Positive electrode active material and preparation method thereof, positive electrode plate, battery monomer, battery and electric device

Abstract

The invention discloses a positive active material and a preparation method thereof, a positive pole piece, a battery monomer, a battery and an electric device, and belongs to the technical field of batteries. The positive electrode active material comprises a positive electrode base material, and a first coating layer and a second coating layer which sequentially coat the surfaces of primary particles of the positive electrode base material; wherein the concentration of the lithium element in the first coating layer is smaller than the concentration of the lithium element in the positive electrode base material, and the second coating layer comprises an ion conductor material. According to the technical scheme, the cycle performance of the battery monomer can be improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery cell, a battery, and an electrical device. Background Art

[0002] As environmental pollution becomes increasingly serious, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor related to its development.

[0003] The development of battery technology needs to consider many design factors, such as energy density, cycle life, reliability, etc. The design of the positive electrode active material in the battery cell is crucial to the performance of the battery cell. Therefore, how to provide a positive electrode active material to improve the cycle performance of the battery cell is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its object is to provide a positive electrode active material to improve the cycle performance of a battery cell.

[0005] In order to achieve the above-mentioned objectives, the present application provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery cell, a battery, and an electrical device.

[0006] In the first aspect, a positive electrode active material is provided, comprising: a positive electrode matrix material, a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode matrix material; wherein the concentration of lithium element in the first coating layer is less than the concentration of lithium element in the positive electrode matrix material, and the second coating layer comprises an ion conductor material.

[0007] The embodiment of the present application provides a positive electrode active material, the surface of the primary particles of the positive electrode matrix material is coated with a first coating layer, the concentration of lithium in the first coating layer is less than the concentration of lithium in the positive electrode matrix material, so that there is a certain lithium concentration gradient between the positive electrode matrix material and the first coating layer, which is conducive to the lithium ions in the positive electrode matrix material to escape from the positive electrode matrix material, thereby facilitating the increase of the content of active lithium ions in the battery cell. The first coating layer and the second coating layer are sequentially coated on the surface of the primary particles of the positive electrode matrix material, that is, the outer surface of the first coating layer is coated with the second coating layer, and the second coating layer includes an ion conductor material. The ion conductor material has good ion transport performance, so that the positive electrode active material has a higher ion conductivity and the impedance of the battery cell is small; the second coating layer is also arranged to suppress the side reaction between the positive electrode matrix material and the electrolyte, reduce the impedance of the solid-liquid interface at the positive electrode, thereby facilitating the improvement of the cycle performance of the battery cell. Therefore, the positive electrode active material of the embodiment of the present application has good performance and can improve the cycle performance of the battery cell.

[0008] In a possible implementation, the chemical formula of the positive electrode matrix material is Li 1+a [Ni x Co y Mn z M b ]O 2 , wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1.

[0009] The battery cell prepared by the positive electrode matrix material of the above chemical formula has a higher energy density. When the positive electrode matrix material satisfies the above chemical formula, the first coating layer is conducive to the deintercalation of lithium ions from the positive electrode matrix material, and the second coating layer is conducive to inhibiting the dissolution of transition metal ions in the positive electrode matrix material, so that the positive electrode active material has better performance, and the battery cell prepared by the positive electrode active material also has better performance.

[0010] In a possible implementation, 0.8≤x<1. In this way, the content of nickel in the positive electrode matrix material is relatively high, so that the positive electrode active material has a higher gram capacity while having better stability.

[0011] In a possible implementation, M includes at least one of Ti, Nb, Te, V or Ta. By doping the positive electrode matrix material with the M element, the crystal structure stability of the positive electrode matrix material can be improved, and the reversibility of the layered structure of the positive electrode matrix material during lithium insertion and extraction can be improved, thereby improving the electrochemical performance of the positive electrode active material. In addition, the M element can form higher valence ions. According to defect chemistry theory, high valence ion doping will produce lithium vacancies inside the material, which is beneficial to promote the transmission of lithium ions inside the positive electrode matrix material.

[0012] In a possible implementation, the ion conductor material includes a compound formed by Li element and at least one of W, Mo or P element; alternatively, the ion conductor material includes Li 2 WO 4 , Li 2 MoO 4 or Li 3 PO 4 At least one of .

[0013] Due to preparation and other reasons, there will be impurity lithium on the surface of the positive electrode matrix material, such as lithium carbonate. W, Mo or P elements can react with impurity lithium to generate a compound formed by Li element and at least one of W, Mo or P elements. The ion conductor material includes the above compounds, which, on the one hand, is conducive to reducing the impedance at the positive electrode interface and reducing the internal resistance of the battery cell; on the other hand, the setting of the above compounds is conducive to the transmission of lithium ions and is conducive to improving the rate performance of the battery cell.

[0014] In a possible implementation, the material of the first coating layer includes a transition metal oxide, and the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode matrix material. That is, the first coating layer can be formed by a certain treatment of the positive electrode matrix material, and the lithium vacancies in the first coating layer are more than the lithium vacancies in the positive electrode matrix material, thereby facilitating the deintercalation of lithium ions in the positive electrode matrix material.

[0015] In a possible implementation, the thickness d1 of the first coating layer satisfies: 1nm≤d1≤5nm; optionally, 1nm≤d1≤2nm. In this way, lithium ions have a suitable length of transmission path, and there is a suitable lithium concentration gradient between the first coating layer and the positive electrode matrix material, which is conducive to improving the capacity of the battery cell.

[0016] In a possible implementation, the thickness d2 of the second coating layer satisfies: d2≤20nm; optionally, 4nm≤d2≤10nm. In this way, lithium ions have a transmission path of appropriate length, which is beneficial to improving the capacity of the battery cell.

[0017] In a possible implementation, the ratio B of the mass of the second coating layer to the mass of the positive electrode matrix material satisfies: 1000ppm≤B≤3000ppm; optionally, 1000ppm≤B≤2000ppm. In this way, the second coating layer has a suitable mass ratio, so that the second coating layer can have a suitable thickness.

[0018] In a possible implementation, the volume particle size distribution of the positive electrode active material satisfies: (D v 90-D v 10) / D v 501≥1.2; Optionally, (D v 90-D v 10) / D v 501≥1.3. In this way, the positive electrode active material contains both large particles with appropriate contents and small particles with appropriate contents, and the positive electrode active material has a wider distribution of particle sizes, which is beneficial to improving the powder compaction density of the positive electrode active material, thereby facilitating improving the volume energy density of the battery cell.

[0019] In a possible implementation, the volume particle size distribution Dv501 of the positive electrode active material satisfies: 7μm≤Dv501≤12μm; optionally, 8μm≤Dv501≤10μm. In this way, lithium ions have a path of appropriate length when being deintercalated from the positive electrode active material, and the battery cell can have higher capacity and cycle performance.

[0020] In a possible implementation, the first coating layer includes a material having a spinel structure. The positive electrode matrix material can react with an ammonium salt, and the product of the ammonium salt decomposition by heat can react with the lithium oxide (e.g., Li 2 O) and residual lithium on the surface, thereby generating lithium vacancies on the surface of the positive electrode substrate material, and the surface of the positive electrode substrate material changes from a layered structure to a spinel structure, thereby generating a first coating layer including a material having a spinel structure.

[0021] In a possible implementation, the positive electrode active material is a material obtained by reacting the secondary particles of the positive electrode matrix material with an ammonium salt. During the reaction, the ammonium salt and its decomposition products can penetrate into the grain boundaries of the positive electrode matrix material, thereby forming a first coating layer and a second coating layer on the surface of the primary particles of the positive electrode matrix material.

[0022] In a second aspect, a method for preparing the positive electrode active material in the first aspect and any possible implementation thereof is provided, comprising: preparing a positive electrode base material; preparing the first coating layer and the second coating layer on the surface of primary particles of the positive electrode base material to obtain the positive electrode active material.

[0023] In a possible implementation, the preparing the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material includes: mixing the positive electrode base material and ammonium salt and sintering them in an inert atmosphere to obtain the positive electrode active material.

