Positive electrode material, electrochemical device, and electric equipment

Abstract

The application relates to a positive electrode material, an electrochemical device and an electric equipment. The positive electrode material comprises a substrate and a coating on at least part of the surface of the substrate. The substrate comprises a first compound with a P63mc structure, and the coating comprises a second compound with an R-3m structure. The positive electrode material can have high specific capacity and cycle stability at high voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a positive electrode material, an electrochemical device comprising the positive electrode material, and an electric equipment. BACKGROUND

[0002] Lithium ion batteries have high energy density, good cycle stability, high working voltage, environmental friendliness and other advantages, and dominate the energy storage field. They are widely used in portable electronic devices, energy storage power grids and electric vehicles. Among the commonly available commercial positive electrode materials, lithium cobaltate has become the mainstream positive electrode material for lithium ion batteries for consumer electronics due to its high volumetric energy density. In order to meet the increasing demand for high energy density of lithium ion batteries, more lithium ions need to be extracted from the lattice of lithium cobaltate material, and the most direct way is to increase the charging voltage of lithium cobaltate. However, the lithium cobaltate in this way has a problem of rapid cycle decay at high voltage, which affects the service life of the battery. SUMMARY

[0003] In view of the above technical problems, the present application provides a positive electrode material with a coating structure, which has a substrate with a P63mc structure and a coating with an R-3m structure. The positive electrode material with a coating structure can have high specific capacity and cycle stability at high voltage. The present application also provides an electrochemical device comprising the aforementioned positive electrode material with a coating structure and an electric equipment.

[0004] In a first aspect of the present application, a positive electrode material is provided, which comprises a substrate and a coating on at least part of the surface of the substrate; wherein the substrate comprises a first compound with a P63mc structure, and the coating comprises a second compound with an R-3m structure.

[0005] In some embodiments, the thickness of the coating is 10 nm to 300 nm. In some embodiments, the thickness of the coating is 30 nm to 200 nm.

[0006] In some embodiments, the first compound is a lithium cobalt oxide, and the first compound comprises Co element and optional T element, wherein the T element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al; the sum of the molar amounts of Co element and the T element in the first compound is n Co+T , the molar amount of the T element is n T , and the ratio y1 of n T to n Co+T satisfies 0≤y1≤0.15.

[0007] In some embodiments, the first compound further comprises Na element, and a molar amount of the Na element in the first compound is n Na , and a ratio z1 of the n Na to the n Co+T satisfies 0 < z1 ≤ 0.03.

[0008] In some embodiments, the second compound is lithium cobalt oxide, and the second compound comprises Co element and optional Q element, wherein the Q element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al; a sum of molar amounts of the Co element and the Q element in the second compound is m Co+Q , a molar amount of the Q element is m Q , and a ratio y2 of the m Q to the m Co+Q satisfies 0 ≤ y2 ≤ 0.5.

[0009] In some embodiments, the second compound further comprises Na element, and a molar amount of the Na element in the second compound is m Na , and a ratio z2 of the m Na to the m Co+Q satisfies 0 < z2 ≤ 0.03.

[0010] In some embodiments, in an X-ray diffraction spectrum of the positive electrode material, a peak intensity of a strongest diffraction peak with a 2θ diffraction angle in a range of 18°-19° is I1, a peak intensity of a strongest diffraction peak with a 2θ diffraction angle in a range of 44°-46° is I2, and 1% ≤ I2 / I1 ≤ 11% is satisfied.

[0011] In some embodiments, a mass ratio m of the coating in the positive electrode material satisfies 0 < m ≤ 10%, wherein the m is obtained by XRD refinement quantitative phase analysis.

[0012] In some embodiments, an average particle size Dv50 of the positive electrode material is 10 μm to 25 μm.

[0013] In a second aspect of the present application, an electrochemical device is provided, which comprises a positive electrode sheet comprising the positive electrode material according to any one of the preceding aspects.

[0014] In a third aspect of the present application, a device using electricity is provided, which comprises the electrochemical device according to the second aspect of the present application.

[0015] The application researches and finds that when the positive electrode material has a substrate with P63mc structure and a cladding with R-3m structure, the cladding structure can be recorded as R-3m@P63mc cladding structure, at high voltage (such as greater than 4.5 V), the P63mc structure of the positive electrode material substrate has high reversible capacity, and the R-3m structure of the cladding can occur spinel phase transition, thereby forming a stable spinel phase transition layer, which can well protect the surface of the P63mc structure of the positive electrode material substrate and also can inhibit the dissolution of transition metals. Therefore, the lithium ion battery prepared by using the positive electrode material with R-3m@P63mc cladding structure as the positive electrode active material can realize high specific capacity and cycle stability when charged to high voltage (such as 4.6 V). BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, more completely understand the present application and its beneficial effects, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art according to these drawings.

[0017] Figure 1 A schematic diagram of the positive electrode material with R-3m@P63mc cladding structure in an embodiment of the present application;

[0018] Figure 2 An XRD pattern of the lithium cobalt oxide with R-3m structure prepared in Comparative Example 1 of the present application;

[0019] Figure 3 XRD patterns of three materials prepared in Comparative Example 2 of the present application, wherein the three XRD patterns from bottom to top correspond to the cobalt oxide precursor prepared in Comparative Example 2, the sodium-containing cobalt oxide precursor with P63 / mmc structure prepared in Comparative Example 2, and the lithium-containing cobalt oxide with P63mc structure prepared in Comparative Example 2;

[0020] Figure 4 An XRD pattern of the lithium cobalt oxide with R-3m@P63mc cladding structure prepared in Example 4 of the present application;

[0021] Figure 5 An XRD pattern of the P63mc structure substrate remaining after the lithium cobalt oxide with R-3m@P63mc cladding structure prepared in Example 4 of the present application is treated with aqua regia.

