Positive electrode material and preparation method and application thereof

Abstract

The invention provides a positive electrode material and a preparation method and application thereof.The positive electrode material comprises a base body and an island-shaped coating layer arranged on the surface of the base body, and the base body is a lithium ion layered oxide with an O2 phase stacking structure; the coating layer is selected from one or more of oxides of an element M, and the element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn and Fe. According to the positive electrode material disclosed by the invention, the surface of the lithium ion layered oxide matrix with the O2 phase accumulation structure is coated with the specific island-shaped oxide coating layer, so that the positive electrode material has relatively high specific capacity, structural stability and positive electrode interface stability under high voltage, and further good cycle performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of batteries and relates to a cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion layered oxides possess high tap density, extremely high theoretical specific capacity, and ultra-high average operating voltage, making them crucial cathode materials for lithium-ion batteries. Currently commercially available lithium-ion cathode materials, such as lithium cobalt oxide and nickel-cobalt-manganese ternary materials, all belong to the R-3m space group structure, exhibiting an O3 phase stacking structure. Taking lithium cobalt oxide as an example, its theoretical specific capacity is 274 mAh / g. To obtain higher specific capacity, it is usually necessary to increase the charging voltage to capture more lithium ions. However, even when charging this type of lithium cobalt oxide to 4.5V, the reversible specific capacity only reaches 190 mAh / g, far below its theoretical value. Furthermore, with further increases in voltage, a large number of lithium ions are released, and the crystal structure undergoes a series of irreversible phase transitions, significantly reducing the cycle performance and safety of the cathode material. In addition, interfacial side reactions intensify at high voltages, leading to severe cobalt metal dissolution. Corresponding high-voltage electrolyte technologies are difficult to implement, and conventional electrolytes decompose and fail more rapidly at high voltages, resulting in severe battery capacity decay.

[0003] Therefore, how to improve the specific capacity, interface stability and structural stability of lithium-ion layered oxides under high voltage, and thus obtain good cycle performance, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This application provides a cathode material, its preparation method, and its application. The cathode material of this application, by coating a specific island-shaped oxide coating layer on the surface of a lithium-ion layered oxide matrix with an O2 phase stacking structure, can achieve high specific capacity, structural stability, and cathode interface stability under high voltage, thereby obtaining good cycle performance.

[0005] The first aspect of this application provides a cathode material, including a matrix and an island-shaped coating layer disposed on the surface of the matrix, wherein the matrix is ​​a lithium-ion layered oxide having an O2 phase stacking structure;

[0006] The coating layer includes one or more oxides of element M, wherein element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe.

[0007] In one alternative embodiment, the coating layer comprises a mixture of a first oxide and a second oxide; the first oxide is selected from Y2O3 or Al2O3, and the second oxide is selected from one or more of Al2O3, MgO, TiO2, ZrO2, and Gd2O3.

[0008] In one optional embodiment, the cathode material as described above includes a first element and a second element, wherein the first element is an element other than O in the coating layer, and the second element is an element other than Li, Na, C, and O in the cathode material.

[0009] Based on the total mass of the cathode material, the content of the first element is A. x The content of the second element is A. m The coating amount on the substrate surface is Q, where Q = A x / A m ×100%, and 0.1%≤Q≤40%.

[0010] In one alternative embodiment, the cathode material as described above, wherein the coating layer consists of a plurality of island-shaped coatings, wherein the D of a single island-shaped coating... V The particle size of 50 particles ranges from 10 nm to 1000 nm.

[0011] In one alternative embodiment, the cathode material as described above, wherein the lithium-ion layered oxide comprises at least Li and X elements, wherein the X element is selected from one or more of Co, Ni, Mn, Na, Fe, Cu, Ti, Zn, Al, Mg, La, Y, Zr, and F.

[0012] In one alternative embodiment, the cathode material as described above, wherein the lithium-ion layered oxide is selected from lithium cobalt oxide materials.

[0013] In one alternative embodiment, the cathode material as described above, wherein the lithium cobalt oxide material is doped with Ni and Mn elements.

[0014] In one alternative embodiment, the cathode material as described above, wherein the mass content of the Na element is 100 to 10000 ppm based on the mass of the lithium-ion layered oxide.

[0015] A second aspect of this application provides a method for preparing the cathode material as described above, comprising the following steps:

[0016] 1) A solid-state mixing treatment is performed on the lithium-ion layered oxide precursor and the coating source to obtain a mixture; the coating source is selected from one or more of the oxides, carbonates, phosphates, and acetates of element M, and element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe;

[0017] 2) The mixture is calcined to obtain a cathode material precursor;

[0018] 3) The cathode material precursor is mixed with a lithium source and then subjected to an ion exchange reaction to obtain the cathode material.

[0019] In an optional embodiment, in the preparation method described above, in step 2), the calcination treatment is carried out at a temperature of 700–1000°C for 2–12 hours.

[0020] In one optional embodiment, in the preparation method described above, in step 3), the temperature of the ion exchange reaction is 230–280°C, and the time is 2–10 h.

