Modified ternary cathode materials, their preparation methods and applications

Abstract

This invention provides a modified ternary cathode material, its preparation method, and its application, relating to the field of lithium-ion battery technology. The preparation method of the modified ternary cathode material includes the following steps: S1, mixing and grinding a ternary precursor material, a lithium source, a lanthanum salt, and a tin salt, and then subjecting the mixture to high-temperature sintering under an oxygen atmosphere to obtain a ternary matrix material. The ternary precursor is a nickel-cobalt-manganese hydroxide with the chemical formula Ni. x Co y Mn z (OH)₂, where 0.6 ≤ x ≤ 0.9, 0.1

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to modified ternary cathode materials, their preparation methods, and applications. Background Technology

[0002] As a core component of new energy power systems, the performance of the cathode material in lithium-ion batteries directly determines the battery's energy density, cycle life, and safety. Nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) ternary layered materials have become the preferred cathode system for high-energy-density power batteries due to their high specific capacity and high operating voltage. However, while increasing the nickel content achieves higher energy density, inherent material defects leading to deteriorated cycle stability and thermal safety risks have become key bottlenecks restricting their commercial application.

[0003] Currently, the industry mainly uses the following methods to improve the cycling and thermal stability of materials, but there are still significant drawbacks: ① Bulk doping (Al, Mg, Ti, etc.): Although it can suppress phase transitions, excessive doping (>3 wt%) leads to a reduction in the specific energy of the material; ② Surface coating (Al2O3, Li3PO4, etc.): Non-in-situ coating layers are prone to insufficient coverage (<70%) or uneven thickness (10-100 nm), which cannot effectively block electrolyte erosion; ③ Single crystallization process: Improves mechanical strength but sacrifices rate performance (5C capacity retention <60%), and the preparation cost is high.

[0004] Therefore, developing a modification strategy for ternary cathode materials that balances high capacity, long cycle life, and intrinsic safety, and solving the problems of surface and interface side reactions and bulk structural instability through multi-level structural synergistic regulation, is of practical significance in meeting the cycle and safety performance requirements of power batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a modified ternary cathode material, its preparation method, and its application, solving the technical problem of poor cycle stability and thermal safety of existing ternary cathode materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a modified ternary cathode material, comprising the following steps:

[0008] S1. The ternary precursor material, lithium source, lanthanum salt, and tin salt are mixed and ground, and then subjected to high-temperature sintering under an oxygen atmosphere to obtain a ternary matrix material. The ternary precursor is nickel-cobalt-manganese hydroxide with the chemical formula Ni. x Co y Mn z(OH)₂, where 0.6 ≤ x ≤ 0.9, 0.1 <y≤0.2、0.1≤z≤0.3、x+y+z=1;

[0009] S2. Lanthanum salt and boron source are dissolved in ethanol solution to obtain coating solution. The pH of the coating solution is adjusted, and then a ternary matrix material is added to the coating solution. The reaction is carried out under heating and stirring conditions. The reaction product is dried under vacuum conditions, then taken out and ground. The coating treatment is completed by high-temperature sintering under an oxygen atmosphere to obtain the modified ternary cathode material.

[0010] The above method uses La / Sn to co-dope and modify the ternary cathode material before carbon coating to prepare the modified ternary cathode material. Wherein, La... 3+ A larger radius can act as a support in modified ternary cathode materials, increasing the interlayer spacing and providing Li + The diffusion provides a transport channel, thereby enhancing the rate performance of the modified ternary cathode material; Sn 4+ The introduction of Co 3+ Doping at certain sites can effectively enhance the stability of lattice oxygen under high voltage, which is beneficial for Li under high voltage. + The migration of oxygen ions is facilitated by the pyrochlore-type La2Sn2O7 structure formed by the two processes. This structure possesses strong oxygen ion transport capabilities, enabling the storage of lattice oxygen released by the material under high voltage. This enhances the electrochemical activity of the modified ternary cathode material under high voltage, thereby significantly improving the structural stability and cycle stability of the modified ternary cathode material through a synergistic effect. Furthermore, wet in-situ coating is more beneficial for improving the electrochemical performance of the material than traditional solid-phase mixed coating methods. The thermal stability of the modified ternary cathode material prepared after coating is significantly improved.

