A high-performance lithium-rich manganese-based positive electrode material based on pre-processed boron nitride, and a preparation method and application thereof

Abstract

This invention relates to the field of lithium-ion battery cathode material technology, specifically a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, its preparation method, and its application. The preparation method includes: introducing hydroxyl and amino groups onto the surface of boron nitride nanosheets; preparing a composite precursor powder by mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source, TiO2, a phosphorus source, and pretreated boron nitride; sequentially performing conventional pre-calcination, a first-segment Joule heat treatment, and a second-segment Joule heat treatment; performing a third-segment instantaneous Joule heat treatment, followed by quenching; by introducing a surface-functionalized high thermal conductivity boron nitride network into the bulk phase of the material, and combining a programmed sequential heat treatment of "pre-calcination-two-segment Joule heat treatment" with instantaneous surface melting and quenching, this method effectively solves the inherent thermal gradient problem of the Joule heating method, simultaneously achieving high bulk phase homogenization and surface stabilization, resulting in a product with excellent comprehensive electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, and in particular to a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, its preparation method, and its application. Background Technology

[0002] Lithium-rich manganese-based layered oxides are considered ideal cathode materials for next-generation high-energy-density lithium-ion batteries due to their high specific capacity and high operating voltage. However, their commercial application remains limited by issues such as low initial coulombic efficiency, severe voltage and capacity decay during cycling, and poor rate performance. These problems are closely related to the structural instability of the material during synthesis and cycling.

[0003] Among the methods for synthesizing lithium-rich manganese-based matrix oxides, besides the traditional long-duration high-temperature solid-state method, the Joule heating method, as an emerging rapid sintering technology, has attracted attention due to its unique advantages such as extremely fast heating and cooling rates (up to 100-1000°C / s), short production cycle, high synthesis efficiency, and low energy consumption. However, the Joule heating method itself has a significant temperature gradient of "internal heat and external cold," leading to poor bulk composition, crystallinity, and structural uniformity of the synthesized material, which may exacerbate performance degradation. Furthermore, lithium-rich materials are extremely sensitive to surface interfaces; how to simultaneously construct stable surface interfaces during rapid synthesis is a key technical bottleneck in the preparation of high-performance lithium-rich materials using the Joule heating method.

[0004] For example, Chinese patent CN113511692B discloses a short-time rapid thermal shock method for synthesizing lithium-rich manganese-based cathode materials. While this improves efficiency, it does not solve the bulk phase uniformity problem caused by uneven thermal field. Chinese patent CN119560517B improves performance by constructing a gradient non-metallic ion-doped core-shell structure near the material surface, but... This scheme mainly targets the surface modification of materials synthesized by traditional high-temperature solid-state methods. It fails to solve the core problem of uneven bulk composition and crystallinity caused by the significant temperature gradient of "internal heat and external cold" in the Joule heating rapid sintering process. Furthermore, its complex gradient doping structure is difficult to accurately control and construct under ultrafast thermal shock conditions.

[0005] Therefore, there is an urgent need for an innovative preparation method for high-performance lithium-rich manganese-based cathode materials that can fundamentally improve the uniformity of Joule thermal synthesis and synergistically optimize the bulk phase and interface. Summary of the Invention

[0006] Based on the background technology, this invention provides a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, its preparation method and application, aiming to solve the inherent thermal gradient problem of the Joule heating method, so as to achieve simultaneous optimization of bulk structure and surface interface, and finally obtain a lithium-rich manganese-based cathode material with excellent comprehensive electrochemical performance.

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention are as follows.

[0008] On the one hand, this invention proposes a method for preparing a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, comprising the following steps: S1. Preparation of pretreated boron nitride: Boron nitride nanosheets were subjected to plasma treatment to introduce active functional groups including hydroxyl and amino groups on their surface to obtain pretreated boron nitride (hereinafter referred to as P-BN). In this operation, the pretreatment of boron nitride is an existing technology. Boron nitride (BN) has high thermal conductivity, chemical inertness, and a layered structure, which can theoretically be used to improve the temperature uniformity during Joule heat treatment. However, the chemical inertness of the original BN surface makes it difficult to form an effective interfacial bond with lithium-rich manganese-based materials, and its poor dispersibility limits its application. By pretreating its surface, hydroxyl and amino bifunctional groups are introduced to ensure that P-BN is uniformly dispersed and interfacially bonded in the lithium-rich manganese-based matrix, which facilitates bonding with subsequent raw materials. S2. Preparation of composite precursor powder: Nickel-cobalt-manganese hydroxide precursor, lithium source, TiO2, phosphorus source and pretreated boron nitride obtained in the previous step are mixed to obtain composite precursor powder. In this operation, the nickel-cobalt-manganese hydroxide precursor and the lithium source are both existing technologies. For example, the general chemical formula of the nickel-cobalt-manganese hydroxide precursor can be Ni. x Co y Mn 1-x-y (OH)2 and 0.1≤x≤0.2, 0.1≤y≤0.2, the lithium source can be Li2CO3; the mixing method of nickel cobalt manganese hydroxide precursor, lithium source, TiO2, phosphorus source and pretreated boron nitride can be existing technologies such as wet ball milling, liquid phase ultrasonic dispersion, etc., with wet ball milling preferred; S3. Sequential heat treatment: The composite precursor powder obtained in the previous step is subjected to conventional pre-calcination, first-section Joule heat treatment and second-section Joule heat treatment in sequence. The temperature of the second-section Joule heat treatment is at least 100°C higher than the temperature of the first-section Joule heat treatment to obtain crystalline material. In this process, conventional pre-calcination is mainly used to gently remove gases, allowing P-BN to initially bond with the surrounding materials, providing a stable foundation for Joule thermal shock. Then, through the first-stage Joule heat treatment, the thermally conductive network of P-BN promotes uniform heat diffusion, initiating the initial uniform crystallization of the bulk phase. Then, through the second-stage Joule heat treatment at a higher temperature and appropriate heat holding, the crystallization is further improved and its solid solution with dopant elements is promoted. P-BN acts as a "thermal homogenizer" to ensure a high degree of bulk phase uniformity. S4. Surface melting modification and quenching: Boron-lithium composite precursor is introduced into the surface of the crystalline material obtained in the previous step by impregnation or spraying. Then, the third-stage instantaneous Joule heat treatment is performed. The instantaneous high temperature causes the boron-lithium composite precursor to melt and spread on the surface of the crystalline material and react with the active sites on the P-BN surface to form a chemically bonded lithium boron oxide glassy coating layer. During quenching, rapid cooling "freezes" the lithium boron oxide glassy coating layer to form an optimized glassy interface, which is the final product.

