provided by this invention is simple and pollution-free; the method of introducing dopant elements is simple and the process is controllable, making it very suitable for industrial production.

[0084] In this invention, the XRD pattern of the composite cathode material showed that the position of the characteristic diffraction peaks of the composite cathode material did not shift, indicating that the crystal structure of the two materials did not change during the mixing process; no other new diffraction peaks were observed, indicating that no impurity phases were generated during the preparation of the composite cathode material.

[0085] According to the present invention, further, in step (4), the conditions for the second heat treatment include: under an oxygen-containing atmosphere, a heat treatment temperature of 150-300°C, a heat treatment time of 2-4 hours, and an oxygen concentration ≥8 vol% in the oxygen-containing atmosphere.

[0086] According to the present invention, in step (4), the mixing process uses one of the following mechanical mixing equipment: ball mill, stirred mill, and high-speed mixer.

[0087] In this invention, the stirring speed during the mixing process is 100-3000 rpm, preferably 400-2000 rpm.

[0088] In this invention, a mechanical mixing device is used to uniformly coat the surface of the multi-component material particles with lithium manganese iron phosphate, which can prevent direct contact between the multi-component materials and the organic electrolyte, reduce the probability of side reactions between the two, and enhance the stability and safety of the composite cathode material during cycling.

[0089] According to the present invention, the optional additive N1 is a compound containing a dopant element G, wherein the dopant element G is selected from at least one element in Groups IIA-IIIA of Periods 2-5.

[0090] Furthermore, the doping element G is selected from at least one element selected from Al, Mg, Ca, Sr, Zr, Nb and Mo.

[0091] In this invention, there is no particular limitation on the specific type of compound containing dopant element G. For example, it can be at least one of oxides, carbonates, fluorides, borides, hydroxides, sulfates, nitrates and chlorides, preferably at least one of sulfates, nitrates and chlorides.

[0092] According to the present invention, the optional additive N2 is a compound containing a dopant element R, wherein the dopant element R is selected from at least one element selected from B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

[0093] In this invention, the specific type of compound containing dopant element R is not particularly limited. For example, it can be at least one of oxides, carbonates, fluorides, borides, hydroxides, sulfates, nitrates and chlorides, preferably at least one of sulfates, nitrates and chlorides.

[0094] According to the present invention, the first carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol and dopamine.

[0095] Furthermore, the first carbon source is selected from at least one of glucose, sucrose, starch, and cellulose.

[0096] In this invention, the first carbon source is added and sintered by doping and coating carbon, which can achieve doping of different elements and coating of different carbon sources, thereby improving electronic conductivity and further enhancing the electrochemical performance of the material.

[0097] According to the present invention, the additive L1 is a compound containing a dopant element D', wherein the dopant element D' is selected from at least one element selected from Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm.

[0098] Furthermore, the doping element D' is selected from at least one element selected from Ti, Nb, and B.

[0099] In this invention, there is no particular limitation on the specific type of compound containing the dopant element D'. For example, it can be at least one of oxides, carbonates, fluorides, borides, hydroxides, sulfates, nitrates and chlorides, preferably at least one of sulfates, nitrates and chlorides.

[0100] In this invention, there is no particular limitation on the types of the first lithium source and the second lithium source. They can be conventional lithium sources in the art, such as at least one selected from lithium carbonate, lithium hydroxide, lithium fluoride, lithium chloride and lithium nitrate. The first lithium source and the second lithium source can be the same or different.

[0101] In this invention, unless otherwise specified, the solvent of the solution is water.

[0102] In this invention, the multi-element material precursor contains Ni, Co and M elements, where M is selected from Al and / or Mn elements.

[0103] According to the present invention, in step (1), the multi-element material is calculated as [n(Ni)+n(Co)+n(M)], the first lithium source is calculated as n(Li), and the amount of the first lithium source is such that 0.9≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.3; the amount of additive N1 is calculated as n(G) such that 0≤[n(G)] / [n(Ni)+n(Co)+n(M)]<0.05, and M is selected from Al and / or Mn elements.

[0104] Furthermore, the amount of the multi-component material is calculated as [n(Ni)+n(Co)+n(M)], and the amount of the first lithium source is calculated as n(Li). The amount of the first lithium source is such that 0.95≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.2; the amount of the additive N1 is such that 0.01≤[n(G)] / [n(Ni)+n(Co)+n(M)]≤0.03.

[0105] According to the present invention, in step (2), the amount of additive N2 in the first calcined material, calculated as [n(Ni)+n(Co)+n(M)], is such that 0≤[n(R)] / [n(Ni)+n(Co)+n(M)]<0.05, and more preferably 0.01≤[n(R)] / [n(Ni)+n(Co)+n(M)]<0.03.

[0106] In this invention, the lithium manganese iron phosphate material precursor includes Mn, Fe and D elements, wherein D is selected from at least one element selected from Mg, Co, Ni, Cu, Zn and Ti.

[0107] According to the present invention, in step (3), the amount of the lithium manganese iron phosphate material precursor and the second lithium source is such that 0.9 < [n(Li)] / [n(Mn)+n(Fe)+n(D)] ≤ 1.2; and the amount of the additive L1 is such that 0 < [n(D')] / [n(Mn)+n(Fe)+n(D)] ≤ 0.04.

[0108] Furthermore, in the lithium manganese iron phosphate precursor, the amount of the second lithium source is such that 1 < [n(Li)] / [n(Mn)+n(Fe)+n(D)] ≤ 1.1; and the amount of additive L1 is such that 0.01 ≤ [n(D')] / [n(Mn)+n(Fe)+n(D)] ≤ 0.03.

[0109] Further, in step (3), the weight ratio of the lithium manganese iron phosphate material precursor to the first carbon source is 1:0.05-0.12, preferably 1:0.06-0.1.

[0110] According to the present invention, in step (1), the conditions for the first calcination include: calcination temperature of 650-900℃, preferably 700-850℃, calcination time of 6-30h, preferably 8-25h, and oxygen concentration of ≥4vol% in the oxygen-containing atmosphere, preferably ≥8vol%.

[0111] In this invention, the first calcination under the above conditions can generate lithium manganese iron phosphate cathode material.

[0112] In this invention, there is no particular limitation on the type of oxygen-containing atmosphere, which can be a conventional atmosphere with an oxygen concentration of ≥4 vol%.

[0113] According to the present invention, in step (2), the conditions for the first heat treatment include: under an oxygen-containing atmosphere, the heat treatment temperature is 300-480℃, preferably 320-460℃, the heat treatment time is 5-15h, preferably 6-12h, and the oxygen concentration in the oxygen-containing atmosphere is ≥4vol%, preferably ≥8vol%.

[0114] In this invention, during the preparation of the multi-component material, the first calcined material is optionally coated with N2 as an additive, and the coated first calcined material is subjected to a first heat treatment. In particular, the first heat treatment under the specific conditions described above enables the lithium manganese iron phosphate material to react only with the residual alkali on the surface of the multi-component material, without further entering the crystal lattice and forming an internal crystal structure that blocks lithium ion shuttle. Only a thin coating layer is formed on the surface of the multi-component material, effectively improving the cycle performance without reducing the material capacity.

