Ternary positive electrode material, preparation method and application thereof

Abstract

The application provides a ternary positive electrode material, a preparation method and application thereof; the ternary positive electrode material comprises a base and a coating on the surface of the base; the base is a ternary material co-doped with titanium elements and nitrogen elements; and the coating is titanium nitride. In the application, titanium nitride is used as a coating agent and a dopant, so that the Ti elements and the N elements are co-doped into the crystal lattice of the ternary material, and titanium nitride is coated on the surface of the ternary material; the doping and the coating have a synergistic effect, so that the prepared ternary positive electrode material has better cycle rate performance and high-temperature storage performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical new materials technology, specifically relating to a ternary cathode material, its preparation method and its application. Background Technology

[0002] In the field of power batteries, with the continuous improvement of the energy density of lithium-ion batteries in recent years, nickel-rich layered oxides have significantly improved the energy density of power batteries, and the driving range of electric vehicles has also been significantly improved. Although nickel-rich layered oxide materials have the advantages of high specific capacity and low cost, they also have defects such as poor cycle performance and poor thermal stability. These inherent shortcomings have limited the industrialization process of NCM system batteries.

[0003] Patent CN113097459A discloses a ternary cathode material@titanium nitride core-shell composite material and its preparation method. The method includes placing ternary cathode material powder in a gas-phase reactor, fluidizing it under an inert atmosphere, and heating it to the coating reaction temperature; introducing titanium source vapor (TiCl4) and water vapor carried by the inert atmosphere into the gas-phase reactor for a deposition reaction; stopping the introduction of the titanium source vapor (TiCl4) and water vapor after the coating reaction time, and cooling to obtain a ternary cathode material@titanium dioxide (TiO2) core-shell intermediate; then introducing nitrogen source gas into the ternary material@TiO2 core-shell intermediate in the gas-phase reactor for conversion at high temperature, transforming the outer TiO2 layer into a titanium nitride (TiN) layer, and cooling to obtain a ternary cathode material@TiN core-shell composite. However, the above preparation method is complex, costly, and difficult to industrialize.

[0004] Patent CN114023936A discloses a nitride / graphitized carbon nanosheet-coated ternary cathode material, comprising: a ternary cathode material substrate and a coating layer, the coating layer being composed of nitride and graphitized carbon, wherein the graphitized carbon is formed in situ during the nitride coating process, and the nitride is one or more of aluminum nitride, silicon nitride, titanium nitride, zirconium nitride, tantalum nitride, and niobium nitride; the preparation method involves wet coating to coat the coating elements onto the surface of the ternary cathode material substrate to obtain an intermediate product; wherein the wet coating process coats the coating elements onto the surface of the ternary cathode material substrate. An intermediate product is obtained; the coating element is one or more of Al, Si, Ti, Zr, Ta, and Nb; then the intermediate product is mixed uniformly with a carbon-nitrogen compound, and after sintering, pulverizing, sieving, and iron removal, a nitride / graphitized carbon nanosheet-coated ternary cathode material is obtained; however, in the above preparation method, multiple organic substances are used in the wet coating process, which are easy to leave residues. The precipitation process has a long reaction time and requires control of multiple parameters, which can easily cause uneven distribution on the material surface. Moreover, the sintering reaction temperature is high, and the primary particles continue to grow, affecting the electrical properties of the material.

[0005] Patent CN113130906 A discloses a modified cathode material, comprising a core material and a shell material covering the core material. The core material includes a cathode active substance, and the shell material includes a solid electrolyte and titanium nitride. The solid electrolyte is selected from solid electrolytes with a NASION structure. However, in the preparation method of the above modified cathode material, due to the sintering reaction under an oxygen atmosphere, some of the titanium nitride reacts with oxygen, and ultimately forms a coating layer in which the solid electrolyte and titanium nitride are intercalated. Summary of the Invention

