Positive electrode material having olivine structure, preparation method therefor, and lithium ion battery

Abstract

The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode material having an olivine structure, a preparation method therefor, and a lithium ion battery. The positive electrode material comprises a base and a carbon coating layer; in a Raman spectrum, the positive electrode material has Raman responses in the wave number ranges of 940-950 cm-1, 1330-1350 cm-1 and 1580-1610 cm-1, and the Raman responses respectively correspond to three characteristic peaks A, B and C; and the positive electrode material satisfies: 0.01≤[the average value of I(A) / I(C)]≤0.3 and 0.01≤[the average value of I(A) / I(B)]≤0.3. The positive electrode material has a uniform carbon coating, so that the positive electrode material has high stability, low specific surface area, low volume resistance and high compacted density; in addition, the positive electrode material is used in the lithium ion battery, achieving excellent electrochemical performance.

Description

Positive electrode material with olivine structure and preparation method thereof, and lithium-ion battery Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a positive electrode material with an olivine structure, a method for preparing the positive electrode material with an olivine structure, and a lithium-ion battery containing the positive electrode material with an olivine structure. Background Art

[0002] Lithium-ion batteries, due to their long cycle life, high energy density, and lack of memory effect, have been widely used in new energy vehicles, mobile electronic devices, new power batteries, and energy storage. As a key component, the electrochemical properties of cathode materials play a crucial role in the overall performance of lithium-ion batteries.

[0003] Olivine structure cathode material (LiMePO4, Me=Fe, Mn, Fe x Mn (1-x) ) has the characteristics of low cost, long cycle life, high safety performance, and environmental friendliness, and has been widely used in the fields of power and energy storage. However, due to its inherent properties, the olivine structure cathode material exhibits low electronic conductivity (LiFePO4=1.8×10 -8 S / cm,LiMnPO4<10 -10 S / cm) and low Li + Diffusion coefficient (LiFePO4≈10 -11 cm 2 / s, LiMnPO4≈10 -14 cm 2 / s), based on the above problems, researchers mainly optimize the positive electrode materials by controlling the primary particle size, surface carbon coating and element doping.

[0004] CN115863596A discloses a method for utilizing a flexible, large-surface-area cyclic carbon composite to facilitate close contact with lithium iron manganese phosphate (LiFePO4), improve the uniformity of the carbon layer, form a continuous conductive network, and enhance the conductivity and stability of the LiFePO4 composite. This technology involves a long preparation cycle, requires large amounts of pure water for cleaning, and emits toxic gases such as methanol. The present invention utilizes a common, well-produced organic carbon source, effectively reducing production costs.

[0005] In the above-mentioned prior art, the carbon-coated olivine structure positive electrode material is usually I D / I G To characterize the degree of graphitization of the coated carbon, but the processing temperature of the olivine structure cathode material is relatively low (generally <900 ° C). In the process of the organic carbon source forming the inorganic carbon coating layer, as the degree of graphitization deepens, the sp3 Hybridization, toward sp 2 Transformation, I D / I G The performance characterization effect of the positive electrode material is relatively simple; at the same time, the thickness of the carbon coating layer and the carbonization quality will affect the energy retention rate of the olivine structure during the cycle.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned technical problems and provide a positive electrode material with an olivine structure, a preparation method thereof, and a lithium-ion battery. The positive electrode material has the characteristics of uniform carbon coating, so that the positive electrode material has high stability, low specific surface area, low volume impedance and high compaction density; at the same time, the positive electrode material is used in lithium-ion batteries, which has excellent electrochemical properties, especially improving the energy retention rate during the cycle.

[0008] In order to achieve the above object, the present invention provides a positive electrode material having an olivine structure in the first aspect, wherein the positive electrode material comprises a matrix and a carbon coating layer; in the Raman spectrum, the positive electrode material has a Raman spectrum of 940-950 cm ‐1 、1330-1350cm ‐1 、1580-1610cm ‐1 There is a Raman response in the wavenumber range, corresponding to three characteristic peaks A, B and C respectively; wherein the positive electrode material satisfies: the average value of 0.01≤[I(A) / I(C)]≤0.3 and the average value of 0.01≤[I(A) / I(B)]≤0.3.

[0009] In the present invention, unless otherwise specified, the positive electrode material having an olivine structure is referred to as the positive electrode material for short.

[0010] The positive electrode material provided by the present invention has a Raman response within a specific wavenumber range, and the intensity ratio of the characteristic peak is within a specific range, that is, the average value of 0.01≤[I(A) / I(C)]≤0.3 and the average value of 0.01≤[I(A) / I(B)]≤0.3, and in particular, the standard deviation of [I(A) / I(C)] is further limited to ≤0.02 and the standard deviation of [I(A) / I(B)] is ≤0.02, indicating that the carbon coating of the positive electrode material has good overall uniformity, the thickness of the carbon coating layer is appropriate, and the content of disordered carbon and ordered carbon in the carbon coating layer is within a suitable range, and the compatibility with the substrate is high. At the same carbon coating layer content, the uniform carbon coating layer in the present invention can effectively reduce the specific surface area and powder impedance of the positive electrode material.

[0011] The second aspect of the present invention provides a method for preparing the positive electrode material having an olivine structure provided in the first aspect, the preparation method comprising: mixing a Mn source, an Fe source, an M source, a phosphorus source, a Li source, an organic carbon source, and water; grinding the obtained mixed slurry, spray drying, and sintering in sequence, so that a carbon coating layer is loaded on the surface of the substrate having Formula I, to obtain a positive electrode material; the sintering is performed in an inert atmosphere;

[0012] Wherein, the particle size D of the grinding is controlled 50 Satisfy: 0.1μm≤D 50 ≤0.48μm, preferably: 0.15μm≤D 50 ≤0.36μm;

[0013] Among them, Li a Mn 1-x Fe x M b (PO4) c (I) M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 0.95≤a≤1.1; 0≤x≤1; 0≤b≤0.2; 1≤c≤1.1.

[0014] A third aspect of the present invention provides a lithium-ion battery, comprising: the positive electrode material provided in the first aspect, or the positive electrode material prepared by the preparation method provided in the second aspect.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The positive electrode material provided by the present invention has an average value and standard deviation of [I(A) / I(C)] and [I(A) / I(B)] within an appropriate range, indicating that the carbon coating on the surface of the positive electrode material is uniform and of appropriate thickness, the carbon coating layer has a high degree of graphitization, and is highly compatible with the substrate. Under the condition of the same carbon coating layer content, the carbon coating layer in the present invention can effectively reduce the specific surface area and volume impedance of the positive electrode material;

[0017] (2) The preparation method provided by the present invention is based on a solid-phase process, which controls the grinding particle size range to prepare a carbon-uniformly coated positive electrode material having an olivine structure, especially by regulating the spray drying particle size, sintering temperature, and type of organic carbon source, which to a certain extent affects the carbon coating content and coating effect;

[0018] At the same time, the preparation method also regulates the addition of organic carbon sources based on the presence and type of main metal elements (Mn and Fe) in the cathode material other than Li, thereby obtaining a cathode material with uniform carbon coating.

