Positive electrode active material, preparation method therefor, and battery

Abstract

A positive electrode active material, a preparation method therefor, and a battery. The positive electrode active material comprises: an inner core, the inner core comprising a lithium metal phosphate; a first coating layer, the first coating layer covering at least part of the surface of the inner core; and a second coating layer, the second coating layer covering at least part of the surface of the first coating layer. The positive electrode active material has an XRD diffraction peak intensity of S1 at a 2θ diffraction angle of 35.5°-35.7°, and the positive electrode active material has an XRD diffraction peak intensity of S2 at a 2θ diffraction angle of 24.1°-25.4°, S2 / S1 being (0.005-0.05):1. The positive electrode active material has an XRD diffraction peak intensity of S3 at a 2θ diffraction angle of 28.8°-29.2°, S3 / S1 being (0.005-0.05):1.

Description

Positive electrode active materials and their preparation methods, batteries

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application No. 202410705712.7, filed on May 31, 2024, the entirety of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, specifically to positive electrode active materials and their preparation methods, and batteries. Background Technology

[0004] With the rapid development of the power battery and energy storage battery market, represented by electric vehicles and energy storage, people have put forward higher requirements for the energy density, cycle life, and safety performance of existing lithium-ion batteries. Among them, the performance of the cathode active material is a key factor affecting the performance of lithium-ion batteries. Among the many cathode active material systems, lithium metal phosphate has received widespread attention. Taking lithium iron phosphate as an example, the theoretical specific capacity of lithium iron phosphate is 170 mAh / g, the working voltage platform is 3.4V, and the corresponding theoretical specific energy is only 578Wh / kg, which cannot meet the growing demand for battery energy density in the future power and energy storage markets. By adding doping elements, the theoretical specific capacity and working voltage platform of the cathode active material can be improved, but problems such as poor capacity utilization and poor cycle performance still exist. Current cathode active materials need further improvement.

[0005] Application content

[0006] In a first aspect, this application proposes a positive electrode active material, comprising: a core comprising lithium metal phosphate; a first coating layer covering at least a portion of the surface of the core; and a second coating layer covering at least a portion of the surface of the first coating layer; wherein the positive electrode active material has an XRD diffraction peak intensity of S1 within a 2θ diffraction angle of 35.5°-35.7°, an XRD diffraction peak intensity of S2 within a 2θ diffraction angle of 24.1°-25.4°, and an S2 / S1 ratio of (0.005-0.05):1; and an XRD diffraction peak intensity of S3 within a 2θ diffraction angle of 28.8°-29.2°, and an S3 / S1 ratio of (0.005-0.05):1. Therefore, the positive electrode active material possesses high specific capacity, superior ionic and electronic conductivity, and superior structural stability.

[0007] In some embodiments, S2 / S1 is (0.01-0.03):1; and / or, S3 / S1 is (0.01-0.02):1.

[0008] In some embodiments, the first coating layer comprises a hexagonal fast ion conductor, and / or the second coating layer comprises an orthorhombic fast ion conductor and a carbon material. This can improve the rate performance of the cathode active material.

[0009] In some embodiments, the lithium metal phosphate satisfies the general formula Li 1+a Fe x G y M 1-x-y PO4C z Wherein, -0.2≤a≤0.2, 0<x<1, 0≤y≤0.05, 0≤z≤0.1; M includes at least one of Mn, Co, V, and Ni; G includes at least one of Ga, Sn, V, Mo, Al, Mg, Ce, Ti, Zr, Nb, Si, W, and In. Therefore, the positive electrode active material possesses a high operating voltage plateau and specific capacity.

[0010] In some embodiments, the hexagonal fast ion conductor satisfies the general formula Li b M 1 d M 2 e M 3 u (PO4) w1 (RO v ) w2 , of which M 1 Including at least one of Mg, Na, and K, M 2 Including at least one of Al, Ga, In, Y, and Sc, M 3 The first coating layer comprises at least one of Ti, Zr, and Ge, and R comprises at least one of Si, Cl, Br, S, Sb, Sn, F, and P, with 0 ≤ b < 3, 0 ≤ d ≤ 0.1, 0 ≤ e ≤ 1, 0 ≤ u ≤ 1, 1 ≤ w1 ≤ 3, 0 ≤ v ≤ 4, and 0 ≤ w2 ≤ 0.5. Therefore, the first coating layer can effectively reduce the ion transport impedance of the core at the interface.

[0011] In some embodiments, the orthorhombic fast ion conductor satisfies the general formula Li3M 4 t Ti 2-t (PO4)3, where M 4 The material includes at least one of Al, Ga, In, Y, and Sc, where 0 ≤ t ≤ 1. Therefore, the second coating layer stabilizes the structure of the positive electrode active material and inhibits the dissolution of transition metals.

[0012] In some embodiments, the mass fraction of carbon in the lithium metal phosphate is 0.5%-3%; and / or, the mass fraction of carbon in the second coating layer is 1%-5%. Thus, the positive electrode active material exhibits superior electronic conductivity.

[0013] In some embodiments, the mass fraction of carbon in the positive electrode active material is 1%-4%. Therefore, the positive electrode active material has a high specific capacity.

[0014] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material, comprising: mixing a first lithium source, a first metal source, and a first phosphorus source to obtain a first slurry; performing a first sintering treatment on the first slurry under an inactive atmosphere to obtain a core; mixing a second lithium source, a second metal source, and a second phosphorus source to obtain a second slurry; performing a second sintering treatment on the second slurry under an oxygen-containing atmosphere to obtain a powder for a first coating layer; mixing the core and the powder for the first coating layer, and then mixing them with a third lithium source, a titanium source, a third phosphorus source, and a second carbon source to obtain a third slurry; and performing a third sintering treatment on the third slurry under an inactive atmosphere to obtain the positive electrode active material. Therefore, the preparation process of the positive electrode active material is simple, the preparation process is easy to stabilize and control, and the production cost is low.