[0021] A third aspect of this application provides a positive electrode sheet, comprising the positive electrode material as described above.

[0022] A fourth aspect of this application provides a battery including the positive electrode as described above.

[0023] This application provides a cathode material, including a substrate and an island-shaped coating layer disposed on the surface of the substrate. The substrate is a lithium-ion layered oxide with an O2 phase stacking structure. The coating layer includes one or more oxides of element M, wherein element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe. The lithium-ion layered oxide with an O2 phase stacking structure has high specific capacity and structural stability under high voltage. By using specific oxides to form island-shaped coatings on its surface, it can maintain good ionic and electronic conductivity, reduce the dissolution of cobalt ions, suppress side reactions between the cathode material and the electrolyte, and enable the cathode material to have good interfacial stability, thereby improving the cycle performance of the cathode material. Attached Figure Description

[0024] Figure 1 The image shows the XRD pattern of the cathode material in Example 1.

[0025] Figure 2 The image shows the XRD pattern of the cathode material in Example 5.

[0026] Figure 3This is a SEM-EDS image of the cathode material in Example 4;

[0027] Figure 4 This is a SEM-EDS image of the cathode material in Example 3;

[0028] Figure 5 The charge-discharge curves of the coin cell assembled from the positive electrode material of Comparative Example 1 are shown.

[0029] Figure 6 The discharge specific capacity of the coin cells assembled with the cathode materials of Examples 1-5 and Comparative Example 1 is compared after 100 cycles at 0.5C.

[0030] Figure 7 The discharge specific capacity of the coin cells assembled with the cathode materials of Examples 6-16 and Comparative Example 1 after 30 cycles at 0.5C is compared.

[0031] Figure 8 The graph shows a comparison of the discharge specific capacity of coin cells assembled with the cathode materials of Examples 17-19 and Comparative Example 1 after 150 cycles at 0.5C. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] The traditional O3 phase stacking structure of lithium cobalt oxide, which belongs to the R-3m space group, will undergo a series of irreversible phase transitions in its crystal structure when the charging voltage is higher than 4.5V, which will accelerate the capacity decay of the battery.

[0034] To address the aforementioned issues, this application provides a cathode material comprising a substrate and an island-shaped coating layer disposed on the surface of the substrate, wherein the substrate is a lithium-ion layered oxide having an O2 phase stacking structure;

[0035] The coating layer includes one or more oxides of element M, wherein element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe.

[0036] Compared to traditional O3-stacking lithium cobalt oxide, lithium-ion layered oxides with O2-stacking structure have higher specific capacity and structural stability at high voltage, enabling batteries to have higher energy density. However, lithium-ion layered oxides with O2-stacking structure lack spinel phase transition during cycling, making it difficult to form an effective inert protective layer to isolate the cathode material from the electrolyte. This leads to severe side reactions between the cathode material and the electrolyte, which is detrimental to cycle performance.

[0037] This application uses a lithium-ion layered oxide with an O2 phase stacking structure as a substrate, and coats its surface with a discontinuous island-shaped coating layer. First, the island-shaped coating layer is selected from oxides of element M. These oxides have certain conductivity, and the cathode material still retains electrochemical activity after coating. Moreover, these oxides are inexpensive and readily available, and besides element M and oxygen, they do not contain other halogens or other environmentally harmful elements, which is beneficial for industrial applications. Second, island coating has particular advantages for lithium-ion cathode materials with an O2 phase stacking structure. Since current O2 phase lithium-ion cathode materials are prepared by ion exchange, island coating can reduce the direct contact between cobalt in the substrate and the electrolyte, thereby suppressing interfacial side reactions between the substrate and the electrolyte. It can also retain certain channels for ion exchange reactions to occur, thereby generating high-purity O2 phase products. The resulting cathode material has good overall conductivity, thus achieving good cycle performance of the cathode material under high voltage.

[0038] In this application, the coating layer may be selected from one or more of the following: aluminum oxide, magnesium oxide, titanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, silicon oxide, tin oxide, copper oxide, tungsten oxide, samarium oxide, gadolinium oxide, indium oxide, zinc oxide, and iron oxide.

[0039] In a preferred embodiment, the coating layer comprises a mixture of a first oxide and a second oxide, wherein the first oxide is selected from Y₂O₃ or Al₂O₃, and the second oxide is selected from one or more of Al₂O₃, MgO, TiO₂, ZrO₂, and Gd₂O₃. The inventors have found that the cathode material obtained by using a mixture of the first and second oxides as the coating layer to coat the substrate exhibits significantly improved cycle performance compared to cathode materials coated with a single component.

[0040] In one specific embodiment, the cathode material of this application includes a first element and a second element, wherein the first element is an element other than O in the coating layer, and the second element is an element other than Li, Na, C, and O in the cathode material.

[0041] The second element, which refers to the elements in the cathode material other than Li, Na, C, and O, means that the second element is the element in both the coating layer and the matrix of the cathode material other than Li, Na, C, and O.