[0115] In this invention, there are no particular limitations on the drying conditions in step (3). Conventional drying conditions in the art can be used. For example, the drying conditions include drying in a vacuum oven at 60-100°C for 2-6 hours, preferably at 65-85°C for 3-5 hours.

[0116] According to the present invention, in step (3), the conditions for the second calcination include: under a protective atmosphere, the calcination temperature is 600℃-700℃, preferably 620℃-660℃, and the calcination time is 8h-12h, preferably 9h-11h.

[0117] In this invention, the second calcination under the specific conditions described above is beneficial for improving the reactivity of the cathode material, facilitating close contact between the ternary materials and lithium manganese iron phosphate material, optimizing the particle size distribution of secondary particles, and effectively improving rate performance and cycle performance. Performing the second heat treatment in an oxygen-containing atmosphere can prevent Ni from forming during the heat treatment process. 3+ Reduced to Ni 2+ The cations migrate to the lithium site and undergo cation mixing, affecting the material's properties.

[0118] In this invention, there is no particular limitation on the type of protective atmosphere, which can be a conventional protective atmosphere in the art, such as at least one selected from nitrogen, argon and helium.

[0119] Multi-material precursors

[0120] In this invention, there are no particular limitations on the multi-component material precursor, and it can be prepared using conventional preparation methods in the art. For example, the multi-component material precursor is prepared according to the following steps:

[0121] (A) Prepare a mixed salt solution by mixing nickel salt, cobalt salt and additive N3; prepare a first precipitant solution and a first complexing agent solution, respectively;

[0122] (B) Prepare a phosphate solution from the phosphate;

[0123] (C) The mixed salt solution, the first precipitant solution, the phosphate solution, and the first complexing agent are added to the reactor to carry out the first coprecipitation reaction. After aging, filtration, washing, and drying, a multi-component material precursor is obtained.

[0124] In this invention, phosphate is introduced in situ during the precursor stage of multi-component materials, resulting in a unique phosphate phase inside the bulk phase during the preparation process. This phase can stabilize the layered structure of the matrix material, effectively prevent the collapse of the layered structure under high charging conditions and the transformation to other rock salt phases, delay the structural failure of the cathode material, and significantly improve the safety performance.

[0125] In this invention, there is no particular limitation on the type of phosphate, which can be a conventional phosphate in the art, such as selected from ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate.

[0126] In this invention, in step (B), the amounts of the mixed salt solution (based on [n(Ni)+n(Co)+n(M)]) and the phosphate solution (based on n(P)) are such that 0 < n(P) / [n(Ni)+n(Co)+n(M)] ≤ 0.01, preferably 0 < n(P) / [n(Ni)+n(Co)+n(M)] ≤ 0.007.

[0127] In this invention, the concentration of the phosphate solution is 1-3 mol / L, preferably 1.5-2.5 mol / L.

[0128] In this invention, there is no particular limitation on the type of nickel salt, which can be a conventional nickel salt in the art, such as at least one of nickel sulfate, nickel chloride, nickel nitrate and nickel acetate.

[0129] In this invention, there is no particular limitation on the type of cobalt salt, which can be a conventional cobalt salt in the art, such as at least one of cobalt sulfate, cobalt chloride, cobalt nitrate and cobalt acetate.

[0130] According to the present invention, the additive N3 is a compound containing element M, wherein element M is selected from Al and / or Mn.

[0131] Furthermore, there is no particular limitation on the type of compound containing element M. For example, it can be at least one of oxides, carbonates, fluorides, borides, hydroxides, sulfates, nitrates, and chlorides, preferably at least one of sulfates, nitrates, and chlorides.

[0132] According to the present invention, the nickel salt, cobalt salt and additive N3 are prepared into a mixed salt solution according to the molar ratio of Ni:Co:M=(1-xyzm):x:y, where 0.5≤1-xyzm<1, x≤(1-xyzm), y≤(1-xyzm), 0<y≤0.25, 0≤z<0.05, and 0≤m<0.05.

[0133] Furthermore, 0.95≤e≤1.2, 0.6≤1-xyzm<0.9, 0.05≤y≤0.2, 0.01≤z≤0.03, 0.01≤m<0.03.

[0134] In this invention, the total concentration of nickel salt, cobalt salt and additive N3 in the mixed salt solution is 1-3 mol / L.

[0135] In this invention, the additive N3 facilitates rapid molecular diffusion, resulting in a homogeneous solution mixture.

[0136] In this invention, there is no particular limitation on the type of the first precipitant, which can be a conventional precipitant in the art, such as at least one selected from ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0137] In this invention, the concentration of the first precipitant solution is 2-8 mol / L, preferably 4-6 mol / L.

[0138] In this invention, the type of the first complexing agent is not particularly limited, and it can be a conventional complexing agent in the art, such as at least one selected from ammonia, disodium ethylenediaminetetraacetate, ammonium nitrate, triammonium citrate, ammonium chloride, and ammonium sulfate.

[0139] In this invention, the concentration of the first complexing agent solution is 2-4 mol / L, preferably 2.5-3.5 mol / L.

[0140] According to the present invention, in step (C), the first coprecipitation reaction conditions include: under a protective atmosphere, the reaction temperature is 40-70°C, preferably 50-60°C, and the pH value is maintained at 11-13, preferably 11.5-12.5, during the reaction.

[0141] According to the present invention, the aging time is 2h-12h, preferably 6-10h.

[0142] In this invention, pure water and / or alkaline solutions are used to wash the aged multi-component material precursors. There are no particular limitations on the type and concentration of the alkaline solution, and conventional alkaline solutions in the art can be used.

[0143] lithium manganese iron phosphate material precursor

[0144] According to the present invention, the lithium manganese iron phosphate material precursor is prepared according to the following steps:

[0145] (a) A first mixture is prepared by combining manganese salt, iron salt and additive L2; a second mixture is prepared by combining phosphorus source and ammonia source; a first suspension is prepared by combining a second complexing agent and a second carbon source;

[0146] (b) The first mixture and the second mixture are added to the first suspension to carry out a second coprecipitation reaction to obtain a second coprecipitation slurry;

[0147] (c) The second coprecipitated slurry is subjected to solid-liquid separation and washing to obtain the lithium manganese iron phosphate material precursor.

[0148] In this invention, the second carbon source is introduced during the precursor preparation process. It can uniformly coat the surface of the primary particles, form a stable conductive network, and cause the primary particles to tightly bond and agglomerate to form dense secondary spherical particles.

[0149] In this invention, there is no particular limitation on the type of manganese salt, which can be a conventional manganese salt in the art, such as at least one of manganese sulfate, manganese chloride, manganese nitrate and manganese acetate.