[0015] In some embodiments, the first slurry satisfies at least one of the following conditions: the first lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate; the first metal source includes at least one of an iron source, an M source, and a G source, wherein the iron source includes at least one of ferric phosphate, ferric nitrate, and ferrous nitrate; the M source includes at least one of a phosphate, nitrate, carbonate, and oxide corresponding to the M element; and the G source includes at least one of a nitrate, carbonate, and oxide corresponding to the G element; the first phosphorus source includes at least one of ferric phosphate, ferric manganese phosphate, phosphoric acid, metaphosphoric acid, pyrophosphate, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxide; and further includes a first carbon source, which includes at least one of glucose, sucrose, starch, graphene, and carbon nanotubes. Thus, the core can be prepared by a relatively simple method.

[0016] In some embodiments, the second slurry satisfies at least one of the following conditions: the second lithium source includes at least one of lithium carbonate and lithium hydroxide; the second phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxide; the second metal source includes M 1 Source, M 2 Source, M 3 At least one of the sources, wherein the M 1 Sources include M 1 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M2 Sources include M 2 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M 3 Sources include M 3 The coating comprises at least one of the following: an oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate of the element; and further comprises an R source, wherein the R source comprises at least one of the following: an elemental substance, an acid, and an oxide of the element R. Thus, the first coating layer can be prepared by a relatively simple method.

[0017] In some embodiments, the third slurry satisfies at least one of the following conditions: the third lithium source includes at least one of lithium carbonate and lithium hydroxide; the titanium source includes at least one of titanium oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate; the third phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphate, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxide; the second carbon source includes at least one of glucose, sucrose, starch, graphite, carbon nanotubes, and graphene; and further includes M. 4 Source, the M 4 Sources include M 4 The element contains at least one of the following: oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate. Therefore, a relatively simple method can be used to prepare the positive electrode active material.

[0018] In some embodiments, the temperature of the first sintering treatment is 600℃-800℃, and the time of the first sintering treatment is 6h-12h; and / or, the temperature of the second sintering treatment is 700℃-900℃, and the time of the second sintering treatment is 8h-12h; and / or, the temperature of the third sintering treatment is 300℃-600℃, and the time of the third sintering treatment is 6h-12h. This can improve the yield of the positive electrode active material.

[0019] In some embodiments, the solid content of the first slurry, the second slurry, and the third slurry is independently 10wt%-70wt%; and / or, the average particle size of the first slurry is less than or equal to 500 nm; and / or, the average particle size of the second slurry is less than or equal to 200 nm; and / or, the average particle size of the third slurry is less than or equal to 1 μm; and / or, the solvent of the first slurry, the second slurry, and the third slurry independently includes at least one of water, isopropanol, ethanol, and ethylene glycol. This improves the processing performance of the slurry.

[0020] In a third aspect, this application proposes a battery comprising a positive electrode sheet, said positive electrode sheet comprising the aforementioned positive electrode active material. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode active material and preparation method, which will not be repeated here. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 is a schematic diagram of the structure of a positive electrode active material according to an embodiment of this application;

[0023] Figure 2 is a schematic flowchart of the preparation of positive electrode active material according to an embodiment of this application;

[0024] Figure 3 is a schematic flowchart of the preparation of positive electrode active material according to another embodiment of this application;

[0025] Figure 4 shows the XRD patterns of the positive electrode active materials in Example 1 and Comparative Example 1 in the range of 2θ from 10° to 80°;

[0026] Figure 5 shows the XRD patterns of the positive electrode active materials in Example 1 and Comparative Example 1 in the range of 2θ from 23° to 37°;

[0027] Figure 6 shows the charge-discharge curves of the batteries in Example 1 and Comparative Example 1.

[0028] Explanation of reference numerals in the attached figures:

[0029] Kernel 100; First wrapper layer 210; Second wrapper layer 220. Detailed Implementation

[0030] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0031] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0032] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0033] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0034] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Taking lithium iron phosphate as an example of a cathode active material, adding doping elements, such as manganese doping at iron sites, can improve the working voltage platform and specific capacity of the material. However, this also leads to excessively low electronic and ionic conductivity, resulting in poor capacity performance. Furthermore, the presence of the Jan-Taylor effect caused by manganese ions results in poor structural stability of the cathode active material, leading to iron dissolution. Carbon coating on the surface of the cathode active material cannot effectively solve the problems of the Jan-Taylor effect caused by manganese ions and the dissolution of transition metal iron, thus resulting in poor cycle performance of the cathode active material.

[0038] In this application, by optimizing the material composition and phase structure, the problems of low electronic and ionic conductivity and easy dissolution of transition metals in the existing olivine structure positive electrode active material are effectively solved. Specifically, the X-ray diffraction peaks of the positive electrode active material within a 2θ diffraction angle of 35.5°-35.7° are the diffraction peaks of the olivine structure core, corresponding to the (311) crystal plane of the Pnma(62) space group of the olivine structure; the X-ray diffraction peaks of the positive electrode active material within a 2θ diffraction angle of 24.1°-25.4° are the diffraction peaks of the hexagonal fast ion conductor, corresponding to the hexagonal phase. The (113) crystal plane of the phase; the diffraction peak of the positive electrode active material for X-rays in the range of 2θ diffraction angle 28.8°-29.2° is the diffraction peak of the orthorhombic fast ion conductor, corresponding to the (024) crystal plane of the orthorhombic phase. Thus, while using the olivine structure core to improve the working voltage platform of the positive electrode active material and thereby improve the energy density, by constructing a protective layer of fast ion conductor on the surface of the core, the direct exposure of the core in the electrolyte during charging and discharging can be effectively suppressed. It has the function of stabilizing the structure and preventing the dissolution of transition metals, and significantly improves the cycle performance and safety performance of the positive electrode active material. Furthermore, the ratio of the peak intensities of the X-ray diffraction characteristic peaks between the core and the coating layer can reflect the content ratio between the core and the coating layer. When S2 / S1 is (0.005-0.05):1 and S3 / S1 is (0.005-0.05):1, the first and second coating layers improve the ionic conductivity and electronic conductivity of the positive electrode active material and inhibit the dissolution of transition metals in the positive electrode active material. At the same time, the proportion of the coating layer in the positive electrode active material is relatively small, and the impact on the specific capacity of the positive electrode active material is small, which helps to give full play to the high-capacity core.

