A high-nickel cathode material with a cage-like oxygen-solidifying structure, a lithium-ion battery, and a preparation method thereof

Abstract

The present invention provides a high-nickel cathode material with a cage-shaped oxygen fixation structure, a lithium-ion battery and a preparation method thereof. The core of the high-nickel cathode material forms a LiTMO phase and a LiTMO2F phase, where TM represents a transition metal element, 0≤α<0.1, the near-surface layer is gradient-doped with a lithium-philic metal element L, and the metal element L forms an L-O bond with O, and a perovskite-phase coating layer is formed on the outer layer. By doping with fluorine elements, the high-nickel cathode material forms stable TM-F bonds in the core to stabilize the main structure of the material. The near-surface layer of the material is gradient-doped with the transition metal L element to form an L-O bond, which can effectively passivate the surface active oxygen. The outer edge of the material is coated with a perovskite phase, which can capture the active oxygen escaping from the surface, jointly constructing a high-nickel ternary material with a cage-shaped oxygen fixation structure from the inside to the outside, protecting the material from the erosion of hydrofluoric acid and moisture, and improving the structural and thermal stability of the material while inhibiting the precipitation of active oxygen. 2‑α phase. Among them, TM represents a transition metal element, 0≤α<0.1, the near-surface layer is gradient-doped with a lithium-philic metal element L, and the metal element L forms an L-O bond with O, and a perovskite-phase coating layer is formed on the outer layer. By doping with fluorine elements, the high-nickel cathode material forms stable TM-F bonds in the core to stabilize the main structure of the material. The near-surface layer of the material is gradient-doped with the transition metal L element to form an L-O bond, which can effectively passivate the surface active oxygen. The outer edge of the material is coated with a perovskite phase, which can capture the active oxygen escaping from the surface, jointly constructing a high-nickel ternary material with a cage-shaped oxygen fixation structure from the inside to the outside, protecting the material from the erosion of hydrofluoric acid and moisture, and improving the structural and thermal stability of the material while inhibiting the precipitation of active oxygen.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a high-nickel cathode material with a cage-shaped solid oxygen structure, a lithium-ion battery, and a preparation method thereof. Background Art

[0002] With the advancement of the new energy process, lithium-ion batteries have become the power sources of major electric or hybrid vehicles. Among them, high-nickel ternary materials with high specific capacity have become an important research direction in lithium batteries. However, the increase in the high specific capacity of high-nickel materials is accompanied by an increase in nickel content, which also means an increase in the instability and gas generation of the materials. Doping and coating modification is an important way to optimize the performance of high-nickel cathode materials. However, due to the influence of doping and coating on the microscopic lattice structure and crystal morphology of the materials, and the complex interaction of multiple elements during doping and coating, how to select suitable elements to modify the materials to make the crystal materials have high specific capacity, stability, safety, etc. has become the research focus in recent years.

[0003] In addition, in order to further improve the safety of the materials, multi-ion co-doping is often used as a technical means. However, in the process of multi-ion doping, how to avoid the formation of reverse conflicts between different doping elements is an important exploration direction.

[0004] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present invention, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a high-nickel cathode material with a cage-shaped solid oxygen structure, a lithium-ion battery, and a preparation method thereof.

[0006] According to a first aspect of the present invention, there is provided a high-nickel cathode material with a cage-shaped solid oxygen structure, wherein a LiTMO phase and a LiTMO2F 2-α phase are formed in the core of the high-nickel cathode material, where TM represents a transition metal element, 0 ≤ α < 0.1, a lithiumophilic metal element L is gradient-doped in the near-surface layer, and the lithiumophilic metal element L forms an L-O bond with O, and a perovskite-phase coating layer is formed on the outer layer.

[0007] In an exemplary embodiment of the present invention, the transition metal element TM is selected from one or more of Ni, Co, and Mn; the lithiumophilic metal element L is selected from one or more of Ti, Zr, Y, V, Nb, Ta, Cr, W, Co, and Fe; and the distribution of the lithiumophilic metal element in the near-surface layer of the high-nickel cathode material shows a gradient distribution decreasing from the outside to the inside.

[0008] In an exemplary embodiment of the present invention, the lithophilic metal element L is preferably selected from one or more of Ti, Zr, and Nb. The metal element L replaces the transition metal TM to form an L-O bond with O and / or reacts with Li on the surface of the material to generate a lithium oxide containing a Li-L-O bond. + to form a lithium oxide containing a Li-L-O bond.

[0009] In an exemplary embodiment of the present invention, the perovskite phase coating is island-shapedly coated on the surface of the high-nickel cathode material. The perovskite phase coating includes a lanthanide perovskite layer composed of an alternating perovskite phase and a layered phase. The lanthanide element of the lanthanide perovskite layer is selected from one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, and gadolinium.

