Composite positive electrode material precursor and preparation method thereof, positive electrode active material and battery

Abstract

The invention discloses a composite positive electrode material precursor and a preparation method thereof, a positive electrode active material and a battery. The composite positive electrode material precursor comprises a precursor core body and a precursor shell body coating the precursor core body; the precursor shell comprises at least two precursor coating layers and at least two precursor growth layers which have different porosities and are alternately arranged in a coating manner. The precursor shell contained in the composite positive electrode material precursor is alternately coated by the precursor coating layer and the precursor growth layer, so that the particle structure stability of the composite positive electrode material precursor and the positive electrode active material prepared from the composite positive electrode material precursor is improved, and the cycle performance and the capacity of the positive electrode active material are improved. The battery contains the positive electrode active material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrode materials, and particularly relates to a composite positive electrode material precursor, a preparation method thereof, a positive electrode active material, and a battery. BACKGROUND

[0002] Lithium ion batteries (LIBs) have become the main power source for electric vehicles due to their high energy density, long service life, and excellent safety. With the rapid development of mobile electronic devices, electric vehicles, and renewable energy fields, the market has increasingly high requirements for the energy density, cycle performance, and safety of lithium ion batteries.

[0003] Among them, the positive electrode material plays a crucial role in the electrical properties of lithium ion batteries, such as energy density, safety performance, and cycle performance. Currently, in order to improve the energy density of lithium ion batteries, the scientific research and industrial communities are committed to developing high-energy-density positive electrode materials. However, despite some progress, it has been found in practical applications that the currently disclosed high-energy-density positive electrode materials have the shortcomings of unsatisfactory structural stability, leading to unsatisfactory cycle performance, and the capacity cannot be fully utilized. For example, layered high-energy-density nickel-rich (Ni≥90%) positive electrode materials are prone to irreversible phase transition and anisotropic volume shrinkage during the cycle process. This phase transition and volume shrinkage can lead to the formation of inert rock salt phases, which greatly hinders the transport of Li + , thereby increasing the DCR of the battery. At the same time, the anisotropic lattice volume change is prone to produce intergranular microcracks in the material, not only leading to a decrease in cycle performance, but also providing a penetration channel for the electrolyte, promoting the continuous penetration of the electrolyte along the grain boundary into the interior of the secondary particles, and exacerbating the chemical side reactions of the internal primary particles. These side reactions lead to an increase in electronic resistance and the blocking of active materials. These problems can reduce the cycle performance and thermal stability of lithium ion batteries, posing a safety hazard to lithium ion batteries. SUMMARY

[0004] The present application aims to overcome the above-mentioned shortcomings of the prior art and provide a composite positive electrode material precursor and a preparation method thereof, as well as a positive electrode active material prepared from the composite positive electrode material precursor and a battery containing the positive electrode active material, to solve the technical problems of unsatisfactory structural stability and cycle performance of existing high-energy-density positive electrode active materials.

[0005] To achieve the above-mentioned application purposes, in a first aspect, the present application provides a composite positive electrode material precursor. The composite positive electrode material precursor of the present application comprises: a precursor core; The precursor shell covers the precursor core, and the precursor shell comprises at least two layers of precursor covering layers and at least one layer of precursor growth layers, the porosities of the precursor covering layers and the precursor growth layers are different, and the precursor covering layers and the precursor growth layers are alternately arranged in a direction away from the precursor core; In the embodiment, the at least two layers of the precursor covering layers comprise a first precursor covering layer and a second precursor covering layer arranged in a direction away from the precursor core, and the porosities of the first precursor covering layer and the second precursor covering layer are different.

[0006] The precursor shell of the composite positive electrode material precursor comprises the precursor covering layers and the precursor growth layers with different porosities, and the precursor covering layers further comprise the first precursor covering layer and the second precursor covering layer with different porosities, thereby forming the precursor layers with relatively large porosities and the precursor layers with relatively small porosities which are alternately arranged in the precursor shell. The precursor layers with relatively small porosities have higher strength than the precursor layers with relatively large porosities, thereby effectively enhancing the mechanical properties of the precursor shell and improving the structural stability of the composite positive electrode material precursor, which can enhance the structural stability and specific capacity of the positive electrode active material prepared from the composite positive electrode material precursor. The precursor layers with relatively large porosities can provide a buffer space for the volume expansion and shrinkage of the positive electrode material in the cycle process. Therefore, the composite positive electrode material precursor comprising the precursor growth layers and the at least two layers of the precursor covering layers which are alternately arranged can effectively improve the structural stability of the positive electrode active material in the cycle process, improve the cycle performance of the positive electrode active material and the stability of the contact interface with the electrolyte.

[0007] In some embodiments, the porosity of the precursor covering layer is greater than that of the precursor growth layer, and the porosity of the precursor growth layer is 1.9% to 5.5%.

[0008] In some embodiments, the porosity of the first precursor covering layer is greater than that of the second precursor covering layer, and the porosity of the first precursor covering layer is 5.3% to 17.2%.

[0009] In some embodiments, the porosity of the first precursor covering layer is greater than that of the second precursor covering layer, and the porosity of the second precursor covering layer is 1.9% to 5.5%.

[0010] In some embodiments, the porosity of the first precursor covering layer is greater than that of the second precursor covering layer, and the length of the whisker of the positive electrode material precursor in the first precursor covering layer is 0.25 to 1.05 μm.

[0011] In some embodiments, the porosity of the first precursor coating layer is greater than that of the second precursor coating layer, and the whisker length of the cathode material precursor in the second precursor coating layer is 0.18~0.85 μm.

[0012] In some embodiments, the porosity of the first precursor coating layer is greater than that of the second precursor coating layer, and the thicknesses of the first and second precursor coating layers satisfy any one of the following (1) to (4): (1) The thickness of the single-layer precursor coating is 0.03~0.25 μm; (2) The thickness of the first precursor coating layer in a single layer is 0.05~0.25 µm.

[0013] (3) The thickness of the second precursor coating layer in a single layer is 0.03~0.20 µm.

[0014] (4) The precursor coating layer and the precursor growth layer both have n layers. Along the direction away from the precursor core, the first layer of the precursor coating layer coats the surface of the precursor core, and the particle size of the precursor core is C0 = 0.618 × Dv50 ± 0.50 μm. The first layer of the precursor growth layer coats the surface of the first layer of the precursor coating layer. The particle size formed from the first layer of the precursor growth layer to the precursor core is C1 = C0 + 2.0 ± 0.50 μm. The second layer of the precursor coating layer coats the surface of the first layer of the precursor growth layer. The second layer of the precursor growth layer coats the surface of the second layer of the precursor coating layer. The particle size formed from the second layer of the precursor growth layer to the precursor core is C2 = C1 + 2.0 ± 0.50 μm. μm, the particle size of the particles formed from the nth layer to the precursor core in the precursor growth layer is C. n =C n-1 +2.0±0.50 μm; wherein, Dv50 is the Dv50 particle size of the composite cathode material precursor, and n≥2.

[0015] In some embodiments, the microstress ε of the composite cathode material precursor is 0.10~1.00.

[0016] In some embodiments, the full width at half maximum (FWHM) of the (001) crystal plane of the composite cathode material precursor is 0.612°~0.735°.

[0017] In some embodiments, the full width at half maximum (FWHM) of the (101) crystal plane of the composite cathode material precursor is 0.521°~0.595°.

[0018] In some embodiments, the peak intensity I of the (001) crystal plane of the composite cathode material precursor is 0.89-1.26 times the peak intensity I of the (101) crystal plane. 001 In some embodiments, the peak intensity I of the (001) crystal plane of the composite cathode material precursor is 0.89-1.26 times the peak intensity I of the (101) crystal plane. 101 In some embodiments, the ratio of the peak intensity I of the (001) crystal plane to the peak intensity I of the (101) crystal plane is 0.89-1.26.

[0019] In some embodiments, the Dv50 particle size of the composite cathode material precursor is 12.5-13.5 µm.

[0020] In some embodiments, the cathode material precursor comprises at least one of a precursor of a ternary material, a precursor of a sodium battery material, a precursor of a manganese-rich material, and a precursor of a four-cobalt material.

[0021] In a second aspect of the present application, a preparation method of the composite cathode material precursor is provided. The preparation method comprises the following steps: preparing a seed crystal of the cathode material precursor; subjecting the seed crystal to a crystal growth treatment in a reaction solution comprising raw materials for preparing the cathode material precursor to prepare a precursor core and grow a precursor shell on a surface layer of the precursor core, thereby obtaining the composite cathode material precursor; In the crystal growth treatment, the environmental atmosphere is alternately set as a protective atmosphere and an oxygen-containing atmosphere, and the number of alternations of the protective atmosphere and the oxygen-containing atmosphere is two or more, so that the precursor shell comprises at least two precursor coating layers and at least one precursor growth layer, and the precursor coating layers and the precursor growth layers are alternately arranged in a direction away from the seed crystal. The at least two precursor coating layers comprise a first precursor coating layer and a second precursor coating layer arranged in a direction away from the precursor core, and the first precursor coating layer and the second precursor coating layer have different porosities.

[0022] In the preparation method of the composite cathode material precursor, the crystal growth treatment is performed on the surface of the seed crystal of the cathode material precursor by alternately setting the protective atmosphere and the oxygen-containing atmosphere, and the precursor core is prepared, and then the precursor shell is grown on the surface layer of the precursor core. This makes the size of the grown precursor whisker different, thereby forming the precursor growth layer and the precursor coating layer with different porosities, and the precursor coating layer further comprises the first precursor coating layer and the second precursor coating layer with different porosities, which gives the formed precursor shell the alternately arranged precursor layers with relatively large porosity and the precursor layers with relatively small porosity. In this way, the mechanical properties and structural stability of the composite cathode material precursor are effectively improved, the consistency of the structure and morphology of the composite cathode material precursor is improved, thereby improving the quality stability and efficiency of the preparation of the composite cathode material precursor, and reducing the production cost.

[0023] In some embodiments, the Dv50 of the seed crystal is 3.0-5.0 µm.

[0024] In some embodiments, the method for performing the crystal growth treatment on the seed crystal and the raw material for preparing the precursor of the positive electrode material in the reaction solution comprises the following steps: The seed crystal is added to the base solution, and the raw material for preparing the precursor of the positive electrode material, the precipitant, and the complexing agent are added to the base solution at a certain feed flow rate to perform the crystal growth treatment.

[0025] In some embodiments, the method for performing the crystal growth treatment on the seed crystal and the raw material for preparing the precursor of the positive electrode material in the reaction solution comprises the following steps: In a first protective atmosphere, the seed crystal is added to the base solution, and the raw material for preparing the precursor of the positive electrode material, the precipitant, and the complexing agent are added to the base solution at a certain feed flow rate to perform a first crystal growth treatment; When the particle size in the reaction solution of the first crystal growth treatment reaches the expected particle size, the feed flow rate of the raw material for preparing the precursor of the positive electrode material, the precipitant, and the complexing agent is maintained, the first protective atmosphere is replaced with a first oxygen-containing atmosphere, and a second crystal growth treatment is performed; One cycle of the first crystal growth treatment to the second crystal growth treatment is performed, and at least one cycle is repeated until the particle size in the reaction solution reaches the target particle size, and the crystal growth treatment is terminated; Or one cycle of the first crystal growth treatment to the second crystal growth treatment is performed, and at least one cycle is repeated, and then the first crystal growth treatment is repeated until the particle size in the reaction solution reaches the target particle size, and the crystal growth treatment is terminated.

[0026] In some embodiments, the pH value of the base solution is 10.30-10.90.

[0027] In some embodiments, the raw material for preparing the precursor of the positive electrode material is added to the base solution at a feed flow rate of 140-240 mL / min.

[0028] In some embodiments, the reaction conditions of the crystal growth treatment comprise at least one of the following (1) to (4): (1) the reaction temperature is 50-70℃; (2) the concentration of the complexing agent ion in the reaction solution system is 2-4 g / L; (3) during the crystal growth treatment, the pH value of the reaction solution system is controlled to be 10.10-10.70, (4) the crystal growth treatment is accompanied by stirring treatment, and the stirring speed of the stirring treatment is 400-500 rpm.

[0029] In some embodiments, the thickness d of the precursor growth layer or the precursor coating layer is controlled to satisfy: d=(D t -D t-1 ) / 2, wherein D t =(m t ×D t-1 (3 / m(t-1)) ) (1 / 3) ; wherein D t represents the Dv50 particle size of the particles in the reaction solution at the tth hour of the crystal growth treatment, D t-1 represents the Dv50 particle size of the particles in the reaction solution at the (t-1)th hour of the crystal growth treatment, m t represents the input amount of the raw material for preparing the positive electrode material precursor at the tth hour of the crystal growth treatment, and m t-1 represents the input amount of the raw material for preparing the positive electrode material precursor at the (t-1)th hour of the crystal growth treatment.

[0030] In some embodiments, the protective gas in the protective atmosphere and the oxygen-containing gas in the oxygen-containing atmosphere are respectively introduced into the environment of the crystal growth treatment at a certain flow rate; wherein the rate of introduction of the oxygen-containing gas is 360-450 L / h, and the time for a single introduction is 30-120 min; and / or, the rate of introduction of the protective gas is 350-500 L / h.

[0031] In some embodiments, after the crystal growth treatment, the following steps are further included: The pH of the reaction solution is adjusted to 11.60-11.90, and the composite positive electrode material precursor is subjected to slurry washing treatment.

