A method for preparing a P2-type high-temperature phase layered oxide positive electrode material by low-temperature calcination

Abstract

The application relates to a method for preparing a P2-type high-temperature phase layered oxide positive electrode material through low-temperature calcination. x Li y TM 1‑y O2, wherein TM represents a transition metal element, preferably at least one of Mn, Ni, Fe, Mg, Ca, Al and Co; 0.6<=x<=0.8 and 0<=y<=0.3; the method comprises the following steps: (1) according to the molecular formula of the P2-type high-temperature phase layered oxide positive electrode material Na x TM O2, sodium sources, lithium sources and transition metal sources are weighed, mixed, pressed to obtain a preform; (2) the obtained preform is calcined to obtain the P2-type high-temperature phase layered oxide positive electrode material; the calcination comprises the following steps: high-temperature calcination first and then low-temperature calcination; or the calcination comprises the following steps: low-temperature calcination first, high-temperature calcination and then second low-temperature calcination.

Description

Technical Field

[0001] This invention relates to a method for preparing P2-type high-temperature phase sodium ion layered cathode material by low-temperature calcination and a sodium ion battery containing the cathode, belonging to the field of energy materials and energy storage. Background Technology

[0002] Low-cost, high-performance sodium-ion batteries are a crucial technology for large-scale energy storage. The cathode is a key component determining the energy density of sodium-ion batteries, with layered oxides attracting significant attention due to their diverse composition and high specific capacity. Solid-state synthesis is simple to operate and allows for large-scale industrial production, making it one of the most commonly used methods for synthesizing layered oxides. P3 and O3 types of sodium-ion layered oxide cathode materials have been extensively studied, each with its own advantages. Compared to O3-type layered oxide cathode materials, P2-type high-temperature phase cathode materials have a simpler phase transition structure and better cycle stability. However, the high-temperature (>900℃) and long-term (>12h) calcination process in traditional solid-state methods not only increases production costs but also exacerbates particle melting, agglomeration, and pulverization, which is detrimental to rapid sodium ion insertion / extraction and electrochemical cycle stability. Therefore, optimizing particle size and morphology to improve rate performance and extend cycle life is a critical issue to be addressed in the commercialization of P2-type high-temperature phase layered cathode materials.

[0003] To address the problem of particle melting and agglomeration during the preparation of P2-type high-temperature layered oxide cathode materials using traditional solid-state synthesis methods, researchers have adopted a series of measures: Chinese patent CN116093307B utilizes Mn... x Ni y (OH)₂ pre-precipitation achieves atomic-level mixing, combined with two calcinations to prepare a uniform, sheet-like single-crystal P₂-type high-temperature layered cathode material; Chinese Patent 1 (Publication No. CN116177606) discloses a rapid high-temperature synthesis method for P₂′-Na 0.67 The method for preparing MnO2 cathode materials involves two calcinations (with an energizing current of 47-49 A and a duration of 30-60 s) to produce fine single-crystal particles of several hundred nanometers. While this method effectively optimizes the size and morphology of the cathode particles and improves electrochemical performance, it involves complex processes, increases production costs, and hinders large-scale production. Therefore, developing an easy-to-operate, low-cost, and high-efficiency solid-state preparation method for P2-type cathode materials, while maintaining high crystallinity, to reduce calcination temperature, shorten calcination time, improve the size and morphology of cathode particles, and optimize electrochemical performance, has high practical value for the large-scale development and application of high-energy-density sodium-ion cathode materials. Summary of the Invention

[0004] To address the problems of high production cost (calcination temperature ~900℃, holding time ~20h), severe particle melting and agglomeration, and poor size and morphology uniformity in the conventional solid-state method for preparing P2-type high-temperature phase layered oxide cathode materials, this invention provides a method for preparing P2-type high-temperature phase sodium ion layered cathode materials by low-temperature calcination and a sodium ion battery containing the cathode.