[0022] Explanation of reference signs: 100, substrate; 200, cladding. DETAILED DESCRIPTION

[0023] The present application will be further described in details with reference to the accompanying drawings, embodiments and examples. It should be understood that these embodiments and examples are only used to explain the present application and not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described in the present application. Those skilled in the art can make various modifications or changes without departing from the spirit and scope of the present application, and the equivalent forms obtained by the modifications or changes also fall within the protection scope of the present application.

[0024] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the present application in the specification are only for the purpose of describing the embodiments and examples and are not intended to limit the present application.

[0025] The conventional lithium cobalt oxide material (usually LiCoO2material) usually has an R-3m crystal structure. When charged to a high voltage (e.g., ≥4.6V vs. Li + / Li), more lithium ions can be extracted from the crystal lattice, resulting in higher capacity. However, for conventional lithium cobalt oxide materials, at high voltage, especially after lithium ion extraction exceeds 0.5 mol, irreversible phase transition (e.g., O3 to H1-3) occurs easily, and side reactions occur at the interface between the positive electrode material and the electrolyte, resulting in rapid deterioration of the cycle. By high concentration doping (e.g., Al, Mg, Ti, etc.), irreversible phase transition can be alleviated to some extent, but it will cause significant deterioration of capacity development.

[0026] The lithium cobalt oxide belonging to the P63mc space group has a low-temperature metastable state, which can be prepared by ion exchange of sodium in sodium-containing oxide with lithium at low temperature. The advantage of this lithium cobalt oxide material is that even if it is charged to a high voltage (e.g., ≥4.6V vs. Li +The lithium in the lattice is close to complete extraction, and the crystal structure can still remain complete. In other words, the lithium cobalt oxide belonging to the P63mc space group has better structural reversibility at high voltage. However, the lithium cobalt oxide belonging to the P63mc space group also has a significant disadvantage, that is, the lithium cobalt oxide material is unstable at high temperature and is prone to phase transition when heated to above 300°C. Unlike the traditional R-3m structure lithium cobalt oxide, it cannot be treated by high-temperature coating to stabilize the material interface, and low-temperature coating is also difficult to achieve. This results in the material being in a bare state in the battery, directly contacting the electrolyte, and being prone to serious interface side reactions. Moreover, cobalt ions continue to dissolve during the cycle process, damaging the solid electrolyte interphase (SEI) film, and causing the long-term cycle performance of the battery to fail to meet the actual application requirements. In the traditional technology, for the lithium cobalt oxide material with the P63mc structure, only low-temperature liquid phase coating can be used, and effective surface coating is difficult to achieve. The interface side reaction at high voltage is difficult to fundamentally suppress, and the liquid phase coating process is complex, the cost is high, and the industrial production is difficult.

[0027] The first aspect of the present application

[0028] In the first aspect of the present application, a positive electrode material with a coating structure is provided, which includes a substrate and a coating on at least part of the surface of the substrate; wherein the substrate comprises a first compound with a P63mc structure, and the coating comprises a second compound with an R-3m structure. The coating structure in the positive electrode material can be denoted as an R-3m@P63mc coating structure.

[0029] Figure 1 A schematic diagram of the positive electrode material with the R-3m@P63mc coating structure in an embodiment of the present application; including a substrate 100 with a P63mc structure and a coating 200 with an R-3m structure.

[0030] In some embodiments, the coating 200 exists on part of the surface of the substrate 100, that is, only part of the substrate is wrapped, and the coating exists on part of the surface of the substrate. In some embodiments, the coating 200 exists on the entire surface of the substrate 100, that is, complete wrapping of the substrate is achieved, and the coating exists on the entire surface of the substrate.

[0031] The present application researches and finds that when the positive electrode material has a substrate with a P63mc structure and a coating with an R-3m structure, the P63mc structure of the positive electrode material substrate has a high reversible capacity at a high voltage (such as greater than 4.5 V), and the R-3m structure of the coating can undergo spinel phase transition to form a stable spinel phase transition layer, which can well protect the surface of the P63mc structure of the positive electrode material substrate and also inhibit the dissolution of transition metals. Therefore, for a lithium ion battery using the positive electrode material with the R-3m@P63mc coating structure as the positive electrode active material, high specific capacity and cycle stability can be achieved when charged to a high voltage (such as ≥4.6 V).

[0032] In some embodiments, the substrate consists essentially of the first compound. In some embodiments, the coating consists essentially of the second compound. In some embodiments, the substrate consists essentially of the first compound and the coating consists essentially of the second compound.

[0033] In the present application, "structure A consists essentially of material a" means that material a is the main active material that provides the active function of structure A. In general, structure A only includes material a, but does not completely exclude the presence of other coexisting substances, but it should be understood that even if other coexisting substances exist, these coexisting substances will not affect the performance of material a. It should be understood that the mass fraction of material a in structure A is high, such as greater than 80%, greater than 85%, greater than 90%, greater than 95%, greater than 99%, and the like, and also such as 100%.

[0034] In some embodiments, the first compound is a first lithium cobalt oxide. In some embodiments, the second compound is a second lithium cobalt oxide.

[0035] In the present application, "lithium cobalt oxide" refers to a substance that at least has Li element, Co element and O element.

[0036] In some embodiments, the positive electrode material with a coating structure has a substrate of a first lithium cobalt oxide with a P63mc crystal structure and a coating of a second lithium cobalt oxide with an R-3m crystal structure. In some of these embodiments, the positive electrode material with a coating structure has a substrate of a first lithium cobalt oxide with a P63mc crystal structure and a coating of a second lithium cobalt oxide with an R-3m crystal structure.