[0009] The specific operation flow of the preparation method is as follows: Figure 1 As shown. Its preparation principle is as follows. Figure 2 As shown: Step S1 is mainly used to introduce hydroxyl and amino active bifunctional groups on the surface of boron nitride to improve its dispersion performance and interfacial bonding performance. Then, in step S2, composite precursor powder is prepared with nickel cobalt manganese hydroxide precursor, lithium source, TiO2 and phosphorus source. In step S3, volatiles are first removed by conventional pre-calcination and preliminary reaction is carried out. Then, degassing and preliminary crystallization are carried out by the first section of Joule heat treatment. Then, crystal growth and doping solid solution are promoted by the second section of Joule heat treatment. Finally, the lithium boron oxide glassy coating layer is formed by rapid quenching in step S4.

[0010] The preparation method proposed in this invention effectively solves the inherent thermal gradient problem of the Joule heating method by introducing surface-functionalized boron nitride and a programmed sequential process of "pre-calcination-two-segment Joule heat treatment-instantaneous melting and quenching", and simultaneously achieves "uniform thermally conductive framework" and "stable chemical interface".

[0011] Furthermore, in step S1, X-ray photoelectron spectroscopy shows that the hydroxyl content on the surface of the pretreated boron nitride is 5-15 at% and the amino content is 2-8 at%. This P-BN has sufficient reactivity while maintaining structural integrity and high thermal conductivity. To obtain the above pretreatment results, the following two plasma treatment methods can be used: Method 1 - Combining oxygen plasma treatment and ammonia plasma treatment, first performing oxygen plasma treatment and then performing ammonia plasma treatment. The conditions for oxygen plasma treatment are: power 50-200W, time 5-30min, oxygen flow rate 10-50sccm. The conditions for ammonia plasma treatment are: power 50-200W, time 10-60min, ammonia flow rate 10-50sccm. Method 2 - Mixed oxygen and ammonia plasma treatment, specifically, oxygen and ammonia are mixed at a volume ratio of 1:(1-3) and treated with a power of 100-300W for 10-30min.

[0012] In this technical solution, the hydroxyl content on the pretreated boron nitride surface can be 5at%, 5.1at%, 5.2at%, 5.3at%, 5.4at%, 5.5at%, 5.6at%, 5.7at%, 5.8at%, 5.9at%, 6at%, 6.5at%, 7at%, 8at%, 9at%, 10at%, 11at%, 12at%, 13at%, 14at%, 15at%, etc.; the amino content can be 2at%, 2.1at%, 2.2at%, 2.3at%, 2.4at%, 2.5at%, 2.6at%, 2.7at%, 2.8at%, 2.9at%, 3at%, 3.5at%, 4at%, 4.5at%, 5at%, 5.5at%, 6at%, 6.5at%, 7at%, 7.5at%, 8at%, etc.

[0013] Furthermore, in step S2, the pretreated boron nitride accounts for 0.5-2 wt% of the composite precursor powder. For example, it can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, etc. 0.5 wt% is the minimum effective amount, otherwise it will affect the overlap of the thermally conductive network. 2 wt% is the maximum amount introduced. If it is too much, it will not only fail to improve the thermal conductivity, but will also isolate electron conduction, and the capacity will begin to decrease. Preferably, the pretreated boron nitride accounts for 1-1.5 wt% of the composite precursor powder, such as 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, etc. This amount of pretreated boron nitride forms a through-thermal conductive network, which maximizes the thermal conductivity. At the same time, it works synergistically with the dopant phosphorus source and TiO2 to help achieve bulk-interface integration and toughness, and obtain the best comprehensive electrochemical performance.

[0014] Furthermore, in step S2, the phosphorus source is (NH4)H2PO4, the TiO2 is nano-TiO2, the proportion of (NH4)H2PO4 in the composite precursor powder is 0.5-1.5wt%, and the proportion of nano-TiO2 in the composite precursor powder is 0.2-0.5wt%.