[0039] The (113) crystal plane of the hexagonal phase is the strongest peak in the X-ray diffraction peak of the first coating layer, and it does not coincide with the X-ray diffraction peak of the core and the second coating layer.

[0040] The (024) crystal plane of the orthorhombic phase is the third strongest peak in the X-ray diffraction peaks of the second coating layer. Its standard peak intensity is 50% of the strongest peak, and it does not coincide with the X-ray diffraction peaks of the core and the first coating layer.

[0041] In a first aspect of this application, a positive electrode active material is proposed, referring to FIG1, comprising: a core 100 comprising lithium metal phosphate; a first coating layer 210 covering at least a portion of the surface of the core 100; and a second coating layer 220 covering at least a portion of the surface of the first coating layer 210; wherein the peak intensity of the XRD diffraction peak of the positive electrode active material is S1 within a 2θ diffraction angle of 35.5°-35.7°, the peak intensity of the XRD diffraction peak of the positive electrode active material is S2 within a 2θ diffraction angle of 24.1°-25.4°, and the ratio of S2 / S1 is (0.005-0.05):1; and the peak intensity of the XRD diffraction peak of the positive electrode active material is S3 within a 2θ diffraction angle of 28.8°-29.2°, and the ratio of S3 / S1 is (0.005-0.05):1. Therefore, the positive electrode active material has high specific capacity, excellent ionic and electronic conductivity, and excellent structural stability, which can improve the rate performance and cycle performance of batteries using this positive electrode active material.

[0042] As an example, S2 / S1 can be 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, or 0.05:1.

[0043] As an example, S3 / S1 can be 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, or 0.05:1.

[0044] In some embodiments, S2 / S1 is (0.01-0.03):1; and / or, S3 / S1 is (0.01-0.02):1.

[0045] In some embodiments, the first cladding layer 210 comprises a hexagonal fast ion conductor.

[0046] The first coating layer 210 is a solid electrolyte with a structure similar to NASICON (Na Superionic Conductor). When the first coating layer has a hexagonal phase structure, it has a high ionic conductivity, which can effectively reduce the ion transport impedance of the olivine core at the interface.

[0047] In some embodiments, the positive electrode active material also exhibits diffraction peaks corresponding to hexagonal fast ion conductors for X-rays within a 2θ diffraction angle range of 20.8°-21.0°, which correspond to the (104) crystal plane of the hexagonal phase.

[0048] In some embodiments, the second coating layer 220 comprises an orthorhombic fast ion conductor and a carbon material.

[0049] The second coating layer 220 includes a solid electrolyte with a structure similar to NASICON (Na Superionic Conductor) and graphitized carbon material. The second coating layer can suppress the direct exposure of the core 100 in the electrolyte during charging and discharging, and has the function of stabilizing the structure and preventing the dissolution of transition metals. Furthermore, the second coating layer also has high electronic conductivity, which effectively reduces the electron transport impedance of the coated olivine core at the interface and improves the material's cycle performance and safety performance.

[0050] In some embodiments, the positive electrode active material also exhibits a diffraction peak for X-rays within a 2θ diffraction angle of 19.6°-19.8° corresponding to the orthorhombic fast ion conductor, which corresponds to the (104) crystal plane of the orthorhombic phase.

[0051] In some embodiments, the mass ratio of the first covering layer 210 to the core 100 is (1-3):100.

[0052] The core 100 is an olivine structure material with high voltage and high capacity. An appropriate amount of the first coating layer can improve the ionic conductivity of the positive electrode active material, but the first coating layer cannot provide capacity. Therefore, when the mass ratio of the first coating layer to the core is within the aforementioned range, the first coating layer 210 can improve the ionic conductivity of the positive electrode active material while having a small impact on the specific capacity of the positive electrode active material.

[0053] In some embodiments, the mass ratio of the second coating layer 220 to the core 100 is (2-4):100. Thus, the second coating layer 220 can both improve the electronic conductivity of the positive electrode active material and suppress the dissolution of transition metals in the positive electrode active material, while having a relatively small impact on the specific capacity of the positive electrode active material.

[0054] The core 100 is an olivine structure material with high voltage and high capacity. An appropriate amount of the second coating layer can improve the electronic and ionic conductivity of the positive electrode active material and reduce the occurrence of side reactions between the core and the electrolyte. However, the second coating layer cannot provide capacity. Therefore, when the mass ratio of the second coating layer to the core is within the aforementioned range, the second coating layer 220 can improve the electronic conductivity of the positive electrode active material and reduce the occurrence of side reactions, while having a small impact on the specific capacity of the positive electrode active material.

[0055] In some embodiments, the lithium metal phosphate satisfies the general formula Li 1+a Fe x G y M 1-x-y PO4C zWherein, -0.2≤a≤0.2, 0<x<1, 0≤y≤0.05, 0≤z≤0.1; M includes at least one of Mn, Co, V, and Ni; G includes at least one of Ga, Sn, V, Mo, Al, Mg, Ce, Ti, Zr, Nb, Si, W, and In. Therefore, the positive electrode active material possesses a high operating voltage plateau and specific capacity.

[0056] In some embodiments, -0.2≤a≤0.2, 0<x<1, 0.001≤y≤0.05, and 0.001≤z≤0.1.

[0057] By multi-directional elemental doping of lithium iron phosphate, the electronic conductivity of lithium iron phosphate can be effectively improved. As a result, the core has a stable polyanionic framework structure, exhibiting better cycle stability and a voltage plateau significantly higher than 3.4V during charge and discharge. The theoretical specific capacity is significantly improved compared to lithium iron phosphate.

[0058] In some embodiments, a carbon source can be added during the preparation of lithium metal phosphate to construct electron channels at the grain boundaries of the core, thereby further improving the electronic conductivity of the core. Therefore, the core of lithium metal phosphate contains carbon elements.

[0059] During the charging and discharging process, lithium insertion / extraction, consumption, and replenishment occur, resulting in varying molar Li content at different discharge states. In the examples of the core in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. The molar Li content changes after the positive electrode active material is applied to the battery system and undergoes charge-discharge cycles.

