Positive electrode active material, positive electrode sheet comprising same, and electrochemical device and electronic apparatus comprising same

Abstract

The invention discloses a positive active material, a positive plate containing the positive active material, an electrochemical device containing the positive active material and electronic equipment, and belongs to the technical field of batteries. The positive electrode active material comprises a matrix containing a P63mc phase, a compound containing an R-3m phase and an amorphous solid electrolyte, and the positive electrode active material can obviously improve the interface stability of the surface of the matrix, so that the battery containing the positive electrode active material has high rate capability and high-temperature cycling stability.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to positive electrode active materials, positive electrode sheets containing the same, and electrochemical devices and electronic devices containing the same. Background Technology

[0002] Currently, lithium cobalt oxide is the most widely used cathode material in consumer lithium-ion batteries. Its conventional crystal structure is the R-3m phase. However, at high voltages of 4.6V and above, the R-3m phase lithium cobalt oxide undergoes an irreversible phase transition, causing a rapid decline in its cycle performance. Therefore, in recent years, researchers have begun to focus on P63mc structure lithium cobalt oxide. P63mc belongs to the hexagonal crystal system and is a derivative phase of the typical layered α-NaFeO2 structure (R-3m space group). This structure consists of alternating layers of transition metal and alkali metal, with oxygen atoms arranged in a cubic close-packed configuration, providing a stable framework for lithium-ion migration. Furthermore, its CoO6 octahedra are connected coplanarly to form a two-dimensional conductive plane, significantly reducing the lithium-ion migration barrier and thus forming a highly efficient two-dimensional lithium-ion transport network. Even when charged to high voltages (e.g., ≥4.6V vs. Li), the lithium-ion transport network remains efficient. + In the P63mc phase lithium cobalt oxide crystal, lithium is almost completely extracted from the lattice, and the crystal structure remains intact. In other words, the P63mc phase lithium cobalt oxide crystal exhibits better structural reversibility under high voltage.

[0003] However, P63mc phase lithium cobalt oxide also has significant drawbacks: it is prone to phase transition above 300℃, making it difficult to achieve solid-phase coating on the surface; it is prone to side reactions at the interface under high voltage; and it has poor long-cycle performance and interface stability.

[0004] Therefore, it is still necessary to continue developing positive electrode active materials with high rate capability, long cycle life, and excellent interface stability. Summary of the Invention

[0005] The purpose of this application is to solve the technical problems of poor rate performance, high-temperature cycling performance and interface stability of lithium cobalt oxide cathode active materials in the prior art, and to propose cathode active materials, cathode sheets containing them, and electrochemical devices and electronic devices containing them.

[0006] To achieve the above objectives, in a first aspect, this application provides a positive electrode active material, comprising a matrix, a second compound located on at least a portion of the surface of the matrix, and a third compound, wherein the matrix comprises a first compound having a crystal structure belonging to space group P63mc, the third compound being present on at least a portion of the surface of the second compound, the second compound having a crystal structure belonging to space group R-3m, and the third compound comprising an amorphous solid electrolyte, the solid electrolyte comprising a metal element R, wherein the metal element R comprises at least one of Zr and Ti.

[0007] In the positive electrode active material of this application, the surface of the matrix containing the P63mc phase includes a second compound with a crystal structure belonging to space group R-3m. Under high voltage, the near-surface layer of this second compound can form a stable spinel phase transition layer after delithiation, providing good interfacial protection for the P63mc phase matrix, suppressing side reactions and the dissolution of transition metals, and improving interfacial stability, thereby achieving the goal of improving the high-temperature cycle stability of the battery. Because the matrix contains the P63mc phase, it has a unique lithium-deficient crystal structure. The irreversible lithium ions extracted from the second compound can enter the lithium vacancies in the matrix during re-intercalation, further improving capacity utilization, slowing down cycle decay, and further improving the cycle stability of the battery. The third compound exists on at least part of the surface of the second compound. The third compound includes a solid electrolyte that is amorphous and contains Zr and / or Ti. It has high ionic conductivity and can alleviate stress concentration at the interface between the matrix and the second compound during charge and discharge due to volume changes (such as the transformation from layered to spinel phase) through a uniform ion transport path, thereby inhibiting the propagation of interface cracks and extending cycle life. It also has good machinability and is stable and not easily decomposed under high voltage, which can significantly improve the overall rate performance and high-temperature cycling stability of the material.

[0008] In some embodiments, the mass percentage of the R metal element is 0.1%-1.2% based on the mass of the positive electrode active material.