[0024] The positive electrode base material can react with the ammonium salt to form a first coating layer on the surface of the positive electrode base material, and the compound generated by the decomposition of the ammonium salt can react with the miscellaneous lithium on the surface of the positive electrode base material to generate a second coating layer while consuming the miscellaneous lithium; in addition, sintering in an inert atmosphere also facilitates the formation and preparation of the first coating layer. Therefore, the positive electrode active material of the embodiment of the present application can be prepared by the reaction of the positive electrode base material with the ammonium salt.

[0025] In a possible implementation, the mixing of the positive electrode matrix material and the ammonium salt and sintering in an inert atmosphere to obtain the positive electrode active material includes: mixing the positive electrode matrix material and the ammonium salt in a high-energy ball mill; and sintering the mixed positive electrode matrix material and the ammonium salt in an inert atmosphere to obtain the positive electrode active material.

[0026] During the ball milling and sintering process in a high-temperature ball mill, the ammonium salt can melt and penetrate into the grain boundaries of the positive electrode matrix material, so that the ammonium salt can fully contact the surface of the primary particles of the positive electrode matrix material; the ball milling process is conducive to the mixing of the ammonium salt and the positive electrode matrix material, which is conducive to the uniform distribution of the ammonium salt on the surface and grain boundaries of the primary particles of the positive electrode matrix material. During the sintering process, the ammonia generated by the decomposition of the ammonium salt reacts with the positive electrode matrix material to generate a spinel structure material with lithium vacancies, thereby forming a first coating layer; in addition, the compound generated by the decomposition of the ammonium salt reacts with the miscellaneous lithium on the surface of the positive electrode matrix material, consuming the miscellaneous lithium and generating a second coating layer.

[0027] In a possible implementation, the rotation speed V of the high energy ball mill satisfies: 500rpm≤V≤1400rpm; optionally, 800rpm≤V≤1200rpm.

[0028] In a possible implementation, the ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

[0029] At the above rotation speed and / or ball milling time, the energy generated by high-energy ball milling can promote the interaction between the ammonium salt and the positive electrode matrix material, allowing the ammonium salt to enter the grain boundary gaps of the positive electrode matrix material, thereby facilitating the reaction between the ammonium salt and the positive electrode matrix material.

[0030] In a possible implementation, the sintering temperature T1 satisfies: 400°C≤T1≤600°C; optionally, 400°C≤T1≤500°C.

[0031] In a possible implementation, the sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

[0032] The above sintering temperature and sintering time are used to facilitate the decomposition of the ammonium salt and the reaction of the decomposition products of the ammonium salt with the positive electrode matrix material and the miscellaneous lithium, and to facilitate the preparation of the first coating layer and the second coating layer.

[0033] In a possible implementation, the ammonium salt includes at least one of W, Mo or P elements; optionally, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate or ammonium dihydrogen phosphate. The W, Mo or P elements can react with the lithium element in the miscellaneous lithium to generate corresponding lithium-containing compounds, thereby forming a second coating layer. The above-mentioned ammonium salt includes W, Mo or P elements and has a suitable melting point, which is convenient for decomposition during the sintering process.

[0034] In one possible implementation, the preparation of the positive electrode matrix material includes: preparing a precursor of the positive electrode matrix material; mixing the precursor, a lithium salt, and a compound containing an M element and sintering them to prepare the positive electrode matrix material, wherein the M element includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr.

[0035] By mixing and sintering a precursor, a lithium salt and a compound containing the M element, a positive electrode matrix material containing the M element can be obtained, so that the positive electrode matrix material has a higher crystal structure stability.

[0036] In a possible implementation, the molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or the sintering temperature T2 satisfies: 650℃≤T2≤950℃; and / or the sintering time t3 satisfies: 10h≤t2≤20h.

[0037] In a possible implementation, based on the total mass of the precursor, the lithium salt, and the compound containing the element M, the mass content D of the compound containing the element M satisfies: 200 ppm≤D≤5000 ppm.

[0038] By reasonably setting the sintering temperature and time of the precursor, lithium salt and compound containing the M element, as well as the mass content of the compound containing the M element, it is beneficial to obtain a positive electrode matrix material uniformly doped with the M element.

[0039] In a possible implementation, the volume particle size distribution Dv502 of the precursor satisfies: 7 μm ≤ Dv502 ≤ 12 μm; optionally, 8 μm ≤ Dv502 ≤ 10 μm. This is conducive to obtaining a positive electrode active material with a suitable volume particle size distribution.

[0040] In a third aspect, a positive electrode plate is provided, comprising the positive electrode active material in the first aspect and any possible implementation thereof, and / or the positive electrode active material prepared by the method in the second aspect and any possible implementation thereof.

[0041] In a fourth aspect, a battery cell is provided, comprising the positive electrode plate described in the third aspect.

[0042] In a fifth aspect, a battery is provided, comprising the battery cell described in the fourth aspect.

[0043] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. 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 paying creative work.

[0045] Figure 1 A schematic diagram of a positive electrode active material according to an embodiment of the present application;

[0046] Figure 2 This is a SEM image of the positive electrode active material of one embodiment of the present application;

[0047] Figure 3 This is an ion milling cross-sectional view of a positive electrode active material according to an embodiment of the present application;

[0048] Figure 4 A schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application;

[0049] Figure 5 A schematic diagram of a battery cell according to an embodiment of the present application;

[0050] Figure 6 A schematic diagram of a battery according to an embodiment of the present application;

[0051] Figure 7 FIG. 1 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0052] The embodiments of the positive electrode active material and preparation method thereof, positive electrode sheet, battery cell, battery, and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually the same structure may be 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 descriptions 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.

[0053] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 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, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] 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.

[0056] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means 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.

[0057] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery, and the battery cell can be the smallest battery unit.

[0058] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, moved and embedded in the negative electrode material; while during the discharging process, lithium ions are released from the negative electrode material, moved and embedded in the positive electrode active material.

[0059] It should be understood that the "embedding" process described in this application refers to the process of lithium ions being embedded in the positive electrode active material and the negative electrode material due to electrochemical reactions, and the "extraction" and "de-embedding" processes described in this application refer to the process of lithium ions being extracted from the positive electrode active material and the negative electrode material due to electrochemical reactions.

[0060] The development of battery technology must consider many design factors at the same time, such as energy density, cycle life, discharge capacity, charge and discharge rate, reliability, etc. The battery cell includes a positive electrode plate. The performance of the positive electrode active material in the positive electrode plate is crucial to the capacity, cycle performance, and charge and discharge rate performance of the battery cell. In order to improve the performance of the positive electrode active material, a coating layer is usually set on the surface of the positive electrode base material to improve the corresponding performance of the battery cell. However, how to set the coating layer and what kind of coating layer to set to improve the performance of the battery cell is a technical problem that needs to be solved urgently.

[0061] In view of this, an embodiment of the present application provides a positive electrode active material, including a positive electrode matrix material, and a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode matrix material, wherein the concentration of lithium element in the first coating layer is lower than the concentration of lithium element in the positive electrode matrix material, and the second coating layer includes an ion conductor material, which is beneficial to improving the cycle performance of the battery cell.

[0062] [Positive electrode active material]

[0063] Figure 1 Schematic diagram of a positive electrode active material according to an embodiment of the present application. The present application embodiment provides a positive electrode active material 1, such as Figure 1 As shown, the positive electrode active material 1 includes a positive electrode base material 10 , and a first coating layer 11 and a second coating layer 12 sequentially coated on the surface of primary particles of the positive electrode base material 10 .

[0064] The positive electrode matrix material 10 may be a transition metal oxide with a layered structure, such as a ternary material, a lithium-rich manganese-based material, etc. During the charge and discharge process of the battery cell, the active lithium ions in the positive electrode matrix material 10 may be released from or embedded in the positive electrode matrix material 10, that is, the positive electrode matrix material 10 may be a material that provides active lithium ions.

[0065] exist Figure 1 Here, the positive electrode base material refers to the positive electrode base material of the primary particles.