[0042] Based on the total mass of the cathode material, the content of the first element is A. x The content of the second element is A. m The coating amount on the substrate surface is Q, where Q = A x / A m ×100%, and 0.1%≤Q≤40%. For example, Q can be a range consisting of any two values ​​of 0.1%, 1%, 3%, 5%, 10%, 13%, 15%, 18%, 20%, 25%, 30%, 35%, 40% or more.

[0043] This application considers the difference in elemental composition between the surface and bulk phases, and thus proposes a calculation formula for the coating amount Q of the island-like coating layer on the substrate surface based on surface EDS results. The coating amount calculated by this formula can accurately reflect the coating status on the substrate surface. Furthermore, by limiting the Q value to the range of 0.1% to 40%, the cathode material can possess both good interfacial stability and ion-electron transport performance, thereby ensuring good cycle stability of the material under high voltage.

[0044] In the above formula, the content A of the first element... x The content of the second element A m It can be obtained through EDS energy dispersive spectroscopy analysis.

[0045] In one specific embodiment, the coating layer consists of a plurality of island-shaped coatings, wherein the D of a single island-shaped coating... V The particle size of 50 particles ranges from 10 nm to 1000 nm.

[0046] In one specific embodiment, the lithium-ion layered oxide includes at least Li and X elements, wherein the X element is selected from one or more of Co, Ni, Mn, Na, Fe, Cu, Ti, Zn, Al, Mg, La, Y, Zr, and F. For example, the lithium-ion layered oxide can be a lithium cobalt oxide material including Li and Co elements, or a lithium nickel cobalt manganese oxide material including Li, Co, Ni, and Mn elements.

[0047] Furthermore, the lithium-ion layered oxide is selected from lithium cobalt oxide materials. Lithium cobalt oxide materials have a typical O2 phase stacking structure, and the O2 phase structure has a high reversible specific capacity. After the surface is coated with an oxide of element M in an island-like manner, the structural stability of the material can be significantly improved, and excellent cycle performance can be obtained.

[0048] Furthermore, the aforementioned lithium cobalt oxide material is also doped with Ni and Mn elements. Ni and Mn elements help stabilize the structure of the O2 phase lithium cobalt oxide material, suppressing unfavorable phase transitions under high voltage and giving the cathode material good structural stability. In addition, the doping of Ni and Mn elements also helps improve the thermal stability during the conversion from P2 phase sodium ion cathode material to O2 phase lithium ion cathode material.

[0049] In one specific embodiment, the lithium-ion layered oxide further includes sodium (Na), and the mass content of Na is 100–10000 ppm based on the mass of the lithium-ion layered oxide. For example, the Na content can be any two values ​​within the range of 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, or higher. Controlling the Na doping amount in the matrix within the above range is beneficial for supporting the layered structure of the cathode material and for the insertion / extraction of lithium ions.

[0050] In one specific embodiment, the chemical composition of the lithium-ion layered oxide is Li x Na y RO2, wherein 0.8≤x≤1.1, 0.0001≤y≤0.04, and R is selected from one or more of Co, Ni, Mn, Fe, Cu, Ti, Zn, Al, Mg, La, Y, Zr, and F.

[0051] The oxide of element M requires high-temperature sintering conditions above 600℃ to coat the surface of the substrate, while the ion exchange reaction needs to be carried out at a lower temperature below 300℃. Higher temperatures will cause the O2 phase structure of lithium cobalt oxide to transform into the O3 phase. Therefore, the conventional method of forming the substrate first and then performing high-temperature coating will cause the O2 phase structure of lithium cobalt oxide in the substrate to transform into the O3 phase structure. If the transformation of the O2 phase structure is avoided at high temperatures and coating is performed at low temperatures, the coating source and the substrate material will not be able to bond tightly.

[0052] Based on this, a second aspect of this application provides a method for preparing the cathode material as described above, comprising the following steps:

[0053] 1) The lithium-ion layered oxide precursor and the coating source are subjected to solid-phase mixing treatment to obtain a mixture;

[0054] The coating source is selected from one or more of the oxides, carbonates, phosphates, and acetates of element M, and element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe.

[0055] 2) The mixture is calcined to obtain the cathode material precursor;

[0056] 3) The cathode material precursor is mixed with the lithium source and then subjected to an ion exchange reaction to obtain the cathode material.

[0057] This application involves calcining a lithium-ion layered oxide precursor with a coating source solid phase, pre-coating the lithium-ion layered oxide precursor with an oxide of element M in a discontinuous island-like morphology, and then mixing it with a lithium salt to carry out an ion exchange reaction. The island-like morphology is more conducive to improving the conversion rate of ion exchange than continuous coating, thereby improving the purity of the O2 phase lithium-ion layered oxide.

[0058] In the above preparation method, the lithium-ion layered oxide precursor in step 1) is obtained by mixing and sintering a compound of elements other than lithium and oxygen in the lithium-ion layered oxide with a sodium source. In the ion exchange reaction in step 3), the sodium element in the precursor will undergo an exchange reaction with the lithium ions in the lithium source, exchanging the sodium element for lithium element, thereby obtaining the cathode material.