[0037] The positive electrode material with the R-3m@P63mc coating structure has the following advantages, including but not limited to: (1) in the process of de-lithiation / lithiation, the phase transition reversibility of the first lithium cobalt oxide with the P63mc structure in the positive electrode material matrix at high voltage is higher than that of the conventional lithium cobalt oxide with the R-3m structure, and the reversible capacity is very high; (2) at high voltage (such as greater than 4.5 V), the second lithium cobalt oxide with the R-3m structure in the coating undergoes spinel phase transition to form a stable spinel phase transition layer, and the interface is very stable, which can provide good protection for the first lithium cobalt oxide with the P63mc structure in the matrix and inhibit the dissolution of transition metals, thus having better high-voltage cycle stability than the pure P63mc structure lithium cobalt oxide; (3) the positive electrode material can be obtained by converting the original spinel phase transition disadvantage into the technical advantage in the present application in a simple way. In summary, the lithium cobalt oxide belonging to the P63mc space group is annealed at a certain temperature (such as below 300°C), the surface layer undergoes in-situ R-3m phase transition, thereby forming a coating structure material with the matrix belonging to the P63mc space group and the coating belonging to the R-3m space group. This not only provides a new direction for modification of lithium cobalt oxide positive electrode materials, but also has simple preparation process, low cost, strong practicability and great industrial application potential.

[0038] In some embodiments, the mass ratio (denoted as m) of the coating in the positive electrode material satisfies 0 < m ≤ 10%, wherein m is obtained by XRD refinement quantitative phase analysis. m can also be ≤ 5.5% (i.e. 0 < m ≤ 5.5%), ≤ 5%, or ≤ 4.5%. m can also be selected from any one of the following percentages or a percentage interval formed by any two of the following percentages: 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, 5%, 5.5%, 6%, 7%, 8%, 9%, 10%, etc.

[0039] In some embodiments, the thickness of the coating is 10 nm to 300 nm. The thickness of the coating can also be selected from any one of the following values or an interval formed by any two of the following values: 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 170 nm, 190 nm, 200 nm, 250 nm, 300 nm.

[0040] In some embodiments, the average particle size Dv50 of the positive electrode material is 10 μm to 25 μm.

[0041] The chemical element types of the matrix and the coating can be the same or different, but should satisfy that the matrix has the P63mc structure and the coating has the R-3m structure.

[0042] In some embodiments, the first compound comprises Co element and optional T element, wherein the T element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al.

[0043] In some embodiments, in the first compound, the sum of the molar amount of Co element and the T element is n Co+T , the molar amount of the T element is n T , and the ratio y1 of n T to n Co+T satisfies 0≤y1≤0.15.

[0044] In some embodiments, the first compound further comprises Li element, and in the first compound, the molar amount of Li element is n Li , the ratio x1 of n Li to n Co+T satisfies 0.6≤x1≤0.95.

[0045] In some embodiments, the first compound further comprises Na element.

[0046] In some embodiments, in the first compound, the molar amount of Na element is n Na , the ratio z1 of n Na to n Co+T satisfies 0<z1≤0.03.

[0047] In some embodiments, the first compound is Li x1 Na z1 Co 1-y1 T y1 O 2±b1 , wherein 0.6≤x1≤0.95, 0<z1≤0.03, 0≤y1≤0.15; 0≤b1≤0.2.

[0048] In some embodiments, the second compound comprises Co element and optional Q element, wherein the Q element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al.

[0049] In some embodiments, in the second compound, the sum of the molar amount of Co element and the Q element is m Co+Q , the molar amount of the Q element is m Q , and the ratio y2 of m Q to m Co+Q satisfies 0≤y2≤0.5.

[0050] In some embodiments, the second compound further comprises Li element, and the molar amount of Li element in the second compound is m Li Li , and the ratio x2 of m Li Li to m Li Co+Q satisfies 0.6≤x2≤1.2. In some embodiments, 0.8≤x2≤1.1.

[0051] In some embodiments, the second compound further comprises Na element.

[0052] In some embodiments, the molar amount of Na element in the second compound is m Na Na , and the ratio z2 of m Na Na to m Na Co+Q satisfies 0<z2≤0.03.

[0053] In some embodiments, the second compound is Li x2 Na z2 Co 1-y2 Q y2 O 2±b2 , wherein 0.6≤x2≤1.2, 0≤z2≤0.03, 0≤y2≤0.15, 0≤b2≤0.2.

[0054] The crystal structure of the substrate and the coating can be identified by characteristic diffraction peaks in the XRD pattern obtained by X-ray diffraction (XRD) method.

[0055] In some embodiments, the X-ray diffraction pattern is obtained using Cu-Kα radiation, and in this case, the target for XRD test is Cu-Kα.

[0056] In some embodiments, in the X-ray diffraction spectrum of the positive electrode material with coating structure, the strongest diffraction peak of the substrate is the (002) crystal face diffraction peak of P63mc structure, and in some embodiments, the (002) crystal face diffraction peak is located in the range of 18°-19°.

[0057] In some embodiments, in the X-ray diffraction spectrum of the positive electrode material with coating structure, the strongest diffraction peak of the coating is the (003) crystal face diffraction peak of R-3m structure, and in some embodiments, the (003) crystal face diffraction peak is located in the range of 18°-19°.

[0058] In some embodiments, the peak intensity of the strongest diffraction peak in the range of 18°-19° of 2θ diffraction angle is I1, the peak intensity of the strongest diffraction peak in the range of 44°-46° of 2θ diffraction angle is I2, and 1%≤I2 / I1≤10% is satisfied. In some of the embodiments, there is only one characteristic diffraction peak in the range of 44°-46° of 2θ diffraction angle (it should be understood that the noise is not considered). The diffraction peak in the range of 44°-46° of 2θ diffraction angle corresponds to the (104) crystal face diffraction peak of the R-3m structure lithium cobalt oxide, and can be used as a characteristic diffraction peak for identifying the presence of the R-3m structure lithium cobalt oxide.