[0011] Preferably, the lanthanum salt is selected from at least one of lanthanum chloride, lanthanum oxide, lanthanum nitrate, and lanthanum carbonate;

[0012] The lithium source is selected from lithium hydroxide or lithium carbonate;

[0013] The tin salt is stannous chloride;

[0014] The molar ratio of metal element: lithium source: lanthanum salt: tin salt in the ternary precursor material is 1: (1-1.08): (0.005-0.01): (0.005-0.01).

[0015] Preferably, in step S1, sintering is divided into two stages: pre-sintering and sintering. The heating rate is 5℃ / min for both stages. The pre-sintering temperature is 450~750℃ and the pre-sintering time is 5~10h. The sintering temperature is 800~950℃ and the sintering time is 10~15h.

[0016] Preferably, the molar ratio of lanthanum salt to boron source in S2 is 1:(1.15-1.20).

[0017] The concentration of the dilute nitric acid is 0.1 mol / L, and the pH range is 5.5 ± 0.2.

[0018] By controlling the pH of the coating solution within a suitable range during the coating process, the modified ternary cathode material can exhibit excellent electrical properties.

[0019] Preferably, in step S2, the mass ratio of the ternary matrix material to the coating liquid is 1:4, and the heating and stirring conditions are: temperature 65°C, stirring speed 800 rppm, and time 3-5 h.

[0020] Preferably, in step S2, the vacuum drying pressure is -0.1 MPa, the temperature is 80-100℃, and the time is 6-8 hours.

[0021] Preferably, in step S2, the sintering step has two stages: the first stage sintering temperature is 300-400℃, the sintering time is 3-5h, and the heating rate is 2℃ / min; the second stage sintering temperature is 650-800℃, the sintering time is 5-8h, and the heating rate is 5℃ / min.

[0022] Preferably, the coating amount of the coating treatment is 1-5 wt%, and the coating thickness is 5-20 nm.

[0023] In a second aspect, the present invention provides a modified ternary cathode material prepared by the preparation method described in the first aspect, wherein the modified ternary cathode material comprises a ternary matrix material co-doped with lanthanum and tin and a coating layer, wherein the coating layer coats the surface of the ternary matrix material.

[0024] Thirdly, the present invention provides an application of the modified ternary cathode material described in the second aspect in lithium-ion batteries.

[0025] Compared with existing technologies, it has the following beneficial effects:

[0026] This invention uses La / Sn to co-dope and modify ternary cathode materials before carbon coating to prepare modified ternary cathode materials. Specifically, La... 3+ A larger radius can act as a support in modified ternary cathode materials, increasing the interlayer spacing and providing Li + The diffusion provides a transport channel, thereby enhancing the rate performance of the modified ternary cathode material; Sn 4+ The introduction of Co 3+ Doping at certain sites can effectively enhance the stability of lattice oxygen under high voltage, which is beneficial for Li under high voltage. +The migration of oxygen ions is facilitated by the pyrochlore-type La2Sn2O7 structure formed by the two processes. This structure has strong oxygen ion transport capabilities and can store lattice oxygen released by the material under high voltage, thereby enhancing the electrochemical activity of the modified ternary cathode material under high voltage. This significantly improves the structural stability and cycle stability of the modified ternary cathode material through a synergistic effect. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 These are the DSC curves of the positive electrode plates of Example 1 and Comparative Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This application provides a modified ternary cathode material, its preparation method, and its application, which solves the technical problem of poor cycle stability and thermal safety of existing ternary cathode materials.

[0031] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0032] This invention modifies the bulk phase of a ternary matrix material by co-doping with lanthanum (La) and tin (Sn), followed by in-situ coating of the material surface with lanthanum borate using a wet chemical method to prepare a modified high-nickel ternary cathode material (NCM). The ternary cathode material provided by this invention exhibits higher cycle stability and thermal stability, while maintaining good chemical performance even at high current densities. This significantly improves upon the poor stability, numerous interfacial side reactions, and unsatisfactory thermal stability of lithium-ion battery ternary cathode materials during long-cycle operation.