[0010] In an exemplary embodiment of the present invention, the lanthanide element is selected from lanthanum, and the lanthanide perovskite layer is a lanthanum-containing perovskite phase oxide of the A2BO4 type with oxygen vacancies.

[0011] According to a second aspect of the present invention, there is provided a method for preparing a high-nickel cathode material with a cage-shaped oxygen-fixing structure as described in any one of the above, including:

[0012] S1, mixing a high-nickel ternary precursor TM(OH)2, a lithium source, a fluorine-containing compound, and a compound containing a metal element L to obtain a first mixture;

[0013] S2, placing the first mixture in an oxygen environment and sintering it at 500-650 °C for 2-8 h. After cooling and sieving, a first sintered product is obtained;

[0014] S3, mixing the first sintered product and a compound containing a lanthanide element to obtain a second mixture;

[0015] S4, placing the second mixture in an oxygen atmosphere and subjecting it to secondary calcination at 650-800 °C for 6-11 h. After cooling, the high-nickel cathode material with a cage-shaped oxygen-fixing structure is obtained.

[0016] In an exemplary embodiment of the present invention, in step S1, the lithium source is selected from one or more of lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxalate, lithium acetate, lithium sulfate, and lithium-containing oxides; the fluorine-containing compound is selected from one or more of LiF, NH4HF2, NH4F, NaF, and KF; and the molar ratio of the lithium source to the fluorine-containing compound is 1:(0-0.1).

[0017] In an exemplary embodiment of the present invention, in step S1, the compound containing metal element L and the compound containing lanthanide elements are selected from one or more of oxides, halides, carbonates, oxalates, phosphates, and acetates. The addition amount of metal element L in the first mixture is 1 to 10,000 mg / kg, and the addition amount of lanthanide elements in the first mixture is 1 to 5,000 mg / kg.

[0018] In an exemplary embodiment of the present invention, the particle sizes of the lithium source, the F-containing compound, and the compound containing metal element L are in the micron level, and the D50 is 0 to 10 μm; the particle size of the lanthanide-containing compound is in the nanometer level, and the D50 is 50 to 100 nm.

[0019] In an exemplary embodiment of the present invention, in steps S1 and S3, the mixing step is to mix the materials by a high-speed mixer at 500 to 1000 rpm for 10 to 20 minutes; in steps S2 and S4, the first mixture and the second mixture are calcined at an oxygen concentration > 99.5% at a heating rate of 1 to 5 °C / min, and finally a sintered product is obtained through cooling and sieving.

[0020] According to the third aspect of the present invention, a lithium-ion battery is provided, which includes the high-nickel cathode material with a cage-shaped solid oxygen structure as described in any one of the above, or the high-nickel cathode material with a cage-shaped solid oxygen structure prepared by the preparation method as described in any one of the above.

[0021] The beneficial effects of the high-nickel cathode material with a cage-shaped solid oxygen structure, the lithium-ion battery, and the preparation method in the embodiments of the present invention are as follows:

[0022] The high-nickel cathode material with a cage-shaped solid oxygen structure provided in the embodiments of the present invention modifies the bulk phase and surface of the cathode material, and synergistically inhibits the instability and oxygen evolution of the high-nickel cathode material from the following three aspects.

[0023] First, when F is doped, F ions can penetrate into the core of the material and replace the oxygen sites, reducing the surface energy of the material, improving the hydrophobicity of the material, and forming a more stable transition metal-fluorine (TM-F) bond in the bulk phase core. At the same time, it can also increase the covalency of the Ni / Co / Mn-O bond, effectively stabilizing the main structure of the material. In addition, F doping can reduce the energy band overlap between the transition metal and O 2- to improve the high-voltage cycling performance of the material. Fluorine replacing oxygen can reduce the P-band energy level of the material, widen the lithium layer spacing, and improve lithium transport; in addition, an appropriate doping amount can enhance the interfacial stability between the active material and the electrolyte, inhibit the polarization of the material, and prevent HF erosion.

[0024] In a second aspect, a lithiophilic metal (L) element is gradient-doped near the surface of the cathode material to form an L-O bond or a Li-L-O structure, regulating the nucleation overpotential of lithium to stabilize lithium deposition, reducing lithium dendrites. The deposited lithium diffuses into the lattice interior through channels with a low diffusion barrier, reducing the residual lithium on the material surface and at the interface while broadening the Li + diffusion channels to improve the lithium diffusion of the material. Secondly, the bond energy of the metal-oxygen (L-O) bond is higher than that of the nickel-cobalt-manganese-oxygen bond, making the lattice structure more stable while also passivating the reactive oxygen near the surface and inhibiting the oxygen loss of the Ni redox center.

