Positive electrode active material, electrochemical device, and electric appliance

Abstract

The invention discloses a positive electrode active material, an electrochemical device and electric equipment, and belongs to the technical field of electrochemical energy storage devices. A button cell is assembled by a positive plate containing the positive electrode active material and a negative plate of lithium metal, the button cell is charged and discharged for 100 cycles at the current multiplying power of 0.5 C and the upper and lower limit voltage of 2.8-4.4 V, the peak position change value of the 003 diffraction peak of the positive electrode active material in the cycle charging state of 100 cycles is small, and the peak position change value of the 003 diffraction peak of the positive electrode active material is small. The positive electrode active material has excellent particle strength and crystal structure stability, lithium ion transmission is facilitated, and the cycle performance of the positive electrode active material is improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to positive electrode active materials, electrochemical devices, and electrical equipment. Background Technology

[0002] Since the dawn of modern society, the excessive consumption of fossil fuels has led to increasingly severe resource depletion and environmental pollution, profoundly impacting human life and national development. Against this backdrop, the development and efficient utilization of new clean energy sources has become an urgent priority. However, clean primary energy sources such as wind, hydro, and solar power are difficult to apply directly and typically require conversion into secondary energy sources like electricity for large-scale utilization. Therefore, constructing efficient energy storage systems has become a core issue. Among various energy storage technologies, lithium-ion batteries have attracted significant attention due to their high energy density and long cycle life. The cathode material, as a key component determining battery performance, directly restricts the battery's energy density due to its capacity characteristics, and its manufacturing cost dominates the overall cost of lithium-ion batteries.

[0003] Among them, lithium-nickel-cobalt-manganese ternary cathode active materials have become the mainstream cathode material system due to their advantages of high specific capacity and low cost. However, with the increasing scarcity and rising price of cobalt resources, ternary active materials are being continuously optimized towards high nickel and low cobalt. It is worth noting that ternary cathode active materials include polycrystalline and single-crystal structures. The single-crystal structure shows significant advantages over the polycrystalline structure: the regular crystal morphology of the single-crystal structure can effectively suppress stability problems such as gas generation and cracking caused by high nickel content; however, the initial coulombic efficiency and discharge capacity of the single-crystal structure both show a downward trend when the nickel content increases. The preparation of the single-crystal structure requires a higher sintering temperature, but high temperature easily leads to lithium-nickel mixing, requiring the addition of excess lithium salt, which in turn causes severe agglomeration of single-crystal particles. To solve this problem, the agglomerated single-crystal particles need to be separated by mechanical crushing, but this process easily damages the crystal structure. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a positive electrode active material, an electrochemical device, and an electrical device.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: Firstly, a positive electrode active material is provided, characterized in that the positive electrode active material comprises Ni, Co, and Mn elements, and the positive electrode active material satisfies: 0°<P= P1-P2≤0.15°, Wherein, P1 is the degree of the 2θ angle corresponding to the 003 diffraction peak in the XRD pattern of the positive electrode active material obtained by XRD testing; P2 is a coin cell assembled with a positive electrode plate containing the positive electrode active material and a lithium metal negative electrode plate. The coin cell is cycled 100 times at a current rate of 0.5C and a voltage limit of 2.8~4.4V. The positive electrode active material under the 100-cycle charging state is subjected to XRD test. In the XRD pattern of the positive electrode active material under the 100-cycle charging state, the degree of the 2θ angle corresponding to the 003 diffraction peak is obtained.

[0006] In some embodiments, the XRD diffraction pattern of the positive electrode active material includes a 104 diffraction peak and a 003 diffraction peak with an intensity of Å. （003） The peak intensity of the 104 diffraction peak is A. （104） The condition is satisfied that: 1.2 ≤ A （003） / A （104） ≤1.85.

[0007] In some embodiments, the positive electrode plate containing the positive electrode active material is assembled with lithium metal as the negative electrode plate to form a coin cell. The coin cell is then cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V. After 100 cycles, the positive electrode active material is subjected to XRD testing. In the XRD pattern of the positive electrode active material after 100 cycles, the following condition is met: 0.987 ≤ θ. （110） / θ （018） ≤0.994; where θ （110） θ （018） The values ​​represent the 2θ angles corresponding to the 110 diffraction peak and the 108 diffraction peak in the XRD pattern of the positive electrode active material in the range of 63° to 68° after 100 cycles of charging.

[0008] In some embodiments, the positive electrode active material includes a layered phase structure and a rock salt phase structure, wherein the rock salt phase structure is disposed on at least a portion of the surface of the layered phase structure.

[0009] In some embodiments, the chemical formula of the positive electrode active material is Li. a Ni x Co y Mn z Mg q O2, where 0.7 ≤ x < 1, 0 <y≤0.1,0<z≤0.2,x+y+z=1,a+q=1,0<q<0.005。

[0010] In some implementations, x satisfies: 0.70 ≤ x ≤ 0.82.

[0011] In some embodiments, the positive electrode active material has a polyhedral morphology.

[0012] In some embodiments, the particle size Dv50 of the positive electrode active material is 0.1~5μm.

[0013] In a second aspect, an electrochemical device is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector; the positive active layer comprises the aforementioned positive active material.