[0009] In some embodiments, in the X-ray diffraction pattern of the positive electrode active material, 2θ has a first peak with an intensity of I1 between 18° and 19°, and a second peak with an intensity of I2 between 18.5° and 20°, the peak position difference between the second peak and the first peak being 0.3~1°, and / or 0. <I2 / I1<1。

[0010] In some embodiments, the first compound includes Li n-α Na α Co 1-x M x O2, where 0.7≤n≤1, 0≤α≤0.1, 0≤x≤0.1, and M is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

[0011] In some embodiments, the second compound includes LiCo. 1-y A y O2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

[0012] In some embodiments, the solid electrolyte includes Li 2+2zRX4O 1+Z R is Zr and / or Ti, X is at least one of F, Cl, and Br, and 0 < z ≤ 0.75.

[0013] In some embodiments, a second compound and a third compound located on at least a portion of the surface of the substrate constitute a first coating layer covering the surface of the substrate, wherein the third compound is present on at least a portion of the surface of the second compound to constitute a second coating layer.

[0014] In some embodiments, the positive electrode active material satisfies the following relationship: 2%≤T / (T+d1)≤20%(1), 0<(T+d1) / (d0+T+d1)≤31%(2); Wherein, d0 is the volume median particle size of the matrix in μm; T is the thickness of the second coating layer in μm; and d1 is the volume median particle size of the second compound in the first coating layer in μm.

[0015] In some embodiments, based on the mass of the positive electrode active material, the total mass percentage of the first coating layer is m, where 0% < m ≤ 5%.

[0016] In some embodiments, the coverage of the first coating layer on the substrate surface is s1, where s1 > 0.

[0017] In some embodiments, the second coating layer has a coverage of at least s0 on the surface of the second compound, where s0 > 50% and s0 > s1.

[0018] Secondly, this application provides a positive electrode sheet, including the aforementioned positive electrode active material.

[0019] Thirdly, this application provides an electrochemical device including the aforementioned positive electrode.

[0020] Fourthly, this application provides an electronic device including the aforementioned electrochemical device.

[0021] Compared with the prior art, the beneficial effects of this application are: the positive electrode active material of this application includes a matrix containing the P63mc phase and a coating layer containing the R-3m phase and an amorphous solid electrolyte, which makes the battery containing the positive electrode active material of this application have excellent rate performance and high temperature cycle stability. Attached Figure Description

[0022] Figure 1 This is the XRD pattern of the positive electrode active material in Example 1 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0027] In a first aspect, this application provides a positive electrode active material, comprising a matrix, a second compound located on at least a portion of the surface of the matrix, and a third compound. The matrix comprises a first compound having a crystal structure belonging to space group P63mc. The third compound is present on at least a portion of the surface of the second compound, which has a crystal structure belonging to space group R-3m. The third compound comprises an amorphous solid electrolyte, which comprises a metal element R, and the metal element R comprises at least one of Zr and Ti.

[0028] In the positive electrode active material of this application, the surface of the matrix containing the P63mc phase includes a second compound with a crystal structure belonging to space group R-3m. Under high voltage (e.g., greater than 4.5V), the near-surface layer of this second compound can form a stable spinel phase transition layer after delithiation, providing good interfacial protection for the P63mc phase matrix, suppressing side reactions and the dissolution of transition metals, and improving interfacial stability, thereby achieving the goal of improving the high-temperature cycle stability of the battery. Because the matrix contains the P63mc phase, it has a unique lithium-deficient crystal structure. The irreversible lithium ions extracted from the second compound can enter the lithium vacancies in the matrix during re-intercalation, further improving capacity utilization, slowing cycle decay, and further improving the cycle stability of the battery. The third compound includes an amorphous solid electrolyte containing Zr and / or Ti, which has a high ionic conductivity (approximately 1~2×10⁻⁶). -3 Scm -1 It can alleviate stress concentration at the interface between the matrix and the second compound phase during charging and discharging due to volume changes (such as the transformation from layered to spinel phase) through a uniform ion transport path, thereby inhibiting the propagation of interface cracks and extending cycle life; it also has good machinability and is stable and not easily decomposed under high voltage; and its coating on the surface of the second compound can significantly improve the overall rate performance and high-temperature cycling stability of the material.

[0029] In some embodiments, the mass percentage content of the R metal element is 0.1%-1.2% based on the mass of the positive electrode active material. For example, the mass percentage content of the R metal element can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, or within any two of the above values.