[0006] To address the shortcomings and defects of existing technologies, this invention aims to provide a ternary cathode material, its preparation method, and its applications. This invention uses titanium nitride (TiN) as both a coating agent and a dopant, co-doping Ti and N elements into the crystal lattice of ternary materials (such as lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide), respectively replacing Ni / Co / Mn or Ni / Co / Al elements and O elements to obtain the matrix, while simultaneously coating the surface of the matrix with titanium nitride; wherein, titanium doping can balance Ni… 2+ The resulting inversion defects suppress Ni 2+ The migration to the lithium layer reduces the degree of lithium-nickel mixing. The Ti-O bond energy is 662 kJ / mol, while the Ni-O bond energy is 382 kJ / mol. The Ti-O bond energy is significantly greater than the Ni-O bond energy. Titanium doping not only improves the structural stability of the material but also reduces the lithium insertion voltage, promoting more lithium insertion / extraction under a fixed overpotential, thus improving discharge capacity and capacity retention. Nitrogen doping can widen the interlayer spacing, thereby improving the rate performance of the material. Furthermore, titanium nitride, due to its high melting point and hardness, can act as a coating agent to provide thermal insulation and temperature control, reducing electrolyte corrosion at high temperatures and reducing the dissolution of transition metals, thereby improving the high-temperature storage performance of the battery. Simultaneously, titanium nitride has good conductivity, and coating the material surface increases its conductivity. In this invention, titanium nitride can both be doped into the material's crystal lattice and coated on its surface. The doping and coating have a synergistic effect, resulting in a ternary cathode material with better cycle rate performance and high-temperature storage performance.

[0007] To achieve the above objectives, the first aspect of the present invention provides a ternary cathode material, which adopts the following technical solution:

[0008] A ternary cathode material includes: a substrate and a coating material covering the surface of the substrate; wherein the substrate is a ternary material co-doped with titanium and nitrogen, and the coating material is titanium nitride.

[0009] In the above-mentioned ternary cathode material, as a preferred embodiment, the chemical formula of the matrix is ​​Li. n Ni xCo y M z Ti (1-x-y-z) N m O (2-1.5m) The element M is selected from one or both of Mn and Al, where 0.95 ≤ n ≤ 1.05 (e.g., n = 0.96, 0.97, 0.98, 1, 1.01, 1.03, 1.04), 0.5 ≤ x < 1 (e.g., x = 0.55, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95), and 0 < y ≤ 0.3 (e.g., y = 0.05, 0.1, 0.15, 0. 0.18, 0.2, 0.25, 0.28), 0 < z ≤ 0.4 (e.g., z = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35), x + y + z < 1, 0.0015 ≤ m ≤ 0.0125 (e.g., m = 0.0020, 0.0050, 0.0060, 0.0080, 0.0100, 0.0110, 0.0120);

[0010] In this invention, titanium doping can replace Ni / Co / Mn or Ni / Co / Al elements in ternary materials, and titanium doping can balance Ni. 2+ The resulting inversion defects suppress Ni 2+ Migrating to the lithium layer reduces the degree of lithium-nickel mixing; the Ti-O bond energy is 662 kJ / mol, while the Ni-O bond energy is 382 kJ / mol. The Ti-O bond energy is much greater than the Ni-O bond energy. Titanium doping not only improves the structural stability of the material but also reduces the lithium insertion voltage, promoting more lithium insertion / extraction under a fixed overpotential, thus improving the discharge capacity and capacity retention. If too much Ti is doped, it will affect the specific capacity of the ternary material; if too little Ti is doped, the performance improvement of the ternary material will be insignificant. In this invention, nitrogen doping can replace the O element in the ternary material. Nitrogen doping can expand the interlayer spacing, thereby improving the rate performance of the material. If too much N is doped, it will affect the specific capacity of the ternary material; if too little N is doped, the performance improvement of the ternary material will be insignificant.

[0011] In the above-mentioned ternary cathode material, as a preferred embodiment, the microstructure of the ternary cathode material is a secondary microsphere composed of primary nanoparticles or a single-crystal large particle; preferably, the diameter of the secondary microsphere is 4-15μm (e.g., 5μm, 6μm, 7μm, 9μm, 10μm, 12μm, 14μm); preferably, the diameter of the single-crystal large particle is 2-6μm (e.g., 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm).

[0012] A second aspect of the present invention provides a method for preparing a ternary cathode material, comprising:

[0013] Co-doping coating method: First, the lithium source and ternary precursor material are mixed, sintered, and pulverized to obtain a primary sintered material; then, the primary sintered material is mixed with titanium nitride and sintered a second time to obtain a ternary cathode material.

[0014] Alternatively, a doping-coating method can be used: First, the lithium source, ternary precursor material, and doped titanium nitride are mixed, sintered, and pulverized to obtain a ternary material. Then, the ternary material and coated titanium nitride are mixed and sintered a second time to obtain a ternary cathode material.