[0066] Primary particles refer to unagglomerated particles, and secondary particles refer to particles after primary particles are agglomerated. In other words, a primary particle is an unagglomerated particle. The positive electrode active material is prepared from the precursor of the positive electrode matrix material. For example, for ternary materials, in the process of preparing the precursor, Ni, Co, and Mn metal ions form primary particles through specific reactions. These primary particles aggregate or agglomerate to form a nearly spherical precursor, and the precursor is the agglomerated secondary particle.

[0067] Figure 2 This is a SEM image of the positive electrode active material of one embodiment of the present application. Figure 3 This is a cross-sectional view of the ion milling of the positive electrode active material according to an embodiment of the present application. Figure 2 and Figure 3 As shown in the SEM image, the spherical large particles are secondary particles, and the secondary particles include multiple primary particles; in the ion milling cross-sectional image, it can be seen that the secondary particles include multiple primary particles; combined with Figure 1 As shown in FIG. 1 , in the positive electrode active material of the embodiment of the present application, the surface of the primary particle is provided with a first coating layer 11 and a second coating layer 12 .

[0068] The first coating layer 11 and the second coating layer 12 are sequentially coated on the surface of the primary particles of the positive electrode base material 10. It can also be said that in the primary particles of the positive electrode active material 1, from the outside to the inside, there are the second coating layer 12, the first coating layer 11 and the positive electrode base material 10.

[0069] In the case where a coating layer is provided on the surface of the secondary particles of the positive electrode matrix material 10, the secondary particles of the positive electrode active material 1 include secondary particles (formed by the agglomeration of a plurality of primary particles of the positive electrode matrix material) and a coating layer that covers the entire secondary particles. In this case, after the secondary particles are cracked, at least part of the surface of the positive electrode matrix material is not provided with a coating layer, and the surface of the positive electrode matrix material is in contact with the electrolyte in the battery cell, and side reactions are more likely to occur at the positive electrode interface, which is not conducive to the improvement of the performance of the battery cell. Compared with providing a coating layer on the surface of the secondary particles of the positive electrode matrix material 10, in the setting of the embodiment of the present application, the surface of the primary particles of the positive electrode active material 1 is provided with a first coating layer 11 and a second coating layer 12, and even after the secondary particles are cracked, the positive electrode matrix material 10 will not contact with the electrolyte or the risk of contacting with the electrolyte is greatly reduced, thereby suppressing the side reactions at the positive electrode interface, which is beneficial to reducing the impedance of the battery cell and improving the cycle performance of the battery cell.

[0070] The concentration of lithium in the first coating layer is lower than that in the positive electrode matrix material. Thus, there is a certain lithium concentration gradient between the positive electrode matrix material 10 and the first coating layer 11, which is conducive to the lithium ions in the positive electrode matrix material 10 being released from the positive electrode matrix material 10, thereby facilitating the increase of the content of active lithium ions in the battery cell, and further increasing the capacity of the battery cell.

[0071] The second cladding layer 12 includes an ion conductor material.

[0072] An ionic conductor is an ionic conductor in which electric current is generated by movable ion loads. Unlike conductors and semiconductors, its charge carriers are neither electrons nor holes, but movable ions. The ionic conductor material in the embodiments of the present application may refer to a fast ionic conductor material, which refers to a material with a high ion migration rate and can quickly transport ions.

[0073] The ion conductor material may be a compound formed by an oxide of one or more elements selected from the group consisting of Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, Bi, P, B, Si, N, S and lithium, or a mixture of the oxide and the compound thereof, for example, Li 3 PO 4 .

[0074] The ion conductor material has good ion transmission performance, which is beneficial to improve the transmission rate of lithium ions and improve the rate performance of the battery cell. In addition, the second coating layer 12 can also reduce the risk of direct contact between the positive electrode matrix material 10 and the electrolyte, which is beneficial to inhibit the side reaction between the positive electrode matrix material 10 and the electrolyte, and reduce the impedance of the solid-liquid interface at the positive electrode, thereby helping to improve the cycle performance of the battery cell.

[0075] The embodiment of the present application provides a positive electrode active material 1, the surface of the primary particles of the positive electrode base material 10 is coated with a first coating layer 11, and the concentration of lithium in the first coating layer 11 is less than the concentration of lithium in the positive electrode base material 10, so that there is a certain lithium concentration gradient between the positive electrode base material 10 and the first coating layer 11, which is conducive to the lithium ions in the positive electrode base material 10 to escape from the positive electrode base material 10, thereby facilitating the increase of the content of active lithium ions in the battery cell, and then improving the capacity of the battery cell. The first coating layer 11 and the second coating layer 12 are sequentially coated on the surface of the particles of the positive electrode base material 10, that is, the outer surface of the first coating layer 11 is coated with the second coating layer 12, and the second coating layer 12 includes an ion conductor material. The ion conductor material has good ion transmission performance, which is beneficial to improve the transmission rate of lithium ions and improve the rate performance of the battery cell; the second coating layer 12 is also beneficial to inhibit the side reaction between the positive electrode matrix material 10 and the electrolyte, and reduce the impedance of the solid-liquid interface at the positive electrode, which is beneficial to improve the cycle performance of the battery cell. Therefore, the positive electrode active material 1 of the embodiment of the present application has good performance and can improve the performance of the battery cell.

[0076] In some embodiments, the chemical formula of the positive electrode matrix material 10 is Li 1+a [Ni x Co y Mn z M b ]O 2 , wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1.

[0077] x can be 0.6, 0.7, 0.8, 0.9 or any value within the above range, y can be 0.1, 0.2, 0.3, 0.4 or any value within the above range, z can be 0.1, 0.2, 0.3, 0.4 or any value within the above range, b can be 0, 0.1 or any value within the above range, and a can be 0, 0.1, 0.2 or any value within the above range.

[0078] When x is greater than or equal to 0.6, the nickel content in the positive electrode matrix material is higher. Compared with the positive electrode matrix material with a lower nickel content (e.g., the material with x less than 0.6), the structure of such a high-nickel positive electrode matrix material is more unstable and more prone to side reactions. By providing the first coating layer 11 and the second coating layer 12 on the primary particles of such a high-nickel positive electrode matrix material, it is beneficial to improve the performance of the positive electrode active material 1, and improve the cycle performance and rate performance of the battery cell while making the battery cell have a higher energy density.

[0079] In addition, for the positive electrode matrix material with x greater than or equal to 0.6, the prepared positive electrode matrix material is mostly in the morphology of secondary particles. During the use of the battery cell, the secondary particles are prone to cracking. Therefore, it is more necessary to set the first coating layer and the second coating layer for the primary particles of the positive electrode matrix material with x greater than or equal to 0.6.

[0080] M can be a doping element. When b is 0, the positive electrode matrix material 10 can be a ternary material. For example, the positive electrode matrix material 10 is LiNi 0.6 Co 0.2 Mn 0.2 O 2 ,LiNi 0.8 Co 0.1 Mn 0.1 O 2 When b is greater than 0, the positive electrode matrix material 10 may be LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O 2 .

[0081] In some embodiments, the M element is uniformly or relatively uniformly doped in the positive electrode matrix material 10, which is conducive to making the performance of the positive electrode matrix material more stable. The uniform doping of the M element can be tested by EDS, for example, by observing whether the content of the M element in different regions is roughly the same to determine whether the M element is uniformly doped.

[0082] Optionally, the positive electrode matrix material 10 having the above chemical formula may be doped with elements such as F, S, P, N, B, etc., and these elements may occupy the position of O.

[0083] It should be noted that the battery cell will be accompanied by the deintercalation and consumption of Li during the charge and discharge process. The molar content of Li is different when the battery is discharged to different states. The above definition of a includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V). In the enumeration of positive electrode matrix materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode matrix material is used in the battery system. After the charge and discharge cycle, the molar content of Li will change. In the enumeration of positive electrode matrix materials in this application, the molar content of O is only a theoretical state value. The release of lattice oxygen will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0084] In this embodiment, the battery cell prepared by the positive electrode matrix material 10 of the above chemical formula has a higher energy density. When the positive electrode matrix material 10 satisfies the above chemical formula, the first coating layer 11 is conducive to the deintercalation of lithium ions from the positive electrode matrix material 10; the second coating layer 12 is conducive to inhibiting the dissolution of transition metal ions in the positive electrode matrix material 10 and the side reaction between the positive electrode matrix material 10 and the electrolyte, so that the positive electrode active material 1 has better crystal structure stability, retains higher active ions and has better storage performance, and thus the battery cell has higher cycle stability and capacity.