[0059] For example, when the matrix of the cathode material is a lithium cobalt oxide material doped with Ni and Mn elements and having an O2 phase structure, the lithium-ion layered oxide precursor can be obtained by calcining a mixture of sodium, cobalt, nickel, and manganese sources in stoichiometric ratios. The sodium, cobalt, nickel, and manganese sources are selected from compounds containing sodium, cobalt, nickel, and manganese elements, respectively.

[0060] Specifically, the sodium source can be selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium oxide, or sodium acetate; the cobalt source can be selected from one or more of cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt chloride, or cobalt acetate; the manganese source can be selected from one or more of manganese nitrate, manganese sulfate, manganese carbonate, manganese chloride, or manganese acetate; and the nickel source can be selected from one or more of nickel nitrate, nickel carbonate, nickel sulfate, nickel chloride, or nickel acetate.

[0061] The oxide of element M can be selected from nano-sized oxide particles to facilitate the formation of island-like coatings on the precursor surface. Specifically, the size of the oxide particles is preferably 10 to 1000 nm.

[0062] The calcination conditions during the preparation of the lithium-ion layered oxide precursor can refer to conventional conditions in the field. In one specific embodiment, the sodium source and the compound of other elements in the lithium-ion layered oxide except lithium and oxygen can be mixed and pre-sintered at 400-600°C, then cooled to room temperature, ground, and heated to 700-900°C for high-temperature sintering.

[0063] Since lithium-ion layered oxide precursors are prone to absorbing water and affecting the synthesis of materials, in step 1), water absorption failure is avoided by solid-phase mixing.

[0064] Furthermore, the solid-phase mixing in step 1) can be carried out in a mixing equipment. To avoid the breakage of precursor particles, the mixing speed of the mixing equipment should be controlled to not be too high, preferably at 200 to 400 rpm for 4 to 8 hours.

[0065] Furthermore, in step 2), the calcination temperature is 700–1000°C, and the time is 2–12 hours. The calcination is carried out in an oxygen-containing atmosphere, such as an oxygen atmosphere or an air atmosphere, preferably an air atmosphere.

[0066] In one specific embodiment, the lithium source in step 3) can be selected from lithium sources conventionally used in the art, including but not limited to one or more of lithium nitrate, lithium chloride, lithium bromide, lithium oxalate, and lithium iodide. Preferably, the lithium source is selected from a mixture obtained by mixing a first lithium source and a second lithium source in a molar ratio of 1:1; wherein the first lithium source is selected from lithium nitrate, and the second lithium source is selected from one or more of lithium chloride, lithium bromide, lithium oxalate, and lithium iodide.

[0067] Furthermore, the ion exchange reaction in step 3) is carried out at 230–280°C for 2–10 h. After the ion exchange reaction is completed, a post-processing procedure is also included, which involves crushing the product and washing it multiple times with deionized water to remove soluble lithium and sodium salts. Washing is considered complete when the conductivity of the supernatant is less than 200 μS / cm. The washing solution is then filtered to obtain residual powder, which is then dried and sieved to obtain the final cathode material.

[0068] A third aspect of this application provides a positive electrode sheet, including the positive electrode material provided in the first aspect of this application. The positive electrode sheet can employ a conventional positive electrode sheet structure in the art. Specifically, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the current collector, wherein the positive active layer includes the positive electrode material as described above.

[0069] This application does not impose any special limitations on the positive electrode current collector; commonly used current collectors in the art, such as aluminum foil, can be used.

[0070] The positive electrode active layer of this application includes the positive electrode material as described above, meaning that the positive electrode active layer uses the positive electrode material as described above as the positive electrode active substance. In addition to the positive electrode active substance, the positive electrode active layer may also include components such as conductive agents and binders. Among them, the conductive agents and binders can be those conventionally used in the art, and will not be described in detail here.

[0071] The positive electrode sheet of this application can be prepared by conventional methods in the art. For example, the positive electrode material, conductive agent, binder and other components are dispersed in a solvent to obtain a positive electrode slurry. The positive electrode slurry is then coated on the surface of the positive electrode current collector. After drying, rolling, slitting and other operations, the positive electrode sheet of this application can be obtained.

[0072] A fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0073] Since the positive electrode sheet of the battery in this application includes the positive electrode material provided in the first aspect of this application, the material has high specific capacity, good interface stability and stability under high pressure conditions, which enables the battery to have excellent cycle performance, rate performance and energy density.

[0074] In addition to the positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator disposed between the positive and negative electrodes. The composition and structure of the negative electrode can refer to conventional negative electrode sheets in the art, and will not be described in detail here. The separator can also be a separator conventionally used in the art, such as a PP separator or a PE separator.

[0075] The battery of this application can be manufactured using conventional methods in the art. For example, positive electrode, separator and negative electrode are stacked in sequence, and a cell is obtained by stacking or winding. Then, the battery can be obtained by baking, liquid injection, formation and packaging.

[0076] The following detailed description of the cathode material, its preparation method, and its application provided in this application is illustrated through specific embodiments.