[0015] This invention prepares ternary cathode materials using either a co-doping coating method or a pre-doping followed by coating method. The co-doping coating method involves first mixing and sintering a lithium source and ternary precursor material to obtain a primary sintered material, then mixing titanium nitride (as both a coating agent and a dopant) with the primary sintered material a second time, followed by a second sintering process to obtain the ternary cathode material. The pre-doping followed by coating method involves first mixing titanium nitride as a dopant with a lithium source and ternary precursor material, followed by a doping and sintering process to obtain a ternary material, then mixing titanium nitride as a coating agent with the ternary material a second time, followed by a coating and sintering process to obtain the ternary cathode material. Both methods can produce ternary cathode materials with a microstructure consisting of secondary microspheres or single-crystal large particles composed of primary nanoparticles.

[0016] In the above preparation method, as a preferred embodiment, in the co-doping coating method or the pre-doping followed by coating method, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide; preferably, the ternary precursor material is nickel cobalt manganese hydroxide and / or nickel cobalt aluminum hydroxide, with the chemical formula: Ni a Co b M c (OH)₂, wherein element M is selected from one or both of Mn and Al, 0.5≤a<1 (e.g., a=0.55, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95), 0<b≤0.3 (e.g., b=0.05, 0.1, 0.15, 0.18, 0.2, 0.25, 0.28), 0<c≤0.4 (e.g., c=0.05, 0. 1, 0.15, 0.2, 0.25, 0.3, 0.35), a+b+c=1; preferably, the molar ratio of lithium element in the lithium source to the total amount of nickel, cobalt and M element in the ternary precursor material is 1.0-1.1:1 (e.g. 1.01:1, 1.02:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1).

[0017] In the above preparation method, as a preferred embodiment, in the co-doping coating method, the primary mixing process is carried out in a high-speed mixer, with a mixing speed of 100-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm) and a time of 5-60 min (e.g., 10 min, 20 min, 30 min, 40 min, 50 min); preferably, the primary sintering process is carried out in a kiln under an oxygen or air atmosphere, with a primary sintering temperature of 700-1200℃ (e.g., 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃) and a time of 8-15 h (e.g., 9 h, 10 h, 11 h, 12 h, 13 h, 14 h).

[0018] In the above preparation method, as a preferred embodiment, in the co-doping coating method, the molar ratio of the total amount of nickel, cobalt and M elements in the titanium nitride to the total amount of nickel, cobalt and M elements in the ternary precursor material is 0.003-0.028:1 (e.g. 0.004:1, 0.005:1, 0.008:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1).

[0019] In the above preparation method, as a preferred embodiment, in the co-doping coating method, the secondary mixing treatment is carried out in a high-speed mixer, the rotation speed of the secondary mixing treatment is 100-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm), and the time is 5-60 min (e.g., 10 min, 20 min, 30 min, 40 min, 50 min); preferably, the secondary sintering treatment is carried out in a kiln under an oxygen or air atmosphere, the temperature of the secondary sintering treatment is 500-700℃ (e.g., 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃), and the time is 5-15 h (e.g., 6 h, 8 h, 10 h, 11 h, 12 h, 14 h).

[0020] In the co-doping coating method of this invention, the temperature of the secondary sintering process is limited to 500-700℃. Within this temperature range, it is not only beneficial for the doping of Ti and N elements, but also for the coating of titanium nitride. If the temperature of the secondary sintering process is too low, Ti and N elements cannot be doped into the lattice of the ternary material. If the temperature of the secondary sintering process is too high, the coating effect of titanium nitride will be poor, and the primary nanoparticles will continue to grow, thereby affecting the cycle performance of the ternary cathode material.

[0021] In the above preparation method, as a preferred embodiment, in the pre-doping and post-coating method, the primary mixing process is carried out in a high-speed mixer, with a mixing speed of 100-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm) and a time of 5-60 min (e.g., 10 min, 20 min, 30 min, 40 min, 50 min); preferably, the doping sintering process is carried out in a kiln under an oxygen or air atmosphere, with a doping sintering temperature of 700-1200℃ (e.g., 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃) and a time of 8-15 h (e.g., 6 h, 8 h, 10 h, 11 h, 12 h, 14 h).

[0022] In this invention, the doping sintering temperature is limited to 700-1200℃. At this temperature, it is beneficial to co-dope titanium and nitrogen elements into the lattice of the ternary material. If the doping sintering temperature is too low, the reaction will not be sufficient, and the material capacity will not be fully realized. If the doping sintering temperature is too high, the primary nanoparticles will grow and easily generate oxygen-deficient compounds, thereby aggravating lithium-nickel mixing and affecting the cycle rate performance of the material. In addition, if the temperature is too high, the secondary microspheres may even crack into single crystals, causing the single crystals to also generate oxygen-deficient compounds, aggravating lithium-nickel mixing and affecting the cycle rate performance of the material.