[0085] In some embodiments, 0.8≤x<1. For example, x is 0.9175. In this way, the content of nickel in the positive electrode matrix material 10 is relatively high, so that the positive electrode active material 1 has a higher gram capacity while having better stability.

[0086] In some embodiments, 0≤x<0.6, for example, the positive electrode matrix material 10 is LiNi 0.3 Co 0.4 Mn 0.3 O 2 That is to say, the positive electrode base material 10 may also be a material with a slightly lower nickel content.

[0087] In some embodiments, M includes at least one of Ti, Nb, Te, V, or Ta.

[0088] By doping the positive electrode matrix material 10 with the M element, the crystal structure stability of the positive electrode matrix material 10 can be improved, and the reversibility of the layered structure of the positive electrode matrix material 10 during lithium insertion and extraction can be improved, thereby improving the electrochemical performance of the positive electrode active material 1. In addition, the M element can form ions with a higher valence state. According to the defect chemistry theory, high-valence ion doping will generate lithium vacancies inside the material, which is conducive to promoting the transmission of lithium ions inside the positive electrode matrix material 10.

[0089] In some embodiments, the ion conductor material includes a compound formed by Li element and at least one of W, Mo or P element.

[0090] Due to preparation and other reasons, there may be miscellaneous lithium (also referred to as residual lithium), such as lithium carbonate, on the surface of the positive electrode matrix material 10. W, Mo or P elements can react with miscellaneous lithium to generate a compound formed by Li element and at least one of W, Mo or P elements. In this way, miscellaneous lithium can be consumed and corresponding compounds can be generated, and the generated compounds have good ion transmission performance and conductivity, which is beneficial to improving the rate performance of the battery cell and reducing the internal resistance of the battery cell.

[0091] Optionally, the ion conductor material includes Li 2 WO4 , Li 2 MoO 4 or Li 3 PO 4 At least one of the above. The ion conductor material includes the above compound, which is beneficial to reducing the impedance at the positive electrode interface and the internal resistance of the battery cell on the one hand; on the other hand, the arrangement of the above compound is beneficial to the transmission of lithium ions and is beneficial to improving the rate performance of the battery cell.

[0092] In some embodiments, the material of the first coating layer 11 includes a transition metal oxide, and the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode base material 10. That is, the first coating layer 11 can be formed by a certain treatment of the positive electrode base material 10, and the lithium vacancies in the first coating layer 11 are more than the lithium vacancies in the positive electrode base material 10, which is conducive to the deintercalation of lithium ions in the positive electrode base material 10.

[0093] In some embodiments, the thickness d1 of the first cladding layer 11 satisfies: 1 nm≤d1≤5 nm.

[0094] d1 can be 1 nm, 2 nm, 3 nm, 5 nm or any value within the above range.

[0095] When d1 is not less than 1 nm, there is a suitable lithium concentration gradient between the first coating layer 11 and the positive electrode matrix material 10, which facilitates the deintercalation of lithium ions from the positive electrode matrix material 10; when d1 is not more than 5 nm, lithium ions have a transmission path of suitable length.

[0096] In this way, by setting 1nm≤d1≤5nm, lithium ions have a transmission path of appropriate length, and there is an appropriate lithium concentration gradient between the first coating layer 11 and the positive electrode substrate 10, which is beneficial to improving the capacity of the battery cell.

[0097] Optionally, 1nm≤d1≤2nm. In this way, the battery cell has a higher rate performance.

[0098] In some embodiments, the thickness d2 of the second cladding layer 12 satisfies: d2≤20 nm.

[0099] d2 can be 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm or any value within the above range.

[0100] When d2 does not exceed 20nm, lithium ions have a transmission path of appropriate length, which is beneficial to improving the capacity of the battery cell.

[0101] When d2 is not less than 1 nm, the second coating layer 12 can play a certain protective role, inhibiting the side reaction between the positive electrode matrix material 10 and the electrolyte, which is beneficial to improving the cycle performance of the battery cell.

[0102] Optionally, 4nm≤d2≤10nm, and the battery cell has both higher capacity and cycle performance.

[0103] In some embodiments, based on the total mass of the positive electrode active material 1 , the mass content B of the second coating layer 12 satisfies: 1000 ppm≤B≤3000 ppm; alternatively, 1000 ppm≤B≤2000 ppm.

[0104] B can be 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm or any value within the above range.

[0105] In this way, the second coating layer 12 has an appropriate mass ratio, so that the second coating layer 12 can have an appropriate thickness.

[0106] In some embodiments, the volume particle size distribution of the positive electrode active material 1 satisfies: (D v 901-D v 101) / D v 501≥1.2; Optionally, (D v 901-D v 101) / D v 501≥1.3.

[0107] D v 10 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 10%, or it can refer to that the particles smaller than it account for 10%.

[0108] D v 50 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 50%, or it can refer to the particle size smaller than it accounting for 50%. v 501 is to match the D below v 502 is used to distinguish and represent the volume average particle size of different materials.

[0109] D v 90 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 90%, which can mean that the particles with a particle size smaller than it account for 90%. v 901, D v 101 is used to represent the D of the positive electrode active material 1 v 90.D v 10.

[0110] In this way, the positive electrode active material 1 contains both appropriate amounts of larger particles and appropriate amounts of smaller particles. The positive electrode active material 1 has a wider distribution of particle sizes, which is beneficial to improving the powder compaction density of the positive electrode active material 1, thereby helping to improve the volume energy density of the battery cell.

[0111] In some embodiments, the volume particle size distribution Dv501 of the positive electrode active material 1 satisfies: 7 μm ≤ Dv501 ≤ 12 μm; alternatively, 8 μm ≤ Dv501 ≤ 10 μm. In this way, lithium ions have a path of appropriate length when being deintercalated from the positive electrode active material 1, and the battery cell can have higher capacity and cycle performance.

[0112] It should be noted that Dv501 and Dv502 in the embodiments of the present application both represent the volume average particle size of the material, wherein the "1" in Dv501 and the "2" in Dv502 are used to distinguish the volume average particle sizes of different materials. Similarly, the "1" in Dv901 and Dv101 and the "2" in Dv502 are used to distinguish the volume average particle sizes of different materials.

[0113] In some embodiments, the positive electrode active material 1 is a material obtained by reacting the secondary particles of the positive electrode base material 10 with an ammonium salt. During the reaction, the ammonium salt and its decomposition products can penetrate into the grain boundaries of the positive electrode base material 10, thereby forming a first coating layer 11 and a second coating layer 12 on the surface of the primary particles of the positive electrode base material 10.

[0114] In some embodiments, the first coating layer 11 includes a spinel structured material having lithium vacancies.

[0115] The spinel structure may refer to the crystal structure of a material. The spinel structured material has a three-dimensional lithium ion transmission channel, which is beneficial to increase the transmission rate of lithium ions, thereby improving the rate performance of the battery cell.

[0116] The positive electrode matrix material 10 can react with the ammonium salt, and the product of the thermal decomposition of the ammonium salt can react with the lithium oxide (such as Li 2 O) and residual lithium on the surface, thereby generating lithium vacancies on the surface of the positive electrode matrix material, and the surface of the positive electrode matrix material changes from a layered structure to a spinel structure, thereby generating a first coating layer including a material having a spinel structure. Taking ammonium tungstate as an example, the generation of lithium vacancies is as follows: ammonium tungstate decomposes under heat to produce NH 3 and WO 3 , NH 3 and WO 3 React with the surface of the positive electrode substrate 10, WO 3 The Li 2O and residual lithium on the surface react to produce lithium vacancies on the surface of the positive electrode matrix material, and then transform from a layered structure to a spinel structure, generating the first coating layer of the spinel phase and Li 2 WO 3 Second coating layer.

