Positive electrode active material and preparation method therefor, battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a battery, and an electric device. The positive electrode active material comprises phosphate particles and a carbon coating layer, the carbon coating layer comprises a first region and a second region, the first region coats the surfaces of the phosphate particles, and the second region coats the side of the first region facing away from the phosphate particles, wherein the mass content of an oxygen element in the first region relative to the total mass of the first region is greater than the mass content of an oxygen element in the second region relative to the total mass of the second region. The positive electrode active material can reduce the expansion rate of a battery cell and improve the cycle performance.

Description

Positive electrode active material and preparation method thereof, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410389161.8, filed on April 1, 2024, entitled “Positive electrode active material, preparation method thereof, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a positive electrode active material and a preparation method thereof, a battery and an electrical device. Background Art

[0004] Batteries, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy planes, and power tools. Due to the significant progress in the battery field, higher performance requirements are being placed on them. As a key component of batteries, the positive electrode active material has a significant impact on battery performance.

[0005] However, current positive electrode active materials have poor cycle performance when used in batteries.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode active material and a preparation method thereof, a battery and an electrical device, which can improve the cycle performance of the battery.

[0008] In one aspect, an embodiment of the present application proposes a positive electrode active material, which includes phosphate particles and a carbon coating layer, wherein the carbon coating layer includes a first region and a second region, wherein the first region is coated on the surface of the phosphate particles, and the second region is coated on the side of the first region away from the phosphate particles, wherein the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

[0009] Therefore, the carbon coating layer of the embodiment of the present application includes a first region and a second region, the first region forms a uniform coating on the phosphate particles, and the second region is located outside the first region. The first region has an inducing effect on the second region, and can induce the second region to form a uniform coating on the phosphate particles again; the first region and the second region cooperate with each other, and can play an excellent protective role on the phosphate particles. When the positive electrode active material is applied to the battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced, thereby improving the interface stability between the positive electrode active material and the electrolyte, improving the cycle performance and storage performance, and reducing the risk of swelling of the battery cell.

[0010] In some embodiments, based on the mass of the first region, the mass content of oxygen in the first region is less than or equal to 4%. The appropriate mass content of oxygen in the first region can more evenly coat the phosphate particles, thereby improving the dynamic properties of the material.

[0011] In some embodiments, the mass content of oxygen in the first region is 3.0% to 3.5%. The appropriate mass content of oxygen in the first region can more evenly coat the phosphate particles, thereby improving the dynamic properties of the material.

[0012] In some embodiments, the mass content of oxygen in the second region is less than or equal to 1% based on the mass of the second region. The relatively low mass content of oxygen in the second region can form a denser film layer, provide more effective protection for phosphate particles, and improve the interfacial stability between the positive electrode active material and the electrolyte.

[0013] In some embodiments, the mass content of oxygen in the second region is 0.4% to 0.48%. The relatively low mass content of oxygen in the second region can form a denser film layer, provide more effective protection for phosphate particles, and improve the interfacial stability between the positive electrode active material and the electrolyte.

[0014] In some embodiments, based on the total mass of the positive electrode active material, the ratio of the mass content of carbon in the first region to the mass content of carbon in the second region is 0.1:1 to 10:1. When the ratio of the mass content of carbon in the first region to the mass content of carbon in the second region falls within the above range, the mass content of carbon in the first region is appropriate, which can effectively reduce the risk of further growth of phosphate grains and provide a more uniform coating effect on phosphate particles, thereby improving the dynamic performance of the material.

[0015] In some embodiments, based on the total mass of the positive electrode active material, the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region is 0.3:1 to 3:1. When the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region falls within the above range, it can further help improve the kinetic properties of the material.

[0016] In some embodiments, the mass content of carbon in the first region is greater than 0 and less than or equal to 6% based on the total mass of the positive electrode active material. When the mass content of carbon in the first region meets the above range, the first region can form a more uniform coating on the phosphate particles, further improving the dynamic performance of the material.

[0017] In some embodiments, the mass content of carbon in the first region is 0.5% to 3% based on the total mass of the positive electrode active material. When the mass content of carbon in the first region meets this range, the first region can more uniformly coat the phosphate particles, further improving the kinetic performance of the material.

[0018] In some embodiments, the mass content of carbon in the second region is greater than 0 and less than or equal to 6% based on the total mass of the positive electrode active material. When the mass content of carbon in the second region falls within the above range, the second region can more fully coat the phosphate particles coated with the first region, further enhancing the protection of the phosphate particles and improving the interfacial stability between the positive electrode active material and the electrolyte, thereby improving the cycling performance of the battery cell and reducing the risk of battery cell swelling.

[0019] In some embodiments, the mass content of carbon in the second region is 0.5% to 3% based on the total mass of the positive electrode active material. When the mass content of carbon in the second region falls within this range, the second region can more fully coat the phosphate particles coated with the first region, further enhancing the protection of the phosphate particles and improving the interfacial stability between the positive electrode active material and the electrolyte, thereby improving the cycling performance of the battery cell and reducing the risk of battery cell swelling.

[0020] In some embodiments, the carbon coating layer has a mass content of 0.01% to 6% based on the total mass of the positive electrode active material.

[0021] When the mass content of the carbon coating layer is within the above range, the mass content of the carbon coating layer is not too small, and the phosphate particles can be more fully coated, providing excellent protection for the phosphate particles, reducing the dissolution of transition metal ions such as manganese ions, and improving the interfacial properties between the positive electrode active material and the electrolyte, which is beneficial to improving the cycle performance and storage performance of the positive electrode active material. Moreover, when the mass content of the carbon coating layer is within the above range, the overall conductivity of the positive electrode active material can be effectively improved, which is beneficial to the utilization of the gram capacity of the phosphate particles. Moreover, the mass content of the carbon coating layer is not too high, and basically does not hinder the migration of active ions, and can ensure that the positive electrode active material has a relatively high gram capacity.

[0022] In some embodiments, the mass content of the carbon coating layer is 1.5% to 4% based on the total mass of the positive electrode active material. When the mass content of the carbon coating layer is within the above range, the interfacial properties between the positive electrode active material and the electrolyte can be improved, which is conducive to further improving the cycle performance and storage performance of the positive electrode active material.

[0023] In some embodiments, the phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Q w A compound, -0.1≤x≤0.9, 0≤y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, N; Q includes at least one of O and F.

[0024] Therefore, in the embodiment of the present application, the surface of the above-mentioned phosphate particles is provided with a carbon coating layer, which can effectively modify the phosphate particles, improve their conductivity and specific capacity, and can play an excellent protective role on the phosphate particles, reduce the dissolution of transition metal ions Mn and A elements in the phosphate particles, and improve their cycle performance and storage performance.