[0030] In some embodiments, in the X-ray diffraction pattern of the positive electrode active material, 2θ has a first peak with an intensity of I1 between 18° and 19°, and a second peak with an intensity of I2 between 18.5° and 20°, the peak position difference between the second peak and the first peak being 0.3~1°, and / or 0. <I2 / I1<1。

[0031] The first peak represents the characteristic diffraction peak of the (002) crystal plane of the first compound matrix material with a P63mc crystal structure. The second peak represents the characteristic diffraction peak of the (003) crystal plane of the second compound with an R-3m crystal structure. The 2θ between the second peak and the first peak is different, and it is represented by the difference in 2θ between the second peak and the first peak, that is, the peak position difference. To a certain extent, the intensity of the characteristic diffraction peak is positively correlated with its substance content, and the I2 / I1 value is used to represent the content difference between the first compound and the second compound. Satisfying 0 < I2 / I1 < 1 represents that the content of the second compound is less than the content of the first compound.

[0032] In some embodiments, I2 / I1 is 0.2 - 0.4; exemplarily, it can specifically be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or within the range composed of any two of the above values.

[0033] In some embodiments, I1 > 8000 cps.

[0034] In some embodiments, I1 is 8100 - 20000 cps. Exemplarily, I1 is 8100 cps, 9000 cps, 10000 cps, 11000 cps, 12000 cps, 13000 cps, 14000 cps, 15000 cps, 16000 cps, 17000 cps, 18000 cps, 19000 cps, 20000 cps, 13000 cps, or within the range composed of any two of the above values.

[0035] In some embodiments, I2 is greater than 3000 cps.

[0036] In some embodiments, I2 is 3005 - 8000 cps. Exemplarily, I2 is 3005 cps, 4000 cps, 5000 cps, 6000 cps, 7000 cps, 8000 cps, or within the range composed of any two of the above values.

[0037] In some embodiments, the first compound includes Li n-α Na α Co 1-x M x O2, where 0.7 ≤ n ≤ 1, 0 ≤ α ≤ 0.1, 0 ≤ x ≤ 0.1, and M is one or more of Al, Mg, La, Y, Ni, Mn, W, V.

[0038] In some embodiments, the second compound includes LiCo 1-y A yO2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, and V.

[0039] In some embodiments, the solid electrolyte includes Li 2+2z RX4O 1+Z R is Zr and / or Ti, X is at least one of F, Cl, and Br, and 0 < z ≤ 0.75.

[0040] In some embodiments, a second compound and a third compound located on at least a portion of the surface of the substrate constitute a first coating layer covering the surface of the substrate.

[0041] In some embodiments, the positive electrode active material satisfies the following relationship: 2%≤T / (T+d1)≤20%(1), 0<(T+d1) / (d0+T+d1)≤31%(2); Wherein, d0 is the volume median particle size of the matrix in μm; T is the thickness of the second coating layer in μm; and d1 is the volume median particle size of the second compound in the first coating layer in μm.

[0042] Within a suitable range, as the thickness of the (first) coating layer outside the substrate increases, the degree of improvement in the interface stability and ionic conductivity of the positive electrode active material increases, which can further improve the rate performance and cycle stability of the battery. However, if the proportion of the coating layer outside the substrate is too large, it will affect the specific capacity of the substrate. The inventors of this invention have discovered that when the above-mentioned relationship (1) and / or (2) is satisfied, the positive electrode active material can simultaneously achieve good interface stability, high ionic conductivity and large specific capacity, thereby further improving the rate performance and high-temperature stability of the battery containing it.

[0043] In some implementations, 5μm ≤ d0 ≤ 15μm. For example, d0 is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or within the range of any two of the above values.

[0044] In some implementations, T is 0.01-0.4 μm. Exemplarily, T is 0.01 μm, 0.025 μm, 0.05 μm, 0.075 μm, 0.1 μm, 0.125 μm, 0.15 μm, 0.175 μm, 0.2 μm, 0.225 μm, 0.25 μm, 0.275 μm, 0.3 μm, 0.325 μm, 0.35 μm, 0.375 μm, 0.4 μm, or a range consisting of any two of the above values.

[0045] In some implementations, 0 μm < d1 ≤ 4 μm. For example, d1 is 0.1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or within the range of any two of the above values.

[0046] In some embodiments, the thickness of the first coating layer is 0.1 μm to 10 μm. For example, it is 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or within any two of the above values.

[0047] In some embodiments, the total mass percentage of the first coating layer is m, based on the mass of the positive electrode active material, where 0% < m ≤ 5%. For example, m is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or within any two of the above values.

[0048] In some embodiments, the coverage of the first coating layer on the substrate surface is s1, where s1 > 0%.