[0059] The second aspect of the present application

[0060] In the second aspect of the present application, a preparation method of the positive electrode material with the coating structure is provided, which can be used for preparing the positive electrode material with the coating structure of the first aspect of the present application, but is not limited to the preparation of the positive electrode material with the coating structure of the first aspect of the present application.

[0061] In some embodiments, the positive electrode material with the coating structure is prepared by in-situ phase transition of the surface layer of the positive electrode active material with the P63mc structure to form the coating with the R-3m structure.

[0062] In some embodiments, a preparation method of the positive electrode material with the coating structure is provided, which comprises the following steps: providing the positive electrode active material with the P63mc structure; annealing the positive electrode active material with the P63mc structure, and in-situ phase transition of the surface layer of the positive electrode active material with the P63mc structure to form the coating with the R-3m structure, thereby obtaining the positive electrode material with the coating structure.

[0063] With the increase of the annealing temperature, the R-3m phase transition of the surface layer of the positive electrode active material with the P63mc structure gradually increases, and the relative content of the coating with the R-3m structure also increases. In some embodiments of the present application, it is found that when the annealing temperature exceeds 300℃, the phase transition is obviously accelerated, and the relative content of the coating with the R-3m structure also increases rapidly.

[0064] In some embodiments, the annealing temperature can be selected from 250℃-300℃. The annealing temperature can also be selected from any one of the following temperatures or a temperature range formed by any two of the following temperatures: 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, 290℃, 295℃, etc.

[0065] In some embodiments, with the extension of the annealing time, the relative content of the coating with the R-3m structure gradually increases.

[0066] In some embodiments, the annealing time can be selected from 0.5 h to 4 h. The annealing time can also be selected from any one of the following time lengths or a range between any two of the following time lengths: 0.5 h (30 min), 0.75 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0067] The annealing temperature and the annealing time can be combined in a suitable manner. In some embodiments, the annealing temperature is 250 °C to 300 °C, and the annealing time is 0.5 h to 4 h. The annealing temperature and the annealing time can be selected from suitable values or suitable ranges in any of the embodiments described above.

[0068] In some embodiments, the positive electrode active material having a P63mc structure can be obtained by a preparation method comprising the following steps: (1) using raw materials including a soluble cobalt salt, obtaining a cobalt oxide precursor by a liquid phase precipitation method, sintering, crushing, and optionally sieving; wherein the raw materials can also optionally include a soluble T salt containing a T element; (2) mixing the cobalt oxide precursor with a sodium salt, and obtaining a sodium-containing cobalt oxide precursor by a solid phase synthesis method; (3) heating the sodium-containing cobalt oxide precursor with a lithium salt solution, washing, drying, and sieving to obtain the positive electrode active material having a P63mc structure.

[0069] In some embodiments, the soluble cobalt salt can be selected from one or more of the following group: cobalt chloride, cobalt acetate, cobalt sulfate, cobalt nitrate, etc.

[0070] In some embodiments, the soluble T salt containing a T element is a sulfate salt.

[0071] In some embodiments, the solvent of the liquid phase precipitation method is selected from water.

[0072] In some embodiments, the liquid phase precipitation method is performed in the presence of a precipitant.

[0073] In some embodiments, examples of suitable precipitants include, but are not limited to, ammonium carbonate.

[0074] In some embodiments, the liquid phase precipitation method is performed at a suitable pH value. Examples of suitable pH values include, but are not limited to, 5 to 9. Suitable pH values can also be selected from any one of the following pH values or a pH range between any two of the following pH values: 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, etc.

[0075] In some embodiments, the sintering temperature of the solid phase synthesis method in step (2) is selected from 700 °C to 1000 °C. The sintering time is selected from 36 h to 56 h. The sintering atmosphere is an oxygen atmosphere.

[0076] In some embodiments, the lithium salt in the lithium salt solution can be selected from lithium bromide.

[0077] In some embodiments, the solvent in the lithium salt solution can be selected from alcohol solvents. Among them, the alcohol solvent can be hexanol.

[0078] In some embodiments, the reaction temperature of heating reflux in step (3) is selected from 175℃ to 185℃, for example 180℃. The reaction time of heating reflux is selected from 7.5h to 8.5h.

[0079] The preparation method of the second aspect of the present application can be realized by converting the original spinel phase change disadvantages into the technical advantages in the present application in a simple way. In summary, by using lithium cobalt oxide belonging to P63mc space group and annealing treatment at a certain temperature (such as below 300℃), R-3m in-situ phase transition occurs in the surface layer, thereby forming a coated structure material with the matrix belonging to P63mc space group and the coating belonging to R-3m space group. This method not only provides a new direction for modification of lithium cobalt oxide positive electrode material, but also has simple preparation process, low cost, strong practicability and great industrial application potential.

[0080] The third aspect of the present application

[0081] In the third aspect of the present application, a positive electrode sheet is provided, which comprises a positive electrode active material layer containing the positive electrode material with a coated structure of the first aspect of the present application or containing the positive electrode material with a coated structure prepared by the preparation method of the second aspect of the present application.

[0082] In some embodiments, the positive electrode sheet further comprises a positive electrode current collector, and in some embodiments, the positive electrode active material layer is located on at least one surface of the positive electrode current collector.

[0083] In some embodiments, the positive electrode active material layer is located on only one surface of the positive electrode current collector.

[0084] In some embodiments, the positive electrode active material layer is located on opposite two surfaces of the positive electrode current collector.