[0025] In a second aspect, an embodiment of the present application proposes a method for preparing a positive electrode active material, the method comprising: providing a first organic carbon source to phosphate particles, heat treating the first organic carbon source to form a first region coated on the surface of the phosphate particles, and obtaining an intermediate; providing a second organic carbon source to the intermediate, heat treating the second organic carbon source to form a second region coated on the surface of the intermediate, and obtaining a positive electrode active material, wherein, based on the total mass of the first region and the second region, the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

[0026] Therefore, according to the method implemented in the present application, the first region and the second region cooperate with each other to effectively protect the phosphate particles. When the positive electrode active material is applied to the battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced, thereby improving the interface stability between the positive electrode active material and the electrolyte, improving the cycle performance, and reducing the risk of swelling of the battery cell.

[0027] In some embodiments, the first organic carbon source may include at least one of a carbohydrate, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, and an organic acid. The first organic carbon source contains oxygen and has good compatibility with the phosphate raw material when mixed with the phosphate raw material.

[0028] In some embodiments, the second organic carbon source includes at least one of an olefin polymer, a non-oxygen heterocyclic polymer, and polyacrylonitrile. These materials have relatively low oxygen content, or even no oxygen at all, resulting in a relatively low residual oxygen content after carbonization. This helps improve the film density of the second region and the electrochemical performance of the positive electrode active material.

[0029] In a third aspect, an embodiment of the present application proposes a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector, and the positive electrode film layer includes a positive electrode active material as in any embodiment of the first aspect of the present application, or a positive electrode active material prepared by the method of any embodiment of the second aspect of the present application.

[0030] In a fourth aspect, the present application further proposes a battery, comprising a positive electrode plate according to any embodiment of the third aspect of the present application.

[0031] In a fifth aspect, the present application further proposes an electrical device, which includes a battery as in any embodiment of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0033] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0034] FIG. 2 is an exploded schematic diagram of an embodiment of the battery cell of FIG. 1 .

[0035] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0036] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0037] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0038] FIG6 is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0039] The drawings are not necessarily drawn to scale.

[0040] The following are the descriptions of the reference numerals:

[0041] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0042] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0043] 53. Cover plate;

[0044] 6. Electrical equipment. DETAILED DESCRIPTION

[0045] Below, the embodiments of the positive electrode active material and its preparation method, battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0046] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0049] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0050] Phosphates have a high theoretical specific capacity, which is beneficial for improving the energy density of battery cells. However, since phosphates usually contain transition metal ions, the transition metal ions are easily dissolved and migrate to the negative electrode through the electrolyte. On the one hand, the transition metal ions can precipitate as transition metals, and on the other hand, they may catalyze the decomposition of the solid electrolyte interphase (SEI) film. The byproducts of the decomposition reaction include gases, which can easily cause the battery cells to swell. Due to the damage to the SEI film, active ions will be continuously consumed to repair the SEI film during the battery cell cycle, resulting in irreversible effects on the capacity retention rate of the battery cell.

[0051] In related technologies, in order to improve the performance of battery cells, phosphates are usually coated and modified, for example, using a carbon coating. However, further research has found that phosphates containing a carbon coating and an electrolyte may still undergo serious side reactions, causing the battery cells to still have the risk of swelling, and the cycle performance of the battery cells cannot be significantly improved.

[0052] In view of the above problems, an embodiment of the present application proposes a positive electrode active material, which includes phosphate particles and a carbon coating layer. The carbon coating layer has a carbon skeleton structure as the main structure, and the carbon coating layer includes a first region and a second region. The first region coats the surface of the phosphate particles, and the second region is arranged on the side of the first region away from the phosphate particles. The mass content of oxygen elements in the first region is greater than the mass content of oxygen elements in the second region. The first region forms a uniform coating on the phosphate particles, and the second region is located outside the first region to form a second coating on the phosphate particles; the first region and the second region cooperate with each other to provide excellent protection for the phosphate particles. When the positive electrode active material is applied to a battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced, thereby improving the interface stability between the positive electrode active material and the electrolyte, reducing the risk of swelling of the battery cell and improving the cycle performance of the battery cell.

[0053] positive electrode active material

[0054] In a first aspect, an embodiment of the present application provides a positive electrode active material.

[0055] The positive electrode active material includes phosphate particles and a carbon coating layer, the carbon coating layer includes a first region and a second region, the first region is coated on the surface of the phosphate particles, and the second region is coated on the side of the first region away from the phosphate particles, wherein the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

[0056] The carbon coating layer uses a carbon skeleton structure as its main material, which can provide good coating and protection for phosphate particles. Since the carbon skeleton structure contains carbon elements, it has excellent electronic conductivity, which is beneficial to improving the overall conductivity of the positive electrode active material and helps to maximize the capacity of the phosphate particles.

[0057] In the related art, since the carbon coating layer is usually formed by sintering an organic carbon source, and the organic carbon source may contain oxygen-containing groups or carry oxygen atoms, during the sintering process of the organic carbon source, some oxygen elements will be released into the external environment in the form of gases such as carbon dioxide and carbon monoxide. During the gas release process, a large number of micropores and mesopores will be formed in the carbon coating layer, resulting in an increase in the specific surface area of ​​the carbon coating layer, which easily leads to an increase in the water absorption of the positive electrode active material, which is not conducive to the drying of the positive electrode sheet. After the organic carbon source is carbonized into a carbon coating layer through heat treatment, the oxygen elements in the organic carbon source may not be completely removed, resulting in excessive oxygen content in the carbon coating layer. The oxygen elements mostly exist in the form of oxygen-containing groups. The oxygen-containing groups can also absorb water vapor in the environment, which increases the water content of the positive electrode active material and further increases the difficulty of drying the positive electrode sheet.

[0058] When the positive electrode active material is applied to a battery cell, the carbon coating contains a large number of micropores and mesopores, which increases the risk of the electrolyte entering the positive electrode active material through the pore structure and reacting with phosphate. In addition, the reactivity of the oxygen-containing groups is relatively high, and the oxygen-containing groups easily catalyze the decomposition of the electrolyte when in contact with the electrolyte, thereby aggravating the interfacial side reactions between the positive electrode active material and the electrolyte, leading to increased gas production, which may cause the battery cell to swell, affecting the reliability of the battery cell. In addition, the decomposed electrolyte may produce hydrofluoric acid HF, which can further dissolve the positive electrode active material, leading to the dissolution of transition metal ions such as manganese ions, and worsening the cycle performance of the battery cell.

[0059] The carbon coating layer of the embodiment of the present application includes a first region and a second region. The first region forms a uniform coating on the phosphate particles, and the second region is located outside the first region. The first region has an inducing effect on the second region, and can induce the second region to form a uniform coating on the phosphate particles again; the first region and the second region cooperate with each other to provide excellent protection for the phosphate particles. When the positive electrode active material is applied to the battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced, thereby improving the interface stability between the positive electrode active material and the electrolyte, improving the cycle performance and storage performance, and reducing the risk of swelling of the battery cell.

[0060] Specifically,

[0061] The first region has a preliminary coating effect on the phosphate particles, and the first region can reduce the further growth of the phosphate grains, so that the particle size of the phosphate particles is relatively small, which is beneficial to improving the kinetic properties of the material; and because the oxygen content in the first region is relatively high, the first region is easier to be evenly dispersed on the surface of the phosphate particles, forming a uniform coating on the phosphate particles, which can improve the gram capacity of the phosphate particles; the oxygen-containing groups help the solvation and desolvation of active ions such as lithium ions, which can further promote the improvement of capacity.