[0023] In the above preparation method, as a preferred embodiment, in the pre-doping and post-coating method, the molar ratio of the total amount of nickel, cobalt, and M elements in the doped titanium nitride to the total amount of nickel, cobalt, and M elements in the ternary precursor material is 0.0015-0.0125:1 (e.g., 0.002:1, 0.005:1, 0.006:1, 0.008:1, 0.01:1, 0.011:1, 0.012:1).

[0024] In the above preparation method, as a preferred embodiment, in the pre-doping and post-coating method, the secondary mixing treatment is performed at 100-800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm) for 5-60 min (e.g., 10 min, 20 min, 30 min, 40 min, 50 min); preferably, the coating sintering treatment is carried out in a kiln under an oxygen or air atmosphere, and the coating sintering treatment temperature is 300-500℃ (e.g., 320℃, 350℃, 380℃, 400℃, 420℃, 450℃, 480℃) for 5-15 h (e.g., 6 h, 8 h, 10 h, 11 h, 12 h, 14 h).

[0025] In this invention, the coating sintering temperature is limited to 300-500℃. At this temperature, it is beneficial to coat titanium nitride onto the surface of the ternary material to the greatest extent. If the coating sintering temperature is too low, the coating effect will be poor. If the coating temperature exceeds 500℃, some titanium nitride can be doped into the lattice of the ternary material, making the titanium nitride coating amount insufficient. If the coating temperature is too high, it will have a greater impact on materials with high nickel content, causing secondary recrystallization of the primary nanoparticles and resulting in larger grains.

[0026] In the above preparation method, as a preferred embodiment, the molar ratio of the coated titanium nitride to the nickel, cobalt, and M elements in the ternary precursor material in the pre-doping and post-coating method is 0.0015-0.0155:1 (e.g., 0.002:1, 0.005:1, 0.006:1, 0.008:1, 0.01:1, 0.012:1, 0.013:1, 0.014:1).

[0027] In this invention, the molar ratio of coated titanium nitride to nickel, cobalt, and M in the ternary precursor material is limited to 0.0015:0.0155. Within this range, the titanium nitride coating on the surface of the substrate is more conducive to exerting its effect and improving performance. If the amount of coating agent titanium nitride is too small, it will not play a role and the performance improvement will not be significant. If the amount of coating agent titanium nitride is too large, it will affect the transport of lithium ions and reduce performance.

[0028] The third aspect of the present invention provides an application of the above-described ternary cathode material or the ternary cathode material prepared by the above-described preparation method in lithium-ion batteries.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) In this invention, titanium nitride (TiN) is used as both a coating agent and a dopant. Ti and N elements replace Ni / Co / M (M is selected from one or two of Mn and Al) and O elements respectively to obtain a matrix. At the same time, titanium nitride is coated on at least a part of the surface of the matrix. The synergistic effect of doping and coating on the doping and coating of titanium nitride, which can both be doped into the crystal lattice of the material and coated on the surface of the material, makes the ternary cathode material have better cycle rate performance and high temperature storage performance.

[0031] (2) The present invention prepares ternary cathode materials by using co-doping coating method or doping followed by coating method; the above preparation methods have the advantages of simple raw materials, low cost and easy industrial production. Attached Figure Description

[0032] Figure 1 This is a SEM image of the ternary cathode material prepared in Example 1 of the present invention;

[0033] Figure 2 The images show the XRD patterns of the ternary cathode materials prepared in Examples 1, 2, and 1 of this invention. Detailed Implementation

[0034] 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. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0036] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0037] In this invention, unless otherwise specified and / or stated, all values ​​relating to component amounts are in "parts by weight". Process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions. The raw materials described in the following examples are all available from publicly available commercial sources. The chemical formula of the ternary precursor material in the embodiments of this invention is Ni. a Co b Mn c (OH)2, wherein 0.5≤a<1, 0<b≤0.3, 0<c≤0.4, a+b+c=1; the method of the present invention is applicable to any ternary precursor material that meets the above conditions. Here, in order to facilitate the comparison of the effects of each embodiment and the prepared cathode material, the molar ratio of Ni:Co:Mn in the ternary precursor material used in the following embodiments and comparative examples is 83:12:5.

[0038] The present invention will now be described in further detail with reference to specific embodiments.