[0150] In this invention, there is no particular limitation on the type of iron salt, which can be a conventional iron salt in the art, such as at least one of ferric sulfate, ferrous sulfate, ferric nitrate, ferric acetate and ferric chloride.

[0151] According to the present invention, the additive L2 is a compound containing a dopant element D, wherein the dopant element D is selected from at least one element selected from Mg, Co, Ni, Cu, Zn and Ti.

[0152] Furthermore, the doping element D is selected from at least one element selected from Mg, Cu and Ti.

[0153] In this invention, the type of compound containing the dopant element D is not particularly limited. For example, it can be at least one of oxides, carbonates, fluorides, borides, hydroxides, sulfates, nitrates and chlorides, preferably at least one of sulfates, nitrates and chlorides.

[0154] According to the present invention, the molar ratio of manganese salt, iron salt and additive L2 in the first mixture is Mn:Fe:D=(1-hkj):h:k, 0.1<h≤0.4, 0<k≤0.04, 0<j≤0.04.

[0155] Furthermore, 0.15 < h ≤ 0.35, 0.01 ≤ k ≤ 0.03, and 0.01 ≤ j ≤ 0.03.

[0156] In this invention, the type of phosphorus source is not particularly limited and can be any conventional phosphate-containing compound in the art, such as at least one of phosphoric acid, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

[0157] In this invention, the type of ammonia source is not particularly limited and can be any conventional ammonium ion-containing compound in the art, such as at least one of ammonia water, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, triammonium phosphate, ammonium bicarbonate, ammonium carbonate, ammonium sulfate, and urea, preferably at least one of ammonia water, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

[0158] In this invention, the amounts of phosphorus source and ammonia source satisfy the following: the molar ratio of phosphorus source (calculated as phosphate ions) to ammonia source (calculated as ammonium ions) is 1:1-3.

[0159] In this invention, the phosphorus source and the ammonia source can be the same compound. When a compound containing phosphorus and ammonia is used as both the phosphorus source and the ammonia source, it is sufficient that the molar ratio of phosphorus to ammonia in the compound is 1:1-3.

[0160] According to the present invention, the second carbon source is selected from at least one of graphene, carbon nanotubes, phenolic resin, polyethylene, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene and toluene diisocyanate.

[0161] In this invention, the type of the second complexing agent is not particularly limited, and it can be a conventional complexing agent in the art, such as at least one selected from ammonia, disodium ethylenediaminetetraacetate, ammonium nitrate, triammonium citrate, ammonium chloride, and ammonium sulfate. The first complexing agent and the second complexing agent can be the same or different.

[0162] In this invention, the concentration of the second complexing agent solution in the first suspension is 0.01-2 mol / L, preferably 0.02-1.5 mol / L.

[0163] According to the present invention, the weight ratio of the second complexing agent to the second carbon source is 1:1-5, preferably 1:2-4.

[0164] In this invention, the second coprecipitation reaction conditions include: under a protective atmosphere, the reaction temperature is 40-70℃, preferably 45-65℃, and the pH value is maintained at 5-7, preferably 5.5-6.5, during the reaction.

[0165] A third aspect of the present invention provides a composite cathode material prepared by the above-described preparation method.

[0166] A fourth aspect of the present invention provides a lithium-ion battery, characterized in that the lithium-ion battery comprises the above-mentioned composite cathode material.

[0167] The composite cathode material provided in this invention exhibits good structural stability during charge and discharge processes when used in lithium-ion batteries, with a discharge specific capacity exceeding the theoretical value and excellent cycle performance. It ensures both high charge and discharge capacity and safe performance.

[0168] In this invention, the structurally stable lithium manganese iron phosphate coating delays the thermal decomposition temperature of the composite cathode material, reduces the heat released during thermal runaway, improves battery safety, and extends the cycle life of the lithium-ion battery.

[0169] According to a particularly preferred embodiment of the present invention, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material obtained by XRD testing (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met:

[0170] 0.2≤FWHM (110) ≤0.24, 0.22≤FWHM (111) ≤0.25;

[0171] 0.7≤FWHM (110) / FWHM (111) ≤1.

[0172] The present invention will be described in detail below through examples. In the following examples and comparative examples, all raw materials used are commercially available products.

[0173] The preparation processes of the composite cathode materials (S1-S12 and T1-T8) obtained in Examples 1-12 and Comparative Examples 1-8 are shown in Tables 1-2, and the chemical composition and formulation of the multi-element materials and lithium manganese iron phosphate materials are shown in Table 3. The physical property parameters of the composite cathode materials (S1-S12 and T1-T8) obtained in Examples 1-12 and Comparative Examples 1-8 are shown in Tables 4-6.

[0174] Preparation Example A1

[0175] Preparation of multi-component cathode material precursors

[0176] (A) Nickel sulfate, cobalt sulfate, and manganese sulfate are added to water in a molar ratio of 60:20:20 to prepare a 2 mol / L mixed salt solution. A 10 mol / L ammonia solution is prepared as the first complexing agent solution, and a 4 mol / L sodium hydroxide solution is prepared as the first precipitating agent solution.

[0177] (B) Prepare a 2 mol / L phosphate solution by dissolving ammonium dihydrogen phosphate at n(P) / [n(Ni)+n(Co)+n(M)]=0.002;

[0178] (C) Nitrogen gas is introduced into the reactor for a certain period of time to ensure that there is no air atmosphere inside the reactor. The mixed salt solution, the first precipitant solution, the phosphate solution, and the first complexing agent solution are added to the reactor to carry out the first coprecipitation reaction. The stirring speed is 500 rpm, the pH value is adjusted to 11.8, and the reactor temperature is controlled at 60℃. After the reaction is completed, the material is aged for 8 hours, and washed alternately with an alkaline solution at 75℃ and pure water. Then the filter cake is dried and sieved to obtain the multi-component material precursor A1.

[0179] Preparation Example A2

[0180] The multi-component material precursor A2 was prepared according to the method of preparation example A1, except that in step (A), nickel sulfate, cobalt sulfate, and manganese sulfate were added to water in a molar ratio of 70:15:15 to prepare a 2 mol / L mixed salt solution. The resulting multi-component material precursor A2 was obtained.

[0181] Preparation Example A3

[0182] The multi-component material precursor A3 was prepared according to the method of preparation example A1, except that in step (A), nickel sulfate, cobalt sulfate, and manganese sulfate were added to water in a molar ratio of 80:10:10 to prepare a 2 mol / L mixed salt solution. The resulting multi-component material precursor A3 was obtained.

[0183] Preparation Example A4

[0184] The multi-component material precursor A4 was prepared according to the method of preparation example A1, except that the preparation of the phosphate solution in step (B) was not performed. The resulting multi-component material precursor A4 was obtained.

[0185] Preparation Example A5

[0186] The multi-component material precursor A5 was prepared according to the method of preparation example A2, except that the preparation of the phosphate solution in step (B) was omitted. The resulting multi-component material precursor A5 was obtained.

