Composite positive electrode active material and preparation method and application thereof

Abstract

This invention provides a composite positive electrode active material, its preparation method, and its application. The composite positive electrode active material includes a core and a shell coating at least a portion of the surface of the core; the core includes a lithium-rich manganese-based positive electrode material, and the shell includes a cationic disordered oxide; the cationic disordered oxide includes Li z A x B 1‑x O 2‑y D y Wherein, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, and Ce, and D includes F and / or S; and in the XRD pattern of the disordered cation oxide, there is a single peak without splitting in the range of 63°~66°. The composite positive electrode active material of this invention can effectively improve the initial coulombic efficiency, rate performance, and cycle performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a composite positive electrode active material, and more particularly to a composite positive electrode active material and its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, power tools, electric bicycles, electric vehicles, aerospace, energy storage systems, and many other fields due to their advantages such as high energy density, voltage platform, cycle life, fast charging capability, no memory effect, wide operating temperature range, and environmental friendliness and renewability. With the continuous expansion of application areas, higher demands are being placed on the energy density of lithium-ion batteries.

[0003] As a crucial component of lithium-ion batteries, the positive electrode active material plays a key role in improving battery energy density. Among various positive electrode active materials, lithium-rich manganese-based positive electrode materials can cycle between 2.0V and 4.8V and exhibit a high reversible capacity (not less than 300 mAh·g). -1 ) and energy density (not less than 900 Wh·kg) -1 However, lithium-rich manganese-based cathode materials generally suffer from poor initial coulombic efficiency, rate performance, and cycle performance.

[0004] Therefore, it is necessary to further improve lithium-rich manganese-based cathode materials to enhance their initial coulombic efficiency, rate performance, and cycle performance. Summary of the Invention

[0005] To address the aforementioned deficiencies, this invention provides a composite positive electrode active material. This composite positive electrode active material exhibits high ion migration rate and electronic conductivity, as well as good structural stability. Therefore, this composite positive electrode active material can effectively improve the initial coulombic efficiency, rate performance, and cycle performance of the battery.

[0006] The present invention also provides a method for preparing the above-mentioned composite positive electrode active material. The composite positive electrode active material prepared by this method can effectively improve the first coulombic efficiency, rate performance and cycle performance of the battery.

[0007] The present invention also provides a method for preparing the above-mentioned composite positive electrode active material. The composite positive electrode active material prepared by this method can effectively improve the first coulombic efficiency, rate performance and cycle performance of the battery.

[0008] The present invention also provides a positive electrode sheet, comprising the above-described composite positive electrode active material, or the composite positive electrode active material prepared by the above-described preparation method. Therefore, using this positive electrode sheet in lithium-ion batteries can effectively improve the battery's initial coulombic efficiency, rate performance, and cycle performance.

[0009] The present invention also provides a lithium-ion battery comprising the above-described composite positive electrode active material, or the composite positive electrode active material prepared by the above-described preparation method, or the above-described positive electrode sheet. Therefore, this battery exhibits high initial coulombic efficiency, rate performance, and cycle performance.

[0010] A first aspect of this invention provides a composite positive electrode active material, the composite positive electrode active material comprising a core and a shell coating at least a portion of the surface of the core; the core comprises a lithium-rich manganese-based positive electrode material, and the shell comprises a cationic disordered oxide; the cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1.

[0011] Li z A x B 1-x O 2-y D y Formula 1

[0012] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0013] The X-ray diffraction pattern of the disordered cation oxide contains a diffraction peak with a 2θ of 63° to 66°, and the diffraction peak is a single peak without splitting.

[0014] In the composite positive electrode active material described above, the mass ratio of the cationic disordered oxide to the lithium-rich manganese-based positive electrode material is (0.5-3):100.

[0015] In the composite positive electrode active material described above, the thickness of the shell layer is 5 nm to 20 nm.

[0016] The composite positive electrode active material described above, wherein the lithium-rich manganese-based positive electrode material comprises a compound with the chemical composition shown in Formula 2,

[0017] Li 1+m Ni a Mn b M c O 2+m-d N d Formula 2

[0018] In Equation 2, 0.2≤m≤0.4, a+b+c=1, 0.42≤a / b≤0.67, 0≤c≤0.02, 0≤d≤0.02; M includes at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce; N includes at least one of S, F, P.

[0019] The second aspect of this invention provides a method for preparing the composite positive electrode active material of the first aspect, comprising the following steps:

[0020] Under an oxygen-rich atmosphere, a first raw material comprising lithium source, source A, source B, and source D is uniformly mixed and then subjected to a first sintering and a second sintering process to obtain a cationic disordered oxide. The first sintering temperature is 300–400°C, and the holding time is 2–4 hours; the second sintering temperature is 450–600°C, and the holding time is 10–40 hours. The cationic disordered oxide comprises compounds with the chemical composition shown in Formula 1.

[0021] Li z A x B 1-x O 2-y D y Formula 1

[0022] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0023] In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ of 63° to 66°, and the diffraction peaks are unsplit single peaks.

[0024] Under an oxygen-containing atmosphere, the second raw material, including the cationic disordered oxide and the lithium-rich manganese-based cathode material, is uniformly mixed and then subjected to a third sintering to obtain the composite cathode active material; wherein, the third sintering temperature is 300-500℃ and the holding time is 2-12h.

[0025] The method for preparing the composite positive electrode active material as described above, wherein the lithium-rich manganese-based positive electrode material is prepared by the following method:

[0026] Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700-1100°C for 10-24 hours in an oxygen atmosphere to obtain the lithium-rich manganese-based cathode material.

[0027] A third aspect of this invention provides a method for preparing a composite positive electrode active material according to the first aspect, comprising the following steps:

[0028] Under an oxygen-rich atmosphere, lithium-rich manganese-based cathode material is uniformly mixed with raw materials including lithium source, source A, source B and source D, and then subjected to a first sintering and a second sintering in sequence to obtain a composite cathode active material; wherein, the temperature of the first sintering is 300-400℃ and the holding time is 3-8h; the temperature of the second sintering is 450-700℃ and the holding time is 20-40h;

[0029] The composite positive electrode active material comprises a core and a shell coating at least a portion of the surface of the core; the core comprises a lithium-rich manganese-based positive electrode material, and the shell comprises a cationic disordered oxide; the cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1.

[0030] Li z A x B 1-x O 2-y D y Formula 1

[0031] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0032] The X-ray diffraction pattern of the disordered cation oxide contains a diffraction peak with a 2θ of 63° to 66°, and the diffraction peak is a single peak without splitting.

[0033] The method for preparing the composite positive electrode active material as described above, wherein the lithium-rich manganese-based positive electrode material is prepared by the following method:

[0034] Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700-1100°C for 10-24 hours in an oxygen atmosphere to obtain the lithium-rich manganese-based cathode material.

[0035] A fourth aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a composite positive electrode active material of the first aspect, or a composite positive electrode active material prepared by the preparation method of the second aspect, or a composite positive electrode active material prepared by the preparation method of the third aspect.

[0036] The fifth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising a composite positive electrode active material of the first aspect, or a composite positive electrode active material prepared by the preparation method of the second aspect, or a composite positive electrode active material prepared by the preparation method of the third aspect, or a positive electrode sheet of the fourth aspect.