[0062] While the first region contains a relatively large number of micropores and mesopores, the formation of a second region outside the first region, with its higher density, provides excellent protection against phosphate particles. Furthermore, the second region protects the first region, reducing the risk of side reactions between oxygen-containing groups in the first region and the electrolyte.

[0063] The second region has a relatively low oxygen content or is even devoid of oxygen. The second region contains fewer micropores and mesopores, resulting in a smaller specific surface area and higher density. This reduces the water absorption of the positive electrode active material, facilitating drying of the positive electrode sheet. Furthermore, due to the higher density of the second region, it effectively protects against phosphate particles, improves interfacial side reactions between the positive electrode active material and the electrolyte, and reduces the dissolution of transition metal elements from the positive electrode active material, thereby improving the cycling performance of the battery cell and reducing the risk of cell swelling. Due to the relatively low oxygen content in the second region and the relatively low content of oxygen-containing groups in the second region, the second region has poor electrochemical activity, resulting in reduced catalytic activity towards the electrolyte. This further improves the interfacial stability between the second region and the electrolyte, thereby further improving the cycling performance of the battery cell and reducing the risk of cell swelling.

[0064] The relatively high oxygen content in the first region facilitates uniform coating of the phosphate particles, improving their conductivity. The oxygen content in the first region is based on the mass of the first region. The mass of the first region may be the sum of the masses of the individual elements. For example, if the first region includes carbon and oxygen, the oxygen content in the first region may be the sum of the mass of the carbon and oxygen elements.

[0065] The second region has a relatively low oxygen content by mass. This allows the second region to form a more complete and dense coating on the phosphate particles, enhancing the interfacial stability between the positive electrode active material and the electrolyte, reducing the dissolution of transition metal ions, thereby improving the cycling performance of the battery cells and reducing the risk of cell swelling. The oxygen content by mass in the second region is based on the mass of the second region. The mass of the second region can be the sum of the masses of each element. For example, if the second region includes carbon and oxygen, the oxygen content in the second region can be the sum of the mass of the carbon and oxygen elements.

[0066] In the embodiment of the present application, the first region and the second region are both film layers with carbon as the main material, and the mass content of carbon in the carbon coating layer is greater than or equal to 90%. The first region and the second region may not have a clear interface, and the range of the first region and the range of the second region can be distinguished by measuring the oxygen content. The oxygen content is higher in the part close to the core surface, and its thickness is set as the first region thickness; the oxygen content is lower in the part away from the core, and its thickness is set as the second region thickness. According to the thickness of the first region and the second region,

[0067] The mass content of the oxygen element in the first region or the second region has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, a focused ion beam (FIB) is first used to cut a plurality of (e.g., 10 to 20) optional positive electrode active materials to obtain corresponding positive electrode active material sheets with a thickness of 20 nm to 40 nm; multiple locations (e.g., 5-10 locations) in the first region or the second region are tested to obtain the mass concentration of the O element at each measurement location (i.e., the mass ratio of the O element at the measurement location to all elements at the measurement location); the average value of the test results of all measurement locations of each positive electrode active material sheet is used as the mass content of the O element in the region, thereby calculating the mass content of the oxygen element.

[0068] In some embodiments, based on the total mass of the positive electrode active material, the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region is 0.1:1 to 10:1, optionally 0.3:1 to 3:1. Illustratively, based on the total mass of the positive electrode active material, the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1 or a range consisting of any two of the above values.

[0069] When the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region is in the range of 0.1:1 to 10:1, the mass content of the carbon element in the first region is appropriate, which can effectively reduce the risk of further growth of the phosphate grains and can more uniformly coat the phosphate particles, thereby improving the kinetic properties of the material. In the embodiments of the present application, by further selecting the mass content of the carbon element in the first region, the first region can form a more uniform coating on the phosphate particles, further improving the kinetic properties of the material. Optionally, based on the total mass of the positive electrode active material, the mass content of the carbon element in the first region is greater than 0% and less than or equal to 6%; optionally, it is 0.5% to 3%, such as 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range consisting of any two of the above values.

[0070] Optionally, based on the mass of the first region, the mass content of oxygen in the first region is less than or equal to 4%, optionally less than or equal to 3.5%, optionally between 3.0% and 3.5%, such as 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of the foregoing values. An appropriate mass content of oxygen in the first region can more evenly coat the phosphate particles, thereby improving the dynamic properties of the material.

[0071] When the ratio of the mass content of the carbon element in the first region to the mass content of the carbon element in the second region is in the range of 0.1:1 to 10:1, the mass content of the carbon element in the second region is appropriate, which can effectively improve the overall coating uniformity and protective effect of the carbon coating layer on the phosphate particles, so that the carbon coating layer, especially the second region, can form a more complete coating on the phosphate particles, improve the interface stability between the positive electrode active material and the electrolyte, reduce the dissolution of transition metal ions, thereby improving the cycle performance of the battery cell and reducing the risk of swelling of the battery cell. The embodiment of the present application further selects the mass content of the carbon element in the second region, so that the second region can more fully coat the phosphate particles coated with the first region, further enhance the protective effect on the phosphate particles, and improve the interface stability between the positive electrode active material and the electrolyte, thereby improving the cycle performance of the battery cell and reducing the risk of swelling of the battery cell. Optionally, based on the total mass of the positive electrode active material, the mass content of the carbon element in the second region is greater than 0% and less than or equal to 6%; it can be optionally 0.5% to 3%; it can be optionally 1% to 2.5%, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% or a range consisting of any two of the above values.

[0072] Optionally, based on the mass of the second region, the mass content of oxygen in the second region is less than or equal to 1%, optionally 0.1% to 1%; optionally less than or equal to 0.5%; optionally 0.4% to 0.48%, for example 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.42%, 0.43%, 0.45%, 0.46%, 0.47%, 0.48%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%. The relatively low mass content of oxygen in the second region can form a denser film layer, provide more effective protection for phosphate particles, and improve the interfacial stability between the positive electrode active material and the electrolyte.

[0073] In the embodiments of the present application, the mass content of carbon in the first region and the mass content of carbon in the second region have meanings well known in the art and can be detected using equipment and methods well known in the art. For example, a focused ion beam (FIB) is first used to cut a plurality (e.g., 10 to 20) of optional positive electrode active materials to obtain corresponding 20nm to 40nm thick positive electrode active material sheets; a spherical aberration corrected scanning transmission electron microscope energy dispersive spectrometer (STEM-EDS) is used to quantitatively analyze the oxygen element in the carbon coating layer of each positive electrode active material sheet; the oxygen element distribution near the core surface is higher, and its thickness is set as the first region thickness; the oxygen element distribution is lower in the portion away from the core, and its thickness is set as the second region thickness. Based on the thickness of the first region and the second region, the volume ratio of the first region and the second region is estimated. The volume ratio is approximately the mass ratio, thereby obtaining the ratio of the mass content of carbon in the first region to the mass content of carbon in the first region. The mass content of carbon in the positive electrode active material is tested by elemental analysis (EA), and then the mass content of carbon in each region of the first region and the second region is calculated based on the mass ratio.

