Composite precursor, composite positive electrode material, secondary battery, and electric device

Abstract

The present application provides a composite precursor, a composite positive electrode material, a secondary battery, and an electric device. The composite precursor comprises an inner core and an outer adhesion layer arranged on at least part of the surface of the inner core. The inner core and the outer adhesion layer are both made of metal oxides or substances capable of being decomposed to form metal oxides. For the inner core and the outer adhesion layer, by means of selection of metal elements in different valences, the composite precursor is combined with active elements, so that substances of the inner core form active element-rich substances, and substances of the outer adhesion layer form positive electrode active substances. After the composite precursor is combined with the active elements, the number of moles of active elements in per mole of inner core substance is greater than the number of moles of active elements in per mole of outer adhesion layer substance. The composite precursor can reduce the surface alkalinity of a lithium supplementing agent and improves the air stability, thereby improving the first cycle charge specific capacity of the secondary battery.

Description

Composite precursors, composite cathode materials, secondary batteries and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on June 29, 2023, with application number 202310794650.7 and application name “Composite Precursors, Composite Positive Electrode Materials, Secondary Batteries and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of battery materials, and specifically to a composite precursor, a composite positive electrode material, a secondary battery, and an electrical device. Background Art

[0004] Using high-capacity silicon-oxygen / silicon-carbon and other negative electrode materials to replace graphite is an effective means to improve the energy density of batteries. However, the first efficiency of silicon-based negative electrodes is low (usually around 70-80%), and when paired with conventional positive electrodes (such as LiCoO2, around 94-97%), it will result in a larger first-cycle irreversible capacity. This problem can be effectively solved by lithium replenishment. Lithium replenishment methods can be roughly divided into two types: negative electrode lithium replenishment and positive electrode lithium replenishment. Positive electrode lithium replenishment is widely used because of its strong process compatibility, convenient operation, and easy industrialization. The existing positive electrode lithium replenishment technology route is mainly achieved by adding sacrificial positive electrode active materials, that is, releasing a large amount of active lithium during the first charging process, thereby providing additional lithium ions to the battery system to make up for the different coulombic first efficiencies of the positive and negative electrodes and the consumption of lithium sources during the formation of the SEI film.

[0005] Currently, the most researched and commercially viable cathode lithium-supplementing additives are primarily lithium-rich transition metal oxides (e.g., Li2NiO2, Li6CoO4, Li5FeO4, etc.). However, existing lithium-supplementing agents often suffer from issues such as excessive surface alkalinity and poor air stability (easily deteriorating due to moisture absorption). Excessive surface alkalinity can damage the binder in the slurry, causing problems such as jelly formation and coating delamination. Moisture absorption and deterioration not only reduce the lithium-supplementing effect but also affect moisture control during the cell manufacturing process, impacting the overall battery performance.

[0006] Summary of the Invention

[0007] The present application provides a composite precursor, a composite positive electrode material, a secondary battery and an electrical device to reduce the surface alkalinity of a lithium supplement and improve air stability.

[0008] In a first aspect, the present application provides a composite precursor for synthesizing a positive electrode material, comprising a core and an outer layer disposed on at least a portion of the surface of the core, wherein the core and the outer layer are both metal oxides or substances that can decompose to form metal oxides, and the core and the outer layer are selected by metal elements of different valence states so that the composite precursor and the active material compound are used to form an active element-rich substance in the core, and the outer layer is used to form a positive electrode active material;

[0009] After the composite precursor is combined with the active element, the molar number of the active element in each mole of the core material is greater than the molar number of the active element in each mole of the outer layer material.

[0010] The composite precursor of the present application has a core and an outer layer, and both the core and the outer layer are metal oxides or substances that can decompose to form metal oxides. After the composite precursor is combined with the active element, since the core contains more active elements, taking lithium-ion batteries as an example, when making positive electrode materials, the core can form a lithium supplement material and the outer layer can form a positive electrode active material. The reduction in the content of active elements in the outer layer can alleviate the problem of excessive alkalinity on the surface of the material to a certain extent, avoid the core from forming a lithium supplement and then contacting the electrolyte, and reduce the damage of the lithium supplement with excessive alkalinity to the binder in the positive electrode material layer. At the same time, the provision of the outer layer can also serve as a protective layer for the core, avoiding direct contact with the air after the core forms a lithium supplement, thereby making the formed lithium supplement have better air stability and alleviating the negative impact of moisture absorption and deterioration.

[0011] The active element is an element that can be reversibly intercalated and deintercalated in the positive electrode active material, such as lithium, sodium, potassium, calcium, etc.

[0012] In an optional implementation, the molecular formula of the kernel is N c Y d The molecular formula of the outer layer is M a X b ,in:

[0013] N is selected from at least one of Co, Mn, Fe, Ni, Cr, Cu, V, Nb and Zr;

[0014] M is selected from at least one of Co, Mn, Fe, Ni, Ti, Cr, Cu and V;

[0015] X, Y are each independently selected from at least one of O, OH, OOH, and CO3;

[0016] 1≤a≤5, 1≤b≤5, 1≤c≤5, 1≤d≤5.

[0017] When X is selected from O, the metal oxide formed by it and M, when used as the outer layer material, can directly react with the active element to form the positive electrode active material of the composite positive electrode material. When Y is selected from O, the metal oxide formed by it and N, when used as the core material, can directly react with the active element to form the active element supplement of the composite positive electrode material.

[0018] In an optional implementation, when the M and the N are selected from the same metal, the M a X b The valence of M is greater than that of N c Y d As a result, the N oxide can combine with more active elements to form a core with a high content of active elements. The M oxide can combine with a lower amount of active elements than N to form an outer layer with a low content of active elements.