[0037] The composite cathode active material of this invention comprises a lithium-rich manganese-based cathode material with a core and a cationic disordered oxide coating at least part of the core surface. In the XRD pattern of this cationic disordered oxide, a single, unsplit peak exists at 2θ between 63° and 66°, indicating that the material simultaneously contains a layered structure and a spinel structure. The layered structure effectively improves the compatibility between the core and the shell, thereby enhancing lithium-ion transport efficiency; the spinel structure exhibits high structural stability under high voltage. The two structures work synergistically to effectively improve the ion diffusion capability and structural stability of the cathode material. Furthermore, the relative contents of nickel and manganese in this cationic disordered oxide are suitable, enabling it to possess both good electrochemical performance and structural stability. Therefore, this composite cathode active material can effectively improve the initial coulombic efficiency, cycle performance, and rate performance of the battery. Attached Figure Description

[0038] Figure 1 This is a SEM image of the composite positive electrode active material in Example 1 of the present invention;

[0039] Figure 2 This is a SEM image of the composite positive electrode active material in Comparative Example 1 of the present invention;

[0040] Figure 3 The cationic disordered oxide and typical ternary layered LiNi in Example 1 of this invention 0.5 Mn 0.5 O2 and typical spinel-type LiNi 0.5 Mn 1.5 Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66°;

[0041] Figure 4 The cationic disordered oxide in Comparative Example 2 of this invention and the typical ternary layered LiNi 0.5 Mn 0.5 O2 and typical spinel-type LiNi 0.5 Mn 1.5 Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66°;

[0042] Figure 5 The cationic disordered oxides in Comparative Examples 5 and 6 of this invention are similar to typical ternary layered LiNi. 0.5 Mn 0.5 O2 and typical spinel-type LiNi0.5 Mn 1.5 Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66°;

[0043] Figure 6 This is a charge-discharge curve of the battery at 1C in Embodiment 1 of the present invention;

[0044] Figure 7 This is a charge-discharge curve of the battery at 1C in Embodiment 3 of the present invention;

[0045] Figure 8 This is a charge-discharge curve of the battery at 1C in Embodiment 14 of the present invention;

[0046] Figure 9 This is a charge-discharge curve of the battery at 1C in Embodiment 15 of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] Lithium-rich manganese-based cathode materials are known for their high energy density (discharge specific capacity can reach 250 mAh·g). -1 The advantages of lithium-rich manganese-based cathode materials, such as high voltage characteristics (voltage window of 2.0-4.8V), high safety, and low cost, make them stand out among many cathode active materials, with broad application prospects and making them one of the current research hotspots in the battery field. However, due to the high activation energy of interfacial reactions in lithium-rich manganese-based cathode materials, high voltage is often required to activate the Li2MnO3 component. During the cyclic charge-discharge process at high voltage, irreversible escape of lattice oxygen often occurs. This leads to irreversible changes in the cathode material structure, preventing some lithium ions from successfully embedding into the material during discharge. Furthermore, the escaped active oxygen reacts with the Li in the electrolyte. + When a reaction occurs, the resulting byproducts adhere to the material surface, increasing the battery's internal resistance, which in turn leads to a decrease in the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0049] Currently, surface coating of lithium-rich manganese-based cathode materials is commonly used to suppress the escape of lattice oxygen and prevent direct contact between the material and the electrolyte, thereby inhibiting side reactions between the electrolyte and the material and improving the battery's initial coulombic efficiency, cycle performance, and rate performance. However, the coating materials used in existing technologies are generally elemental carbon, metal oxides (such as Al2O3, ZrO2, MgO), or metal fluorides (such as MgF2, AlF3, CeF3). These coating materials lack electrochemical activity and also affect lithium-ion transport efficiency, which is not only detrimental to the battery's rate performance but also significantly reduces the mass energy density of the cathode material, limiting the improvement of the cathode material's overall performance.

[0050] The inventors discovered that using cationic disordered oxides as coating materials can effectively suppress the escape of lattice oxygen in lithium-rich manganese-based cathode materials and improve their structural stability. At the same time, under high voltage, the anions in the cationic disordered oxides undergo redox reactions and can participate in charge compensation, which is beneficial to improving the discharge capacity of the cathode material without causing energy density loss. Furthermore, the oxygen atoms in this material have a close-packed structure and are not easy to escape, which can further reduce the oxygen evolution problem and help to enhance the overall structural stability of the composite cathode active material to a certain extent.

[0051] However, the inventors discovered that existing cationic disordered oxides contain a high proportion of metal elements, resulting in a complex composition and consequently a complex crystal structure. This makes them incompatible with lithium-rich manganese-based cathode materials, hindering lithium-ion transport and affecting battery rate performance. Therefore, it is necessary to optimize the structure of cationic disordered oxides to improve the compatibility between the coating layer and the core, thereby enhancing lithium-ion migration efficiency.

[0052] Based on the above analysis, the inventors discovered that the structure of lithium-rich manganese-based cathode materials is typically layered. Incorporating layered structures into the cationic disordered oxides is an effective way to improve the compatibility between cationic disordered oxides and lithium-rich manganese-based cathode materials. However, layered cationic disordered oxides exhibit poor structural stability under high voltage, which affects the overall structural stability of the cathode active material and negatively impacts the battery's cycle performance. Since some tetrahedral and octahedral sites in the spinel structure are coplanar, they can form interconnected three-dimensional ion diffusion channels. This not only facilitates lithium-ion insertion / extraction but also reduces electrostatic repulsion during lithium extraction, effectively suppressing phase transformation under high voltage. Therefore, the spinel structure exhibits less lattice expansion and volumetric strain under high voltage, demonstrating higher structural stability.

[0053] Based on the above analysis, it can be concluded that when the cationic disordered oxide includes both layered structure and spinel structure, it can not only improve the compatibility of the cationic disordered oxide with lithium-rich manganese-based cathode materials, but also ensure the structural stability of the cationic disordered oxide under high voltage.

[0054] In X-ray diffraction patterns, lithium nickel manganese oxide (such as LiNi) exhibits a typical layered structure. 0.5 Mn 0.5 O2) exhibits two diffraction peaks at 2θ between 63° and 66°, and lithium nickel manganese oxide (such as LiNi) has a typical spinel structure. 0.5 Mn 1.5 The characteristic peak of O4 at 2θ of 63° to 66° is a sharp splitting peak; when the characteristic peak of the disordered cation oxide at 2θ of 63° to 66° is a single peak without splitting and in the shape of a steamed bun, it indicates that its internal crystal is not a single layered structure or spinel structure, but a composite material in which both structures coexist.

[0055] It can be inferred that when there is a diffraction peak with 2θ of 63° to 66° in the X-ray diffraction pattern of the disordered cation oxide, and the diffraction peak is a single peak without splitting, the material has both layered structure and spinel structure in its internal crystal, which can effectively improve the lithium-ion transport efficiency of the positive electrode active material and the structural stability under high voltage.

[0056] However, it is also necessary to control the proportion of spinel structure in the cationic disordered oxide. When the proportion of spinel structure is large, Mn is easily dissolved during cycling, leading to capacity decay. Moreover, it has a negative impact on the ion migration rate and electronic conductivity of the oxide, which is not conducive to improving the discharge capacity and rate of the battery.

[0057] The inventors further discovered that the relative content of nickel and manganese in cationic disordered oxides has a significant impact on their structure. When there is too little nickel and too much manganese, the overall structure of the oxide transforms into a spinel structure; when there is too much nickel and too little manganese, dislocations occur in the oxide crystal structure, hindering lithium-ion insertion and extraction and affecting the electrochemical performance of the material. Therefore, the inventors attempted to control the relative content of nickel and manganese in cationic disordered oxides to adjust their structure, resulting in a layered structure that improves the compatibility between the coating layer and the core, and achieves both good electrochemical performance and structural stability.

[0058] Based on the above analysis, the first aspect of this invention provides a composite positive electrode active material, comprising a core and a shell coating at least a portion of the surface of the core; the core comprises a lithium-rich manganese-based positive electrode material, and the shell comprises a cationic disordered oxide; the cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1.

[0059] Li z A x B 1-x O 2-y D y Formula 1

[0060] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0061] In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ ranging from 63° to 66°, and these diffraction peaks are unsplit single peaks.

[0062] For example, the molar ratio of Ni to Mn in the cationic disordered oxide is 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1 or 1:1.

[0063] It should be noted that when B includes multiple specific elements of the aforementioned elements, the present invention does not impose specific limitations on the proportions between the specific elements; when D includes multiple specific elements of the aforementioned elements, the present invention does not impose specific limitations on the proportions between the specific elements.

[0064] This invention does not specifically limit the chemical composition of the lithium-rich manganese-based cathode material, and any conventional choice in the art can be used; furthermore, this invention does not specifically limit the source of the lithium-rich manganese-based cathode material, and any commercially available product or product prepared by conventional preparation methods well known to those skilled in the art can be used.

[0065] The present invention does not specifically limit the source of the cationic disordered oxide. Commercially available products or products prepared by conventional methods known to those skilled in the art can be used. It is only necessary that the chemical composition of the cationic disordered oxide satisfies Formula 1 and that there is a diffraction peak with 2θ of 63° to 66° in its X-ray diffraction pattern, and that the diffraction peak is a single peak without splitting.

[0066] The composite cathode active material of this invention uses lithium-rich manganese-based cathode material as the core and cationic disordered oxide as the coating shell, which can effectively suppress the escape of lattice oxygen in lithium-rich manganese-based cathode material and improve the structural stability of lithium-rich manganese-based cathode material. At the same time, cationic disordered oxide can also participate in electrochemical reactions as active material under high voltage, which is beneficial to improving the discharge capacity of cathode material without causing energy density loss. Moreover, since the oxygen atoms in this material have a close-packed structure, they are not easy to escape, so they have high structural stability and can improve the overall structural stability of composite cathode active material.