[0074] In some embodiments, based on the total mass of the positive electrode active material, the mass content of the carbon element in the carbon coating layer is 0.01% to 6%, optionally 2% to 5%; optionally 1.5% to 4%, for example 0.01%, 0.02%, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7% , 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6% or a range consisting of any two of the above values.

[0075] When the mass content of the carbon element in the carbon coating layer is within the above range, the mass content of the carbon coating layer is not too low, and the phosphate particles can be more fully coated, providing excellent protection for the phosphate particles, reducing the dissolution of transition metal ions such as manganese ions, and improving the interfacial properties between the positive electrode active material and the electrolyte, which is beneficial to improving the cycle performance and storage performance of the positive electrode active material. Moreover, when the mass content of the carbon coating layer is within the above range, the overall conductivity of the positive electrode active material can be effectively improved, which is beneficial to the utilization of the gram capacity of the phosphate particles. Moreover, the mass content of the carbon coating layer is not too high, which basically does not hinder the migration of active ions and can ensure that the positive electrode active material has a relatively high gram capacity.

[0076] In some embodiments, the oxygen-containing groups may include at least one of a hydroxyl group, a carbonyl group, a carboxyl group, an ester group, and a quinone group. Alternatively, the oxygen-containing groups may include a hydroxyl group. For example, the oxygen-containing groups in the first region may include the aforementioned groups. For example, when the second region includes oxygen-containing groups, the oxygen-containing groups may include the aforementioned groups. When the second region does not contain oxygen, the second region does not include oxygen-containing groups.

[0077] In some embodiments, the positive electrode active material may further include a fast ion conductor layer. The fast ion conductor layer may be located between the carbon coating layer and the phosphate particles, or may be located on the side of the carbon coating layer facing away from the phosphate particles.

[0078] For example, a fast ion conductor layer can be located between the carbon coating layer and the phosphate particles. The fast ion conductor can increase the migration rate of active ions in the positive electrode active material, thereby facilitating the utilization of the capacity of the positive electrode active material and improving power performance. The fast ion conductor layer can include fast ion conductor materials such as one or more of lithium phosphate, sodium phosphate, potassium phosphate, and pyrophosphate. Pyrophosphate can include one or more of lithium pyrophosphate, sodium pyrophosphate, and potassium pyrophosphate.

[0079] In some embodiments, the mass content of the fast ion conductor layer is 1% to 3% based on the total mass of the positive electrode active material, for example, 1%, 2%, 3%, or a range consisting of any two of the foregoing values.

[0080] In some embodiments, the phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Q wCompound, -0.1≤x≤0.9, 0≤y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, and N; Q includes at least one of O and F. The surface of the phosphate particles is provided with a carbon coating layer, which can effectively modify the phosphate particles, improve their conductivity and specific capacity, and provide excellent protection for the phosphate particles, reduce the dissolution of transition metal ions such as Mn and A elements in the phosphate particles, and improve their cycling performance and storage performance.

[0081] For example, x can be -0.1, -0.05, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or a range consisting of any two of the above values.

[0082] For example, y can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or a range consisting of any two of the above values. Optionally, 0<1-y<0.5. The relatively high Mn content means that during the battery cell's charge and discharge process, the battery cell spends a significant portion of its time at high voltage. This makes the oxygen-containing groups in the second region more catalytic on the electrolyte, which can more easily deteriorate the battery cell's performance. However, in the present embodiment, the addition of a carbon coating layer comprising a first region and a second region protects the second region, reducing the catalytic effect of the oxygen-containing groups on the electrolyte. This effectively enhances the electrochemical performance of the positive electrode active material, thereby improving the cycling and storage performance of the battery cell. Of course, y can also meet the following requirement: 0 < y < 0.5.

[0083] Illustratively, z can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, or a range consisting of any two of the above values.

[0084] Illustratively, w can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or a range consisting of any two of the above values.

[0085] Illustratively, the phosphate particles include Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.5 Fe0.5 Mo 0.001 P 0.999 Si 0.001 O 3.999 F0. 001 、Li0.994Mn 0.4 Fe 0.6 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.60 Fe 0.4 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 PO 3.999 F 0.001 At least one of .

[0086] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0087] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0088] In the embodiment of the present application, the content of elements in the phosphate particles in the positive electrode active material has a meaning well known in the art and can be detected by equipment and methods well known in the art, for example, with reference to EPA 6010D-2014, tested by inductively coupled plasma atomic emission spectrometry, and measured by plasma atomic emission (ICP-OES, instrument model: Thermo ICAP7400). First, 0.4g of the positive electrode active material was weighed and 10ml (50% concentration) of aqua regia was added thereto. Then it was placed on a 180°C plate for 30min. After digestion on the plate, the volume was fixed to 100mL, and the standard curve method was used for quantitative testing.

[0089] In some embodiments, the initial gram capacity of the positive electrode active material is 140 mAh / g to 165 mAh / g. The initial gram capacity of the positive electrode active material is relatively high, and the gram capacity utilization is improved.

[0090] Illustratively, the initial gram capacity of the positive electrode active material can be 140 mAh / g, 142 mAh / g, 145 mAh / g, 148 mAh / g, 150 mAh / g, 152 mAh / g, 155 mAh / g, 158 mAh / g, 160 mAh / g, 162 mAh / g, 165 mAh / g, or a range consisting of any two of the above values.

[0091] In the embodiment of the present application, the initial gram capacity of the positive electrode active material is detected by forming a button battery with a positive electrode sheet containing the positive electrode active material and a lithium metal sheet. Under a constant temperature environment of 25°C, the button battery is charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V to a current of less than or equal to 0.05mA, allowed to stand for 5 minutes, and then discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0. The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt includes 1 mol / L LiPF6.

[0092] Method for preparing positive electrode active material

[0093] In a second aspect, the present application also provides a method for preparing a positive electrode active material. The positive electrode active material of any embodiment of the first aspect of the present application can be prepared by this method. Of course, the positive electrode active material can also be prepared by commonly used methods in the art.

[0094] Methods include:

[0095] Step S100, providing a first organic carbon source to phosphate particles, and heat-treating the first organic carbon source to form a first region coated on the surface of the phosphate particles to obtain an intermediate;

[0096] In step S200, a second organic carbon source is provided to the intermediate, and the second organic carbon source is heat-treated to form a second region coated on the surface of the intermediate to obtain a positive electrode active material, wherein, based on the total mass of the first region and the second region, the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

[0097] According to the method of the embodiment of the present application, the first organic carbon source can be heat-treated to form a first region mainly composed of a carbon layer, and the first region is coated on the surface of the phosphate particles to form an intermediate. The first organic carbon source contains a relatively high amount of oxygen, which makes the first organic carbon source and the phosphate particles more compatible, and is conducive to the uniform dispersion of the first organic carbon source on the surface of the phosphate particles. The carbon layer formed by carbonization can evenly coat the phosphate particles, thereby improving the conductivity of the positive electrode active material. In addition, the oxygen-containing groups facilitate the solvation and desolvation of active ions such as lithium ions, which can promote the utilization of capacity.