[0049] Within a suitable range, the coating layer located on the particle surface effectively reduces the contact between the material and the electrolyte, reduces interfacial side reactions and the dissolution of transition metals, and improves the electrochemical performance of the positive electrode active material. As the coating amount on the substrate surface increases, the improvement effect on the high-temperature storage performance and cycle performance of the positive electrode material gradually increases, and the high-temperature performance of the battery also continuously improves. However, the coating amount on the substrate surface affects the rate performance of the positive electrode active material. The inventors of this application have discovered that when s1 and m are within the aforementioned range, the positive electrode active material can simultaneously possess high interfacial stability and rate performance, thereby further improving the high-temperature storage performance and cycle performance of the battery containing it.

[0050] In some embodiments, the coverage of the second coating layer on the surface of the first coating layer is at least s0, where s0 > 50% and s0 > s1. Exemplarily, s0 is 55%, 60%, 70%, 80%, 85%, 86%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value greater than 50%.

[0051] In some implementations, s0 is 90%-95%. For example, s0 is 90%, 91%, 92%, 93%, 94%, 95%, or any range greater than 50%.

[0052] In some implementations, s1 is 1-10%. For example, s1 is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range greater than 50%.

[0053] In some embodiments, the method for preparing the first compound includes the following steps: S1. Sodium source, cobalt source and compound containing element M are mixed and sintered in air or oxygen atmosphere to obtain first compound precursor; S2. The lithium source and the first compound precursor are dispersed in water, ion exchange is performed, and then dried to obtain the first compound.

[0054] In some embodiments, in step S1, the sintering temperature is 600-900°C and the sintering time is 8-50 hours.

[0055] In some embodiments, in step S1, the sodium source includes one or more of sodium oxide, sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, and sodium sulfate.

[0056] In some embodiments, in step S1, the cobalt source includes one or more of cobalt hydroxide, cobalt tetroxide, doped cobalt tetroxide, cobalt suboxide, cobalt hydroxyl oxide, cobalt nitrate, and cobalt sulfate.

[0057] In some embodiments, in step S1, the compound containing element M contains one or more of the following: oxide, carbonate, and hydroxide of element M.

[0058] In some embodiments, in step S2, the lithium source includes one or more of lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, and lithium fluoride.

[0059] In some embodiments, in step S2, the temperature of the ion exchange is 70-125°C, and the time of the ion exchange is 5-15 hours.

[0060] In some embodiments, in step S2, the mass ratio of the lithium source to the first compound precursor ranges from 1 to 4:1.

[0061] In some embodiments, in step S2, the mass ratio of water to the first compound precursor ranges from 5 to 150:1.

[0062] In some embodiments, the preparation method of the second compound includes the following steps: mixing a lithium source, a cobalt source and a compound containing element A and sintering them in air or oxygen to obtain the second compound.

[0063] In some embodiments, the sintering temperature is 600-1000°C, and the sintering time is 5-50 hours.

[0064] In some embodiments, the method for preparing the amorphous solid electrolyte includes the following steps: mixing RCl4 and a lithium source under an argon atmosphere, followed by a first grinding and a second grinding to obtain the amorphous solid electrolyte.

[0065] In some embodiments, the first grinding speed is 50-200 rpm, and the first grinding time is 1-3 hours; the second grinding speed is 400-900 rpm, and the second grinding time is 5-24 hours.

[0066] In some embodiments, the lithium source includes one of LiCl and Li2O.

[0067] In some implementations, R in RCl4 is Zr and / or Ti.

[0068] This application does not impose any particular restrictions on the preparation method of amorphous solid electrolytes, as long as it can achieve the purpose of this application.

[0069] In some embodiments, the preparation method of the positive electrode active material includes the following steps: S1. The second compound and the third compound are sequentially subjected to a first ball milling and a second ball milling to obtain a coating material; the rotational speed in the first ball milling is lower than the rotational speed in the second ball milling. S2. The first compound and the coating material are sequentially subjected to a third ball milling and a fourth ball milling to obtain the positive electrode active material; the rotation speed in the third ball milling is less than the rotation speed in the fourth ball milling.

[0070] In some embodiments, the rotational speed in the first ball milling, the rotational speed in the second ball milling, the rotational speed in the third ball milling, and the rotational speed in the fourth ball milling are each independently selected from 50 r / min to 400 r / min.

[0071] In some embodiments, the time for the first ball milling mixture, the time for the second ball milling mixture, the time for the third ball milling mixture, and the time for the fourth ball milling mixture are each independently selected from 0.5-10 hours.

[0072] In some embodiments, the time spent in the first ball milling mixture is shorter than the time spent in the second ball milling mixture.