[0025] In a third aspect, a perovskite phase layer is coated on the outer edge of the cathode material to further improve the structural stability of the cathode material, inhibit metal dissolution, and reduce side reactions with the electrolyte. When the high-nickel layered oxide cathode material is in a highly delithiated state at high voltage, the energy barrier for the surface reactive oxygen to diffuse to adjacent positions is higher than that to diffuse into the oxygen vacancies in the perovskite phase. As a result, the surface reactive oxygen will be captured by the oxygen vacancies in the perovskite phase, achieving stable lattice oxygen oxidation while capturing the free reactive oxygen diffusing from the bulk to the surface. At the same time, the perovskite phase structure acts as a "rivet" at the interface, significantly reducing the harmful structural evolution through the fixing effect, inhibiting the accumulation of lattice strain, and greatly enhancing the stability and safety of the high-nickel cathode material.

[0026] In addition, the modification treatments in the above three aspects all participate in the formation of the CEI film during charge and discharge. While eliminating the NiO-like phase, they provide fast ion channels, protect the cathode from electrolyte erosion, reduce the interfacial resistance and improve stability. The three do not conflict with each other and synergistically inhibit the release of oxygen, forming a cage-like oxygen fixation effect, effectively improving the electrochemical performance of the cathode material.

[0027] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present disclosure, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 Schematic diagram of the structure of the high-nickel cathode material with a cage-like oxygen fixation structure according to an embodiment of the present invention;

[0030] Figure 2XRD patterns of the cage-like oxygen-solidified high-nickel cathode material prepared in Example 1 of the present invention and Comparative Example 1. The XRD pattern of Example 1 shows the A2BO4 perovskite phase and the LiTMO2F 2-α phase;

[0031] Figure 3 XRD pattern of the perovskite phase of the high-nickel cathode material prepared in Comparative Example 3 of the present invention;

[0032] Figure 4a Scanning electron microscope energy spectrum (SEM-EDS) of the high-nickel cathode material prepared in Example 1 of the present invention;

[0033] Figure 4b Showing the La element in Figure 4a Scanning electron microscope energy spectrum (SEM-EDS) of the distribution;

[0034] Figure 4c Showing the Ti element in Figure 4a Scanning electron microscope energy spectrum (SEM-EDS) of the distribution;

[0035] Figure 4d Showing the Nb element in Figure 4a Scanning electron microscope energy spectrum (SEM-EDS) of the distribution;

[0036] Figure 4e Showing the F element in Figure 4a Scanning electron microscope energy spectrum (SEM-EDS) of the distribution;

[0037] Figure 5 Cross-section - scanning electron microscope energy spectrum (CP-SEM-EDS) line scan distribution map of F, Ti and Nb elements of the high-nickel cathode material prepared in Example 1 of the present invention;

[0038] Figure 6 Cycling performance graphs of the high-nickel cathode materials prepared in Examples 1 to 4 and Comparative Example 1 of the present invention;

[0039] Figure 7 Comparison graph of the high-nickel cathode materials prepared in Example 1 and Comparative Example 1 of the present invention through in-situ XRD testing. Detailed implementation manners

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0041] The high-nickel cathode material, lithium-ion battery, and preparation method of the cage-shaped oxygen-solidifying structure according to the embodiments of the present invention will be specifically described below.

[0042] The embodiments of the present invention provide a high-nickel cathode material with a cage-shaped oxygen-solidifying structure. The core of the high-nickel cathode material forms a LiTMO phase and a LiTMO2F 2-α phase, where TM represents a transition metal element, 0 ≤ α < 0.1. The near-surface layer is gradient-doped with a lithium-philic metal element L, and the metal element L forms an L-O bond with O. The outer layer forms a perovskite-phase coating layer.

[0043] Further, in the preferred embodiments of the present invention, the transition metal element TM is selected from one or more of Ni, Co, and Mn. Preferably, the transition metal TM includes Ni, Co, and Mn.

[0044] Further, in the preferred embodiments of the present invention, the cathode material is doped with F. The source of F can be selected from one or more of LiF, NH4HF2, NH4F, NaF, and KF. The ionic radius of F is 0.007 nm lower than that of O ions. Therefore, F ions can penetrate into the core of the material and replace the oxygen sites, reducing the surface energy of the material and improving the hydrophobicity of the material. Moreover, F has a higher affinity energy than O, can form a more stable TM-F bond, and can also increase the covalency of the Ni / Co / Mn-O bond. In addition, F-doping can reduce the energy band overlap between the transition metal and O 2- to improve the high-voltage cycling performance of the material. Fluorine replacing oxygen can reduce the P-band energy level of the material, widen the lithium layer spacing, and improve lithium transport. In addition, an appropriate doping amount can improve the interfacial stability between the active material and the electrolyte, inhibit the polarization of the material, and prevent HF erosion.