[0019] In one optional implementation, the outer layer is a continuous outer layer or a discontinuous outer layer. The continuous outer layer covers the entire surface of the inner core, while the discontinuous outer layer covers a portion of the inner core in a dispersed manner. The outer layer can cover the inner core in various forms, including full coverage, partial coverage, or island coverage.

[0020] In an optional implementation, the core has a single-particle structure or a multi-particle structure. When the core has a single-particle structure, the outer layer can be a full coating layer, a semi-coating layer, or a dispersed island-shaped coating layer. When the core has a multi-particle structure, the outer layer can be a full coating layer.

[0021] In an optional implementation, the thickness of the outer layer is 0.1 nm-0.1 μm, preferably 0.1 nm-50 nm, and more preferably 5 nm-15 nm. The thickness of the outer layer is limited to the above range to achieve effective coating of the core.

[0022] In an optional implementation, the material forming the core may include at least one of a metal oxide, a metal hydroxide, a metal oxyhydroxide, or a metal salt. The metal oxide forming the core may include at least one of NiO, CoO, MnO, CuO, Fe2O3, Cr2O3, Fe3O4, Cr3O4, ZrO2, V2O5, or Nb2O5. The metal hydroxide forming the core may include at least one of Ni(OH)2, Co(OH)2, Mn(OH)2, or Cu(OH)2. The metal oxyhydroxide forming the core may include at least one of FeOOH or CrOOH. The metal salt forming the core may include at least one of NiCO3, CoCO3, MnCO3, CuCO3, Zr(CO3)2, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2, CuCO3·Cu(OH)2, or ZrCO3(OH)2.

[0023] In an optional implementation, the material forming the outer layer may include at least one of a metal oxide, a metal hydroxide, a metal oxyhydroxide, or a metal salt. The metal oxide forming the outer layer includes at least one of CuO, Ni2O3, Co2O3, Mn2O3, Fe2O3, Cr2O3, Co3O4, Mn3O4, Fe3O4, Ni3O4, Cr3O4, TiO2, MnO2, or V2O5. The metal hydroxide forming the outer layer includes at least one of Ni(OH)2, Co(OH)2, Mn(OH)2, Cu(OH)2, V(OH)2, Al(OH)3, Fe(OH)3, Cr(OH)3, V(OH)3, and Ti(OH)4. The metal oxyhydroxide forming the outer layer includes at least one of NiOOH, CoOOH, MnOOH, FeOOH, CrOOH, and VOOH. The metal salt forming the outer layer includes at least one of NiCO3, CoCO3, MnCO3, CuCO3, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2 or CuCO3·Cu(OH)2.

[0024] In a second aspect, the present application provides a composite cathode material prepared using the composite precursor of the present application, wherein in the composite precursor, a substance in the form of a metal oxide is combined with an active element to form the composite cathode material; or, a composite precursor that can decompose to form a metal oxide is sintered and combined with an active element to obtain the composite cathode material;

[0025] In the composite positive electrode material, the number of moles of active elements in each mole of the core material is greater than the number of moles of active elements in each mole of the outer layer material.

[0026] In a third aspect, the present application provides a secondary battery comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode collector and a positive electrode material layer coated on at least one side surface of the positive electrode collector, wherein the positive electrode material layer comprises the composite positive electrode material of the present application.

[0027] In a fourth aspect, the present application provides an electrical device, which includes the secondary battery of the present application.

[0028] The technical effects that can be achieved in the second to fourth aspects mentioned above can be described with reference to the corresponding effects in the first aspect mentioned above, and will not be repeated here.

[0029] Among them, the data in the above-mentioned possible implementation methods of the present application, such as the thickness of the outer layer and other data, when measured, the values ​​within the engineering measurement error range should be understood to be within the range specified in the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of a composite precursor according to an embodiment;

[0031] FIG2 is a schematic structural diagram of a composite precursor according to another embodiment;

[0032] FIG3 is a schematic structural diagram of another composite precursor;

[0033] FIG4 is a SEM photograph of CoCO3 seed crystals in Example 1;

[0034] Figure 5 is the X-ray diffraction pattern of LiCoO2@Li6CoO4 powder material;

[0035] Figure 6 is a transmission electron microscope image of LiCoO2@Li6CoO4 powder;

[0036] FIG7 is a comparison chart of the first-cycle charging specific capacities of the secondary batteries of Examples 1-2 and Comparative Example 1.

[0037] Reference numerals: 11 - inner core; 12 - outer layer. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of this application clearer, this application will be further described in detail below with reference to the accompanying drawings.

[0039] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "above", "the", and "this" are intended to also include expressions such as "one or more", unless the context clearly indicates otherwise.

[0040] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0041] Existing lithium supplements are typically lithium-rich compounds, which have high surface alkalinity and poor air stability, easily affecting the overall performance of secondary batteries. Core-shell lithium supplements typically have a protective layer coated on the outer layer of the lithium-rich compound to protect the lithium-rich compound. Existing lithium supplements are prepared by directly coating the surface of the lithium-rich compound with other lithium compounds. High-temperature sintering is usually required during the coating process to achieve the combination of the two. However, the lithium-rich compound often produces byproducts during the sintering process, which reduces the lithium supplement performance of the lithium supplement.

[0042] To address the above-mentioned issues, an embodiment of the present application provides a composite precursor for synthesizing a composite positive electrode material. The composite precursor includes an inner core and an outer layer disposed on at least a portion of the inner core's surface. Both the inner core and the outer layer are metal oxides or substances that can decompose to form metal oxides. The inner core and the outer layer are selected from metal elements of different valence states to allow the composite precursor to combine with an active element, so that the inner core material forms an active element-rich material, and the outer layer material forms a positive electrode active material. After the composite precursor is combined with the active element, the number of moles of active element per mole of the inner core material is greater than the number of moles of active element per mole of the outer layer material.