[0117] Combination of the above Figure 1-3 The positive electrode active material is described below. Figure 4 The preparation method of the positive electrode active material is described below. The parts of the preparation method corresponding to or similar to the product of the positive electrode active material can be referred to the above description and will not be repeated hereinafter.

[0118] [Method for preparing positive electrode active material]

[0119] Figure 4 FIG. 1 is a schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application. Figure 4 As shown, the embodiment of the present application provides a method 200 for preparing a positive electrode active material, comprising the following steps. The method 200 can be used to prepare the positive electrode active material 1 in any of the above embodiments.

[0120] Step 210 , preparing a positive electrode base material 10 .

[0121] The positive electrode matrix material 10 may be a layered lithium-containing transition metal oxide, such as a ternary material.

[0122] Step 220 , preparing a first coating layer 11 and a second coating layer 12 on the surface of the primary particles of the positive electrode base material 10 to obtain a positive electrode active material.

[0123] For example, in step 220, the first coating layer 11 is obtained by acid etching and sintering, and then the second coating layer 12 is obtained by mixing with an ion conductor material and sintering.

[0124] In some embodiments, step 220 includes: mixing the positive electrode matrix material 10 and the ammonium salt and sintering them in an inert atmosphere to obtain the positive electrode active material 1 .

[0125] The inert atmosphere may be a nitrogen atmosphere or an argon atmosphere. Sintering in an inert atmosphere facilitates the formation of the first coating layer 11 .

[0126] The positive electrode base material 10 can react with the ammonium salt to form a first coating layer 11 on the surface of the positive electrode base material 10, and the compound generated by the decomposition of the ammonium salt can react with the miscellaneous lithium on the surface of the positive electrode base material 10, and the second coating layer 12 is generated while consuming the miscellaneous lithium. Therefore, the positive electrode active material 1 of the embodiment of the present application can be prepared by the reaction of the positive electrode base material 10 with the ammonium salt. In addition, the method is relatively simple, and the first coating layer 11 and the second coating layer 12 can be formed with fewer sintering times.

[0127] In some embodiments, the positive electrode matrix material 10 and the ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material 1, including: placing the positive electrode matrix material 10 and the ammonium salt in a high-energy ball mill for mixing; placing the mixed positive electrode matrix material 10 and the ammonium salt in an inert atmosphere for sintering to obtain the positive electrode active material 1.

[0128] During the ball milling and sintering process in the high-temperature ball mill, the ammonium salt can melt and penetrate into the grain boundaries of the positive electrode matrix material 10, so that the ammonium salt can fully contact the surface of the primary particles of the positive electrode matrix material 10; the ball milling process is conducive to the mixing of the ammonium salt and the positive electrode matrix material 10, and is conducive to uniformly distributing the ammonium salt on the surface and grain boundaries of the primary particles of the positive electrode matrix material 10. During the sintering process, the ammonia generated by the decomposition of the ammonium salt reacts with the positive electrode matrix material 10 to generate a spinel structure material with lithium vacancies, thereby forming a first coating layer 11; in addition, the compound generated by the decomposition of the ammonium salt reacts with the miscellaneous lithium on the surface of the positive electrode matrix material 10, and while consuming the miscellaneous lithium, a second coating layer 12 is generated.

[0129] In some embodiments, the rotation speed V of the high energy ball mill satisfies: 500rpm≤V≤1400rpm; optionally, 800rpm≤V≤1200rpm.

[0130] V can be 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm or any value within the above range.

[0131] In some embodiments, the ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

[0132] t1 can be 0.5h, 1h, 2h, 3h or any value within the above range.

[0133] At the above rotation speed and / or ball milling time, the energy generated by high-energy ball milling can promote the interaction between the ammonium salt and the positive electrode matrix material 10, allowing the ammonium salt to enter the grain boundary gaps of the positive electrode matrix material 10, thereby facilitating the reaction between the ammonium salt and the positive electrode matrix material 10.

[0134] In some embodiments, the sintering temperature T1 satisfies: 400°C≤T1≤600°C; optionally, 400°C≤T1≤500°C.

[0135] T1 can be 400°C, 500°C, 600°C or any value within the above range.

[0136] When the temperature T1 is not less than 400°C, the risk of the positive electrode matrix material 10 being difficult to react with the ammonium salt due to too low a temperature can be reduced; when the temperature T1 is not more than 600°C, the risk of more oxygen vacancies being formed inside the positive electrode matrix material 10 due to too high a temperature can be reduced, thereby reducing the risk of deteriorating the performance of the positive electrode active material 1 and the performance of the battery cell.

[0137] In some embodiments, the sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

[0138] t2 can be 4h, 5h, 6h, 8h, 10h or any value within the above range.

[0139] When the time t1 is not less than 4 hours, the risk of insufficient reaction between the positive electrode matrix material 10 and the ammonium salt due to too short a time can be reduced; when the time t1 is not more than 6 hours, the risk of more oxygen vacancies forming inside the positive electrode matrix material 10 due to too long a time can be reduced.

[0140] The above sintering temperature and sintering time are used to facilitate the decomposition of the ammonium salt and the reaction of the decomposition products of the ammonium salt with the positive electrode matrix material 10 and the impurity lithium, and to facilitate the preparation of the first coating layer 11 and the second coating layer 12 .

[0141] In some embodiments, the ammonium salt includes at least one of W, Mo, or P. W, Mo, or P can react with the lithium element in the miscellaneous lithium to generate a corresponding lithium-containing compound, thereby forming the second coating layer 12 .

[0142] In some embodiments, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate. The ammonium salt includes W, Mo, or P elements and has a suitable melting point to facilitate decomposition during sintering.

[0143] In some embodiments, step 210 includes: preparing a precursor of the positive electrode matrix material 10; mixing the precursor, a lithium salt, and a compound containing an element M and sintering them to prepare the positive electrode matrix material 10, wherein the element M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr.

[0144] As an example, the positive electrode matrix material 10 is a ternary material, and the chemical formula of the precursor of the positive electrode matrix material 10 is [Ni x Co y Mn z ](OH) 2 , wherein 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4. Optionally, 0.8≤x<1.

[0145] Precursors, lithium salts, and compounds containing M elements can be heated in air or in an atmosphere of oxygen. 2 The sintering is carried out in an atmosphere, and the lithium salt can be at least one of lithium carbonate or lithium hydroxide.

[0146] As an example, the mixing can be performed specifically by the following operation: the precursor, the lithium salt and the compound containing the M element are added into a plowshare mixer, a high speed mixer or an inclined mixer in a certain proportion for mixing, and then sintered in an air atmosphere.

[0147] As an example, the positive electrode matrix material 10 is a ternary material, and the precursor of the positive electrode matrix material 10 can be prepared by the following steps. (1) Synthesizing seed crystals: according to the molar ratio of nickel, cobalt and manganese in the ternary material, a mixed metal solution of nickel salt, cobalt salt and manganese salt with a concentration of 0.5-2.5 mol / L is prepared; a 1-10 mol / L NaOH alkaline solution is prepared, and an ammonia solution with a concentration of 2-14 mol / L is prepared, and 10%-50% pure water is added to a 100L reactor, stirring is started, and a constant temperature of 40-75°C is maintained, and a certain amount of NaOH solution is added to a pH of 11.5-12.5, and can be 11.8-12.2, and a certain amount of ammonia solution is added to an ammonia concentration of 0.2-0.6 mol / L, and can be 0.3-0.5 mol / L. The prepared nickel-cobalt-manganese mixed metal solution, NaOH alkaline solution and ammonia solution were added to the reactor at a certain flow rate, and the ammonia concentration and pH in the reactor were kept constant. The volume particle size distribution D was synthesized by continuous reaction. v 50 is a seed slurry product of 1 to 5 μm. (2) Synthesizing a precursor: Add 10% to 50% pure water to a 100L reactor, add 1 to 20 kg of the seed core slurry synthesized in step (1), start stirring, maintain a constant temperature of 40 to 75°C, add NaOH solution to a pH of 11.0 to 12.0, optionally 11.1 to 11.7, add a certain amount of ammonia solution to an ammonia concentration of 0.2 to 0.6 mol / L, optionally 0.3 to 0.5 mol / L. Add the nickel-cobalt-manganese mixed metal solution, NaOH alkaline solution, ammonia solution and the seed slurry synthesized in step (1) to the reactor at a certain flow rate, keep the ammonia concentration and pH in the reactor unchanged, and continuously react to synthesize a slurry product with a certain volume particle size distribution. Then centrifuge the product slurry, wash, filter and dry to obtain a precursor.