[0039] Example 1: A method for preparing a ternary cathode material, comprising:

[0040] (1) Lithium hydroxide and ternary precursor materials are added to a high-speed mixer, and then titanium nitride is added for a mixing process. The mixing speed is 500 rpm and the mixing time is 20 min. The molar ratio of lithium in lithium hydroxide to the total amount of nickel, cobalt and manganese in ternary precursor materials is 1.04:1; the molar ratio of titanium nitride to the total amount of nickel, cobalt and manganese in ternary precursor materials is 0.004:1. Then, the doping sintering process is carried out in a kiln at a temperature of 780℃ and a holding time of 12 h under an oxygen atmosphere. After that, the material is crushed by a mechanical mill to obtain ternary materials.

[0041] (2) Titanium nitride and the ternary material obtained in step (1) are mixed twice. The mixing speed is 300 rpm and the time is 15 min. The molar ratio of the total amount of nickel, cobalt and manganese in the titanium nitride and the ternary precursor material is 0.008:1. Then, the coating sintering treatment is carried out in a kiln at a temperature of 450℃ and a holding time of 12 h under an oxygen atmosphere. After cooling to room temperature, the material is passed through a 325-mesh sieve to obtain the ternary cathode material. Figure 1 This is a SEM image of the ternary cathode material prepared in Example 1 of the present invention. The image shows that titanium nitride was successfully coated onto the surface of the substrate. Figure 2 The XRD patterns of the ternary cathode materials prepared by Examples 1, 2, and 1 of the present invention are shown in the figures. It can be seen from the figures that the diffraction peaks of the ternary cathode materials prepared by the preparation methods of Examples 1 and 2 of the present invention are shifted at (003) and (104) compared with the diffraction peaks of the ternary cathode materials prepared by Comparative Example 1, indicating that the preparation methods of Examples 1 and 2 successfully incorporated titanium nitride into the crystal lattice of the material.

[0042] Example 2: A method for preparing a ternary cathode material, comprising:

[0043] (1) Lithium hydroxide and ternary precursor materials are added to a high-speed mixer for primary mixing. The mixing speed is 500 rpm and the time is 20 min. The molar ratio of lithium in lithium hydroxide to the total amount of nickel, cobalt and manganese in ternary precursor materials is 1.04:1. Then, a primary sintering treatment is carried out in a kiln at a temperature of 780℃ and a holding time of 12 h under an oxygen atmosphere. After that, the material is crushed by a mechanical mill to obtain the primary sintered material.

[0044] (2) Add titanium nitride and the primary sintering material obtained in step (1) into a high-speed mixer for secondary mixing. The mixing speed is 300 rpm and the time is 15 min. The molar ratio of titanium nitride to nickel, cobalt and manganese in the ternary precursor material is 0.012:1. Then, in the kiln, the secondary sintering is carried out at a temperature of 680℃ and a holding time of 12 h in an oxygen atmosphere. After cooling to room temperature, the material is passed through a 325-mesh sieve to obtain the ternary cathode material.

[0045] Example 3: A method for preparing a ternary cathode material:

[0046] (1) Lithium hydroxide and ternary precursor materials are added to a high-speed mixer for primary mixing. The mixing speed is 500 rpm and the time is 20 min. The molar ratio of lithium in lithium hydroxide to the total amount of nickel, cobalt and manganese in ternary precursor materials is 1.04:1. Then, a primary sintering treatment is carried out in a kiln at a temperature of 780℃ and a holding time of 12 h under an oxygen atmosphere. After that, the material is crushed by a mechanical mill to obtain the primary sintered material.

[0047] (2) Add titanium nitride and the primary sintering material obtained in step (1) into a high-speed mixer for secondary mixing. The mixing speed is 300 rpm and the time is 15 min. The molar ratio of titanium nitride to nickel, cobalt and manganese in the ternary precursor material is 0.012:1. Then, a secondary sintering treatment is carried out in a kiln at a temperature of 600℃ and a holding time of 12 h. After cooling to room temperature, the material is passed through a 325-mesh sieve to obtain the ternary cathode material.

[0048] Example 4

[0049] The difference between Example 4 and Example 2 is that the molar ratio of titanium nitride to nickel, cobalt and manganese in the ternary precursor material is 0.003:1, while the rest are the same as in Example 2.

[0050] Example 5

[0051] The difference between Example 5 and Example 2 is that the molar ratio of titanium nitride to nickel, cobalt and manganese in the ternary precursor material is 0.028:1, while the rest are the same as in Example 2.