[0032] In a third aspect, the present application provides a positive electrode active material. The positive electrode active material is prepared by calcining a composite positive electrode material precursor and a lithium source in a certain proportion, wherein the composite positive electrode material precursor is prepared by the composite positive electrode material precursor or the method for preparing the composite positive electrode material precursor described above.

[0033] The surface layer of the positive electrode active material of the embodiment of the present application has a positive electrode material ring layer with relatively large porosity and a positive electrode material ring layer with relatively small porosity, and the positive electrode material ring layer with relatively large porosity and the positive electrode material ring layer with relatively small porosity are alternately arranged. The positive electrode material ring layer with relatively small porosity has relatively high mechanical properties, can resist the volume expansion and shrinkage of the positive electrode active material during the charging and discharging process, enhances the structural stability and cycle performance of the positive electrode active material, and can also enhance the electronic conductivity and specific capacity of the positive electrode active material. The positive electrode material ring layer with relatively large porosity can provide a buffer space for the volume expansion of the positive electrode material, and the positive electrode material ring layer with relatively small porosity can play a good mechanical role in resisting volume expansion and shrinkage. Therefore, the structural stability and cycle performance of the positive electrode active material during the cycle process are improved, and the stability of the contact interface with the electrolyte is also improved.

[0034] In a third aspect, the present application provides a battery. The battery of the present application comprises a positive electrode sheet, and the positive electrode active material contained in the positive electrode sheet comprises the positive electrode active material of the present application.

[0035] The positive electrode sheet of the battery of the present application contains the positive electrode active material of the present application described above, so that the battery of the present application has good cycle performance, high energy density, and stable DCR. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0037] Figure 1 It is a cross-sectional schematic view of the composite positive electrode material precursor particle passing through the precursor core; Figure 2 The SEM images of the ternary material precursor particles not subjected to the slurry washing treatment and the ternary material precursor particles subjected to the slurry washing treatment in step S4 in the preparation method of the ternary material precursor in embodiment A1 and comparative example A1, respectively; wherein, a is the SEM image of the ternary material precursor particles not subjected to the slurry washing treatment in embodiment A1; b is the SEM image of the ternary material precursor particles subjected to the slurry washing treatment in embodiment A1; c is the SEM image of the ternary material precursor particles not subjected to the slurry washing treatment in comparative example A1; d is the SEM image of the ternary material precursor particles subjected to the slurry washing treatment in comparative example A1; Figure 3Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 4 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 5 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 6 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 7 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 8 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 9 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 10 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; Figure 11 Figure 1 is a partial enlarged SEM image of the particle surface of the ternary material precursor and the ternary active material in Example Al; wherein, Figure a is a partial enlarged SEM image of the particle surface of the ternary material precursor; Figure b is a partial enlarged SEM image of the particle surface of the ternary active material; The reference signs in the detailed description are as follows: 01 - precursor core; 02 - precursor shell, 21 - precursor growth layer, 211 - first precursor growth layer, 212 - second precursor growth layer, 22 - precursor coating layer, 221 - first precursor coating layer, 222 - second precursor coating layer. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application and not to limit the present application.

[0039] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0040] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one" or similar expressions refer to any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0041] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0043] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the weight ratio relationship between each component. Therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass mentioned in the specification of the embodiments of the present application can be µg, mg, g, kg and other mass units commonly known in the chemical field.

[0044] The terms "first", "second", "third", etc., are used only for the purpose of description, to distinguish between objects, such as substances, from each other, and cannot be understood as indicating or implying relative importance or implying the number of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0045] [Composite cathode material precursor] In a first aspect, the embodiments of the present application provide a composite cathode material precursor. The composite cathode material precursor comprises a precursor core and a precursor shell covering the precursor core. The precursor shell comprises at least two layers of precursor cladding layers and at least one layer of precursor growth layers. The porosities of the precursor cladding layers and the precursor growth layers are different, and the precursor growth layers and the precursor cladding layers are alternately arranged in a direction away from the precursor core. Meanwhile, the at least two layers of precursor cladding layers comprise a first precursor cladding layer and a second precursor cladding layer arranged in a direction away from the precursor core, and the porosities of the first precursor cladding layer and the second precursor cladding layer are different.

[0046] The precursor core, the precursor growth layer and the precursor cladding layer comprise cathode material precursor materials, and the cathode material precursor materials contained in the precursor core, the precursor growth layer and the precursor cladding layer can be the same or different.

[0047] In the composite cathode material precursor, the at least one layer of precursor growth layers and the at least two layers of precursor cladding layers divide the precursor shell into a plurality of ring layer structures. The at least one layer can be one layer or more than two layers, that is, the number of the precursor growth layers can be one layer or more than two layers; the at least two layers are more than two layers, that is, the number of the precursor cladding layers is more than two layers. The alternately arranged precursor growth layers and precursor cladding layers mean that the precursor cladding layers are arranged between the adjacent two precursor growth layers in the precursor shell, and it can also be understood that the precursor growth layers are arranged between the adjacent two precursor cladding layers. The cathode material precursor material refers to a raw material or an intermediate chemical substance that can be converted into a cathode material.

[0048] The precursor shell contained in the composite cathode material precursor of the embodiments of the present application is alternately coated by the precursor coating layer and the precursor growth layer, and the precursor coating layer comprises a first precursor coating layer and a second precursor coating layer with different porosities. Thus, the precursor shell is formed with alternately distributed precursor layers with relatively large porosity and relatively small porosity, wherein the precursor layer with relatively small porosity has higher strength than the precursor layer with relatively large porosity, thereby effectively enhancing the mechanical properties of the precursor and improving the structural stability of the composite cathode material precursor.

[0049] Based on the structure of the composite cathode material precursor of the embodiments of the present application, after the composite cathode material precursor is prepared into a cathode active material, the cathode active material also has alternately distributed cathode material layers with relatively large porosity and relatively small porosity. In this way, the cathode material layer with relatively small porosity has relatively high mechanical properties, thereby enhancing the structural stability of the cathode active material and simultaneously enhancing the electronic conductivity and specific capacity of the cathode active material. During the cycle process, the cathode active material will expand and shrink in volume due to irreversible phase change and anisotropy, and the cathode material layer with relatively large porosity can provide a buffer space for the volume expansion and shrinkage of the cathode material, and the cathode material layer with relatively small porosity will play a good mechanical role in resisting volume expansion and shrinkage. Therefore, through the synergistic effect of the alternately distributed cathode material layer with relatively large porosity and the cathode material layer with relatively small porosity in the cathode active material, the structural stability of the cathode active material during the cycle process can be effectively improved, the adverse phenomenon of particle rupture and structure collapse of the cathode active material during the charging and discharging process can be effectively alleviated, thereby the cycle performance of the cathode active material and the stability of the contact interface with the electrolyte can be effectively improved. Meanwhile, the electronic conductivity of the cathode active material can also be further improved.

[0050] The precursor core: In the composite cathode material precursor of the embodiments of the present application, the precursor core as described above comprises a precursor material for preparing a cathode material. Therefore, in the embodiments of the present application, the material of the precursor core can be a precursor material of an existing cathode material, or a newly developed and improved precursor material of an existing cathode material.

[0051] As in some embodiments, the material of the precursor core comprises at least one of a precursor of a ternary material, a precursor of a sodium-based material, a precursor of a manganese-rich material, and a precursor of a four-cobalt material. The cathode materials corresponding to the precursors of these cathode materials have high energy density and other properties.

[0052] In some embodiments, the Dv50 particle size of the precursor core can be 3.0-8.5 µm. In exemplary embodiments, the Dv50 particle size of the precursor core can be 3 µm, 3.5 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8.0 µm, 8.5 µm, or any range between any two of the above exemplary but non-limiting particle sizes. The particle size range of the precursor core can be adjusted together with the precursor cladding layer to adjust the particle size range of the composite cathode material precursor of the embodiments, and thus the particle size range of the corresponding cathode active material.

[0053] The precursor shell: In the precursor shell, due to the difference in porosity between different precursor cladding layers. Therefore, the precursor growth layer and the at least two layers of precursor cladding layers are arranged by alternating cladding, forming the precursor ring layer with relatively large porosity and the precursor ring layer with relatively small porosity in the precursor shell. In some embodiments, as shown in Figure 1 As shown in FIG. 1, the composite cathode material precursor includes a precursor core 01 and a precursor shell 02 cladded on the surface of the precursor core 01, wherein the precursor shell 02 includes a precursor growth layer 21 and a precursor cladding layer 22 arranged alternately. When the precursor growth layer 21 and the precursor cladding layer 22 each have a two-layer structure, the precursor growth layer includes a first precursor growth layer 211 and a second precursor growth layer 212, and the precursor cladding layer 22 includes a first precursor cladding layer 221 and a second precursor cladding layer 222. Therefore, in the cross section of the composite cathode material precursor with the precursor core as shown in Figure 1 As shown in FIG. 1, the precursor growth layer 21 and the at least two layers of precursor cladding layers 22 constitute the alternatingly distributed annular rings with different porosities.

[0054] In some embodiments, the porosity of the precursor growth layer can be greater than the porosity of the precursor cladding layer. In some embodiments, the porosity of the precursor growth layer can be in the range of 1.9% to 5.5%, optionally in the range of 2.5% to 5%, optionally in the range of 3% to 5%, and in exemplary embodiments, can be 1.9%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, or any range between any two of the above-mentioned values. By controlling the porosity of the precursor growth layer in the above-mentioned range, the strength of the precursor growth layer, and thus the strength of the precursor shell, and the strength and structural stability of the composite cathode material precursor can be improved. After the precursor growth layer is sintered to form a cathode material layer, i.e., after a layer of the cathode material shell is formed, the strength of the layer of the cathode material shell can be improved, and the volume expansion of the cathode material during charging and discharging can be inhibited. Together with the cathode material layer formed by sintering the precursor cladding layer, the structural stability of the cathode active material formed by sintering the composite cathode material precursor can be improved, and the cycle performance and capacity of the cathode active material can be improved.

[0055] Of course, in other embodiments, the porosity of the precursor growth layer can also be less than the porosity of the precursor cladding layer. The porosity of the precursor growth layer can be flexibly set according to the actual production or application needs.

[0056] The porosities of different precursor cladding layers also differ. When there are multiple layers of precursor cladding layers, the porosity of the precursor cladding layer closer to the precursor core is greater than the porosity of the precursor cladding layer farther from the precursor core.

[0057] In some embodiments, the precursor cladding layer is provided with at least a first precursor cladding layer and a second precursor cladding layer in a direction away from the precursor core, and the porosity of the first precursor cladding layer is greater than the porosity of the second precursor cladding layer.

[0058] Of course, in other embodiments, a third precursor cladding layer, a fourth precursor cladding layer, etc., can also be provided.

[0059] As some embodiments, the porosity of the first precursor coating layer is greater than the porosity of the second precursor coating layer. In embodiments, the porosity of the first precursor coating layer can be 5.3% to 17.2%, optionally 7.1% to 14.7%, and in exemplary embodiments, can be 5.3%, 6.0%, 6.5%, 7.1%, 7.5%, 9.3%, 13.1%, 14.7%, 15.0%, 16.0%, 17.2%, or a range between any two of the foregoing values. By controlling the porosity of the first precursor coating layer within the foregoing range, the volume and distribution of the microcavities contained in the first precursor coating layer can be effectively adjusted. After the first precursor coating layer is sintered to form the positive electrode material layer, i.e., after the first positive electrode material coating layer is formed, the first positive electrode material coating layer has an appropriate amount of microcavities and distribution, which provides a buffer space for the volume expansion of the positive electrode material during the charging and discharging process, improves the structural stability of the positive electrode active material formed by sintering the composite positive electrode material precursor, and improves the cycle performance and capacity of the positive electrode active material.

[0060] In embodiments, when the porosity of the first precursor coating layer is greater than the porosity of the second precursor coating layer, the porosity of the second precursor coating layer can be 1.9% to 5.5%, optionally 2.5% to 5%, and in exemplary embodiments, can be 1.9%, 2.3%, 2.5%, 3.1%, 3.8%, 4.6%, 5.0%, 5.5%, or a range between any two of the foregoing values. By controlling the porosity of the second precursor coating layer within the foregoing range, the mechanical properties such as the strength of the second precursor coating layer can be effectively improved, thereby improving the strength of the precursor coating layer and the structural stability of the particles of the composite positive electrode material precursor. After the second precursor coating layer is sintered to form the positive electrode material layer, i.e., after the second positive electrode material coating layer is formed, the strength of the second positive electrode material coating layer is improved, which can inhibit the volume expansion of the positive electrode material during the charging and discharging process, together with the first positive electrode material coating layer formed by sintering the first precursor coating layer, improve the structural stability of the positive electrode active material formed by sintering the composite positive electrode material precursor, and improve the cycle performance and capacity of the positive electrode active material.

[0061] Further research shows that the porosity of the first precursor coating layer and the second precursor coating layer is affected by the size of the single whisker of the positive electrode material precursor in the first precursor coating layer and the second precursor coating layer. For example, when the size of the single whisker of the positive electrode material precursor is smaller, the porosity of the formed precursor coating layer is larger; on the contrary, when the size of the single whisker of the positive electrode material precursor is larger, the porosity of the formed precursor coating layer is smaller. Therefore, when the porosity of the first precursor coating layer is larger than the porosity of the second precursor coating layer, the size of the single whisker of the positive electrode material precursor in the first precursor coating layer (such as length) is smaller than the size of the single whisker of the positive electrode material precursor in the second precursor coating layer (such as length).