[0187] Preparation Example A6

[0188] The multi-component material precursor A6 was prepared according to the method of preparation example A3, except that the preparation of the phosphate solution in step (B) was omitted. The resulting multi-component material precursor A6 was obtained.

[0189] Preparation Example B1

[0190] Preparation of lithium manganese iron phosphate material precursors

[0191] (a) Prepare 2 L of a first mixed solution with a total metal ion concentration of 2 mol / L by mixing manganese sulfate, ferric sulfate, and magnesium sulfate in a molar ratio of 60:39:1; mix phosphoric acid and ammonia water in a molar ratio of n(PO4) + ):n(NH3 + A second mixture of phosphate ions was prepared in a molar ratio of 1:3 to form 4 L of phosphate ion concentration of 1 mol / L; a first suspension of 1 L of triammonium citrate and polyvinylidene fluoride was prepared in a mass ratio of 1:3, wherein the concentration of the second complexing agent in the first suspension was 0.05 mol / L.

[0192] (b) The first suspension is added to the reaction vessel as the reaction base liquid, and the first mixture and the second mixture are added dropwise to the reaction vessel. The pH of the reaction system is controlled at 5.5-6.5, the temperature is controlled at 60℃, and the stirring speed is 800rpm. After the addition is completed, stirring is continued for 1 hour to obtain the second coprecipitated slurry.

[0193] (c) The second coprecipitated slurry is filtered and washed until the conductivity of the filtrate is ≤200μs / cm to obtain lithium manganese iron phosphate material precursor B1.

[0194] Example 1

[0195] (1) The multi-component precursor A1 and lithium hydroxide were dry-premixed at a molar ratio of n(Li)] / [n(Ni)+n(Co)+n(M)] of 1:1.03. After the premixing was completed, Nb2O5 was used as additive N1 and the premixing was further dry-mixed. The amount of premixing and additive N1 was calculated based on the molar ratio of multi-component precursor A1 and Nb, n(Nb) / [n(Ni)+n(Co)+n(M)]=0.003. The mixture was calcined at 765℃ for 20h in an oxygen atmosphere with an oxygen concentration of 8 vol%.

[0196] (2) The first calcined material was coated with Y2O3 as additive N2. The first calcined material was calculated as [n(Ni)+n(Co)+n(M)], and the additive N2 was calculated as n(Y). n(Y) / [n(Ni)+n(Co)+n(M)]=0.001. The above materials were mixed by a dry method. The first heat treatment was carried out at 350℃ in an oxygen-containing atmosphere with an oxygen concentration of 8 vol% for 12 hours. After completion, the first heat treatment product was cooled and sieved to obtain the multi-element material.

[0197] (3) Take lithium manganese iron phosphate precursor B1, lithium carbonate and titanium dioxide in a molar ratio of 1:0.52:0.01, and lithium manganese iron phosphate precursor B1 and glucose in a mass ratio of 1:0.08. Mix them with pure water, homogenize, evaporate to dryness, and then dry in a vacuum oven at 85°C for 4 hours to obtain dry material. Calcine the dry material at 650°C for 10 hours under a nitrogen atmosphere. After sieving, obtain lithium manganese iron phosphate cathode material.

[0198] (4) The multi-element material and the lithium manganese iron phosphate material are simultaneously placed into a high-speed mixer at a mass ratio of 8:2 and mixed at 400 rpm for 4 hours. After a second heat treatment at 200°C for 3 hours in an oxygen-containing atmosphere of 8 vol%, the material is discharged and sieved to obtain the composite cathode material, denoted as S1.

[0199] Example 2

[0200] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0201] (4) The multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 9:1 and subjected to a second heat treatment at 200°C for 3 hours in an oxygen-containing atmosphere of 8 vol%. The material is then discharged and sieved to obtain a composite cathode material, denoted as S2.

[0202] Example 3

[0203] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0204] Step (4) Mix the multi-element material and lithium manganese iron phosphate material at a mass ratio of 7:3, and perform a second heat treatment at 200°C for 3 hours in an oxygen-containing atmosphere with an oxygen concentration of 8 vol%. Then discharge and sieve to obtain the composite cathode material, denoted as S3.

[0205] Example 4

[0206] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0207] In step (4), the multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 6:4. After a second heat treatment at 200°C for 3 hours in an oxygen-containing atmosphere with an oxygen concentration of 8 vol%, the material is discharged and sieved to obtain the composite cathode material, denoted as S4.

[0208] Example 5

[0209] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0210] In step (4), the multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 5:5. After a second heat treatment at 200°C for 3 hours in an oxygen-containing atmosphere with an oxygen concentration of 8 vol%, the material is discharged and sieved to obtain the composite cathode material, denoted as S5.

[0211] Example 6

[0212] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0213] (1) The multi-component precursor A2 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0214] A composite cathode material, denoted as S6, was prepared.

[0215] Example 7

[0216] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0217] (1) The multi-component precursor A3 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0218] The resulting composite cathode material is denoted as S7.

[0219] Example 8

[0220] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0221] (1) The multi-component precursor A4 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0222] After preparation, a composite cathode material was obtained, denoted as S8.

[0223] Example 9

[0224] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0225] (1) The multi-component precursor A5 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0226] After preparation, a composite cathode material was obtained, denoted as S9.

[0227] Example 10

[0228] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0229] (1) The multi-component precursor A6 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0230] After preparation, a composite cathode material is obtained, denoted as S10.

[0231] Example 11

[0232] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0233] (4) The multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 8:2 and subjected to a second heat treatment at 120°C for 3 hours in an oxygen-containing atmosphere of 8 vol%. The material is then discharged and sieved to obtain a composite cathode material, denoted as S11.

[0234] Example 12

[0235] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0236] (4) The multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 8:2 and subjected to a second heat treatment at 350°C for 3 hours in an oxygen-containing atmosphere of 8 vol%. The material is then discharged and sieved to obtain a composite cathode material, denoted as S12.

[0237] Table 1

[0238]

[0239]

[0240]

[0241] Table 1 (continued)

[0242]

[0243]

[0244] Comparative Example 1

[0245] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0246] Without performing the preparation process in steps (3)-(4), a multi-element material is obtained, denoted as T1.

[0247] Comparative Example 2

[0248] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0249] (1) The multi-component precursor A2 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0250] Without performing the preparation process in steps (3)-(4), a multi-element material is obtained, denoted as T2.

[0251] Comparative Example 3

[0252] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0253] (1) The multi-component precursor A3 and lithium hydroxide were dry-premixed at a molar ratio of 1:1.03.

[0254] Without performing the preparation process in steps (3)-(4), a multi-element material is obtained, denoted as T3.

[0255] Comparative Example 4

[0256] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0257] Without performing steps (1)-(2) and (4), lithium manganese iron phosphate material is obtained, denoted as T4.

[0258] Comparative Example 5

[0259] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0260] (4) Without performing a second heat treatment, a composite cathode material is obtained, denoted as T5.