[0098] A second organic carbon source is further provided to the intermediate, the surface of the intermediate is the first region, and the main structure of the first region is a carbon layer. The carbon layer can induce the second organic carbon source to form a second region uniformly coated on the surface of the intermediate after carbonization, thereby improving the coating effect of the intermediate; the second organic carbon source contains relatively less oxygen element, or even no oxygen element, so that the second organic carbon source releases less gas during the heat treatment process, and can form a carbon layer with higher density (i.e., the second region), which can play a better protective role on the phosphate particles; the first region and the second region cooperate with each other to effectively protect the phosphate particles. When the positive electrode active material is applied to the battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced, thereby improving the interface stability between the positive electrode active material and the electrolyte, improving the cycle performance, and reducing the risk of swelling of the battery cell.

[0099] [Step S100]

[0100] The step of providing the first organic carbon source to the phosphate particles can be performed by mixing the first organic carbon source and the phosphate particles; or, in the process of preparing the phosphate particles, mixing the raw materials for preparing the phosphate particles and the first organic carbon source.

[0101] For example, the raw material for preparing phosphate particles is mixed with the first organic carbon source. In some embodiments, step S100 includes:

[0102] Step S110, dissolving the manganese source and the A source in a solvent, and drying the mixture to obtain a metal precursor;

[0103] In step S120 , a metal precursor, a lithium source, a phosphorus source, an R source, and a first organic carbon source are added to a solvent, ground and mixed, and then spray-dried and calcined in sequence to obtain an intermediate.

[0104] In step S110,

[0105] In some embodiments, the manganese source may be a manganese-containing substance known in the art that can be used to prepare phosphate. For example, the manganese source may include at least one of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, and manganese sulfate.

[0106] In some embodiments, the source of A may include at least one of oxalate, phosphate, acetate, sulfate, citrate, and nitrate.

[0107] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0108] In step S120,

[0109] In some embodiments, the lithium source may include at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, lithium oxalate, lithium phosphate, lithium hydrogen phosphate, lithium citrate, lithium silicate, and lithium metaborate.

[0110] In some embodiments, the phosphorus source may include at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0111] In some embodiments, the R source may include at least one of an R-containing acid, an R-containing oxide, and an R-containing organic compound. For example, the silicon source may include at least one of silicic acid, metasilicic acid, silicon tetrachloride, silicon dioxide, and tetraethyl orthosilicate. For example, the boron source may include at least one of boric acid, ammonium borate, and boron oxide.

[0112] The stoichiometric ratio of each substance in the above steps can be set according to the chemical formula of the desired phosphate particles. The content of each element in the material can be detected by inductively coupled plasma emission spectroscopy (ICP).

[0113] In some embodiments, the first organic carbon source may include at least one of a carbohydrate compound, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, and an organic acid. The above-mentioned first organic carbon source contains oxygen elements, and when mixed with the phosphate raw material, it has good compatibility with the phosphate raw material. For example, the first organic carbon source contains a large number of oxygen-containing groups such as hydroxyl, carbonyl, and ester groups, which can have good compatibility with lithium sources, phosphorus sources, and R sources, is relatively easy to disperse, and is easy to form a uniform coating layer; and can also play a role in reducing the enlargement of phosphate grains. However, since the first solvent carbon source contains a large amount of oxygen elements, the oxygen elements will produce a large amount of carbon dioxide, carbon monoxide and other gases during the pyrolysis process of the carbon source. After the gas is released, a large number of micropores and mesopores will be formed in the first region, and more oxygen-containing groups will be formed in the first region. The embodiment of the present application also has a second region coated outside the first region. The second region can form a relatively dense coating on the outer surface of the first region, which can effectively reduce the adverse effects of the second region. The second region and the first region interact with each other, which can effectively enhance the protective effect on phosphate particles.

[0114] Illustratively, the carbohydrate compound may include at least one of starch, sucrose, glucose, and cellulose.

[0115] Illustratively, the organic acid may include at least one of citric acid, lactic acid, and succinic acid.

[0116] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0117] In some embodiments, the grinding can be performed using a sand mill, for example, grinding and stirring in a sand mill for 8 to 10 hours.

[0118] In some embodiments, the spray drying granulation process can be carried out at 230° C. to 270° C. for 3.5 h to 5 h.

[0119] In some embodiments, the calcination process may be performed under an inert atmosphere, and the inert atmosphere may be at least one of nitrogen and argon.

[0120] In some embodiments, the calcination temperature may be 650° C. to 750° C., and the calcination time may be 8 to 12 hours. During the calcination process, phosphate nuclei are formed and grow, and the first organic carbon source is carbonized into a first region that coats the surface of the phosphate grains. The first region can constrain the phosphate grains, reducing the risk of excessive growth of the phosphate grains and resulting in a relatively small particle size of the phosphate grains.

[0121] For another example, the first organic carbon source and phosphate particles are mixed, the phosphate particles are polyanionic compounds, and may include manganese phosphate, and further, include a molecular formula of Li 1+xMn 1-y A y P 1-z R z Q w The compound, phosphate particles can be commercially obtained or synthesized according to the following method.

[0122] In some embodiments, a method for preparing phosphate particles comprises:

[0123] Step S130, dissolving the manganese source and the A source in a solvent, and drying the mixture to obtain a metal precursor;

[0124] Step S140, adding a metal precursor, a lithium source, a phosphorus source, and an R source into a solvent, grinding and mixing, and then spray drying to obtain a phosphate precursor;

[0125] Step S150 , sintering the phosphate precursor to form phosphate particles.

[0126] The materials of the above raw materials are as mentioned above and will not be repeated here.

[0127] [Step S200]

[0128] The second organic carbon source and the intermediate are added into a solvent, mixed, and then sintered to obtain a positive electrode active material.

[0129] After the second organic carbon source and the intermediate are mixed for 4 to 8 hours, the system is heat treated; the heat treatment process is as follows: the system can be pre-heat-treated and dried at 120°C to 200°C for 4 to 6 hours to remove the solvent; then it is sintered at 650°C to 800°C, and the sintering temperature can be 8 to 12 hours. The second organic carbon source is carbonized into a carbon layer (i.e., the second region), and the second region is coated on the surface of the intermediate, i.e., the second region is coated on the surface of the first region.

[0130] The main structure of the first region is a carbon structure, and the main structure of the second region is a carbon structure. When the intermediate includes the first region, the first region helps to induce the second organic carbon source to be coated outside the first region; since the first region coats the phosphate particles more uniformly, the first region can promote the second region formed by carbonization of the second organic carbon source to uniformly coat the phosphate particles. The cooperation between the first region and the second region can achieve a more uniform coating effect on the phosphate particles, thereby enhancing the protective effect on the phosphate particles.