[0045] Further, in the preferred embodiments of the present invention, the lithium-philic metal element L is selected from one or more of Ti, Zr, Y, V, Nb, Ta, Cr, W, Co, and Fe. The distribution of the lithium-philic metal element in the near-surface layer of the high-nickel cathode material shows a gradient distribution that decreases from the outside to the inside. More preferably, the lithium-philic metal element L is selected from one or more of Ti, Zr, and Nb. The metal element L replaces the transition metal TM to form an L-O bond with O and / or reacts with Li + on the surface of the material to generate a lithium oxide containing a Li-L-O bond. Compared with other lithium-philic metal elements, Ti, Zr, and Nb can better form a gradient distribution on the surface of the cathode material, avoid segregation, and further improve the safety performance of the cathode material.

[0046] The lithiophilicity of lithiophilic elements (L) is utilized to form a Li-L-O structure, regulate the nucleation overpotential of lithium to stabilize lithium deposition, reduce lithium dendrites, and the deposited lithium diffuses into the lattice interior through channels with low diffusion barriers, reducing the residual lithium on the material surface and interface while broadening the Li+ diffusion channels to improve the lithium diffusion of the material. Secondly, the bond energy of the metal-oxygen (L-O) bond is higher than that of the nickel cobalt manganese-oxygen bond, making the lattice structure more stable while also passivating the reactive oxygen near the surface and inhibiting the oxygen loss of the Ni redox center.

[0047] Further, in a preferred embodiment of the present invention, the perovskite phase coating layer comprises a lanthanide perovskite layer composed of alternating perovskite phases and layered phases. Specifically, the lanthanide elements of the lanthanide perovskite layer are selected from one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, and gadolinium. More preferably, the lanthanide element of the lanthanide perovskite layer is lanthanum, and the lanthanide perovskite layer is a lanthanum-containing perovskite phase oxide of the A2BO4 type rich in oxygen vacancies.

[0048] The ionic radius of lanthanum is 0.102 nm, which is much larger than that of Li + (0.076 nm), Ni 2+ (0.069 nm), Co 3+ (0.055 nm), Mn 4+ (0.053 nm) and other elements. During high-temperature calcination, lanthanum forms a perovskite phase with elements such as Li, Ni, and O on the surface, forming a lanthanum-containing perovskite phase oxide of the A2BO4 type, stabilizing the valence state and structural changes of transition metals in the redox reaction and epitaxially growing to form a coating layer, achieving the stability of the material structure, inhibiting the metal dissolution while reducing the side reactions with the electrolyte. When the high-nickel layered oxide cathode material is in a highly delithiated state under high voltage, the energy barrier for the diffusion of surface reactive oxygen to adjacent positions is higher than that for diffusion into the oxygen vacancies in the perovskite phase, so that the surface reactive oxygen will be captured by the oxygen vacancies in the perovskite phase, achieving stable lattice oxygen oxidation while capturing the free reactive oxygen diffusing from the bulk to the surface. This structure acts as a "rivet" at the interface, significantly reducing the harmful structural evolution through the fixing effect, inhibiting the accumulation of lattice strain, and greatly improving the stability and safety of the high-nickel cathode material.

[0049] Further, in a preferred embodiment of the present invention, the perovskite phase coating layer is island-shapedly coated on the surface of the high-nickel cathode material. Through high-temperature calcination, the perovskite phase coating layer is distributed in an island-shaped coating, which is more conducive to forming a "rivet" effect, effectively reducing the harmful structural evolution, inhibiting the accumulation of lattice strain, and improving the stability and safety of the material.

[0050] The embodiment of the present invention also provides a preparation method of a high-nickel cathode material with the cage-shaped oxygen-fixing structure as described above, including:

[0051] S1. Mix a high-nickel ternary precursor TM(OH)₂, a lithium source, a fluorine-containing compound, and a compound containing a metal element L to obtain a first mixture.

[0052] S2. Place the first mixture in an oxygen environment and sinter it at 500 - 650 °C for 2 - 8 h. After cooling and sieving, obtain a first sintered product.

[0053] S3. Mix the first sintered product and a compound containing a lanthanide element to obtain a second mixture.

[0054] S4. Place the second mixture in an oxygen atmosphere and calcine it at 650 - 800 °C for 6 - 11 h. After cooling, obtain the high-nickel cathode material with a cage-like oxygen-solidifying structure.

[0055] Further, in a preferred embodiment of the present invention, in step S1, the high-nickel ternary precursor TM(OH)₂ can be, for example, Ni 0.95 Co 0.04 Mn 0.01 (OH)₂. The high-nickel ternary precursor can be synthesized by methods such as the solid-phase method and the hydrothermal method, and the present disclosure does not specifically limit it.

[0056] Further, in a preferred embodiment of the present invention, in step S1, the lithium source is selected from one or more of lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxalate, lithium acetate, lithium sulfate, and lithium-containing oxides.