[0043] When using this precursor to prepare a composite cathode material, it can first undergo a sintering process, followed by an active element reaction to form a cathode material rich in active elements. Since the sintering process is performed first and then reacted with the active elements, the formation of byproducts during the sintering process can be reduced.

[0044] The active element can be an active ion that can shuttle back and forth between the positive electrode material and the negative electrode material in a secondary battery, and can reversibly deintercalate from the positive electrode material. In lithium-ion batteries, the active element is lithium ions. In sodium-ion batteries, the active element is sodium ions. In calcium-ion batteries, the active element is calcium ions. In magnesium-ion batteries, the active element is magnesium ions. The above is merely an illustrative description of the active element; in other types of secondary batteries, the active element can also be a corresponding type of ion.

[0045] The structure and composition of the composite precursor of the present application are further described in detail below, with reference to the accompanying drawings. Figure 1 is a schematic diagram of the structure of a composite precursor according to one embodiment. As shown in Figure 1, the composite precursor includes an inner core 11 and an outer layer 12 coated on the surface of the inner core 11. In the embodiment shown in Figure 1, the outer layer 12 is a continuous outer layer 12, coating the entire surface of the inner core 11 to form a continuous coating. Figure 2 is a schematic diagram of the structure of a composite precursor according to another embodiment. As shown in Figures 1 and 2, the inner core 11 can have a single-particle structure or a multi-particle structure. A single-particle structure can be a single-crystal particle. A multi-particle structure can be a plurality of primary particles agglomerated to form secondary particles. Figure 3 is a schematic diagram of the structure of another composite precursor. As shown in Figure 3, in an optional embodiment, the outer layer 12 is a discontinuous outer layer 12. At least a portion of the surface of the inner core 11 is not coated by the outer layer 12. The discontinuous outer layer 12 can form an island-like coating structure with the inner core 11. That is, the discontinuous outer layer 12 is dispersed and attached to the surface of the inner core 11.

[0046] 1 to 3 , the thickness of the outer layer 12 may be 0.1 nm to 0.1 μm, preferably 0.1 nm to 50 nm, and more preferably 5 nm to 15 nm. For example, the thickness of the outer layer 12 may be 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, 10 nm, 20 nm, 30 nm, 50 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0047] The composite precursor of the embodiment of the present application has a molecular formula of N c Y d The molecular formula of the outer layer 12 is M a X b Wherein: N is selected from at least one of Co, Mn, Fe, Ni, Cr, Cu, V, Nb or Zr; M is selected from at least one of Co, Mn, Fe, Ni, Ti, Cr, Cu or V; X and Y are each independently selected from at least one of O, OH, OOH, CO3; 1≤a≤5, 1≤b≤5, 1≤c≤5, 1≤d≤5.

[0048] Wherein, N and M are both metal elements. Y and X can be O, or other elements or element combinations that can combine with metals to form metal compounds. c Y d and outer layer 12M a X b After sintering, both the core 11 and the outer layer 12 are converted into metal oxides, which can form gases with the elements to be discharged. After sintering, the core 11 and the outer layer 12 are both formed into metal oxides to prevent other elements from affecting the performance of the subsequently formed composite positive electrode material.

[0049] In the core 11 and the outer layer 12, M and N can be the same metal or different metals. When M and N are the same metal, their valences are different, and the valence of M can be greater than that of N. This ensures that, in the composite positive electrode material ultimately formed by combining with the active element, the active element contained in the core 11 is greater than the active element contained in the outer layer 12. When M and N are different metals, in the composite positive electrode material ultimately formed by combining with the active element, the active element contained in the core 11 is greater than the active element contained in the outer layer 12.

[0050] As can be seen from the above, the material forming the core 11 may include at least one of a metal oxide, a metal hydroxide, a metal oxyhydroxide, or a metal salt. The metal oxide forming the core 11 includes one or more of MO (M=Cu), M2O3 (M=Ni, Co, Mn, Fe, Cr), M3O4 (M=Co, Mn, Fe, Ni, Cr), MO2 (M=Ti, Mn), and M2O5 (M=V). Exemplarily, it includes but is not limited to at least one of NiO, CoO, MnO, CuO, Fe2O3, Cr2O3, Fe3O4, Cr3O4, ZrO2, V2O5, or Nb2O5.

[0051] The metal hydroxides forming the core 11 include M(OH)2 (M=Ni, Co, Mn, Cu, V), M(OH)3 (M=Fe, Cr, V), M(OH)4 (M=Ti), (Ni x Co y Mn 1-x-y (OH)2(0 <x<1,0<y<1)、Ni x Co y Al 1-x-y (OH)2(0 <x<1,0<y<1)、M 1-y-z-p-q M' y M” z M"' p M”” q(OH)2 (0 < y < 1, 0 ≤ z < 1, 0 ≤ p < 1, 0 ≤ q < 1; M / M' / M” / M”” / M”” = Ni, Co, Mn, Fe, Ti, Cu, V, Cr), a combination of one or more of them; Exemplarily, it includes at least one of Ni(OH)2, Co(OH)2, Mn(OH)2 or Cu(OH)2.

[0052] The metal hydroxyoxide forming the core 11 includes a combination of MOOH (M = Ni, Co, Mn, Fe, Cr, V); Exemplarily, it includes at least one of FeOOH or CrOOH.

[0053] The metal salts forming the core 11 include a combination of one or more of MCO3 (M = Ni, Co, Mn, Cu), MCO3·M(OH)2 (M = Ni, Co, Mn, Cu); Exemplarily, it includes at least one of NiCO3, CoCO3, MnCO3, CuCO3, Zr(CO3)2, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2, CuCO3·Cu(OH)2 or Zr CO3(OH)2.