[0014] Thirdly, an electrical device is provided, including the aforementioned electrochemical device.

[0015] Compared with the prior art, the beneficial effects of this application are as follows: In this application, a positive electrode plate containing positive electrode active material is assembled with lithium metal as a negative electrode plate to form a coin cell. When the coin cell is cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V, the peak position change of the 003 diffraction peak of the positive electrode active material is small after 100 cycles, indicating that the positive electrode active material of this application has excellent particle strength and crystal structure stability, which is beneficial to lithium ion transport and improves the cycle performance of the positive electrode active material. Attached Figure Description

[0016] Figure 1 This is a SEM image of the positive electrode active material in Example 1; Figure 2 Here is a SEM image of the positive electrode active material from Example 2; Figure 3 Here is a SEM image of the positive electrode active material in Example 3; Figure 4 Here is a SEM image of the positive electrode active material in Comparative Example 1; Figure 5 This is a TEM image of the positive electrode active material in Example 1; Figure 6 The XRD patterns are of the positive electrode active materials of Examples 1-3 and Comparative Example 1; Figure 7 These are refined XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1; Figure 8 XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1 after 100 charge cycles; Figure 9 XRD patterns of the 003 diffraction peaks of the positive electrode active materials of Example 1 and Comparative Example 1 before 100 cycles and in the charged state; Figure 10 The diagram shows the cycle test results of the positive electrode active materials in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0017] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0018] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0019] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0020] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0021] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0022] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0023] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0024] A first aspect of this application provides a positive electrode active material, characterized in that the positive electrode active material comprises Ni, Co, and Mn elements, and the positive electrode active material satisfies: 0°<P= P1-P2≤0.15°, Wherein, P1 is the degree of the 2θ angle corresponding to the 003 diffraction peak in the XRD pattern of the positive electrode active material obtained by XRD testing; P2 is a coin cell assembled with a positive electrode plate containing the positive electrode active material and a lithium metal negative electrode plate. The coin cell is cycled 100 times at a current rate of 0.5C and a voltage limit of 2.8~4.4V. The positive electrode active material under the 100-cycle charging state is subjected to XRD test. The degree of the 2θ angle corresponding to the 003 diffraction peak in the XRD pattern of the positive electrode active material after 100 cycles is obtained.

[0025] In this application, a positive electrode plate containing positive electrode active material is assembled with lithium metal as the negative electrode plate to form a coin cell. The coin cell is cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V. The small change in the peak position of the 003 diffraction peak of the positive electrode active material after 100 cycles indicates that the positive electrode active material of this application has excellent particle strength and crystal structure stability, which is beneficial to lithium-ion transport and improves the cycle performance of the positive electrode active material. In this application, "under charging conditions" refers to the state when the battery charging voltage reaches 4.4V, i.e., the battery is fully charged.

[0026] Specifically, P can be a range of values ​​consisting of one or any two of the following: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, and 0.15.

[0027] In some implementations, P1 is 18.9~19.0 and P2 is 18.8~18.9.

[0028] P1 represents the XRD test performed on the positive electrode active material. In the XRD pattern of the positive electrode active material obtained by the test, the degree of the 2θ angle corresponding to the 003 diffraction peak represents the interlayer spacing of the positive electrode active material. Under long-term cycling, the positive electrode active material will inevitably undergo a phase transition, causing the 003 diffraction peak of the positive electrode active material to shift to a smaller angle, and the interlayer spacing to shrink. The greater the shift, the worse the structural stability of the positive electrode active material. P1 and P2 are within the above range, indicating that the shift of the 003 diffraction peak of the positive electrode active material is small under long-term cycling, indicating that the structural stability of the positive electrode active material is high under long-term cycling, which is beneficial to the cycling performance of the positive electrode active material.

[0029] In some embodiments, the XRD diffraction pattern of the positive electrode active material includes a 104 diffraction peak and a 003 diffraction peak with an intensity of Å. （003） The peak intensity of the 104 diffraction peak is A. （104） The condition is satisfied that: 1.2 ≤ A （003） / A （104） ≤1.85.

[0030] In this application, the positive electrode active material A （003） / A （104） Within the aforementioned range, the lithium-nickel mixing degree of the positive electrode active material is low, which can further improve the electrochemical performance of the positive electrode active material.

[0031] Specifically, A （003） / A （104） It can be a range of values ​​consisting of one or any two of the following: 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, and 1.85.

[0032] In some embodiments, a positive electrode plate containing the positive electrode active material is assembled with lithium metal as the negative electrode plate to form a coin cell. The coin cell is cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V. The positive electrode active material under the 100-cycle charging state is then subjected to XRD testing. In the XRD pattern of the positive electrode active material under the 100-cycle charging state obtained by the test, the following condition is met: 0.987≤θ （110） / θ （018） ≤0.994; where θ （110） θ （018） The values ​​represent the 2θ angles corresponding to the 110 diffraction peak and the 108 diffraction peak in the XRD pattern of the positive electrode active material in the range of 63° to 68° after 100 cycles of charging.