[0062] The porosity of the first precursor coating layer and the second precursor coating layer is also affected by the position of the first precursor coating layer and the second precursor coating layer in the composite positive electrode material precursor, that is, the distance of the precursor coating layer from the center of the precursor core. For example, when the size of the whisker and other factors are the same, the closer the formed precursor coating layer is to the center of the precursor core, the larger the porosity of the precursor coating layer is; on the contrary, the farther the formed precursor coating layer is to the center of the precursor core, the smaller the porosity of the precursor coating layer is.

[0063] It is detected that when the porosity of the first precursor coating layer is larger than the porosity of the second precursor coating layer, and the porosity of the first precursor coating layer can be 5.3%~17.2%, the length of the whisker of the positive electrode material precursor in the first precursor coating layer is distributed in the range of 0.25 μm~1.05 μm; when the porosity of the second precursor coating layer can be 1.9%~5.5%, the length of the whisker of the positive electrode material precursor in the second precursor coating layer is distributed in the range of 0.18 μm~0.85 μm.

[0064] The thickness of the single-layer precursor coating layer can be 0.03~0.25 μm, and can be 0.03~0.20 μm. In the exemplary embodiment, it can be 0.03 µm, 0.05 µm, 0.10 µm, 0.15 µm, 0.20 µm, 0.25 µm, and the like, which are typical but not limited thicknesses or ranges between any two thickness values.

[0065] In some embodiments, when the porosity of the first precursor coating layer is greater than the porosity of the second precursor coating layer, the monolayer thickness of the first precursor coating layer can be 0.05-0.25 µm, optionally 0.05-0.20 µm, and in exemplary embodiments, can be a typical but non-limiting thickness of 0.05 µm, 0.10 µm, 0.15 µm, 0.20 µm, 0.25 µm, or a range between any two thickness values. Controlling the monolayer thickness of the first precursor coating layer within the above range can further adjust the volume and distribution of the microcavities in the first precursor coating layer, thereby further improving the buffering effect of the first positive electrode material coating layer generated after sintering when the volume expands, and improving the structural stability and cycle performance of the corresponding positive electrode active material.

[0066] In some embodiments, when the porosity of the first precursor coating layer is greater than the porosity of the second precursor coating layer, the monolayer thickness of the second precursor coating layer can be 0.03-0.20 µm, optionally 0.03-0.15 µm, and in exemplary embodiments, can be a typical but non-limiting thickness of 0.03 µm, 0.05 µm, 0.08 µm, 0.12 µm, 0.15 µm, 0.20 µm, or a range between any two thickness values. Controlling the monolayer thickness of the second precursor coating layer within the above range can further adjust the mechanical properties such as the strength of the second precursor coating layer, thereby further improving the structural stability of the composite positive electrode material precursor, and improving the mechanical properties such as the resistance to volume expansion and contraction of the second positive electrode material coating layer generated after sintering, and improving the structural stability and cycle performance of the corresponding positive electrode active material.

[0067] In some embodiments, when the porosity of the first precursor coating layer is greater than the porosity of the second precursor coating layer, the number of layers of the precursor coating layer and the precursor growth layer is n, wherein n is a positive integer and n≥2. Then in the direction away from the precursor core body, the first layer of the precursor coating layer is coated on the surface of the precursor core body, and the particle size of the precursor core body is C0=0.618×Dv50±0.50 µm (which can also be understood as the diameter C0 of the region formed by the precursor core body). The first layer of the precursor growth layer is coated on the surface of the first layer of the precursor coating layer, and the particle size of the first layer of the precursor growth layer to the precursor core body is C1=C0+2.0±0.50 µm (which can also be understood as the diameter C1 of the first layer of the precursor growth layer to the region formed by the precursor core body). The second layer of the precursor coating layer is coated on the surface of the first layer of the precursor growth layer, and the second layer of the precursor growth layer is coated on the surface of the second layer of the precursor coating layer, and the particle size of the second layer of the precursor growth layer to the precursor core body is C2=C1+2.0±0.50 µm. By analogy, the particle size Cn of the nth layer of the precursor growth layer to the precursor core body is Cn=Cn-1+2.0±0.50 µm. nSatisfies: C n =C n-1 +2.0±0.50 μm. Wherein, the position area of C0, C1 and C2 in the composite cathode material precursor is as shown in Figure 1 n The position area of C0, C1 and C2 in the composite cathode material precursor can be analogized according to the position area of C1 and C2 in Figure 1 n Dv50 in the relationship is the Dv50 particle size of the composite cathode material precursor; C1 to C n 0.618 in the relationship is the value based on the formula of golden section point ( ).

[0068] Therefore, based on the porosity of the first precursor coating layer being greater than the porosity of the second precursor coating layer, and the above C0 to C n relationship, when the Dv50 particle size of the composite cathode material precursor of the embodiment of the present application is 13±0.50 μm, the particle size C0 of the precursor core is 8.034±0.50 μm, at this time, the thickness d1 of the first layer in the precursor coating layer is 0.16 μm≤d1≤0.20 μm; the particle size C1 of the first layer to the second layer in the precursor growth layer to the particle formed by the precursor core is 10.034±0.50 μm, the thickness d2 of the second layer in the precursor coating layer is 0.09 μm≤d2≤0.13 μm; the particle size C2 of the second layer to the second layer in the precursor growth layer to the particle formed by the precursor core is 12.034±0.50 μm, at this time, the thickness d3 of the third layer of the precursor coating layer is 0.06 μm≤d3≤0.10 μm. Wherein, the thickness of d1, d2 is as shown in Figure 1 .

[0069] Further control the relationship between the thickness of different precursor coating layers and the precursor particle size in the above relationship shown by the C1 to C n relationship, can further improve the respective roles of different precursor coating layers as described above, thereby further improving the particle structure stability of the composite cathode material precursor, corresponding to improve the structure stability and cycle performance of the positive active material.

[0070] ​​In some embodiments, the precursor coating layer and the precursor growth layer of the composite cathode material precursor of the embodiments of the present application contain precursors for preparing cathode materials. Therefore, in the embodiments of the present application, the materials of the precursor coating layer and the precursor growth layer of the precursor shell can be precursors of existing cathode materials, or newly developed and improved precursors of existing cathode materials. Moreover, the materials of the precursor coating layer and the precursor growth layer in the precursor shell can be the same as or different from the material of the precursor core. When they are different, the composite cathode material precursor of the embodiments of the present application contains precursors of two or more types of cathode materials, so that the cathode active material generated by sintering the composite cathode material precursor also contains the corresponding two or more types of cathode materials, which can realize the electrical complementation and synergistic effect of the two or more types of cathode materials.

[0071] In some embodiments, the materials of the precursor coating layer and the precursor growth layer in the precursor shell can include at least one of precursors of ternary materials, precursors of sodium-based materials, precursors of manganese-rich materials, and precursors of four-cobalt materials, etc. In embodiments, the precursors can be hydroxides of metal elements, and of course can also be other precipitates of metal elements, such as carbonates, etc. The cathode materials corresponding to the precursors of the cathode materials have high energy density and other properties.

[0072] Based on the precursor core and the precursor shell in the above embodiments, it is detected that the composite cathode material precursor of the embodiments of the present application at least has the following characteristics in each of the embodiments: In some embodiments, the microstress ε of the composite cathode material precursor is 0.10-1.00, and optionally 0.30-0.90. From the microstress ε in this range, it can be known that the stress of the composite cathode material precursor particles is small, and the structure is stable. The microstress ε can be calculated according to the formula F×cosθ=ε4sinθ. In the formula, F is the half-peak width of a diffraction peak in the X-ray diffraction (XRD) spectrum of the composite cathode material precursor particles, and θ is the diffraction angle corresponding to the diffraction peak in the XRD spectrum; taking 4sinθ as the abscissa and Fcosθ as the ordinate, a plurality of coordinate points are obtained based on the half-peak width F and the diffraction angle θ of a plurality of diffraction peaks in the XRD spectrum, the obtained coordinate points are fitted into a straight line, and the slope of the obtained straight line is the microstress ε.

[0073] In some embodiments, according to the XRD spectrum of the composite cathode material precursor, the half-peak width of the (001) crystal plane of the composite cathode material precursor is 0.612°-0.735°; the half-peak width of the (101) crystal plane of the composite cathode material precursor is 0.521°-0.595°; and the peak intensity I 001 and the peak intensity I 101The ratio is 0.89-1.26. According to the crystallinity of the (001) crystal face and the crystallinity of the (101) crystal face, the composite positive electrode material precursor passes through the precursor shell including the precursor coating layer and the precursor growth layer, and compared with the traditional positive electrode material precursor, the half-peak width of the (001) crystal face and the (101) crystal face of the composite positive electrode material precursor is narrowed, and the peak intensity ratio I(001) / (101) is increased, which indicates that the number of (001) dominant crystal faces of the composite positive electrode material precursor is increased, the crystal of the composite positive electrode material precursor grows along the dominant crystal face, and the lithium ion transmission performance is improved.

[0074] [Preparation method of composite positive electrode material precursor] In a second aspect, the embodiments of the present application further provide a preparation method of the composite positive electrode material precursor. The preparation method of the composite positive electrode material precursor includes the following steps: S10: preparing a seed crystal of the positive electrode material precursor; S20: performing a crystal growth treatment on the seed crystal and a reaction solution including raw materials for preparing the positive electrode material precursor to prepare a precursor core and grow a precursor shell on a surface layer of the precursor core, thereby obtaining the composite positive electrode material precursor.

[0075] In the preparation method of the composite positive electrode material precursor, in the crystal growth treatment of step S20, the environmental atmosphere is alternately set as a protective atmosphere and an oxygen-containing atmosphere, and the number of alternations of the protective atmosphere and the oxygen-containing atmosphere is two or more. That is, by controlling the environmental atmosphere of the crystal growth treatment to be alternately set as the protective atmosphere and the oxygen-containing atmosphere, the precursor core is first prepared in the first protective atmosphere, and then the crystal growth treatment is affected by the alternately set environmental atmosphere of the oxygen-containing atmosphere and the protective atmosphere to change the morphology of the precursor crystal grown on the surface layer of the precursor shell and the related characteristics such as porosity of the precursor shell formed, so as to form the precursor coating layer and the precursor growth layer alternately coated and arranged on the surface of the precursor core and in the direction away from the precursor core, thereby constituting the precursor shell.

[0076] Specifically, when the environmental atmosphere of the crystal growth treatment is set as the oxygen-containing atmosphere in stages, due to the presence of oxygen in the oxygen-containing atmosphere, compared with the protective atmosphere, the oxygen-containing atmosphere changes the deposition reaction and the crystal growth environment of the crystal growth treatment, which is specifically manifested as that the growth direction of the whisker generated by the deposition reaction in the oxygen-containing atmosphere is adjusted, and compared with the protective atmosphere, the consistency of the whisker growth is improved, and then the size such as length of the whisker is relatively small (the size of the primary particle is relatively small), so that the porosity of the precursor coating layer generated in the oxygen-containing atmosphere is larger than that of the precursor growth layer generated in the protective atmosphere.

[0077] In some embodiments, when the ambient atmosphere is alternately a protective atmosphere and an oxygen-containing atmosphere, and the number of alternations of the protective atmosphere and the oxygen-containing atmosphere is more than twice, that is, the ambient atmosphere comprises at least a first protective atmosphere, a first oxygen-containing atmosphere, a second protective atmosphere, and a second oxygen-containing atmosphere, the precursor core is prepared under the first protective atmosphere, the first precursor cladding layer (the first layer in the precursor cladding layer) is formed under the first oxygen-containing atmosphere, the first layer in the precursor growth layer is formed under the second protective atmosphere, and the second precursor cladding layer (the second layer in the precursor cladding layer) is formed under the second oxygen-containing atmosphere. When the crystal growth is performed under the oxygen-containing atmosphere, the precursor cladding layers of different layers are formed under different oxygen-containing atmospheres of different alternations, the distances of the precursor cladding layers of different layers from the precursor core are different, and the porosities of the precursor cladding layers of different layers are also different. The first precursor cladding layer is the innermost precursor cladding layer, is relatively close to the precursor core, and has a relatively large porosity. The second precursor cladding layer is the outermost precursor cladding layer, is relatively far from the precursor core, and has a relatively small porosity.

[0078] In this way, the method for preparing the composite cathode material precursor according to the embodiments of the present application uses the alternately arranged protective atmosphere and oxygen-containing atmosphere to adjust the crystal growth on the surface of the seed crystal of the cathode material precursor, so that the sizes of the grown precursor whiskers are different, at least two precursor cladding layers and the precursor growth layer with different porosities are formed, and the precursor cladding layers and the precursor growth layer are alternately arranged in the precursor shell. The formed precursor shell has alternately arranged precursor layers with relatively large porosities and relatively small porosities. The precursor layer with the relatively small porosity has a higher strength than the precursor layer with the relatively large porosity, so that the mechanical properties of the precursor cladding layer are effectively enhanced, and the structural stability of the composite cathode material precursor is improved. Moreover, the method for preparing the composite cathode material precursor according to the embodiments of the present application mainly adjusts the protective atmosphere and the oxygen-containing atmosphere to flexibly change the size and morphology of the precursor whisker, flexibly adjust the structure of the precursor cladding layer, effectively improve the consistency of the structure and morphology of the composite cathode material precursor, improve the quality stability and efficiency of the preparation of the composite cathode material precursor, and reduce the production cost.

[0079] Step S10: The seed crystal of the cathode material precursor prepared in step S10 can be the precursor core contained in the composite cathode material precursor according to the embodiments of the present application. The material and particle size of the seed crystal can be the same as those of the precursor core. In some embodiments, the Dv50 particle size of the seed crystal can be 3.0-5.0 µm, or 3.0-4.0 µm.