[0067] Meanwhile, the X-ray diffraction pattern of the cationic disordered oxide in this invention shows a characteristic peak at 2θ of 63°–66°, which is a single peak without splitting, indicating that the material contains both layered and spinel structures. The layered structure can effectively improve the compatibility of the cationic disordered oxide with lithium-rich manganese-based cathode materials, thereby improving lithium-ion transport efficiency. The spinel structure can form interconnected three-dimensional ion diffusion channels, which not only facilitates lithium-ion insertion / extraction but also reduces electrostatic repulsion during lithium extraction. Under high voltage, its lattice expansion and volume strain are small, exhibiting high structural stability. The synergy of these two structures can effectively improve the lithium-ion transport efficiency and structural stability of the cathode active material. Furthermore, by controlling the relative content of nickel and manganese in the cationic disordered oxide, this invention achieves a suitable nickel and manganese content, avoiding excessive spinel structure due to insufficient nickel or excessive manganese, and dislocations in the crystal structure due to excessive nickel or insufficient manganese. This results in the cationic disordered oxide possessing both good electrochemical performance and structural stability.

[0068] Furthermore, when F and S are doped into the cationic disordered oxide, F has a stronger electronegativity than O and can form a more stable bond with the cation; S can provide electrons to the lattice oxygen under high voltage to prevent oxidation, which can further improve the structural stability of the cationic disordered oxide, thereby improving the structural stability of the composite cathode active material and enabling the battery to have higher cycle performance.

[0069] Therefore, the composite positive electrode active material in this invention can effectively improve the first coulombic efficiency, cycle performance and rate performance of the battery.

[0070] Furthermore, the mass ratio of cationic disordered oxides to lithium-rich manganese-based cathode materials in composite cathode active materials also has a significant impact on the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0071] In one specific embodiment, the mass ratio of cationic disordered oxide to lithium-rich manganese-based cathode material is (0.5–3):100. Within this range, not only can the structural stability and ion transport capacity of the composite cathode active material be effectively improved, but also excessive cationic disordered oxide can be avoided from hindering lithium-ion migration, thereby further improving the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0072] For example, the mass ratio of the cationic disordered oxide to the lithium-rich manganese-based cathode material is 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100 or 3:100.

[0073] Furthermore, the thickness of the shell also affects the battery's initial coulombic efficiency, cycle performance, and rate performance. If the shell is too thin, it cannot effectively isolate the electrolyte from the core lithium-rich manganese-based cathode material, leading to side reactions; if the shell is too thick, it will lengthen the lithium-ion migration path, affecting the lithium-ion migration efficiency.

[0074] In one specific embodiment, the thickness of the shell layer is 5 nm to 20 nm. Within this range, the occurrence of side reactions between the electrolyte and the lithium-rich manganese-based cathode material can be effectively suppressed, while the shell layer is not too thick, which helps the smooth transport of lithium ions, thereby further improving the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0075] For example, the thickness of the shell is 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm.

[0076] In this invention, the "shell thickness" can be obtained by transmission electron microscopy (TEM).

[0077] Furthermore, the lithium-rich manganese-based cathode material can be doped to further enhance the structural stability of the composite cathode active material. In one embodiment, the structural stability of the lithium-rich manganese-based cathode material can be improved by doping with metal cations (e.g., at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce). The metal cations can form bonds with oxygen in the lithium-rich manganese-based cathode material with higher bond energy, thereby suppressing the escape of lattice oxygen and improving its structural stability. In another embodiment, the structural stability can also be improved by doping with anions (e.g., at least one of S, F, P).

[0078] In one specific embodiment, the lithium-rich manganese-based cathode material comprises a compound with the chemical composition shown in Formula 2.

[0079] Li 1+m Ni a Mn b M c O 2+m-d N d Formula 2

[0080] In Equation 2, 0.2≤m≤0.4, a+b+c=1, 0.42≤a / b≤0.67, 0≤c≤0.02, 0≤d≤0.02; M includes at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce; N includes at least one of S, F, P.

[0081] At this point, lithium-rich manganese-based cathode materials exhibit higher structural stability, which can further improve the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0082] It should be noted that when M includes multiple specific elements of the aforementioned elements, the present invention does not impose specific limitations on the proportions between the specific elements; when N includes multiple specific elements of the aforementioned elements, the present invention does not impose specific limitations on the proportions between the specific elements.

[0083] The second aspect of this invention provides a method for preparing the composite positive electrode active material of the first aspect, comprising the following steps:

[0084] Under an oxygen-rich atmosphere, a first raw material comprising lithium source, source A, source B, and source D is uniformly mixed and then subjected to a first sintering and a second sintering to obtain a cationic disordered oxide. The first sintering temperature is 300–400℃, and the holding time is 2–4 h; the second sintering temperature is 450–600℃, and the holding time is 10–40 h. The cationic disordered oxide includes compounds with the chemical composition shown in Formula 1.

[0085] Li z A x B 1-x O 2-y D y Formula 1

[0086] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0087] In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ ranging from 63° to 66°, and the diffraction peaks are unsplit single peaks.

[0088] Under an oxygen-rich atmosphere, a second raw material, comprising cationic disordered oxide and lithium-rich manganese-based cathode material, is uniformly mixed and then subjected to a third sintering to obtain a composite cathode active material; wherein the temperature of the third sintering is 300-500℃ and the holding time is 2-12h.

[0089] Specifically, under an oxygen-containing atmosphere, raw materials including lithium source, source A, source B and source D are uniformly mixed to obtain a first raw material; the first raw material is subjected to a first sintering at a temperature of 300-400℃ for a holding time of 2-4 hours; subsequently, the product obtained after the first sintering is subjected to a second sintering at 450-600℃ for a holding time of 10-40 hours. After sintering, a cationic disordered oxide is obtained; the cationic disordered oxide includes a compound with the chemical composition shown in Formula 1, and in the X-ray diffraction pattern of the cationic disordered oxide, there is a diffraction peak with 2θ of 63°-66°, which is a single peak without splitting;

[0090] According to the set mass ratio, the cationic disordered oxide prepared above and the raw materials of lithium-rich manganese-based cathode material are uniformly mixed to obtain the second raw material; the second raw material is subjected to a third sintering in an oxygen atmosphere at a temperature of 300-500℃ for 2-12 hours; during this process, the cationic disordered oxide coating material coats at least part of the surface of the lithium-rich manganese-based cathode material to prepare the composite cathode active material.

[0091] For example, the temperature of the first sintering is 300°C, 320°C, 340°C, 360°C, 380°C or 400°C; the holding time is 2h, 2.5h, 3h, 3.5h or 4h.

[0092] For example, the second sintering temperature is 450°C, 475°C, 500°C, 525°C, 550°C, 575°C or 600°C; the holding time is 10h, 15h, 20h, 25h, 30h, 35h or 40h.

[0093] For example, the temperature of the third sintering is 300℃, 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃ or 500℃; the holding time is 2h, 4h, 6h, 8h, 10h or 12h.

[0094] This invention does not specifically limit the source of lithium-rich manganese-based cathode materials; commercially available products or products prepared by conventional methods known to those skilled in the art can be used.

[0095] In this invention, "oxygen atmosphere" refers to an atmosphere containing oxygen. This invention does not specifically limit the volume content of oxygen in the atmosphere; for example, sintering can be carried out in an air atmosphere or an oxygen atmosphere.

[0096] It should be noted that during the first sintering, the temperature is raised from room temperature to the temperature required for the first sintering; after the first sintering is completed, the temperature is directly raised to the temperature required for the second sintering for the second sintering; during the third sintering, the product obtained after the second sintering is cooled to room temperature and then mixed with lithium-rich manganese-based cathode material before the third sintering is carried out.

[0097] The present invention does not specifically limit the heating rate during the first sintering, the second sintering and the third sintering. The appropriate heating rate can be selected according to the actual situation. For example, the heating rate can be 2 to 10°C.

[0098] In this invention, the lithium source refers to a raw material providing Li, the A source refers to a raw material providing element A (Ni and Mn), the B source refers to a raw material providing element B (at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, and Ce), and the D source refers to a raw material providing element D (F and / or S). Any raw material containing the target element (Li, A, B, or D) is considered within the scope of this invention, and a target element can be introduced into the reaction system through one or more raw materials. It should be noted that when the raw material simultaneously includes two or more of the target elements, the raw material can be understood as an element source for two target elements.