[0060] In some embodiments, the hexagonal fast ion conductor satisfies the general formula Li b M 1 d M 2 e M 3 u (PO4) w1 (RO v ) w2 , of which M 1 Including at least one of Mg, Na, and K, M 2 Including at least one of Al, Ga, In, Y, and Sc, M 3 The first coating layer 210 includes at least one of Ti, Zr, and Ge, and R includes at least one of Si, Cl, Br, S, Sb, Sn, F, and P, with 0 ≤ b < 3, 0 ≤ d ≤ 0.1, 0 ≤ e ≤ 1, 0 ≤ u ≤ 1, 1 ≤ w1 ≤ 3, 0 ≤ v ≤ 4, and 0 ≤ w2 ≤ 0.5. Therefore, the first coating layer 210 can effectively reduce the ion transport impedance of the core 100 at the interface.

[0061] In some embodiments, 0.001 ≤ b < 3, 0.001 ≤ d ≤ 0.1, 0.001 ≤ e ≤ 1, 0.001 ≤ u ≤ 1, 1 ≤ w1 ≤ 3, 0.001 ≤ v ≤ 4, and 0.001 ≤ w2 ≤ 0.5

[0062] When the fast ion conductor with a hexagonal phase structure in the first coating layer 210 satisfies the aforementioned conditions, the first coating layer can stabilize the interface structure of the core 100 material, enabling the core to have a capacity retention rate close to that of lithium iron phosphate. Furthermore, since the first coating layer is a solid electrolyte with high ionic conductivity, the coated olivine structure core has low ion transport impedance at the interface, resulting in superior rate performance.

[0063] As an example, since the core 100 is oxidizing, when the hexagonal fast ion conductor contains +4 valence titanium ions, the hexagonal phase coating layer is not easily oxidized after contacting the core, and the first coating layer has high structural stability.

[0064] In some embodiments, the orthorhombic fast ion conductor satisfies the general formula Li3M 4 t Ti 2-t (PO4)3, where M 4 The material includes at least one of Al, Ga, In, Y, and Sc, where 0 ≤ t ≤ 1, and more preferably, 0.001 ≤ t ≤ 1. Thus, the second coating layer 220 has the function of stabilizing the structure of the positive electrode active material and inhibiting the dissolution of transition metals.

[0065] When the fast ion conductor with a tetragonal phase structure in the second coating layer 220 meets the aforementioned conditions, the second coating layer can stabilize the interface structure of the core 100 material, enabling the core to have a capacity retention rate similar to that of lithium iron phosphate. Furthermore, the fast ions of the aforementioned tetragonal phase structure, after combining with graphitized carbon material, exhibit high electronic conductivity, resulting in low electron transport impedance at the interface of the coated olivine structure core. Thus, the first and second coating layers achieve the coating of the core as a mixed ion and electron conductor, giving the positive electrode active material superior rate performance.

[0066] As an example, because the electrolyte has reducing properties and the core 100 has oxidizing properties, side reactions can occur when the core comes into direct contact with the electrolyte, causing adverse effects such as the dissolution of metal elements in the core. When the second coating layer 220 contains +3 valent titanium ions, the second coating layer is not easily reduced after contact with the electrolyte, thereby improving the chemical stability between the positive electrode active material and the electrolyte and suppressing the dissolution of transition metal elements in the core 100 caused by the reduction of the electrolyte.

[0067] As an example, when the orthorhombic fast ion conductor includes Li3Ti2(PO4)3, the positive electrode active material has two discharge platforms at 4.0V and 3.5V during the charge-discharge process from 2.0V to 4.25V, and there is also a discharge platform corresponding to the orthorhombic Li3Ti2(PO4)3 at 2.8V.

[0068] In some embodiments, the mass fraction of carbon in the lithium metal phosphate is 0.5%-3%.

[0069] When the mass fraction of carbon in lithium metal phosphate is within the aforementioned range, the electronic conductivity of the core can be improved by adding a carbon source during the preparation of lithium metal phosphate and constructing a three-dimensional electronic conductive channel through carbon coating at the core grain boundaries and surface.

[0070] In some embodiments, the carbon mass fraction in the second coating layer 220 is 1%-5%.

[0071] When the mass fraction of carbon in the second coating layer is within the aforementioned range, a three-dimensional electronic conductive channel is constructed by coating the core and the grain boundaries and surfaces of the first coating layer with carbon, thereby improving the electronic conductivity of the positive electrode active material.

[0072] In some embodiments, the mass fraction of carbon in the positive electrode active material is 1%-4%. Therefore, the positive electrode active material has a high specific capacity.

[0073] When the mass fraction of carbon in the positive electrode active material is as described above, an appropriate amount of carbon can not only construct a three-dimensional electronic conductive channel and improve the electronic conductivity of the positive electrode active material, but also have little impact on the specific capacity of the positive electrode active material, thereby improving the discharge capacity and rate performance of the positive electrode active material.

[0074] In some embodiments, the average particle size Dv50 of the positive electrode active material can be 0.5 μm-20 μm. As an example, the average particle size Dv50 of the positive electrode active material and the core can be measured using a laser particle size analyzer.

[0075] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material. This method is simple, the preparation process is easy to stabilize and control, the introduction of doping elements and electron transport channels is simple, the performance improvement effect is significant, and the production cost is low. Specifically, referring to Figures 2 and 3, the method for preparing the positive electrode active material includes:

[0076] S110: A first slurry is obtained by mixing a first lithium source, a first metal source, and a first phosphorus source.

[0077] In some embodiments, in this step, a first lithium source, a first metal source, a first phosphorus source, and a solvent are mixed to obtain a first slurry, thereby obtaining a core material by sintering the first slurry.

[0078] In some embodiments, the first lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.

[0079] In some embodiments, the first metal source includes at least one of an iron source, an M source, and a G source, wherein the iron source includes at least one of ferric phosphate, ferric nitrate, and ferrous nitrate, the M source includes at least one of phosphate, nitrate, carbonate, and oxide corresponding to the M element, and the G source includes at least one of nitrate, carbonate, and oxide corresponding to the G element.

[0080] In some embodiments, the first phosphorus source includes at least one of iron phosphate, manganese iron phosphate, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides.