[0077] It should be noted that the particle size D of the coating material in the coating layer on the surface of the cathode material substrate obtained in the following embodiments is... V 50 and the particle size D of the nano-oxide coating source used V The values ​​of 50 are basically the same.

[0078] Example 1

[0079] This embodiment provides a positive electrode material, including a matrix and an Al2O3 coating layer that covers the surface of the matrix in a discontinuous island-like morphology. The chemical composition of the matrix is ​​Li. 0.98 Co 0.86 Ni 0.07 Mn0.07 O2, the preparation method of which includes the following steps:

[0080] 1) Sodium carbonate, cobalt oxalate, nickel oxalate, and manganese oxalate were mechanically mixed in a molar ratio of 0.43:0.86:0.07:0.07. The mixture was then added to a crucible and pre-sintered at 450°C for 4 hours. After cooling to room temperature, it was ground and then sintered at 800°C for 24 hours to obtain the chemical formula Na. 0.86 Co 0.86 Ni 0.07 Mn 0.07 Sodium-ionized precursor of O2;

[0081] 2) The sodium-ion precursor obtained in step 1) and particle size D V 50 nm nano-Al2O3 was added to a mixing device at a mass ratio of 1000:5 and stirred at 200 rpm for 5 hours to obtain a mixture.

[0082] 3) Transfer the mixture obtained in step 2) into a crucible and sinter it at 800°C for 10 hours in an air atmosphere to obtain a secondary sintered material;

[0083] 4) The secondary sintering material obtained in step 3), lithium nitrate and lithium oxalate are mixed in a molar ratio of 1:1:1 and heated to 250°C in air for ion exchange reaction for 10 hours to obtain ion exchange material.

[0084] 5) The ion exchange material obtained in step 4) is crushed and then washed multiple times with deionized water to remove soluble sodium and lithium salts until the conductivity of the supernatant is less than 200 μS / cm. After filtration, drying, and sieving, the particle size D is obtained. V 50 is a cathode material with a diameter of approximately 10 μm.

[0085] Example 2

[0086] This embodiment provides a positive electrode material, including a matrix and an MgO coating layer that is discontinuously island-shaped and covers the surface of the matrix. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-MgO.

[0087] Example 3

[0088] This embodiment provides a cathode material, including a substrate and a TiO2 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-TiO2.

[0089] Example 4

[0090] This embodiment provides a positive electrode material, including a matrix and a ZrO2 coating layer that is discontinuously island-shaped and covers the surface of the matrix. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano ZrO2.

[0091] Example 5

[0092] This embodiment provides a positive electrode material, including a substrate and a Y2O3 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-Y2O3.

[0093] Example 6

[0094] This embodiment provides a cathode material, including a substrate and a Gd2O3 coating layer that is discontinuously island-shaped and covers the surface of the substrate. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-Gd2O3.

[0095] Example 7

[0096] This embodiment provides a positive electrode material, including a substrate and a SnO2 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano SnO2.

[0097] Example 8

[0098] This embodiment provides a positive electrode material, including a matrix and a WO3 coating layer that covers the surface of the matrix in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano WO3.

[0099] Example 9

[0100] This embodiment provides a positive electrode material, including a substrate and a SiO2 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-SiO2.

[0101] Example 10

[0102] This embodiment provides a positive electrode material, including a substrate and a Fe3O4 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano Fe3O4.

[0103] Example 11

[0104] This embodiment provides a positive electrode material, including a substrate and a CeO2 coating layer that is discontinuously island-shaped and covers the surface of the substrate. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano CeO2.

[0105] Example 12

[0106] This embodiment provides a positive electrode material, including a substrate and a La2O3 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-La2O3.

[0107] Example 13

[0108] This embodiment provides a positive electrode material, including a substrate and a Pr2O3 coating layer that is discontinuously island-shaped and covers the surface of the substrate. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano Pr2O3.

[0109] Example 14

[0110] This embodiment provides a positive electrode material, including a substrate and a CuO coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano CuO.

[0111] Example 15

[0112] This embodiment provides a positive electrode material, including a matrix and a ZnO coating layer that covers the surface of the matrix in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano Al2O3 in step 2) is replaced with nano ZnO.

[0113] Example 16

[0114] This embodiment provides a positive electrode material, including a substrate and an In2O3 coating layer that covers the surface of the substrate in a discontinuous island-like morphology. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with nano-In2O3.

[0115] Example 17

[0116] This embodiment provides a cathode material, including a matrix and a coating layer of Y2O3 and MgO in a discontinuous island-like morphology covering the surface of the matrix. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with a mixture of nano-Y2O3 and nano-MgO, and the mass ratio of sodium-ion precursor, nano-Y2O3 and nano-MgO is 1000:10:10.

[0117] Example 18

[0118] This embodiment provides a positive electrode material, including a matrix and a coating layer of Y2O3 and Al2O3 in a discontinuous island-like morphology covering the surface of the matrix. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with a mixture of nano-Y2O3 and nano-Al2O3, and the mass ratio of sodium-ion precursor, nano-Y2O3 and nano-Al2O3 is 1000:5:5.