[0015] In this technical solution, Ti is used. 4+ With PO4 3- Co-doping of cations and anions, Ti 4+ Limiting the additions to the above range helps optimize Li +The diffusion pathway forms Ti-OB bonds with the -OH groups on the P-BN surface, enhancing the interface and stabilizing the structure; PO4 3- Limiting the addition to the above range helps to weaken the TM-O bond, inhibit oxygen loss, and form hydrogen bonds with -NH2 on the P-BN surface, promoting dispersion; Joule heat treatment rapidly raises the temperature, promoting the simultaneous reaction of P-BN, (NH4)H2PO4, and nano-TiO2 to form a chemically bonded composite structure.

[0016] Furthermore, in step S3, the conventional pre-calcination is carried out in an air or oxygen atmosphere, with a calcination temperature of 450-500℃, a heating rate of 2-5℃ / min, and a holding time of 3-6h; the first section of Joule heat treatment is carried out in a flowing dry air atmosphere, using a DC constant current mode, with a current density of 10-50A / cm². 2 The heating time is 2-4 seconds, and power is immediately cut off for cooling after reaching 750-800℃, i.e., the holding time is 0 seconds; the second section of Joule heat treatment is carried out in a flowing dry air atmosphere, using DC constant current mode, with a current density of 55-100 A / cm. 2 The heating time is 3-5 seconds, and after reaching 900-950℃, it is held for 8-12 seconds; Preferably, the first section Joule heat treatment and the second section Joule heat treatment are performed in the same equipment.

[0017] Furthermore, in step S4, the boron-lithium composite precursor is a mixture of trimethyl borate and lithium acetate in anhydrous ethanol, with a molar ratio of B to Li of 0.5-2.

[0018] In this technical solution, the molar ratio of B to Li in the boron-lithium composite precursor can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.

[0019] Furthermore, in step S4, the instantaneous Joule heat treatment in the third section is carried out in a mixed atmosphere of argon and oxygen, using a capacitor single-pulse discharge mode with a capacitor capacity of 50-200mF, a charging voltage of 50-150V, a single-pulse energy density of 0.5-2KJ / g, and a pulse width of 50-100ms, so that the instantaneous temperature of the powder surface reaches 700-800℃. Preferably, the volume of oxygen is 1%-5% of the volume of argon; Preferably, the quenching is carried out in liquid nitrogen or ice water, with a cooling rate ≥100℃ / s.

[0020] On the other hand, the present invention also proposes a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride prepared according to the above preparation method.

[0021] Furthermore, this high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride has a high thermal conductivity network in its bulk phase composed of pretreated boron nitride, and a lithium boron oxide glassy composite coating layer generated in situ and connected to the pretreated boron nitride by BOB chemical bonds on its surface. Preferably, the matrix is ​​Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 and doped with P and Ti.

[0022] In addition, the present invention also proposes a lithium-ion battery, including a positive electrode sheet, wherein the positive active material on the positive electrode sheet contains the above-mentioned high-performance lithium-rich manganese-based positive electrode material based on pretreated boron nitride; as for other conventional components of lithium-ion batteries such as negative electrode sheet, separator, and electrolyte, conventional technical means are used.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: 1. By introducing surface-functionalized boron nitride (P-BN) as a bulk thermally conductive framework to construct a high thermal conductivity network, the "internal heat and external cold" is transformed into "rapid and uniform heating", so that the bulk temperature gradient is no more than 50℃, ensuring the spatial consistency of the synthesis reaction and fundamentally solving the temperature gradient problem in the Joule heating method. 2. For the first time, a sequential heat treatment method of "conventional pre-calcination and two-stage heat treatment" was proposed. First, the precursor was stabilized by "conventional pre-calcination". Then, rapid and uniform crystallization initiation was achieved by "first-stage Joule heat treatment". Then, high-temperature "second-stage Joule heat treatment" was used to complete high-temperature perfection and doping solid solution. This achieved the distribution control of "degassing-nucleation-growth". The synergistic effect of each stage not only ensured the heat treatment effect, but also compressed the traditional sintering time of several hours to less than 20 seconds (excluding conventional pre-calcination), which greatly reduced energy consumption and improved production efficiency. 3. Through instantaneous Joule heat treatment and quenching in the third section, controllable fabrication of a glassy lithium boron oxide coating layer with a thickness of less than 1 μm was achieved. This interface optimization layer helps to improve the Li + Increase electrical conductivity and reduce interface impedance; 4. P-BN is connected to the glassy coating layer of lithium boron oxide via BOB bonds to form a complete chemical bonding network from the bulk phase to the surface, which significantly improves the cycling stability.

[0024] In summary, through innovative material design and multi-step synergistic processes, the resulting high-performance lithium-rich manganese-based cathode material possesses a high thermal conductivity enhancement network composed of pretreated boron nitride, ensuring excellent structural and compositional uniformity. The surface exhibits a stable, high ionic conductivity lithium boron oxide glassy coating layer, which is tightly bonded to the bulk high thermal conductivity enhancement network via chemical bonds. This integrated design of a "uniform thermally conductive bulk framework" and a "stable chemical interface" results in a product with high specific capacity, high initial efficiency, excellent long-cycle stability, significantly suppressed voltage decay, and good rate performance, overcoming the performance shortcomings of traditional lithium-rich materials and existing Joule-thermal synthesis materials. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the operation process of a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride proposed in this invention.