[0099] Exemplarily, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, and lithium fluoride; source A includes a nickel source and a manganese source, wherein the nickel source includes at least one of nickel oxide, carbonate, hydroxide, and oxalate, such as at least one of nickel oxide (NiO), nickel carbonate (NiCO3), nickel hydroxide (Ni(OH)2), and nickel oxalate (NiC2O4); the manganese source includes at least one of manganese oxide, carbonate, hydroxide, and oxalate, such as at least one of manganese tetroxide (Mn3O4), manganese carbonate (MnCO3), manganese hydroxide (Mn(OH)2), and manganese oxalate (MnC2O4); source B includes element B pairs. The appropriate oxide, hydroxide, and carbonate may be at least one of the following: strontium oxide (SrO), yttrium oxide (Y2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), niobium pentoxide (Nb2O5), tantalum oxide (Ta2O5), chromium trioxide (Cr2O3), molybdenum trioxide (MoO3), tungsten trioxide (WO3), aluminum oxide (Al2O3), tin oxide (SnO2), antimony oxide (Sb2O5), tellurium oxide (TeO2), cerium oxide (CeO2), lanthanum hydroxide (La(OH)3), cobalt hydroxide (Co(OH)2), and magnesium carbonate (MgCO3); the D source may be a sulfide and / or a fluoride.

[0100] The present invention does not specifically limit the source of lithium, source A, source B, and source D, and products prepared by commercially available products or conventional preparation methods known to those skilled in the art can be used.

[0101] This invention does not impose specific limitations on the molar ratio of lithium source, source A, source B, and source D. It only requires that the chemical composition of the prepared disordered cationic oxide satisfies Formula 1 and that there is an unsplit single peak at 2θ of 63° to 66° in its X-ray diffraction pattern.

[0102] This invention does not specifically limit the mass ratio of cationic disordered oxide to lithium-rich manganese-based cathode material; furthermore, by controlling the mass ratio between the two, the mass ratio of cationic disordered oxide to lithium-rich manganese-based cathode material in the prepared composite cathode active material can be (0.5~3):100.

[0103] This invention does not specify a particular mixing method; conventional methods in the art can be used, as long as the raw materials are mixed evenly. For example, a high-speed mixer can be used for mixing.

[0104] The preparation method of the composite cathode active material in this invention first prepares a cationic disordered oxide through a special method. This material has the chemical composition shown in Formula 1, and its XRD pattern shows a single, unsplit peak at 2θ of 63°–66°, indicating that the material simultaneously possesses a layered structure and a spinel structure. Using this material as a coating material to coat the surface of a lithium-rich manganese-based cathode material can effectively improve the compatibility between the cationic disordered oxide and the lithium-rich manganese-based cathode material, thereby improving the lithium-ion migration efficiency. This coating layer can also suppress side reactions between the lithium-rich manganese-based cathode material and the electrolyte, thus effectively suppressing the escape of lattice oxygen and improving the structural stability of the cathode material. The cationic disordered oxide can also serve as an active material, which is beneficial for improving the discharge capacity of the cathode material and reducing energy density loss. Meanwhile, the spinel structure can form interconnected three-dimensional ion diffusion channels, which not only facilitates lithium-ion insertion / extraction but also reduces electrostatic repulsion during lithium extraction. Under high voltage, its lattice expansion and volume strain are small, exhibiting high structural stability. The synergistic effect of these two factors effectively improves the lithium-ion transport efficiency and structural stability of the cathode active material. Furthermore, the relative amounts of nickel and manganese in this cationic disordered oxide are optimal, effectively avoiding excessive spinel structure due to insufficient nickel or excessive manganese, and dislocation formation in the crystal structure due to excessive nickel or insufficient manganese. This results in the cationic disordered oxide possessing both excellent electrochemical performance and structural stability.

[0105] Therefore, the composite positive electrode active material prepared by the above preparation method can effectively improve the first coulombic efficiency, cycle performance and rate performance of the battery.

[0106] In one specific embodiment, the lithium-rich manganese-based cathode material is prepared by the following method:

[0107] Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700-1100℃ for 10-24h in an oxygen atmosphere to obtain lithium-rich manganese-based cathode material.

[0108] The lithium-rich manganese-based cathode material prepared by the above preparation method is doped with M element (at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce) and N element (at least one of S, F, P), which can further improve the structural stability of the lithium-rich manganese-based cathode material.

[0109] For example, the sintering temperature is 700℃, 800℃, 900℃, 1000℃ or 1100℃; the holding time is 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0110] This invention does not specifically limit the chemical composition of the nickel-manganese precursor, and conventional materials in the art can be used; for example, it can be one or more of nickel-manganese oxides, carbonates, hydroxides, and oxalates; this invention also does not specifically limit the source of the nickel-manganese precursor, and commercially available products well known to those skilled in the art or products prepared by conventional preparation methods can be used.

[0111] In this invention, the M source refers to a raw material providing element M, which includes at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, and Ce. The N source refers to a raw material providing element N, which includes at least one of S, F, and P. Any material containing the aforementioned target elements (Li, M, N) is considered within the scope of this invention. For example, the M source can be at least one of the oxides, hydroxides, and carbonates of the aforementioned metal elements; the N source can be at least one of sulfides, fluorides, and phosphates.

[0112] The present invention does not specifically limit the source of M and N, and products prepared by commercially available products or conventional preparation methods known to those skilled in the art can be used.

[0113] This invention does not specifically limit the molar ratio of nickel-manganese precursor material, lithium source, M source and N source; furthermore, by controlling the molar ratio among the four, the prepared lithium-rich manganese-based cathode material can satisfy Equation 2.

[0114] The present invention does not impose a specific limit on the heating rate during the sintering process. A suitable heating rate can be selected according to the actual situation. For example, the heating rate is 2 to 10 °C / min.

[0115] A third aspect of this invention provides a method for preparing a composite positive electrode active material, comprising the following steps:

[0116] Under an oxygen-rich atmosphere, lithium-rich manganese-based cathode material is uniformly mixed with raw materials including lithium source, source A, source B and source D, and then subjected to a first sintering and a second sintering in sequence to obtain a composite cathode active material; wherein, the temperature of the first sintering is 300-400℃ and the holding time is 3-8h; the temperature of the second sintering is 450-700℃ and the holding time is 20-40h;

[0117] The aforementioned composite positive electrode active material includes a core and a shell coating at least a portion of the surface of the core; the core includes a lithium-rich manganese-based positive electrode material, and the shell includes a cationic disordered oxide; the cationic disordered oxide includes a compound with the chemical composition shown in Formula 1.

[0118] Li z A x B 1-x O 2-y Dy Formula 1

[0119] In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn in a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S;

[0120] In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ ranging from 63° to 66°, and these diffraction peaks are unsplit single peaks.

[0121] Specifically, in an oxygen-rich atmosphere, lithium-rich manganese-based cathode material is uniformly mixed with raw materials including lithium source, source A, source B, and source D according to a set ratio to obtain a mixture. This mixture is then subjected to a first sintering at 300–400°C for 3–8 hours. Subsequently, the product obtained after the first sintering is subjected to a second sintering at 450–700°C for 20–40 hours. During the sintering process, the raw materials including lithium source, source A, source B, and source D undergo a chemical reaction, resulting in a reaction within the lithium-rich manganese-based cathode material. In-situ generation of cationic disordered oxides on the surface results in a composite positive electrode active material comprising a core (lithium-rich manganese-based positive electrode material) and a shell (cationic disordered oxide) covering at least part of the surface of the core. The cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1, and under the above-mentioned special sintering conditions, a cationic disordered oxide with a special crystal structure is formed. That is, in the XRD pattern of the cationic disordered oxide, there is a diffraction peak located at 2θ of 63° to 66°, and the diffraction peak is a single peak without splitting.

[0122] For example, the temperature of the first sintering is 300°C, 320°C, 340°C, 360°C, 380°C or 400°C; the holding time is 3h, 4h, 5h, 6h, 7h or 8h.

[0123] For example, the second sintering temperature is 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, or 700°C; and the holding time is 20h, 25h, 30h, 35h, or 40h.

[0124] The limitation of the oxygen atmosphere in this invention is consistent with the limitation in the preparation method of the composite positive electrode active material in the second aspect above, and will not be repeated here.