[0081] In some embodiments, referring to S111 in FIG3, a first lithium source, a first metal source, a first phosphorus source, a first carbon source, and a solvent are mixed in this step to obtain a first slurry. The core material can then be obtained by sintering the first slurry. Specifically, the first carbon source may include at least one of glucose, sucrose, starch, graphene, and carbon nanotubes. The addition of the first carbon source can construct electron channels at the grain boundaries of the core, thereby improving the electronic conductivity of the core.

[0082] In some embodiments, the solid content of the first slurry is 10wt%-70wt%.

[0083] In some embodiments, the average particle size of the first slurry is less than or equal to 500 nm. For example, the average particle size of the first slurry can be 5 nm-100 nm, 10 nm-200 nm, 50 nm-500 nm, etc.

[0084] In some embodiments, the solvent for the first slurry includes at least one of water, isopropanol, ethanol, and ethylene glycol.

[0085] It is understandable that during the first sintering process, some of the first carbon source will be lost and volatile substances such as carbon dioxide will be generated. Therefore, the amount of first carbon source added to the first slurry can be greater than the design value in the finished product.

[0086] S120: The first sintering treatment of the first slurry is carried out under an inactive atmosphere.

[0087] In some embodiments, the first slurry is dried in this step and subjected to a first sintering process under an inactive atmosphere to obtain a core with an olivine structure.

[0088] In some embodiments, the temperature of the first sintering treatment is 600℃-800℃, and the time of the first sintering treatment is 6h-12h.

[0089] When the temperature and time of the first sintering treatment are within the aforementioned range, it is conducive to the formation of the olivine structure core, and the phase structure has high stability, few impurities, and the resulting core particles have a moderate particle size.

[0090] In some embodiments, the inactive atmosphere includes nitrogen and / or argon.

[0091] In some embodiments, the drying conditions are as follows: a drying temperature of 80°C-400°C, for example, a drying temperature of 100°C-300°C, and a drying time of 0.1h-10h, for example, a drying time of 0.5h-3h. Further, the drying process includes at least one of a spray dryer, a fluidized bed dryer, a belt dryer, a flash dryer, and a disc mill.

[0092] S210: A second slurry is obtained by mixing a second lithium source, a second metal source, and a second phosphorus source.

[0093] In some embodiments, the raw material compound used to form the first coating layer is mixed with a solvent to obtain a second slurry. Specifically, a second lithium source, a second metal source, and a second phosphorus source can be mixed to obtain the second slurry. Thus, the powder material of the first coating layer can be obtained by sintering the second slurry.

[0094] In some embodiments, the second lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0095] In some embodiments, the second phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides.

[0096] In some embodiments, the second metal source includes M 1 Source, M 2 Source, M 3 At least one of the sources, wherein the M 1 Sources include M 1 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M 2 Sources include M 2 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M 3 Sources include M3 At least one of the following: oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate of the element.

[0097] In some embodiments, referring to S211 in FIG3, the second lithium source, the second metal source, the second phosphorus source, the R source and the solvent are mixed in this step to obtain a second slurry, wherein the R source includes at least one of the elemental substance, acid and oxide corresponding to the R element.

[0098] In some embodiments, the solid content of the second slurry is 10wt%-70wt%.

[0099] In some embodiments, the average particle size of the second slurry is less than or equal to 200 nm. Specifically, the average particle size of the second slurry can be 5 nm-100 nm, 10 nm-200 nm, etc.

[0100] In some embodiments, the solvent for the second slurry includes at least one of water, isopropanol, ethanol, and ethylene glycol.

[0101] S220: Second sintering treatment of the second slurry under an oxygen-containing atmosphere.

[0102] In some embodiments, the second slurry is dried in this step and subjected to a second sintering treatment in an oxygen-containing atmosphere to obtain a micron-sized first coating layer powder material. The powder material is then nano-sized in a solvent and dried to obtain a hexagonal phase first coating layer nano-sized powder material.

[0103] In some embodiments, the temperature of the second sintering treatment is 700℃-900℃, and the time of the second sintering treatment is 8h-12h.

[0104] When the temperature and time of the second sintering treatment are within the aforementioned range, it is conducive to the formation of the first coating layer of hexagonal phase powder, and the phase structure has high stability and few impurities.

[0105] In some embodiments, the oxygen-containing atmosphere includes oxygen.

[0106] In some embodiments, the drying conditions are as follows: a drying temperature of 80°C-400°C, for example, a drying temperature of 100°C-300°C, and a drying time of 0.1h-10h, for example, a drying time of 0.5h-3h. Further, the drying process includes at least one of a spray dryer, a fluidized bed dryer, a belt dryer, a flash dryer, and a disc mill.

[0107] It is understandable that the preparation of the nanoscale powder materials of the core and the first coating layer does not have a specific order, as long as both are prepared before the formation of the second coating layer. Those skilled in the art can choose according to the actual situation.

[0108] S310: Mix the core powder with the powder of the first coating layer, and then mix with the third lithium source, titanium source, third phosphorus source and second carbon source to obtain a third slurry.

[0109] In some embodiments, after the olivine core and the powder of the first coating layer are mixed evenly in this step, they are then mixed with a third lithium source, a titanium source, a third phosphorus source, a second carbon source, and a solvent to obtain a third slurry.

[0110] In some embodiments, the third lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0111] In some embodiments, the titanium source includes at least one of the following: oxides, hydroxides, nitrates, oxalates, organic alkoxides, and carbonates of titanium.

[0112] In some embodiments, the third phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides.

[0113] In some embodiments, the second carbon source includes at least one of glucose, sucrose, starch, graphite, carbon nanotubes, and graphene.

[0114] The addition of a second carbon source can construct conductive channels on the surface of the positive electrode active material, thereby improving the electronic conductivity of the positive electrode active material.

[0115] In some embodiments, referring to S311 in FIG3, after the powder of the core and the first coating layer is mixed evenly in this step, it is then mixed with the third lithium source, titanium source, third phosphorus source, second carbon source, and M. 4 The source and solvent are mixed to obtain a third slurry, wherein M 4 Sources include M 4 At least one of the following: oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate of the element.