[0027] Figure 2 for Figure 1 A schematic diagram illustrating the principle.

[0028] Figure 3 The following images are of the product obtained in Example 1: A, SEM image; B, TEM image.

[0029] Figure 4 The first charge-discharge curve of the coin cell obtained in Example 1 at a rate of 0.1C is shown.

[0030] Figure 5 The voltage decay curve of the button cell obtained in Example 1 is shown.

[0031] Figure 6 This is a comparison chart of the first charge-discharge curves of the coin cells obtained in Example 1 and Comparative Examples 1, 2, and 3 at a 0.1C rate.

[0032] Figure 7 This is a performance comparison chart of the button cells obtained in Example 1 and Comparative Examples 1, 2, and 3 after 100 cycles at a 1C rate.

[0033] Figure 8 This is a comparison chart of the voltage decay of the button cells obtained in Example 1 and Comparative Examples 1, 2, and 3.

[0034] Figure 9The images are SEM images of the products obtained in Example 1 and Comparative Example 1 after 100 cycles at 1C magnification.

[0035] Figure 10 A comparison of the first charge-discharge curves of the coin cells obtained in Example 1 with those of Comparative Examples 5 and 6 at a rate of 0.1C.

[0036] Figure 11 Performance comparison chart of the button cells obtained in Example 1 and Comparative Examples 5 and 6 after 100 cycles at 1C rate.

[0037] Figure 12 Comparison of voltage decay of coin cells obtained in Example 1 with those in Comparative Examples 5 and 6. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0039] All chemical raw materials used in the following examples and comparative examples are commercially available, and all apparatus and operations involved are conventional in the art.

[0040] Example 1

[0041] A high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride was prepared according to the following steps: S1. Preparation of pretreated boron nitride P-BN Boron nitride nanosheets were subjected to plasma treatment with a mixture of oxygen and ammonia at a volume ratio of 1:2 (220 W) for 18 min to obtain pretreated boron nitride. X-ray photoelectron spectroscopy analysis showed that the surface content of the pretreated boron nitride was 12.5 at% hydroxyl content and 4.8 at% amino content. S2. Preparation of composite precursor powder According to Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 Weigh out 10g of Ni (stoichiometric amount of O2). 0.13 Mn 0.54 Co 0.13(OH)2, 4.68g Li2CO3, 0.04g nano TiO2 (0.27wt% in the raw material), 0.12g (NH4)H2PO4 (0.8wt% in the raw material) and 0.15g P-BN (1wt% in the raw material) were added to anhydrous ethanol, ball-milled at 300rpm for 6h, and then vacuum dried at 80℃ for 12h. The composite powder M1 was obtained by passing through a 200-mesh sieve. S3, Sequential heat treatment The composite powder M1 was subjected to conventional pre-calcination, first-stage Joule heat treatment, and second-stage Joule heat treatment in sequence. The specific operations were as follows: M1 was placed in a tube furnace and heated to 480°C at 3.5°C / min under air atmosphere, and held for 4 hours to obtain P0; 0.2g of P0 was taken and spread on carbon cloth, and heated to 30A / cm under dry air atmosphere. 2 The material was heated to approximately 780°C within 3 seconds using a current of 80 A / cm², and then immediately cooled by cutting off the power. P1 was then ground to obtain P1. P1 was then spread onto new carbon cloth and heated in dry air at 80 A / cm². 2 The current was used to heat the material to about 920°C within 4 seconds, and after holding it at that temperature for 10 seconds, the power was cut off and the material was cooled and ground to obtain P2. S4, Surface melting and quenching P2 was immersed in an ethanol solution of trimethyl borate and lithium acetate (0.1 mol / L for trimethyl borate and 0.15 mol / L for lithium acetate) for 30 min, then removed and dried to obtain P2-BLi. P2-BLi was then spread on carbon cloth and subjected to a single-pulse discharge with a capacitance of 120 mF and a charging voltage of 100 V under an Ar and O2 atmosphere (O2 being 2% of the volume of Ar). The single-pulse energy density was 1 KJ / g and the pulse width was 80 ms, causing the surface to reach approximately 750 °C instantaneously. The surface was then rapidly cooled in liquid nitrogen to obtain the final product.

[0042] like Figure 1 As shown: SEM images show that the particle size of the obtained product is approximately 6-10 μm; TEM images show that the bulk phase of the obtained product has a layered structure with a lattice spacing of 0.48 nm and a glassy coating of lithium boron oxide on the surface.

[0043] Example 2

[0044] Compared with Example 1: the amount of P-BN added in step S2 was adjusted from 0.15g to 0.075g, so that the proportion of P-BN in the composite precursor powder was adjusted from 1wt% to 0.5wt%, and the rest remained the same as in Example 1.

[0045] Example 3

[0046] Compared with Example 1: the amount of P-BN added in step S2 was adjusted from 0.15g to 0.18g, so that the proportion of P-BN in the composite precursor powder was adjusted from 1wt% to 1.2wt%, and the rest remained the same as in Example 1.