[0119] Example 19

[0120] This embodiment provides a cathode material, including a matrix and a coating layer of Y2O3, Al2O3 and MgO in a discontinuous island-like morphology covering the surface of the matrix. The preparation method is basically the same as that in Example 1, except that the nano-Al2O3 in step 2) is replaced with a mixture of nano-Y2O3, nano-Al2O3 and nano-MgO, and the mass ratio of the sodium electrode precursor, nano-Y2O3, nano-Al2O3 and nano-MgO is 1000:2.5:2.5:2.5.

[0121] Comparative Example 1

[0122] This comparative example provides a cathode material that differs from the cathode material of Example 1 in that it does not include a coating layer. The preparation method of this material differs from that of Example 1 in that step 2) is omitted. Accordingly, in step 3), the mixture is replaced with the sodium-ion precursor obtained in step 1).

[0123] Preparation Example

[0124] After fabricating the positive electrode materials of the above embodiments and comparative examples into positive electrode sheets, they were assembled into coin cells according to the following method:

[0125] A positive electrode material, conductive carbon black, and PVDF were added to NMP at a mass ratio of 96:2:2 and uniformly dispersed to obtain a positive electrode slurry. This slurry was then coated onto an aluminum foil current collector and rolled to obtain an electrode with an areal density of 12 mg / cm³. 3The positive electrode is then punched into a small disc with a diameter of 12mm using a film punch. After drying and weighing, it is assembled into a coin cell using a 2025 coin cell case and a Li metal disc as the negative electrode in a glove box under an Ar protective atmosphere, together with the Xinzhoubang LBC448A11 electrolyte.

[0126] Test case

[0127] 1. XRD test

[0128] Test method: The material was tested using an X-ray powder diffractometer (XRD, instrument model Bruker D8 ADVANCE), with Cu Kα as the target material, voltage and current of 40KV / 35mA, scanning angle range of 10° to 90°, and scanning rate of 5° / min.

[0129] Figure 1 The image shows the XRD pattern of the cathode material in Example 1. Figure 2 The image shows the XRD pattern of the cathode material in Example 5. Figure 1 and Figure 2 As can be seen, the cathode materials of Examples 1 and 5 have diffraction peaks with 2θ of 18.469° and 18.467° respectively, and the half-peak width is between 0.05 and 0.1, showing significant O2 phase structure characteristics. They also have diffraction peaks with 2θ of 38.2° and 46.95°, indicating that they are lithium cobalt oxide materials with O2 phase stacking structure.

[0130] 2. SEM-EDS test

[0131] Test method: A small amount of positive electrode material was prepared into a sample and attached to a conductive clip. Gold was then sputtered onto the sample for 45 seconds using a Quorum SC7620 sputtering coating instrument at a sputtering current of 10 mA. Subsequently, the surface morphology of the positive electrode material sample was imaged using a TESCAN MIRA LMS scanning electron microscope at an accelerating voltage of 3 kV. During EDS testing, the accelerating voltage was 15 kV, and an SE2 secondary electron detector was used.

[0132] Figure 3 This is a SEM-EDS image of the cathode material in Example 4. Figure 3 As can be seen, ZrO2 is coated on the substrate surface in an island-like discontinuous form, and the particle size of a single island-like coating is between 10-1000 nm. Figure 4 This is a SEM-EDS image of the cathode material in Example 3. Figure 4 As can be seen, TiO2 is coated on the substrate surface in an island-like discontinuous form, and the particle size of a single island-like coating is between 10-1000 nm.

[0133] 3. Coating amount Q

[0134] Test method: Following the method described above, SEM was used to observe the surface morphology of the cathode material sample. EDS analysis was then performed at the center of the coating and the center of the matrix to obtain the content of elements other than Li, O, Na, and C in the coating and matrix. The contents were then summed to obtain the total content, denoted as A. m And the content A of coating elements other than O in the coating was obtained. x According to Q=A x / A m The coating amount Q is calculated by multiplying by 100%.

[0135] 4. Elemental content analysis

[0136] Test method: The content of metal elements in the cathode materials of Example 5 and Comparative Example 1 was tested using an inductively coupled plasma atomic emission spectrometry (ICP) instrument (PE Optima 7000DV, USA). The test results are shown in Table 1.

[0137] 5. Charge-discharge curves

[0138] Test method: After aging the coin cell assembled from the positive electrode material of Comparative Example 1 at 25°C for 24 hours, the first charge-discharge capacity test was carried out. The cell was charged to 4.62V at 0.1C, charged at constant voltage to 0.025C, left to stand for 3 minutes, and then discharged to 3.0V at 0.1C. The charge-discharge curve was obtained. Figure 5 The above is a charge-discharge curve of the positive electrode material of Comparative Example 1 after it was assembled into a coin cell. Figure 5 As can be seen, the electrochemical curve of the cathode material has the characteristics of multiple plateaus, which indicates that the cathode material has an O2 phase stacking structure.