[0033] In this application, a positive electrode plate containing positive electrode active material is assembled with lithium metal as the negative electrode plate to form a coin cell. The coin cell is cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V. The positive electrode active material, under θ after 100 cycles of charging and discharging... （110） / θ （018） Within the above range, it is evident that the positive electrode active material maintains a good layered phase structure and high crystal structure stability even in a highly delithiated state.

[0034] Specifically, θ （110） / θ （018） It can be a range of values ​​consisting of one or any two of 0.95, 0.96, 0.97, 0.98, and 0.99.

[0035] In some embodiments, the positive electrode active material includes a layered phase structure and a rock salt phase structure, wherein the rock salt phase structure is disposed on at least a portion of the surface of the layered phase structure.

[0036] In this application, the locally ordered rock salt phase structure in the positive electrode active material can improve the structural stability of the layered phase structure in the positive electrode active material under high delithiation, thereby improving the first-efficiency, capacity and cycle stability of the positive electrode active material.

[0037] In some embodiments, the chemical formula of the positive electrode active material is Li. a Ni x Co y Mn z Mg q O2, where 0.7 ≤ x < 1, 0 <y≤0.1,0<z≤0.2,x+y+z=1;a+q=1,0<q<0.005。

[0038] Specifically, x can be a range of values ​​consisting of one or any two of the following: 0.7, 0.73, 0.75, 0.77, 0.8, 0.82, 0.85, 0.87, 0.9, 0.93, 0.95, and 0.98.

[0039] Specifically, y can be a range of values ​​consisting of one or any two of the following: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1.

[0040] Specifically, z can be a range of values ​​consisting of one or any two of the following: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1.

[0041] In some implementations, x satisfies: 0.70 ≤ x ≤ 0.82.

[0042] In this application, x is within the above-mentioned range, which can balance the energy density and structural stability of the positive electrode active material, improve the specific capacity of the battery, and ensure a better cycle life.

[0043] In some embodiments, the positive electrode active material has a polyhedral morphology.

[0044] In this application, the positive electrode active material with a polyhedral morphology is beneficial to improving the agglomeration and bonding of particles, which helps to maintain the integrity of particles in the preparation and testing of the positive electrode sheet, suppress the generation of cracks, and improve cycle stability.

[0045] In some embodiments, the bulk density of the positive electrode active material is 1.8~2.5 g / cm³. 3 Loose density refers to the mass per unit volume in a loosely packed state of particles, calculated by dividing the mass of the powder by the volume of the container it occupies. Polyhedral cathode active materials possess suitable loose density. When the loose density of the cathode active material is within the aforementioned range, it can improve the volumetric energy density of the cathode active material, balance the compaction performance and pore structure of the cathode sheet, and improve the charge-discharge performance of the electrochemical device.

[0046] In some embodiments, the particle size Dv50 of the positive electrode active material is 0.1~5μm; for example, it can be a range of one or any combination of two of the following: 0.1μm, 0.3μm, 0.5μm, 0.7μm, 1μm, 1.2μm, 1.5μm, 1.7μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, and 5μm.

[0047] In this application, the particle size Dv50 of the positive electrode active material is within the above range, which can effectively improve the breakage problem of the positive electrode active material during cold pressing and cycling, increase the compaction density of the positive electrode active material, and thus improve the electrochemical performance of the positive electrode active material.

[0048] In this application, the Dv50 of the positive electrode active material can be measured by a laser particle size analyzer. Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the sample.

[0049] In some embodiments, the preparation method of the positive electrode active material includes the following steps: S1: Mix nickel-cobalt-manganese hydroxide precursor, lithium metal salt and molten salt to form a mixture; S2: After multi-stage sintering of the mixture, the positive electrode active material is obtained; The multi-stage sintering process includes sequential steps of heating and oxygen-free sintering, holding and oxygen-enriched sintering, and cooling sintering.

[0050] In this application, the mixture is sintered under an oxygen-free atmosphere. The nickel-cobalt-manganese hydroxide precursor first forms a crystal structure, and with the help of molten salt, the crystal nuclei grow rapidly into micron-sized single crystals. The heat-preserving oxygen-enriched sintering can further improve the crystal structure of the micron-sized single crystals. The multi-stage sintering method can not only shorten the high-temperature sintering time, but also reduce the agglomeration of single crystal particles and reduce lithium-nickel mixing defects in the positive electrode active material.

[0051] In some embodiments, the molten salt comprises a metallic inorganic nitride; for example, it may be Mg3N2.

[0052] In this application, metal ions (such as Mg) in the molten salt can occupy lithium ion sites in the positive electrode active material and form a locally ordered rock salt structure on the surface of the positive electrode active material, thereby improving the crystal structure stability of the layered structure of the positive electrode active material under high delithiation and further improving the electrochemical performance of the positive electrode active material.

[0053] In some embodiments, the molar ratio of the lithium metal salt to the nickel cobalt manganese hydroxide precursor is (1~1.15):1; for example, it can be a range of values ​​consisting of one or any two of 1:1, 1.02:1, 1.05:1, 1.07:1, 1.1:1, 1.13:1, and 1.15:1.

[0054] In some embodiments, the molar ratio of the molten salt to the nickel cobalt manganese hydroxide precursor is a range of (0.1~1):100; 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, or any combination of both.