[0047] Example 4

[0048] Compared with Example 1: the amount of P-BN added in step S2 was adjusted from 0.15g to 0.226g, so that the proportion of P-BN in the composite precursor powder was adjusted from 1wt% to 1.5wt%, and the rest remained the same as in Example 1.

[0049] Example 5

[0050] Compared with Example 1: the amount of P-BN added in step S2 was adjusted from 0.15g to 0.303g, so that the proportion of P-BN in the composite precursor powder was adjusted from 1wt% to 2wt%, and the rest remained the same as in Example 1.

[0051] Example 6

[0052] Compared with Example 1, the amount of nano TiO2 added was adjusted from 0.04g to 0.03g, so that the proportion of nano TiO2 in the composite precursor powder was adjusted from 0.27wt% to 0.2wt%, while the rest remained the same as in Example 1.

[0053] Example 7

[0054] Compared with Example 1, the amount of nano TiO2 added was adjusted from 0.04g to 0.045g, so that the proportion of nano TiO2 in the composite precursor powder was adjusted from 0.27wt% to 0.3wt%, while the rest remained the same as in Example 1.

[0055] Example 8

[0056] Compared with Example 1, the amount of nano TiO2 added was adjusted from 0.04g to 0.06g, so that the proportion of nano TiO2 in the composite precursor powder was adjusted from 0.27wt% to 0.4wt%, while the rest remained the same as in Example 1.

[0057] Example 9

[0058] Compared with Example 1, the amount of nano TiO2 added was adjusted from 0.04g to 0.075g, so that the proportion of nano TiO2 in the composite precursor powder was adjusted from 0.27wt% to 0.5wt%, while the rest remained the same as in Example 1.

[0059] Example 10

[0060] Compared with Example 1, the amount of (NH4)H2PO4 added was adjusted from 0.12g to 0.075g, so that the proportion of (NH4)H2PO4 in the composite precursor powder was adjusted from 0.8wt% to 0.5wt%, while the rest remained the same as in Example 1.

[0061] Example 11

[0062] Compared with Example 1, the amount of (NH4)H2PO4 added was adjusted from 0.12g to 0.15g, so that the proportion of (NH4)H2PO4 in the composite precursor powder was adjusted from 0.8wt% to 1wt%, and the rest remained the same as in Example 1.

[0063] Example 12

[0064] Compared with Example 1, the amount of (NH4)H2PO4 added was adjusted from 0.12g to 0.18g, so that the proportion of (NH4)H2PO4 in the composite precursor powder was adjusted from 0.8wt% to 1.2wt%, while the rest remained the same as in Example 1.

[0065] Example 13

[0066] Compared with Example 1, the amount of (NH4)H2PO4 added was adjusted from 0.12g to 0.227g, so that the proportion of (NH4)H2PO4 in the composite precursor powder was adjusted from 0.8wt% to 1.5wt%, while the rest remained the same as in Example 1.

[0067] Example 14

[0068] Compared with Example 1, step S2 remains unchanged, and the rest is as follows: The operation of step S1 was adjusted as follows: boron nitride nanosheets were subjected to plasma treatment with oxygen and ammonia in a volume ratio of 1:1 at a power of 300W for 10 minutes to obtain pretreated boron nitride; X-ray photoelectron spectroscopy determined that the hydroxyl content on the surface of the pretreated boron nitride was 14.7 at% and the amino content was 2.1 at%. Step S3 is adjusted as follows: the composite powder M1 is subjected to conventional pre-calcination, first-section Joule heat treatment, and second-section Joule heat treatment in sequence. The specific operations are as follows: M1 is placed in a tube furnace and heated to 500℃ at 2°C / min in air atmosphere, and held for 6 hours to obtain P0; 0.2g of P0 is taken and spread on carbon cloth, and heated to 50A / cm in dry air. 2 The material was heated to approximately 750°C within 3 seconds using a current of 55 A / cm², and then immediately cooled by cutting off the power. P1 was then ground to obtain P1. P1 was then spread onto new carbon cloth and heated in dry air at 55 A / cm². 2 The current was used to heat the material to about 900°C within 4 seconds, and after holding it at that temperature for 12 seconds, the power was cut off and the material was cooled. The material was then ground to obtain P2. The operation of step S4 is adjusted as follows: P2 is immersed in an ethanol solution of trimethyl borate and lithium acetate (the concentration of trimethyl borate is 0.1 mol / L and the concentration of lithium acetate is 0.05 mol / L), and after 30 min, it is taken out and dried to obtain P2-BLi; P2-BLi is spread on carbon cloth, and under an Ar and O2 atmosphere (O2 is 1% of the volume of Ar), a single-pulse discharge is performed with a capacitance of 50 mF and a charging voltage of 150 V. The single-pulse energy density is 2 KJ / g and the pulse width is 50 ms, so that the surface layer instantly reaches about 800°C. Then it is placed in ice water for rapid cooling to obtain the final product.