[0052] Example 6

[0053] The difference between Example 6 and Example 1 is that in step (1), the molar ratio of the total amount of nickel, cobalt and manganese in the ternary precursor material to titanium nitride is 0.0015:1; in step (2), the molar ratio of the total amount of nickel, cobalt and manganese in the ternary precursor material to titanium nitride is 0.0015:1; the rest are the same as in Example 1.

[0054] Example 7

[0055] The difference between Example 7 and Example 1 is that in step (1), the molar ratio of the total amount of nickel, cobalt and manganese in the ternary precursor material to titanium nitride is 0.0125:1; in step (2), the molar ratio of the total amount of nickel, cobalt and manganese in the ternary precursor material to titanium nitride is 0.0155:1; the rest are the same as in Example 1.

[0056] Comparative Example 1: A method for preparing a ternary cathode material, comprising:

[0057] Lithium hydroxide and ternary precursor materials were added to a high-speed mixer for mixing at a speed of 500 rpm for 20 minutes. The molar ratio of lithium in lithium hydroxide to the total amount of nickel, cobalt and manganese in the ternary precursor materials was 1.04:1. Then, the materials were sintered in a kiln at a temperature of 780℃ for 12 hours under an oxygen atmosphere. After that, the materials were crushed by a mechanical mill and passed through a 325-mesh sieve to obtain the ternary cathode material.

[0058] Comparative Example 2: A method for preparing a ternary cathode material, comprising:

[0059] Lithium hydroxide and ternary precursor materials were added to a high-speed mixer, and then titanium nitride was added for mixing. The mixing speed was 500 rpm and the mixing time was 20 min. The molar ratio of lithium in lithium hydroxide to the total amount of nickel, cobalt and manganese in ternary precursor materials was 1.04:1.

[0060] The molar ratio of titanium nitride to the total amount of nickel, cobalt and manganese in the ternary precursor material is 0.004:1; then, the material is subjected to doping sintering treatment in an oxygen atmosphere at a temperature of 780℃ for 12 hours, and then the material is pulverized by mechanical mill to obtain the ternary cathode material.

[0061] The difference between Comparative Example 2 and Example 1 is that only doping sintering treatment was performed, and no coating sintering treatment was performed. The cathode material prepared in Comparative Example 2 is a ternary material with Ti and N elements co-doped in the crystal lattice, and its surface is not coated with titanium nitride.

[0062] Comparative Example 3: A method for preparing a ternary cathode material, comprising:

[0063] (1) Lithium hydroxide and ternary precursor materials are added to a high-speed mixer for a first mixing process. The mixing speed is 500 rpm and the time is 20 min. The molar ratio of lithium element in lithium hydroxide to total amount of nickel, cobalt and manganese element in ternary precursor material is 1.04:1. Then, a first sintering process is carried out in a kiln at a temperature of 780℃ and a holding time of 12 h under an oxygen atmosphere. After that, the material is crushed and sieved by a mechanical mill to obtain ternary material.

[0064] (2) The titanium nitride and the ternary material obtained in step (1) are mixed for a second time. The mixing speed is 300 rpm and the time is 15 min. The molar ratio of the total amount of nickel, cobalt and manganese in the titanium nitride and the ternary precursor material is 0.008:1. Then, the coating sintering treatment is carried out in a kiln at a temperature of 450℃ and a holding time of 12 h. After cooling to room temperature, the material is sieved to obtain the ternary cathode material.

[0065] The difference between Comparative Example 3 and Example 1 is that only the coating sintering process was performed, and no doping sintering process was performed. The cathode material prepared in Comparative Example 3 is a ternary material with titanium nitride coated on the surface. There is no Ti or N element doping in the lattice of the ternary material.

[0066] Comparative Example 4

[0067] The difference between Comparative Example 4 and Example 1 is that the coating sintering temperature in step (2) is 700°C; the rest are the same as in Example 1.

[0068] Comparative Example 5

[0069] The difference between Comparative Example 5 and Example 1 is that the temperature of the coating sintering treatment in step (2) is 250°C; the rest are the same as in Example 1.

[0070] Comparative Example 6

[0071] The difference between Comparative Example 6 and Example 2 is that the temperature of the secondary sintering treatment in step (2) is 450°C; the rest are the same as in Example 2.

[0072] Comparative Example 7

[0073] The difference between Comparative Example 7 and Example 2 is that the temperature of the secondary sintering treatment in step (2) is 750°C; the rest are the same as in Example 2.