[0054] The material forming the outer attached layer 12 may include at least one of substances such as metal oxides, metal hydroxides, metal hydroxyoxides or metal salts. Among them, the metal oxides forming the outer attached layer 12 include a combination of one or more of MO (M = Ni, Co, Mn, Cu), M2O3 (M = Fe, Cr), M3O4 (M = Fe, Cr) or MO2 (M = Zr), M2O5 (M = V, Nb); Exemplarily, it includes at least one of CuO, Ni2O3, Co2O3, Mn2O3, Fe2O3, Cr2O3, Co3O4, Mn3O4, Fe3O4, Ni3O4, Cr3O4, TiO2, MnO2 or V2O5.

[0055] The metal hydroxides forming the outer attached layer 12 include a combination of M(OH)2 (M = Ni, Co, Mn, Cu); Exemplarily, it includes at least one of Ni(OH)2, Co(OH)2, Mn(OH)2, Cu(OH)2, V(OH)2, Al(OH)3, Fe(OH)3, Cr(OH)3, V(OH)3, Ti(OH)4.

[0056] The metal hydroxyoxides forming the outer attached layer 12 include a combination of one or more of MOOH (M = Fe, Cr); Exemplarily, it includes at least one of NiOOH, CoOOH, MnOOH, FeOOH, CrOOH, VOOH.

[0057] The metal salts forming the outer coating layer 12 include one or more combinations of MCO3 (M = Ni, Co, Mn, Cu), M(CO3)2 (M = Zr), MCO3·M(OH)2 (M = Ni, Co, Mn, Cu), MCO3(OH)2 (M = Zr). Exemplarily, it includes at least one of NiCO3, CoCO3, MnCO3, CuCO3, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2 or CuCO3·Cu(OH)2.

[0058] Based on the same technical concept, the embodiment of the present application provides a composite cathode material. The composite cathode material is prepared from the composite precursor of the present application. Among them, the substance in the form of metal oxide combines with the active element to form the composite cathode material; or, the composite precursor capable of decomposing to form metal oxide is sintered and combined with the active element to obtain the composite cathode material. The composite cathode material of the present application retains the core-shell structure of the composite precursor. Among them, in the composite cathode material, the number of moles of the active element in each mole of the inner core substance is greater than the number of moles of the active element in each mole of the outer coating layer substance.

[0059] Among them, the inner core 11 part in the composite cathode material can be used as an active element supplement. In a lithium-ion battery, the inner core 11 can be used as a lithium supplement agent. In a sodium-ion battery, the inner core 11 can be used as a sodium supplement agent.

[0060] Taking the lithium-ion cathode material as an example, in the composite cathode material, the compounds formed by the outer coating layer 12 can be one or more combinations of LiCoO2, LiNiO2, LiMnO2, LiNi x Co y Mn 1-x-y O2, LiNi x Co y Al 1-x-y O2; where 0 < x < 1, 0 < y < 1. The compounds formed by the inner core 11 include one or more combinations of Li3VO4, Li2MnO2, Li3NbO4, Li5FeO4, Li6CoO4, Li2NiO2, Li2CuO2, Li8ZrO6.

[0061] Taking the sodium-ion cathode material as an example, in the composite cathode material, the compounds formed by the outer coating layer 12 are NaMO2 (M = Ni, Co, Mn, Fe, Ti, Cu, V, Cr), Na x M 1-y-z-p-q M' y M” z M”' p M”” qOne or more combinations of O2 (0 < x ≤ 1, 0 < y < 1, 0 ≤ z < 1, 0 ≤ p < 1, 0 ≤ q < 1; M / M' / M” / M”” / M”” = Ni, Co, Mn, Fe, Ti, Cu, V, Cr). The compounds formed by the core 11 include one or more combinations of Na6CoO4, Na5FeO4, Na6MnO4, Na5CrO4, and Na4NiO3.

[0062] The following will further elaborate on the composite precursor of the present application in combination with specific examples and comparative examples.

[0063] Example 1

[0064] Composite precursor CoOOH + Co(OH)2@CoCO3

[0065] Step S11: Prepare CoCO3 seeds: Weigh industrial-grade cobalt chloride raw materials and prepare a cobalt chloride solution with a molar concentration of 2.0 mol / L. Weigh industrial-grade sodium carbonate raw materials and prepare a sodium carbonate solution with a molar concentration of 2.0 mol / L. Add 8 L of the cobalt chloride solution to a 50 L stainless steel reactor, start the stirring device, and add deionized water to adjust the ionic concentration of Co 2+ to 0.04 mol / L. Control the reaction temperature at 40 °C, and simultaneously pump in the cobalt chloride and sodium carbonate solutions, and make the pH of the solution in the reactor remain within the range of 8.0 - 8.5 through an online pH control system. React at a constant temperature for 24 h.

[0066] Step S12: After removing the supernatant, centrifuge and wash the precipitate three times each with deionized water and absolute ethanol, and dry it in a blast oven at 90 °C for 4 h to obtain CoCO3 seeds.

[0067] Step S13: Precipitate a layer of Co(OH)2 on the surface of the CoCO3 seeds. Weigh industrial-grade cobalt nitrate raw materials and prepare a cobalt nitrate solution with a cobalt concentration of 20 g / L. Take an ammonia water solution with an ammonia concentration of 20 g / L and mix it with a sodium hydroxide solution with a concentration of 200 g / L at a volume ratio of 0.1:1, denoted as solution A. First, add the CoCO3 seeds to the reactor, and then add the cobalt nitrate solution and solution A in a co-current manner for reaction, and start the stirring device. During the reaction, strictly control the pH value at 8.4 and the temperature at 75 °C, and react at a constant temperature for 48 h. After the reaction, the suspension contains CoCO3 (Co(OH)2@CoCO3) seeds with Co(OH)2 precipitated on the surface.