[0131] When sintering at 650°C to 800°C, the sintering temperature will not be too low, and the second organic carbon source can be fully pyrolyzed and carbonized to form a second region with a higher degree of graphitization, which is beneficial to improving the conductivity of the second region and can improve the specific capacity and kinetic performance of the positive electrode active material; and the pore structure in the second region formed by the carbonization of the second organic carbon source is relatively small, and the oxygen content is low, which can effectively improve the interfacial stability between the positive electrode active material and the electrolyte. When sintering at 650°C to 800°C, the sintering temperature will not be too high, and the phosphate particles will basically not grow further. The particle size of the phosphate particles is relatively small, which can further improve the interfacial stability between the positive electrode active material and the electrolyte and improve the kinetic performance of the material; and the carbon coating layer is not easy to react with the phosphate particles to produce impurities, thereby improving the overall structural stability of the positive electrode active material. Exemplarily, the sintering temperature is 650°C, 700°C, 750°C, 800°C, or a range consisting of any two of the above values.

[0132] In some embodiments, the second organic carbon source includes at least one of an olefin polymer and a non-oxygen heterocyclic polymer. These materials have relatively low oxygen content, or even contain no oxygen at all. The residual oxygen content after carbonization is relatively low, which helps improve the film density of the second region and the electrochemical performance of the positive electrode active material.

[0133] Optionally, the second organic carbon source includes at least one of an olefin polymer containing non-oxygen heteroatoms, a non-oxygen heterocyclic polymer, and polyacrylonitrile. Specifically, the second organic carbon source may include at least one doping element selected from the group consisting of fluorine, nitrogen, and sulfur. The aforementioned atoms can act as a doping agent for the positive electrode active material. The atoms of the doping element can change the charge distribution around the carbon atoms, thereby improving the conductivity of the carbon coating layer. Furthermore, the atoms of the doping element can create defect structures within the carbon material, which is beneficial for the rapid migration of active ions. In addition, new functional groups containing the doping element can be generated on the surface of the carbon coating layer, forming new active sites, thereby increasing the solvation and desolvation rates of active ions such as lithium ions, thereby improving the capacity and rate performance of the positive electrode active material.

[0134] Illustratively, the olefin polymer includes at least one of polyethylene, polytetrafluoroethylene, polyvinylidene fluoride, and polyacrylonitrile. Alternatively, the olefin polymer includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, and polyacrylonitrile.

[0135] Illustratively, the non-oxygen heterocyclic polymer includes at least one of polypyrrole and polythiophene.

[0136] Positive electrode

[0137] In a third aspect, an embodiment of the present application proposes a positive electrode plate.

[0138] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0139] The positive electrode active material may include the positive electrode active material of any embodiment of the first aspect of the present application, or the positive electrode active material obtained by the method of any embodiment of the second aspect of the present application. Since the positive electrode active material has good conductivity, its capacity utilization is improved, which is beneficial to improving the electrochemical performance of the positive electrode plate; in addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode plate is applied to the battery cell, it can reduce the expansion rate of the battery cell and improve the cycle performance of the battery cell.

[0140] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0141] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylic resins. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0142] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0143] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0144] battery cells

[0145] In the fourth aspect, the embodiments of the present application also propose a battery cell, which includes a positive electrode plate as in any embodiment of the third aspect of the present application. Since the positive electrode active material in the positive electrode plate has good conductivity, its capacity is improved and the electrochemical performance of the positive electrode plate is improved; in addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode plate is applied to the battery cell, the expansion rate of the battery cell can be reduced and the cycle performance of the battery cell can be improved.

[0146] [Negative electrode]

[0147] In some embodiments, the battery cell further includes a negative electrode plate.

[0148] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0149] The negative electrode active material can be any negative electrode active material known in the art for use in battery cells. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0150] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present embodiments do not particularly limit the type of negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent based on the total weight of the negative electrode film layer is ≤5%.

[0151] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application embodiment does not particularly limit the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0152] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, the weight percentage of the other additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0153] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0154] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0155] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0156] [Electrolyte]

[0157] In some embodiments, the battery cell further includes an electrolyte.

[0158] During the charge and discharge process of a battery cell, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. The present application embodiment does not specifically limit the type of electrolyte, and the electrolyte can be selected based on actual needs.

[0159] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0160] As an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0161] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0162] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0163] [Isolation film]

[0164] The battery cell also includes a separator.

[0165] In some embodiments, the battery cell further includes a separator. The embodiments of the present application have no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0166] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0167] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0168] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0169] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0170] The present invention has no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape. FIG1 shows a battery cell 5 with a square structure as an example.

[0171] In some embodiments, as shown in FIG2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to demand.

[0172] The preparation methods of the battery cells of the embodiments of the present application are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0173] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0174] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0175] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0176] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0177] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0178] Electrical devices

[0179] A fifth aspect of the embodiments of the present application provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs of the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0180] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0181] FIG6 is a schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0182] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0183] Example

[0184] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0185] Example 1

[0186] 1. Preparation of positive electrode sheet

[0187] The positive electrode sheet includes a positive electrode current collector aluminum foil and a positive electrode film layer. The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode current collector aluminum foil, and a film layer formed after drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 92:2.5:5.5.

[0188] The positive electrode active material includes Li 0.994 Mo 0.001 Mn 0.65 Fe 0.349 P 0.999 Si 0.001 O 3.999 F 0.001 The preparation process of particles and carbon coating, positive electrode active material is as follows:

[0189] Preparation of doped manganese oxalate: 1.3 mol of MnSO4﹒H2O and 0.7 mol of FeSO4﹒H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reactor and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reactor was heated to 80°C and stirred at 600 rpm for 6 hours. The reaction was terminated (no bubbles were generated) to obtain an Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C and then ground to obtain a median particle size D v 50 is Fe-doped manganese oxalate particles of about 100 nm.

[0190] Preparation of lithium manganese phosphate coated in the first region: Take 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 37.3 g of sucrose and add them to 20 L of deionized water. Transfer the mixture to a sand mill and grind and stir thoroughly for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C, dry for 4 hours, and obtain particles. In a protective atmosphere of nitrogen (90 volume%) and hydrogen (10 volume%), sinter the above powder at 700°C for 10 hours to obtain carbon-coated phosphate particles Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 , as an intermediate.

[0191] Prepare the second layer of carbon coating of the intermediate coated in the second region: disperse 37.3g of polyvinylidene fluoride in 500ml of deionized water, then stir and fully dissolve to obtain a coating liquid, add the above intermediate to the coating liquid, stir and mix together for 6 hours, after mixing evenly, transfer to a 150℃ oven and dry for 6 hours, and then sinter at 700℃ for 10 hours to obtain the positive electrode active material.

[0192] 2. Preparation of negative electrode sheet

[0193] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode film layer. The negative electrode film layer includes a film layer formed by evenly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector copper foil, drying, and cold pressing. The negative electrode film layer includes a negative electrode active material, a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC-Na) in a weight ratio of 95:2:2:1.

[0194] The negative electrode active material includes artificial graphite and hard carbon (mass ratio is 90:5).