[0074] Performance testing

[0075] The ternary cathode materials prepared in Examples 1-7 and Comparative Examples 1-7 of this invention were used as active materials, PVDF as binder, and SP as conductive agent. The ratio of active material: binder: conductive agent was 90:5:5. These materials were dissolved in NMP solvent to prepare a slurry. The slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 2 hours. Finally, it was cut into circular electrode sheets with a diameter of 11 mm using a punch as working electrodes. In a clean glove box filled with Ar (O2 content less than 0.1 ppm, H2O content less than 0.1 ppm), a lithium metal sheet was used as the counter electrode. A 1 mol / L lithium hexafluorophosphate (LiPF6) solution was used as the separator, and the solvent was a 1:1 volume ratio mixture of ethylene carbonate (EC) and ethyl carbonate (DMC). A button cell (model CR2032) was prepared according to a specific assembly process. After assembly, the cell was allowed to stand for 24 hours to allow the electrolyte and electrode materials to fully wet. Under room temperature (25℃±1), the initial discharge specific capacity was tested at a voltage of 3.0V-4.25V, and cycle performance tests were conducted at room temperature and 60℃.

[0076] The method for determining the capacity retention rate after 10 days of storage at 60℃ is as follows: the battery is first charged and discharged at 0.1C to obtain the battery capacity C1, then charged at 0.1C, and after charging, it is stored at 60℃ for 10 days. After that, it is discharged at a discharge rate of 0.1C to obtain the discharge capacity C2; the capacity retention rate = C1 / C2. The method for determining the capacity recovery rate after 10 days of storage at 60℃ is as follows: the battery is first charged at 0.1C, and then stored at 60℃ for 10 days. After that, it is discharged at a discharge rate of 0.1C to obtain the capacity C1. After standing for 30 minutes, it is charged and discharged at 0.1C to obtain the discharge capacity C2; the capacity recovery rate = C1 / C2.

[0077] The thermal decomposition temperature was tested as follows: After the assembled button cell underwent 0.1C charge, 0.1C discharge, and 0.1C charge tests, it was removed and disassembled to obtain intact and fresh positive electrode sheets. These sheets were then immersed in dimethyl carbonate (DMC) for several minutes and dried in a vacuum dryer. The positive electrode material was scraped off the dried sheet using a sharp tool, placed in a crucible, and sealed. The thermal analysis test atmosphere was inert gas. The starting point of the heating phase was room temperature, and the endpoint could be set between 350℃ and 610℃ depending on the material. The heating rate was 5–10℃ / min. After the test, the spectral lines were analyzed. The test results are shown in Tables 1 and 2.

[0078] Table 1 shows the coin cell tests conducted at a 0.1C rate and a voltage range of 3.0V-4.25V. Compared to Comparative Example 1, Example 1, with its titanium nitride doping coating, improved the specific discharge capacity of the material. Since titanium nitride reduces the lithium insertion voltage, it promotes more lithium insertion / extraction at a fixed overpotential, thus improving discharge capacity and capacity retention. Comparative Example 2 showed a decrease in specific charge / discharge capacity compared to Example 1, while Comparative Example 3 showed an increase. This is because the titanium nitride coating on the material surface improves conductivity and reduces material impedance. Example 2's specific charge / discharge capacity was slightly lower than Example 1 but higher than Comparative Example 1, indicating that the synthesis method of Example 2 can incorporate titanium into the material, thereby improving the specific charge / discharge capacity. However, due to the one-step doping coating, the effect is not as good as Example 1. Example 3's specific charge / discharge capacity was relatively low because the lower sintering temperature resulted in a slightly reduced amount of titanium incorporated into the material, affecting capacity performance.

[0079] The rate performance of Examples 1 / 2 and Comparative Example 2 is significantly higher than that of Comparative Example 1 and Comparative Example 3. This is because the incorporation of nitrogen ions into the crystal lattice can expand the interlayer spacing and improve the rate performance of the material.

[0080] Table 1

[0081]

[0082]

[0083] Because titanium nitride coats the material surface, forming a protective layer that inhibits electrolyte corrosion, cycling performance is significantly improved. The Ti-O bond energy is much greater than the Ni-O bond energy, which stabilizes lattice oxygen during cycling or storage. Ti doping also suppresses lithium-nickel mixing, inhibits layered structure transformation, and improves the material's cycling and storage performance. Therefore, the cycling performance of Example 1 / 2 is significantly better than that of Comparative Example 1 / 2.