[0080] In some embodiments, the method for preparing the seed crystal of the cathode material precursor in step S10 can include the following steps: The raw materials for preparing the cathode material precursor, the precipitator, and the complexing agent are added into the reaction base solution in a certain proportion, and a precipitation reaction is performed in a protective atmosphere to generate the seed crystal of the cathode material precursor.

[0081] In some embodiments, at least one of the raw materials for preparing the cathode material precursor, the precipitator, and the complexing agent can be added into the reaction base solution in the form of a solution to improve the efficiency of the precipitation reaction and control the particle size of the growing seed crystal. In the embodiments, the raw materials for preparing the cathode material precursor, the precipitator, and the complexing agent are respectively dissolved in a solvent such as water to prepare a raw material solution, a precipitator solution, and a complexing agent solution. In the embodiments, the total molar concentration of metal ions in the cathode material precursor raw material solution can be 2-5 mol / L, and optionally 2-3 mol / L; the concentration of the precipitator solution prepared by the precipitator can be 4.0-12.0 mol / L, and optionally 7-10 mol / L; and the concentration of the complexing agent solution prepared by the complexing agent can be 2-12 mol / L, and optionally 5-10 mol / L, and further 4-7 mol / L.

[0082] In some embodiments, when at least one of the raw materials for preparing the cathode material precursor, the precipitator, and the complexing agent is added into the reaction base solution in the form of a solution, the raw material solution, the precipitator solution, and the complexing agent solution can be added into the reaction base solution at a certain flow rate. In the embodiments, the raw material solution is added into the base solution at a feed flow rate of 40-120 mL / min for the precipitation reaction, so as to adjust the number and particle size of the generated seed crystal.

[0083] In the embodiments, the reaction base solution can be a mixed solution prepared by the precipitator and the complexing agent, and the pH value of the mixed solution is 10.30-11.80, and optionally 11.60-11.80. For example, the reaction base solution can be a mixed solution prepared by the 4.0-12.0 mol / L precipitator solution and the 5-12 mol / L complexing agent solution, and the pH value of the mixed solution is 10.30-11.80.

[0084] The raw materials for preparing the cathode material precursor can be determined according to the type of the cathode material precursor. In some embodiments, when the cathode material precursor is a ternary cathode material precursor, the raw materials for preparing the cathode material precursor can include a soluble nickel (Ni) source, a soluble cobalt (Co) source, and a soluble manganese (Mn) source in a certain proportion. In the exemplary embodiments, the soluble nickel (Ni) source, the soluble cobalt (Co) source, and the soluble manganese (Mn) source can be soluble salts of nickel, cobalt, and manganese, such as sulfates, chlorides, and nitrates.

[0085] In some embodiments, the precipitating agent can include, but is not limited to, a hydroxide, and in exemplary embodiments, the hydroxide can be sodium hydroxide, potassium hydroxide, or the like. The complexing agent can include, but is not limited to, ammonia water. The complexing agent can effectively react with metal ions in the raw materials of the positive electrode material precursor, and precipitates can be generated in the reaction of the precipitating agent, such as metal hydroxide precipitates, so as to optimize the number and particle size of the crystal seeds.

[0086] In some embodiments, the conditions of the precipitation reaction can include at least one of the following (1) to (4): (1) The pH value of the reaction solution system during the precipitation reaction process can be 11.30-11.90 (pH value measured at 45°C); (2) During the precipitation reaction process, the concentration of the complexing agent ions in the reaction solution system is 1-3 g / L of ammonia value (3) The reaction temperature can be 50-70°C, and optionally 55-70°C; (4) The precipitation reaction process is also accompanied by stirring treatment, such as stirring treatment at a rotation speed of 400-500 r / min.

[0087] By controlling the conditions of the precipitation reaction, such as the temperature and the pH value of the reaction solution system, in the above ranges, and further accompanied by stirring treatment, the rate of the precipitation reaction can be controlled, so as to improve the generation rate of the crystal seeds and adjust the particle size of the crystal seeds. In embodiments, the precipitation reaction can be flexibly controlled according to the requirements of the particle size of the crystal seeds, such as terminating the precipitation reaction when the Dv50 particle size of the generated crystal seeds reaches 3.0-5.0 μm, and optionally the Dv50 particle size of the crystal seeds reaches 3.0-4.5 μm, and optionally 3.0-4.0 μm. After the precipitation reaction is terminated, solid-liquid separation can be performed, and the collected crystal seed precipitates can be washed to obtain purified crystal seed particles.

[0088] In some embodiments, the protective atmosphere of the precipitation reaction can be an oxygen-free or chemically inert gas constructed protective atmosphere. In exemplary embodiments, when the protective atmosphere is constructed by a chemically inert gas, it can be a nitrogen atmosphere, a helium atmosphere, an argon atmosphere, or the like, so as to improve the stability of the precipitation reaction, improve the stability of the particle structure of the crystal seeds, and the like.

[0089] Step S20: In step S20, the crystal growth treatment is performed to prepare a precursor core, and a precursor shell including a precursor coating layer and a precursor growth layer contained in the precursor of the composite positive electrode material precursor is formed on the surface of the precursor core.

[0090] In some embodiments, the method for performing the crystal growth treatment on the seed crystals prepared in step S10 and the raw materials for preparing the precursor of the positive electrode material in the reaction solution can include the following step S21: Step S21: adding the seed crystals into the base solution, and then adding the raw materials for preparing the precursor of the positive electrode material, the precipitant, and the complexing agent into the base solution at a certain feeding flow rate to perform the crystal growth treatment.

[0091] By adding the raw materials for preparing the precursor of the positive electrode material, the precipitant, and the complexing agent into the base solution containing the seed crystals at a certain feeding flow rate to perform the crystal growth treatment, the feeding can be continuously and stably performed, and only the environmental atmosphere for the crystal growth treatment needs to be controlled, such as controlling the crystal growth treatment to be performed in the alternating protective atmosphere and the oxygen-containing atmosphere, respectively, to control the morphology and size of the grown whiskers, so that the precursor coating layer and the precursor growth layer can be continuously formed in the alternating coating arrangement, the uniformity and stability of the structure of the precursor coating layer and the precursor growth layer can be improved, and the formation efficiency of the precursor shell can also be improved.

[0092] In some embodiments, the thickness of the precursor coating layer and the precursor growth layer can be controlled by controlling the time for the crystal growth treatment, the addition amount of the raw materials for preparing the precursor of the positive electrode material, and the like, such as controlling the thickness d of the formed precursor coating layer or the precursor growth layer to satisfy d=(D t -D t-1 ) / 2, where D t =(m t ×D t-1 (3 / m(t-1)) ) (1 / 3) ; where D t represents the Dv50 particle size of the particles in the reaction solution at t hours (h) of the crystal growth treatment, D t-1 represents the Dv50 particle size of the particles in the reaction solution at t-1 hours (h) of the crystal growth treatment, m t represents the input amount of the raw materials for preparing the precursor of the positive electrode material at t hours (h) of the crystal growth treatment, m t-1 represents the input amount of the raw materials for preparing the precursor of the positive electrode material at t-1 hours (h) of the crystal growth treatment, m t and m t-1 are the values in kg. By controlling the crystal growth treatment of the formed precursor coating layer and the precursor growth layer, the thickness of the precursor coating layer and the precursor growth layer in the composite positive electrode material precursor of the above embodiments can be controlled, and the precursor coating layer and the precursor growth layer can play their respective roles as described above.

[0093] In one embodiment, the frequency of alternately setting the protective atmosphere and the oxygen-containing atmosphere can be flexibly controlled according to the particle size in the reaction solution system during the growth of the crystal seeds in the reaction solution system during the crystal growth process. For example, in one embodiment, the method for performing the crystal growth process on the crystal seeds prepared in step S10 in the reaction solution including the raw materials for preparing the positive electrode material precursor can include the following steps: Step S22: adding the crystal seeds prepared in step S10 into the bottom solution in the first protective atmosphere, and adding the raw materials for preparing the positive electrode material precursor, the precipitating agent, and the complexing agent into the bottom solution at a certain feeding flow rate to perform a first crystal growth process; Step S23: when the particle size in the reaction solution during the first crystal growth process reaches the expected particle size, maintaining the feeding flow rate of the raw materials for preparing the positive electrode material precursor, the precipitating agent, and the complexing agent, replacing the first protective atmosphere with the first oxygen-containing atmosphere, and performing a second crystal growth process; Step S24: taking steps S22 (the first crystal growth process) to S23 (the second crystal growth process) as one cycle, and performing at least one cycle until the particle size in the reaction solution reaches the target particle size, and then terminating the crystal growth process; Step S25: taking steps S22 (the first crystal growth process) to S23 (the second crystal growth process) as one cycle, and performing at least one cycle, and then repeating the first crystal growth process of step S22 until the particle size in the reaction solution reaches the target particle size, and then terminating the crystal growth process.

[0094] One of steps S24 and S25 is selected for the process.

[0095] In step S22, the first growth process on the surface of the crystal nucleus layer makes the particle size reach the target expectation, and the precursor nucleus is prepared. In step S23, the second crystal growth process forms the first precursor coating layer (the first layer in the precursor coating layer) on the surface of the precursor nucleus. In steps S24 or S25, the first growth process forms the precursor growth layer, the second growth process forms the precursor coating layer, and the second growth process in the first cycle in steps S24 or S25 forms the second precursor coating layer (i.e., the second layer in the coating layer).

[0096] In the embodiments, when the particle size of the particles contained in the reaction solution in step S24 or step S25 is 12.50-13.50 μm, the first crystal growth treatment of step S22 is repeated at least 2 cycles in total according to step S24, or the first crystal growth treatment of step S22 is repeated at least 2 cycles in total according to step S25, and then the second crystal growth treatment of step S23 is performed until the particle size of the particles in the reaction solution reaches the target particle size, and the crystal growth treatment is terminated.

[0097] In the embodiments, the composite positive electrode material precursor with a particle size of 12.50-13.50 μm is prepared according to the method of step S22, step S23, and step S25 described above: In the first cycle, when the particle size of the particles in the reaction solution in the first crystal growth treatment of step S22 reaches the expected particle size of 7.70-8.30 μm, the second crystal growth treatment of step S23 is performed; In the second cycle, when the particle size of the particles in the reaction solution in the first crystal growth treatment of step S22 reaches the expected particle size of 9.70-10.30 μm, the second crystal growth treatment of step S23 is performed; In the third cycle, when the particle size of the particles in the reaction solution in the first crystal growth treatment of step S22 reaches the expected particle size of 11.70-12.30 μm, the second crystal growth treatment of step S23 is performed; Then, step S25 is performed: the first crystal growth treatment of step S22 is repeated until the particle size of the particles in the reaction solution reaches the particle size range of 12.50-13.50 μm, and the crystal growth treatment is terminated.

[0098] In some embodiments, at least one of the raw materials, the precipitating agent, and the complexing agent used for preparing the positive electrode material precursor in step S21 to step S24 or step S25 described above in step S20 can be added to the reaction solution, such as the bottom solution, in the form of a solution to improve the efficiency of the crystal growth reaction on the surface of the crystal nucleus, improve the particle morphology of the prepared precursor nucleus, and improve the uniformity of the thickness of the precursor coating layer or the precursor growth layer. In the embodiments, the raw materials, the precipitating agent, and the complexing agent used for preparing the positive electrode material precursor are dissolved in a solvent, such as water, to prepare a raw material solution, a precipitating agent solution, and a complexing agent solution, respectively. In the embodiments, the total molar concentration of the raw materials in the raw material solution can be 2-5 mol / L, the concentration of the precipitating agent solution prepared from the precipitating agent can be 4.0-12.0 mol / L, and the concentration of the complexing agent solution prepared from the complexing agent can be 4-8 mol / L.

[0099] In some embodiments, when at least one of the raw materials, the precipitant, and the complexing agent used for preparing the precursor of the cathode material in step S20, such as steps S21-S24 or step S25 above, is added to the reaction solution, such as the base solution, in the form of a solution, the solution of the raw material, the solution of the precipitant, and the solution of the complexing agent can be added to the reaction solution, such as the base solution, at a certain flow rate, so as to adjust the number and particle size of the generated seed crystals. In some embodiments, the solution of the raw material is added to the reaction solution, such as the base solution, at a feed flow rate of 140-240 mL / min for the crystal growth reaction.

[0100] In some embodiments, the base solution used for the crystal growth process in steps S21-S24 or step S25 above can be a mixed solution of the precipitant and the complexing agent with a pH value of 10.30-10.90, such as a mixed solution of the precipitant solution with a concentration of 4.0-12.0 mol / L and the complexing agent solution with a concentration of 4-8 mol / L, and the pH value of the mixed solution is 10.30-10.90, or optionally 10.30-10.70.

[0101] In step S20, such as the crystal growth process in steps S21-S24 or step S25 above, the raw material used for preparing the precursor of the cathode material can be the same as or different from the raw material used for preparing the seed crystal in step S10, depending on the type of the precursor of the cathode material. In some embodiments, when the precursor of the cathode material is a ternary cathode material precursor, the raw material used for preparing the precursor of the cathode material can include soluble nickel (Ni) sources, soluble cobalt (Co) sources, and soluble manganese (Mn) sources in a certain proportion. In some embodiments, the soluble nickel (Ni) sources, the soluble cobalt (Co) sources, and the soluble manganese (Mn) sources can be soluble salts of nickel, cobalt, and manganese, such as sulfates, chlorides, and nitrates.