[0055] In this application, the physicochemical properties of the cathode active material can be adjusted by changing the molar ratio of molten salt to nickel-cobalt-manganese hydroxide precursor. For example, the range of characteristic peaks in the XRD pattern of the cathode active material can be adjusted.

[0056] In some embodiments, the chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni x Co y Mn 1-x-y (OH)₂, where 0.7 ≤ x < 1, 0 <y≤0.1。

[0057] In some embodiments, the particle size Dv50 of the nickel cobalt manganese hydroxide precursor is 1~5 μm; for example, it can be a range of one or any combination of two of the following: 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.3 μm, 4.5 μm, 4.8 μm, and 5 μm.

[0058] In this application, the particle size Dv50 of the positive electrode active material can be changed by the particle size Dv50 of the nickel cobalt manganese hydroxide precursor.

[0059] In some embodiments, the lithium metal salt includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate.

[0060] In some embodiments, the multi-segment sintering step includes: S21: Heat from room temperature to 450-550°C in an oxygen-free atmosphere at a heating rate of 3-10°C / min, and hold for 1-5 hours; S22: Continue heating to 800-850°C in an oxygen-free atmosphere at a heating rate of 1-5°C / min, and hold for 3-6 hours; S23: After heat preservation at 800~850°C and in an oxygenated atmosphere for 3-6 hours; S24: Cool to room temperature at a cooling rate of 3~10°C / min.

[0061] With the assistance of molten salt, in step S21, low-temperature sintering pretreats the nickel-cobalt-manganese hydroxide precursor to initially form a crystal structure; in step S22, oxygen-free high-temperature sintering allows the crystal nuclei to grow rapidly to form micron-sized single crystals, and the short sintering time can avoid excessive particle adhesion, alleviate lithium-nickel mixing, and reduce internal defects in the material; in step S23, oxygen-enriched high-temperature sintering allows ions in the bulk phase to rearrange their positions, reduce the lithium-nickel mixing rate, repair crystal structure defects, improve the crystallinity and structural integrity of the cathode active material, and improve the overall performance of the cathode active material.

[0062] In this application, the physicochemical properties of the positive electrode active material can be adjusted by changing the heating rate, sintering temperature, sintering time, and cooling rate in at least one of steps S21, S22, S23, and S24. For example, the range of characteristic peaks in the XRD pattern of the positive electrode active material and the particle size Dv50 of the positive electrode active particles can be adjusted.

[0063] In some embodiments, the oxygen flow rate in the oxygenated atmosphere is 80~200 mL / min; for example, it can be a range of one or any combination of 80 mL / min, 100 mL / min, 120 mL / min, 140 mL / min, 160 mL / min, 180 mL / min, 200 mL / min.

[0064] In a second aspect, an electrochemical device is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector; the positive active layer comprises the aforementioned positive active material.

[0065] This application does not have any special requirements on the composition or structure of the positive electrode and the negative electrode. Without departing from the inventive concept of this application, any known positive electrode active material, negative electrode active material, current collector, and corresponding auxiliary structure and composition can be used in this application.

[0066] In some embodiments, the positive current collector may be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals may be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0067] In some embodiments, the positive electrode active layer further includes a positive electrode binder and a positive electrode conductive agent.

[0068] As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0069] The positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the mass percentage of the positive electrode active material is 95% to 98%, with the mass of the positive electrode active layer being 100%. For example, it can be one or any two of 95%, 95.5%, 96%, 96.5%, 97%, or 98%.

[0071] In some embodiments, the mass percentage of the positive electrode binder is 1% to 3% based on the mass of the positive electrode active layer as 100%, for example, it can be a range of 1%, 1.5%, 2%, 2.5% or 3% or any two of them.

[0072] In some embodiments, the mass percentage of the positive electrode conductive agent is 1% to 3%, based on the mass of the positive electrode active layer as 100%, for example, it can be a range of 1%, 1.5%, 2%, 2.5% or 3% or any two of them.

[0073] This application does not limit the preparation method of the positive electrode sheet. For example, the positive active material, positive conductive agent and positive binder are added to the solvent in a certain ratio and stirred to adjust the fluidity of the slurry to obtain a positive slurry. Then, the prepared positive slurry is coated on the positive current collector, dried and rolled to obtain the positive electrode sheet.

[0074] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active layer disposed on the negative current collector.

[0075] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. 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.).

[0076] In some embodiments, the negative electrode active layer may also include other negative electrode active materials known in the art for use in electrochemical devices. As examples, other negative electrode active materials may include at least one of the following: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in electrochemical devices may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0077] In some embodiments, the negative electrode active layer may optionally include a negative electrode binder. As an example, the negative electrode binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0078] In some embodiments, the negative electrode active layer may optionally include a negative electrode conductive agent. As an example, the negative electrode conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0080] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0081] In some embodiments, the electrochemical device further includes an electrolyte and a membrane located between the negative electrode and the positive electrode.

[0082] In some embodiments, the electrolyte includes lithium salts, non-aqueous solvents, and additives.

[0083] In specific embodiments of this application, the mass of the lithium salt is 10% to 15% based on the total mass of the electrolyte. Typically, without limitation, the mass of the lithium salt is 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or any combination thereof.