[0033] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0034] I. Preparation Method

[0035] Example 1

[0036] This embodiment provides a method for preparing a modified ternary cathode material, comprising the following steps:

[0037] S1, the ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2, LiOH, LaCl3, and SnCl4 were mixed and ground in a metal molar ratio of 1:1.04:0.005:0.005. After thorough and uniform grinding, the material was placed in an oxygen atmosphere for high-temperature sintering treatment. The heating rate was 5℃ / min, the pre-sintering temperature was 500℃, the sintering time was 5h, and then the temperature was raised to 850℃ for sintering for 15h to obtain a ternary matrix material.

[0038] S2. Dissolve LaCl3 and H3BO3 in an ethanol solution at a molar ratio of 1:1.12, stir until clear and transparent, and then add 0.1 mol / L dilute nitric acid dropwise to control the pH of the solution at 5.5.

[0039] S3. The ternary matrix material prepared in S1 is poured into the solution prepared in S2 at a solid-liquid ratio of 1:4. The solution is heated in a constant temperature water bath at 65℃ and treated at a rotation speed of 300 rpm for 5 hours. The slurry is then dried in a vacuum oven at 80℃. After grinding, the material is sintered at 350℃ for 3 hours under an oxygen atmosphere at a heating rate of 2℃ / min. Then, it is sintered at 750℃ for 5 hours at a heating rate of 5℃ / min to obtain a modified ternary cathode material with a coating amount of 3wt% and a coating layer thickness of 5nm.

[0040] Example 2

[0041] The difference between this embodiment and Embodiment 1 is that Ni in S1 0.8 Co 0.1 Mn 0.1 The molar ratio of (OH)2, LiOH, LaCl3, and SnCl4 is 1:1.04:0.005:0.01, and other parameters are the same as in Example 1, resulting in a modified ternary cathode material with a coating amount of 3wt% and a coating layer thickness of 5nm.

[0042] Example 3

[0043] The difference between this embodiment and embodiment 1 is that the molar ratio of LaCl3 to H3BO3 in S2 is 1:1.2, while the rest is the same as in embodiment 1, resulting in a modified ternary cathode material with a coating amount of 5wt% and a coating layer thickness of 10nm.

[0044] Example 4

[0045] Compared with Example 1, the commercial ternary precursor in this embodiment is Ni. 0.65 Co 0.1Mn 0.3 Using (OH)2, and other parameters as in Example 1, a modified ternary cathode material with a coating amount of 3wt% and a coating layer thickness of 5nm was obtained.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that steps S2 and S3, the material surface coating steps, are omitted. Otherwise, the same as in Example 1 is obtained, resulting in a modified ternary cathode material.

[0048] Comparative Example 2

[0049] The difference between this comparative example and Example 1 is that the wet coating steps S2 and S3 are omitted. Instead, commercially available LaBO3 is directly used for solid-phase mixing and coating with the ternary matrix material obtained in S1. Specifically, LaBO3 and the ternary matrix material obtained in S1 are mixed uniformly at a molar ratio of 1:0.005 and then sintered at 350°C for 3 hours, followed by sintering at 750°C for 5 hours at a rate of 5°C / min. Other steps are the same as in Example 1, resulting in a modified ternary cathode material.

[0050] Comparative Example 3

[0051] The difference between this comparative example and Example 1 is that S1 does not include LaCl3, and the commercial ternary precursor Ni is used. 0.8 Co 0.1 Mn 0.1 (OH)2, LiOH, and SnCl4 were mixed and ground in a metal molar ratio of 1:1.04:0.01, and other procedures were the same as in Example 1.

[0052] Comparative Example 4

[0053] The difference between this comparative example and Example 1 is that S1 does not include SnCl4, and the commercial ternary precursor Ni is used. 0.8 Co 0.1 Mn 0.1 (OH)2, LiOH, and LaCl3 were mixed and ground in a metal molar ratio of 1:1.04:0.01, and other processes were the same as in Example 1.