[0073] In some embodiments, the time spent in the third ball milling mixture is less than the time spent in the fourth ball milling mixture.

[0074] In some embodiments, the mass ratio of the first compound, the second compound, and the third compound is (92-99):(0.1-3.5):(0.5-5.5). In a second aspect, this application provides a positive electrode sheet comprising the aforementioned positive electrode active material.

[0075] In some embodiments, the positive electrode sheet includes a positive current collector and a layer containing positive active material disposed on at least one side of the positive current collector.

[0076] In some embodiments, the positive current collector is a metal foil or a composite current collector.

[0077] In some embodiments, the metal foil is aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0078] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0079] In some embodiments, the layer containing the positive electrode active material may include the positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0080] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0081] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon fibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon.

[0082] The positive electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode conductive agents for batteries.

[0083] Thirdly, this application provides an electrochemical device including the aforementioned positive electrode.

[0084] Electrochemical devices include any apparatus in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa, including, but not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0085] In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive and negative electrodes.

[0086] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0087] In some embodiments, the negative current collector is a metal foil or a composite current collector.

[0088] In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0089] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0090] In some embodiments, the negative electrode active material includes natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, and Li4Ti5O. 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0091] In some embodiments, the negative electrode sheet further includes a negative electrode binder and / or a negative electrode conductive agent.

[0092] In some embodiments, the negative electrode binder includes at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0093] In one embodiment, the negative electrode binder has a mass percentage content of 20%-50% in the negative electrode sheet.

[0094] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0095] In one embodiment, the negative electrode conductive agent has a mass percentage content of 20%-50% in the negative electrode sheet.

[0096] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0097] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0098] In some embodiments, the substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0099] In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate. The inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2OmTiO2, K2OnTiO2, BaOx, MTiO3, and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6, or 8, x is 1 or 2, and M is Ba, Sr, or Ca. The inorganic filler can be spherical, flake-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes.

[0100] In some embodiments, the inorganic material is not spherical, sheet-like, disc-like, needle-like, cylindrical, or irregular in shape. The inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate.

[0101] In some implementations, the binder is a water-soluble polymer.

[0102] In some implementations, the water-soluble polymer is a homopolymer or copolymer.

[0103] In some embodiments, the water-soluble binder includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethyl cellulose, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0104] In some embodiments, the electrolyte may include at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0105] In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a lithium salt.

[0106] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0107] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0108] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0109] In some embodiments, the chain carbonate compound may include ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), ethylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0110] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0111] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0112] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0113] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0114] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0115] Fourthly, this application provides an electronic device including the aforementioned electrochemical device.

[0116] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. The electrochemical device of this invention is not particularly limited in its application and can be used in any electronic device known in the prior art. According to some embodiments of the invention, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0117] Test method: (1) XRD test: X-ray diffraction (XRD) is primarily used to study the internal crystal structure of materials. Because X-rays have wavelengths close to the interplanar spacing and possess a certain penetrating power, a beam of X-rays passes through a crystal and diffracts. Analyzing the diffraction pattern allows for phase identification and structural analysis. X-ray diffraction (XRD) was performed on the positive electrode active material to obtain its X-ray diffraction pattern, and its crystal phase, peak intensity, and positional differences of different diffraction peaks were analyzed. The testing conditions were: a Bruker D8 ADVANCE X-ray diffractometer (Cu-Kα1, λ=1.5406Å), operating current 250mA, continuous scanning, operating voltage 40kV, scanning range 2θ 15-90°, step size 0.02, and scanning speed 2°·min. -1 .

[0118] (2) Scanning electron microscopy (SEM): The spherical structure and particle size of the first, second, and third compounds prepared in this application were analyzed by scanning electron microscopy (SEM) at a magnification of 5000-1000x. The instrument used was a JEOL JSM-7610F plus field emission electron microscope.

[0119] Samples of positive electrode active material particles with cross-sections were prepared. Images of the particle cross-sections were observed and photographed. The particles of positive electrode active material can be regarded as spherical particles with a circular cross-section. The area of ​​the circle can be calculated by testing the particle size of each particle. 100 positive electrode active material particles as a whole, as well as particles in the matrix, the first coating layer, and the second coating layer of the positive electrode active material were randomly selected. The particle size and area were tested and statistically analyzed. The following statistics were compiled: the area ratio of the first coating layer on the matrix (i.e., the coverage rate s1 of the first coating layer on the matrix surface) and the area ratio of the third compound on the surface of the second compound particles (i.e., the coverage rate s0 of the second coating layer on the surface of the second compound), the median volumetric particle size d0 in the matrix, and the median volumetric particle size d1 of the second compound in the first coating layer.