[0084] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0085] In specific embodiments of this application, the mass of the non-aqueous solvent is 70% to 90% based on the total mass of the electrolyte. Typically, without limitation, the mass of the non-aqueous solvent can be a range of 70%, 75%, 80%, 85%, 90%, or any combination thereof.

[0086] In some embodiments, the non-aqueous solvent includes any one or a combination of at least two of carbonate compounds, carboxylic acid ester compounds, and ether compounds. For example, it may be a combination of carbonate compounds and carboxylic acid ester compounds, a combination of carboxylic acid ester compounds and ether compounds, or a combination of carbonate compounds, carboxylic acid ester compounds, and ether compounds, etc.

[0087] In some embodiments, the carbonate compound includes any one or a combination of at least two of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), or ethylene carbonate (EC). For example, it may be a combination of diethyl carbonate and dimethyl carbonate, a combination of dimethyl carbonate and dipropyl carbonate, a combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, or a combination of diethyl carbonate, dimethyl carbonate, dipropyl carbonate, and ethylene carbonate, etc.

[0088] In some embodiments, the carboxylic acid ester compound includes any one or a combination of at least two of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, or methyl formate, such as a combination of methyl acetate and ethyl acetate, a combination of ethyl acetate and methyl propionate, a combination of ethyl propionate and methyl formate, etc.

[0089] In some embodiments, the ether compound includes any one or a combination of at least two of dibutyl ether, tetraethylene glycol dimethyl ether, ethoxymethoxyethane, or tetrahydrofuran. For example, it may be a combination of dibutyl ether and tetraethylene glycol dimethyl ether, a combination of tetraethylene glycol dimethyl ether and ethoxymethoxyethane, or a combination of tetraethylene glycol dimethyl ether, ethoxymethoxyethane, and tetrahydrofuran, etc.

[0090] In some embodiments, the mass of the additive is 0.1% to 6% based on the total mass of the electrolyte. Typically, without limitation, the mass of the additive can be a range of 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or any combination thereof.

[0091] In the electrolyte described in this application, the amount of additives affects the thickness of the interfacial film formed on the positive and negative electrodes, especially the positive electrode surface. Since the interfacial film itself has the function of blocking the two electrodes and the electrolyte and has a certain resistance, the sample performance of the electrolyte obtained is better when it is maintained within the above-mentioned preferred range.

[0092] In some embodiments, the additive includes at least one of fluoroethylene carbonate (FEC), dimethyl glycol ether (DME), trifluorophosphate (TFP), vinylene carbonate (VC), 1,3-propane sulpholol (PS), and methyl methacrylate (MMA).

[0093] In some embodiments, the diaphragm comprises a porous substrate.

[0094] In some embodiments, the porous substrate comprises woven or nonwoven polymer fibers. In some embodiments, the porous substrate is a nonwoven material comprising polymer fibers.

[0095] In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefin, polyester, polyacetal, polyamide, 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.

[0096] 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.

[0097] In some embodiments, the thickness of the porous substrate is from 4 μm to 10 μm, for example, but not limited to 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or within any two of the above values. A porous substrate thickness within this range not only allows the separator to have higher puncture strength to better suppress lithium dendrites, but also maintains lower internal resistance and higher energy density. If the porous substrate is too thick, it will increase the lithium-ion transport path and increase the internal resistance of the electrochemical device; if the porous substrate is too thin, the separator is prone to rupture, causing short-circuit failure.

[0098] In some embodiments, the porosity of the porous substrate is 30% to 70%, for example, but not limited to 30%, 32%, 35%, 37%, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, or within any two of the above values. A porosity within this range not only benefits the membrane by providing more ion channels, thereby reducing internal resistance and improving charge / discharge efficiency and high-rate discharge capability, but also gives the membrane higher mechanical strength, thus reducing the risk of lithium dendrite penetration.

[0099] In some embodiments, the diaphragm further includes an inorganic coating located on at least one side of the surface of the porous substrate.

[0100] In some embodiments, the inorganic coating comprises inorganic fillers, which may include boehmite, ceramic fibers, Al2O3, SiO, SiO2, CaO, ZnO, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, BaTi2O5, BaTiO3, TiN, AlN, Na2O·mTiO2 (m is 3 or 6), K2O·nTiO2 (n is 1, 2, 4, 6 or 8), BaO x(x is 1 or 2), MTiO3 (M is Ba, Sr or Ca) at least one of the following. Preferably, the inorganic particles include at least one of silica particles, barium disitinathate particles, zirconium dioxide particles, alumina particles, barium metatitanate particles, barium sulfate particles, tin oxide particles, titanium nitride particles, aluminum nitride particles, silica particles, calcium oxide particles, magnesium oxide particles, magnesium hydroxide particles, zinc oxide particles, titanium dioxide particles, boehmite particles, hydrated alumina particles, and ceramic particles.

[0101] This application does not impose any particular restrictions on the shape of the inorganic filler, as long as it can achieve the purpose of this application.

[0102] Inorganic fillers can be spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes. In some embodiments, the inorganic material is not spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, or irregular. Preferably, the inorganic filler is spherical. Spherical particles have a higher packing density, can form a continuous thermally conductive network, reduce the risk of local thermal runaway, and have a small surface curvature, a low contact angle with the electrolyte, higher liquid absorption, and better wettability.