[0054] Comparative Example 5

[0055] The difference between this embodiment and embodiment 1 is that dilute nitric acid is not added in step S2, while the rest is the same as in embodiment 1.

[0056] Battery assembly

[0057] The materials prepared in the above embodiments and comparative examples were used as positive electrode active materials. The positive electrode active material, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5 and dissolved in an N-methylpyrrolidone solution. This solution was then uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain a compacted density of 3.5 g / cm³. 3 Positive electrode plate;

[0058] An electrolyte was prepared by dissolving 1.0 mol / L LiPF6 in EC / DMC / DEC (1:1:1 in wt.%). The positive electrode, separator (Celgard 24), electrolyte, and lithium metal negative electrode were assembled into a CR2016 coin cell in a glove box.

[0059] II. Testing Methods

[0060] 1. The assembled coin cells were subjected to electrochemical performance tests at 25°C, with an initial voltage of 2.8V and a cutoff voltage of 4.35V. First, the cells were charged and discharged sequentially at rates of 0.2C / 0.2C, 0.33C / 0.33C, 1C / 1C, and 0.2C / 0.2C for the first four weeks, followed by a charge-discharge test at a rate of 1C / 1C until 300 cycles were completed. The test results are shown in Table 1.

[0061] 2. Thermal stability test

[0062] The positive electrode sheets of Example 1 and Comparative Example 1 were immersed in the electrolyte for at least 30 minutes. After removal, excess electrolyte was absorbed with filter paper. The samples were then placed in a high-pressure sealed crucible in a glove box, immediately sealed, and the total mass of the sealed crucible was recorded (to calculate the net weight of the electrode sheet). Subsequently, under an N2 atmosphere with a constant N2 flow rate of 40.0 ml / min, the temperature was increased from room temperature to 500°C at a rate of 5°C / min to test the thermal stability of the electrode sheets. The test results are shown below. Figure 1 .

[0063] III. Test Results

[0064] Table 1 Electrochemical performance of cathode materials in examples and comparative examples

[0065]

[0066] As shown in Table 1, the battery assembled with the modified ternary cathode material prepared in Example 1 exhibits superior capacity, rate performance, and cycle performance. However, the batteries assembled with the modified ternary cathode materials prepared in Comparative Examples 3 and 4 fail to achieve the same capacity, rate performance, and cycle performance as those in Example 1. This is because La... 3+ A larger radius can act as a support in modified ternary cathode materials, increasing the interlayer spacing and providing Li +The diffusion provides a transport channel, thereby enhancing the rate performance of the modified ternary cathode material; Sn 4+ The introduction of Co 3+ Doping at certain sites can effectively enhance the stability of lattice oxygen under high voltage, which is beneficial for Li under high voltage. + The migration of oxygen ions is facilitated by the pyrochlore-type La2Sn2O7 structure formed by the two processes. This structure has strong oxygen ion transport capabilities and can store lattice oxygen released by the material under high voltage, thereby enhancing the electrochemical activity of the modified ternary cathode material under high voltage. This results in a significant improvement in the structural stability and electrochemical performance of the modified ternary cathode material through a synergistic effect.

[0067] The data from Comparative Example 2 further demonstrate that the wet in-situ coating method used in this invention is more beneficial to improving the electrochemical performance of the material than the traditional solid-phase mixing coating method. Furthermore, the battery assembled from the modified ternary cathode material prepared in Comparative Example 5 exhibited poor capacity, rate performance, and cycle performance, indicating that the pH of the coating solution is also a key factor affecting the electrical performance of the modified ternary cathode material during the coating process. Figure 1 It can be seen that the exothermic peak onset temperature of the material shifts backward after LaBO3 coating, proving that coating modification has a significant improvement on the thermal stability of ternary cathode materials.

[0068] In summary, compared with existing technologies, it has the following beneficial effects:

[0069] (1) This invention uses La / Sn to co-dope the ternary cathode material, which significantly improves the structural stability and electrochemical performance of the material through a synergistic effect: La 3 + A larger radius can act as a support in the material, increasing the interlayer spacing, thus benefiting Li. + The diffusion provides a transmission channel, thereby enhancing rate performance; Sn 4+ The introduction of Co 3+ Doping at certain sites can effectively enhance the stability of lattice oxygen under high voltage, which is beneficial for Li under high voltage. + The migration of oxygen ions; at the same time, the pyrochlore-type La2Sn2O7 structure induced by the two has a strong oxygen ion transport capability, which can store lattice oxygen released by the material under high voltage and enhance the electrochemical activity of the material under high voltage.