[0148] In this embodiment, the positive electrode base material 10 containing the M element can be obtained by mixing and sintering the precursor, the lithium salt and the compound containing the M element, so that the positive electrode base material 10 has a higher crystal structure stability.

[0149] In some embodiments, the molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or, the sintering temperature T2 satisfies: 650℃≤T2≤950℃; and / or, the sintering time t3 satisfies: 10h≤t2≤20h.

[0150] The metal elements in the precursor include nickel, cobalt and manganese. C is the ratio of the molar number of lithium salt to the total molar number of nickel, cobalt and manganese elements.

[0151] C can be 0.95, 1, 1.15 or any value within the above range. T2 can be 650°C, 800°C, 950°C or any value within the above range. t3 can be 10h, 15h, 20h or any value within the above range.

[0152] In some embodiments, based on the total mass of the precursor, the lithium salt, and the compound containing the element M, the mass content D of the compound containing the element M satisfies: 200 ppm≤D≤5000 ppm. For example, D is 200 ppm, 1000 ppm, 3000 ppm, 5000 ppm, or any value within the above range.

[0153] By properly setting the sintering temperature and time of the precursor, lithium salt and compound containing element M, as well as the mass content of the compound containing element M, it is advantageous to obtain a positive electrode matrix material 10 uniformly doped with element M. The positive electrode matrix material 10 uniformly doped with element M has higher stability.

[0154] In some embodiments, the volume particle size distribution Dv502 of the precursor satisfies: 7 μm ≤ Dv502 ≤ 12 μm; alternatively, 8 μm ≤ Dv502 ≤ 10 μm. This is conducive to obtaining a positive electrode active material 1 with a suitable volume particle size distribution.

[0155] Dv502 can be 7μm, 8μm, 10μm, 12μm or any value within the above range.

[0156] [Positive electrode]

[0157] An embodiment of the present application provides a positive electrode plate, comprising the positive electrode active material in any of the above embodiments, and / or the positive electrode active material prepared by the preparation method in any of the above embodiments.

[0158] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0159] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector may be an aluminum foil.

[0160] The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0161] The positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0162] The positive electrode film layer may also optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0163] [Negative electrode]

[0164] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0165] The negative electrode current collector may be a metal foil or a composite current collector. The negative electrode current collector may be a copper foil. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0167] The negative electrode film layer may also optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0168] [Electrolytes]

[0169] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application embodiment has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0170] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0171] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorobisoxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0172] The solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0173] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high temperature or low temperature performance, etc.

[0174] [Isolator]

[0175] The separator is used to separate the positive electrode sheet from the negative electrode sheet. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0176] 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.

[0177] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0178] [Battery Cell]

[0179] An embodiment of the present application provides a battery cell, comprising the positive electrode plate in the above embodiment.

[0180] The embodiment of the present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. The battery cell may be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc.

[0181] Figure 5 FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application. Figure 5 As shown, the battery cell 3 includes a shell 31 , an end cover assembly 32 and an electrode assembly 33 . The electrode assembly 33 is disposed in the shell 31 , and the end cover assembly 32 is used to cover the shell 31 .

[0182] The end cap assembly 32 includes an electrode terminal 322, such as Figure 5 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0183] The electrode assembly 33 includes an electrode assembly body 331 and a tab 332 extending from the electrode assembly body 331 . The electrode assembly 33 can be made of a positive electrode sheet, a negative electrode sheet and a separator by a winding process or a lamination process.

[0184] The battery cell 3 further includes a current collecting member 34, which is used to connect the electrode tab 332 of the electrode assembly 33 and the electrode terminal 322. Figure 3 As shown, the battery cell 3 includes two current collecting members 34 , one current collecting member 34 is used to connect the positive electrode tab and the positive electrode terminal, and the other current collecting member 34 is used to connect the negative electrode tab and the negative electrode terminal.

[0185] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0186] [Battery]

[0187] An embodiment of the present application provides a battery, comprising the battery cell in the above embodiment. Figure 6 Schematic diagram of a battery according to an embodiment of the present application. Figure 6 As shown, the battery 5 may include a plurality of battery cells (not shown in the figure).

[0188] The battery cells 3 can directly form the battery 5 , or can first form a battery module, and then multiple battery modules form the battery 5 .

[0189] [Electrical devices]

[0190] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0191] Figure 7 FIG. 1 is a schematic diagram of an electrical device according to an embodiment of the present application. Figure 7 As shown, the present application provides an electrical device 6, including the battery in the above embodiment.

[0192] Optionally, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc. The embodiments of the present application include but are not limited to these.

[0193] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0194] [Example]

[0195] Example 1

[0196] The positive electrode active material in Example 1 was prepared by the following steps.

[0197] (1) Synthesis of precursors for positive electrode matrix materials

[0198] In the precursor of the positive electrode matrix material, the molar ratio of the three elements of nickel, cobalt and manganese is 92:7:1, the volume particle size distribution Dv502 of the precursor is 8.5μm, and the volume particle size distribution (D v 902-D v 102) / D v 502 is 1.35.

[0199] (2) Synthesis of positive electrode active materials

[0200] S1: Lithium salt, Nb 2 O 5 、ZrO 2 The above precursors are mixed in a plowshare mixer according to a certain ratio, the Li / Me molar ratio is 1.05 (Me is the total molar number of the three elements of nickel, cobalt and manganese), the Nb doping amount is 500ppm, the Zr doping amount is 2000ppm, and the mixed material is sintered in a kiln, the sintering temperature T2 is 750℃, the sintering time t3 is 20h, and the sintering atmosphere is O 2 , and sintering to obtain a positive electrode matrix material uniformly doped with Nb and Zr. The doping amount of Nb and Zr is the doping amount of Nb element and Zr element based on the total weight of the positive electrode matrix material.

[0201] S2: The positive electrode matrix material and ammonium molybdate are mixed in a high-energy ball mill, the ball milling speed V is 1000 rpm, the ball milling time t1 is 2 h, the amount of Mo element added is 2000 ppm, the mixed material is sintered in a kiln, the sintering temperature T1 is 400 ° C, the sintering time t2 is 6 h, and the sintering atmosphere is N 2 , sintering to obtain primary particles of positive electrode active material, the first coating layer includes a spinel structure material with lithium vacancies, and the second coating layer includes Li 2 MoO 4 The doping amount of the Mo element is based on the total weight of the positive electrode base material.

[0202] In Example 1, the positive electrode matrix material is LiNi 0.92 Co 0.07 Mn 0.01 O 2 The thickness d1 of the first coating layer is 2 nm, the thickness d2 of the second coating layer is 6 nm, and the mass content B of the second coating layer is 2000 ppm. The volume particle size distribution Dv501 of the positive electrode active material is 8.7 μm, (D v 901-D v 101) / D v 501 is 1.35.

[0203] Example 2

[0204] The difference between Example 2 and Example 1 is that the added amount of Mo element is 1000 ppm. Accordingly, in the prepared positive electrode active material, the thickness d2 of the second coating layer is 4 nm.

[0205] Example 3

[0206] The difference between Example 3 and Example 1 is that in step S2, the amount of Mo element added is 3000 ppm.

[0207] In the prepared positive electrode active material, the thickness d2 of the second coating layer was 9 nm, and the mass content B of the second coating layer was 3000 ppm.

[0208] Example 4

[0209] The difference between Example 4 and Example 1 is that the added amount of Mo element is 5000 ppm. Accordingly, in the prepared positive electrode active material, the thickness d1 of the first coating layer is 5 nm, and the thickness d2 of the second coating layer is 20 nm.