[0057] Further, in a preferred embodiment of the present invention, in step S1, the fluorine-containing compound is selected from one or more of LiF, NH₄HF₂, NH₄F, NaF, and KF. More preferably, the molar ratio of the lithium source to the fluorine-containing compound is 1:(0 - 0.1). Even more preferably, the molar ratio of the lithium source to the fluorine-containing compound is 1:(0 - 0.01). By regulating the molar ratio of the lithium source to the fluorine-containing compound, the bulk core doping structure of the cathode material is regulated to ensure the uniform distribution of the F element in the bulk phase.

[0058] Further, in a preferred embodiment of the present invention, in step S1, the compound containing a metal element L and the compound containing a lanthanide element are selected from one or more of oxides, halides, carbonates, oxalates, phosphates, and acetates.

[0059] Further, in a preferred embodiment of the present invention, in step S1, the addition amount of the metal element L in the first mixture is 1 - 10000 mg / kg. Even more preferably, the compound containing a metal element L is an oxide. For example, the Zr source is nano-ZrO₂, the Ti source is nano-TiO₂, the Nb source is nano-Nb₂O₅, and the La source is La₂O₃.

[0060] Further, in a preferred embodiment of the present invention, in step S3, the addition amount of the lanthanide element in the first mixture is 1 to 5000 mg / kg. More preferably, the addition amount of the lanthanide element is 2000 mg / kg. The increase in the doping amount of the lanthanide element can form more perovskite phases on the surface of the cathode material and improve the material stability. However, the excessive doping of the lanthanide element will lead to an increase in the interfacial resistance, which is not conducive to the electrochemical performance of the cathode material.

[0061] Further, in a preferred embodiment of the present invention, the particle sizes of the lithium source, the fluorine-containing compound, and the compound containing the metal element L are selected from the micron level, and D50 is 0 to 10 μm; the particle size of the lanthanide-containing compound is selected from the nano level, and D50 is 50 to 100 nm. By controlling the particle sizes of the added components, the effects of the bulk phase and surface modification are ensured.

[0062] Further, in a preferred embodiment of the present invention, in step S1, the precursor powder, the lithium source, the fluorine-containing compound, and the compound containing the metal element L are uniformly mixed by a high-speed mixer at 500 to 1000 rpm for 10 to 20 min. Similarly, in step S3, the first mixed sintered product and the lanthanide-containing compound adopt the same mixing parameters as in step S1. Mixing is performed by a high-speed mixer to ensure uniform mixing of the materials and ensure the sintering effect.

[0063] Further, in a preferred embodiment of the present invention, in steps S2 and S4, the first mixture and the second mixture are calcined at a heating rate of 1 to 5 °C / min in an oxygen concentration > 99.5%, and finally the sintered product is obtained through cooling and sieving.

[0064] The embodiment of the present invention also provides a lithium-ion battery, including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the high-nickel cathode material with a cage-like oxygen-solid structure described above. It can be understood that the lithium-ion battery can be prepared by known methods in the prior art.

[0065] The features and performance of the present invention are further described in detail below in conjunction with embodiments. Example 1

[0066] This example provides a high-nickel cathode material with a cage-like oxygen-solid structure, which is obtained according to the following steps:

[0067] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01(OH)₂ with a particle size of 17.5 μm large particle high-nickel ternary precursor, 5.9 g of Nb₂O₅, 12.1 g of TiO₂, 3.2 g of LiF and 966.8 g of LiOH were thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0068] Step (2): During the process of continuously supplying oxygen with an oxygen content of more than 99.95% in the sintering furnace, mixture 1 was heated to 580 °C at a rate of 2 °C / min, maintained at a high temperature of 580 °C for pre-sintering for 2 h, then heated to 640 °C at a heating rate of 1.5 °C / min, maintained at a high temperature of 640 °C for calcination for 4 h, and then cooled to room temperature at a rate of 15 °C / min, and the product 1 was obtained by sieving.

[0069] Step (3): Weigh 2000.0 g of product 1, add 4.9 g of nano-La₂O₃, and thoroughly mix by a high-speed mixer at a rotation speed of 500 rpm for 10 minutes to obtain mixture 2.

[0070] Step (4): Heat mixture 2 to 700 °C at a rate of 2 °C / min. During the process of continuously supplying oxygen with an oxygen content of more than 99.95% in the sintering furnace, maintain a high temperature of 700 °C for sintering for 9 h, and then cool to room temperature at a rate of 15 °C / min to obtain a high-nickel cathode material with a cage-like oxygen-solidifying structure. Example 2

[0071] This example provides a high-nickel cathode material with a cage-like oxygen-solidifying structure, and the difference from Example 1 lies in the different addition amount of LiF, specifically:

[0072] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01 (OH)₂ with a particle size of 17.5 μm large particle high-nickel ternary precursor, 5.9 g of Nb₂O₅, 12.1 g of TiO₂, 9.6 g of LiF and 966.8 g of LiOH were thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0073] The remaining steps are the same as those in Example 1. Example 3

[0074] This example provides a high-nickel cathode material with a cage-like oxygen-solidifying structure, and the difference from Example 1 lies in the different addition amount of nano-La₂O₃, specifically:

[0075] Step (3): Weigh 2000.0 g of product 1, add 9.8 g of nano-La₂O₃, and thoroughly mix by a high-speed mixer at a rotation speed of 500 rpm for 10 minutes to obtain mixture 2.