[0195] 3. Isolation film

[0196] The isolation film is a polyethylene film.

[0197] 4. Preparation of electrolyte

[0198] The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt includes 1 mol / L LiPF6.

[0199] 5. Preparation of batteries

[0200] The lithium-ion battery includes an outer packaging shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer packaging shell. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The electrode assembly is a wound electrode assembly, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0201] Comparative Example 1

[0202] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the positive electrode was prepared using the following steps:

[0203] The positive electrode sheet includes a positive electrode current collector aluminum foil and a positive electrode film layer. The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode current collector aluminum foil, and a film layer formed after drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 92:2.5:5.5.

[0204] The positive electrode active material includes phosphate particles and a carbon coating layer. The preparation process of the positive electrode active material is as follows:

[0205] Preparation of doped manganese oxalate: 1.3 mol of MnSO4﹒H2O and 0.7 mol of FeSO4﹒H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reactor and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reactor was heated to 80°C and stirred at 600 rpm for 6 hours. The reaction was terminated (no bubbles were generated) to obtain an Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C and then ground to obtain a median particle size D v 50 is Fe-doped manganese oxalate particles of about 100 nm.

[0206] Preparation of lithium manganese phosphate coated in the first region: Take 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 74.6 g of sucrose and add them to 20 L of deionized water. Transfer the mixture to a sand mill and grind and stir thoroughly for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C, dry for 4 hours, and obtain particles. In a protective atmosphere of nitrogen (90 volume%) and hydrogen (10 volume%), sinter the above powder at 700°C for 10 hours to obtain carbon-coated phosphate particles Li 0.994 Mo0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 , and obtain the positive electrode active material.

[0207] Example 2-1 to Example 2-4

[0208] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of the second organic carbon source was adjusted.

[0209] Example 3

[0210] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of the first organic carbon source was adjusted.

[0211] Example 4-1 to Example 4-5

[0212] A lithium ion battery was prepared using a method similar to that of Example 1, except that the content of the second organic carbon source was adjusted.

[0213] Example 5-1 and Example 5-2

[0214] A lithium ion battery was prepared using a method similar to that of Example 1, except that the content of the first organic carbon source was adjusted.

[0215] Example 6-1 to Example 6-2

[0216] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the material of the positive electrode active material was adjusted.

[0217] In Example 6-1, the positive electrode active material includes Li 0.994 Mn 0.5 Fe 0.499 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 Particles and carbon coating layer, the carbon coating layer is the carbon coating layer prepared in Example 1.

[0218] In Example 6-2, the positive electrode active material includes Li 0.994 Mn 0.4 Fe 0.599 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001Particles and carbon coating layer, the carbon coating layer is the carbon coating layer prepared in Example 1.

[0219] Example 7

[0220] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that a pyrophosphate coating layer was added between the phosphate particles and the carbon coating layer.

[0221] 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to 5, and then stirred and reacted at room temperature for 2 h to obtain a solution. The solution was then heated to 80° C. and maintained at this temperature for 4 h to obtain a Li2FeP2O7 suspension.

[0222] 1571.9157.2 g of phosphate particles were added to the suspension obtained in step S3 (the coating material content was 15.71.572 g), and the mixture was stirred and mixed for 6 h. After mixing evenly, the mixture was transferred to a 120°C oven and dried for 6 h, and then sintered at 650°C for 6 h to obtain the pyrophosphate-coated material.

[0223] The pyrophosphate-coated material is then subjected to carbon coating using the method described in Example 1, with a carbon coating layer being provided on the outer layer.

[0224] Performance Testing

[0225] 1. Preparation of button batteries

[0226] The positive electrode sheet in Example 1 is used as the positive electrode sheet of the button battery;

[0227] A lithium sheet was used as the negative electrode, and the electrolyte included 1 mol / L LiPF6 and an organic solvent, wherein the organic solvent included ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0228] It is assembled into a button battery in a button box with the negative electrode sheet, positive electrode sheet and electrolyte.

[0229] 2. Measurement method of initial gram capacity of positive electrode active material in button battery

[0230] At a constant temperature of 25°C, charge the button battery to 4.3V at 0.1C, then charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.0V at 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0.

[0231] 3. Cycling performance test of lithium-ion batteries at 45°C

[0232] At a constant temperature of 45°C, charge the lithium-ion battery at 1C to 4.3V. Then, charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it rest for 5 minutes, then discharge it at 1C to 2.5V. Record the discharge capacity at this point as E0. Repeat the charge and discharge cycle until the discharge capacity drops to 80% of E0. Record the number of cycles the lithium-ion battery has completed.

[0233] 4. Measurement method of Mn and Mn-doped Fe dissolution after lithium-ion battery cycling

[0234] At 45°C, after the capacity of the lithium-ion battery has decayed to 80% (this step can be tested using the cycle performance test of the lithium-ion battery at 45°C, that is, in a constant temperature environment of 45°C, the lithium-ion battery is charged to 4.3V at 1C, and then constant voltage charged at 4.3V until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.5V at 1C, and the discharge capacity at this time is recorded as E0. The above charge and discharge cycle is repeated until the discharge capacity is reduced to 80% of E0)

[0235] The battery was discharged at a rate of 0.1C to a cut-off voltage of 2.5V.

[0236] Then disassemble the lithium-ion battery, take out the negative electrode sheet, and randomly select 30 (1540.25mm 2 ) discs were measured by inductively coupled plasma emission spectroscopy (ICP) using an Agilent ICP-OES730. The amounts of Fe (if Fe is doped at the Mn site of the cathode active material) and Mn were calculated based on the ICP results, thereby estimating the amount of Mn (and Fe doped at the Mn site) released after cycling. This testing was conducted in accordance with EPA-6010D-2014.

[0237] 5. Lithium-ion battery flatulence test at 60°C

[0238] Lithium-ion batteries with 100% state of charge (SOC) were stored at 60°C as test samples. The open circuit voltage (OCV) and AC internal resistance (IMP) of the lithium-ion batteries were measured before, during and after storage to monitor the SOC, and the volume of the lithium-ion batteries was measured.

[0239] After every 48 hours of storage, remove the lithium-ion battery, let it stand for 1 hour, test the open circuit voltage (OCV) and internal resistance (IMP), and measure the battery volume using the water displacement method after cooling to room temperature. The water displacement method is to first use a balance that automatically converts the dial data to measure the gravity F1 of the battery alone, and then completely place the lithium-ion battery in deionized water (density is known to be 1g / cm 3 ), measure the gravity F2 of the battery at this time, and the buoyancy F 浮That is F1-F2, and then according to Archimedes principle F 浮 =ρ×g×V, and the battery volume V is calculated to be V=(F1-F2) / (ρ×g).

[0240] From the OCV and IMP test results, the battery of the embodiment always maintained an SOC of more than 99% during the test until the end of storage.

[0241] After storage for 30 days, the battery volume was measured, and the percentage increase in the battery volume after storage relative to the battery volume before storage was calculated.