[0125] The limitations on the mixing method in this invention are consistent with those in the preparation method of the composite positive electrode active material in the second aspect above, and will not be repeated here.

[0126] It should be noted that during the first sintering, the temperature is raised from room temperature to the temperature required for the first sintering; after the first sintering is completed, the temperature is directly raised to the temperature required for the second sintering for the second sintering.

[0127] The present invention does not specifically limit the heating rate during the first and second sintering processes. A suitable heating rate can be selected according to the actual situation. For example, the heating rate can be 2 to 10 °C / min.

[0128] The limitations of the lithium-rich manganese-based cathode material, lithium source, A source, B source, and D source in this invention are consistent with the limitations in the preparation method of the composite cathode active material in the second aspect above, and will not be repeated here.

[0129] This invention does not impose specific limitations on the molar ratio of lithium source, source A, source B, and source D. It only requires that the chemical composition of the prepared disordered cationic oxide satisfies Formula 1 and that there is an unsplit single peak at 2θ of 63° to 66° in its X-ray diffraction pattern.

[0130] This invention does not specifically limit the mass ratio of lithium-rich manganese-based cathode material to raw materials including lithium source, A source, B source and D source; further, by controlling the mass ratio between lithium-rich manganese-based cathode material and raw materials, the mass ratio of cationic disordered oxide to lithium-rich manganese-based cathode material in the prepared composite cathode active material can be (0.5~3):100.

[0131] The preparation method of the composite positive electrode active material in this invention involves mixing and sintering a lithium-rich manganese-based positive electrode material with raw materials including a lithium source, an A source, a B source, and a D source under specific sintering conditions. This allows the lithium source, A source, B source, and D source to react, generating a cationic disordered oxide in situ on the surface of the lithium-rich manganese-based positive electrode material. This material has the chemical composition shown in Formula 1, and its XRD pattern shows a single, unsplit peak at 2θ of 63°–66°, indicating that the material possesses both a layered structure and a spinel structure. Coating the surface of the lithium-rich manganese-based positive electrode material with this cationic disordered oxide effectively improves the compatibility between the shell and the core, thereby enhancing the lithium-ion migration efficiency. This coating layer also effectively suppresses side reactions between the lithium-rich manganese-based positive electrode material and the electrolyte, thus inhibiting the escape of lattice oxygen and improving the structural stability of the positive electrode material. Furthermore, this cationic disordered oxide can participate in electrochemical reactions during charge and discharge, increasing the discharge capacity of the positive electrode material and effectively reducing energy density loss. Meanwhile, the spinel structure can form interconnected three-dimensional ion diffusion channels, which not only facilitates lithium-ion insertion / extraction but also reduces electrostatic repulsion during lithium extraction. Under high voltage, its lattice expansion and volume strain are small, exhibiting high structural stability. The synergy of these two factors effectively improves the lithium-ion transport efficiency and structural stability of the cathode active material. Furthermore, the relative amounts of nickel and manganese in this cationic disordered oxide are optimal, effectively avoiding the problems of excessive spinel structure due to insufficient nickel or excessive manganese, and dislocations in the crystal structure due to excessive nickel or insufficient manganese. This results in the cationic disordered oxide possessing both excellent electrochemical performance and structural stability.

[0132] Therefore, the composite positive electrode active material prepared by the above preparation method can effectively improve the first coulombic efficiency, cycle performance and rate performance of the battery.

[0133] In one specific embodiment, the lithium-rich manganese-based cathode material is prepared by the following method:

[0134] Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700-1100℃ for 10-24h in an oxygen atmosphere to obtain lithium-rich manganese-based cathode material.

[0135] The lithium-rich manganese-based cathode material prepared by the above preparation method is doped with M element (at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce) and N element (at least one of S, F, P), which can further improve the structural stability of the lithium-rich manganese-based cathode material.

[0136] For example, the sintering temperature is 700℃, 800℃, 900℃, 1000℃ or 1100℃; the holding time is 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0137] The limitations of the nickel-manganese precursor, lithium source, M source and N source in this invention are consistent with the limitations in the preparation method of the composite positive electrode active material in the second aspect above, and will not be repeated here.

[0138] This invention does not specifically limit the molar ratio of nickel-manganese precursor material, lithium source, M source and N source; furthermore, by controlling the molar ratio among the four, the prepared lithium-rich manganese-based cathode material can satisfy Equation 2.

[0139] The present invention does not impose a specific limit on the heating rate during the sintering process. A suitable heating rate can be selected according to the actual situation. For example, the heating rate is 2 to 10 °C / min.

[0140] A fourth aspect of this invention provides a positive electrode sheet, which includes the composite positive electrode active material of the first aspect, or the composite positive electrode active material prepared by the preparation method of the second aspect, or the composite positive electrode active material prepared by the preparation method of the third aspect. Therefore, using this positive electrode sheet in a lithium-ion battery can effectively improve the battery's initial coulombic efficiency, cycle performance, and rate performance.

[0141] It is understood that the positive electrode sheet also includes a positive electrode current collector and a positive electrode active layer, with the positive electrode active layer disposed on at least a portion of the surface of the positive electrode current collector; the positive electrode active layer includes the aforementioned composite positive electrode active material.

[0142] The present invention does not specifically limit the type of positive electrode current collector, and conventional current collectors in the art can be used, for example, aluminum foil can be selected as the positive electrode current collector.

[0143] Furthermore, the positive electrode active layer also includes a binder and a conductive agent.

[0144] This invention does not specifically limit the types of binders and conductive agents, and conventional materials in the art can be used. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), lithium polyacrylate (LiPAA), and polyvinyl acid (PAA); the conductive agent may include at least one of carbon black, graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes.

[0145] This invention does not impose specific limitations on the mass ratio of composite positive electrode active material, binder and conductive agent in the positive electrode active layer, and appropriate mass ratios can be selected according to actual needs.

[0146] This invention does not specify a particular method for preparing the positive electrode sheet, which can be prepared by conventional methods in the art.

[0147] A fifth aspect of this invention provides a lithium-ion battery comprising a composite positive electrode active material as described in the first aspect, or a composite positive electrode active material prepared by the preparation method of the second aspect, or a composite positive electrode active material prepared by the preparation method of the third aspect, or a positive electrode sheet as described in the fourth aspect. Therefore, this lithium-ion battery exhibits high initial coulombic efficiency, cycle performance, and rate performance.

[0148] This invention does not specifically limit the battery preparation method. For example, a bare cell is obtained by winding or stacking a positive electrode sheet, a separator and a negative electrode sheet, and then the bare cell is packaged, dried, injected with electrolyte, placed, formed and resealed to obtain a battery.

[0149] It is understandable that lithium-ion batteries also include negative electrode plates, separators, and electrolytes.

[0150] The present invention does not specifically limit the composition of the negative electrode sheet. In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least a portion of the surface of the negative electrode current collector; the negative electrode active layer includes a negative electrode active material, a binder and a conductive agent.

[0151] The present invention does not specifically limit the type of negative electrode current collector, and conventional current collectors in the art can be used, for example, copper foil can be selected as the negative electrode current collector.

[0152] This invention does not specifically limit the type of negative electrode active material, and conventional materials in the art can be used. For example, it may include carbon negative electrode active materials and / or silicon negative electrode active materials. The carbon negative electrode active materials include at least one of natural graphite, artificial graphite, hard carbon, soft carbon, and carbon black; the silicon negative electrode active materials include at least one of elemental silicon, silicon-based composite materials, and silicon alloys.

[0153] The present invention does not specifically limit the type of adhesive, and conventional materials in the art can be used, such as at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and nitrile rubber (NBR).

[0154] The present invention does not specifically limit the type of conductive agent, and conventional materials in the art can be used, such as at least one of acetylene black, Ketjen black, graphite, graphene, and carbon nanotubes.

[0155] This invention does not specify the mass content of negative electrode active material, binder and conductive agent in negative electrode active layer, and appropriate mass ratio can be selected according to actual needs.

[0156] The composite positive electrode active material provided by the present invention will be described in detail below through specific embodiments.