[0103] The method for assembling the electrochemical device in this application is prior art, and those skilled in the art can assemble it by referring to the methods disclosed in the prior art. For example, the positive electrode, separator, and negative electrode are wound or stacked in sequence to form a battery cell, which is then installed in a battery case, injected with electrolyte, formed, and packaged to obtain the electrochemical device.

[0104] In some embodiments, the electrochemical device may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0105] In some embodiments, the outer casing of the electrochemical device can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] This application does not impose any particular restrictions on the shape of the electrochemical device, which can be cylindrical, square, or any other arbitrary shape.

[0107] A third aspect of this application provides an electrical device comprising any of the electrochemical devices described herein.

[0108] The electrical equipment used in this application is not particularly limited and can be any electronic device known in the prior art.

[0109] The application of the electrical device in this application is not particularly limited, and it can be used in any electrical device known in the prior art. According to some embodiments of this application, the electrical 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.

[0110] The following embodiments are provided to facilitate understanding of the present application. These embodiments are provided not to limit the scope of the claims.

[0111] Example 1 <Preparation of Positive Electrode Active Materials> S1: Ni cobalt manganese hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2 (particle size Dv50=2μm), lithium metal salt LiOH·H2O and molten salt Mg3N2 were added to a three-dimensional mixer for premixing. The resulting premix was added to a planetary mixer and mixed at 500 rpm for 10 min to obtain a mixture. The molar ratio of lithium metal salt to nickel cobalt manganese hydroxide precursor was 1.05:1, and the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor was 0.5:100. S2: The mixture was placed in a tube furnace and heated from room temperature to 550°C at a rate of 3°C / min in an oxygen-free atmosphere, and held for 5 hours. Then, the temperature was further increased to 800°C at a rate of 3°C / min and held for 6 hours. Subsequently, oxygen was introduced at 800°C at a flow rate of 100 mL / min and held for 6 hours. Finally, the temperature was cooled to room temperature at a rate of 3°C / min to obtain the positive electrode active material. The chemical formula of the obtained positive electrode active material is LiNi. 0.7 Co 0.1 Mn 0.2 Mg 0.001 O2.

[0112] <Preparation of the positive electrode> The positive electrode active material, conductive carbon, and polyvinylidene fluoride (PVDF) were mixed uniformly at a mass ratio of 90:5:5 and then uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The obtained positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 12 μm and dried in a vacuum drying oven at 120°C for 12 h. Then, it was rolled and cut to obtain a positive electrode sheet with a diameter of 12 mm and a thickness of 40 μm.

[0113] <Preparation of Electrolyte> At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly in a volume ratio of 1:1:1, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to the mixed solvent and mixed uniformly to obtain an electrolyte. The molar concentration of LiPF6 was 1 mol / L.

[0114] <Preparation of Button Cells> The negative electrode uses a lithium metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator uses a 25 μm thick polypropylene porous membrane (Celgard). ® 2400); The positive electrode, separator, negative electrode, and electrolyte are assembled into a CR2032 coin cell.

[0115] Example 2 Except for the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor in the <Preparation of Positive Electrode Active Material>, which is different from that in Example 1, all other aspects are the same as in Example 1. In this example, the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor is 0.3:100.

[0116] Example 3 Except for the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor in the <Preparation of Positive Electrode Active Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor is 0.7:100.

[0117] Example 4 Except for the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor in the <Preparation of Positive Electrode Active Material>, which is different from that in Example 1, all other aspects are the same as in Example 1. In this example, the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor is 1:100.

[0118] Example 5 Except for the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor in the <Preparation of Positive Electrode Active Material>, which is different from that in Example 1, all other aspects are the same as in Example 1. In this example, the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor is 0.1:100.

[0119] Examples 6-17 Except for adjusting the parameters in each step as shown in Table 1 in the <Preparation of Positive Electrode Active Material>, all other steps are the same as in Example 1. The change in nickel content of the positive electrode active material can be achieved by adjusting the molar ratio of Ni in the precursor. The Dv50 of the positive electrode active material can be achieved by adjusting at least one of the following: the molar ratio of lithium metal salt to nickel cobalt manganese hydroxide precursor in step S1, the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor, and the holding temperature in step S2. P, A(003), A(104), θ(110), and θ(018) can be achieved by adjusting at least one of the following: the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor in step S1, and the holding temperature in step S2.

[0120] Comparative Example 1 Except for the preparation of the positive electrode active material, which differs from Example 1, all other steps are the same as in Example 1. This comparative example, the preparation of the positive electrode active material, includes the following steps: S1: Ni cobalt manganese hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2 (particle size Dv50=2μm) and lithium metal salt LiOH·H2O were added to a three-dimensional mixer for premixing. The resulting premix was added to a planetary mixer and mixed at 500 rpm for 10 min to obtain a mixture. The molar ratio of lithium metal salt to nickel cobalt manganese hydroxide precursor was 1.05:1. S2: The mixture was placed in a tube furnace and heated from room temperature to 550°C at a rate of 3°C / min in an oxygen-free atmosphere, and held for 5 hours. Then, the temperature was further increased to 800°C at a rate of 3°C / min and held for 6 hours. Subsequently, oxygen was introduced at 800°C at a flow rate of 100 mL / min and held for 6 hours. Finally, the temperature was cooled to room temperature at a rate of 3°C / min to obtain the positive electrode active material. The chemical formula of the obtained positive electrode active material is LiNi. 0.7 Co 0.1 Mn 0.2 O2.