[0102] In some embodiments, in step S20, such as the crystal growth process in steps S21-S24 or step S25 above, the precipitant can include but is not limited to hydroxides, such as sodium hydroxide and potassium hydroxide. The complexing agent can include but is not limited to ammonia. The complexing agent can effectively react with metal ions in the raw material of the precursor of the cathode material, and the precipitant can generate precipitates, so as to grow the precursor crystals, such as whiskers, in situ on the surface of the seed crystals. In the alternating protective atmosphere and oxygen-containing atmosphere, the morphology and size of the precursor crystals, such as whiskers, can be affected, so as to form the precursor coating layer and the precursor growth layer with different porosities on the surface of the seed crystals.

[0103] In some embodiments, the conditions of the crystal growth process in step S20, such as the crystal growth process in step S21, the first crystal growth process in step S22, and the second crystal growth process in step S23, can include at least one of the following (1) to (4): (1) During the crystal growth process, the pH value of the reaction solution system can be controlled to be 10.10 to 10.70, and optionally, the pH value can be 10.40 to 10.60. In exemplary embodiments, the pH value can be a typical but non-limiting pH value of 10.10, 10.20, 10.30, 10.40, 10.50, 10.60, or a range between any two pH values. (2) During the crystal growth process, the concentration of complexing agent ions in the reaction solution system, such as ammonia, can be controlled to be 2 to 4 g / L. In exemplary embodiments, the ammonia value can be a typical but non-limiting ammonia value of 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, or a range between any two ammonia values. (3) The reaction temperature of the crystal growth process can be 50 to 70°C, and optionally, 55 to 65°C. In exemplary embodiments, the reaction temperature can be a typical but non-limiting temperature of 50°C, 55°C, 60°C, 65°C, 70°C, or a range between any two temperature values. (4) During the crystal growth process, stirring treatment is also accompanied, such as stirring treatment at a rotation speed of 400 to 500 r / min. In exemplary embodiments, the rotation speed can be a typical but non-limiting rotation speed of 400 r / min, 450 r / min, 500 r / min, or a range between any two rotation speed values.

[0104] By controlling the conditions of the crystal growth process, such as the temperature, the pH control of the crystal growth reaction solution system in the above range, and further accompanied by stirring treatment, the rate of the crystal growth reaction can be controlled. In addition, the alternating protective atmosphere and oxygen-containing atmosphere environment can affect the morphology and size of the in-situ grown precursor crystals, such as whiskers, on the surface of the seed crystal and the precursor nucleus, etc., to form a precursor coating layer and a precursor growth layer with different porosities on the surface of the precursor nucleus.

[0105] In some embodiments, the protective gas in the protective atmosphere or the oxygen-containing gas in the oxygen-containing atmosphere in the crystal growth process in step S20, such as the protective gas in the protective atmosphere in step S21 and step S22, and the oxygen-containing gas in the oxygen-containing atmosphere in step S21 and step S23, can be introduced into the environment for the crystal growth process at a certain flow rate; the rate of the oxygen-containing gas can be 360-450 L / h, and the time for a single introduction can be determined according to the relatively large porosity of the precursor shell in the composite positive electrode material precursor of the embodiments of the present application, such as the thickness of the precursor coating layer, and can be 30-120 min; the rate of the protective gas can be 350-500 L / h, and the time for a single introduction can also be determined according to the relatively small porosity of the precursor shell in the composite positive electrode material precursor of the embodiments of the present application, such as the thickness of the precursor growth layer, and the time for a single introduction should ensure that the entire single precipitation reaction is covered. By continuously introducing the protective gas or the oxygen-containing gas at the rate into the environment for the crystal growth process, the crystal growth process can be carried out in a protective atmosphere or an oxygen-containing atmosphere, thereby effectively adjusting the properties of the precursor coating layer and the precursor growth layer, including porosity.

[0106] In some embodiments, the protective atmosphere in the crystal growth process in step S20, such as the crystal growth process in step S21, the first crystal growth process in step S22, and the second crystal growth process in step S23, can be a protective atmosphere constructed by oxygen-free or chemically inert gas. In an exemplary embodiment, when the protective atmosphere is constructed by chemically inert gas, it can be an atmosphere of nitrogen, helium, argon, etc., to improve the stability of the precipitation reaction, improve the stability of the particle structure of the seed crystal, and the like; in an exemplary embodiment, when it is an oxygen-containing atmosphere, the oxygen-containing atmosphere can be an air atmosphere, a mixed gas of oxygen and the above-mentioned chemically inert gas, etc.

[0107] In some embodiments, after the crystal growth process in step S20 is completed, the following steps are further included: Step S26: adjusting the pH of the reaction solution after the crystal growth process to 11.60-11.90, and performing slurry washing treatment on the composite positive electrode material precursor, and then performing washing treatment.

[0108] Since the composite positive electrode material precursor particles obtained by the crystal growth process have cracks, as shown in FIG. 1, by performing slurry washing treatment on the composite positive electrode material precursor in an alkaline solution with a pH of 11.60-11.90, small molecules OH Figure 2 - The large molecules such as SO4 2 ​- replace, thereby effectively repairing the cracks of the composite cathode material precursor, thereby improving the stability of the composite cathode material precursor particle structure.

[0109] In the embodiment, the temperature of the slurry washing treatment in step S26 can be 60-90 ℃, and the slurry washing treatment at this temperature should be sufficient to improve the effect of the slurry washing treatment, thereby further improving the stability of the composite cathode material precursor particle structure.

[0110] In the embodiment, the washing treatment in step S26 is to remove the unreacted reactants, other ions and other impurities contained in the composite cathode material precursor particles. In the embodiment, the washing treatment can be multiple times, and the temperature of the washing treatment can be 60-90 ℃ to improve the effect of the washing treatment and improve the purity of the composite cathode material precursor particles. After the washing treatment is completed, the composite cathode material precursor particles can be dried, such as drying at 80-200 ℃ until the moisture content of the dried material is <0.5 wt%, and finally post-processing such as sieving and iron removal.

[0111] [Positive electrode active material] In a third aspect, the embodiments of the present application also provide a positive electrode active material. The positive electrode active material of the embodiments of the present application is formed by calcining a composite cathode material precursor and a lithium source in a certain proportion, wherein the composite cathode material precursor comprises the composite cathode material precursor of the embodiments of the present application.

[0112] Therefore, the positive electrode active material is formed by using the composite positive electrode material precursor as a raw material and by lithium intercalation sintering. The surface layer of the positive electrode active material has a positive electrode material layer with relatively high porosity and a positive electrode material layer with relatively low porosity, and the positive electrode material layer with relatively high porosity and the positive electrode material layer with relatively low porosity are alternately arranged. The positive electrode material layer with relatively low porosity has relatively high mechanical properties, and can prevent the volume expansion and contraction of the positive electrode active material during the charging and discharging process, thereby improving the structural stability and cycle performance of the positive electrode active material, and improving the ionic conductivity and specific capacity of the positive electrode active material. The positive electrode material layer with relatively high porosity can provide a buffer space for the volume expansion of the positive electrode active material, and the positive electrode material layer with relatively low porosity can prevent the volume expansion and contraction of the positive electrode active material. Therefore, the positive electrode active material can effectively improve the structural stability of the positive electrode active material during the cycle process, effectively alleviate the adverse phenomena of particle breakage and structure collapse of the positive electrode active material during the charging and discharging process, thereby effectively improving the cycle performance and the stability of the contact interface between the positive electrode active material and the electrolyte. In addition, the electronic conductivity of the positive electrode active material can also be improved.

[0113] In addition, when the composite positive electrode material precursor and the lithium source are calcined in proportion, the composite positive electrode material precursor and the lithium source can be mixed in proportion according to the proportion of lithium elements and metal elements contained in the corresponding positive electrode active material, and the calcination conditions can also be controlled according to the type of the corresponding positive electrode active material, such as a sintering temperature of 600-800°C.

[0114] In the embodiment, the lithium source can include lithium compounds commonly used to prepare lithium positive electrode active materials, such as lithium carbonate, lithium hydroxide, etc.

[0115] [Battery] In a fourth aspect, the application also provides a battery. The battery of the application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a separator or a solid-state electrolyte, and of course other necessary or auxiliary components. The separator or solid-state electrolyte is arranged between the positive electrode sheet and the negative electrode sheet. When the battery of the application is an ionic battery, it contains a separator; when the battery of the application is a solid-state battery, it contains a solid-state electrolyte.

[0116] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer combined on the surface of the positive electrode current collector. In the embodiment, the positive electrode current collector of the positive electrode sheet can be, but is not limited to, any one of copper foil and aluminum foil.

[0117] The positive electrode active material layer of the positive electrode sheet includes positive electrode active material, binder, and conductive agent, and the like. Among them, the positive electrode active material in the positive electrode active material layer includes the positive electrode active material of the application.

[0118] Since the positive electrode sheet of the battery of the application contains the positive electrode active material of the application, the battery of the application has good cycle performance and high energy density and the like.

[0119] In the positive electrode active material layer, the content of the positive electrode active material, the binder, and the conductive agent can be a conventional content, or a content adjusted relative to the conventional content.

[0120] The composite positive electrode material precursor, the positive electrode active material, and the preparation method and application thereof of the application are illustrated by a plurality of specific embodiments.

[0121] 1. Composite positive electrode material precursor and positive electrode active material and preparation method thereof embodiment: Embodiment A1: The embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0122] In the embodiment, the composite positive electrode material precursor is a lithium nickel cobalt manganese oxide (NCM) ternary precursor, which includes a ternary precursor core and a ternary precursor shell covering the ternary precursor core; wherein the ternary precursor shell includes three layers of ternary precursor coating layers and three layers of ternary precursor growth layers, and the porosity of the ternary precursor coating layer is greater than that of the ternary precursor growth layer; along the direction away from the ternary precursor core, the ternary precursor coating layer and the ternary precursor growth layer are alternately arranged, and the ternary precursor forms a multi-layer structure. The number of layers, thickness, and porosity of each ternary precursor coating layer and ternary precursor growth layer are shown in Table 2 as follows.

[0123] The preparation method of the composite positive electrode material precursor of the embodiment includes the following steps: S1. Preparation of solution: prepare a mixed metal salt solution with a total metal ion concentration of 4 mol / L according to the molar ratio Ni:Co:Mn=(0.95±0.05):(0.04±0.05):(0.01±0.05); prepare a sodium hydroxide solution with a concentration of 8.0 mol / L as a precipitant; prepare an ammonia solution with a concentration of 5.29 mol / L (90 g / L) as a complexing agent; S2. Seed crystal synthesis: a certain amount of pure water, precipitant and complexing agent were added to a reaction kettle (200 L) to prepare a base solution, the pH value of the base solution was controlled at 11.60-11.80 (45℃) by the precipitant, and the ammonia concentration in the base solution was controlled at 0.118 mol / L (2.0 g / L) by the complexing agent, the reaction temperature was maintained at 50℃, and the stirring speed was 430 rpm; a mixed metal salt solution prepared in step S1, a precipitant and a complexing agent were introduced for co-precipitation reaction, wherein the flow rate of the mixed metal salt was 70 mL / min; the reaction was continued until precursor particles with a particle size D50 of 3.8 μm were obtained, and after washing by a centrifugal machine, seed crystals were obtained; S3. Crystal growth to form a precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), and ammonia solution (6.0±2.0 mol / L) were added to a reaction kettle to prepare a base solution with a pH value of 11.30, and nitrogen gas was introduced as a protective gas; the stirring speed during the reaction process was adjusted to 450 r / min, the reaction temperature was 58±1℃, and the seed crystals prepared in step S2 were added, the metal salt solution prepared in step S1 was introduced at a flow rate of 8.35% of the total capacity of the reaction vessel per hour, the sodium hydroxide solution was introduced at a flow rate of 4.59% of the total capacity of the reaction vessel per hour, and the ammonia water was introduced at a flow rate of 0.80% of the total capacity of the reaction vessel per hour, the pH value of the reaction was controlled at 10.60~10.70, the stirring was started, and the reaction parameters were controlled for stable synthesis; when the synthesis particle size in the reaction solution was detected to be 7.70~8.30 μm, 9.70~10.30 μm, and 11.70~12.30 μm, respectively, the nitrogen gas was stopped and air was introduced for 30 min (air introduction rate: 420±30 L / h) before the nitrogen atmosphere was restored, and the synthesis reaction was continued until the target particle size of 13±0.50 μm was reached; S4. Slurry washing: after the crystal growth treatment in step S3, an alkali solution was added to the reaction kettle to wash the slurry until the pH value reached 11.80, and then the slurry was washed for 4 h, and the supernatant was removed to obtain a multi-layer structure composite positive electrode material precursor (ternary precursor); S5. Post-treatment: the composite positive electrode material precursor obtained after slurry washing was washed, dried, sieved, and iron-removed.

[0124] The positive electrode active material in this embodiment is a ternary active material, which is formed by sintering the ternary precursor material of this embodiment with lithium hydroxide.

[0125] Preparation of the positive electrode active material: the ternary precursor material provided in A1 of this embodiment was mixed with lithium hydroxide in a ratio of 0.97:1 after pre-burning, and then sintered at 750℃ for 11 h to prepare a ternary active material.

[0126] Example A2: The embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0127] The composite positive electrode material precursor in the embodiment is a lithium nickel cobalt manganese oxide (NCM) ternary precursor, and the ternary precursor structure is different from that of the embodiment A1 in that the number of layers, thickness and porosity of the ternary precursor coating layer and the ternary precursor growth layer are different, and are respectively shown in Table 2.