[0076] The remaining steps are the same as those in Example 1. Example 4

[0077] This example provides a high-nickel cathode material with a cage-shaped oxygen-solidifying structure, which is different from Example 1 in that 5.9 g of Nb2O5 is replaced by 17.5 g of ZrO2. Specifically:

[0078] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01 (OH)2 with a particle size of 17.5 um large-particle high-nickel ternary precursor, 17.5 g of ZrO2, 12.1 g of TiO2, 3.2 g of LiF, and 966.8 g of LiOH are thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0079] The remaining steps are the same as those in Example 1.

[0080] Comparative Example 1

[0081] This comparative example provides a high-nickel cathode material, which is obtained according to the following steps:

[0082] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01 (OH)2 with a particle size of 17.5 um large-particle high-nickel ternary precursor and 971.7 g of LiOH are thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0083] Step (2): During the process of continuously supplying oxygen with an oxygen content of more than 99.95% in the sintering furnace, mixture 1 is heated to 580 °C at a rate of 2 °C / min, maintained at a high temperature of 580 °C for pre-sintering for 2 h, then heated to 640 °C at a heating rate of 1.5 °C / min, maintained at a high temperature of 640 °C for calcination for 4 h, then heated to 700 °C at a rate of 2 °C / min, maintained at a high temperature of 700 °C for calcination for 9 h, and then cooled to room temperature at a rate of 15 °C / min, and sieved to obtain the high-nickel cathode material.

[0084] Comparative Example 2

[0085] This comparative example provides a high-nickel cathode material, which is different from Example 1 in that La2O3 is not added. Specifically:

[0086] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01(OH)2 with a particle size of 17.5 μm, large particle high-nickel ternary precursor, 5.9 g of Nb2O5, 12.1 g of TiO2, 3.2 g of LiF, and 966.8 g of LiOH were thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0087] The remaining steps were the same as those in Comparative Example 1.

[0088] Comparative Example 3

[0089] This comparative example provides a high-nickel cathode material, which is different from that in Example 1 in that LiF is not added. Specifically:

[0090] Step (1): Weigh 2000.0 g of Ni 0.95 Co 0.04 Mn 0.01 (OH)2 with a particle size of 17.5 μm, large particle high-nickel ternary precursor, 5.9 g of Nb2O5, 12.1 g of TiO2, and 966.8 g of LiOH were thoroughly mixed by a high-speed mixer at a rotation speed of 600 rpm for 15 minutes to obtain mixture 1.

[0091] The remaining steps were the same as those in Example 1.

[0092] Test Example 1 Basic Performance Analysis

[0093] The high-nickel cathode materials prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were analyzed for specific surface area (BET) and X-ray diffraction (XRD), and Example 1 was subjected to line scan test analysis of scanning electron microscope energy spectrum (SEM-EDS) and cross-section-scanning electron microscope energy spectrum (CP-SEM-EDS), as shown in Table 1:

[0094] Table 1

[0095]

[0096] It can be seen from Table 1 that by analyzing the data of Example 1, Example 2, Comparative Example 1, and Comparative Example 3, it is found that the formation of the TM-F bond leads to an increase in Li / Ni mixing. This is mainly because the substitution of F for the O site increases. For charge balance, Ni 3+ shifts to Ni 2+ , resulting in an increase in mixing; by analyzing the data of Example 1, Example 3, and Comparative Example 2, it can be found that the epitaxial coating of perovskite has no obvious effect on the c-axis lattice parameter and Li / Ni mixing in the relative crystal structure. On the contrary, due to the island-like distribution of the perovskite phase, as the distribution of the perovskite phase increases, its specific surface area increases; by analyzing Example 1 and Example 4, due to the difference in grain size of elements: Zr 4+ (0.072 nm) > Ni 2+ (0.069 nm) > Nb5+ (0.068 nm) > Ti 4+ (0.061 nm). The Zr element is slightly precipitated on the grain surface. While the near-surface gradient coating effect is poor, the Zr substitution of the Ni site is relatively low, and its c-axis lattice parameter is relatively small. As can be seen from Table 1, Example 1 with the optimal ratio of co-doping coating has lower BET and Li / Ni mixing, indicating that the construction of a stable high-nickel cathode material with a cage-like oxygen fixation structure can effectively optimize structural defects and improve the stability of the material.