[0070] (2) In this invention, LaBO3 is used to coat ternary materials, which acts as a physical barrier on the surface of the material, thus alleviating the corrosion of the material by the electrolyte. LaBO3 can neutralize acidic substances, especially HF, and improve the stability of the chemical interface. At the same time, LaBO3 can suppress phase transformation stress and increase the structural stability of the material. In addition, LaBO3 has a high melting point, which can suppress oxygen release during high-temperature cycling or thermal runaway.

[0071] (3) The present invention uses an in-situ wet chemical coating method and adopts a segmented sintering method to uniformly coat a layer of LaBO3 on the surface of the material, avoiding problems such as agglomeration or local exposure caused by dry mechanical mixing.

[0072] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0074] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified ternary cathode material, characterized in that, Includes the following steps: S1. The ternary precursor material, lithium source, lanthanum salt, and tin salt are mixed and ground, and then subjected to high-temperature sintering under an oxygen atmosphere to obtain a ternary matrix material. The ternary precursor is nickel-cobalt-manganese hydroxide with the chemical formula Ni. x Co y Mn z (OH)₂, where 0.6 ≤ x ≤ 0.9, 0.1 <y≤0.2、0.1≤z≤0.3、x+y+z=1; S2. Lanthanum salt and boron source are dissolved in ethanol solution to obtain coating solution. The pH of the coating solution is adjusted, and then a ternary matrix material is added to the coating solution. The reaction is carried out under heating and stirring conditions. The reaction product is dried under vacuum conditions, then taken out and ground. The coating treatment is completed by high-temperature sintering under an oxygen atmosphere to obtain the modified ternary cathode material.

2. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, At least one of the following conditions must be met: The lanthanum salt is selected from at least one of lanthanum chloride, lanthanum oxide, lanthanum nitrate, and lanthanum carbonate; The lithium source is selected from lithium hydroxide or lithium carbonate; The tin salt is stannous chloride; The molar ratio of metal element: lithium source: lanthanum salt: tin salt in the ternary precursor material is 1: (1-1.08): (0.005-0.01): (0.005-0.01).

3. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, In S1, sintering is divided into two stages: pre-sintering and sintering. The heating rate is 5℃ / min for both stages. The pre-sintering temperature is 450~750℃ and the pre-sintering time is 5~10h. The sintering temperature is 800~950℃ and the sintering time is 10~15h.

4. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, The molar ratio of lanthanum salt to boron source in S2 is 1:(1.15-1.20). The concentration of the dilute nitric acid is 0.1 mol / L, and the pH range is 5.5 ± 0.

2.

5. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, In S2, the mass ratio of the ternary matrix material to the coating liquid is 1:4, and the heating and stirring conditions are: temperature 65℃, stirring speed 800rppm, and time 3-5h.

6. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, In step S2, the vacuum drying pressure is -0.1 MPa, the temperature is 80-100℃, and the time is 6-8 hours.

7. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, In S2, the sintering step has two stages. The first stage sintering temperature is 300-400℃, the sintering time is 3-5h, and the heating rate is 2℃ / min. The second stage sintering temperature is 650-800℃, the sintering time is 5-8h, and the heating rate is 5℃ / min.

8. The method for preparing the modified ternary cathode material as described in claim 1, characterized in that, The coating amount of the coating treatment is 1-5 wt%, and the coating thickness is 5-20 nm.

9. A modified ternary cathode material prepared by the preparation method according to any one of claims 1-8, characterized in that, The modified ternary cathode material includes a ternary matrix material co-doped with lanthanum and tin and a coating layer, wherein the coating layer is coated on the surface of the ternary matrix material.

10. The application of the modified ternary cathode material according to claim 9 in a lithium-ion battery.

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