[0069] Example 15

[0070] Compared with Example 1, step S2 remains unchanged, and the rest is as follows: The operation of step S1 was adjusted as follows: boron nitride nanosheets were subjected to plasma treatment with oxygen and ammonia in a volume ratio of 1:3 at a power of 100W for 30 minutes to obtain pretreated boron nitride; X-ray photoelectron spectroscopy determined that the hydroxyl content on the surface of the pretreated boron nitride was 5.3 at% and the amino content was 7.8 at%. Step S3 is adjusted as follows: the composite powder M1 is subjected to conventional pre-calcination, first-section Joule heat treatment, and second-section Joule heat treatment in sequence. Specifically, M1 is placed in a tube furnace and heated to 450°C at 5°C / min in air atmosphere, and held for 3 hours to obtain P0; 0.2g of P0 is taken and spread on carbon cloth, and heated in dry air at 10A / cm 2 The material was heated to approximately 800°C within 3 seconds by a current of 100 A / cm², and then immediately cooled by cutting off the power. P1 was then ground to obtain P1. P1 was then spread onto new carbon cloth and heated in dry air at 100 A / cm². 2 The current was used to heat the material to about 950°C within 4 seconds, and after holding it at that temperature for 8 seconds, the power was cut off and the material was cooled. The material was then ground to obtain P2. The operation of step S4 is adjusted as follows: P2 is immersed in an ethanol solution of trimethyl borate and lithium acetate (the concentration of trimethyl borate is 0.1 mol / L and the concentration of lithium acetate is 0.2 mol / L), and after 30 min, it is taken out and dried to obtain P2-BLi; P2-BLi is spread on carbon cloth, and under an Ar and O2 atmosphere (O2 is 5% of the volume of Ar), a single-pulse discharge is performed with a capacitance of 200 mF and a charging voltage of 50 V. The single-pulse energy density is 0.5 KJ / g and the pulse width is 100 ms, so that the surface layer instantly reaches about 700°C. Then it is placed in liquid nitrogen for rapid cooling to obtain the final product.

[0071] Comparative Example 1 Compared to Example 1, P-BN was not added, but everything else was the same as in Example 1.

[0072] Comparative Example 2 Compared to Example 1, the pretreated boron nitride P-BN was adjusted to an equal amount of original boron nitride nanosheets BN, while all other aspects remained the same as in Example 1.

[0073] Comparative Example 3 Compared to Example 1, the P-BN was replaced with an equal amount of multi-walled carbon nanotubes, while all other aspects remained the same as in Example 1.

[0074] Comparative Example 4 Compared with Example 1, the trimethyl borate in step S4 was changed to an equal amount of tetraethyl orthosilicate, that is, the "boron-lithium composite precursor" was changed to the "silicon-lithium composite precursor", and the rest remained the same as in Example 1.

[0075] Comparative Example 5 Compared with Example 1, step S3 does not involve the first-stage Joule heat treatment. Instead, the product after conventional pre-calcination is directly subjected to the second-stage Joule heat treatment. All other steps remain the same as in Example 1.

[0076] Comparative Example 6 Compared with Example 1, the temperatures of the first and second Joule heat treatments were both adjusted to 850°C, while the rest remained the same as in Example 1.

[0077] The products obtained in the above examples and comparative examples were used as positive electrode active materials, and were mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1 to form a coin cell. The counter electrode was a lithium metal sheet, the separator was a microporous PP film, and the electrolyte was a 1 M LiPF6 solution (solvent: DEC, EC in a volume ratio of 7:3). Assembly was carried out in a glove box with water and oxygen content both less than 0.1 ppm. After assembly, the battery was allowed to stand for 12 hours to allow the electrolyte to fully wet the electrodes. The electrochemical performance was tested using a Blue Battery testing system within a voltage window of 2.0-4.8 V (specific operations were performed using conventional techniques in the art). The test environment temperature was 25±1℃. The results are shown in Table 1.

[0078]

[0079] like Figures 3-12 As shown in Table 1: (1) The test results of Examples 1-15 show that the high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride prepared by the present invention has excellent comprehensive electrochemical performance. The first-cycle coulombic efficiency at 0.1C is 94.2%-96.1%, the first-cycle coulombic efficiency at 1C is 88.2%-93.5%, the capacity retention rate after 100 cycles at 1C is 88%-96.5%, and the voltage decay is controlled at 260-320mV. Among them, the product obtained in Example 1 has the best performance.

[0080] Furthermore, a comparison of the test results from Examples 1-5 reveals that as the P-BN addition increases from 0.5 wt% to 2 wt%, the overall electrochemical performance of the material exhibits a trend of first increasing and then decreasing. Example 1 (P-BN addition 1.0 wt%) shows the best performance, with a first-cycle coulombic efficiency of 96.1% at 0.1C, a capacity retention rate of 95.2% after 100 cycles at 1C, and a voltage decay of only 260 mV. Examples 3 (1.2 wt%) and 4 (1.5 wt%) show the next best performance, while Examples 2 (0.5 wt%) and 5 (2 wt%) show relatively poor performance. It is evident that when the P-BN addition is low (0.5 wt%), it is difficult to form a complete high thermal conductivity network in the bulk phase, resulting in insufficient temperature homogenization and uneven bulk crystallization. When the addition is high (2 wt%), excessive insulating BN hinders electron conduction, reducing the material's capacity and rate performance, and may also agglomerate, affecting interfacial stability. In summary, the P-BN addition amount can be controlled within the range of 0.5-2wt% to achieve better results than the comparative example, with 1.0-1.5wt% being the preferred range and 1.0wt% being the optimal value.