[0261] Comparative Example 6

[0262] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0263] (1) The multi-component precursor A4: lithium hydroxide was dry-premixed at a molar ratio of 1:1.03 and then directly calcined without doping with any elements.

[0264] (2) The first calcined material is directly subjected to the first heat treatment without any doping elements. The heat treatment temperature is controlled at 350℃ and the heat treatment time is 12h in an oxygen-containing atmosphere with an oxygen concentration of 8 vol%. After completion, the first heat treatment product is cooled and sieved to obtain a multi-element material.

[0265] (4) Without performing a second heat treatment, a composite cathode material is obtained, denoted as T6.

[0266] Comparative Example 7

[0267] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0268] (4) The composite cathode material was obtained by performing a second heat treatment at 200°C for 3 hours in a muffle furnace under nitrogen atmosphere, and it was denoted as T7.

[0269] Comparative Example 8

[0270] The composite cathode material was prepared according to the method in Example 1, with the following difference:

[0271] (4) The multi-element material and lithium manganese iron phosphate material are mixed at a mass ratio of 8:2 and subjected to a second heat treatment at 500°C for 3 hours in an oxygen-containing atmosphere of 8 vol%. The material is then discharged and sieved to obtain a composite cathode material, denoted as T8.

[0272] Table 2

[0273]

[0274]

[0275]

[0276] Table 2 (continued)

[0277]

[0278]

[0279] Table 3

[0280]

[0281]

[0282] Test Example 1

[0283] The particle size of the composite cathode material was measured using a MASTERSIZER2000 laser particle size analyzer.

[0284] Two g of the composite cathode material prepared in the examples and comparative examples were subjected to XRD tests. The instrument used was an X-ray diffractometer (λ = 0.15406 nm) from Rigaku Corporation, Japan. The test conditions were: working voltage of 40 kV, working current of 250 mA, scanning speed of 4° / min, step size of 0.02°, and scanning range of 2θ of 10°-80°.

[0285] The microstructure of the composite cathode material was obtained by scanning electron microscopy (SEM), using a Hitachi S-4800 scanning electron microscope from Japan.

[0286] The crystal grain size and full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The results are shown in Table 4.

[0287] Table 4

[0288]

[0289]

[0290] Note: ※ indicates that the half-maximum widths (WHMs) of the (110) and (111) crystal planes of the composite cathode material were not measured. Therefore, the test results for the WHMs of the (110) and (111) crystal planes are partially missing.

[0291] The average particle size of the composite cathode materials prepared in Examples 1-12 is in the range of 2-10 μm. Lithium manganese iron phosphate material is uniformly attached to the surface of the multi-element material. The lithium manganese iron phosphate material is enriched and agglomerated on the surface of the multi-element material, embedding the multi-element material in it, so that the composite cathode material particles are more tightly arranged.

[0292] Figure 1 This is a scanning electron microscope (SEM) image of the composite cathode material prepared in Comparative Example 1, magnified 10K times. Comparative Example 1 is a multi-element material without lithium manganese iron phosphate coating. The image shows that the microstructure of the multi-element material prepared in Comparative Example 1 is spherical particles. Figure 2 The image shows a 10Kx magnified scanning electron microscope image of the composite cathode material prepared in Comparative Example 4. Comparative Example 4 is a coated lithium manganese iron phosphate material. The lithium manganese iron phosphate material has uniform particle size, with the primary particle size at the submicron level and a particle size of 500 nm.

[0293] Figure 3 , Figure 4 , Figure 5The images shown are scanning electron microscope (SEM) images at 10.0Kx magnification of the composite cathode materials T5, T7, and T8 prepared in Comparative Examples 5, 7, and 8, respectively. It can be observed that the lithium manganese iron phosphate particles on the surface of the composite cathode material particles in T5, T7, and T8 are not uniformly attached to the multi-element material particles, and the particles are relatively loosely spaced. A second heat treatment in an oxygen-containing atmosphere at a temperature of 100-400℃ can uniformly coat the lithium manganese iron phosphate material onto the surface of the multi-element material, while also resulting in a more compact arrangement of the composite cathode material particles.

[0294] Figure 6 This is a scanning electron microscope image of the composite cathode material prepared in Example 1, magnified 10K times. Figure 6 As can be seen from Example 1, the composite cathode material prepared by Example 1 has lithium manganese iron phosphate material uniformly attached to the surface of the multi-element material. The lithium manganese iron phosphate material is enriched and agglomerated on the surface of the multi-element material, embedding the multi-element material in it, making the composite cathode material particles more compactly arranged.

[0295] As can be seen from Table 4, compared with Comparative Examples 1-8, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material provided in Examples 1-12 of the present invention is significantly higher. (110) Satisfying 0.18≤FWHM (110) ≤0.25, FWHM of the (111) crystal plane (111) Satisfying 0.2≤FWHM (111) ≤0.26.

[0296] Furthermore, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material provided in Examples 1-12 of the present invention... (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The ratio satisfies 0.6 ≤ FWHM (110) / FWHM (111) ≤1.1.

[0297] Figure 7 These are X-ray diffraction patterns of the composite cathode materials prepared in Comparative Examples 1, 4, and 1. Comparative Example 1 is a multi-element material without lithium manganese iron phosphate coating, consisting of... Figure 7It can be seen that in the XRD pattern of Comparative Example 1, there are no other impurity peaks except for the characteristic peaks of the main phase of the multi-component material. The two pairs of characteristic peaks (006) / (012) and (018) / (110) are clearly split, and the intensity ratio of (003) and (104) is greater than 1.2, indicating that the multi-component material itself has good crystallinity and a good layered structure. Comparative Example 4 is the XRD pattern of a simple lithium manganese iron phosphate material. In the XRD pattern, there are no impurity peaks except for the characteristic diffraction peaks of the main phase. However, the XRD pattern of the composite cathode material S1 prepared in Example 1 shows the characteristic diffraction peaks of the multi-component material and lithium manganese iron phosphate. The position of the peaks has not shifted at all, indicating that the crystal structure of the two materials has not changed during the mechanical mixing process and the second heat treatment process of this invention.

[0298] The XRD test results of Examples 1-12 show that the lithium manganese iron phosphate material used as a coating layer in the composite cathode material provided by the present invention does not enter the crystal lattice of the multi-element material, ensuring that the structure of the multi-element material remains unchanged. Under the condition of not affecting the capacity of the multi-element material, the stability and safety of the composite cathode material during cycling are improved.

[0299] Figure 7 The XRD pattern of the composite cathode material prepared in Comparative Example 5 without the second heat treatment is shown. The figure exhibits characteristic diffraction peaks of both the multi-element material and lithium manganese iron phosphate material, with no shift in peak position. However, the full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material provided in Comparative Example 5 is significantly higher. (110) =0.178, (111) crystal plane full width at half maximum (FWHM) (111) =0.262, which is outside the specific range defined in this invention.