[0242] 7. Test of saturated water absorption of positive electrode active materials

[0243] The positive electrode active material powder was placed in a constant temperature and humidity chamber at 25°C and a relative humidity of 60%. After 2 hours, 1 g of the positive electrode active material powder was taken out and placed in a cillin bottle and quickly sealed. The water content of the positive electrode active material powder was then determined using a Karl Fischer moisture meter and recorded as the saturated water absorption.

[0244] Test results

[0245] The test results are shown in Table 1.

[0246] Table 1

[0247] In Table 1,

[0248] The mass content of the carbon element in the first region is based on the mass of the positive electrode active material.

[0249] The mass content of the carbon element in the second region is based on the mass of the positive electrode active material.

[0250] The mass content of the oxygen element in the first region is based on the mass of the first region.

[0251] The mass content of the oxygen element in the second region is based on the mass of the second region.

[0252] As can be seen from Table 1, in Comparative Example 1, a carbon coating layer made of carbonized sucrose is coated on the surface of the phosphate particles. The carbon coating layer has a high oxygen content and is easily in direct contact with the electrolyte and produces side reactions, so that the battery cell still has the risk of swelling, and the cycle performance of the battery cell cannot be significantly improved.

[0253] Compared with Comparative Example 1, the embodiment of the present application coats a carbon coating layer on the surface of the phosphate particles, and the carbon coating layer includes a first region and a second region. The first region is close to the surface of the phosphate particles, and the mass content of oxygen elements in the layer is relatively high, which can improve the overall conductivity of the positive electrode active material; the second region is located outside the first region, and the mass content of oxygen elements in the second region is relatively low, and it is not easy to have side reactions with the electrolyte; the first region and the second region cooperate with each other to play an excellent protective role for the phosphate particles. When the positive electrode active material is applied to a battery cell, the water absorption performance of the positive electrode active material can be reduced, and the dissolution amount of transition metal elements in the phosphate particles can be reduced. After the cycle, the total amount of Fe and Mn dissolution is less than or equal to 168ppm; optionally less than or equal to 125ppm; the saturated water absorption of the positive electrode active material is less than or equal to 3300ppm, optionally less than or equal to 2900ppm; and it can improve the interface stability between the positive electrode active material and the electrolyte, reduce the risk of swelling of the battery cell and improve the cycle performance of the battery cell.

[0254] In Example 1 and Example 2-1 to Example 2-4, by adjusting the material of the second organic carbon source, the risk of swelling of the battery cell can be further reduced and the cycle performance of the battery cell can be improved.

[0255] By adjusting the material of the first organic carbon source, Example 1 and Example 3 can further reduce the risk of battery cell swelling and improve the cycle performance of the battery cell.

[0256] In Example 1, Example 4-1 to Example 4-5, by adjusting the mass content of the second organic carbon source (corresponding to the mass content of the carbon element in the second region), the mass content of the carbon element in the second region can be 0.5% to 3.0%, optionally 1.0% to 2.5%, which can further reduce the risk of swelling of the battery cell and improve the cycle performance of the battery cell, and ensure that the gram capacity of the positive electrode active material will not be too low.

[0257] In Example 1, Example 5-1 and Example 5-2, by adjusting the mass content of the first organic carbon source (corresponding to the mass content of the carbon element in the first region), the mass content of the carbon element in the first region can be 0.5% to 3.0%, optionally 1.0% to 3%, which can further reduce the risk of swelling of the battery cell and improve the cycle performance of the battery cell, and ensure that the gram capacity of the positive electrode active material will not be too low.

[0258] In Example 1, Example 6-1, and Example 6-2, the material of the phosphate is adjusted to regulate the amount of metal ions dissolved and the cycle performance of the battery cell.

[0259] In Example 7, by adding a fast ion conductor layer, the cycle performance of the battery cell can be further improved.

[0260] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A positive electrode active material comprising: phosphate granules; as well as The carbon coating layer includes a first region and a second region, wherein the first region is coated on the surface of the phosphate particles, and the second region is coated on the side of the first region away from the phosphate particles, wherein the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

2. The positive electrode active material according to claim 1, wherein Based on the mass of the first region, the mass content of oxygen in the first region is less than or equal to 4%; or The mass content of oxygen in the second region is less than or equal to 1% based on the mass of the second region.

3. The positive electrode active material according to claim 2, wherein The mass content of oxygen in the first region is 3.0% to 3.5%.

4. The positive electrode active material according to claim 2 or 3, wherein The mass content of oxygen in the second region is 0.4% to 0.48%.

5. The positive electrode active material according to any one of claims 1 to 4, wherein A ratio of a mass content of the carbon element in the first region to a mass content of the carbon element in the second region is 0.1:1 to 10:1 based on the total mass of the positive electrode active material.

6. The positive electrode active material according to claim 5, wherein A ratio of a mass content of the carbon element in the first region to a mass content of the carbon element in the second region is 0.3:1 to 3:1 based on the total mass of the positive electrode active material.

7. The positive electrode active material according to any one of claims 1 to 6, wherein The mass content of the carbon element in the first region is greater than 0 and less than or equal to 6% based on the total mass of the positive electrode active material.

8. The positive electrode active material according to claim 7, wherein The mass content of the carbon element in the first region is 0.5% to 3% based on the total mass of the positive electrode active material.

9. The positive electrode active material according to any one of claims 1 to 8, wherein The mass content of the carbon element in the second region is greater than 0 and less than or equal to 6% based on the total mass of the positive electrode active material.

10. The positive electrode active material according to claim 9, wherein The mass content of the carbon element in the second region is 0.5% to 3% based on the total mass of the positive electrode active material.

11. The positive electrode active material according to any one of claims 1 to 10, wherein The carbon coating layer has a carbon content of 0.01% to 6% by mass based on the total mass of the positive electrode active material.

12. The positive electrode active material according to claim 11, wherein The carbon coating layer has a mass content of 1.5% to 4% based on the total mass of the positive electrode active material.

13. The positive electrode active material according to any one of claims 1 to 12, wherein The phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Q w A compound, -0.1≤x≤0.9, 0≤y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, N; Q includes at least one of O and F.

14. A method for preparing a positive electrode active material, comprising: providing a first organic carbon source to phosphate particles, and heat-treating the first organic carbon source to form a first region coated on the surface of the phosphate particles to obtain an intermediate; A second organic carbon source is provided to the intermediate, and the second organic carbon source is heat-treated to form a second region coated on the surface of the intermediate to obtain a positive electrode active material, wherein, based on the total mass of the first region and the second region, the mass content of the oxygen element in the first region relative to the total mass of the first region is greater than the mass content of the oxygen element in the second region relative to the total mass of the second region.

15. The method according to claim 14, wherein The first organic carbon source may include at least one of a carbohydrate, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose and an organic acid; and / or The second organic carbon source includes at least one of an olefin polymer, a non-oxygen heterocyclic polymer and polyacrylonitrile.

16. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material according to any one of claims 1 to 13, or the positive electrode active material prepared by the method according to any one of claims 14 or 15.

17. A battery comprising the positive electrode sheet according to claim 16.

18. An electrical device comprising the battery according to claim 17.

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