[0019] (3) The positive electrode material provided by the present invention is used in lithium-ion batteries, which can effectively improve the electrochemical performance of lithium-ion batteries, especially the energy retention rate; at the same time, the present invention provides different carbon-forming properties, so that the positive electrode material with an olivine structure has different characteristics in Raman properties, which is reflected in the capacity retention of lithium-ion batteries, and can better guide the preparation of positive electrode materials and process monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic diagram of the Raman spectrum of the positive electrode material S1 prepared in Example 1. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] In the present invention, unless otherwise specified, the terms "first," "second," and "third" do not indicate a sequential order, nor do they limit the materials or steps involved. They are used only to distinguish or indicate that they are not the same material or step. For example, the terms "first," "second," and "third" in "first slurry," "second slurry," and "third slurry" are used only to indicate that they are not the same slurry; similarly, the terms "first," "second," and "third" in "first sintering," "second sintering," and "third sintering" are used only to indicate that they are not the same sintering.

[0023] The first aspect of the present invention provides a positive electrode material having an olivine structure, wherein the positive electrode material comprises a matrix and a carbon coating layer; in the Raman spectrum, the positive electrode material has a Raman spectrum of 940-950 cm ‐1 、1330-1350cm ‐1 and 1580-1610cm ‐1 There is a Raman response in the wavenumber range, corresponding to three characteristic peaks A, B and C respectively; wherein the positive electrode material satisfies: 0.01≤[I(A) / I(C)] average value≤0.3 and 0.01≤[I(A) / I(B)] average value≤0.3.

[0024] In the present invention, unless otherwise specified, the positive electrode material is subjected to Raman testing, and the test conditions include: an excitation wavelength of 532 nm, a laser power of 0.1 mW, an objective lens magnification of 50X, a test range of 20×30 μm, and 600 measurement points.

[0025] In the present invention, unless otherwise specified, I(A), I(B) and I(C) refer to the positive electrode materials in the Raman spectrum, corresponding to 940-950cm ‐1 、1330-1350cm ‐1 、1580-1610cm ‐1 The intensity of peak A, peak B and peak C in the wavenumber range; I(A) / I(C) represents the intensity ratio of peak A and peak C in the Raman spectrum of the positive electrode material; similarly, I(A) / I(B) represents the intensity ratio of peak A and peak B in the Raman spectrum of the positive electrode material.

[0026] In the Raman spectrum of the cathode material provided by the present invention, 940-950cm ‐1 The A peak in the wavenumber range is mainly attributed to PO4 in the matrix 3- ; 1330-1350cm ‐1 The B peak in the wavenumber range is mainly attributed to carbon D, that is, disordered carbon in the carbon coating layer; 1580-1610 cm ‐1 The C peak in the wavenumber range is mainly attributed to carbon G, namely the ordered carbon / graphitized carbon in the carbon coating layer.

[0027] In the present invention, the average value of [I(A) / I(C)] represents the average value of the [I(A) / I(C)] values ​​obtained at each measuring point during the measurement process; the average value of [I(A) / I(B)] represents the average value of the [I(A) / I(B)] values ​​obtained at each measuring point during the measurement process.

[0028] In some embodiments of the present invention, the positive electrode material satisfies: 0.01≤[I(A) / I(C)] average value ≤ 0.3, for example, 0.01, 0.05, 0.06, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, and any value in the range of any two values, preferably 0.05≤[I(A) / I(C)] average value ≤ 0.25, more preferably 0.1≤[I(A) / I(C)] average value ≤ 0.25; and at the same time satisfies: 0.01≤ The average value of [I(A) / I(B)] is ≤0.3, for example, 0.01, 0.05, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, and any value in the range consisting of any two numerical values, preferably the average value of 0.05≤[I(A) / I(B)]≤0.25, more preferably the average value of 0.1≤[I(A) / I(B)]≤0.25.

[0029] In some embodiments of the present invention, the positive electrode material preferably further satisfies the following: the standard deviation of [I(A) / I(C)] ≤ 0.02; preferably, the positive electrode material further satisfies the following: the standard deviation of [I(A) / I(B)] ≤ 0.02. In the present invention, the above-mentioned standard deviation ranges of [I(A) / I(C)] and [I(A) / I(B)] are met, the positive electrode material has excellent overall uniformity and appropriate thickness of the carbon coating layer, a high degree of graphitization of the carbon coating layer, a low specific surface area and a small volume impedance, and excellent performance.

[0030] In some embodiments of the present invention, the positive electrode material preferably further satisfies: the average value of [I(B) / I(C)] is ≤ 1; further preferably, the average value of [I(B) / I(C)] is ≤ 0.9, for example, 0.7, 0.75, 0.8, 0.85, 0.9, and any value within a range consisting of any two values. In the present invention, if the [I(B) / I(C)] of the carbon coating layer is within the above-specified range, it indicates that the carbon coating layer has a high degree of graphitization.

[0031] In some embodiments of the present invention, preferably, the matrix has a composition shown in Formula I: Li a Mn 1-x Fe x M b (PO4) c (I); wherein, M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd, 0.95≤a≤1.1; 0≤x≤1; 0≤b≤0.2; 1≤c≤1.1.

[0032] In the present invention, preferably, in Formula I, M is selected from at least one of Ti, W, Co, V and Mg.

[0033] In the present invention, in Formula I, 0.95≤a≤1.1, for example, 0.95, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.1, and any value in the range consisting of any two values, preferably 1≤a≤1.05.

[0034] In the present invention, in Formula I, 0≤x≤1, for example, 0, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and any value in the range of any two values, preferably 0.3≤x≤1.

[0035] In the present invention, in Formula I, 0≤b≤0.2, for example, 0, 0.1, 0.12, 0.15, 0.18, 0.2, and any value in the range of any two values, preferably 0.1≤b≤0.2.

[0036] In the present invention, in Formula I, 1≤c≤1.1, for example, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.08, 1.1, and any value in the range consisting of any two values, preferably 1≤c≤1.05.

[0037] In the present invention, by regulating a, x, b, c and M in formula I, the value of a is regulated within a certain range, thereby affecting the Li ratio in the positive electrode material, thereby affecting the capacity and compaction level of the positive electrode material; adjusting the value of x will affect the voltage platform of the positive electrode material; adjusting the values ​​of b and M mainly affects the electrochemical kinetics and compaction density of the positive electrode material; adjusting the value of c will also affect the capacity and compaction density of the material by affecting the ratio of P in the material.

[0038] In some embodiments of the present invention, preferably, based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.8-3wt%, for example, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 3wt%, and any value in a range consisting of any two values, preferably 1-2.5wt%. In the present invention, the content parameter of the carbon coating layer is measured using a carbon-sulfur analyzer.

[0039] In some embodiments of the present invention, preferably, the thickness of the carbon coating layer is 1-10 nm, for example, 1 nm, 1.5 nm, 2 nm, 3 nm, 4 nm, 5 nm, 8 nm, 10 nm, and any value in a range consisting of any two values, preferably 1.5-5 nm. In the present invention, the thickness parameter of the carbon coating layer is measured by Raman spectroscopy and TEM imaging.

[0040] In some embodiments of the present invention, preferably, the average particle size of the matrix is ​​40-290 nm, for example, 40 nm, 70 nm, 90 nm, 100 nm, 150 nm, 200 nm, 230 nm, 290 nm, and any value in the range consisting of any two values, preferably 70-230 nm.