[0085] In some embodiments, the positive electrode current collector can be an aluminum foil, and other positive electrode current collectors commonly used in the art can also be used.

[0086] The positive electrode active material layer can also include one or more of a conductive agent and a binder. In some embodiments, the conductive agent in the positive electrode active material layer can include one or more of carbon nanotubes, acetylene black, graphene, ketjen black, conductive carbon black, and the like. In some embodiments, the binder in the positive electrode active material layer can include one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, and the like. In some embodiments, the mass ratio of the positive electrode material, the conductive agent, and the binder in the positive electrode active material layer is (84-98):(0.5-10):(0.5-5). It should be understood that the above-described materials and mass ratios are merely exemplary and are not intended to limit the present application, and other suitable materials and mass ratios can be used.

[0087] A fourth aspect of the present application

[0088] In the fourth aspect of the present application, an electrochemical device is provided, which includes the positive electrode tab of the third aspect of the present application, and further includes a negative electrode tab and a separator disposed between the positive electrode tab and the negative electrode tab.

[0089] In some embodiments, the negative electrode tab can include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In some embodiments, the negative electrode active material layer is disposed on both opposite sides of the negative electrode current collector. In other embodiments, the negative electrode active material layer is disposed on only one side of the negative electrode current collector.

[0090] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes one or more of a carbon material, a silicon material, and the like. In some embodiments, the carbon material includes one or more of graphite, hard carbon, and the like. In some embodiments, the silicon material includes one or more of silicon, silicon oxide compounds, silicon carbon compounds, silicon alloys, and the like. In some embodiments, the negative electrode current collector can include one or more of a copper foil, an aluminum foil, a nickel foil, or a carbon-based current collector.

[0091] The negative active material layer can further include one or more of a conductive agent and a binder. In some embodiments, the conductive agent in the negative active material layer includes one or more of conductive carbon black, acetylene black, carbon nanotube, ketjen black, conductive graphite, graphene, etc. In some embodiments, the mass percentage content of the conductive agent in the negative active material layer is 0.5% to 10%. In some embodiments, the binder in the negative active material layer includes one or more of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, styrene butadiene rubber, etc. In some embodiments, the mass percentage content of the binder in the negative active material layer is 0.5% to 10%. It should be understood that the above are merely exemplary and are not intended to limit the present application.

[0092] In some embodiments, the separator film includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc. For example, the separator film can include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base material layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. The surface treatment layer is provided on at least one surface of the base material layer, and can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). In some embodiments, the thickness of the separator film is 5 μm to 500 μm.

[0093] The electrochemical device of the present application further includes an electrolyte including a lithium salt and a non-aqueous solvent.

[0094] In some embodiments, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, the lithium salt can be LiPF6.

[0095] In some embodiments, the non-aqueous solvent can include a carbonate compound, a carboxylic acid ester compound, an ether compound, or any suitable combination thereof.

[0096] In some embodiments, the carbonate compound can be selected from a chain carbonate compound, a cyclic carbonate compound, a fluoro-carbonate compound, or any suitable combination thereof.

[0097] In some embodiments, the chain carbonate compound can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. The cyclic carbonate compound can be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. The fluoro-carbonate compound can be selected from 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, or any suitable combination thereof.

[0098] In some embodiments, the carboxylic acid ester compound can be selected from methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, caprolactone, methyl formate, or any suitable combination thereof.

[0099] In some embodiments, the ether compound can be selected from dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or any suitable combination thereof.

[0100] According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to, all kinds of primary or secondary batteries. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0101] Fifth aspect of the present application

[0102] In the fifth aspect of the present application, there is provided an electric device comprising the electrochemical device of the fourth aspect of the present application.

[0103] The electric device of the embodiments of the present application is not particularly limited, and can be any electronic device currently available. In some embodiments, the electric device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, a lithium ion capacitor, and the like.

[0104] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0105] Test method:

[0106] 1. XRD test

[0107] The anode material was tested by an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with a Cu Kα target, a voltage current of 40 KV / 35 mA, a scanning angle range of 10° to 90°, a scanning rate of 0.02° / s, and a requirement of a strongest diffraction peak intensity greater than 10000, units of counts. The collected XRD spectrum was refined by Fullprof software to determine the phase structure and I2 / I1.

[0108] 2. Anode material element composition test

[0109] The anode material element composition test, in which the content of elements such as Li, Na, and transition metals, was measured by an inductively coupled plasma spectrometer (ICP) of Optima 7000DV of USA PE Company.

[0110] 3. Discharge specific capacity and cycle capacity retention rate test

[0111] After the button cell was aged at constant temperature (25°C) for 24 h, 50 cycles of charge-discharge test were repeatedly carried out in the voltage range of 3 V to 4.6 V (relative to Li / Li + ). Among them, the first 2 cycles used low current charge-discharge at 0.2C rate to activate the battery; from the 3rd cycle, 1C rate current was used for charge-discharge. Among them, 1C = 273 mA / g.

[0112] Among them, the 3rd cycle discharge gram capacity was taken as the reference benchmark for cycle gram capacity decay, that is, the nth capacity retention rate = nth discharge capacity / 3rd discharge capacity x 100%.

[0113] 4. Average particle size Dv50 test

[0114] The average particle size Dv50 of the positive electrode material was measured by a laser particle size analyzer. The instrument model was MasterSizer 3000, the sampling system was Hydro 2000SM & Hydro 2000MU, the measurement range was 0.01-3500um, the detection angle range was 0.0153-144°, the test snapshot rate was 1000 times / s, the detector was photosensitive silicon material, and the test reference standard was GB / T19077-2016 / ISO 13320:2009. Before testing, an appropriate amount of sample to be tested was taken, deionized water was added, and ultrasonic treatment was carried out for 5 min at a power of 120 W to make it uniformly dispersed.