[0300] Compared with the composite cathode materials prepared in Comparative Examples 1, 5, 7, and 8, the specific second heat treatment conditions described in this invention enable the multi-element materials and lithium manganese iron phosphate materials to be tightly bonded, and the small particles to be uniformly attached to the surface of the large particles. This results in the composite cathode material containing the above-mentioned multi-element materials and lithium manganese iron phosphate materials having suitable crystallinity and good structural stability.

[0301] Application Example 1

[0302] The composite cathode materials prepared in the examples and comparative examples were assembled into lithium-ion batteries. The specific assembly process is as follows:

[0303] The manufacturing process of the CR2025 coin cell is as follows:

[0304] The prepared composite cathode material sample was thoroughly compounded with conductive carbon black, polyvinylidene fluoride, and lithium bis(trifluoromethanesulfonyl)imide at a mass ratio of 90:5:5 with an appropriate amount of N-methylpyrrolidone to form a uniform slurry. This slurry was then coated onto aluminum foil, dried in a vacuum oven at 120℃ for 0.5 h, and finally rolled and punched into circular electrode sheets with a diameter of 11 mm. The composite cathode material loading was approximately 7 mg / cm³. 2 A CR2025 coin cell was assembled in an argon-filled glove box using lithium metal sheets as the negative electrode, a polypropylene microporous membrane as the separator, and ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate containing 1 mol / L LiPF6 as the electrolyte.

[0305] The charge-discharge cycle performance of lithium-ion batteries assembled from composite cathode materials was tested using CR2025 coin cells. The instrument used was the Xinwei Battery Testing System. The test conditions were 25℃ and 3-4.3V voltage. The charge-discharge cycle performance was tested after 80 charge-discharge cycles. The results are shown in Table 5.

[0306] Table 5

[0307]

[0308]

[0309] Figure 8 The charge-discharge curves of lithium-ion batteries assembled from the composite cathode materials prepared in Comparative Examples 1, 4, and 1 are shown at 0.1C. Figure 8 It can be seen that, compared with Comparative Examples 1 and 4, the lithium-ion battery assembled from the composite cathode material provided in Example 1 of the invention exhibits a higher first charge-discharge efficiency. This is because the carbon coating of the submicron-sized lithium manganese iron phosphate material in the composite cathode material inhibits particle growth and reduces the diffusion distance of lithium ions. On the other hand, it can enhance the overall conductivity of the material, provide a convenient electron transport path, facilitate charge transport and lithium ion diffusion, and help to maximize the capacity of the multi-element material, thereby improving the electrochemical performance of the composite cathode material.

[0310] Figure 9 This is a graph showing the cycle performance of lithium-ion batteries assembled from the composite cathode materials prepared in Comparative Examples 1, 4, and 1 at 0.1C. Figure 9 It can be seen that the discharge specific capacities of Comparative Example 1, Example 1 and Comparative Example 4 after 80 cycles are 160.2 mAh / g, 158.2 mAh / g and 136.6 mAh / g, respectively, and the capacity retention rates are 94.9%, 95.7% and 97.4%, respectively.

[0311] The multi-component material sample prepared in Comparative Example 1 has good crystallinity, few internal defects, small specific surface area, good compatibility with electrolyte, and good cycle stability. The lithium manganese iron phosphate material prepared in Comparative Example 4 has PO4 tetrahedra composed of strong PO bonds, which can effectively stabilize the oxygen skeleton in the crystal structure, reduce oxygen release side reactions, and has excellent cycle performance.

[0312] The composite cathode material prepared in Example 1 exhibits a better capacity retention rate than that of the multi-element material. When the composite cathode material is mainly composed of multi-element materials, the carbon coating on the surface of the surrounding lithium manganese iron phosphate material enhances the electronic conductivity of the conductive carbon black in the cathode sheet, thereby reducing battery polarization and improving redox reversibility. The lithium manganese iron phosphate material can block the direct contact between the multi-element materials and the organic electrolyte, reducing the probability of side reactions between the two and enhancing the stability of the composite cathode material during cycling.

[0313] As can be seen from the results in Table 5, Comparative Example 5 used the same preparation method as Example 1, except that no second heat treatment was performed. Compared with Example 1, the lithium-ion battery assembled from the composite cathode material prepared by Comparative Example 5 had lower initial discharge specific capacity, initial coulombic efficiency, discharge specific capacity after 80 cycles, and capacity retention rate than Example 1.

[0314] Furthermore, Comparative Examples 7 and 8 employed the same preparation method as Example 1, except that Comparative Example 7 underwent a second heat treatment in an oxygen-free atmosphere, while Comparative Example 8 increased the second heat treatment temperature to 500°C. Compared to Example 1, the lithium-ion batteries assembled from the composite cathode materials prepared in Comparative Examples 7 and 8 exhibited lower initial discharge specific capacity, initial coulombic efficiency, discharge specific capacity after 80 cycles, and capacity retention rate than those of Example 1.

[0315] This invention demonstrates that by performing a second heat treatment on a mixture of multi-component materials and lithium manganese iron phosphate materials in an oxygen-containing atmosphere at a temperature of 100-400°C, the cycle performance is effectively improved without reducing the capacity of the multi-component materials.

[0316] Furthermore, Example 8 has the same Ni:Co:M molar ratio and the same multi-component material: lithium manganese iron phosphate material blending ratio as Example 1, the difference being that phosphate was not added. Compared to Example 1, the initial discharge specific capacity, initial coulombic efficiency, discharge specific capacity after 80 cycles, and capacity retention of Example 8 are all lower than those of Example 1. This indicates that introducing phosphate in the precursor preparation of this invention helps to improve the electrochemical performance of the composite cathode material.

[0317] Examples 1, 6, and 7 prepared composite cathode materials using different Ni:Co:M molar ratios. Examples 6 and 7 had higher Ni content than Example 1. The lithium-ion batteries assembled from the composite cathode materials of Examples 6 and 7 exhibited higher initial discharge specific capacity than those of Example 1, but lower initial coulombic efficiency, discharge specific capacity after 80 cycles, and capacity retention. Increasing the Ni content can improve the initial discharge specific capacity of lithium-ion batteries assembled from composite cathode materials, but it weakens electrochemical stability.

[0318] Application Example 2

[0319] The composite cathode materials prepared in the examples and comparative examples were assembled into lithium-ion batteries for thermal stability testing. The thermal stability of the composite cathode materials was evaluated by differential thermal analysis-thermogravimetric analysis (DTA-TGA) using a Mettler Toledo thermal analysis instrument (made in Sweden).

[0320] CR2025 coin cells were prepared using the same method as in Application Example 1. The test conditions were as follows: the CR2025 coin cells were charged and discharged twice at 3-4.3V, 0.2C, and 25℃, and then charged to full charge. After disassembling to obtain the positive electrode, the positive electrode was placed in a differential thermal-thermogravimetric analyzer for testing. The corresponding DSC curves of the samples were obtained, and the test results are shown in Table 6.