[0139] 6. Specific capacity and coulombic efficiency of the first discharge cycle at 0.1C

[0140] Test method: The coin cells assembled from the cathode materials of the above examples and comparative examples were aged at 25°C for 24 hours, then charged at 0.1C to 4.62V, and then charged at a constant voltage to 0.025C. After being left to stand for 3 minutes, they were discharged at 0.1C to 3.0V. The specific capacity of the first charge cycle C0 and the specific capacity of the first discharge cycle C1 were recorded. The coulombic efficiency of the first cycle at 0.1C was calculated according to C1 / C0. The test results are shown in Table 2.

[0141] 7. Discharge specific capacity after 3 cycles at 0.5C, discharge specific capacity after 30 cycles at 0.5C, and capacity retention after 30 cycles at 0.5C.

[0142] Test method: The coin cells assembled from the cathode materials of Examples 6-16 and Comparative Example 1 were aged at 25°C for 24 hours, then charged at 0.5C to 4.62V, charged at a constant voltage to 0.025C, allowed to stand for 3 minutes, and then discharged at 0.5C to 3.0V. This constitutes one cycle. The discharge specific capacity from the 1st cycle to the 30th cycle was recorded, and the discharge specific capacity curve for 30 cycles was plotted.

[0143] The coin cells assembled from the cathode materials of Examples 1-5 and Comparative Example 1 were aged at 25°C for 24 hours, then charged at 0.5C to 4.62V, charged at a constant voltage to 0.025C, allowed to stand for 3 minutes, and then discharged at 0.5C to 3.0V. This constitutes one cycle. The discharge specific capacity from the first cycle to the 100th cycle was recorded, and the discharge specific capacity curve for 100 cycles was plotted.

[0144] The coin cells assembled from the cathode materials of Examples 17-19 and Comparative Example 1 were aged at 25°C for 24 hours, then charged at 0.5C to 4.62V, constant-voltage charged to 0.025C, allowed to stand for 3 minutes, and then discharged at 0.5C to 3.0V. This constitutes one cycle. The discharge specific capacity from the first cycle to the 150th cycle was recorded, and the discharge specific capacity curve for 150 cycles was plotted.

[0145] The discharge specific capacity C3 after 3 cycles and the discharge specific capacity C30 after 30 cycles were recorded for all the above embodiments and comparative examples. The capacity retention rate after 30 cycles at 0.5C was calculated according to C30 / C3 (the first three cycles are the activation process of the positive electrode material, and the discharge specific capacity fluctuates. Therefore, the calculation method of C30 / C3 can more objectively represent the capacity retention rate after 30 cycles). The calculation results are shown in Table 2.

[0146] The discharge specific capacity C3 for 3 cycles and the discharge specific capacity C100 for 100 cycles were recorded for Examples 5, Examples 17-19, and Comparative Example 1. The capacity retention rate after 100 cycles at 0.5C was calculated using C100 / C3. The calculation results are shown in Table 3.

[0147] Figure 6 This is a comparison chart of the discharge specific capacity of coin cells assembled from the positive electrode materials of Examples 1-5 after 100 cycles at 0.5C. Figure 6 As can be seen, Examples 1-5, by coating with individual components such as Y2O3, MgO, TiO2, ZrO2, and Al2O3 nano-oxides, showed a significant improvement in cycling performance compared to the uncoated sample in Comparative Example 1, while the capacity was not significantly affected.

[0148] Figure 7This is a comparison graph showing the discharge specific capacity of coin cells assembled with the cathode materials of Examples 6-16 and Comparative Example 2 after 30 cycles at 0.5C. Figure 7 As can be seen, in Examples 6-16, the cycling performance was improved compared to the uncoated Comparative Example 1 sample by coating with nano-oxides of elements such as Gd, Sn, W, Si, Fe, La, Pr, Cu, Zn, and In.

[0149] Figure 8 This is a comparison chart showing the discharge specific capacity of coin cells assembled using the cathode materials of Examples 17-19 and Comparative Example 1 after 150 cycles at 0.5C. Figure 8 As can be seen from the examples 17-19, the coating with a combination of various nano-oxides further improves the cycling performance compared to the uncoated samples, and from... Figure 8 and Figure 6 The comparison shows that when the cycle reaches 100 cycles, the discharge specific capacity of the cathode material obtained by coating with a single Y2O3 is only half of that of Examples 17-19.

[0150] Table 1

[0151]

[0152] As can be seen from Table 1, both the cathode materials of Example 5 and Comparative Example 1 contain Na, which can help prove that the cathode materials were prepared by ion exchange method.

[0153] Table 2

[0154]

[0155]

[0156] Table 3

[0157]

[0158] A. The following conclusions can be drawn from Table 2:

[0159] 1. As can be seen from the comparison between Examples 1-16 and Comparative Examples 1-3, the island-like coating of nano-oxides of elements such as Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Gd, In, Zn, and Fe on the surface of lithium-ion layered oxides can significantly improve the cycle performance of cathode materials.

[0160] 2. As can be seen from the comparison of Examples 1 to 16, when the coating amount is basically the same, the island coating using nano-oxides of elements such as Al, Ti, Zr, Y, and Gd can make the cycle performance of the cathode material better than other coating elements.