[0041] In some embodiments of the present invention, preferably, the average particle size of the positive electrode material is 50-300 nm, for example, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 240 nm, 300 nm, and any value in a range consisting of any two values, preferably 80-240 nm. In the present invention, the average particle size of the positive electrode material = the average particle size of the substrate + the thickness of the coating layer.

[0042] In some embodiments of the present invention, preferably, the specific surface area BET of the positive electrode material is 5-40 m 2 / g, for example, 5m 2 / g、8m 2 / g、10m 2 / g、15m 2 / g、18m 2 / g, 20m 2 / g, 25m 2 / g, 40m 2 / g, and any value in the range of any two values, preferably 8-25m 2 / g.

[0043] In some embodiments of the present invention, preferably, the volume impedance of the positive electrode material is 0-200Ω·cm, for example, 0Ω·cm, 5Ω·cm, 10Ω·cm, 20Ω·cm, 30Ω·cm, 50Ω·cm, 60Ω·cm, 80Ω·cm, 100Ω·cm, 150Ω·cm, 200Ω·cm, and any value in the range consisting of any two values, preferably 0-100Ω·cm.

[0044] In some embodiments of the present invention, preferably, the compaction density of the positive electrode material is 2-2.7 g / m 3 , for example, 2g / m 3 , 2.2g / m 3 , 2.3g / m 3 , 2.4g / m 3 , 2.5g / m 3 , 2.6g / m 3 , 2.7g / m 3 , and any value in the range of any two values, preferably 2.2-2.6g / m 3 .

[0045] In the present invention, unless otherwise specified, the specific surface area BET parameters are measured using a static adsorption method; the volume impedance parameters are measured using a four-probe method; and the compacted density parameters are measured using an in-situ static method.

[0046] The second aspect of the present invention provides a method for preparing the positive electrode material having an olivine structure provided in the first aspect, the preparation method comprising: mixing a Mn source, an Fe source, an M source, a phosphorus source, a Li source, an organic carbon source, and water; grinding the obtained mixed slurry, spray drying, and sintering in sequence, so that a carbon coating layer is loaded on the surface of the substrate having Formula I, to obtain a positive electrode material; the sintering is performed in an inert atmosphere;

[0047] Wherein, the particle size D of the grinding is controlled 50Satisfy: 0.1μm≤D 50 ≤0.48μm, preferably: 0.15μm≤D 50 ≤0.36μm;

[0048] Among them, Li a Mn 1-x Fe x M b (PO4) c (I) M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 0.95≤a≤1.1; 0≤x≤1; 0≤b≤0.2; 1≤c≤1.1.

[0049] The preparation method provided by the present invention adopts a solid-phase coating method to prepare a positive electrode material with an olivine structure, which has a high-quality carbon coating effect, so that the positive electrode material has high stability and good electrochemical properties; at the same time, the preparation method simplifies the process flow, facilitates product utilization, and is applied to lithium-ion batteries, which can effectively improve the energy retention rate during the cycle.

[0050] In the present invention, by controlling the particle size D of the grinding 50 Satisfy: 0.1μm≤D 50 ≤0.48μm, for example, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.36μm, 0.4μm, 0.48μm, and any value in the range of any two values, preferably satisfying: 0.15μm≤D 50 ≤0.36μm. In the present invention, by adjusting the particle size D of the grinding 50 , thereby controlling the primary particle size of the positive electrode material, thereby affecting the uniformity and thickness of the carbon coating layer, so that the positive electrode material satisfies: 0.01≤[the average value of I(A) / I(B)]≤0.3 and 0.01≤[the average value of I(A) / I(C)]≤0.3.

[0051] In the present invention, unless otherwise specified, the particle size D of the grinding is controlled. 50 That is, control the particle size D of the grinding material 50 Satisfy: 0.1μm≤D 50 ≤0.48μm, preferably 0.15μm≤D 50 ≤0.36μm; similarly, control the particle size D of the second grinding 2 50 That is, control the particle size D of the second grinding material 2 50 ; Control the particle size D' of the first coarse grinding 1 50That is, control the particle size D' of the first coarse abrasive 1 50 ; Control the particle size D of the first fine grinding 1 50 That is, control the particle size D of the first fine abrasive 1 50 ; Control the particle size D" of the first spray drying 1 50 That is, control the particle size D" of the first spray-dried material 1 50 ; Control the particle size D" of the second spray drying 2 50 That is, control the particle size D" of the second spray-dried material 2 50 ; Control the particle size D of the third grinding 3 50 That is, control the particle size D of the third grinding material 3 50 ; Control the particle size D" of the third spray drying 3 50 That is, control the particle size D" of the third spray-dried material 3 50 .

[0052] In the present invention, unless otherwise specified, the inert atmosphere includes but is not limited to nitrogen atmosphere, helium atmosphere, argon atmosphere, etc.

[0053] In some embodiments of the present invention, preferably, calculated on an elemental basis, the amounts of the Mn source, Fe source, M source, phosphorus source and Li source satisfy n(Mn):n(Fe):n(M):n(P):n(Li), wherein 0≤n(Mn)≤1, 0≤n(Fe)≤1, 0≤n(M)≤0.2, 1≤n(P)≤1.1, 0.95≤n(Li)≤1.1; further preferably, 0≤n(Mn)≤0.7, 0.3≤n(Fe)≤1, 0.1≤n(M)≤0.2, 1≤n(P)≤1.05, 1≤n(Li)≤1.05.

[0054] In some embodiments of the present invention, preferably, the M source is selected from compounds containing Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; further preferably, the M source is selected from compounds containing Ti, W, Co, V and Mg.

[0055] In some embodiments of the present invention, preferably, the Li source is selected from at least one of lithium dihydrogen phosphate, lithium carbonate, lithium oxalate, lithium oxide, lithium powder and lithium phosphate.

[0056] In some embodiments of the present invention, preferably, the phosphorus source is selected from at least one of lithium dihydrogen phosphate, manganese iron phosphate monohydrate, iron phosphate and phosphorus pentoxide.

[0057] In some embodiments of the present invention, the amount of the organic carbon source added preferably satisfies: the content of the carbon coating layer in the positive electrode material is 0.8-3wt%, preferably 1-2.5wt%. In the present invention, the amount of the organic carbon source added accounts for 5-40wt% of the solid content in the mixed slurry, and is adjusted according to the type of different organic carbon sources and the residual carbon rate, so that the content of the carbon coating layer in the positive electrode material satisfies 0.8-3wt%, preferably 1-2.5wt%.

[0058] In some embodiments of the present invention, preferably, the organic carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, polyvinyl pyrrolidone, tannic acid, and polydopamine; further preferably, the organic carbon source is selected from at least one of glucose, sucrose, and starch, and at least one of polyethylene glycol, polyvinyl pyrrolidone, tannic acid, and polydopamine. In the present invention, the weight average molecular weight of the polyethylene glycol is 1500-6000 g / mol, the weight average molecular weight of the polyvinyl pyrrolidone is 10000-40000 g / mol, and the weight average molecular weight of the polydopamine is 400-2000 g / mol.

[0059] In the present invention, the above-mentioned specific organic carbon source type is used so that the inorganic carbon formed after sintering the organic carbon source is evenly coated on the surface of the substrate having Formula I.