[0321] Table 6

[0322]

[0323]

[0324] As can be seen from the results in Table 6, compared with Comparative Examples 1-8, the composite cathode materials provided by Examples 1-12 of this invention have less heat release and better thermal stability. The structurally stable lithium manganese iron phosphate material delays the occurrence of thermal decomposition temperature of the multi-element materials, reduces the heat released in thermal runaway, and improves battery safety.

[0325] Comparative Example 5 uses the same preparation method as Example 1, except that no second heat treatment is performed. Compared with Example 1, the composite cathode material obtained by Comparative Example 5 has a larger heat release in the DSC test results, and the initial heat release temperature and peak heat release temperature appear earlier. This indicates that mechanical mixing alone cannot fully combine the multi-element material and lithium manganese iron phosphate material, and there is still a problem of poor thermal stability.

[0326] Furthermore, Comparative Example 7 underwent a second heat treatment in an oxygen-free atmosphere, and Comparative Example 8 increased the second heat treatment temperature to 500°C. DSC testing showed that the composite cathode materials prepared in Comparative Examples 7 and 8 exhibited greater heat release, earlier onset and peak heat release temperatures, and poorer thermal stability compared to Example 1. This indicates that heat treatment under specific conditions can effectively improve the thermal stability of the composite material.

[0327] Furthermore, Example 8 has the same Ni:Co:M molar ratio and the same multi-component material:lithium manganese iron phosphate material mixing ratio as Example 1, the difference being that no phosphate ions were added. Compared to Example 1, the composite cathode material prepared in Example 8 exhibited greater heat release in DSC testing, and the onset and peak heat release temperatures appeared earlier. This indicates that adding phosphate ions to the multi-component material also helps improve the thermal stability of the composite cathode material.

[0328] In Example 2, the mixing ratio of the multi-component material and the lithium manganese iron phosphate material in the composite cathode material was 9:1, while the ratio of the composite cathode material in Example 1 was 8:2. The amount of lithium manganese iron phosphate material coated in Example 1 was greater than that in Example 2. The composite cathode material prepared in Example 1 had less heat release in the thermal stability test, and the thermal stability was improved. As the amount of lithium manganese iron phosphate material added increased, the heat release of the composite cathode material decreased, and the thermal stability was better.

[0329] Figure 10 The graphs are differential scanning calorimetry (DSC) results of the composite cathode material cathode sheets prepared in Example 1 and Comparative Example 1. Figure 10 It can be seen that the maximum heat flux and total heat release of the composite cathode material prepared in Example 1 are much smaller than those in Comparative Example 1, and the initial heat release temperature and maximum heat flux temperature also appear later. This indicates that the composite cathode material prepared in Example 1 exhibits better thermal stability than the multi-component material. The structurally stable lithium manganese iron phosphate composite material reduces the heat release of the composite material and improves the overall thermal stability of the material.

[0330] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes a multi-element material and a lithium manganese iron phosphate material; The full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material was obtained by XRD testing. (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met: 0.18≤FWHM (110) ≤0.25,0.2≤FWHM (111) ≤0.26; The composite cathode material is a composite cathode material with a multi-element material as the core and lithium manganese iron phosphate as the coating layer. The average thickness of the coating layer is 10-400 nm; The multi-element material has the composition shown in Formula I: Li e (Ni 1-x-y-z-m Co x M y G z R m )O q (PO4) n Formula I; Wherein, 0.9≤e≤1.3, x≤(1-xyzm), y≤(1-xyzm), 0.5≤1-xyzm<1, 0<y≤0.25, 0≤z<0.05, 0≤m<0.05, 0<n≤0.01, q=(4-3n) / 2; M is selected from Al and / or Mn, G is selected from at least one element in Groups IIA-IIIA of Periods 2-5, and R is selected from at least one element in B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al; Li i Mn 1-h-k-j Fe h D k D' j (PO4) / C type II; Wherein, 0.1<h≤0.4, 0<k≤0.04, 0<j≤0.04, 0.9<i≤1.2; D is selected from at least one element from Mg, Co, Ni, Cu, Zn and Ti, and D' is selected from at least one element from Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm; based on the total weight of lithium manganese iron phosphate material, the weight percentage of carbon element is 5% to 12%.

2. The composite cathode material according to claim 1, wherein, The full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material was obtained by XRD testing. (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following condition must be met: 0.2 ≤ FWHM (110) ≤0.24, 0.22≤FWHM (111) ≤0.

25.

3. The composite cathode material according to claim 1, wherein, The full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material was obtained by XRD testing. (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following conditions must be met: 0.6≤FWHM (110) / FWHM (111) ≤1.1。 4. The composite cathode material according to claim 3, wherein, The full width at half maximum (FWHM) of the (110) crystal plane of the composite cathode material was obtained by XRD testing. (110) The full width at half maximum (FWHM) of the (111) crystal plane (111) The following condition must be met: 0.7 ≤ FWHM (110) / FWHM (111) ≤1.

5. The composite cathode material according to claim 1, wherein, The multi-element material has the composition shown in Formula I: Li e (Ni 1-x-y-z-m Co x M y G z R m )O q (PO4) n Formula I; Wherein, 0.95≤e≤1.2, x≤(1-xyzm), y≤(1-xyzm), 0.6≤1-xyzm<0.9, 0.05≤y≤0.2, 0.01≤z≤0.03, 0.01≤m<0.03, 0<n≤0.007, q=(4-3n) / 2; G is selected from at least one element from Al, Mg, Ca, Sr, Zr, Nb and Mo.

6. The composite cathode material according to claim 1, wherein, The lithium manganese iron phosphate material has the composition shown in Formula II: Li i Mn 1-h-k-j Fe h D k D' j (PO4) / C type II; Wherein, 0.15<h≤0.35, 0.01≤k≤0.03, 0.01≤j≤0.03, 1<i≤1.1; D is selected from at least one element among Mg, Cu and Ti; D' is selected from at least one element among Ti, Nb and B; and the weight percentage of carbon element is 8% to 10% based on the total weight of the lithium manganese iron phosphate material.

7. The composite cathode material according to claim 1 or 2, wherein, The average particle size D of the composite cathode material 50 It ranges from 1 to 20 μm.

8. The composite cathode material according to claim 7, wherein, The average particle size D of the composite cathode material 50 It is 2-10μm.

9. The composite cathode material according to claim 1 or 2, wherein, The average particle size D of the multi-element material 50 It ranges from 1 to 20 µm.

10. The composite cathode material according to claim 9, wherein, The average particle size D of the multi-element material 50 It is 2-10µm.

11. The composite cathode material according to claim 1, wherein, The average thickness of the coating layer is 50-300 nm.

12. The composite cathode material according to claim 1 or 2, wherein, Based on the total weight of the composite cathode material, the weight ratio of the multi-element material to the lithium manganese iron phosphate material is 1-9:

1.

13. The composite cathode material according to claim 12, wherein, Based on the total weight of the composite cathode material, the weight ratio of the multi-element material to the lithium manganese iron phosphate material is 1.5-4:

1.