[0157] Example 1

[0158] 1) Using Li 1.36 (Ni 0.32 Mn 0.68 ) 0.995 Nb 0.005 O 2.36 Based on the stoichiometric ratio, lithium salt, Nb2O5, and nickel-manganese precursor materials (Ni) were used. 0.32 Mn 0.68 (OH)2) Mix evenly to obtain a mixture; place the mixture in an atmosphere box furnace, heat to 900℃ at 2℃ / min in an air atmosphere, and sinter for 15h; after cooling, crush and sieve to obtain the lithium-rich manganese-based cathode material of this embodiment;

[0159] 2) Mix the coating precursor with the lithium-rich manganese-based cathode material at a mass ratio of 1:100. The coating precursor includes a nickel-manganese precursor (Ni... 0.5 Mn 0.5 The mixture contains (OH)2), LiCO3, LiF, and AlF3, with a molar ratio of Li, Ni, Mn, Al, O, and F of 0.97:0.495:0.495:0.01:1.97:0.03. After being thoroughly mixed, the mixture is placed in an atmosphere box furnace and sintered at 300°C at a rate of 2°C / min under air atmosphere for the first sintering, and held for 5 hours. Then, the mixture is sintered at 480°C at a rate of 2°C / min for the second sintering, and held for 25 hours. After cooling to room temperature, the mixture is crushed and sieved to obtain the composite positive electrode active material of this embodiment.

[0160] This composite cathode active material comprises a lithium-rich manganese-based cathode material as its core and a cationic disordered oxide coating layer on the surface of the core; the chemical composition of this cationic disordered oxide is Li. 0.97 Ni 0.495 Mn 0.495 Al 0.01 O 1.97 F 0.03 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0161] Example 2

[0162] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 2), the mass ratio of the coating precursor to the lithium-rich manganese-based positive electrode material is 0.5:100, and the others remain unchanged.

[0163] Example 3

[0164] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 2), the mass ratio of the coating precursor to the lithium-rich manganese-based positive electrode material is 2:100, and the others remain unchanged.

[0165] Example 4

[0166] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 2), the mass ratio of the coating precursor to the lithium-rich manganese-based positive electrode material is 3:100, and the others remain unchanged.

[0167] Example 5

[0168] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor Ni. 0.45 Mn 0.55 The mixture consists of (OH)2, LiCO3, LiF, and AlF3, with the molar ratio of Li, Ni, Mn, Al, O, and F being 0.87:0.455:0.545:0.01:1.97:0.03, while other parameters remain unchanged.

[0169] The chemical composition of the disordered cation oxide in the prepared composite positive electrode active material is Li 0.87 Ni 0.445 Mn 0.545 Al 0.01 O 1.97 F 0.03 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0170] Example 6

[0171] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor Ni. 0.4 Mn 0.6 The ingredients are (OH)2, LiCO3, LiF, and MgF2, and the molar ratio of Li, Ni, Mn, Mg, O, and F is 0.792:0.396:0.594:0.01:1.98:0.02, with other parameters remaining unchanged.

[0172] The chemical composition of the disordered cation oxide in the prepared composite positive electrode active material is Li 0.792 Ni 0.396 Mn 0.594 Mg 0.01 O 1.98 F 0.02XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0173] Example 7

[0174] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor Ni. 0.5 Mn 0.5 The ingredients are (OH)2, LiCO3, LiF, AlF3, and MoO3, with the molar ratio of Li, Ni, Mn, Al, Mo, O, and F being 0.94:0.49:0.49:0.01:0.01:1.97:0.03, and the others remaining unchanged.

[0175] The chemical composition of the disordered cation oxide in the prepared composite positive electrode active material is Li 0.94 Ni 0.4 9Mn 0.49 Al 0.01 Mo 0.01 O 1.97 F 0.03 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0176] Example 8

[0177] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor Ni. 0.5 Mn 0.5 The ingredients are (OH)2, LiCO3, LiF, AlF3, and ZrO2, with the molar ratio of Li, Ni, Mn, Al, Zr, O, and F being 0.96:0.49:0.49:0.01:0.01:1.97:0.03, and the others remaining unchanged.

[0178] The chemical composition of the disordered cation oxide in the prepared composite positive electrode active material is Li 0.96 Ni 0.4 9Mn 0.49 Al 0.01 Zr 0.01 O 1.97 F 0.03 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0179] Example 9

[0180] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor Ni. 0.5 Mn 0.5 The ingredients are (OH)2, LiCO3, LiF, and WO3, with the molar ratio of Li, Ni, Mn, W, O, and F being 0.92:0.49:0.49:0.02:1.98:0.02, and other parameters remaining unchanged.

[0181] The chemical composition of the disordered cation oxide in the prepared composite positive electrode active material is Li 0.92 Ni 0.4 9Mn 0.49 W 0.02 O 1.98 F 0.02 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0182] Example 10

[0183] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), Li... 1.32 (Ni 0.35 Mn 0.65 ) 0.985 Sb 0.015 O 2.32 Based on the stoichiometric ratio, lithium salt, Sb₂O₅, and nickel-manganese precursor (nickel-manganese hydroxide Ni) were added. 0.35 Mn 0.65 (OH)2) Mix evenly to obtain a mixture; place the mixture in an atmosphere box furnace, heat it to 920°C at a heating rate of 5°C / min in an air atmosphere, and hold for sintering for 15 hours to prepare the lithium-rich manganese-based cathode material of this embodiment.

[0184] Example 11

[0185] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), Li... 1.34 (Ni 0.32 Mn 0.68 ) 0.995 Mg 0.005 O 2.34 F 0.01 Based on the stoichiometric ratio, lithium salt, MgF2 and nickel-manganese precursor materials (Ni 0.32 Mn 0.68(OH)2) Mix evenly to obtain a mixture; place the mixture in an atmosphere box furnace, heat to 900℃ at 2℃ / min in an air atmosphere, and sinter for 15h to prepare the lithium-rich manganese-based cathode material of this embodiment.

[0186] Example 12

[0187] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1. The difference is that in step 2), the mass ratio of the coating precursor to the lithium-rich manganese-based positive electrode material is 4:100.

[0188] Example 13

[0189] 1) Using Li 1.36 (Ni 0.32 Mn 0.68 ) 0.995 Nb 0.005 O 2.36 Based on the stoichiometric ratio, lithium salt, Nb2O5, and nickel-manganese precursor materials (Ni) were used. 0.32 Mn 0.68 (OH)2) Mix evenly to obtain a mixture; place the mixture in an atmosphere box furnace, heat to 900℃ at 2℃ / min in an air atmosphere, and sinter for 15h; after cooling, crush and sieve to obtain the lithium-rich manganese-based cathode material of this embodiment;

[0190] 2) Including nickel-manganese precursors (Ni 0.5 Mn 0.5 The first raw material is obtained by uniformly mixing (OH)2), LiCO3, LiF, and AlF3. The molar ratio of Li, Ni, Mn, Al, O, and F in the first raw material is 0.97:0.495:0.495:0.01:1.97:0.03. The first raw material is placed in an atmosphere box furnace and subjected to first sintering in an air atmosphere. The heating rate in the first sintering is 2℃ / min, the sintering temperature is 300℃, and the holding time is 4h. Subsequently, the temperature of the box furnace is raised to 470℃ at a heating rate of 2℃ / min and held for 30h. After cooling to room temperature, it is crushed and sieved to obtain the cationic disordered oxide of this embodiment. The chemical composition of the cationic disordered oxide is Li 0.97 Ni 0.495 Mn 0.495 Al 0.01 O 1.97 F 0.03 XRD analysis of the disordered cation oxide revealed diffraction peaks with 2θ values ​​between 63° and 66° in its X-ray diffraction pattern, and these peaks were unsplit single peaks.

[0191] 3) The cationic disordered oxide prepared above is mixed with lithium-rich manganese-based cathode material at a mass ratio of 1:100 to obtain the second raw material; the second raw material is placed in an atmosphere box furnace and heated to 300°C at 5°C / min in an air atmosphere for the third sintering, and the holding time is 6h. After cooling, it is crushed and sieved to obtain the composite cathode active material of this embodiment.

[0192] Example 14

[0193] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), Li... 1.61 (Ni 0.2 Mn 0.8 ) 0.995 Nb 0.005 O 2.61 Based on the stoichiometric ratio, lithium salt, Nb2O5, and nickel-manganese precursor (Ni) were used. 0.2 Mn 0.8 (OH)2) Mix evenly to obtain a mixture and then sinter it under the same sintering conditions.

[0194] Example 15

[0195] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), Li... 1.11 (Ni 0.45 Mn 0.55 ) 0.995 Nb 0.005 O 2.11 Based on the stoichiometric ratio, lithium salt, Nb2O5, and nickel-manganese precursor (Ni) were used. 0.45 Mn 0.55 (OH)2) Mix evenly to obtain a mixture and then sinter it under the same sintering conditions.