[0097] After XRD pattern analysis, as Figure 2 shown, when a certain amount of F-containing compound is doped into the high-nickel cathode material, the characteristic peak of LiTMO2F appears in the XRD pattern, and the layered structure of the high-nickel material is not affected. The LiTMO phase and LiTMO2F 2-α phase coexist in the high-nickel cathode material; in addition, when a certain amount of lanthanum-containing compound is simultaneously doped into the high-nickel cathode material, the XRD patterns thereof all show the perovskite characteristic peaks (101), (004), (103), which are the characteristic peaks of the A2BO4-type perovskite phase, as 2-α shown; while in Comparative Examples 1 and 2, due to the absence of La source, the characteristic peaks of the perovskite phase do not appear, and in Comparative Example 3, due to the absence of F source, only the characteristic peaks of the perovskite phase appear, as Figure 2 shown; indicating that the high-nickel cathode material has successfully realized the construction of a cage-like oxygen fixation structure that synergistically stabilizes the bulk structure and captures surface free oxygen of the LiTMO phase, LiTMO2F Figure 3 phase and perovskite phase inside and outside. 2-α phase and perovskite phase inside and outside.

[0098] As Figure 4a , Figure 4b , Figure 4c , Figure 4d , Figure 4e , through the analysis of the scanning electron microscope energy spectrum (SEM-EDS) results of Example 1, it can be known that: the La element is unevenly segregated and enriched on the grain surface, while elements such as Ti, Nb, and F penetrate into the bulk phase, and there are no obvious segregation highlights of elements such as Ti, Nb, and F in the EDS spectrum.

[0099] The cross-section-scanning electron microscope energy spectrum (CP-SEM-EDS) line scan test analysis was carried out on the high-nickel cathode material obtained in Example 1, and the analysis results are as Figure 5 shown; it can be found that the F element aggregates in the core to stabilize the main structure of the material, and the Ti and Nb elements show a gradient decrease from the outside to the inside near the surface of the material. Forming L-O bonds near the surface can make the lattice structure more stable while also passivating the reactive oxygen near the surface.

[0100] Test Example 2 Analysis of Electrical Performance and Safety Performance

[0101] The high-nickel cathode materials prepared in Examples 1-4 and Comparative Examples 1-3 were mixed with conductive agent acetylene black and binder PVDF to prepare a slurry in a mass ratio of 96.5:1.5:2, and then coated and rolled to form a cathode sheet. Coin cells were assembled in an argon atmosphere glove box, and charge-discharge capacity and 50-cycle coin cell tests were carried out in a constant current charge-discharge mode within a voltage range of 3.0-4.3V. Coin cells were also assembled using the same process, charged to a high voltage of 4.5V, left standing, disassembled to remove the electrode sheet, and the electrolyte was eluted for TG-DSC testing. The test results are shown in Table 2 and Figure 6 as follows.

[0102] Table 2

[0103]

[0104] As shown in Table 2 and Figure 6 as follows, Examples 1-4 have higher capacity retention rates after 50 cycles, lower heat release, and higher DSC peak temperatures, showing better cycle performance and safety performance, and reducing the risk of thermal runaway; although Comparative Example 2 also shows good cycle performance, due to the lack of doping with La element, its safety performance is poor; the electrical properties of Comparative Example 3 are less different from those of Example 2, but compared with Example 2, the F content in Comparative Example 3 is excessive. Without F, the lack of the influence of TM-F on the structural stability in Comparative Example 3 results in lower safety.

[0105] Test Example 3 In-situ XRD Analysis

[0106] The samples prepared in Example 1 and Comparative Example 1 were tested by in-situ XRD. The test results are as Figure 7 shown. When charged to 4.25V, the lattice parameters c of Example 1 and Comparative Example 1 changed by 0.71 Å (4.84%) and 0.86 Å (5.69%) respectively. The shrinkage Δc value (5.69%) of the c-axis of Comparative Example 1 is larger. This result indicates that during the cycling process, more electrons are lost from the eg orbit of Ni 2+ - Ni 4+ reaction, resulting in the oxidation of lattice O 2- ions. The formation of holes in the O2p band releases the anion-anion electrostatic repulsion between adjacent oxygen layers, accompanied by stronger local strain, leading to the c lattice contraction in deep attenuation, thus causing capacity attenuation and structural failure.

[0107] It can be seen that the high-nickel cathode material with a cage-like oxygen fixation structure provided in this example can regulate anion redox, inhibit the activation of surface lattice oxygen ions, reduce oxygen evolution, promote Ni migration at the same time, relieve irreversible phase transformation and cracks, and achieve excellent electrochemical performance and safety performance.