[0121] Comparative Example 2 Except for the type of molten salt used in <Preparation of Positive Electrode Active Material>, which differs from Example 1, all other aspects are the same as in Example 1. The molten salt used in this comparative example, <Preparation of Positive Electrode Active Material>, is magnesium oxide.

[0122] Comparative Example 3 Except for the type of molten salt used in <Preparation of Positive Electrode Active Material>, which differs from Example 1, all other aspects are the same as in Example 1. The molten salt used in this comparative example, <Preparation of Positive Electrode Active Material>, is MoO3.

[0123] Comparative Example 4 Except for the preparation of the positive electrode active material, which differs from Example 1, all other steps are the same as in Example 1. This comparative example, the preparation of the positive electrode active material, includes the following steps: S1: Ni cobalt manganese hydroxide precursor Ni 0.7 Co 0.1 Mn 0.2 (OH)2 (particle size Dv50=2μm), lithium metal salt LiOH·H2O and molten salt Mg3N2 were added to a three-dimensional mixer for premixing. The resulting premix was added to a planetary mixer and mixed at 500 rpm for 10 min to obtain a mixture. The molar ratio of lithium metal salt to nickel cobalt manganese hydroxide precursor was 1.05:1, and the molar ratio of molten salt to nickel cobalt manganese hydroxide precursor was 0.5:100. S2: The mixture was placed in a tube furnace and heated from room temperature to 550°C at a heating rate of 3°C / min under an oxygen atmosphere of 100 mL / min, and held for 5 h; then the temperature was further increased to 800°C at a heating rate of 3°C / min and held for 12 h; finally, the temperature was cooled to room temperature at a cooling rate of 3°C / min to obtain the positive electrode active material; the chemical formula of the obtained positive electrode active material is Li. 0.999 Ni 0.7 Co 0.1 Mn 0.2 Mg 0.001 O2.

[0124] Performance testing (1) The 003, 104, 018 and 110 diffraction peaks of the positive electrode active material were obtained by XRD. The specific test conditions were: Cu Kα radiation (λ = 1.546 Å), scan rate 5 °min -1 The scanning range is 10-80°, the X-ray tube voltage is 40 kV, and the tube current is 40 mA.

[0125] (2) The particle size Dv50 of the positive electrode active material was measured by a British Malvern Panalytical-Mastersizer2000 laser particle size analyzer. The specific test conditions were: laser wavelength of 633 nm, powder dispersed in anhydrous ethanol, sample concentration controlled at 0.1%-1% (w / v), and ultrasonic cleaner (power 20-50W) used to disperse the sample for 5-10 minutes.

[0126] (3) Electrochemical testing: First charge-discharge test: constant temperature at 25℃, voltage range 2.8~4.4V, charging rate 0.1C, discharging rate 0.1C; Charge-discharge cycle test: constant temperature at 25℃, voltage range of 2.8~4.4V, charging rate of 0.5C, discharging rate of 0.5C, 100 cycles.

[0127] (4) The morphology of the positive electrode active material was measured by scanning electron microscopy (SEM).

[0128] (5) The crystal phase structure of the positive electrode active material was measured by transmission electron microscopy (TEM).

[0129] The test results are shown in Table 1-2 and Figures 1-10 As shown.

[0130] Table 1. Some performance parameters of the positive electrode active material In Table 1, P1 represents the degree of the 2θ angle corresponding to the 003 diffraction peak in the XRD pattern of the positive electrode active material obtained by XRD testing. P2 represents the positive electrode plate containing the positive electrode active material, which is assembled into a coin cell with lithium metal as the negative electrode plate. The coin cell is cyclically charged and discharged 100 times at a current rate of 0.5C and a voltage limit of 2.8~4.4V. XRD testing is performed on the positive electrode active material under the 100-cycle charging state. In the XRD pattern of the positive electrode active material under the 100-cycle charging state obtained by XRD testing, the degree of the 2θ angle corresponding to the 003 diffraction peak is A(003). A(104) represents the peak intensity of the 003 diffraction peak in the XRD diffraction pattern of the positive electrode active material, A(104) represents the peak intensity of the 104 diffraction peak in the XRD diffraction pattern of the positive electrode active material, and the particle size Dv50 represents the particle size Dv50 of the positive electrode active material.