[0115] 5. Thickness test of coating

[0116] The lithium ion battery was fully discharged to below 3.5V at a current density of 0.05C, and after standing for 10 min, the positive electrode sheet was obtained by disassembling in the glove box; the positive electrode sheet was transferred to the cavity of a scanning electron microscope equipped with a focused ion beam (model: FEI Vion Plasma FIB), and a sample for transmission scanning electron microscope (STEM, model: FEI Titan3 G2 60-300) analysis was processed. The sample surface was required to be protected with Pt, and processed with Ga ion beam, and the sample thickness was not more than 100 nm; and cleaned with low voltage mode to remove the residual surface of sample processing.

[0117] The sample was observed under STEM, and the thickness of the coating was measured. At least 3 different positions were collected, and the average value was taken.

[0118] Comparative Example 1.

[0119] Cobalt sulfate (CoSO4), nickel sulfate (NiSO4) and manganese sulfate (MnSO4) were weighed according to a molar ratio of 0.85:0.05:0.15, respectively, and then added to deionized water and stirred rapidly to dissolve. Then, ammonium carbonate was added, and the pH was adjusted to 8 until the reaction was complete to form a homogeneous carbonate precipitate. The precipitate was sintered at 650°C for 12h, and then subjected to crushing and sieving processes to obtain an oxide precursor of cobalt, nickel and manganese.

[0120] Lithium carbonate (Li2CO3) was mixed with the above metal oxide according to a molar ratio of 1.05:1, and then heat-treated at 900°C for 12h. After post-processing, a corresponding lithium cobalt oxide material (denoted as Comparative Example 1 material) was obtained. The Dv50 of the Comparative Example 1 material was 13μm.

[0121] The XRD test results can be seen in the XRD spectrum shown in Figure 2 The results show that the obtained lithium cobalt oxide has an R-3m structure. The ICP test results can be seen in Table 1. The results show that the elemental composition of the positive electrode material obtained in Comparative Example 1 is Li 1.002 Co 0.857 Ni 0.053 Mn 0.090 O2.

[0122] The above Comparative Example 1 material having an R-3m structure was used as a positive electrode active material, and conductive carbon (SP) was used as a conductive agent, and polyvinylidene fluoride (PVDF) was used as an adhesive. The three were mixed according to a mass ratio of 90:5:5, and then solvent N-methyl-2-pyrrolidone (NMP) was added to form a slurry. The slurry was coated on an aluminum foil with a thickness of 12μm. Then, the coated aluminum foil was dried in a 90°C air-drying oven for 4h, and then baked in a 110°C vacuum drying oven for 24h. After the aluminum foil was fully dried, the aluminum foil was subjected to processes such as cold pressing, punching and weighing to obtain a positive electrode.

[0123] The above positive electrode, a separator, a negative electrode and an electrolyte were assembled into a coin half-cell under an inert atmosphere. The negative electrode was a lithium metal, and the electrolyte was a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the concentration of LiPF6 was 1mol / L.

[0124] The above assembled coin cell was subjected to electrochemical performance testing, and the first discharge capacity was measured to be 205.7mAh / g, and the capacity retention rate after 80 cycles was 62.2%.

[0125] Comparative Example 2.

[0126] Cobalt sulfate (CoSO4), nickel sulfate (NiSO4), and manganese sulfate (MnSO4) were weighed out according to a molar ratio of 0.85:0.05:0.10, respectively. They were added to deionized water and stirred rapidly to dissolve. Then, ammonium carbonate was added to adjust the pH to 8 until the reaction was complete, forming a homogeneous carbonate precipitate. The precipitate was sintered at 650℃ for 12 hours. After crushing and sieving, cobalt-nickel-manganese metal oxide precursor 1 (corresponding to the aforementioned cobalt oxide precursor, denoted as precursor 1) was obtained.

[0127] Sodium carbonate (Na₂CO₃) and precursor 1 were weighed and mixed evenly at a molar ratio of 0.35:1, and kept at 800℃ for 48 hours. After post-processing, the product with the composition Na₂CO₃ was obtained. 0.7 Co 0.85 Ni 0.05 Mn 0.10 O2 sodium cobalt oxide precursor 2 (corresponding to the aforementioned sodium cobalt oxide precursor, denoted as precursor 2). XRD test results show that the obtained sodium cobalt oxide has a P63 / mmc structure.

[0128] The sodium cobalt oxide precursor 2 was mixed with a 5 mol / L LiBr hexanol solution at a mass-volume ratio of 20 g: 600 ml. The mixture was then refluxed at 180 °C for 12 h until the reaction was complete. After the reaction was complete, the resulting powder was filtered, washed with methanol, and dried in a vacuum oven at 180 °C. Finally, the dried powder was passed through a 200-mesh sieve to obtain the lithium cobalt oxide material (which can be referred to as Comparative Example 2 material).

[0129] XRD test results can be found in [link to XRD test results]. Figure 3 The XRD pattern is shown. The test results indicate that the cathode material obtained in Comparative Example 2 is a pure phase belonging to the P63mc crystal structure. The ICP test results are shown in Table 1, indicating that the elemental composition of the material in Comparative Example 2 is Li. 0.912 Na 0.007 Co 0.854 Ni 0.052 Mn 0.094 O2.

[0130] The assembly and testing methods for coin cells using the material from Comparative Example 2 as the positive electrode active material were exactly the same as those for Comparative Example 1. The initial discharge specific capacity of the material from Comparative Example 2 was measured to be 218.4 mAh / g, and the capacity retention rate after 80 cycles was 75.3%.