[0120] (3) The elemental distribution of the positive electrode active material was analyzed by electron probe X-ray micro-area analysis (EPMA) under the following conditions: temperature 20±2℃, relative humidity ≤60%RH, no vibration, no strong magnetic field (<0.1 mT), independent UPS power supply (10 kVA), and field emission X-ray equipment JEOL JXA-8530F Plus was used for EPMA analysis. The thickness (T) of the second coating layer in the positive electrode active material was analyzed based on its elemental location. The thickness of the first coating layer can also be obtained by referring to the above method.

[0121] (4) The contents of Na, R, and Co in the positive electrode active material were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). 2 g of powder sample was dissolved in 10 mL of high-purity hydrochloric acid (at least 30 wt% HCl relative to the total weight of the solution) in a conical flask. The flask was covered with a glass cap and heated on a hot plate at 380 °C until the precursor was completely dissolved. After cooling to room temperature, the solution in the conical flask was poured into a 250 mL volumetric flask. The volumetric flask was then filled to the 250 mL mark with deionized water and completely homogenized. A standard curve was plotted based on the analytes and corresponding analytical wavelengths. The contents of Na, R, and Co in the positive electrode active material were analyzed, and the total mass percentage m of the first coating layer and the mass percentage of R were calculated using the stoichiometric ratios in the chemical formulas of the three elements.

[0122] (5) Gram volume test: Five lithium-ion secondary batteries from the comparative example and the embodiment were taken and charged at a constant current rate of 0.1C at room temperature until the voltage reached 4.55V. They were then further charged at a constant voltage of 4.55V until the current dropped below 0.025C, bringing them to a fully charged state of 4.55V. Subsequently, they were discharged at a constant current rate of 0.1C until the voltage reached 2.5V. The capacity of the battery was calculated based on the capacity obtained from the above testing process and the mass of the positive electrode active material.

[0123] (6) Rate discharge test: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the rate discharge performance of the lithium-ion secondary batteries was calculated.

[0124] First, in an environment of 25℃, the first charge and discharge were performed. The device was charged at a constant current of 0.5C (i.e., the current value at which the theoretical capacity is completely discharged within 2 hours) until the voltage reached 4.55V. Then, it was charged at a constant voltage of 4.55V until the current dropped below 0.025C. Finally, it was discharged at a constant current of 0.2C until the final voltage reached 2.5V, and the 0.2C discharge capacity was recorded. Then, the device was charged at a constant current of 0.5C (i.e., the current value at which the theoretical capacity is completely discharged within 2 hours) until the voltage reached 4.55V. Then, it was charged at a constant voltage of 4.55V until the current dropped below 0.025C. Finally, it was discharged at a constant current of 2C until the final voltage reached 2.5V, and the 2C discharge capacity was recorded.

[0125] Rate discharge capacity retention rate (%) = (2C discharge capacity / 0.2C discharge capacity) × 100%.

[0126] (7) Cyclic performance test: Five lithium-ion secondary batteries were taken from each of the comparative and example samples. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the cycle capacity retention rate of the lithium-ion secondary batteries was calculated.

[0127] First, in an environment of 45℃, the first charge and discharge cycle was performed. Constant current and constant voltage charging was carried out at a charging current of 2C (i.e., the current value that completely discharges the theoretical capacity within 0.5h) until the upper limit voltage is 4.55V. Then, constant current discharging was carried out at a discharging current of 0.7C until the final voltage is 2.5V. The discharge capacity of the first cycle was recorded. Then, 400 charge and discharge cycles were performed, and the discharge capacity of the 400th cycle was recorded.

[0128] Cycle capacity retention = (Discharge capacity of the 400th cycle / Discharge capacity of the first cycle) × 100%.

[0129] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0130] Example 1 A method for preparing a lithium-ion secondary battery includes the following steps: (1) Preparation of the first compound: According to Li 0.97 Na 0.03 Co 0.95 Al 0.05 O2 stoichiometrically weigh Na2CO3, Co3O4, Al2O3, and Li2CO3; thoroughly ball-mill the Na2CO3, Co3O4, and Al2O3 for 5 hours and sinter them in air at 800°C for 24 hours to obtain the first compound precursor; Li2CO3 and the first compound precursor were dispersed in deionized water at a mass ratio of 1:100. Ion exchange was carried out at 100 rpm and 100 °C for 10 h, and then dried to obtain the first compound.