[0060] In the present invention, the amount of water used has a wide range of selection, as long as the solid content of the mixed slurry is 30-50wt%, preferably 35-45wt%.

[0061] In some embodiments of the present invention, preferably, calculated as metal elements, the Mn source and the Fe source are each independently selected from at least one of a simple substance, an oxide, a carbonate, an oxalate and a phosphate.

[0062] In a specific embodiment of the present invention, the Mn source includes but is not limited to manganese powder, manganese dioxide, manganese tetraoxide, manganese carbonate, manganese oxalate, manganese phosphate, ferromanganese phosphate, ferromanganese phosphate monohydrate, ferromanganese carbonate, ferromanganese oxalate, ferromanganese hydroxide, ferromanganese oxide, ferromanganese oxyhydroxyl, etc.

[0063] In a specific embodiment of the present invention, the Fe source includes but is not limited to iron powder, ferric oxide, ferrous oxide, ferrous oxalate, ferric phosphate, ferromanganese phosphate, ferromanganese phosphate monohydrate, ferromanganese carbonate, ferromanganese oxalate, ferromanganese hydroxide, ferromanganese oxide, ferromanganese oxyhydroxy, etc.

[0064] In a first specific embodiment of the present invention, preferably, the preparation method comprises the following steps: (I-1) mixing the Mn source, Fe source, M source, phosphorus source, Li source, first carbon source and water, and sequentially performing a first grinding, a first spray drying and a first slurry to obtain a first slurry; (I-2) mixing the first slurry and a second carbon source in water, and sequentially performing a second grinding, a second spray drying and a second slurry to obtain a second slurry, and using the obtained second slurry as the positive electrode material;

[0065] wherein the organic carbon source is divided into the first carbon source and the second carbon source; and the particle size D of the second grinding is controlled. 2 50 Satisfy: 0.1μm≤D 2 50 ≤0.48μm, preferably: 0.15μm≤D 2 50 ≤0.36μm; wherein the first sintering and the second sintering are each independently performed in an inert atmosphere.

[0066] In some embodiments of the present invention, preferably, in step (I-1), the mass ratio of the first carbon source to the second carbon source is 0.1-1:1, for example, 0.1:1, 0.15:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1:1, and any value in a range consisting of any two values, preferably 0.15-0.8:1. In the present invention, the mass ratio meeting the above range can effectively reduce the specific surface area of ​​the positive electrode material, increase the compaction density of the positive electrode material, and have a better degree of graphitization.

[0067] In some embodiments of the present invention, preferably, the first carbon source is selected from at least one of glucose, sucrose, starch and polyethylene glycol; the second carbon source is selected from at least one of glucose, sucrose and starch, and at least one of polyethylene glycol, polyvinyl pyrrolidone, tannic acid and polydopamine.

[0068] In the present invention, the first grinding is to grind the particles in the first slurry with a solid content of 30-50wt%. Preferably, the first grinding includes a first coarse grinding and a first fine grinding, and the particle size D' of the first coarse grinding is controlled. 1 50 Satisfy: 0.3μm≤D' 1 50 ≤10 μm, for example, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, and any value in a range consisting of any two values, preferably 0.5 μm ≤ D' 150 ≤5μm; Control the particle size D of the first fine grinding 1 50 Satisfy: 0.1μm≤D 1 50 ≤0.5μm, for example, 0.1μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.5μm, and any value in the range of any two values, preferably 0.2μm≤D 1 50 ≤0.4μm.

[0069] In the present invention, by adjusting the final particle size of the first grinding (ie, the particle size D 1 50 ), which can directly achieve a more uniform mixing of the various components, which is beneficial to the purity of the positive electrode material phase. Too coarse grinding is not conducive to the uniformity of the components, and too fine grinding is difficult and affects the size of the primary particles after sintering, thereby affecting the compaction density and cycle stability of the positive electrode material; at the same time, the size of the first grinding particle size will determine the uniformity of the carbon source in the first carbon replenishing process, thereby affecting the carbon distribution on the particle surface in the first sintering.

[0070] In some embodiments of the present invention, preferably, the particle size D" of the first spray drying is controlled 1 50 Satisfy: 2μm≤D” 1 50 ≤30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 30 μm, and any value in a range consisting of any two values, preferably 5 μm ≤ D" 1 50 ≤20μm. In the present invention, during the first spray drying process, the first carbon source forms an effective coating on the surface of the spray material as the water in the first slurry evaporates. If the particle size of the spray material is too large, it will affect the evaporation of water in the particles, thereby affecting the uniform coating of the organic carbon source on the surface of the spray material.

[0071] In some embodiments of the present invention, preferably, the conditions for the first sintering include: temperature T1 of 350-650°C, preferably 400-600°C; heating rate V1 of 0.5-10°C / min, preferably 1-5°C / min; constant temperature time t1 of 0.5-6h, preferably 1-3h.

[0072] In the present invention, unless otherwise specified, the first sintered material obtained by the first sintering is an agglomerate, and the average particle size of the first sintered material is equal to the particle size D" of the first spray-dried material. 1 50Preferably, the primary particle size of the first sintering material is 40-240 nm, preferably 60-180 nm.

[0073] In some embodiments of the present invention, in step (I-2), the particle size D of the second grinding is controlled 2 50 Satisfy: 0.1μm≤D 2 50 ≤0.48μm, for example, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.36μm, 0.4μm, 0.48μm, and any value in the range of any two values, preferably satisfying: 0.15μm≤D 2 50 ≤0.36μm. In the present invention, by controlling the second grinding particle size D 2 50 range, which can effectively form a second carbon coating effect on the surface of the primary particles, thereby having specific I(A) / I(C) and I(A) / I(B).

[0074] In some embodiments of the present invention, preferably, the particle size D" of the second spray drying is controlled 2 50 Satisfy: 2μm≤D” 2 50 ≤30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 30 μm, and any value in a range consisting of any two values, preferably 5 μm ≤ D" 2 50 ≤20μm. Too small a particle size of the second spray drying is not conducive to improving production efficiency, while too large a particle size is not conducive to the volatilization of water, thereby affecting the uniform adhesion of the second carbon source.

[0075] In some embodiments of the present invention, preferably, the conditions for the second sintering include: temperature T2 of 550-850°C, preferably 600-750°C; heating rate V2 of 0.5-50°C / min, preferably 0.8-5°C / min; constant temperature time t2 of 2-14h, preferably 6-12h.

[0076] In the present invention, when the second sintering temperature T2 is low, the degree of graphitization of the carbon coating layer of the positive electrode material decreases, the carbon content increases, and the corresponding [I(A) / I(C)] and [I(A) / I(B)] decrease, the specific surface area increases, the compaction decreases, and the impedance increases, which affects the electrochemical performance to a certain extent; when the second sintering temperature T2 is too high, it will lead to abnormal growth of the primary particles of the positive electrode material, and at the same time, impurities such as Fe2P will be generated, thereby affecting the electrochemical performance of the positive electrode material.