[0131] Examples 1 to 5: Changing the annealing temperature

[0132] Take about 10g of the P63mc structure of Comparative Example 2 material, place it in a tube furnace, and heat it to a preset holding temperature (T, corresponding to the annealing temperature described above) at a heating rate of 1.5°C / min, then hold for 30 min, and then cool down with the furnace to obtain a composite material with a P63mc structure and a R-3m structure (R-3m@P63mc coated structure positive electrode material) for the substrate and coating, respectively. The subsequent battery production and testing methods of the obtained positive electrode material are the same as those of Comparative Example 2. The holding temperature T of the materials of Example 1 to Example 5 is 250°C, 270°C, 280°C, 290°C, and 300°C, respectively, and the obtained positive electrode materials are denoted as Example 1 material, Example 2 material, Example 3 material, Example 4 material, and Example 5 material, respectively. The subsequent testing process of the obtained positive electrode material is the same as that of Comparative Example 2. The powder test results and electrochemical performance test results of the materials can be seen in Table 1.

[0133] Examples 6 to 9. Change the annealing time

[0134] Take about 10g of the P63mc structure of Comparative Example 2 material, place it in a tube furnace, and heat it to 270°C at a heating rate of 1.5°C / min, then hold for a certain time (t, corresponding to the annealing time described above), and then cool down with the furnace to obtain a composite material with a P63mc structure and a R-3m structure (R-3m@P63mc coated structure positive electrode material) for the substrate and coating, respectively. The subsequent battery production and testing methods of the obtained positive electrode material are the same as those of Comparative Example 2. The holding time t of the materials of Example 6 to Example 9 is 15 min, 45 min, 60 min, and 75 min, respectively, and the obtained positive electrode materials are denoted as Example 6 material, Example 7 material, Example 8 material, and Example 9 material, respectively. The subsequent testing process of the obtained positive electrode material is the same as that of Comparative Example 2. The powder test results and electrochemical performance test results of the materials of Example 6 to Example 9 can be seen in Table 1.

[0135] Example 10. Change the doping element

[0136] According to the molar ratio of 0.85:0.15, respectively, weigh the cobalt sulfate (CoSO4) and zinc sulfate (ZnSO4), add deionized water and stir quickly to dissolve, then add ammonium carbonate, adjust the pH to 8, and continue until the reaction is complete to form a homogeneous carbonate precipitate. Sinter the precipitate at 650°C for 12h, and then perform crushing and sieving processes to obtain a cobalt-zinc metal oxide precursor 1 (corresponding to the cobalt oxide precursor described above).

[0137] Mix sodium carbonate (Na2CO3) and the above precursor 1 according to a molar ratio of 0.35:1, and heat at 800°C for 48h. After post-processing, a material with a composition of Na 0.7 Co 0.85 Zn0.15 O2, a zinc-doped sodium-containing cobalt oxide precursor 2 (corresponding to the aforementioned sodium-containing cobalt oxide precursor).

[0138] The zinc-doped sodium-containing cobalt oxide precursor 2 was mixed with a 5 mol / L LiBr hexanol solution at a mass-volume ratio of 20 g:600 mL, and then subjected to reflux at 180°C for 12 h until the reaction was complete. After the reaction was completed, the obtained powder was filtered, washed with methanol, and then dried in a vacuum oven at 180°C. Finally, the dried powder was sieved through a 200-mesh sieve to obtain a zinc-doped lithium cobalt oxide material with a P63mc structure.

[0139] About 10 g of the zinc-doped lithium cobalt oxide material with a P63mc structure was placed in a tube furnace and heated to 270°C at a heating rate of 1.5°C / min, and then held at 270°C for 45 min. After cooling in the furnace, a zinc-doped composite material with a P63mc structure and a R-3m structure was obtained (a positive electrode material with a R-3m@P63mc coated structure, denoted as the material of Example 10). The subsequent test process of the obtained positive electrode material was the same as that of Comparative Example 2. The powder test results and the electrochemical performance test results of the material of Example 10 can be seen in Table 1.

[0140] Examples 11 to 17. Changing the doping element

[0141] Except that zinc sulfate was replaced by aluminum nitrate, manganese sulfate, yttrium nitrate, zirconium nitrate, lanthanum nitrate, nickel sulfate, and titanium nitrate in turn, and that these soluble salts were added to deionized water together with cobalt sulfate, the remaining steps and test processes for preparing the materials of Examples 11 to 17 were the same as those of Example 10. The powder test results and the electrochemical performance test results of the materials can be seen in Table 1.

[0142] In Table 1, I2 / I1 is the ratio between the intensity (I2) of the diffraction peak in the range of 44°-46° of the 2θ diffraction angle and the intensity (I1) of the strongest diffraction peak in the range of 18°-19° of the 2θ diffraction angle in the XRD pattern.

[0143] In Table 1, m represents the mass percentage content of the R-3m structure in the positive electrode material with a R-3m@P63mc coated structure. The value of m was obtained by XRD refinement quantitative phase analysis.

[0144] Table 1.

[0145]

[0146]

[0147] The lithium cobalt oxide positive electrode material with the coating structure prepared in the application mainly consists of two parts, wherein the matrix and the coating have the crystal structures of P63mc and R-3m (denoted as R-3m@P63mc coating structure).

[0148] In order to verify the structure, the XRD pattern of the material of Example 4 was first tested, and the XRD test result can be seen from the XRD pattern shown in Figure 4 The test result shows that the phase composition of the material of Example 4 is mainly P63mc composite with a small amount of R-3m structure lithium cobalt oxide, and the mass percentage m of the R-3m structure material obtained by XRD structure refinement is 5.24%.