[0108] In summary, the high-nickel cathode material with a cage-shaped oxygen-solidifying structure prepared by the present invention has excellent capacity cycling performance and safety performance. By selecting a variety of elements for doping, the positive superposition of the oxygen-solidifying ability of the material is realized, while improving the lithium-ion conduction and electrical properties of the material, the oxygen release ability of the material is optimized, providing a new idea for the safety modification of high-nickel ternary materials. In addition, the preparation process of the high-nickel cathode material is simple, and the cathode material is obtained by secondary calcination, which is suitable for large-scale industrial production.

[0109] The above description is not all embodiments. The detailed description of the embodiments of the present disclosure is not intended to limit the scope of the present disclosure claimed, but merely represents selected embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts fall within the scope of protection of the present disclosure.

Claims

1. A high-nickel cathode material with a cage-shaped oxygen-solidifying structure, characterized in that, The core of the high-nickel cathode material forms a LiTMO phase and a LiTMO2F 2-α phase, where TM represents a transition metal element, 0 ≤ α < 0.1, the near-surface layer is gradient-doped with a lithiumophilic metal element L, and the metal element L forms an L-O bond with O, and a perovskite phase coating layer is formed on the outer layer; The perovskite-phase coating layer is island-shapedly coated on the surface of the high-nickel cathode material. The perovskite-phase coating layer includes a lanthanide perovskite layer composed of alternating perovskite phases and layered phases. The lanthanide element of the lanthanide perovskite layer is selected from one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, and gadolinium; The preparation method of the high-nickel cathode material with a cage-shaped oxygen fixation structure includes: S1. Mix a high-nickel ternary precursor TM(OH)₂, a lithium source, a fluorine-containing compound, and a compound containing a metal element L to obtain a first mixture; S2. Place the first mixture in an oxygen environment and sinter it at 500-650 °C for 2-8 h. After cooling and sieving, a first sintered product is obtained; S3. Mix the first sintered product and a compound containing a lanthanide element to obtain a second mixture; S4. Place the second mixture in an oxygen atmosphere and calcine it at 650-800 °C for 6-11 h. After cooling, the high-nickel cathode material with a cage-shaped oxygen fixation structure is obtained.

2. The high-nickel cathode material with a cage-shaped oxygen-solidifying structure according to claim 1, characterized in that, The transition metal element TM is selected from one or more of Ni, Co, and Mn; the lithium-philic metal element L is selected from one or more of Ti, Zr, Y, V, Nb, Ta, Cr, W, Co, and Fe; the distribution of the lithium-philic metal element in the near-surface layer of the high-nickel cathode material shows a gradient distribution decreasing from the outside to the inside.

3. The high-nickel cathode material with a cage-shaped oxygen-solidifying structure according to claim 2, characterized in that, The lithiophilic metal element L is selected from one or more of Ti, Zr, and Nb. The metal element L replaces the transition metal TM to form an L-O bond with O and / or reacts with Li on the surface of the material + to generate a lithium oxide containing an Li-L-O bond.

4. The high-nickel cathode material with a cage-shaped oxygen fixation structure according to claim 1, wherein The lanthanide element is selected from lanthanum, and the lanthanide perovskite layer is an A₂BO₄-type lanthanum-containing perovskite-phase oxide with oxygen vacancies.

5. The high-nickel cathode material with a cage-shaped oxygen fixation structure according to claim 1, characterized in that, In step S1, the lithium source is selected from one or more of lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxalate, lithium acetate, lithium sulfate, and lithium-containing oxides; the fluorine-containing compound is selected from one or more of LiF, NH₄HF₂, NH₄F, NaF, and KF; the molar ratio of the lithium source to the fluorine-containing compound is 1:(0-0.1).

6. The high-nickel cathode material with a cage-shaped oxygen fixation structure according to claim 1, characterized in that, In step S1, the compound containing the metal element L and the compound containing the lanthanide element are selected from one or more of oxides, halides, carbonates, oxalates, phosphates, and acetates; the addition amount of the metal element L in the first mixture is 1-10000 mg / kg. In step S3, the addition amount of the lanthanide element in the first mixture is 1-5000 mg / kg.

7. The high-nickel cathode material with a cage-shaped oxygen fixation structure according to claim 1, characterized in that, The particle sizes of the lithium source, the fluorine-containing compound, and the compound containing the metal element L are in the micron level, and D50 is 0-10 μm; the particle size of the compound containing the lanthanide element is in the nanometer level, and D50 is 50-100 nm.

8. The high-nickel cathode material with a cage-shaped oxygen fixation structure according to claim 1, characterized in that, In steps S1 and S3, the mixing step is to mix the materials by a high-speed mixer at 500-1000 rpm for 10-20 min; in steps S2 and S4, the first mixture and the second mixture are calcined in an oxygen concentration >99.5% at a heating rate of 1-5 °C / min, and finally a sintered product is obtained through cooling and sieving.

9. A lithium-ion battery, characterized in that, It includes the high-nickel cathode material with a cage-shaped oxygen fixation structure according to any one of claims 1-8.

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