[0196] Example 16

[0197] The preparation method of the composite positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step 1), Li... 1.47 (Ni 0.32 Mn 0.68 ) 0.93 Nb 0.07 O 2.47 Based on the stoichiometric ratio, lithium salt, Nb2O5, and nickel-manganese precursor (nickel-manganese hydroxide Ni) were added. 0.32 Mn 0.68 (OH)2) Mix evenly and sinter, keeping the sintering conditions unchanged.

[0198] Comparative Example 1

[0199] The preparation method of the composite positive electrode active material in this comparative example is basically the same as that in Example 1, except that the lithium-rich manganese-based positive electrode material is not coated.

[0200] Comparative Example 2

[0201] The preparation method of the composite positive electrode active material in this comparative example is basically the same as that in Example 1. The difference is that in step 2), the coating precursor and the lithium-rich manganese-based positive electrode material are mixed evenly and then placed in an atmosphere box furnace. The temperature is increased to 500°C at 2°C / min under air atmosphere and sintered for 35 hours to obtain the composite positive electrode active material of this comparative example.

[0202] Comparative Example 3

[0203] The preparation method of the composite positive electrode active material in this comparative example is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor (Ni). 0.6 Mn 0.4 The ingredients are (OH)2), Li2CO3, LiF and AlF3, and the molar ratio of Li, Ni, Mn, Al, O and F is 0.996:0.588:0.392:0.02:1.8:0.2, with other components remaining unchanged.

[0204] The chemical formula of the disordered cation oxide in the prepared composite positive electrode active material is Li. 0.996 Ni 0.588 Mn 0.392 Al 0.02 O 1.8 F 0.2 .

[0205] Comparative Example 4

[0206] The preparation method of the composite positive electrode active material in this comparative example is basically the same as that in Example 1, except that in step 2), the coating precursor includes a nickel-manganese precursor (Ni). 0.3 Mn 0.7 The ingredients are (OH)2), Li2CO3, LiF and MgF2, and the molar ratio of Li, Ni, Mn, Mg, O and F is 0.594:0.297:0.693:0.01:1.98:0.02, with other parameters remaining unchanged.

[0207] The chemical formula of the disordered cation oxide in the prepared composite positive electrode active material is Li. 0.594 Ni 0.297 Mn 0.693 Mg 0.01 O 1.98 F 0.02 .

[0208] Comparative Example 5

[0209] The preparation method of the composite positive electrode active material in this comparative example differs from that in Example 13 in that the cationic disordered oxide is different. Specifically, the lithium-rich manganese-based positive electrode material is combined with the high-entropy cationic disordered oxide Li(Mn) 0.2 Ni 0.2 Fe 0.2 Ti 0.2 Nb 0.2 The mixed powder of O2 (the mass ratio of lithium-rich manganese-based cathode material to high-entropy cation disordered oxide is 100:1) was placed in a ball mill for mechanical ball milling. The ball milling speed was 300 rpm / min, the mass ratio of mixed powder to milling beads was 1:10, and the ball milling time was 2 h. The ball-milled mixed powder was then transferred to a tube furnace and sintered at 700 °C for 4 h to obtain the composite cathode active material of this comparative example.

[0210] The high-entropy cationic disordered oxide Li(Mn) in the comparative example 0.2 Ni 0.2 Fe 0.2 Ti 0.2 Nb 0.2 XRD analysis of O2 revealed no diffraction peaks with a 2θ value between 63° and 66° in its X-ray diffraction pattern. Figure 5 As shown.

[0211] Comparative Example 6

[0212] The preparation method of the composite positive electrode active material in this comparative example differs from that in Example 1 in that the cationic disordered oxide is different. Specifically, the lithium-rich manganese-based positive electrode material and the cationic disordered material Li2Mn are used. 2 / 3 Nb 1 / 3 After O2F was mixed evenly at a mass ratio of 100:1, it was placed in a muffle furnace and sintered at 400-700℃ for 8 hours; the sintered product was crushed to obtain the positive electrode active material of this comparative example.

[0213] The cationic disordered material Li2Mn in the comparative example 2 / 3 Nb 1 / 3 XRD analysis of O2F revealed no diffraction peaks with a 2θ value between 63° and 66° in its X-ray diffraction pattern. Figure 5 As shown.

[0214] Test case

[0215] 1. The activity of the composite cathodes prepared in Example 1 and Comparative Example 1 was tested using a Hitachi SU 8010 scanning electron microscope (SEM) from Japan. The test results are shown in the figure. Figure 1 and Figure 2 .

[0216] Figure 1 This is a SEM image of the composite positive electrode active material in Example 1. Figure 2 This is a SEM image of the composite positive electrode active material in Comparative Example 1. Figure 1 and Figure 2 It can be seen that the composite positive electrode active material in Example 1 has a significant coating on its surface compared to the lithium-rich manganese-based positive electrode material in Comparative Example 1, which was not treated in any way.

[0217] 2. The cationic disordered oxides prepared in the above examples and comparative examples were subjected to XRD tests to observe whether there were unsplit single peaks in the XRD patterns within the range of 2θ of 63° to 66°. The test results are shown in Table 1 and... Figures 3-5 .

[0218] Figure 3 The cationic disordered oxide and typical ternary layered LiNi in Example 1 0.5 Mn 0.5 O2 and typical spinel-type LiNi 0.5 Mn 1.5 Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66° Figure 3 In the figure, curve a represents LiNi with a typical spinel structure. 0.5 Mn 1.5 The local XRD diffraction curves of O4 at 2θ of 63°–66°, with curve b representing the typical layered structure of LiNi. 0.5 Mn 0.5 The local XRD diffraction curves of O2 at 2θ of 63°–66° are shown in Figure c, which is the local XRD diffraction curve of the cationic disordered oxide in Example 1 at 2θ of 63°–66°. Figure 3 It can be seen that the typical layered structure of LiNi 0.5 Mn 0.5 O2 exhibits two peaks at 2θ between 63° and 66°, indicating a complete layered structure; LiNi has a typical spinel-type structure. 0.5 Mn 1.5 The characteristic peak of O4 at 2θ of 63° to 66° is a sharp split peak, indicating that it has a good spinel-type structure and high crystallinity; while the characteristic peak of the cationic disordered oxide synthesized in Example 1 is a single peak without splitting at 2θ of 63° to 66°, which appears as a bun shape, indicating that its crystallinity is slightly lower and the internal crystals are not a single layered or spinel structure.

[0219] Figure 4 The cationic disordered oxide in Comparative Example 2 and the typical ternary layered LiNi 0.5 Mn 0.5 O2 and typical spinel-type LiNi 0.5 Mn 1.5Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66° Figure 4 In the middle, by Figure 2 It can be seen that curve a represents LiNi with a typical spinel structure. 0.5 Mn 1.5 The local XRD diffraction curves of O4 at 2θ of 63°–66°, with curve b representing the typical layered structure of LiNi. 0.5 Mn 0.5 The local XRD diffraction curve of O2 at 2θ of 63°–66° is shown in Figure c, which is the local XRD diffraction curve of the disordered cation oxide in Comparative Example 2 at 2θ of 63°–66°. Figure 4 In Comparative Example 2, the synthesized cationic disordered oxide exhibits split diffraction peaks at 2θ of 63°–66°, as well as impurity phase peaks, indicating that the synthesized cationic disordered oxide contains impurity phases and has low phase purity.

[0220] Figure 5 The cationic disordered oxides in Comparative Examples 5 and 6 are compared with typical ternary layered LiNi 0.5 Mn 0.5 O2 and typical spinel-type LiNi 0.5 Mn 1.5 Comparison of local XRD diffraction peaks of O4 at 2θ of 63°–66° Figure 5 In the figure, curve a represents LiNi with a typical spinel structure. 0.5 Mn 1.5 The local XRD diffraction curves of O4 at 2θ of 63°–66°, with curve b representing the typical layered structure of LiNi. 0.5 Mn 0.5 The local XRD diffraction curves of O2 at 2θ of 63°–66° are shown in Figure c. The local XRD diffraction curves of the cationic disordered oxide in Comparative Example 5 at 2θ of 63°–66° are shown in Figure d. Figure 5 In Comparative Examples 5 and 6, the synthesized cationic disordered oxides did not exhibit diffraction peaks at 2θ of 63°–66°, indicating that the synthesized cationic disordered oxides did not possess a layered and spinel composite structure.