[0149] Further, a small amount of the material of Example 4 was taken and placed in aqua regia solution (volume ratio V 浓HCl :V 浓HNO3 = 3:1) at 80°C. The hot aqua regia can slowly erode the lithium cobalt oxide material from the surface. After soaking for about 30 minutes, the residual powder was filtered out, washed, dried, and then the material was tested by XRD again. The XRD test result can be seen from the XRD pattern shown in Figure 5 The test result shows that after the material of Example 4 is treated by aqua regia, the obtained material only remains the phase of P63mc structure, and the original R-3m structure has been completely dissolved, which is specifically manifested by the disappearance of the characteristic diffraction peak near 45°. It is thus illustrated that the R-3m structure lithium cobalt oxide mainly exists in the surface layer (i.e. the coating layer) of the material, and the positive electrode material prepared in the application has the R-3m@P63mc coating structure.

[0150] By comparing the XRD diffraction spectra of Example 4 and Comparative Example 2, it can be seen that the XRD diffraction spectrum of the material of Example 4 has an additional set of R-3m structure diffraction spectrum. Among them, the (003) crystal face diffraction peak of the R-3m structure in the material of Example 4 is located at about 18.5°, which is highly overlapped with the (002) crystal face diffraction peak of the main phase P63mc structure, indicating that the R-3m structure lithium cobalt oxide material is also a lithium-deficient state, which is the same as the P63mc structure lithium cobalt oxide before the aqua regia heat treatment of the material of Example 4, and further illustrates that the R-3m structure lithium cobalt oxide material in each example material (including the material of Example 4) is obtained by in-situ conversion of the P63mc structure lithium cobalt oxide material. In addition, it can also be seen that there is only one diffraction peak near the diffraction angle of 45°, which is the (104) crystal face diffraction peak of the R-3m structure lithium cobalt oxide, and can be used as a characteristic diffraction peak for identifying the presence or absence of the R-3m structure lithium cobalt oxide.

[0151] From the test data of Comparative Example 1 to Example 17 and the materials of Comparative Example 1 and Comparative Example 2, it can be seen that the comprehensive electrical performance of each positive electrode material is: R-3m@P63mc structure > P63mc structure > R-3m structure. In the case of similar components, the lithium cobalt oxide material with R-3m structure has the worst initial discharge gram capacity and cycle stability, such as the material of Comparative Example 1, which has an initial discharge gram capacity of 205 mAh / g when charged to 4.6 V, and a capacity retention rate of 62.2% after 80 cycles. For the pure P63mc structure lithium cobalt oxide (such as the material of Comparative Example 2), its initial discharge gram capacity is significantly better than that of the R-3m structure lithium cobalt oxide material, mainly due to the material characteristics that can still maintain structural stability at a high delithiation state, but due to the lack of interface protection on the surface of the material, the transition metal elements are dissolved very seriously during the cycle process, resulting in a capacity retention rate of only 75.3% after 80 cycles. From Table 1, it can be seen that the lithium cobalt oxide material with R-3m@P63mc coated structure provided by the present application has obvious advantages.

[0152] The technical features of the above embodiments and examples can be combined in any suitable manner. To make the description concise, not all possible combinations of the technical features in the above embodiments and examples are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0153] The above embodiments only express several embodiments of the present application, which are convenient for specifically and detailedly understanding the technical solutions of the present application, but should not be understood as limitations on the protection scope of the present application. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, some modifications and improvements can be made, which are within the protection scope of the present application. In addition, it should be understood that, after reading the above teaching content of the present application, those skilled in the art can make various modifications or improvements to the present application, and the equivalent forms are also within the protection scope of the present application. It should also be understood that, based on the technical solutions provided by the present application, those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments, which are within the protection scope of the appended claims of the present application. Therefore, the protection scope of the present application should be subject to the content of the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A positive electrode material comprising a substrate and a coating on at least a portion of the surface of the substrate; wherein, The substrate comprises a first compound having a P63mc structure, and the coating comprises a second compound having an R-3m structure. The first compound is a lithium cobalt oxide, and the first compound comprises a Co element and a T element, wherein the T element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al; in the first compound, the sum of the molar amounts of the Co element and the T element is nCo+T, the molar amount of the T element is nT, and the ratio y1 of the nT to the nCo+T satisfies 0≤y1≤0.

15. The first compound further comprises a Na element, and in the first compound, the molar amount of the Na element is nNa, and the ratio z1 of the nNa to the nCo+T satisfies 0<z1≤0.

03. The second compound is a lithium cobalt oxide, and the second compound comprises a Co element and a Q element, wherein the Q element comprises at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al; in the second compound, the sum of the molar amounts of the Co element and the Q element is mCo+Q, the molar amount of the Q element is mQ, and the ratio y2 of the mQ to the mCo+Q satisfies 0≤y2≤0.

5. The second compound further comprises a Na element, and in the second compound, the molar amount of the Na element is mNa, and the ratio z2 of the mNa to the mCo+Q satisfies 0<z2≤0.

03.

2. The positive electrode material according to claim 1, wherein the thickness of the coating is 10 nm to 300 nm.

3. The positive electrode material of claim 1, wherein, In the X-ray diffraction spectrum of the positive electrode material, the peak intensity of the strongest diffraction peak in the range of 18°-19° of the 2θ diffraction angle is I1, and the peak intensity of the strongest diffraction peak in the range of 44°-46° of the 2θ diffraction angle is I2, and 1%≤I2 / I1≤11% is satisfied.

4. The positive electrode material according to claim 1, wherein at least one of the following conditions is satisfied: Condition a1: the mass proportion m of the coating in the positive electrode material satisfies 0 < m≤ 10%, wherein, m is obtained by XRD refinement quantitative phase analysis; condition a2: the average particle size Dv50 of the positive electrode material is 10 μm to 25 μm.

5. An electrochemical device comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 4.

6. An electrical apparatus comprising the electrochemical device according to claim 5.

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