14. A method for preparing the composite cathode material according to any one of claims 1-13, characterized in that, The preparation method includes the following steps: Step 1: Preparation of multi-component materials (1) Mix the multi-component precursor, the first lithium source, and optionally the additive N1, and perform a first calcination to obtain the first calcined material; (2) The first calcined material is coated with optional additive N2 and then subjected to a first heat treatment to obtain the multi-element material; Step 2: Preparation of lithium manganese iron phosphate materials (3) The lithium manganese iron phosphate material precursor, the second lithium source, the first carbon source, and the additive L1 are mixed, homogenized, dried, and calcined for the second time to obtain the lithium manganese iron phosphate material. Step 3: Preparation of composite cathode material (4) The composite cathode material is obtained by mixing the multi-element material with the lithium manganese iron phosphate material, performing a second heat treatment, and sieving. In step (4), the conditions for the second heat treatment include: under an oxygen-containing atmosphere, the heat treatment temperature is 100-400℃, the heat treatment time is 1-6h, and the oxygen concentration in the oxygen-containing atmosphere is ≥8vol.

15. The preparation method according to claim 14, wherein, The conditions for the second heat treatment include: in an oxygen-containing atmosphere, the heat treatment temperature is 150-300℃, the heat treatment time is 2-4h, and the oxygen concentration in the oxygen-containing atmosphere is ≥8vol.

16. The preparation method according to claim 14, wherein, In step (1), the additive N1 is a compound containing dopant element G, and the dopant element G is selected from at least one element in the groups IIA-IIIA of the 2nd to 5th periods.

17. The preparation method according to claim 16, wherein, In step (1), the doping element G is selected from at least one element selected from Al, Mg, Ca, Sr, Zr, Nb and Mo.

18. The preparation method according to claim 14, wherein, The additive N2 is a compound containing a dopant element R, wherein the dopant element R is selected from at least one element selected from B, Mg, Ca, Sr, Y, Ti, V, Cr, Fe, Cu, Zr, W, Nb and Al.

19. The preparation method according to claim 14, wherein, The first carbon source is selected from at least one of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

20. The preparation method according to claim 19, wherein the first carbon source is selected from at least one of glucose, sucrose, starch and cellulose.

21. The preparation method according to claim 14, wherein, The additive L1 is a compound containing a dopant element D', wherein the dopant element D' is selected from at least one element selected from Mg, Ca, Sr, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Y, Mo, Nb, B, Al, W, La and Sm.

22. The preparation method according to claim 21, wherein, The doping element D' is selected from at least one element selected from Ti, Nb and B.

23. The preparation method according to claim 14, wherein, The multi-element material precursor contains Ni, Co and M elements, where M is selected from Al and / or Mn elements; In step (1), the multi-element material is calculated as [n(Ni)+n(Co)+n(M)], the first lithium source is calculated as n(Li), and the amount of the first lithium source is such that 0.9≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.3; the amount of additive N1 is calculated as n(G) and the amount of additive N1 is such that 0≤[n(G)] / [n(Ni)+n(Co)+n(M)]<0.

05.

24. The preparation method according to claim 14, wherein, The multi-element material precursor contains Ni, Co and M elements, where M is selected from Al and / or Mn elements; In step (1), the multi-element material is calculated as [n(Ni)+n(Co)+n(M)], the first lithium source is calculated as n(Li), and the amount of the first lithium source is such that 0.95≤[n(Li)] / [n(Ni)+n(Co)+n(M)]≤1.2; the amount of additive N1 is calculated as n(G) and the amount of additive N1 is such that 0.01≤[n(G)] / [n(Ni)+n(Co)+n(M)]≤0.

03.

25. The preparation method according to claim 14, wherein, In step (2), the amount of the first calcined material, calculated as [n(Ni)+n(Co)+n(M)], and the amount of the additive N2, calculated as n(R), are such that 0≤[n(R)] / [n(Ni)+n(Co)+n(M)]<0.

05.

26. The preparation method according to claim 25, wherein, In step (2), the amount of the first calcined material, calculated as [n(Ni)+n(Co)+n(M)], and the amount of the additive N2, calculated as n(R), are such that 0.01≤[n(R)] / [n(Ni)+n(Co)+n(M)]<0.

03.

27. The preparation method according to claim 14, wherein, The lithium manganese iron phosphate material precursor includes Mn, Fe and D elements, wherein D is selected from at least one element selected from Mg, Co, Ni, Cu, Zn and Ti.

28. The preparation method according to claim 14, wherein, In step (3), the amount of the second lithium source in the lithium manganese iron phosphate precursor is such that 0.9 < [n(Li)] / [n(Mn)+n(Fe)+n(D)] ≤ 1.2; and the amount of additive L1 is such that 0 < [n(D')] / [n(Mn)+n(Fe)+n(D)] ≤ 0.

04.

29. The preparation method according to claim 28, wherein, In step (3), the amount of the lithium manganese iron phosphate material precursor and the second lithium source is such that 1 < [n(Li)] / [n(Mn)+n(Fe)+n(D)] ≤ 1.1; the amount of the additive L1 is such that 0.01 ≤ [n(D')] / [n(Mn)+n(Fe)+n(D)] ≤ 0.

03.

30. The preparation method according to claim 14, wherein, In step (3), the weight ratio of the lithium manganese iron phosphate material precursor to the first carbon source is 1:0.05-0.

12.

31. The preparation method according to claim 30, wherein, In step (3), the weight ratio of the lithium manganese iron phosphate material precursor to the first carbon source is 1:0.06-0.

1.

32. The preparation method according to claim 14, wherein, In step (1), the conditions for the first calcination include: calcination temperature of 650-900℃ and calcination time of 6-30h in an oxygen-containing atmosphere, and oxygen concentration ≥4vol in the oxygen-containing atmosphere.

33. The preparation method according to claim 32, wherein, In step (1), the conditions for the first calcination include: calcination temperature of 700-850℃ and calcination time of 8-25h in an oxygen-containing atmosphere, and oxygen concentration of ≥8vol in the oxygen-containing atmosphere.

34. The preparation method according to claim 14, wherein, The conditions for the first heat treatment in step (2) include: under an oxygen-containing atmosphere, the heat treatment temperature is 300-480℃, the heat treatment time is 5-15h, and the oxygen concentration in the oxygen-containing atmosphere is ≥4vol.

35. The preparation method according to claim 34, wherein, The conditions for the first heat treatment in step (2) include: under an oxygen-containing atmosphere, the heat treatment temperature is 320-460℃, the heat treatment time is 6-12h, and the oxygen concentration in the oxygen-containing atmosphere is ≥8vol.

36. The preparation method according to claim 14, wherein, In step (3), the conditions for the second calcination include: calcination temperature of 600℃-700℃ and calcination time of 8h-12h under a protective atmosphere.

37. The preparation method according to claim 36, wherein, In step (3), the conditions for the second calcination include: calcination temperature of 620℃-660℃ and calcination time of 9h-11h under a protective atmosphere.

38. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the composite cathode material as described in any one of claims 1-13.

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