[0081] Furthermore, a comparison of the test results from Examples 1 and 6-9 shows that the amount of nano-TiO2 added has a significant impact on the performance of the cathode material. Example 1 (TiO2 content 0.27wt%) exhibits the best performance, followed by Examples 7 (0.3wt%) and 8 (0.4wt%), while Examples 6 (0.2wt%) and 9 (0.5wt%) show relatively poor performance. Appropriate amounts of TiO2... 4+ Doping (0.2-0.5 wt%) can enter the crystal lattice and partially replace Mn. 4+ Increase interlayer spacing and optimize Li + Diffusion path; simultaneously Ti 4+ It can form Ti-OB chemical bonds with the hydroxyl groups on the P-BN surface, enhancing interfacial bonding and stabilizing the crystal structure; when the doping concentration is below 0.2wt%, the modification effect is not obvious; when the doping concentration is above 0.5wt%, excess Ti… 4+ Possibly occupying Li + These sites hinder lithium-ion transport and introduce impurity phases, thus degrading electrochemical performance. The preferred amount of nano-TiO2 added in this invention is 0.2-0.5 wt%, more preferably 0.27-0.3 wt%.

[0082] Furthermore, a comparison of the test results of Example 1 and Examples 10-13 shows that the amount of (NH4)H2PO4 added also has a significant impact on the performance of the cathode material. Example 1 (0.8 wt%) exhibits the best performance, followed by Examples 11 (1.0 wt%) and 12 (1.2 wt%), while the performance of Examples 10 (0.5 wt%) and 13 (1.5 wt%) decreases. The reason for this is that an appropriate amount of PO4... 3- Doping (0.5-1.5 wt%) can weaken the transition metal-oxygen (TM-O) bond energy, suppress the irreversible loss of lattice oxygen during charging and discharging, and stabilize the crystal structure; at the same time, PO4 3- It can form hydrogen bonds with the amino groups on the surface of P-BN, promoting the uniform dispersion of P-BN in the matrix. When its addition amount is less than 0.5 wt%, the stabilizing effect is insufficient; when its addition amount is more than 1.5 wt%, excess phosphate may form inert impurity phases such as Li3PO4, increasing interfacial impedance and reducing capacity and cycle stability. Therefore, the present invention limits the addition amount of (NH4)H2PO4 to 0.5-1.5 wt%, preferably 0.8-1.0 wt%.

[0083] A comparison of the test results of Example 1 with Comparative Examples 1, 2, and 3 shows that Comparative Example 1 (without P-BN) exhibits a capacity retention of only 78.6% after 100 cycles at 1C, with a voltage drop as high as 440mV, significantly inferior to Example 1. This demonstrates that without a high thermal conductivity network, the thermal gradient problem in Joule heating significantly leads to inhomogeneous bulk crystallization and poor cycle stability. Furthermore, as... Figure 9 As shown: After cycling, the surface of the product obtained in Example 1 remained smooth, indicating its structural stability, which corresponds to a high capacity retention rate. In contrast, the surface of Comparative Example 1 cracked, indicating large volume changes and poor structural stability during charge and discharge, resulting in rapid capacity loss. Comparative Example 2 (with added untreated raw BN) showed better capacity retention (85.3%) and voltage decay (380mV) than Comparative Example 1, but was still significantly worse than Example 1. This is because the raw BN surface is chemically inert, making it difficult to form an effective interface with the matrix, resulting in poor dispersibility and an incomplete thermally conductive network. Comparative Example 3 (with added multi-walled carbon nanotubes) performed the worst, with a capacity retention rate of only 80.1% and a voltage decay of 450mV. This is because while carbon nanotubes have good electrical conductivity, their thermal conductivity is inferior to BN, and they may undergo side reactions with the lithium-rich matrix at high temperatures, damaging the material structure. The above comparison fully demonstrates the key role of pretreated boron nitride (P-BN) in constructing a bulk high thermal conductivity network. Its surface hydroxyl and amino functional groups ensure good compatibility and chemical bonding with the matrix, thereby effectively solving the thermal gradient problem of the Joule heating method.

[0084] A comparison of the test results of Example 1 with those of Comparative Examples 5 and 6 shows that Comparative Example 5, which skips the first stage of Joule heat treatment and directly undergoes the second stage of high-temperature treatment, exhibits significantly deteriorated performance. This indicates that without the low-temperature pre-crystallization step (first stage), the precursor is directly exposed to high-temperature Joule thermal shock, resulting in a violent and uncontrollable reaction, uneven nucleation of the bulk phase, and poor crystal integrity. Comparative Example 6, with the same Joule heat treatment temperature for both stages, also performs worse than Example 1. This demonstrates that a gradient heating strategy (750-800℃ in the first stage to initiate initial crystallization, and 900-950℃ in the second stage to perfect crystal growth and doping solid solution) is crucial for achieving stepwise control of "degassing-nucleation-growth," as a single temperature cannot simultaneously meet the dual requirements of uniform nucleation and high-temperature solid solution. The unique "pre-calcination-two-stage Joule heat treatment" sequential mode of this invention, through precise temperature gradient design, ensures high homogeneity of the bulk phase and structural stability.