[0128] The preparation method of the composite positive electrode material precursor in the embodiment comprises the following steps: S1. Preparing a solution: as in step S1 in the embodiment A1; S2. Seed synthesis: as in step S2 in the embodiment A1; S3. Forming a precursor coating layer by crystal growth: a certain amount of pure water, a sodium hydroxide solution (concentration: 8.0±2.0 mol / L) and an ammonia solution (6.0±2.0 mol / L) are added to a reaction kettle to prepare a bottom solution with a pH value of 11.30, and nitrogen protection gas is introduced; the stirring speed of the reaction process is adjusted to 450 r / min, the reaction temperature is 64±1℃, the seed prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced at a set flow rate (the flow rate is 8.35% of the total capacity of the reaction container per hour), the sodium hydroxide solution is introduced at a flow rate of 4.59% of the total capacity of the reaction container per hour, and the ammonia water is introduced at a flow rate of 0.80% of the total capacity of the reaction container per hour, the pH value of the reaction is controlled to be 10.20-10.30, the stirring is started, and the reaction parameters are controlled to perform stable synthesis; when it is detected that the synthesis particle sizes in the reaction solution reach 7.70-8.30 μm, 9.70-10.30 μm and 11.70-12.30 μm, respectively, the introduction of nitrogen is stopped and air is introduced for 60 min (air introduction rate: 420±30 L / h), and then the nitrogen atmosphere is restored, and the synthesis reaction is continued until the target particle size of 13±0.50 μm is reached; S4. Slurry washing: as in step S4 in the embodiment A1; S5. Post-treatment: as in step S5 in the embodiment A1.

[0129] The positive electrode active material in the embodiment is a ternary active material, which is formed by sintering the ternary precursor material in the embodiment with lithium hydroxide.

[0130] Preparation of the positive electrode active material: the ternary precursor material provided in the embodiment A2 is uniformly mixed with lithium hydroxide at a ratio of 0.97:1 after pre-burning, and is sintered at 750℃ for 11h to prepare a ternary active material.

[0131] Embodiment A3: The embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0132] The composite positive electrode material precursor in the embodiment is a sodium iron manganese acid nickel (NFM) sodium battery material precursor, which comprises a sodium battery precursor core and a sodium battery precursor shell covering the sodium battery precursor core; wherein the sodium battery precursor shell comprises a sodium battery precursor coating layer and a sodium battery precursor growth layer, and the porosity of the sodium battery precursor coating layer is greater than that of the sodium battery precursor growth layer; along the direction away from the sodium battery precursor core, the sodium battery precursor coating layer and the sodium battery precursor growth layer are alternately arranged, forming a multi-layer structure on the surface of the sodium battery precursor. The number of layers, thickness and porosity of each sodium battery precursor coating layer and sodium battery precursor growth layer are shown in Table 2 as follows.

[0133] The preparation method of the composite positive electrode material precursor in the embodiment comprises the following steps: S1. Preparation of solution: prepare a mixed metal salt solution with a total metal ion concentration of 4 mol / L according to the molar ratio Ni:Fe:Mn=(0.95±0.05):(0.04±0.05):(0.01±0.05); prepare a sodium hydroxide solution with a concentration of 8.0 mol / L as a precipitant; prepare an ammonia solution with a concentration of 90 g / L as a complexing agent; S2. Seed synthesis: add a certain amount of pure water, precipitant and complexing agent to the bottom liquid of the reaction kettle (200 L), control the pH value of the bottom liquid to be 11.60-11.80 (45℃) by the precipitant, control the ammonia concentration in the bottom liquid to be 2.0 g / L by the complexing agent, and maintain the reaction temperature at 50℃ and the stirring speed at 430 rpm; pass the mixed metal salt solution, precipitant and complexing agent prepared in step S1 to carry out co-precipitation reaction, wherein the flow rate of the mixed metal salt solution is 70 mL / min; the reaction is carried out until the precursor particles with a particle size D50 of 3.8 μm are obtained, and the seed is obtained after washing by a centrifuge; S3. Crystal growth forms precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), ammonia solution (6.0±2.0 mol / L) is added to the reaction kettle to prepare a bottom solution with pH value of 11.30, and nitrogen protection gas is introduced; adjust the stirring speed of the reaction process to 430 r / min, the reaction temperature is 54±1℃, and the seed crystal prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced at a set flow rate (flow rate is 8.35% of the total capacity of the reaction vessel per hour), sodium hydroxide solution (flow rate is 4.59% of the total capacity of the reaction vessel per hour) and ammonia (flow rate is 0.80% of the total capacity of the reaction vessel per hour), control the reaction pH value to be 10.10~10.20, start stirring, control the reaction parameters to stabilize the synthesis; when it is detected that the synthesis particle size in the reaction solution reaches 7.70~8.30 μm, 9.70~10.30 μm, 11.70~12.30 μm respectively, stop introducing nitrogen and introduce air for 30 min (air introduction rate: 420±30 L / h) after the nitrogen atmosphere is restored, continue the synthesis reaction until the target particle size of 13±0.50 μm is reached; S4. Slurry washing: After the crystal growth treatment in step S3, add alkali solution to the reaction kettle until the pH is 11.80, then start slurry washing, and after slurry washing for 4 h, start to clear, to obtain a multi-layer structure composite positive electrode material precursor (sodium electrode precursor); S5. Post-processing: as in step S5 of example A1.

[0134] The positive electrode active material in this example is a sodium electrode active material, which is formed by sintering the sodium electrode precursor material in this example with lithium hydroxide.

[0135] Preparation of positive electrode active material: the sodium electrode precursor material provided in example A3 is mixed with sodium hydroxide in a ratio of 0.97:1 after pre-burning, and a sodium electrode active material is prepared after sintering at 750℃ for 11h.

[0136] Example A4: This example provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0137] The composite positive electrode material precursor in this example is a lithium nickel cobalt manganese oxide (NCM) ternary precursor. Compared with the ternary precursor structure in example A1, it only contains one layer of ternary precursor coating layer and one layer of ternary precursor growth layer, and the thickness and porosity of the ternary precursor coating layer and the ternary precursor growth layer are shown in Table 2 below.

[0138] The preparation method of the composite positive electrode material precursor in this example includes the following steps: S1. Preparation of solution: as in step S1 of example A1; S2. Seed synthesis: as in step S2 of Example A1; S3. Crystal growth to form a precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), and ammonia solution (6.0±2.0 mol / L) were added to a reaction kettle to prepare a bottom solution with a pH value of 11.30 under nitrogen protection; the stirring speed of the reaction process was adjusted to 450 r / min, the reaction temperature was 58±1℃, and the seed prepared in step S2 was added; the metal salt solution prepared in step S1 was introduced at a set flow rate (flow rate of 8.35% of the total capacity of the reaction vessel per hour), sodium hydroxide solution (flow rate of 4.59% of the total capacity of the reaction vessel per hour), and ammonia (flow rate of 0.80% of the total capacity of the reaction vessel per hour); the reaction pH value was controlled at 10.60-10.70, the stirring was started, and the reaction parameters were controlled for stable synthesis; when the particle size of the synthesized particles in the reaction solution was detected to be 7.70-8.30 μm, the nitrogen was stopped and air was introduced for 30 min (air introduction rate: 420±30 L / h), and then the nitrogen atmosphere was restored, and the synthesis reaction was continued until the target particle size of 13±0.50 μm was reached; S4. Slurry washing: as in step S4 of Example A1; S5. Post-treatment: as in step S5 of Example A1.

[0139] The positive electrode active material in this example is a ternary active material, which is formed by sintering the ternary precursor material of this example with lithium hydroxide.

[0140] Preparation of the positive electrode active material: the ternary precursor material provided in Example A4 was pre-burned and mixed uniformly with lithium hydroxide at a ratio of 0.97:1, and then sintered at 750℃ for 11 h to prepare a ternary active material.

[0141] Example A5: This example provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0142] The composite positive electrode material precursor in this example is a lithium nickel cobalt manganese oxide (NCM) ternary precursor, which has two layers of ternary precursor coating layers and two layers of ternary precursor growth layers, and the thickness and porosity of the two layers of ternary precursor coating layers and the two layers of ternary precursor growth layers are shown in Table 2 below.

[0143] The preparation method of the composite positive electrode material precursor in this example includes the following steps: S1. Preparation of solution: as in step S1 of Example A1; S2. Seed synthesis: as in step S2 of Example A1; S3. Crystal growth forms precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), ammonia solution (6.0±2.0 mol / L) is added to the reaction kettle to prepare a bottom solution with a pH value of 11.30, and nitrogen protection gas is introduced; adjust the stirring speed of the reaction process to 450 r / min, the reaction temperature is 58±1℃, and the seed crystal prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced at a set flow (the flow rate is 8.35% of the total capacity of the reaction vessel per hour), sodium hydroxide solution (the flow rate is 4.59% of the total capacity of the reaction vessel per hour) and ammonia (the flow rate is 0.80% of the total capacity of the reaction vessel per hour), control the reaction pH value to be 10.60~10.70, start stirring, control the reaction parameters to stabilize the synthesis; when it is detected that the synthesis particle size in the reaction solution reaches 9.70~10.30 μm, 11.70~12.30 μm respectively, stop introducing nitrogen and introduce air for 30 min (air introduction rate: 420±30 L / h) after the nitrogen atmosphere is restored, continue the synthesis reaction until the target particle size of 13±0.50 μm is reached; S4. Slurry washing: as in step S4 of example A1; S5. Post-treatment: as in step S5 of example A1.

[0144] The positive electrode active material in this embodiment is a ternary active material, which is formed by sintering the ternary precursor material of this embodiment with lithium hydroxide.

[0145] Preparation of positive electrode active material: the ternary precursor material provided in example A5 is mixed uniformly with lithium hydroxide at a ratio of 0.97:1 after pre-burning, and a ternary active material is prepared after sintering at 750℃ for 11h.

[0146] Example A6: This embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0147] The composite positive electrode material precursor in this embodiment is a lithium nickel cobalt manganese oxide (NCM) ternary precursor. Compared with example A1, the ternary precursor structure only contains two layers of ternary precursor coating layers and two layers of ternary precursor growth layers, and the thickness and porosity of the two layers of ternary precursor coating layers and the two layers of ternary precursor growth layers are shown in Table 2 as follows.

[0148] The preparation method of the composite positive electrode material precursor of this embodiment includes the following steps: S1. Preparation of solution: as in step S1 of example A1; S2. Seed crystal synthesis: as in step S2 of example A1; S3. Crystal growth forms precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), ammonia solution (6.0±2.0 mol / L) is added to the reaction kettle to prepare a bottom solution with a pH value of 11.30, and nitrogen protection gas is introduced; adjust the stirring speed of the reaction process to 450 r / min, the reaction temperature is 58±1℃, and the seed crystal prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced at a set flow (the flow rate is 8.35% of the total capacity of the reaction vessel per hour), sodium hydroxide solution (the flow rate is 4.59% of the total capacity of the reaction vessel per hour) and ammonia (the flow rate is 0.80% of the total capacity of the reaction vessel per hour), control the reaction pH value to be 10.60~10.70, start stirring, control the reaction parameters to stabilize the synthesis; when it is detected that the synthesis particle size in the reaction solution reaches 7.70~8.30 μm, 11.70~12.30 μm respectively, stop introducing nitrogen and introduce air for 30 min (air introduction rate: 420±30 L / h) after the nitrogen atmosphere is restored, continue the synthesis reaction until the target particle size of 13±0.50 μm is reached; S4. Slurry washing: as in step S4 of example A1; S5. Post-treatment: as in step S5 of example A1.

[0149] The positive electrode active material in this embodiment is a ternary active material, which is formed by sintering the ternary precursor material of this embodiment with lithium hydroxide.

[0150] Preparation of positive electrode active material: the ternary precursor material provided in example A6 is mixed uniformly with lithium hydroxide at a ratio of 0.97:1 after pre-burning, and a ternary active material is prepared after sintering at 750℃ for 11h.

[0151] Example A7: This embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0152] The composite positive electrode material precursor in this embodiment is a lithium nickel cobalt manganese oxide (NCM) ternary precursor. Compared with example A1, the ternary precursor structure only contains two layers of ternary precursor coating layers and two layers of ternary precursor growth layers, and the thickness and porosity of the two layers of ternary precursor coating layers and the two layers of ternary precursor growth layers are shown in Table 2 as follows.

[0153] The preparation method of the composite positive electrode material precursor of this embodiment includes the following steps: S1. Preparation of solution: as in step S1 of example A1; S2. Seed crystal synthesis: as in step S2 of example A1; S3. Crystal growth forms precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), ammonia solution (6.0±2.0 mol / L) is added to the reaction kettle to prepare a bottom solution with pH value of 11.30, and nitrogen protection gas is introduced; adjust the stirring speed of the reaction process to 450 r / min, the reaction temperature is 58±1℃, and the seed crystal prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced according to the set flow (the flow rate is 8.35% of the total capacity of the reaction container per hour), sodium hydroxide solution (the flow rate is 4.59% of the total capacity of the reaction container per hour) and ammonia (the flow rate is 0.80% of the total capacity of the reaction container per hour), control the reaction pH value to be 10.60~10.70, start stirring, control the reaction parameters to stabilize the synthesis; when it is detected that the synthesis particle size in the reaction solution reaches 7.70~8.30 μm, 9.70~10.30 μm respectively, stop introducing nitrogen and introduce air for 30 min (air introduction rate: 420±30 L / h) after the nitrogen atmosphere is restored, continue the synthesis reaction until the target particle size of 13±0.50 μm is reached; S4. Slurry washing: as in step S4 of example A1; S5. Post-treatment: as in step S5 of example A1.