[0116] In some embodiments, the solid content of the third slurry is 10wt%-70wt%.

[0117] In some embodiments, the average particle size of the third slurry is less than or equal to 1 μm. Specifically, the average particle size of the third slurry can be 5 nm-100 nm, 10 nm-200 nm, 50 nm-500 nm, 200 nm-1 μm, etc.

[0118] In some embodiments, the solvent of the third slurry includes at least one of water, isopropanol, ethanol, and ethylene glycol.

[0119] It is understandable that during the third sintering process, some of the second carbon source will be lost and volatile substances such as carbon dioxide will be generated. Therefore, the amount of second carbon source added to the third slurry can be greater than the design value in the finished product.

[0120] S320: Third sintering treatment of the third slurry under an inactive atmosphere.

[0121] In some embodiments, the third slurry is dried in this step and sintered in an inactive atmosphere to obtain the positive electrode active material.

[0122] In some embodiments, the temperature of the third sintering treatment is 300℃-600℃, and the time of the third sintering treatment is 6h-12h. This can improve the yield of the positive electrode active material.

[0123] When the temperature and time of the third sintering treatment are within the aforementioned range, it is conducive to the formation of the second coating layer of the orthorhombic phase, and the phase structure has high stability and few impurities.

[0124] In some embodiments, the inactive atmosphere includes nitrogen and / or argon.

[0125] In some embodiments, the drying conditions are as follows: a drying temperature of 80°C-400°C, for example, a drying temperature of 100°C-300°C, and a drying time of 0.1h-10h, for example, a drying time of 0.5h-3h. Further, the drying process includes at least one of a spray dryer, a fluidized bed dryer, a belt dryer, a flash dryer, and a disc mill.

[0126] In some embodiments, after the third sintering process, a crushing process may be performed to obtain a positive electrode active material with a suitable particle size. The equipment used for the crushing process includes air jet mills, mechanical mills, and colloid mills.

[0127] In a third aspect, this application proposes a battery comprising a positive electrode sheet, said positive electrode sheet comprising the aforementioned positive electrode active material. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode active material and preparation method, which will not be repeated here.

[0128] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0129] Example 1

[0130] (1) Lithium carbonate, iron phosphate, manganese oxide, phosphoric acid, and glucose were mixed in pure water at a molar ratio of Li:Fe:Mn:P:C (carbon source) = 1.03:0.3:0.7:1:1.16. The mixture was ball-milled with zirconium oxide for 4 hours to obtain a first slurry with an average particle size of less than 500 nm. The first slurry was then treated with a spray dryer to obtain powder. The powder was sintered in a tube furnace at 700 °C for 8 hours under a nitrogen atmosphere. The sintered material was then dissociated and sieved to obtain a final product with the composition Li 1.03 Mn 0.7 Fe 0.3 PO4 / C 0.16 The kernel.

[0131] (2) Lithium carbonate, alumina, titanium dioxide, and ammonium dihydrogen phosphate were mixed in pure water at a molar ratio of Li:Al:Ti:P = 1.3:0.3:1.7:3. The mixture was ball-milled with zirconia for 4 hours to obtain a slurry with an average particle size less than 500 nm. The slurry was then spray-dried to obtain powder. The powder was sintered at 700°C for 8 hours in an air-filled chamber. The sintered material was then ball-milled with zirconia for 6 hours to obtain a second slurry with an average particle size less than 200 nm. The second slurry was then spray-dried to obtain powder. The powder was then dissociated and sieved to obtain a final product with the composition Li... 1.3 Al 0.3 Ti 1.7 Nanoscale powder of the first coating layer of (PO4)3.

[0132] (3) The core obtained in (1), the nano-sized powder of the first coating layer obtained in (2), lithium carbonate, titanium oxide, ammonium dihydrogen phosphate, and glucose are mixed in pure water at a molar ratio of Mn:Al:Li:Ti:P:C = 70:0.3:3:2:3:16. The mixture is ball-milled with zirconium oxide for 4 hours to obtain a third slurry with an average particle size of less than 1 micrometer. The third slurry is then processed by a spray dryer to obtain powder. The powder is sintered at 500°C for 6 hours under a nitrogen atmosphere. Finally, the sintered material is crushed to obtain a positive electrode active material. The second coating layer consists of graphitized carbon and Li3Ti2(PO4)3.

[0133] Example 2

[0134] Example 2 is consistent with Example 1, except that in step (3), the core obtained in (1), the nano-sized powder of the first coating layer obtained in (2), lithium carbonate, titanium oxide, ammonium dihydrogen phosphate, and glucose are mixed in pure water in a molar ratio of Mn:Al:Li:Ti:P:C = 70:1.5:15:10:15:16.

[0135] Example 3

[0136] Example 3 is consistent with Example 1, except that in step (3), the core obtained in (1), the nano-sized powder of the first coating layer obtained in (2), lithium carbonate, titanium oxide, ammonium dihydrogen phosphate, and glucose are mixed in pure water in a molar ratio of Mn:Al:Li:Ti:P:C = 70:0.3:15:10:15:16.

[0137] Example 4

[0138] Example 4 is consistent with Example 1, except that in step (1), lithium carbonate, titanium dioxide, iron phosphate, manganese oxide, phosphoric acid, and glucose are mixed in pure water at a molar ratio of Li:Ti:Fe:Mn:P:C (carbon source) = 1.03:0.01:0.3:0.699:1:1.16. The mixture is then ball-milled with zirconium oxide for 4 hours to obtain a first slurry with an average particle size of less than 500 nm. The first slurry is then treated by a spray dryer to obtain powder. The powder is sintered in a tube furnace at 700 °C for 8 hours under a nitrogen atmosphere. The sintered material is then dissociated and sieved to obtain a final product with the composition Li 1.03 Mn 0.699 Ti 0.01 Fe 0.3 PO4 / C 0.16 The kernel.