[0221] 3. The composite positive electrode active material prepared in the above embodiments and comparative examples is used to fabricate a coin cell, including the following steps:

[0222] The composite positive electrode active material prepared above was mixed with binder PVDF and conductive agent Super-P at a mass ratio of 90:5:5, and then dispersed evenly in N-methylpyrrolidone to obtain a positive electrode active slurry. The positive electrode active slurry was coated on one side of an aluminum foil, dried at 120°C, rolled, and punched to form a positive electrode sheet with a diameter of 13 mm and an areal density of 12 mg / cm³. 2 The compacted density is 2.8 mg / cm³. 3 Inside an argon-filled glove box, a 2032 coin cell was assembled with a lithium sheet as the negative electrode, a polypropylene microporous membrane (Celgard 2400) as the separator, and an electrolyte. The lithium salt in the electrolyte was lithium hexafluorophosphate (LiPF6) at a concentration of 1M, and the solvent was ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

[0223] The electrochemical performance of the 2032 coin cells prepared above was tested at 25°C using the Newway battery testing system as follows:

[0224] 1) First Coulomb efficiency

[0225] The charge / discharge voltage window is 2.5V to 4.55V. After the assembled battery has been resting for 5 hours, it is charged at a constant current of 0.2C to 4.55V, and then charged at a constant voltage of 4.55V until the cutoff current is 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V (the charge / discharge current density of 1C is 230mA / g). The first charge / discharge specific capacity is obtained. The first coulombic efficiency (%) of the battery is then calculated as (first discharge specific capacity / first charge specific capacity) × 100%.

[0226] 2) Cyclic performance

[0227] The charge / discharge voltage window is 2.5V to 4.55V. After the battery completes the first discharge capacity test, it is charged at a constant current of 1C to 4.55V, and then charged at a constant voltage of 4.55V until the cutoff current is 0.05C. After resting for 5 minutes, it is discharged at a constant current of 1C to 2.5V, and the discharge capacity is recorded as C0. The battery is cycled 100 times according to the aforementioned charge / discharge mechanism, and the discharge capacity after the cycle is recorded as C1. The cycle capacity retention rate (%) is then calculated as (C1 / C0) × 100%.

[0228] 3) Ratio performance

[0229] After the assembled battery has been left to stand for 5 hours, it is charged at a constant current of 0.2C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V. This cycle is repeated 3 times, and the discharge capacity after each discharge is obtained. The average value is recorded as C2. Then, it is charged at a constant current of 1C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is 0.05C. After standing for 5 minutes, it is discharged at a constant current of 1C to 2.5V. This cycle is repeated 3 times, and the discharge capacity after each discharge is obtained. The average value is recorded as C3. The rate performance (%) is calculated as (C3 / C2) × 100%.

[0230] The test results are shown in Table 1 and Figures 6-9 .

[0231] Figure 6 This is a charge-discharge curve of the battery in Example 1 at 1C. Figure 7 This is a charge-discharge curve of the battery in Example 3 at 1C. Figure 8 This is a charge-discharge curve of the battery in Example 14 at 1C. Figure 9 This is a charge / discharge curve of the battery in Example 15 at 1C.

[0232] Table 1

[0233]

[0234]

[0235] As shown in Table 1:

[0236] Compared to Comparative Examples 1-6, the coin cells in Examples 1-16 exhibit higher initial coulombic efficiency, cycle performance, and rate performance. Specifically, the coin cell in Example 1 achieves an initial coulombic efficiency of 86.2%, and correspondingly, its cycle capacity retention reaches 92.7%, and its rate performance reaches 96.5%, significantly higher than the performance of the cells in Comparative Examples 1-6. Therefore, the composite positive electrode active material of this invention can effectively improve the initial coulombic efficiency, rate performance, and cycle performance of the battery.

[0237] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite positive electrode active material, characterized in that, The composite positive electrode active material comprises a core and a shell coating at least a portion of the surface of the core; the core comprises a lithium-rich manganese-based positive electrode material, and the shell comprises a cationic disordered oxide; the cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1. Li z A x B 1-x O 2-y D y Formula 1 In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn with a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S; In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ of 63°~66°, and the diffraction peaks are unsplit single peaks; The thickness of the shell layer is 5nm~20nm.

2. The composite positive electrode active material according to claim 1, characterized in that, The mass ratio of the cationic disordered oxide to the lithium-rich manganese-based cathode material is (0.5~3):

100.

3. The composite positive electrode active material according to claim 1 or 2, characterized in that, The lithium-rich manganese-based cathode material comprises a compound with the chemical composition shown in Formula 2. Li 1+m Ni a Mn b M c O 2+m-d N d Formula 2 In Equation 2, 0.2≤m≤0.4, a+b+c=1, 0.42≤a / b≤0.67, 0≤c≤0.02, 0≤d≤0.02; M includes at least one of Na, Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce; N includes at least one of S, F, P.

4. A method for preparing the composite positive electrode active material according to any one of claims 1-3, characterized in that, Includes the following steps: Under an oxygen-rich atmosphere, a first raw material comprising lithium source, source A, source B, and source D is uniformly mixed and then subjected to a first sintering and a second sintering process to obtain a cationic disordered oxide. The first sintering temperature is 300–400°C, and the holding time is 2–4 hours; the second sintering temperature is 450–600°C, and the holding time is 10–40 hours. The cationic disordered oxide comprises compounds with the chemical composition shown in Formula 1. Li z A x B 1-x O 2-y D y Formula 1 In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn with a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S; In the X-ray diffraction pattern of the disordered cation oxide, there are diffraction peaks with 2θ of 63°~66°, and the diffraction peaks are unsplit single peaks; Under an oxygen-containing atmosphere, the second raw material, including the cationic disordered oxide and the lithium-rich manganese-based cathode material, is uniformly mixed and then subjected to a third sintering to obtain the composite cathode active material; wherein, the temperature of the third sintering is 300~500℃ and the holding time is 2~12h.

5. The method for preparing the composite positive electrode active material according to claim 4, characterized in that, The lithium-rich manganese-based cathode material was prepared by the following method: Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700~1100℃ for 10~24h in an oxygen atmosphere to obtain the lithium-rich manganese-based cathode material.

6. A method for preparing the composite positive electrode active material according to any one of claims 1-3, characterized in that, Includes the following steps: Under an oxygen-rich atmosphere, lithium-rich manganese-based cathode material is uniformly mixed with raw materials including lithium source, source A, source B and source D, and then subjected to a first sintering and a second sintering in sequence to obtain a composite cathode active material; wherein, the temperature of the first sintering is 300~400℃ and the holding time is 3~8h; the temperature of the second sintering is 450~700℃ and the holding time is 20~40h; The composite positive electrode active material comprises a core and a shell coating at least a portion of the surface of the core; the core comprises a lithium-rich manganese-based positive electrode material, and the shell comprises a cationic disordered oxide; the cationic disordered oxide comprises a compound with the chemical composition shown in Formula 1. Li z A x B 1-x O 2-y D y Formula 1 In Formula 1, 0.90≤x<1.0, 0≤y≤0.2, 0.78<z<1.1, A includes Ni and Mn with a molar ratio of (0.6~1):1, B includes at least one of Mg, Sr, Y, Ti, Zr, Nb, Ta, Cr, Mo, W, Co, Al, Ga, Sn, Sb, Te, La, Ce, and D includes F and / or S; The X-ray diffraction pattern of the disordered cation oxide shows a diffraction peak with a 2θ value of 63° to 66°, which is a single peak without splitting.

7. The method for preparing the composite positive electrode active material according to claim 6, characterized in that, The lithium-rich manganese-based cathode material was prepared by the following method: Raw materials including nickel-manganese precursor, lithium source, M source and N source are mixed to obtain a mixture; the mixture is sintered at 700~1100℃ for 10~24h in an oxygen atmosphere to obtain the lithium-rich manganese-based cathode material.

8. A positive electrode plate, characterized in that, The positive electrode sheet includes the composite positive electrode active material according to any one of claims 1-3, or the composite positive electrode active material prepared by the preparation method according to claim 4 or 5, or the composite positive electrode active material prepared by the preparation method according to claim 6 or 7.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite positive electrode active material according to any one of claims 1-3, or the composite positive electrode active material prepared by the preparation method according to claim 4 or 5, or the composite positive electrode active material prepared by the preparation method according to claim 6 or 7, or the positive electrode sheet according to claim 8.

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