[0068] Step S14: Surface micro-oxidation. For the suspension that has completely reacted in step S13, under the premise of starting the stirring device, introduce a nitrogen-oxygen mixed gas with a low oxygen content, and the flow rate is 0.8 m 3 / h, and react for 10 hours. After the reaction is completed, Co(OH)2 on the surface of CoCO3 is slightly oxidized to produce CoOOH, forming a thin coating layer.

[0069] Step S15: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain a composite precursor CoOOH+Co(OH)2@CoCO3.

[0070] The SEM images of CoCO3 seeds are shown in (a) to (c) in Figure 4, where (a) to (c) are SEM images at different magnifications. The SEM images of Co(OH)2@CoCO3) seeds are shown in (d) to (f) in Figure 4, where (d) to (f) are SEM images at different magnifications. The SEM images of CoOOH+Co(OH)2@CoCO3 are shown in (g) to (i) in Figure 4, where (g) to (i) are SEM images at different magnifications. As shown in Figure 4, there is a significant morphological change on the surface of the particles from CoCO3 to Co(OH)2@CoCO3 and then to CoOOH+Co(OH)2@CoCO3, indicating that an outer layer has formed on the surface of the inner core.

[0071] The cobalt valence states of the powder materials at each stage of the reaction, as determined by X-ray photoelectron spectroscopy, are listed in Table 1. As can be seen from the data in Table 1, a small amount of cobalt (2.93%) was converted from divalent to trivalent after surface micro-oxidation of Co(OH)2@CoCO3.

[0072] Table 1

[0073] Composite cathode materials

[0074] Step S21: Place the CoOOH+Co(OH)2@CoCO3 powder in an argon atmosphere in a muffle furnace and sinter at 780°C for 15 hours to obtain Co2O3@CoO powder.

[0075] Step S22: Co2O3@CoO and Li2O were weighed in a molar ratio of 3:1 and ball-milled for 6 hours. The mixture was then reacted at 600°C in an argon atmosphere for 12 hours to obtain a core-shell LiCoO2@Li6CoO4 powder with a thin LiCoO2 coating layer.

[0076] Figure 5 shows the X-ray diffraction pattern of the LiCoO2@Li6CoO4 powder material, and Figure 6 shows a transmission electron micrograph of the LiCoO2@Li6CoO4 powder. As shown in Figure 5, when the LiCoO2 coating layer is thin, the X-ray diffraction pattern does not show obvious LiCoO2 characteristic peaks, but is dominated by Li6CoO4 characteristic peaks. However, as shown in the transmission electron micrograph in Figure 6, a clear coating layer with a thickness of approximately 10 nm is present on the particle surface, and this coating layer has a clear and regular lattice structure, corresponding to the layered characteristics of LiCoO2.

[0077] Secondary battery preparation

[0078] After LiCoO2@Li6CoO4 was placed in the air for 0, 1, 2, 4, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0079] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0080] Example 2

[0081] Composite precursor CoOOH@Co(OH)2:

[0082] Step S11, prepare Co(OH)2 seed crystals. Weigh industrial-grade cobalt nitrate raw material and prepare a cobalt nitrate solution with a cobalt concentration of 20g / L. Take an ammonia solution with an ammonia concentration of 20g / L and mix it with a sodium hydroxide solution with a concentration of 200g / L in a volume ratio of 0.1:1, recorded as solution A. In the reactor, the cobalt nitrate solution and solution A are added in parallel to react, and the stirring device is turned on. During the reaction, the pH value is strictly controlled to 8.4 and the temperature is 75°C, and the reaction is carried out at a constant temperature for 48h. After the reaction is completed, the suspension contains Co(OH)2 seed crystals.

[0083] Step S12: Surface strong oxidation. For the suspension that has been completely reacted in (1), a nitrogen-oxygen mixture with low oxygen content is introduced with a flow rate of 0.8 m 3 / h, and react for 10 hours. After the reaction is completed, the surface of the Co(OH)2 particles will be strongly oxidized to produce CoOOH, forming a thick coating layer.

[0084] Step S13: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain the composite metal compound precursor CoOOH@Co(OH)2.

[0085] During the above reaction process, the cobalt valence states obtained from X-ray photoelectron spectroscopy analysis of the powder materials at each stage are listed in Table 2. As shown in Table 2, after strong surface oxidation, the cobalt element (25.3%) with a relatively high content in the powder material is converted from divalent to trivalent.

[0086] Table 2

[0087] Composite cathode materials

[0088] Step S21: Place the CoOOH@Co(OH)2 powder in an argon atmosphere in a muffle furnace and sinter at 780°C for 15 hours to obtain Co2O3@CoO powder.

[0089] Step S21: Co2O3@CoO and Li2O were weighed in a molar ratio of 3:1 and ball-milled for 6 hours. The mixture was then reacted at 600°C in an argon atmosphere for 12 hours to obtain a core-shell LiCoO2@Li6CoO4 powder with a thick LiCoO2 coating layer.

[0090] The X-ray diffraction pattern of the powder material is shown in Figure 5. Since the LiCoO2 coating layer generated under these conditions is relatively thick, the X-ray diffraction pattern shows a relatively strong LiCoO2 characteristic peak.