[0077] In a second specific embodiment of the present invention, preferably, the preparation method comprises the following steps: (II) mixing the Mn source, Fe source, M source, phosphorus source, Li source, organic carbon source and water, and sequentially performing a third grinding, a third spray drying and a third sintering on the obtained third slurry to obtain a third sintered product; wherein the particle size D of the third grinding is controlled 3 50 Satisfy: 0.1μm≤D 3 50 ≤0.48μm, preferably: 0.15μm≤D 3 50 ≤0.36μm; the third sintering is carried out in an inert atmosphere;

[0078] Wherein, when the matrix represented by Formula I contains both Mn and Fe, the Mn source and the Fe source are each independently selected from compounds containing both Mn and Fe; or, when the matrix represented by Formula I does not contain both Mn and Fe, the Mn source is selected from manganese phosphate, and the Fe source is selected from iron phosphate.

[0079] In the present invention, by comparing the above two preparation methods, it can be seen that the first preparation method, that is, the technical means of twice grinding, twice spray drying and twice sintering, does not impose any restrictions on the types of Mn source and Fe source in the raw material, that is, it is applicable to all Mn sources and Fe sources defined above; the second preparation method, that is, the technical means of single grinding, single spray drying and single sintering, has restrictions on the types of Mn source and Fe source in the raw material.

[0080] At the same time, using specific Mn source and Fe source as raw materials, it is possible to avoid using the technical means of double grinding, double spray drying and double sintering. Instead, the technical means of single grinding, single spray drying and single sintering can be used, which not only can obtain specific positive electrode materials with olivine structure, but also simplifies the process flow and saves costs.

[0081] In the present invention, unless otherwise specified, when the matrix represented by Formula I contains both Mn and Fe, it means that in Formula I, the superscript (1-x) and x of Mn and Fe are both not equal to 0; the Mn source and the Fe source are each independently selected from a compound containing both Mn and Fe, which means that the Mn source is selected from a compound containing Mn and Fe, and the Fe source is also selected from a compound containing Mn and Fe; when the matrix represented by Formula I does not contain Mn and Fe at the same time, it means that in Formula I, the superscript (1-x) of Mn is equal to 0 and the superscript x of Fe is not equal to 0; or, the superscript (1-x) of Mn is not equal to 0 and the superscript x of Fe is equal to 0.

[0082] In some embodiments of the present invention, when the matrix represented by Formula I contains both Mn and Fe, the Mn source and the Fe source are each independently selected from compounds containing both Mn and Fe. Preferably, the Mn source and the Fe source are each independently selected from at least one of ferromanganese phosphate, ferromanganese phosphate monohydrate, ferromanganese carbonate, ferromanganese oxalate, ferromanganese hydroxide, ferromanganese oxide, and ferromanganese oxyhydroxide.

[0083] In some embodiments of the present invention, when the matrix represented by Formula I does not contain Mn and Fe at the same time, the Mn source is selected from manganese phosphate, and the Fe source is selected from iron phosphate.

[0084] In some embodiments of the present invention, preferably, in step (II), the third grinding includes a third coarse grinding and a third fine grinding, and the particle size D' of the third coarse grinding is controlled. 3 50 Satisfy: 0.3μm≤D' 3 50 ≤10 μm, for example, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, and any value in a range consisting of any two values, preferably 0.5 μm ≤ D' 3 50 ≤5μm; Control the particle size D of the third fine grinding 3 50 Satisfy: 0.1μm≤D 3 50 ≤0.48 μm, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.36 μm, 0.4 μm, 0.48 μm, and any value in a range consisting of any two values, preferably 0.15 μm≤D 3 50 In the present invention, the particle size within the above range is satisfied so that the carbon is evenly coated on the surface of the positive electrode material, and has specific average values ​​of [I(A) / I(C)] and [I(A) / I(B)].

[0085] In some embodiments of the present invention, preferably, the particle size D" of the third spray drying is controlled 3 50 Satisfy: 2μm≤D” 3 50 ≤30 μm, for example, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 30 μm, and any value in a range consisting of any two values, preferably 5 μm ≤ D" 3 50 ≤20μm.

[0086] In some embodiments of the present invention, preferably, the conditions of the third sintering include: temperature T3 of 550-850°C, preferably 600-750°C; heating rate V3 of 0.5-50°C / min, preferably 0.8-5°C / min; constant temperature time t3 of 2-14h, preferably 6-12h.

[0087] In the present invention, when the temperature T3 of the third sintering is low, the degree of graphitization of the carbon coating layer of the positive electrode material is reduced, the carbon content is increased, and the corresponding average values ​​of [I(A) / I(C)] and [I(A) / I(B)] are reduced, the specific surface area BET is increased, the compaction is reduced, and the impedance is increased, which to a certain extent affects the electrochemical performance; when the temperature T3 of the third sintering is high, the content of the carbon coating layer of the positive electrode material is reduced, the average value of [I(B) / I(C)] is reduced, the degree of graphitization is increased, and the primary particles grow, thereby improving the compaction of the material and reducing the specific surface area, which is beneficial to the improvement of the electrochemical and processing performance.

[0088] A third aspect of the present invention provides a lithium-ion battery, which contains the positive electrode material provided by the first aspect, or the positive electrode material prepared by the preparation method provided by the second aspect.

[0089] The present invention will be described in detail below through examples.

[0090] The physical properties of the positive electrode materials prepared in the examples and comparative examples are listed in Table 1.

[0091] Energy retention rate 80 th Test method:

[0092] (1) Assembling a battery: the positive electrode material to be tested, the conductive agent (acetylene black), and the binder (PVDF) were mixed with the solvent (NMP) in a mass ratio of 95:3:2 (temperature 25°C, rotation speed 1000 rpm, time 40 min) to obtain a positive electrode slurry with a solid content of 40 wt%;

[0093] The positive electrode slurry is applied on the surface of the aluminum foil to form a positive electrode slurry coating on the surface of the aluminum foil, dried at 135° C., and then rolled using a roller press (with a pressure of 15T) to form a positive electrode active material layer on the surface of the aluminum foil to obtain a positive electrode sheet;

[0094] In an argon-filled glove box with a water and oxygen content of less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into 2025 button cells and left to stand for 6 hours. The negative electrode used a lithium metal sheet with a diameter of 16 mm and a thickness of 0.5 mm; the separator used a polyethylene porous membrane (Celgard 2325) with a thickness of 25 μm; and the electrolyte was a mixture of equal parts of ethylene carbonate (EC) and diethyl carbonate (DEC) containing 1 mol / L LiPF6.

[0095] (2) Test conditions: Control the charge and discharge voltage range to 2.5-4.35V. At 25°C, charge and discharge the button battery twice at 0.1C, and then charge and discharge for 80 times at 1C. The first discharge capacity at 0.1C is the discharge capacity of the button battery in the first cycle, and the 80th discharge capacity at 1C is the discharge capacity of the button battery in the 80th cycle.

[0096] Among them, the energy retention rate is 80 th =(discharge capacity of the button cell at the 80th cycle / discharge capacity of the button cell at the 1st cycle)×100%.