[0154] The positive electrode active material in this embodiment is a ternary active material, which is formed by sintering the ternary precursor material of this embodiment with lithium hydroxide.

[0155] Preparation of positive electrode active material: the ternary precursor material provided in example A7 is mixed uniformly with lithium hydroxide in a ratio of 0.97:1 after pre-burning, and a ternary active material is prepared after sintering at 750℃ for 11h.

[0156] Example A8: This embodiment provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0157] The composite positive electrode material precursor in this embodiment is a lithium nickel cobalt manganese oxide (NCM) ternary precursor. Compared with the ternary precursor structure of example A1, it contains four layers of ternary precursor coating layers and four layers of ternary precursor growth layers, and the thickness and porosity of the four layers of ternary precursor coating layers and the four layers of ternary precursor growth layers are shown in Table 2 as follows.

[0158] The preparation method of the composite positive electrode material precursor of this embodiment includes the following steps: S1. Preparation of solution: as in step S1 of example A1; S2. Seed crystal synthesis: as in step S2 of example A1; S3. Crystal growth forms a precursor coating layer: a certain amount of pure water, sodium hydroxide solution (concentration of 8.0±2.0 mol / L), ammonia solution (6.0±2.0 mol / L) is added to the reaction kettle to prepare a bottom solution with pH value of 11.30, and nitrogen protection gas is introduced; adjust the stirring speed of the reaction process to 450 r / min, the reaction temperature is 58±1℃, and the seed crystal prepared in step S2 is added, the metal salt solution prepared in step S1 is introduced at a set flow rate (the flow rate is 8.35% of the total capacity of the reaction container per hour), sodium hydroxide solution (the flow rate is 4.59% of the total capacity of the reaction container per hour) and ammonia (the flow rate is 0.80% of the total capacity of the reaction container per hour), control the reaction pH value to be 10.60~10.70, start stirring, control the reaction parameters to stabilize the synthesis; when it is detected that the synthesis particle size in the reaction solution reaches 7.70~8.30 μm, 9.70~10.30 μm, 11.70~12.30 μm, 13.70~15.70 μm, respectively, stop introducing nitrogen and introduce air for 30 min (air introduction rate: 420±30 L / h) after the nitrogen atmosphere is restored, and continue the synthesis reaction until the target particle size of 15±0.50 μm is reached; S4. Slurry washing: as in step S4 of example A1; S5. Post-treatment: as in step S5 of example A1.

[0159] The positive electrode active material in this example is a ternary active material, which is formed by sintering the ternary precursor material of this example with lithium hydroxide.

[0160] Preparation of the positive electrode active material: the ternary precursor material provided in example A8 is pre-burned and mixed with lithium hydroxide at a ratio of 0.97:1, and then sintered at 750℃ for 11h to prepare a ternary active material.

[0161] Comparative example A1: This comparative example A1 provides a composite positive electrode material precursor and a positive electrode active material and a preparation method thereof.

[0162] The composite positive electrode material precursor of this comparative example is a ternary precursor. Compared with the ternary precursor in example A1, the ternary precursor of this comparative example does not contain a three-layer structure with different porosities.

[0163] The preparation method of the composite positive electrode material precursor is different from the preparation method of the composite positive electrode material precursor in example 1 in that the nitrogen atmosphere is maintained throughout the crystal growth process in step S3 until the solution particles are synthesized to the target particle size of 13±0.50 μm, that is, no precipitation reaction in an air atmosphere is set in step S3.

[0164] Comparative example A2: The comparative example A2 provides a composite cathode material precursor and a cathode active material and a preparation method thereof.

[0165] The composite cathode material precursor of the comparative example is a ternary precursor. Compared with the ternary precursor in the example A2, the ternary precursor of the comparative example does not contain a ternary precursor shell with a multi-coil layer structure with different porosities.

[0166] The preparation method of the composite cathode material precursor is different from the preparation method of the composite cathode material precursor in the example 2 in that the nitrogen atmosphere is maintained during the crystal growth process in step S3 until the solution particles are synthesized to the target particle size of 13±0.50 μm, that is, the precipitation reaction in the air atmosphere is not set in step S3. Among them, the reaction temperature is adjusted to 63-65℃, and the reaction pH value is 10.20-10.30.

[0167] Comparative example A3: The comparative example A3 provides a composite cathode material precursor and a cathode active material and a preparation method thereof.

[0168] The composite cathode material precursor of the comparative example is a sodium material precursor. Compared with the sodium material precursor in the example A3, the sodium precursor does not contain a sodium precursor shell with a multi-coil layer structure with different porosities.

[0169] The preparation method of the composite cathode material precursor is different from the preparation method of the composite cathode material precursor in the example A3 in that the nitrogen atmosphere is maintained during the crystal growth process in step S3 until the solution particles are synthesized to the target particle size of 13±0.50 μm, that is, the precipitation reaction in the air atmosphere is not set in step S3. Among them, the reaction temperature is adjusted to 54±1℃, and the reaction pH value is 10.10-10.20, and the stirring speed is 430 r / min.

[0170] The preparation method conditions of the composite cathode material precursor in each of the above examples A1 to A8 and comparative examples A1 to A3 are shown in Table 1.

[0171] Table 1

[0172] 2. Related performance detection of the composite cathode material precursor and the cathode active material: 2.1 Scanning electron microscope (SEM) analysis of the composite cathode material precursor and the cathode active material: The cross sections of the composite cathode material precursor and the corresponding cathode active material particles in each of the above examples were subjected to SEM analysis. The SEM photos of the ternary material precursor particles without slurry washing (the precursor particles prepared in step S3 of the preparation methods of examples A1 and comparative example A1) and the ternary material precursor particles after slurry washing (the precursor particles prepared in step S4 of the preparation methods of examples A1 and comparative example A1) are shown in Figure 2 As can be seen from the comparison Figure 2 , the cracks in the ternary material precursor particles obtained in example A1 without slurry washing are significantly less than those in the ternary material precursor particles obtained in comparative example A1 without slurry washing. This shows that the composite cathode material precursor preparation method of the present application can significantly improve the structural stability of the composite cathode material precursor particles and reduce the cracks in the composite cathode material precursor particles. After slurry washing, the cracks in the composite cathode material precursor particles can be significantly repaired, and the composite cathode material precursor particles after slurry washing can be almost free of cracks.

[0173] The partial magnified SEM photos of the particle surfaces of the ternary material precursor and the ternary active material final product in example A1 are shown in Figure 3 The partial magnified SEM photos of the particle surfaces of the ternary material precursor and the ternary active material in comparative example A1 are shown in Figure 4 As can be seen from the comparison Figure 3 and Figure 4 , the whiskers on the surface of the ternary material precursor particles in example A1 are significantly smaller than those on the surface of the ternary material precursor particles in comparative example A1. Therefore, the composite cathode material precursor preparation method of the present application can destroy the inherited growth of the whiskers of the composite cathode material precursor and effectively reduce the primary particle size during the crystal growth by alternately introducing a protective atmosphere and an air atmosphere in step S3.

[0174] According to the radial analysis of the whiskers contained in the primary particles of the ternary material precursor in example A1 and comparative example A1 (the length-width ratio of the primary particles), the results are shown in Figure 11 As can be seen from the results Figure 11 , the composite cathode material precursor preparation method of the present application can control the growth trend of the primary particles of the whiskers and make them grow in the same direction, thereby improving the radiality of the precursor particles. In this way, the corresponding cathode active material also has a relatively good radiality, which is conducive to the infiltration of the electrolyte, improves the ion diffusion rate, shortens the ion transmission path, and avoids side reactions with the electrolyte in the cycle, so that it has a high cycle capacity retention rate in the long cycle process.

[0175] The ternary material precursor in Example A1 and Comparative Example A1 and the particle cross-section SEM photos of the ternary active material are shown in Figure 5 , Figure 6 and Figure 7 It can be seen from Figure 5 and Figure 6 that the ternary material precursor in Example A1 also presents a plurality of ternary material rings with different and alternating distribution of porosity enclosing the central region on the cross-section of the ternary active material particles. Therefore, there are ternary material ring layers with different and alternating distribution of porosity in the surface layer of the ternary active material particles. According to the SEM photos of the ternary material precursor particles provided by other embodiments, the ternary material precursor particles provided by other embodiments also have a plurality of ternary material precursor ring layers with different and alternating distribution of porosity, respectively, the same as the ternary material precursor in Example A1, and the corresponding ternary active material particles also have a plurality of ternary material ring layers with different and alternating distribution of porosity, respectively, the same as the ternary active material particles in Example A1.

[0176] And it can be seen from Figure 7 that the cross-section of the ternary material precursor particles in Comparative Example A1 ( Figure 7 a) and the cross-section of the corresponding ternary active material particles ( Figure 7 b) are obviously uniformly distributed, and the cross-section of the ternary material precursor particles does not show the ternary material precursor ring layers with alternating distribution, and the cross-section of the corresponding ternary material particles also does not show the ternary material ring layers with alternating distribution.

[0177] 2.2 Analysis of the thickness of the precursor coating layer grown in nitrogen and air environments by the composite cathode material precursor: The thickness of the precursor coating layer grown in air environment by the composite cathode material precursor provided in each of the above embodiments was analyzed. Among them, the thickness detection data of the precursor coating layer grown in air environment by the composite cathode material precursor provided in each of the embodiments is shown in Table 2 as follows: Table 2

[0178] The nitrogen particle size in Table 2 refers to the particle size of the particles after the nitrogen gas is introduced into the reaction. Among them, the first circle particle size refers to the particle size of the particles formed by the crystal growth on the surface of the crystal nucleus to prepare the precursor core; the second circle particle size refers to the particle size of the particles formed by the first layer to the precursor core in the precursor growth layer; the third circle particle size refers to the particle size of the particles formed by the second layer to the precursor core in the precursor growth layer, and the fourth circle particle size refers to the particle size of the particles formed by the third layer to the precursor core in the precursor growth layer.

[0179] In combination with Figure 5 to Figure 7As shown in Table 2, in step S3 of the composite cathode material precursor preparation method in this application embodiment, when the particle size of the synthesis in the reaction solution reaches 7.70~8.30 μm, 9.70~10.30 μm, and 11.70~12.30 μm respectively, air is introduced into the main reactor to create an air atmosphere. This makes the whiskers generated by the precipitation reaction in the air atmosphere more refined and significantly increases the porosity of the corresponding precursor shell. By controlling the air atmosphere time, the thickness of the formed precursor coating layer can be controlled as shown in Table 1. For example, the thickness of the precursor shell (set precursor coating layer) formed in an oxygen-containing environment (air environment) can be controlled between 0.07 μm and 0.19 μm. The precursor nucleus is prepared in a protective atmosphere, and the precursor shell (precursor growth layer) is formed in the protective atmosphere. The particle size of each layer in the precursor nucleus and precursor growth layer can be controlled between 7 μm and 16.0 μm.

[0180] 2.3 Analysis of XRD patterns and cracking rate of precursor particles during crystal growth of composite cathode materials: The particles in the reaction solution of step S3 in the preparation method of the composite cathode material precursor in the above embodiments and comparative examples were subjected to XRD analysis at particle sizes of 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, and after slurry washing, respectively. The Dv50 particle size, particle size distribution (Span), and microstress ε of the particles were obtained respectively. The XRD patterns of each particle in Example A1 and Comparative Example A1 are shown below. Figure 8 As shown ( Figure 8 (TJXL represents the particles after sulfur washing during shutdown). The Dv50 particle size, particle size distribution (Span), and microstress ε detection data of the two particles are shown in Table 3 below: Table 3

[0181] From Table 3 and Figure 8It can be seen that in the crystal growth process in step S3, the micro stress ε of the precursor particles in the reaction solution of example A1 and comparative example A1 presents an increasing trend with the increase of the Dv50 particle size. When the Dv50 particle size of the precursor particles reaches 8 microns, the internal structure stability of the particles is poor due to the accumulation of micro stress, and the cracking phenomenon of the particles is obviously increased, which affects the subsequent cycle stability. However, in the crystal growth process of example A1, the growth of the whisker is refined due to the oxidation after the air is introduced at intervals, and the micro stress of the particles is obviously smaller than that in comparative example A1. The micro stress is released, the structure is stable, and the capacity loss in the cycle process is reduced, which can correspondingly improve the cycle life of the battery. Therefore, when the micro stress ε of the precursor particles of the composite cathode material in the example is controlled in the range of 0.10-1.00, which can be optionally selected in the range of 0.01-0.36, the particle structure is more stable, and the cycle performance of the corresponding positive electrode active material is more excellent.

[0182] 2.4 Analysis of composite cathode material precursor and positive electrode active material particle crystal: The composite cathode material precursors and the corresponding positive electrode active materials provided in each of the above examples and comparative examples were subjected to XRD analysis, respectively, to obtain the (001) crystal face, (100) crystal face, (101) crystal face of the composite cathode material precursor and the (003) crystal face, (004) crystal face of the positive electrode active material. Among them, the XRD patterns of the composite cathode material precursors provided in example A1 and comparative example A1 are as shown in Figure 9 and Table 4, and the XRD patterns of the positive electrode active materials prepared from the composite cathode material precursors provided in example A1 and comparative example A1 are as shown in Figure 10 and Table 4.