[0091] Secondary battery preparation

[0092] After LiCoO2@Li6CoO4 was placed in the air for 0, 1, 2, 4, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0093] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0094] Comparative Example 1

[0095] Precursor CoCO3

[0096] Step S11: Preparation of CoCO3 seed crystals

[0097] Weigh industrial grade cobalt chloride raw material and prepare a cobalt chloride solution with a molar concentration of 2.0 mol / L. Weigh industrial grade sodium carbonate raw material and prepare a sodium carbonate solution with a molar concentration of 2.0 mol / L. Add 8 L of cobalt chloride solution to a 50 L stainless steel reactor, turn on the stirring device, and add deionized water to adjust the Co 2+The ion concentration is 0.04 mol / L. The reaction temperature is controlled at 40°C, and cobalt chloride and sodium carbonate solutions are pumped in simultaneously. The pH of the solution in the reactor is maintained in the range of 8.0-8.5 through an online pH control system, and the reaction is carried out at a constant temperature for 24 hours.

[0098] Step S12: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and three times with anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain CoCO3 powder.

[0099] Positive electrode lithium supplement materials

[0100] Step S21: CoCO3 powder is placed in an argon atmosphere in a muffle furnace and sintered at 780°C for 15 hours to obtain CoO powder.

[0101] Step S22: CoO and Li2O were weighed in a molar ratio of 3:1, ball-milled for 6 h, and then reacted at 600°C in an argon atmosphere for 12 h to obtain Li6CoO4 powder.

[0102] The X-ray diffraction pattern of the powder material is shown in Figure 5. The X-ray diffraction pattern of Comparative Example 1 in Figure 5 shows a characteristic peak of Li6CoO4 with relatively high purity.

[0103] Secondary battery preparation

[0104] After Li6CoO4 was placed in the air for 0, 1, 2, 4, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0105] The positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled with 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical tests were performed.

[0106] The first-cycle charge capacity of Examples 1-2 and Comparative Example 1 was tested, and the test results are shown in Figure 7. As shown in Figure 7, the stability of the lithium supplement Li6CoO4 in air is greatly improved after the surface coating of the composite positive electrode materials of Examples 1-2. Therefore, the first-cycle charge capacity released after long-term exposure to air is significantly increased.

[0107] Example 3

[0108] Composite precursor NiOOH+Ni(OH)2@NiCO3·Ni(OH)2:

[0109] Step S11: Preparation of NiCO3·Ni(OH)2 seed crystals

[0110] Weigh industrial-grade nickel sulfate raw material and prepare a nickel sulfate solution with a molar concentration of 2.0 mol / L. Weigh industrial-grade sodium carbonate raw material and prepare a sodium carbonate solution with a molar concentration of 2.0 mol / L. Pump cobalt chloride and sodium carbonate solution into a 50L stainless steel reactor at the same time, adjust the flow rate of sodium carbonate solution to 5-1000L / h and the flow rate of nickel sulfate solution to 50-1000L / h, and turn on the stirring device. Control the reaction temperature to 80°C, and use an online pH control system to keep the pH of the solution in the reactor in the range of 8.0-8.3, and react at a constant temperature for 24 hours.

[0111] Step S12: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and three times with anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain NiCO 3 ·Ni(OH) 2 seed crystals.

[0112] Step S13: precipitate a layer of Ni(OH)2 on the surface of the NiCO3·Ni(OH)2 seed crystal.

[0113] Weigh industrial-grade nickel sulfate raw material to prepare a 5.0 mol / L nickel sulfate solution. Weigh industrial-grade cobalt sulfate raw material to prepare a 5.0 mol / L cobalt sulfate solution. The two solutions are mixed with a molar ratio of cobalt ions to nickel ions of 1:100, designated Solution B. An ammonia solution with a concentration of 20 g / L is mixed with a sodium hydroxide solution with a concentration of 200 g / L at a volume ratio of 0.1:1. NiCO₃·Ni(OH)₂ seed crystals are first added to a reactor, followed by Solution B, and the reaction is stirred. The pH is strictly controlled at 11 and the temperature is 55°C, and the reaction is continued at this constant temperature for 12 hours. Upon completion of the reaction, the suspension contains NiCO₃·Ni(OH)₂ seed crystals with Ni(OH)₂ precipitated on the surface.

[0114] Step S14: surface micro-oxidation.

[0115] For the suspension liquid that has been completely reacted in step S13, a nitrogen-oxygen mixture with low oxygen content is introduced with a flow rate of 1.0 m 3 / h, and the reaction lasts for 6 hours. After the reaction is completed, Ni(OH)2 on the surface of NiCO3·Ni(OH) is slightly oxidized to produce NiOOH, forming a thin coating layer.

[0116] Step S15: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and anhydrous ethanol, and dry it in a 90°C forced air oven for 4 hours to obtain the composite metal compound precursor NiOOH+Ni(OH)2@NiCO3·Ni(OH)2.

[0117] cathode materials

[0118] Step S21: Place NiOOH+Ni(OH)2@NiCO3·Ni(OH)2 powder in an argon atmosphere in a muffle furnace and sinter at 780°C for 15 hours to obtain Ni2O3@NiO powder.

[0119] Step S22: Ni2O3@NiO and Li2O were weighed in a molar ratio of 3:2 and ball-milled for 6 hours. The mixture was then reacted at 600°C in an argon atmosphere for 24 hours to obtain a core-shell LiNiO2@Li2NiO2 powder with a relatively thin LiNiO2 coating layer.

[0120] Secondary battery preparation

[0121] After LiNiO2@Li2NiO2 was placed in the air for 0, 2, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0122] The aforementioned cathode electrode was matched with a lithium sheet, and a half-cell was assembled using 1M LiPF6 + EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte. Electrochemical testing was then performed. The results are shown in Table 3.