[0097] Example 1

[0098] (1) A manganese source (manganese tetraoxide), an iron source (ferric phosphate), a lithium source (lithium dihydrogen phosphate, lithium carbonate), a phosphorus source (lithium dihydrogen phosphate, iron phosphate), an M source (titanium dioxide, tungsten oxide), and a first carbon source (glucose) are mixed in water to obtain a first slurry with a solid content of 40 wt %, wherein the element moles are represented by the chemical formula Li 1.04 Mn 0.65 Fe 0.35 Ti 0.05 W 0.05 (PO4) 1.01 Add

[0099] The first slurry is subjected to a first coarse grinding to obtain a first coarse abrasive particle size D' 1 50 =3.3μm; the first coarse abrasive is subjected to a first fine grinding to obtain a first fine abrasive D 1 50 =0.3μm;

[0100] The first finely ground material is subjected to a first spray drying to obtain a first spray-dried material D" 150 =10.2μm, BET=7.2m 2 / g;

[0101] The first spray-dried material was first sintered in a nitrogen atmosphere, heated to T1 = 500 ° C at a heating rate of V1 = 1.5 ° C / min, and kept at this temperature for t1 = 3 h. The average particle size of the first sintered material was 10.5 μm, the primary particle size was 80 nm, and the specific surface area was 7.3 m 2 / g;

[0102] (2) dispersing the first sintered material in water, adding a second carbon source (glucose and PEG in a mass ratio of 5.6:4) to obtain a second slurry; wherein the mass ratio of the first carbon source to the second carbon source is 0.45:1, and the total amount of the first carbon source and the second carbon source added satisfies: the carbon coating content in the finished positive electrode material is 1.57 wt%;

[0103] The second slurry is subjected to a second grinding to obtain a second grinding material D 2 50 =0.25μm;

[0104] The second ground material is subjected to a second spray drying to obtain a second spray dried material D" 2 50 =8.0μm, BET=8.8m 2 / g;

[0105] The second spray-dried material was subjected to a second sintering process, wherein the temperature was raised to T2 = 675°C at a heating rate of V2 = 1.5°C / min and kept at this temperature for t2 = 10h to obtain a second sintered material;

[0106] The second sintered material is crushed to obtain a positive electrode material S1 having an olivine structure.

[0107] The Raman spectrum of the positive electrode material S1 is shown in FIG1 . As can be seen from FIG1 , the positive electrode material S1 has a Raman spectrum of 950 cm ‐1 、1350cm ‐1 and 1580cm ‐1 There will be peaks A, B and C near the Raman shift, and peaks A, B and C correspond to the PO4 3- , characteristic peaks of carbon D and carbon G.

[0108] Example 2

[0109] According to the method of Example 1, the difference is that

[0110] In step (2), the mass ratio of glucose to PEG in the second carbon source is changed to 7:4;

[0111] The mass ratio of the first carbon source to the second carbon source is replaced with 0.39:1, and the total amount of the first carbon source and the second carbon source added satisfies: the carbon coating content in the finished positive electrode material is 1.85wt%;

[0112] Get the second mill base D 2 50 =0.25μm;

[0113] The second ground material is subjected to a second spray drying to obtain a second spray dried material D" 2 50 =8.3μm, BET=9.1m 2 / g;

[0114] The remaining conditions were the same to obtain the positive electrode material S2.

[0115] Example 3

[0116] According to the method of Example 1, the difference is that

[0117] In step (2), the mass ratio of glucose to PEG in the second carbon source is changed to 2.5:12;

[0118] The mass replacement ratio of the first carbon source and the second carbon source is 0.3:1, and the total amount of the first carbon source and the second carbon source added satisfies: the carbon coating content in the finished positive electrode material is 1.55wt%;

[0119] Get the second mill base D 2 50 =0.25μm;

[0120] The second ground material is subjected to a second spray drying to obtain a second spray dried material D" 2 50 =8.8μm, BET=8.5m 2 / g;

[0121] The other conditions were the same to obtain the positive electrode material S3.

[0122] Example 4

[0123] A manganese source (manganese ferrophosphate monohydrate), an iron source (manganese ferrophosphate monohydrate), a lithium source (lithium dihydrogen phosphate, lithium carbonate), a phosphorus source (lithium dihydrogen phosphate, manganese ferrophosphate monohydrate), an M source (titanium dioxide, tungsten oxide), and an organic carbon source (glucose, PEG) were mixed in water to obtain a third slurry with a solid content of 40 wt %, wherein the element moles are represented by the chemical formula Li 1.04 Mn 0.65 Fe 0.35 Ti 0.05 W 0.05 (PO4)1.01 The organic carbon source is added in an amount such that the carbon coating content in the finished positive electrode material is 1.83 wt %;

[0124] The third slurry is subjected to a third coarse grinding to obtain a third coarse grinding material D' 3 50 = 2μm; the third coarse abrasive is subjected to a third fine grinding to obtain a third fine abrasive D 3 50 =0.3μm;

[0125] The third finely ground material is subjected to a third spray drying to obtain a third spray-dried material D" 3 50 =10.8μm, BET=30.1μm;

[0126] The third spray-dried material was subjected to a third sintering process, heated to T3 = 650°C at a heating rate of V3 = 1.5°C / min, and kept at this temperature for t3 = 10h. The obtained third sintered material was crushed to obtain a positive electrode material S4 having an olivine structure.

[0127] Example 5

[0128] The iron source (ferric phosphate), lithium source (lithium carbonate), phosphorus source (ferric phosphate), M source (titanium dioxide, tungsten oxide), and organic carbon source (glucose, PEG) were mixed in water to obtain a third slurry with a solid content of 45 wt%, wherein the element moles are represented by the chemical formula Li 1.04 FeTi 0.05 W 0.05 (PO4) 1.03 The organic carbon source is added in an amount such that the carbon coating content in the finished positive electrode material is 1.40 wt %;

[0129] The third slurry is subjected to a third coarse grinding to obtain a third coarse grinding material D' 3 50 = 2.8 μm; the third coarse abrasive is subjected to a third fine grinding to obtain a third fine abrasive D 3 50 =0.35μm;

[0130] The third finely ground material is subjected to a third spray drying to obtain a third spray-dried material D" 3 50 =12.1μm, BET=6.1m 2 / g;

[0131] The third spray-dried material was subjected to a third sintering process, heated to T3 = 780°C at a heating rate of V3 = 3°C / min, and kept warm for t3 = 8h. The obtained third sintered material was crushed to obtain a positive electrode material S5 having an olivine structure.

[0132] Example 6

[0133] According to the method of Example 1, the difference is that

[0134] In step (2), the second sintering temperature T2 is changed from 675°C to 650°C;

[0135] The other conditions were the same, and the positive electrode material S6 with olivine structure was obtained.

[0136] Example 7

[0137] According to the method of Example 1, the difference is that

[0138] In step (2), the mass ratio of the first carbon source to the second carbon source is 0.67:1, and the total amount of the first carbon source and the second carbon source added satisfies: the carbon coating content in the finished positive electrode material is 1.67 wt%;

[0139] The remaining conditions were the same, and the positive electrode material S7 with olivine structure was obtained.

[0140] Comparative Example 1

[0141] The method of Example 4 is as follows, except that

[0142] Control the third fine abrasive D 3 50 =0.5μm;

[0143] The other conditions were the same, and the olivine structure positive electrode material DS1 was obtained.

[0144] Comparative Example 2

[0145] According to the method of Example 1, the difference is that

[0146] In step (2), adjust the D of the second grinding material 2 50 0.5μm;

[0147] The other conditions were the same, and the olivine structure positive electrode material DS2 was obtained.