[0131] Table 2 Figure 1 This is a SEM image of the positive electrode active material in Example 1; Figure 2 Here is a SEM image of the positive electrode active material from Example 2; Figure 3 Here is a SEM image of the positive electrode active material in Example 3; Figure 4 Here is a SEM image of the positive electrode active material in Comparative Example 1; Figure 5 This is a TEM image of the positive electrode active material in Example 1. Figures 1-4 As can be seen from the data, the morphology of the positive electrode active material in this application is polyhedral. Comparative Example 1 did not use molten salt, and the resulting positive electrode active material exhibits adhesion between particles, with relatively small particles. From... Figure 5 As can be seen, the layered phase structure at the single-crystal interface of the positive electrode active material undergoes significant changes. At the interface, within 10 nm, some lithium sites are occupied by magnesium ions, forming a locally ordered rock salt phase structure. Figure 6 The images show the XRD patterns of the positive electrode active materials prepared in Examples 1-3 and Comparative Example 1; from Figure 6 As can be seen from the XRD patterns, there are no significant changes in the positive electrode active materials of Examples 1-3 compared to Comparative Example 1. This indicates that the positive electrode active materials prepared in Examples 1-3 did not form new impurity phases and maintained their original layered structure.

[0132] Figure 7 The images show the refined XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1. Compared to Comparative Example 1, the cation mixing degree of the positive electrode active material of Example 1 is increased, indicating that the cations (Mg) in the molten salt are more mixed. 2+ It enters the structure of the positive electrode active material.

[0133] Figure 8 Here are the XRD patterns of the positive electrode active materials of Example 1 and Comparative Example 1 after 100 charge cycles; from Figure 8 As can be seen from the data, compared to Example 1, the positive electrode active material in Comparative Example 1 showed a lower θ after 100 cycles. （110） / θ （018） The small value indicates a high degree of separation between the 018 and 110 diffraction peaks, and the phase transition structure of the positive electrode active material in Comparative Example 1 after 100 cycles is severe.

[0134] Figure 9 XRD patterns of the 003 diffraction peaks of the positive electrode active materials of Example 1 and Comparative Example 1 before 100 cycles and in the charged state; from Figure 9 As can be seen from the data, compared with Comparative Example 1, the 2θ angle corresponding to the 003 diffraction peak of the positive electrode active material in Example 1 before 100 cycles and in the charging state has a smaller degree of shift, indicating that the positive electrode active material of this application still maintains a good layered structure and has high crystal structure stability even in a highly delithiated state.

[0135] Figure 10 The figures show the cycle test results of the positive electrode active materials in Examples 1-3 and Comparative Example 1. Compared to Comparative Example 1, the positive electrode active material of this application has higher discharge specific capacity and cycle performance.

[0136] 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 in that, The positive electrode active material contains Ni, Co, and Mn elements, and the positive electrode active material satisfies the following: 0°<P= P1-P2≤0.15°, Wherein, P1 is the degree of the 2θ angle corresponding to the 003 diffraction peak in the XRD pattern of the positive electrode active material obtained by XRD testing; P2 is a coin cell assembled with a positive electrode plate containing the positive electrode active material and a lithium metal negative electrode plate. The coin cell is cycled 100 times at a current rate of 0.5C and a voltage limit of 2.8~4.4V. The positive electrode active material under the 100-cycle charging state is subjected to XRD test. In the XRD pattern of the positive electrode active material under the 100-cycle charging state, the degree of the 2θ angle corresponding to the 003 diffraction peak is obtained.

2. The positive electrode active material as described in claim 1, characterized in that, The XRD diffraction pattern of the positive electrode active material includes a 104 diffraction peak and a 003 diffraction peak with an intensity of Å. （003） The peak intensity of the 104 diffraction peak is A. （104） The condition is satisfied that: 1.2 ≤ A （003） / A （104） ≤1.

85.

3. The positive electrode active material as described in claim 1, characterized in that, The positive electrode plate containing the positive electrode active material is assembled with lithium metal as the negative electrode plate to form a coin cell. The coin cell is then cycled 100 times at a current rate of 0.5C and an upper and lower limit voltage of 2.8~4.4V. XRD testing is performed on the positive electrode active material after 100 cycles. In the XRD pattern of the positive electrode active material after 100 cycles, the following condition is met: 0.987 ≤ θ. （110） / θ （018） ≤0.994; Where θ （110） θ （018） The values ​​represent the 2θ angles corresponding to the 110 diffraction peak and the 108 diffraction peak in the XRD pattern of the positive electrode active material in the range of 63° to 68° after 100 cycles of charging.

4. The positive electrode active material as described in claim 1, characterized in that, The positive electrode active material includes a layered phase structure and a rock salt phase structure, wherein the rock salt phase structure is disposed on at least a portion of the surface of the layered phase structure.

5. The positive electrode active material as described in claim 1, characterized in that, The chemical formula of the positive electrode active material is Li a Ni x Co y Mn z Mg q O2, where 0.7 ≤ x < 1, 0 <y≤0.1,0<z≤0.2,x+y+z=1,a+q=1,0<q<0.005。 6. The positive electrode active material as described in claim 5, characterized in that, The x satisfies: 0.70≤x≤0.

82.

7. The positive electrode active material as described in claim 1, characterized in that, The positive electrode active material has a polyhedral morphology.

8. The positive electrode active material as described in claim 1, characterized in that, The particle size Dv50 of the positive electrode active material is 0.1~5μm.

9. An electrochemical device, characterized in that, The device includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the surface of the positive current collector. The positive active layer includes the positive active material as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, Includes the electrochemical device as described in claim 9.

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