[0123] Example 4

[0124] Composite precursor NiOOH@Ni(OH)2

[0125] Step S11: Preparation of Ni(OH)2 seed crystals

[0126] Weigh industrial-grade nickel sulfate raw material and prepare a nickel sulfate solution with a concentration of 5.0 mol / L. Weigh industrial-grade cobalt sulfate raw material and prepare a cobalt sulfate solution with a concentration of 5.0 mol / L. The above two solutions are mixed, wherein the molar ratio of cobalt ions to nickel ions is 1:100, recorded as solution B. First, add an ammonia solution with an ammonia concentration of 20 g / L to the reactor and mix it with a sodium hydroxide solution with a concentration of 200 g / L at a volume ratio of 0.1:1. Then add solution B to react and turn on the stirring device. During the reaction, the pH value is strictly controlled at 11 and the temperature is 55°C, and the reaction is kept at a constant temperature for 12 hours. After the reaction is completed, the suspension contains Ni(OH)2 seed crystals.

[0127] Step S12: Surface strong oxidation. In step S11, the suspension liquid that has been completely reacted is introduced into a nitrogen-oxygen mixture with a low oxygen content at a flow rate of 1.0 m 3 / h, and react for 6 hours. After the reaction is completed, the surface of the Ni(OH)2 particles will be strongly oxidized to produce NiOOH, forming a thick coating layer.

[0128] Step S12: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and anhydrous ethanol, and dry it in a 90° C. forced air oven for 4 hours to obtain the composite metal compound precursor NiOOH@Ni(OH)2.

[0129] Composite cathode materials

[0130] Step S21: Place NiOOH@Ni(OH)2 powder in an argon atmosphere in a muffle furnace and sinter at 780°C for 15 hours to obtain Ni2O3@NiO powder.

[0131] Step S22: Ni2O3@NiO and Li2O were weighed separately in a molar ratio of 3:2 and ball-milled for 6 hours. The mixture was then reacted at 600°C in an argon atmosphere for 24 hours to obtain a core-shell LiNiO2@Li2NiO2 powder with a thick LiNiO2 coating layer.

[0132] Secondary battery preparation

[0133] After LiNiO2@Li2NiO2 was placed in the air for 0, 2, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0134] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0135] Comparative Example 2

[0136] Precursor NiCO3·Ni(OH)2

[0137] Step S11: Preparation of NiCO3·Ni(OH)2 seed crystals

[0138] Weigh industrial-grade nickel sulfate raw material and prepare a nickel sulfate solution with a molar concentration of 2.0 mol / L. Weigh industrial-grade sodium carbonate raw material and prepare a sodium carbonate solution with a molar concentration of 2.0 mol / L. Pump cobalt chloride and sodium carbonate solution into a 50L stainless steel reactor simultaneously, adjust the flow rate of sodium carbonate solution to 5-1000 L / h and the flow rate of nickel sulfate solution to 50-1000 L / h, and start the stirring device. Control the reaction temperature to 80°C, and use an online pH control system to maintain the pH of the solution in the reactor in the range of 8.0-8.3. The reaction is carried out at a constant temperature for 24 hours. The suspension contains NiCO3·Ni(OH)2.

[0139] Step S12: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and three times with anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain NiCO 3 ·Ni(OH) 2 powder.

[0140] cathode materials

[0141] NiCO₃·Ni(OH)₂ powder was sintered at 780°C for 15 hours in an argon atmosphere in a muffle furnace to produce NiO powder. NiO and Li₂O were separately weighed in a molar ratio of 3:2 and ball-milled for 6 hours. Subsequently, the mixture was reacted at 600°C for 24 hours in an argon atmosphere to obtain Li₂NiO₂ powder with a core-shell structure.

[0142] Secondary battery preparation

[0143] After Li2NiO2 was placed in the air for 0, 2, 8, and 24 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0144] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0145] The first cycle charge specific capacity of the secondary batteries of Examples 3-4 and Comparative Example 2 was tested, and the test results are listed in Table 3.

[0146] Table 3

[0147] As can be seen from Table 3, the composite positive electrode materials of Examples 3-4 have a significantly improved stability of the lithium supplement Li2NiO2 in the air after surface coating, so the first cycle charge capacity released after being placed in the air for a long time is significantly increased.

[0148] Example 5

[0149] Composite precursor MnCO3@Fe2O3

[0150] Step S11: Weigh industrial-grade manganese sulfate as a raw material and prepare a 0.5 mol / L manganese sulfate solution. Weigh industrial-grade ammonium bicarbonate as a raw material and prepare a 2.0 mol / L ammonium bicarbonate solution. In a reaction kettle, first add industrial-grade nano-Fe2O3 powder, then add the manganese sulfate solution. Turn on the stirring device, and then add the ammonium bicarbonate solution at a rate of 10 ml / min to react. Continue stirring for 6 hours and then let it stand overnight. The resulting suspension contains MnCO3@Fe2O3.

[0151] Step S12: remove the supernatant and centrifuge, wash the precipitate three times with deionized water and three times with anhydrous ethanol, and dry it in a forced air oven at 90° C. for 4 hours to obtain the composite metal compound precursor MnCO 3 @Fe 2 O 3 .

[0152] Composite cathode materials

[0153] Step S21: Place the MnCO3@Fe2O3 powder in an air atmosphere in a muffle furnace and sinter at 780°C for 15 hours to obtain Mn2O3@Fe2O3 powder.

[0154] Step S22: Mn2O3@Fe2O3 and Li2O were weighed in a molar ratio of 3:1 and ball-milled for 6 h. The mixture was then reacted at 600°C in an argon atmosphere for 24 h to obtain a core-shell LiMnO2@Li5FeO4 powder.