[0139] Example 5

[0140] Example 5 is consistent with Example 1, except that in step (2), lithium carbonate, alumina, titanium dioxide, ammonium dihydrogen phosphate, and silica are mixed in pure water at a molar ratio of Li:Al:Ti:P:Si = 1.3:0.3:1.7:2.98:0.03. The mixture is then ball-milled with zirconia for 4 hours to obtain a slurry with an average particle size less than 500 nm. The slurry is then treated by a spray dryer to obtain powder. The powder is sintered at 700°C for 8 hours in an air-filled chamber. The sintered material is then ball-milled with zirconia for 6 hours to obtain a second slurry with an average particle size less than 200 nm. The second slurry is then treated by a spray dryer to obtain powder. The powder is then dissociated and sieved to obtain a final product with the composition Li. 1.3 Al 0.3 Ti 1.7 (PO4) 2.98 (SiO3) 0.03 The first coating layer is made of nano-sized powder.

[0141] Example 6

[0142] Example 6 is consistent with Example 1, except that in step (3), the nano-sized powder of the core obtained in (1), the first coating layer obtained in (2), lithium carbonate, yttrium oxide, titanium oxide, ammonium dihydrogen phosphate, and glucose are mixed in pure water at a molar ratio of Mn:Al:Li:Y:Ti:P:C = 70:0.3:3:0.01:1.99:3:16. The mixture is ball-milled with zirconium oxide for 4 hours to obtain a third slurry with an average particle size of less than 1 micrometer. The third slurry is then treated by a spray dryer to obtain powder. The powder is sintered at 500°C for 6 hours under a nitrogen atmosphere. Finally, the sintered material is crushed to obtain the positive electrode active material. The second coating layer is composed of graphitized carbon and Li3Y. 0.01 Ti 1.99 (PO4)3.

[0143] Comparative Example 1

[0144] Comparative Example 1 is the same as Example 1, except that no first and second coating layers are provided.

[0145] Comparative Example 2

[0146] Comparative Example 2 is consistent with Example 1, except that a second coating layer is not provided. Specifically, in the third slurry, only the nano-sized powders of the core obtained in (1) and the first coating layer obtained in (2) are mixed in pure water at a molar ratio of Mn:Al = 70:0.3 to form a slurry. After being processed by a spray dryer, powder is obtained. The powder is then dissociated and sieved to finally obtain a powder with the composition Li. 1.3 Al 0.3 Ti 1.7 Nanoscale powder of the first coating layer of (PO4)3.

[0147] Comparative Example 3

[0148] Comparative Example 3 is the same as Example 1, except that the first coating layer is not set. Specifically, the nano-sized powder of the first coating layer is not added to the third slurry.

[0149] Comparative Example 4

[0150] Comparative Example 4 is consistent with Example 1, except that in the third slurry, only the core obtained in (1), the nano-sized powder of the first coating layer obtained in (2), and glucose are mixed in pure water at a molar ratio of Mn:Al:C (carbon source) = 70:0.3:16.

[0151] The specific composition of the positive electrode active material in the aforementioned embodiments and comparative examples is shown in Table 1.

[0152] Table 1

[0153] The positive electrode active materials from the aforementioned embodiments and comparative examples were assembled into coin cells. Details are as follows:

[0154] The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:5:5, coated onto aluminum foil, and dried. The mixture was then pressed into a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm under a pressure of 100 MPa. The positive electrode sheet was then dried in a vacuum drying oven at 120°C for 12 hours. The negative electrode sheet used was a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm. The separator used was a Celgard 2400 porous membrane with a thickness of 25 μm. The electrolyte used was 1 mol / L LiPF6, with the solvent being an equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a 2025 coin cell in an argon-filled glove box with a water and oxygen content of less than 5 ppm.

[0155] The button cells assembled from the positive electrode active materials in the aforementioned embodiments and comparative examples were tested as follows, and the test results are shown in Table 2:

[0156] Rate performance: The battery was charged and discharged at room temperature within the range of 2.5V-4.3V at rates of 0.1C and 1C, respectively. The specific capacity C at 0.1C discharge was compared. 0.1C and 1C discharge specific capacity C 1C Ratio performance = C 1C / C 0.1C ×100%.

[0157] Cycling performance: The battery was charged and discharged 80 times at room temperature under conditions of 2.5V-4.3V and 0.1C. The discharge specific capacity C0 in the first cycle and the discharge specific capacity C1 after 80 cycles were compared. The capacity retention rate = C1 / C0 × 100%.

[0158] Iron dissolution: Measured using ICP method. Specifically, the battery was charged and discharged 80 times at room temperature under conditions of 2.5V-4.3V and 1C. After cycling, the separator and negative electrode were removed from the battery. The separator and negative electrode were dissolved in hydrochloric acid and then placed in an ICP instrument to test the Fe content.

[0159] Table 2

[0160] The initial charge-discharge curves of the batteries in Example 1 and Comparative Example 1 are shown in Figure 5. The XRD test results of the positive electrode active materials in Example 1 and Comparative Example 1 are shown in Figures 4 and 5. As shown in Figure 5, the positive electrode active material in Example 1, in addition to having the standard diffraction peaks corresponding to LiFePO4, has a diffraction peak at 2θ = 24.5° corresponding to the (113) crystal plane of the first hexagonal coating layer, and a diffraction peak near 2θ = 29.0° corresponding to the (024) crystal plane of the second orthorhombic coating layer. The positive electrode active material in Comparative Example 1 has the standard diffraction peaks corresponding to LiFePO4.

[0161] The performance of the batteries in Examples 1-6 is better than that of the batteries in Comparative Examples 1-4. The test results show that the first coating layer and the second coating layer can improve the ionic conductivity and electronic conductivity of the positive electrode active material and suppress the dissolution of transition metals in the positive electrode active material. At the same time, the proportion of the coating layer in the positive electrode active material is small, which has little impact on the specific capacity of the positive electrode active material and helps to give full play to the high-capacity core.

[0162] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0163] In the description of this application, the first feature located on the surface of the second feature may include direct contact between the first and second features, or contact between the first and second features not in direct contact but through another feature between them.