[0131] (2) Preparation of the second compound: According to LiCo 0.95 Al 0.05 O2 was stoichiometrically weighed Co3O4, Al2O3, and Li2CO3; the above raw materials were thoroughly ball-milled for 5 hours and sintered in air at 900°C for 20 hours to obtain the second compound; (3) Preparation of the third compound: According to Li3ZrCl4O 1.5 Weigh out ZrCl4 and anhydrous Li2O, mix them under an argon atmosphere, and then grind them at a low speed (100 r / min) for 2 h and then at a high speed (500 r / min) for 10 h to obtain an amorphous solid electrolyte (third compound).

[0132] (4) Preparation of positive electrode active material: The third compound and the second compound were placed in a mixing device at a certain mass ratio and mixed at 400 r / min for 60 min until homogeneous. The mixture was then ground at a low speed (50 r / min) for 30 min and then at a high speed (350 r / min) for 6 h at a ball milling temperature of 100℃ to obtain a coating material in which the third compound coated the surface of the second compound.

[0133] The first compound was then mixed with the obtained coating material in a certain proportion (as shown in Table 1 below), and the mixture was ground at low speed (50 r / min) for 60 min and then at high speed (400 r / min) for 8 h to obtain the positive electrode active material.

[0134] The positive electrode active material prepared in this embodiment was analyzed by scanning electron microscopy (SEM) at 5000x magnification. The coverage of the first coating layer on the substrate surface was s1, which was about 5%, and the area of ​​the third compound on the surface of the second compound particles was s0, which was about 93%.

[0135] As used herein, “about” includes the stated value and includes a range of deviations that are determined and acceptable to a person skilled in the art, taking into account the error (limitations of the measurement system) associated with the measurement of the stated value. For example, “about” may mean within one or more standard deviations of the stated value, more specifically, for example, within ±30%, ±20%, ±10%, ±5%, or ±1%.

[0136] (5) Preparation of the positive electrode sheet: The obtained positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture was then coated onto the positive electrode current collector Al foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0137] (6) Preparation of negative electrode sheet: The negative electrode active material, artificial graphite, silicon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 76:20:1:1.5:1.5. The mixture is then coated onto the negative electrode current collector Cu foil, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0138] (7) Selection of the separator: Polyethylene (PE) porous polymer film is used as the separator.

[0139] (8) Preparation of electrolyte: A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent at a mass ratio of 8:92 was used as the electrolyte for lithium-ion secondary batteries. The mass ratio of each solvent in the non-aqueous organic solvent was EC:DEC:PC:PP:VC = 20:30:20:28:2.

[0140] (9) Preparation of lithium-ion secondary batteries: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound up to form the electrode assembly. The electrode assembly is placed in a packaging shell, electrolyte is injected, and the package is sealed to obtain a lithium-ion secondary battery.

[0141] Example 2 The difference between this embodiment and Example 1 is that ZrCl4 is replaced with TiCl4, and the mass percentages of Ti and Zr elements in the positive electrode active material are the same. The chemical formula of the third compound in this embodiment is Li3TiCl4O. 1.5 The rest are the same.

[0142] Examples 3-7 Compared with Example 1, the difference in this embodiment is that, based on the same total mass of the first compound, the second compound, and the third compound, the mass ratio of the three compounds is changed, so that the mass percentage content of R metal element in the positive electrode active material and / or the thickness T of the second coating layer and / or the total mass percentage content m of the first coating layer are different, while the rest are the same.

[0143] Examples 8-11 Compared with Example 1, this embodiment differs in that, based on the same total mass of the first compound, the second compound, and the third compound, the mass ratio of the three compounds is changed, so that the total mass percentage m of the first coating layer and the thickness T of the second coating layer are different, while the rest are the same.

[0144] Examples 12-13 The difference between this embodiment and Example 1 is that the sintering time for preparing the first compound precursor is changed, resulting in different volume median particle size d0 of the matrix. Specifically, the sintering times for preparing the first compound precursor in Examples 12 and 13 are 16h and 40h, respectively, while the rest are the same.

[0145] Examples 14-17 The difference between this embodiment and Example 1 is that the sintering time for preparing the second compound is changed, so that the median particle size d1 of the second compound in the first coating layer is different. The sintering times for preparing the second compound in Examples 14-17 are 6h, 30h, and 48h, respectively, while the rest are the same.

[0146] Comparative Example 1 Compared with Example 1, this comparative example did not prepare a second coating layer in the positive electrode active material, that is, no third compound was added to the positive electrode active material, but the rest were the same.