[0183] Table 4

[0184] From Figure 9 and Table 4, compared with comparative example A1, the (001) crystal face half peak width and (101) crystal face half peak width of the composite cathode material precursor particles in example A1 are narrowed, which indicates that after air is introduced in step S3 of the preparation method, the crystallinity of the (001) crystal face and (101) crystal face of the composite cathode material precursor particles is improved, the peak intensity ratio I(001) / (101) is increased, the (001) dominant crystal face in the composite cathode material precursor particles is increased, the crystal grows along the dominant crystal face, and it is beneficial to the transmission of lithium ions.

[0185] From Figure 10 and Table 4, the peak intensity ratio I(003) / (104) of the positive electrode active materials in example A1 and comparative example A1 is close, which proves that the Li + / Ni2+ The mixing degree has no influence.

[0186] 2.5 Analysis of Na content, S content, specific surface area (BET) and tap density (TD) of the composite cathode material precursor particles: The composite cathode material precursors provided in the above examples and comparative examples were respectively subjected to Na content, S content, BET and TD analysis. The results of the detection of the composite cathode material precursors provided in Example A1 and Comparative Example A1 are shown in Table 5.

[0187] Table 5

[0188] As can be seen from Table 5, there is no obvious difference in the indexes of the composite cathode material precursors provided in Example A1 and Comparative Example A1. It is shown that the adoption of the staged oxidation process in step S3 of the composite cathode material precursor preparation method of the present application has no adverse effect on the physical and chemical indexes of the composite cathode material precursor, and can also optimize the internal structure of the precursor end particles.

[0189] 3. Lithium ion battery examples: Examples B1, B2, B4 to B8 and Comparative Examples B1 to B2 each provide a lithium ion battery. Each lithium ion battery is assembled into a lithium ion battery according to the following method: 3.1 Positive electrode sheet: The positive electrode active materials provided in Examples A1, A2, A4 to A8 and Comparative Examples A1 to A2 are respectively used as the positive electrode material of the lithium ion battery in Examples B1, B2, B4 to B8 and Comparative Examples B1 to B2, and the positive electrode sheet of each lithium ion battery is prepared according to the following method: Preparation of positive electrode sheet: the positive electrode active material, superconducting carbon black (SP) and binder polyvinylidene fluoride (PVDF) are prepared into a positive electrode slurry in a mass ratio of 90:5:5 in N-methyl pyrrolidone (NMP) solvent; the scale of the doctor blade of the coating machine is adjusted, and the ball-milled slurry is uniformly coated on an aluminum foil; the coated electrode sheet is placed in a vacuum drying oven for drying treatment; then the coated positive electrode sheet is rolled; the front surface of the rolled positive electrode sheet is tightly attached to the punching position, and the sheet is punched in sequence; the punched positive electrode sheet is placed in a vacuum drying oven, and baked at a temperature of 130°C for 3 h; 3.2 Negative electrode sheet: lithium sheet; 3.3 Electrolyte: lithium hexafluorophosphate (LiPF6) solution; 3.4 Separator: 20 μm-PP; 3.5 Assemble the button cell: in the glove box, assemble the button cell in the order of negative electrode shell, spring, steel sheet, lithium sheet, separator, positive electrode sheet and positive electrode shell, inject 10 μL electrolyte in the process, and then seal the button cell using a sealing machine.

[0190] 3. Performance detection of the button cell: The assembled button cells of each example were subjected to the following performance tests in Table 6, and the results are shown in Table 6.

[0191] Table 6

[0192] As shown in Table 6, the DCR growth rate of the button cells in Comparative Examples B1 to B2 is much higher than that of the button cells in Examples B1 to B8, and the capacity retention rate of the button cells in Comparative Examples B1 to B2 is also much lower than that of the button cells in Examples B1 to B8. Therefore, the composite positive electrode material precursor containing the multi-layer structure provided by the examples of the present application provides space for the volume expansion and contraction of the positive electrode active material caused by irreversible phase change and anisotropy during the cycle process, slows down the particle breakage and structure collapse of the positive electrode active material during the charging and discharging process, thereby shortens the diffusion path of lithium ions, and achieves the purpose of reducing the internal resistance of the battery, improving the cycle performance and safety performance.

[0193] In addition, as shown in Table 6, in each example button cell, the DCR growth rate of Example B2 is lower than that of Example B1, and the capacity retention rate of Example B2 is higher than that of Example B1. Among them, the air inlet time of the composite positive electrode material precursor of Example A2 in the preparation of each multi-layer structure is 60 min, which is higher than the air inlet time of 30 min of Example A1, and the thickness and porosity of the coating layer of Example A2 are greater than those of the coating layer of Example A1. This shows that the porosity of the precursor coating layer in the composite positive electrode material precursor of the examples of the present application is within a certain range, and as the porosity increases, the space provided for the volume expansion and contraction of the positive electrode active material caused by irreversible phase change and anisotropy during the cycle process increases, and the buffering effect can be further improved, thereby further slowing down the particle breakage and structure collapse of the positive electrode active material during the charging and discharging process, thereby shortening the diffusion path of lithium ions, and achieving the technical effects of further reducing the internal resistance of the battery, improving the cycle performance and safety performance.

[0194] The above embodiments only express several implementation ways of the present application, and the description is specific and detailed, but it should not be understood as a limitation to the patent scope of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A composite cathode material precursor, characterized in that, The composite positive electrode material precursor comprises: a precursor core; a precursor shell covering the precursor core, and the precursor shell comprises at least two layers of precursor covering layers and precursor growth layers, the porosities of the precursor covering layers and the precursor growth layers are different, and the precursor covering layers and the precursor growth layers are alternately arranged in a direction away from the precursor core; wherein the at least two layers of the precursor covering layers comprise a first precursor covering layer and a second precursor covering layer arranged in a direction away from the precursor core, and the porosities of the first precursor covering layer and the second precursor covering layer are different.

2. The composite positive electrode material precursor of claim 1, wherein: the porosity of the precursor covering layer is greater than that of the precursor growth layer; and / or the porosity of the precursor growth layer is 1.9% to 5.5%; and / or the porosity of the first precursor covering layer is greater than that of the second precursor covering layer, and the porosity of the first precursor covering layer is 5.3% to 17.2%, and / or; the porosity of the second precursor covering layer is 1.9% to 5.5%, and / or; the whisker length of the positive electrode material precursor in the first precursor covering layer is 0.25 to 1.05 μm, and / or; the whisker length of the positive electrode material precursor in the second precursor covering layer is 0.18 to 0.85 μm.

3. The composite cathode material precursor of claim 1, wherein: The thicknesses of the first precursor covering layer and the second precursor covering layer satisfy any one of the following (1) to (4): (1) the thickness of the single-layer precursor covering layer is 0.03 to 0.25 μm; (2) the thickness of the single-layer first precursor covering layer is 0.05 to 0.25 μm; (3) the thickness of the single-layer second precursor covering layer is 0.03 to 0.20 μm; (4) the number of layers of the precursor coating layer and the precursor growth layer is n, the first layer of the precursor coating layer is coated on the surface of the precursor core body in the direction away from the precursor core body, the particle size of the precursor core body is C1=0.618×Dv50±0.50 μm, the first layer of the precursor growth layer is coated on the surface of the first layer of the precursor coating layer, the particle size of the particle formed by the first layer of the precursor growth layer and the precursor core body is C1=C0+2.0±0.50 μm, the second layer of the precursor coating layer is coated on the surface of the first layer of the precursor growth layer, the second layer of the precursor growth layer is coated on the surface of the second layer of the precursor coating layer, the particle size of the particle formed by the second layer of the precursor growth layer and the precursor core body is C2=C1+2.0±0.50 μm, the particle size of the particle formed by the n layer of the precursor growth layer and the precursor core body is Cn=Cn-1+2.0±0.50 μm; wherein, the Dv50 is the Dv50 particle size of the composite cathode material precursor, and the n≥2. n n-1 +2.0±0.50 μm; wherein, the Dv50 is the Dv50 particle size of the composite cathode material precursor, and the n≥2.​ 4. The composite cathode material precursor of any one of claims 1-3, wherein: The composite positive electrode material precursor comprises at least one of the following (1) to (5): (1) the microstress ε of the composite positive electrode material precursor is 0.10 to 1.00; (2) the half-peak width of the (001) crystal plane of the composite positive electrode material precursor is 0.612° to 0.735°; (3) the half-peak width of the (101) crystal plane of the composite positive electrode material precursor is 0.521° to 0.595°; (4) the peak intensity I of the (001) crystal face of the composite cathode material precursor is 0.89~1.26 times the peak intensity I of the (101) crystal face of the composite cathode material precursor. 001 the peak intensity I of the (001) crystal face of the composite cathode material precursor is 0.89~1.26 times the peak intensity I of the (101) crystal face of the composite cathode material precursor. 101 the (5) the Dv50 particle size of the composite positive electrode material precursor is 12.5 to 13.5 μm.

5. The composite cathode material precursor of any one of claims 1-3, wherein: The positive electrode material precursor comprises at least one of the precursors of ternary materials, sodium materials, manganese-rich materials, and four-cobalt materials.

6. A method for preparing a composite cathode material precursor, characterized in that, The method comprises the following steps: preparing a seed crystal of a positive electrode material precursor; performing a crystal growth treatment on the seed crystal and a reaction solution comprising raw materials for preparing a positive electrode material precursor to prepare a precursor core and grow a precursor shell on the surface layer of the precursor core, thereby obtaining a composite positive electrode material precursor; In the crystal growth treatment, the environmental atmosphere is alternately set as a protective atmosphere and an oxygen-containing atmosphere, and the number of times of alternation between the protective atmosphere and the oxygen-containing atmosphere is two or more, so that the precursor shell comprises at least two precursor cladding layers and at least one precursor growth layer, and the precursor cladding layers and the precursor growth layer are alternately arranged in a direction away from the seed crystal; The at least two precursor cladding layers comprise a first precursor cladding layer and a second precursor cladding layer arranged in a direction away from the precursor core, and the porosity of the first precursor cladding layer is different from that of the second precursor cladding layer.

7. The production method according to claim 6, characterized by: The Dv50 of the seed crystal is 3.0-5.0 μm; And / or, The method for performing the crystal growth treatment on the seed crystal and the raw material for preparing the positive electrode material precursor in the reaction solution comprises the following steps: The seed crystal is added to a bottom liquid, and the raw material for preparing the positive electrode material precursor, a precipitating agent and a complexing agent are added to the bottom liquid at a certain feed flow rate to perform the crystal growth treatment.

8. The production method according to claim 7, wherein The method for performing the crystal growth treatment on the seed crystal and the raw material for preparing the positive electrode material precursor in the reaction solution comprises the following steps: In the first protective atmosphere, the seed crystal is added to a bottom liquid, and the raw material for preparing the positive electrode material precursor, a precipitating agent and a complexing agent are added to the bottom liquid at a certain feed flow rate to perform a first crystal growth treatment; When the particle size in the reaction solution in the first crystal growth treatment reaches an expected particle size, the feed flow rate of the raw material for preparing the positive electrode material precursor, the precipitating agent and the complexing agent is maintained, the first protective atmosphere is replaced by a first oxygen-containing atmosphere, and a second crystal growth treatment is performed; One cycle from the first crystal growth treatment to the second crystal growth treatment is performed, and the cycle is repeated at least once until the particle size in the reaction solution reaches a particle size target value, and the crystal growth treatment is terminated; Or one cycle from the first crystal growth treatment to the second crystal growth treatment is performed, and the cycle is repeated at least once, and then the first crystal growth treatment is repeated until the particle size in the reaction solution reaches a particle size target value, and the crystal growth treatment is terminated; And / or, the pH value of the bottom liquid is 10.30-10.

90.

9. The production method according to any one of claims 6 to 8, characterized by: The raw material for preparing the positive electrode material precursor is added to the bottom liquid at a feed flow rate of 140-240 mL / min; and / or, The reaction conditions of the crystal growth treatment comprise at least one of the following (1) to (4): (1) the reaction temperature is 50-70°C; (2) the concentration of complexing agent ions in the reaction solution system is 2-4 g / L; (3) during the crystal growth treatment, the pH value of the reaction solution system is controlled to be 10.10-10.70; (4) the crystal growth treatment is also accompanied by a stirring treatment, and the stirring speed of the stirring treatment is 400-500 rpm; And / or, The thickness d of the precursor growth layer or the precursor coating layer is controlled to satisfy: d = (D t -D t-1 ) / 2, where D t =(m t ×D t-1 (3 / m(t-1)) ) (1 / 3) ; where D t D represents the Dv50 particle size of the particles in the reaction solution after t hours of crystal growth treatment. t-1 This indicates the Dv50 particle size (in meters) of the particles in the reaction solution after t-1 hours of crystal growth treatment. t The amount of raw material used to prepare the cathode material precursor is expressed in m during the crystal growth process for t hours. t-1 This indicates the amount of raw materials used to prepare the cathode material precursor during crystal growth treatment t-1 hours; And / or, The protective gas in the protective atmosphere and the oxygen-containing gas in the oxygen-containing atmosphere are respectively introduced into the environment of the crystal growth treatment at a certain flow rate; wherein the rate of the oxygen-containing gas is 360-450 L / h, and the time of single introduction is 30-120 min; and / or, the rate of the protective gas is 350-500 L / h; and / or, After the crystal growth treatment is completed, the following step is further included: The pH of the reaction solution is adjusted to 11.60-11.90, and the slurry washing treatment is performed on the composite positive electrode material precursor.

10. A positive electrode active material, characterized by: The composite positive electrode material precursor prepared by the preparation method of any one of claims 1-9 is calcined with a lithium source in a certain proportion to form.

11. A battery comprising a positive electrode sheet, characterized by: The positive electrode sheet comprises the positive electrode active material of claim 10.

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