[0155] Secondary battery preparation

[0156] After LiMnO2@Li5FeO4 was placed in the air for 0, 6, and 12 hours, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0157] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0158] Comparative Example 3

[0159] Preparation of secondary batteries using lithium supplement additive Li5FeO4

[0160] Fe₂O₃ and Li₂O were weighed in a molar ratio of 3:1 and ball-milled for 6 h. The mixture was then reacted at 600°C in an argon atmosphere for 24 h to obtain Li₅FeO₄ powder.

[0161] After Li5FeO4 was placed in the air for 0, 6, and 12 hours respectively, it was uniformly mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. The slurry was coated on the aluminum foil current collector and then dried, rolled, and cut to obtain the positive electrode sheet.

[0162] The above-mentioned positive electrode sheet was matched with the lithium sheet, and a half-cell was assembled using 1M LiPF6+EC / EMC / DMC (1:1:1, v / v / v) as the electrolyte, and electrochemical testing was performed.

[0163] The first cycle charge specific capacity of the secondary batteries of Example 5 and Comparative Example 2 was tested, and the test results are listed in Table 4.

[0164] Table 4

[0165] From the test data in Table 4, it can be seen that after the surface coating, the stability of the lithium supplement Li5FeO4 in the air of the positive electrode material of Example 5 is greatly improved, so the first cycle charge capacity released after being placed in the air for a long time is significantly increased.

[0166] In summary, the positive electrode composite material can be formed by in-situ reaction using a composite precursor, which can reduce the occurrence of side reactions. The composite positive electrode material of the embodiment of the present application can be used as a lithium supplement additive. The core structure can be used as a lithium supplement agent, and the outer layer can be used as a positive electrode active material. In addition, the composite positive electrode material of the embodiment of the present application can still release a high lithium supplement capacity after being placed in the air for a long time, thereby improving the first-cycle charging capacity of the secondary battery. This shows that the composite positive electrode material of the present application has high air stability.

[0167] The above embodiments are merely illustrative. The active element may be other active elements besides lithium, such as sodium. Other active elements will not be described in detail here. However, the composite precursors of the embodiments of the present application can also be used with other types of active element compounds in corresponding secondary batteries.

[0168] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A composite precursor for synthesizing a positive electrode material, characterized in that: It comprises an inner core and an outer layer arranged on at least part of the surface of the inner core, wherein the inner core and the outer layer are both metal oxides or substances that can be decomposed to form metal oxides, and the inner core and the outer layer are selected by metal elements of different valence states so that the composite precursor is combined with active elements to form active element-rich substances in the inner core, and the substances in the outer layer form positive electrode active substances; After the composite precursor is combined with the active element, the molar number of the active element in each mole of the core material is greater than the molar number of the active element in each mole of the outer layer material.

2. The composite precursor according to claim 1, characterized in that The molecular formula of the core is N c Y d The molecular formula of the outer layer is M a X b ,in: N is selected from at least one of Co, Mn, Fe, Ni, Cr, Cu, V, Nb and Zr; M is selected from at least one of Co, Mn, Fe, Ni, Ti, Cr, Cu and V; X, Y are each independently selected from at least one of O, OH, OOH, and CO3; 1≤a≤5, 1≤b≤5, 1≤c≤5, 1≤d≤5.

3. The composite precursor according to claim 1 or 2, characterized in that: When the M and the N are selected from the same metal, the M a X b The valence of M is greater than that of N c Y d Compounds containing N.

4. The composite precursor according to any one of claims 1 to 3, characterized in that: The outer layer is a continuous outer layer or a discontinuous outer layer. The continuous outer layer covers the entire surface of the inner core, and the discontinuous outer layer covers part of the surface of the inner core in a dispersed manner.

5. The composite precursor according to any one of claims 1 to 4, characterized in that: The thickness of the outer layer is 0.1 nm-0.1 μm.

6. The composite precursor according to any one of claims 1 to 5, characterized in that: The material forming the inner core includes at least one of NiO, CoO, MnO, CuO, Fe2O3, Cr2O3, Fe3O4, Cr3O4, ZrO2, V2O5, Nb2O5, Ni(OH)2, Co(OH)2, Mn(OH)2, Cu(OH)2, FeOOH, CrOOH, NiCO3, CoCO3, MnCO3, CuCO3, Zr(CO3)2, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2, CuCO3·Cu(OH)2, and Zr CO3(OH)2.

7. The composite precursor according to any one of claims 1 to 6, characterized in that: The substances forming the outer layer include at least one of CuO, Ni2O3, Co2O3, Mn2O3, Fe2O3, Cr2O3, Co3O4, Mn3O4, Fe3O4, Ni3O4, Cr3O4, TiO2, MnO2, V2O5, Ni(OH)2, Co(OH)2, Mn(OH)2, Cu(OH)2, V(OH)2, Al(OH)3, Fe(OH)3, Cr(OH)3, V(OH)3, Ti(OH)4, NiOOH, CoOOH, MnOOH, FeOOH, CrOOH, VOOH, NiCO3, CoCO3, MnCO3, CuCO3, NiCO3·Ni(OH)2, CoCO3·Co(OH)2, MnCO3·Mn(OH)2 or CuCO3·Cu(OH)2.

8. A composite positive electrode material, characterized in that: In the composite precursor according to any one of claims 1 to 7, the substance in the form of a metal oxide is combined with an active element to form the composite positive electrode material; or, the composite precursor that can be decomposed to form a metal oxide is sintered and combined with an active element to obtain the composite positive electrode material; In the composite positive electrode material, the number of moles of active elements in each mole of the core material is greater than the number of moles of active elements in each mole of the outer layer material.

9. A secondary battery, characterized in that: It comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer coated on at least one side surface of the positive electrode current collector, wherein the positive electrode material layer comprises the composite positive electrode material as claimed in claim 8.

10. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 9.

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