[0147] Comparative Example 2 The difference between this comparative example and Example 1 is that no second compound is added to the first coating layer in the positive electrode active material in this comparative example, but the rest are the same.

[0148] Comparative Example 3 The difference between this comparative example and Example 1 is that no first coating layer was prepared in the positive electrode active material in this comparative example, that is, no second compound and third compound were added to the positive electrode active material, but the rest are the same.

[0149] Comparative Example 4 The difference between this comparative example and Example 1 is that the third compound in the positive electrode active material of this comparative example is a crystalline solid electrolyte Li3ZrCl4O. 1.5 It was obtained by holding an amorphous solid electrolyte at 850℃ for 12 hours, and the rest were the same.

[0150] The relevant information, parameters, and performance test results of the above embodiments and comparative examples are shown in Tables 1 and 2.

[0151] Table 1 Continued from Table 1 Table 2 The XRD pattern results of the positive electrode active material in Example 1 show that the first peak with an intensity of I1 = 15101 cps at 18.7° is 2θ. This first peak corresponds to the characteristic diffraction peak of the (002) crystal plane, indicating that the first compound in the positive electrode active material has a crystal structure belonging to space group P63mc. The second peak with an intensity of I2 = 5200 cps is 2θ at 19°. This second peak represents the characteristic diffraction peak of the (003) crystal plane of the second compound with an R-3m crystal structure. The peak position difference between the second and first peaks is 0.5°, and I2 / I1 = 0.344. The absence of peaks for the third compound in the XRD pattern further confirms that it is an amorphous solid electrolyte.

[0152] As can be seen from Comparative Examples 1-4 and Examples 1-17, the first coating layer containing the second and third compounds in the positive electrode active material can improve the specific capacity of the positive electrode active material, thereby significantly improving the overall rate performance and cycle stability of the material.

[0153] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material comprises a substrate, a second compound on at least part of the surface of the substrate, and a third compound, the substrate comprises a first compound having a crystal structure belonging to space group P63mc, the third compound is present on at least part of the surface of the second compound, the second compound has a crystal structure belonging to space group R-3m, and the third compound comprises a solid-state electrolyte having an amorphous state, the solid-state electrolyte comprises an R metal element, and the R metal element comprises at least one of Zr and Ti.

2. The positive electrode active material according to claim 1, characterized by The mass percentage content of the R metal element is 0.1%-1.2% based on the mass of the positive electrode active material.

3. The positive electrode active material according to claim 1, characterized by At least one of the following I-IV is included: I. The X-ray diffraction spectrum of the positive electrode active material has a first peak with a peak intensity I1 at 2θ between 18° and 19°, and a second peak with a peak intensity I2 at 2θ between 18.5° and 20°, the peak position difference between the second peak and the first peak is 0.3-1°, and / or 0 II. The first compound includes Li n-α Na α Co 1-x M x O2, wherein 0.7≤n≤1, 0≤α≤0.1, 0≤x≤0.1, M is one or more of Al, Mg, La, Y, Ni, Mn, W, V; III. The second compound includes LiCo 1-y A y O2, 0≤y≤0.1, A is one or more of Al, Mg, La, Y, Ni, Mn, W, V; IV. The solid-state electrolyte comprises Li 2+2z RX4O 1+Z , R is Zr and / or Ti, X is at least one of F, Cl, Br, and 0 4. The positive electrode active material according to claim 1, characterized by The second compound on at least part of the surface of the substrate and the third compound form a first coating layer on the surface of the substrate, and the third compound on at least part of the surface of the second compound forms a second coating layer on the surface of the second compound.

5. The positive electrode active material according to claim 4, characterized by The positive electrode active material at least meets one of the following relationship formulas (1) or (2): 2%≤T / (T+d1) ≤20% (1), 0 Wherein, d0 is the volume median particle size of the substrate, unit: μm; T is the thickness of the second coating layer, unit: μm; d1 is the volume median particle size of the second compound in the first coating layer, unit: μm.

6. The positive electrode active material according to claim 4, characterized by The total mass percentage content of the first coating layer is m based on the mass of the positive electrode active material, and 0 7. The positive electrode active material according to claim 4, characterized by The coverage of the first coating layer on the surface of the substrate is s1, and s1>0%; the coverage of the second coating layer on the surface of the first coating layer is at least s0, s0>50%, and s0>s1.

8. A positive electrode sheet characterized by comprising: The positive electrode active material of any one of claims 1-7 is included.

9. An electrochemical device, characterized by, The positive electrode sheet of claim 8 is included.

10. An electronic device, comprising: The electrochemical device of claim 9 is included.

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