[0148] Table 1

[0149] Table 1

[0150] Table 1

[0151] Based on the data in Table 1, it can be seen that, in combination with Examples 1-7 and Comparative Examples 1-2, when the preparation process, sintering temperature, grinding particle size, and type of organic carbon source of the positive electrode material with an olivine structure are changed, the content and coating effect of the carbon coating layer will be affected to a certain extent.

[0152] By comparing Examples 1 and 2, it can be seen that when the content of the carbon coating layer of the positive electrode material is increased, the average values ​​of [I(A) / I(C)] and [I(A) / I(B)] both decrease, and are inversely proportional to the thickness of the carbon coating layer; the average values ​​of [I(B) / I(C)] are at the same level, and the degree of graphitization of the organic carbon source is more related to the temperature; when the carbon coating layer is uniformly coated, the content and thickness of the carbon coating layer are positively correlated.

[0153] By comparing Example 1 and Example 3, it can be seen that by adjusting the amount of the second carbon source added, at the same sintering temperature and the content of the carbon coating layer, the mass ratio of the first carbon source to the second carbon source is regulated, the specific surface area of ​​the positive electrode material can be reduced, the compaction density can be increased, and a better degree of graphitization can be achieved.

[0154] The positive electrode material S3 sample prepared in Example 3 was tested at two laser intensities, 0.1mW and 0.3mW. When the laser intensity was 0.3mW, the average and standard deviation of [I(A) / I(C)] were 0.31 and 0.03, respectively, the average and standard deviation of [I(A) / I(B)] were 0.38 and 0.03, respectively, and the average value of [I(B) / I(C)] was 0.81. That is, compared with the laser intensity of 0.1mW, the average and standard deviation of [I(A) / I(C)] and [I(A) / I(B)] increased when the laser intensity was 0.3mW. During the test, the surface carbon coating was damaged to a certain extent, making the carbon coating uneven and thinner, resulting in an enhanced A signal and a larger standard deviation. Therefore, a specific laser intensity must be defined to characterize this feature of the material.

[0155] By comparing Example 2 and Example 4, it can be seen that when the same olivine-structured positive electrode material is prepared under different processes, the average values ​​of [I(A) / I(C)] and [I(A) / I(B)] show a similar pattern, indicating that this pattern can effectively guide the preparation of positive electrode materials under different preparation processes.

[0156] By comparing Examples 4 and 5, it can be seen that two different positive electrode materials were prepared under similar processes. Due to the differences in sintering temperature, carbon loading, and grinding particle size, there are certain differences in the average values ​​of [I(A) / I(C)] and [I(A) / I(B)]. Therefore, this rule should guide the preparation of the same material.

[0157] By comparing Example 1 and Example 6, it can be seen that when the second sintering temperature is lowered, the degree of graphitization of the carbon coating layer of the positive electrode material decreases, the content of the carbon coating layer increases, and the corresponding average values ​​of [I(A) / I(C)] and [I(A) / I(B)] decrease, BET increases, compaction decreases, and impedance increases, which to a certain extent affects the electrochemical performance.

[0158] By comparing Example 1 and Example 7, it can be seen that in the second sintering process, when the carbon mixing method is changed, the residual carbon amount of the first sintering increases, and the uneven coating of inorganic carbon during the second grinding affects the quality of the carbon coating layer on the surface of the positive electrode material, resulting in abnormalities in the average values ​​and standard deviations of [I(A) / I(C)] and [I(A) / I(B)].

[0159] By comparing Example 4 and Comparative Example 1, as well as Example 1 and Comparative Example 2, it can be seen that increasing the grinding particle size is not conducive to uniform coating of carbon on the primary particles of the positive electrode material during the sintering process, and some primary particles will be exposed, resulting in enhanced A signal, and abnormal average values ​​and standard deviations of [I(A) / I(C)] and [I(A) / I(B)].

[0160] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A cathode material with an olivine structure, characterized in that, The positive electrode material includes a matrix and a carbon coating layer; in the Raman spectrum, the positive electrode material has Raman responses in the wavenumber ranges of 940-950 cm ‐1 , 1330-1350 cm ‐1 , 1580-1610 cm ‐1 and respectively correspond to three characteristic peaks A, B, and C; among them, the positive electrode material satisfies: 0.01 ≤ average value of [I(A) / I(C)] ≤ 0.3 and 0.01 ≤ average value of [I(A) / I(B)] ≤ 0.

3.

2. The cathode material according to claim 1, wherein, The positive electrode material satisfies: 0.05 ≤ average value of [I(A) / I(C)] ≤ 0.25 and 0.05 ≤ average value of [I(A) / I(B)] ≤ 0.25; Preferably, the positive electrode material satisfies: 0.1 ≤ average value of [I(A) / I(C)] ≤ 0.25 and 0.1 ≤ average value of [I(A) / I(B)] ≤ 0.25; And / or, the positive electrode material further satisfies: standard deviation of [I(A) / I(C)] ≤ 0.02; And / or, the positive electrode material further satisfies: standard deviation of [I(A) / I(B)] ≤ 0.02; And / or, the positive electrode material further satisfies: average value of [I(B) / I(C)] ≤ 1, preferably average value of [I(B) / I(C)] ≤ 0.

9.

3. The cathode material according to claim 1 or 2, wherein, The matrix has a composition shown by formula I: Li a Mn 1-x Fe x M b (PO4) c (I), Wherein, M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 0.95 ≤ a ≤ 1.1; 0 ≤ x ≤ 1; 0 ≤ b ≤ 0.2; 1 ≤ c ≤ 1.1; Preferably, in formula I, M is selected from at least one of Ti, W, Co, V and Mg; 1 ≤ a ≤ 1.05; 0.3 ≤ x ≤ 1; 0.1 ≤ b ≤ 0.2; 1 ≤ c ≤ 1.

05.

4. The cathode material according to any one of claims 1-3, wherein, Based on the total weight of the positive electrode material, the content of the carbon coating layer is 0.8 - 3 wt%, preferably 1 - 2.5 wt%; And / or, the thickness of the carbon coating layer is 1 - 10 nm, preferably 1.5 - 5 nm; And / or, the average particle size of the matrix is 40 - 290 nm, preferably 70 - 230 nm; And / or, the average particle size of the positive electrode material is 50 - 300 nm, preferably 80 - 240 nm.

5. The cathode material according to any one of claims 1-4, wherein, The specific surface area BET of the positive electrode material is 5 - 40 m 2 / g, preferably 8 - 25 m 2 / g; And / or, the volume impedance of the positive electrode material is 0 - 200 Ω·cm, preferably 0 - 100 Ω·cm; And / or, the tap density of the positive electrode material is 2-2.7 g / m 3 , preferably 2.2-2.6 g / m 3 .

6. A method for preparing a cathode material with olivine structure according to any one of claims 1-5, characterized in that, The preparation method includes: mixing an Mn source, an Fe source, an M source, a phosphorus source, an Li source, an organic carbon source and water, and subjecting the obtained mixed slurry to grinding, spray drying and sintering in sequence to load a carbon coating layer on the surface of the matrix having formula I to obtain a positive electrode material; the sintering is carried out in an inert atmosphere; Among them, the particle size D of the grinding is controlled 50 to satisfy: 0.1 μm ≤ D 50 ≤ 0.48 μm, preferably satisfying: 0.15 μm ≤ D 50 ≤ 0.36 μm; Among them, Li a Mn 1-x Fe x M b (PO4) c (I), M is selected from at least one of Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd; 0.95 ≤ a ≤ 1.1; 0 ≤ x ≤ 1; 0 ≤ b ≤ 0.2; 1 ≤ c ≤ 1.