[0161] 3. As can be seen from the comparison of Examples 1, 2, and 5 with Examples 17-18, when the coating amount is basically the same, using MgO and, or Al2O3 and Y2O3 mixed as the coating layer, can further improve the cycle performance of the cathode material compared with using MgO, Al2O3 and Y2O3 as the coating layer alone. The reason may be that: Y doping at the Co site provides support and improves the bulk stability of the near-surface part; Al blocks the side reactions between the cathode material and the electrolyte; and Mg can improve the conductivity of the bulk phase. Therefore, the use of their mixture can play a synergistic role to obtain better cycle performance.

[0162] 4. Examples 3, 4, 17, and 18 show that the first-cycle coulombic efficiency is greater than 100%. The reason is that the reversible specific capacity of the O2 phase cathode material is high, almost close to 100%. However, the material is not fully intercalated with lithium in the initial state. After the first charge-discharge cycle, the material is activated and is in a fully intercalated lithium state. This may result in the first charge capacity being less than the first discharge capacity, thus causing the first-cycle coulombic efficiency to be greater than 100%.

[0163] B. The following conclusions can be drawn from Table 3:

[0164] After 100 cycles, the cathode material coated with Al2O3 and MgO alone had a discharge specific capacity of 0, while the cathode material coated with Y2O3 alone retained 44.1% of its capacity. The cathode materials coated with a mixture of Y2O3 and MgO, a mixture of Y2O3 and Al2O3, and a mixture of Y2O3, MgO, and Al2O3 all retained more than 80% of their capacity, demonstrating excellent cycle performance. This indicates that compared to single coating, coating with a mixture of Y2O3, MgO, and Al2O3 can significantly improve the cycle performance of cathode materials. Furthermore, as can be seen from Table 3, the cathode material obtained by mixing and coating with three oxides, Y2O3, MgO, and Al2O3, not only has excellent 100-cycle performance, but also has the highest discharge specific capacity at 0.5C for 3 cycles compared to cathode materials coated with a single oxide or a mixture of the three oxides. This indicates that the cathode material coated with the mixture of these three oxides has the greatest advantage.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of this application, and are not intended to limit them. Although the embodiments of this application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode material, characterized in that, It includes a substrate and an island-shaped coating layer disposed on the surface of the substrate, wherein the substrate is a lithium-ion layered oxide with an O2 phase stacking structure; The coating layer includes one or more oxides of element M, wherein element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe.

2. The cathode material according to claim 1, characterized in that, The coating layer comprises a mixture of a first oxide and a second oxide; the first oxide is selected from Y2O3 or Al2O3, and the second oxide is selected from one or more of Al2O3, MgO, TiO2, ZrO2, and Gd2O3.

3. The cathode material according to claim 1, characterized in that, The cathode material includes a first element and a second element. The first element is an element other than O in the coating layer, and the second element is an element other than Li, Na, C, and O in the cathode material. Based on the total mass of the cathode material, the content of the first element is A. x The content of the second element is A. m The coating amount on the substrate surface is Q, where Q = A x / A m ×100%, and 0.1%≤Q≤40%.

4. The cathode material according to any one of claims 1-3, characterized in that, The coating layer consists of several island-shaped coatings, wherein the D of a single island-shaped coating... V The particle size of 50 particles ranges from 10 nm to 1000 nm.

5. The positive electrode material according to claim 1, characterized in that, The lithium-ion layered oxide comprises at least Li and X elements, wherein the X element is selected from one or more of Co, Ni, Mn, Na, Fe, Cu, Ti, Zn, Al, Mg, La, Y, Zr, and F.

6. The cathode material according to claim 5, characterized in that, The lithium-ion layered oxide is selected from lithium cobalt oxide materials.

7. The cathode material according to claim 6, characterized in that, The lithium cobalt oxide material is doped with Ni and Mn elements.

8. The cathode material according to any one of claims 5-7, characterized in that, The lithium-ion layered oxide includes Na element, and the mass content of Na element is 100 to 10000 ppm based on the mass of the lithium-ion layered oxide.

9. A method for preparing the cathode material according to any one of claims 1-8, characterized in that, Includes the following steps: 1) A solid-state mixing treatment is performed on the lithium-ion layered oxide precursor and the coating source to obtain a mixture; the coating source is selected from one or more of the oxides, carbonates, phosphates, and acetates of element M, and element M is selected from one or more of Al, Mg, Ti, Y, Zr, La, Ce, Pr, Si, Sn, Cu, W, Sm, Gd, In, Zn, and Fe; 2) The mixture is calcined to obtain a cathode material precursor; 3) The cathode material precursor is mixed with a lithium source and then subjected to an ion exchange reaction to obtain the cathode material.

10. The preparation method according to claim 9, characterized in that, In step 2), the calcination treatment is carried out at a temperature of 700–1000°C for 2–12 hours.

11. The preparation method according to claim 9, characterized in that, In step 3), the temperature of the ion exchange reaction is 230–280°C, and the time is 2–10 h.

12. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1-8.

13. A battery, characterized in that, The battery includes the positive electrode as described in claim 12.

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