[0210] Example 5

[0211] The difference between Example 5 and Example 1 is that in step S2, the ammonium salt is ammonium metatungstate. Accordingly, the sintering temperature T1 is 500°C.

[0212] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 5 nm, the mass content B of the second coating layer is 2000 ppm, and the second coating layer includes Li 2 WO 4 .

[0213] Example 6

[0214] The difference between Example 6 and Example 1 is that in step S2, the ammonium salt is ammonium phosphate, the amount of P element added is 2500 ppm, and accordingly, the sintering temperature T1 is 400°C.

[0215] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 4.5 nm, the mass content B of the second coating layer is 2500 ppm, and the second coating layer includes Li 3 PO 4 .

[0216] Example 7

[0217] The difference between Example 7 and Example 1 is that in step S2, ammonium metatungstate is additionally added, and the amount of W element added is 1000 ppm. Accordingly, the sintering temperature T1 is 450°C.

[0218] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 10 nm, the mass content B of the second coating layer is 3000 ppm, and the second coating layer includes Li 2 MoO 4 and Li 2 WO 4 .

[0219] Example 8

[0220] The difference between Example 8 and Example 1 is that in step S2, the ammonium salt is ammonium molybdate and diammonium phosphate, the added amount of Mo element is 1000 ppm, and the added amount of P element is 1000 ppm. Accordingly, the sintering temperature T1 is 450°C.

[0221] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 8.5 nm, the mass content B of the second coating layer is 3000 ppm, and the second coating layer includes Li 2 MoO 4 and Li 3 PO 4 .

[0222] Examples 9-10

[0223] The difference between Examples 9-10 and Example 1 is that the volume particle size distribution (D v 901-D v 101) / D v 501 is different.

[0224] In Examples 1-10, the positive electrode matrix material is the same. In the process of preparing the positive electrode active material, the sintering time t2 is 6 hours, the ball milling speed is 1000 rpm, and the ball milling time t1 is 2 hours.

[0225] Embodiment 11

[0226] The difference between Example 11 and Example 1 is that: Nb in step S1 is 2 O 5 Replace with Ta 2 O 5 , the Ta doping amount is 500ppm.

[0227] Example 12

[0228] The difference between Example 12 and Example 1 is that the ZrO 2 Replaced with TiO 2 , the doping amount of Ti is 1000ppm.

[0229] Example 13

[0230] The difference between Example 13 and Example 1 is that SrCO is added in step S1. 3 , the Sr doping amount is 1000ppm and the sintering temperature T2 is 730℃.

[0231] Embodiment 14

[0232] The difference between Example 14 and Example 1 is that Nb is not added in step S1. 2 O5 、ZrO 2 .

[0233] Embodiment 15

[0234] The difference between Example 15 and Example 1 is that: Nb in step S1 is 2 O 5 Replaced with TiO 2 , the doping amount of Ti is 750ppm. In step S2, the ammonium molybdate is replaced with ammonium phosphate, and the added amount of P element is 2500ppm.

[0235] In Examples 11-15, the positive electrode matrix materials are different; in the preparation process of the positive electrode active material, the sintering temperature T1 is 400°C, the sintering time t2 is 6h, the ball milling speed is 1000rpm, and the ball milling time t1 is 2h; the positive electrode active material (D v 901-D v 101) / D v Same as 501.

[0236] Examples 16-19

[0237] The difference between Examples 16 to 19 and Example 1 is that the volume average particle size Dv501 of the positive electrode active material is different.

[0238] Examples 20-21

[0239] The difference between Example 20-21 and Example 1 is that the reaction temperature and time of the ammonium salt and the precursor are different.

[0240] Comparative Example 1

[0241] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material in Comparative Example 1 is a positive electrode matrix material and does not include a coating layer.

[0242] Comparative Example 2

[0243] The difference between Comparative Example 2 and Example 1 is that in step S2, the positive electrode matrix material uniformly doped with Nb and Zr is mixed with Li 2 MoO 4 The mixed materials are put into a high-energy ball mill for mixing, and the mixed materials are put into a kiln for sintering. The sintering atmosphere is O 2 , sintered to obtain Li 2 MoO 4 The coated high-nickel ternary positive electrode material, excluding the first coating layer, is the same as in Example 1.

[0244] Table 1 Experimental parameters of Examples 1-19 and Comparative Examples 1-2

[0245]

[0246]

[0247] Table 2 Experimental parameters of Examples 20-21

[0248]

[0249] Table 3 Performance test results of embodiments and comparative examples

[0250]

[0251] [Preparation of battery cells]

[0252] (1) Preparation of positive electrode sheets: The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent (acetylene black) are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 94:3:3, and the mixture is stirred and mixed thoroughly to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain positive electrode sheets.

[0253] (2) Preparation of negative electrode sheets: artificial graphite and hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 90:5:2:2:1, and the mixture is stirred thoroughly to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0254] (3) Isolation film: polyethylene film is used.

[0255] (4) Preparation of lithium-ion battery cells: stack and wind the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order to obtain an electrode assembly; place the electrode assembly in an outer package, add an electrolyte solution whose electrolyte salt is lithium hexafluorophosphate, and obtain a lithium-ion battery cell after packaging, standing, forming, aging, and other processes.

[0256] [Preparation of button cell]

[0257] The positive electrode active material, PVDF and conductive carbon are added to a certain amount of NMP in a ratio of 90:5:5, stirred in a drying room to form a slurry, coated on aluminum foil, dried and cold pressed to form a positive electrode sheet; a lithium sheet is used as the negative electrode, and the electrolyte salt in the electrolyte is LiPF 6 The solvent is EC, DEC and DMC in a volume ratio of 1:1:1, the concentration of the electrolyte salt is 1 mol / L, and the button battery is assembled in a button box.

[0258] It should be noted that the mass content of the first coating layer and the second coating layer in the positive electrode active material in the embodiments of the present application, the volume average particle size of the positive electrode active material, the cycle performance of the battery cell, etc. are common knowledge in the art, have meanings known in the art, and can be measured by test methods and instruments known in the art.

[0259] [Testing of the first and second coating layers]

[0260] The positive electrode active material particles are placed in the conventional mode, HAADF mode or ABF mode of the transmission electron microscope for observation. Using EDS element surface distribution, it can be observed that one or more elements of W, Mo, P are concentrated in the grain boundaries of the positive electrode active material particles, thereby determining the second coating layer and the material of the second coating layer.

[0261] By using HAADF-STEM to observe the surface of the primary particles of the positive electrode active material and performing Fourier transform on them, the spinel phase can be observed on the surface of the primary particles, thereby determining the first coating layer. In addition, the thickness of the first coating layer and the second coating layer can also be observed.

[0262] XPS is used to characterize the relative content of each element in the positive electrode matrix material and the first coating layer, and then the concentration of Li is calculated, so that the concentration of lithium in the positive electrode matrix material and the first coating layer can be obtained.

[0263] [Button cell initial gram capacity test]

[0264] At 2.8-4.3V, charge to 4.3V at 0.1C, then charge at constant voltage at 4.3V to a current ≤ 0.05mA, let stand for 2min, the charging capacity at this time is recorded as C0, then discharge to 2.8V at 0.1C, the discharge capacity at this time is the initial gram capacity, recorded as D0, the first efficiency is D0 / C0×100%.

[0265] The higher the first efficiency, the more lithium ions can be reversibly deintercalated. In the later stage of discharge, due to the reduction of lithium vacancies in the positive electrode active material, the lithium ions diffuse slowly inside the positive electrode active material particles, making it difficult to intercalate lithium. By constructing the first coating layer on the surface of the positive electrode active material, the diffusion of lithium ions can be promoted and the first efficiency of the material can be improved.

[0266] [Lithium-ion battery monomer initial gram capacity test]

[0267] Under the constant temperature environment of 25℃, let it stand for 5min, discharge to 2.8V at 1 / 3C, let it stand for 5min, charge to 4.25V at 1 / 3C, then charge at constant voltage at 4.25V to current ≤0.05mA, let it stand for 5min, the charging capacity at this time is recorded as C0, then discharge to 2.8V at 1 / 3C, the discharge capacity at this time is the initial gram capacity, recorded as D0, the first efficiency is D0 / C0*100%.