[0084] Titanium nitride, as a coating layer, can provide thermal insulation and temperature control, reducing electrolyte corrosion and transition metal dissolution at high temperatures, thereby improving the high-temperature storage performance of the battery. Due to the synergistic effect of titanium nitride doping and coating, the material exhibits better high-temperature storage performance and significantly improved thermal runaway.

[0085] Table 2

[0086]

[0087] Note: The capacity retention rate at 60℃-1C for 100 cycles is the ratio of the discharge capacity at 1C for 100 cycles to the discharge capacity at the first cycle.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing a ternary cathode material, characterized in that, include: Co-doping coating method: First, the lithium source and ternary precursor material are mixed, sintered, and crushed to obtain a sintered material. Then, the primary sintering material is mixed with titanium nitride in a secondary mixing process and sintered in a secondary process to obtain a ternary cathode material; Alternatively, the doping-coating method can be used: First, the lithium source, ternary precursor material, and doped titanium nitride are mixed, sintered, and pulverized to obtain a ternary material. Then, the ternary material and coated titanium nitride are mixed and sintered to obtain a ternary cathode material. In the co-doping coating method, the primary sintering process is carried out in a kiln under an oxygen or air atmosphere, and the temperature of the primary sintering process is 700-1200℃, and the time is 8-15h. The secondary sintering process is carried out in a kiln under an oxygen or air atmosphere. The temperature of the secondary sintering process is 580-700℃ and the time is 5-15h. In the pre-doping and post-coating method, the doping sintering treatment is carried out in a kiln under an oxygen or air atmosphere, and the temperature of the doping sintering treatment is 700-1200℃, and the time is 8-15h. The coating sintering process is carried out in a kiln under an oxygen or air atmosphere, with a temperature of 300-500℃ and a time of 5-15 hours. The ternary cathode material includes: a substrate and a coating material covering the surface of the substrate; wherein, the substrate is a ternary material co-doped with titanium and nitrogen, and the coating material is titanium nitride; The chemical formula of the matrix is ​​Li n Ni x Co y M z Ti (1-x-y-z) N m O (2-1.5m) The element M is selected from one or both of Mn and Al, where 0.95≤n≤1.05, 0.5≤x<1, 0<y≤0.3, 0<z≤0.4, x+y+z<1, and 0.0015≤m≤0.0125. In the co-doping coating method or the pre-doping followed by coating method, the ternary precursor material is nickel cobalt manganese hydroxide and / or nickel cobalt aluminum hydroxide, with the chemical formula: Ni a Co b M c (OH)2, where the element M is selected from one or both of Mn and Al, wherein 0.5≤a<1, 0<b≤0.3, 0<c≤0.4, and a+b+c=1; In the co-doping coating method, the molar ratio of the total amount of nickel, cobalt, and M elements in the titanium nitride to that in the ternary precursor material is 0.003-0.028:1; In the pre-doping and post-coating method, the molar ratio of the doped titanium nitride to the total amount of nickel, cobalt, and M elements in the ternary precursor material is 0.0015-0.0125:1; the molar ratio of the coated titanium nitride to the total amount of nickel, cobalt, and M elements in the ternary precursor material is 0.0015-0.0155:

1.

2. The preparation method according to claim 1, characterized in that, The microstructure of the ternary cathode material is a secondary microsphere or a single crystal large particle composed of primary nanoparticles. The diameter of the secondary microspheres is 4-15 μm; The diameter of the single-crystal large particles is 2-6 μm.

3. The preparation method according to claim 1, characterized in that, In the co-doping coating method or the pre-doping and post-coating method, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide; And / or, the molar ratio of lithium in the lithium source to the total amount of nickel, cobalt and M in the ternary precursor material is 1.0-1.1:

1.

4. The preparation method according to claim 1, characterized in that, In the co-doping coating method, the primary mixing process is carried out in a high-speed mixer, with a rotation speed of 100-800 rpm and a time of 5-60 min.

5. The preparation method according to claim 1, characterized in that, In the co-doping coating method, the secondary mixing process is carried out in a high-speed mixer, with a rotation speed of 100-800 rpm and a time of 5-60 min.

6. The preparation method according to claim 1, characterized in that, In the pre-doping and post-coating method, the primary mixing process is carried out in a high-speed mixer, with a rotation speed of 100-800 rpm and a time of 5-60 min.

7. The preparation method according to claim 1, characterized in that, In the pre-doping and post-coating method, the secondary mixing process is carried out at 100-800 rpm for 5-60 min.

8. The application of a ternary cathode material prepared by the method of any one of claims 1-7 in a lithium-ion battery.

Images