[0085] A comparison of the test results of Example 1 and Comparative Example 4 shows that although the performance of the material improved after replacing the "boron-lithium composite precursor" used for surface modification with the "silicon-lithium composite precursor" (Comparative Example 4), the cycling performance and voltage decay suppression effect were significantly worse than those of Example 1. This demonstrates that the BOB chemical bonding network formed by the boron-lithium precursor is crucial for interfacial stability. The present invention uses a boron-lithium composite precursor, which not only forms a high-ionic-conductivity lithium boron oxide glassy coating layer, but more importantly, achieves a complete chemical bonding network from the bulk phase to the surface through BOB bonds and P-BN, significantly improving interfacial stability and structural integrity, thereby obtaining superior cycling performance and voltage decay suppression effect.

[0086] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

Claims

1. A method for preparing a high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, characterized in that: The following steps are included: S1. Preparation of pretreated boron nitride: Boron nitride nanosheets were subjected to plasma treatment to introduce active functional groups including hydroxyl and amino groups on their surface to obtain pretreated boron nitride. S2. Preparation of composite precursor powder: Nickel-cobalt-manganese hydroxide precursor, lithium source, TiO2, phosphorus source and pretreated boron nitride obtained in the previous step are mixed to obtain composite precursor powder. S3. Sequential heat treatment: The composite precursor powder obtained in the previous step is subjected to conventional pre-calcination, first-section Joule heat treatment and second-section Joule heat treatment in sequence. The temperature of the second-section Joule heat treatment is at least 100°C higher than the temperature of the first-section Joule heat treatment to obtain crystalline material. S4. Surface melting modification and quenching: A boron-lithium composite precursor is introduced onto the surface of the crystalline material obtained in the previous step, followed by a third-stage instantaneous Joule heat treatment, and then quenching to obtain the final product.

2. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 1, characterized in that: In step S1, X-ray photoelectron spectroscopy was used to determine that the hydroxyl content on the pretreated boron nitride surface was 5-15 at% and the amino content was 2-8 at%. Preferably, the plasma treatment includes oxygen plasma treatment and ammonia plasma treatment. The conditions for oxygen plasma treatment are: power 50-200W, time 5-30min, and oxygen flow rate 10-50sccm. The conditions for ammonia plasma treatment are: power 50-200W, time 10-60min, and ammonia flow rate 10-50sccm. Preferably, the plasma treatment employs an oxygen-ammonia mixed plasma treatment, with the following specific conditions: oxygen to ammonia volume ratio of 1:(1-3), power of 100-300W, and time of 10-30min.

3. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 1, characterized in that: In step S2, the pretreated boron nitride accounts for 0.5-2 wt% of the composite precursor powder; Preferably, the pretreated boron nitride accounts for 1-1.5 wt% of the composite precursor powder.

4. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 3, characterized in that: In step S2, the phosphorus source is (NH4)H2PO4, the TiO2 is nano TiO2, the proportion of (NH4)H2PO4 in the composite precursor powder is 0.5-1.5 wt%, and the proportion of nano TiO2 in the composite precursor powder is 0.2-0.5 wt%.

5. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 1, characterized in that: In step S3, the conventional pre-calcination is carried out in an air or oxygen atmosphere, with a calcination temperature of 450-500℃, a heating rate of 2-5℃ / min, and a holding time of 3-6h; the first section Joule heat treatment is carried out in a flowing dry air atmosphere, using a DC constant current mode, with a current density of 10-50A / cm. 2 The heating time is 2-4 seconds, and power is immediately cut off for cooling after reaching 750-800℃; the second section of Joule heat treatment is carried out in a flowing dry air atmosphere, using a DC constant current mode with a current density of 55-100 A / cm². 2 The heating time is 3-5 seconds, and after reaching 900-950℃, it is held for 8-12 seconds.

6. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 1, characterized in that: In step S4, the boron-lithium composite precursor is a mixture of trimethyl borate and lithium acetate in anhydrous ethanol, with a molar ratio of B to Li of 0.5-2.

7. The method for preparing high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 1, characterized in that: In step S4, the instantaneous Joule heat treatment in the third section is carried out in a mixed atmosphere of argon and oxygen, using a capacitor single-pulse discharge mode with a capacitor capacity of 50-200mF, a charging voltage of 50-150V, a single-pulse energy density of 0.5-2KJ / g, and a pulse width of 50-100ms, so that the instantaneous temperature of the powder surface reaches 700-800℃. Preferably, the volume of oxygen is 1%-5% of the volume of argon; Preferably, the quenching is performed using liquid nitrogen or ice water.

8. A high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride, prepared according to the preparation method of any one of claims 1-7.

9. The high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride according to claim 8, characterized in that: Its bulk phase has a high thermal conductivity network composed of pretreated boron nitride, and its surface has a lithium boron oxide glassy composite coating layer generated in situ and connected to the pretreated boron nitride by BOB chemical bonds; Preferably, the matrix is ​​Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 and doped with P and Ti.

10. A lithium-ion battery, characterized in that: It includes the high-performance lithium-rich manganese-based cathode material based on pretreated boron nitride as described in claim 8 or 9.

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