[0164] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0165] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, wherein, include: The core comprises lithium metal phosphate; A first coating layer covers at least a portion of the surface of the core; A second coating layer covers at least a portion of the surface of the first coating layer; The peak intensity of the XRD diffraction peak of the positive electrode active material within the 2θ diffraction angle range of 35.5°-35.7° is S1, the peak intensity of the XRD diffraction peak of the positive electrode active material within the 2θ diffraction angle range of 24.1°-25.4° is S2, and the ratio of S2 to S1 is (0.005-0.05):1; the peak intensity of the XRD diffraction peak of the positive electrode active material within the 2θ diffraction angle range of 28.8°-29.2° is S3, and the ratio of S3 to S1 is (0.005-0.05):

1.

2. The positive electrode active material according to claim 1, wherein, S2 / S1 is (0.01-0.03):1; and / or, S3 / S1 is (0.01-0.02):

1.

3. The positive electrode active material according to claim 1, wherein, The first coating layer comprises a hexagonal fast ion conductor, and / or the second coating layer comprises an orthorhombic fast ion conductor and a carbon material.

4. The positive electrode active material according to any one of claims 1-3, wherein, The lithium metal phosphate satisfies the general formula Li 1+a Fe x G y M 1-x-y PO4 / C z Wherein, -0.2≤a≤0.2, 0<x<1, 0≤y≤0.05, 0≤z≤0.1; M includes at least one of Mn, Co, V, and Ni; G includes at least one of Ga, Sn, V, Mo, Al, Mg, Ce, Ti, Zr, Nb, Si, W, and In.

5. The positive electrode active material according to claim 3, wherein, The hexagonal fast ion conductor satisfies the general formula Li b M 1 d M 2 e M 3 u (PO4) w1 (RO v ) w2 , of which M 1 Including at least one of Mg, Na, and K, M 2 Including at least one of Al, Ga, In, Y, and Sc, M 3 It includes at least one of Ti, Zr, and Ge, and R includes at least one of Si, Cl, Br, S, Sb, Sn, F, and P, 0≤b<3, 0≤d≤0.1, 0≤e≤1, 0≤u≤1, 1≤w1≤3, 0≤v≤4, and 0≤w2≤0.

5.

6. The positive electrode active material according to claim 3, wherein, The orthorhombic fast ion conductor satisfies the general formula Li3M 4 t Ti 2-t (PO4)3, where M 4 It includes at least one of Al, Ga, In, Y, and Sc, where 0 ≤ t ≤ 1.

7. The positive electrode active material according to claim 3, wherein, The lithium metal phosphate contains 0.5%-3% carbon by mass; and / or, the second coating layer contains 1%-5% carbon by mass.

8. The positive electrode active material according to claim 7, wherein, The mass fraction of carbon in the positive electrode active material is 1%-4%.

9. A method for preparing the positive electrode active material according to any one of claims 1-8, wherein, include: A first slurry is obtained by mixing a first lithium source, a first metal source, and a first phosphorus source, and then subjected to treatment in an inactive atmosphere. The first sintering process is performed to obtain the core; A second lithium source, a second metal source, and a second phosphorus source are mixed to obtain a second slurry. The second slurry is then subjected to a second sintering treatment under an oxygen-containing atmosphere to obtain the powder of the first coating layer. The core and the powder of the first coating layer are mixed evenly, and then mixed with the third lithium source, titanium source, third phosphorus source and second carbon source to obtain a third slurry. The third slurry is subjected to a third sintering treatment under an inactive atmosphere to obtain the positive electrode active material.

10. The method according to claim 9, wherein, The first slurry satisfies at least one of the following conditions: The first lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate; The first metal source includes at least one of an iron source, an M source, and a G source, wherein the iron source includes at least one of ferric phosphate, ferric nitrate, and ferrous nitrate, the M source includes at least one of phosphate, nitrate, carbonate, and oxide corresponding to the M element, and the G source includes at least one of nitrate, carbonate, and oxide corresponding to the G element. The first phosphorus source includes at least one of iron phosphate, manganese iron phosphate, phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides; It further includes a first carbon source, which includes at least one of glucose, sucrose, starch, graphene, and carbon nanotubes.

11. The method according to claim 9, wherein, The second slurry satisfies at least one of the following conditions: The second lithium source includes at least one of lithium carbonate and lithium hydroxide; The second phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides; The second metal source includes M 1 Source, M 2 Source, M 3 At least one of the sources, wherein the M 1 Sources include M 1 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M 2 Sources include M 2 The element is selected from at least one of its oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate, wherein M 3 Sources include M 3 At least one of the following: the oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate of the element; It further includes an R source, wherein the R source includes at least one of the elemental substance, acid, and oxide corresponding to the R element.

12. The method according to claim 9, wherein, The third slurry satisfies at least one of the following conditions: The third lithium source includes at least one of lithium carbonate and lithium hydroxide; The titanium source includes at least one of the following: oxides, hydroxides, nitrates, oxalates, organic alkoxides, and carbonates corresponding to the element titanium. The third phosphorus source includes at least one of phosphoric acid, metaphosphoric acid, pyrophosphoric acid, ammonium dihydrogen phosphate, diamine hydrogen phosphate, and phosphorus oxides. The second carbon source includes at least one of glucose, sucrose, starch, graphite, carbon nanotubes, and graphene; Further including M 4 Source, the M 4 Sources include M 4 At least one of the following: oxide, hydroxide, nitrate, oxalate, organic alkoxide, and carbonate of the element.

13. The method according to any one of claims 9-12, wherein, The temperature of the first sintering treatment is 600℃-800℃, and the time of the first sintering treatment is 6h-12h; and / or, The second sintering treatment is performed at a temperature of 700℃-900℃ for a duration of 8h-12h; and / or, The temperature of the third sintering treatment is 300℃-600℃, and the time of the third sintering treatment is 6h-12h.

14. The method according to any one of claims 9-12, wherein, The solid content of the first slurry, the second slurry, and the third slurry is independently 10wt%-70wt%; and / or, The average particle size of the first slurry is less than or equal to 500 nm; and / or, The average particle size of the second slurry is less than or equal to 200 nm; and / or, The average particle size of the third slurry is less than or equal to 1 μm; and / or, The solvents of the first slurry, the second slurry, and the third slurry each independently include at least one of water, isopropanol, ethanol, and ethylene glycol.

15. A battery, wherein, It includes a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode active material according to any one of claims 1-8.

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