[0268] [25 / 45℃ Cycle Performance Test of Lithium-ion Battery Cells]

[0269] At a constant temperature of 25℃ or 45℃, charge at 0.5C to 4.25V at 2.8~4.25V, then charge at a constant voltage at 4.25V until the current is ≤0.05mA, let stand for 5min, then discharge at 0.5C to 2.8V, the capacity is recorded as D n (n=0, 1, 2...), repeat the previous process for 500 times.

[0270] [DC internal resistance of lithium-ion battery cells]

[0271] Under a constant temperature environment of 25℃, charge to 4.25V at 1 / 3C at 2.8-4.25V, then charge at constant voltage at 4.25V to a current ≤0.05mA. After standing for 30min, discharge to 20% SOC at 1 / 3C. After standing for 60min, discharge at 4C for 30s. After standing for 30min, charge at 4C for 30s to obtain the DCR at 20% SOC.

[0272] As shown in the embodiment and comparative examples 1-2, by setting the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode matrix material, it is beneficial to improve the cycle performance of the battery cell. After a certain number of cycles, the battery cell prepared by the positive electrode active material of the embodiment of the present application has a higher capacity retention rate. In addition, in combination with the embodiment and comparative example 1, the setting of the first coating layer in the embodiment of the present application can improve the first efficiency of the battery cell. In combination with the embodiment and comparative examples 1-2, the battery cell prepared by the positive electrode active material of the embodiment of the present application has a smaller DC internal resistance.

[0273] As shown in Examples 1-4, in the process of preparing the positive electrode active material, different contents of ammonium salt are added to prepare the first coating layer and the second coating layer of different thicknesses. The more ammonium salt is added, the easier it is to obtain the first coating layer and the second coating layer of greater thickness.

[0274] As shown in Examples 5-6, various types of ammonium salts can be used in the embodiments of the present application; as shown in Examples 7-8, various ammonium salts can also be mixed and added to prepare the positive electrode active material.

[0275] As shown in Examples 9-10, when the volume particle size distribution of the positive electrode active material satisfies (Dv90-Dv10) / Dv50 in the range of 1.2 to 1.35, it is beneficial to make the powder of the positive electrode active material have a higher compaction density (not shown in the table), and the compaction density can reach 3.5 g / cm 3 .

[0276] As shown in Examples 11-13 and 15, a variety of different M elements can be doped into the positive electrode matrix material to improve the corresponding performance of the positive electrode matrix material; as shown in Example 14, the M element may not be added to the positive electrode matrix material.

[0277] As shown in Examples 16-19, the volume average particle size of the positive electrode active material is in the range of 7 μm-12 μm, and the battery cell has a good capacity retention rate.

[0278] As shown in Examples 20-21, by setting the reaction temperature of the ammonium salt and the positive electrode matrix material in the range of 400°C-600°C and the reaction time in the range of 4h-6h, the first coating layer and the second coating layer are easily prepared.

[0279] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, It is characterized in that include: A positive electrode base material, a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode base material; The concentration of lithium in the first coating layer is lower than the concentration of lithium in the positive electrode matrix material, and the second coating layer includes an ion conductor material.

2. The positive electrode active material according to claim 1, It is characterized in that The chemical formula of the positive electrode matrix material is Li 1+a [Ni x Co y Mn z M b ]O 2 , wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1; optionally, 0.8≤x<1; optionally, M includes at least one of Ti, Nb, Te, V or Ta.

3. The positive electrode active material according to claim 1 or 2, It is characterized in that The ion conductor material includes a compound formed by Li element and at least one of W, Mo or P element; optionally, the ion conductor material includes Li 2 WO 4 , Li 2 MoO 4 or Li 3 PO 4 At least one of .

4. The positive electrode active material according to any one of claims 1 to 3, It is characterized in that The material of the first coating layer includes a transition metal oxide, and the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode matrix material.

5. The positive electrode active material according to any one of claims 1 to 4, It is characterized in that The thickness d1 of the first coating layer satisfies: 1nm≤d1≤5nm; optionally, 1nm≤d1≤2nm.

6. The positive electrode active material according to any one of claims 1 to 5, It is characterized in that The thickness d2 of the second coating layer satisfies: d2≤20nm; optionally, 4nm≤d2≤10nm.

7. The positive electrode active material according to any one of claims 1 to 6, It is characterized in that The ratio B of the mass of the second coating layer to the mass of the positive electrode matrix material satisfies: 1000ppm≤B≤3000ppm; optionally, 1000ppm≤B≤2000ppm.

8. The positive electrode active material according to any one of claims 1 to 7, It is characterized in that The volume particle size distribution of the positive electrode active material satisfies: (D v 901-D v 101) / D v 501≥1.2; Optionally, (D v 901-D v 101) / D v 501≥1.

3.

9. The positive electrode active material according to any one of claims 1 to 8, It is characterized in that The volume particle size distribution Dv501 of the positive electrode active material satisfies: 7 μm≤Dv501≤12 μm; optionally, 8 μm≤Dv501≤10 μm.

10. The positive electrode active material according to any one of claims 1 to 9, It is characterized in that The first cladding layer includes a material having a spinel structure.

11. A method for preparing a positive electrode active material as claimed in any one of claims 1 to 10, It is characterized in that include: preparing a positive electrode matrix material; The first coating layer and the second coating layer are prepared on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material.

12. The method according to claim 11, It is characterized in that The step of preparing the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material comprises: The positive electrode base material and ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material.

13. The method according to claim 12, It is characterized in that The positive electrode matrix material and the ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material, comprising: Putting the positive electrode matrix material and ammonium salt into a high energy ball mill and mixing them; The mixed positive electrode matrix material and the ammonium salt are placed in an inert atmosphere and sintered to obtain the positive electrode active material.

14. The method according to claim 13, It is characterized in that The rotation speed V of the high energy ball mill satisfies: 500rpm≤V≤1400rpm; optionally, 800rpm≤V≤1200rpm.

15. The method according to claim 13 or 14, It is characterized in that The ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

16. The method according to any one of claims 13 to 15, It is characterized in that The sintering temperature T1 satisfies: 400°C≤T1≤600°C; optionally, 400°C≤T1≤500°C.

17. The method according to any one of claims 13 to 16, It is characterized in that The sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

18. The method according to any one of claims 13 to 17, It is characterized in that The ammonium salt includes at least one of W, Mo or P elements; optionally, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate or ammonium dihydrogen phosphate.

19. The method according to any one of claims 11 to 18, It is characterized in that The method for preparing the positive electrode matrix material comprises: Preparing a precursor of the positive electrode matrix material; The precursor, lithium salt, and compound containing element M are mixed and sintered to prepare the positive electrode matrix material, wherein element M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta, or Sr.

20. The method according to claim 19, It is characterized in that The molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or, the sintering temperature T2 satisfies: 650°C≤T2≤950°C; and / or, the sintering time t3 satisfies: 10h≤t3≤20h.

21. The method according to claim 19 or 20, It is characterized in that Based on the total mass of the precursor, the lithium salt and the compound containing the element M, the mass content D of the compound containing the element M satisfies: 200 ppm≤D≤5000 ppm.

22. The method according to any one of claims 19 to 21, It is characterized in that The volume particle size distribution Dv502 of the precursor satisfies: 7μm≤Dv502≤12μm; optionally, 8μm≤Dv502≤10μm.

23. A positive electrode sheet, It is characterized in that The invention comprises the positive electrode active material according to any one of claims 1 to 10, and / or the positive electrode active material prepared by the method according to any one of claims 11 to 22.

24. A battery cell, It is characterized in that Comprising the positive electrode sheet as described in claim 23.

25. A battery, It is characterized in that Comprising the battery cell as claimed in claim 24.

26. An electrical device, It is characterized in that Comprising a battery as claimed in claim 25.

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