1.

7. The preparation method according to claim 6, wherein In terms of elements, the dosages of the Mn source, the Fe source, the M source, the phosphorus source and the Li source satisfy n(Mn):n(Fe):n(M):n(P):n(Li), wherein, 0 ≤ n(Mn) ≤ 1, 0 ≤ n(Fe) ≤ 1, 0 ≤ n(M) ≤ 0.2, 1 ≤ n(P) ≤ 1.1, 0.95 ≤ n(Li) ≤ 1.1; preferably, 0 ≤ n(Mn) ≤ 0.7, 0.3 ≤ n(Fe) ≤ 1, 0.1 ≤ n(M) ≤ 0.2, 1 ≤ n(P) ≤ 1.05, 1 ≤ n(Li) ≤ 1.05; And / or, the M source is selected from compounds containing Ti, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu and Gd, preferably selected from compounds containing Ti, W, Co, V and Mg; And / or, the Li source is selected from at least one of lithium dihydrogen phosphate, lithium carbonate, lithium oxalate, lithium oxide, lithium powder and lithium phosphate; And / or, the phosphorus source is selected from at least one of lithium dihydrogen phosphate, manganese iron phosphate monohydrate, iron phosphate, phosphorus pentoxide and phosphoric acid; And / or, the addition amount of the organic carbon source satisfies that the content of the carbon coating layer in the positive electrode material is 0.8-3 wt%, preferably 1-2.5 wt%; And / or, the organic carbon source is selected from at least one of glucose, sucrose, starch, polyethylene glycol, polyvinylpyrrolidone, tannic acid and polydopamine, more preferably at least one of glucose, sucrose and starch, and at least one of polyethylene glycol, polyvinylpyrrolidone, tannic acid and polydopamine.

8. The preparation method according to claim 6 or 7, wherein Calculated by metal element, the Mn source and the Fe source are each independently selected from at least one of elemental substances, oxides, carbonates, oxalates and phosphates.

9. The preparation method according to any one of claims 6-8, wherein, The preparation method includes the following steps: (I-1) Mix the Mn source, Fe source, M source, phosphorus source, Li source, first carbon source and water to obtain a first slurry, and the obtained first slurry is successively subjected to first grinding, first spray drying and first sintering to obtain a first sintered product; (I-2) Mix the first sintered product and the second carbon source in water, and the obtained second slurry is successively subjected to second grinding, second spray drying and second sintering, The obtained second sintered product is used as the positive electrode material; Among them, the organic carbon source is divided into the first carbon source and the second carbon source; the particle size D of the second grinding is controlled 2 50 to satisfy: 0.1 μm ≤ D 2 50 ≤ 0.48 μm, preferably satisfying: 0.15 μm ≤ D 2 50 ≤ 0.36 μm; wherein, the first sintering and the second sintering are each independently carried out in an inert atmosphere.

10. The preparation method according to claim 9, wherein, In step (I-1), the mass ratio of the first carbon source to the second carbon source is 0.1-1:1, preferably 0.15-0.8:1; And / or, the first carbon source is selected from at least one of glucose, sucrose, starch and polyethylene glycol; the second carbon source is selected from at least one of glucose, sucrose and starch, and at least one of polyethylene glycol, polyvinylpyrrolidone, tannic acid and polydopamine; And / or, the first grinding includes first rough grinding and first fine grinding, and the particle size D' of the first rough grinding is controlled 1 50 to satisfy: 0.3 μm ≤ D' 1 50 ≤ 10 μm, preferably 0.5 μm ≤ D' 1 50 ≤ 5 μm; the particle size D of the first fine grinding is controlled 1 50 to satisfy: 0.1 μm ≤ D 1 50 ≤ 0.5 μm, preferably 0.2 μm ≤ D 1 50 ≤ 0.4 μm; and / or, controlling the particle size D” of the first spray drying 1 50 satisfies: 2μm ≤ D” 1 50 ≤ 30μm, preferably 5μm ≤ D” 1 50 ≤ 20μm; And / or, the conditions of the first sintering include: the temperature T1 is 350-650 °C, preferably 400-600 °C; the heating rate V1 is 0.5-10 °C / min, preferably 1-5 °C / min; the constant temperature time t1 is 0.5-6 h, preferably 1-3 h; And / or, in step (I-2), controlling the particle size D” of the second spray drying 2 50 Satisfy: 2μm ≤ D” 2 50 ≤ 30μm, preferably 5μm ≤ D” 2 50 ≤ 20μm; And / or, the conditions of the second sintering include: the temperature T2 is 550-850 °C, preferably 600-750 °C; the heating rate V2 is 0.5-50 °C / min, preferably 0.8-5 °C / min; the constant temperature time t2 is 2-14 h, preferably 6-12 h.

11. The preparation method according to any one of claims 6-8, wherein, The preparation method includes the following steps: (II) Mix the Mn source, Fe source, M source, phosphorus source, Li source, organic carbon source and water, and subject the obtained third slurry to third grinding, third spray drying and third sintering in sequence to obtain a third sintered product; wherein, control the particle size D of the third grinding 3 50 to satisfy: 0.1 μm ≤ D 3 50 ≤ 0.48 μm, preferably satisfy: 0.15 μm ≤ D 3 50 ≤ 0.36 μm; the third sintering is carried out in an inert atmosphere; Wherein, when the matrix shown in formula I contains both Mn and Fe at the same time, the Mn source and the Fe source are each independently selected from compounds containing both Mn and Fe; or, when the matrix shown in formula I does not contain both Mn and Fe at the same time, the Mn source is selected from manganese phosphate and the Fe source is selected from iron phosphate.

12. The preparation method according to claim 11, wherein, In step (II), The third grinding includes third rough grinding and third fine grinding, and the particle size D' of the third rough grinding is controlled 3 50 to satisfy: 0.3 μm ≤ D' 3 50 ≤ 10 μm, preferably 0.5 μm ≤ D' 3 50 ≤ 5 μm; the particle size D of the third fine grinding is controlled 3 50 to satisfy: 0.1 μm ≤ D 3 50 ≤ 0.48 μm, preferably 0.15 μm ≤ D 3 50 ≤ 0.36 μm; And / or, controlling the particle size D” of the third spray drying 3 50 Satisfying: 2μm ≤ D” 3 50 ≤ 30μm, preferably 5μm ≤ D” 3 50 ≤ 20μm; And / or, the conditions of the third sintering include: the temperature T3 is 550-850 °C, preferably 600-750 °C; the heating rate V3 is 0.5-50 °C / min, preferably 0.8-5 °C / min; the constant temperature time t3 is 2-14 h, preferably 6-12 h.

13. A lithium-ion battery, characterized in that, The lithium-ion battery is selected from the cathode materials described in any one of claims 1-5, or the cathode materials prepared by the preparation method described in any one of claims 6-12.

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