[0005] On one hand, this invention provides a method for preparing P2-type high-temperature phase layered oxide cathode material by low-temperature calcination, wherein the molecular formula of the P2-type high-temperature phase layered oxide cathode material is Na. x Li y TM 1-y O2, where TM refers to a transition metal element, preferably at least one of Mn, Ni, Fe, Mg, Ca, Al, and Co; 0.6≤x≤0.8, 0≤y≤0.3;

[0006] The method includes:

[0007] (1) According to the molecular formula of P2 type high-temperature phase layered oxide cathode material Na x TMO2 is weighed, and sodium source, lithium source and transition metal source are mixed and then pressed to obtain a preform;

[0008] (2) The obtained preform is calcined to obtain the P2 type high-temperature phase layered oxide cathode material;

[0009] The calcination includes: first high-temperature calcination followed by low-temperature calcination;

[0010] Alternatively, the calcination may include: first undergoing a low-temperature calcination, then a high-temperature calcination, and finally a second low-temperature calcination.

[0011] In this invention, the brief high-temperature process during the calcination step promotes crystal nucleus formation and ensures high crystallinity; the low-temperature calcination process is beneficial for uniform grain growth. The assisted low-temperature calcination method provided by this invention reduces production energy consumption while ensuring high material crystallinity; the uniform and fine primary particles shorten the sodium ion transport path, which is beneficial for improving the rate performance of the cathode material; the pulverization phenomenon of secondary particles is alleviated, reducing crack formation during electrochemical cycling, effectively inhibiting electrolyte corrosion of the active material, and improving the cycle stability of the cathode material. Therefore, the P2-type high-temperature phase layered oxide cathode material prepared using this invention has high reversible specific capacity, good rate performance, and long cycle life. In summary, the solid-state assisted low-temperature calcination synthesis process provided by this invention is easy to operate, has a short cycle time, low energy consumption, and high efficiency, and has strong commercial application value in the field of sodium-ion batteries.

[0012] Preferably, in step (1), the sodium source includes at least one of sodium carbonate, sodium oxide, and sodium hydroxide; the lithium source includes at least one of lithium carbonate, lithium oxide, and lithium hydroxide; and the transition metal source includes at least one of carbonates of transition metal elements, oxides of transition metal elements, and hydroxides of transition metal elements.

[0013] Preferably, the sodium source is Na2CO3 and the lithium source is LiOH·H2O.

[0014] Preferably, in step (1), the mixing method is grinding; preferably, the grinding speed is 100-1500 rpm, the grinding time is 15 min-6 h, and the solvent used is deionized water, anhydrous ethanol or isopropanol.

[0015] Preferably, the grinding includes: manual grinding, ball milling, or sand milling;

[0016] More preferably, the parameters of the ball milling process include: a rotation speed of 200-300 rpm, a time of 2-4 h, and a solvent of deionized water, anhydrous ethanol, or isopropanol.

[0017] More preferably, the parameters of the sand milling process include: a rotation speed of 500 to 1000 rpm, a time of 30 min to 2 h, and a solvent of deionized water, anhydrous ethanol, or isopropanol.

[0018] The drying temperature is 50–200°C;

[0019] Preferably, when deionized water is selected as the solvent, the drying temperature is 100–150°C;

[0020] Preferably, when anhydrous ethanol or isopropanol is selected as the solvent, the drying temperature is 60–90°C. In this invention, grinding, mixing, and drying pre-processing facilitate the uniform dispersion of each element.

[0021] Preferably, in step (1), the amount of sodium source used is 1-15 wt% in excess based on the stoichiometric ratio to compensate for the volatilization of sodium element during high-temperature calcination, and preferably the amount of sodium source is 2-5 wt% in excess; the amount of lithium source used is 1-15 wt% in excess based on the stoichiometric ratio, and preferably the amount of lithium source is 2-5 wt% in excess.

[0022] Preferably, in step (2), the pressure required for pressing is 2 to 100 MPa, and more preferably 10 to 50 MPa.

[0023] Preferably, in step (2), when the calcination includes: first high-temperature calcination followed by low-temperature calcination, the parameters of the high-temperature calcination include: a temperature of 800–1000°C and a holding time not exceeding 90 min; the parameters of the low-temperature calcination include:

[0024] The temperature is 500–900℃, and the holding time is 4–20 hours;

[0025] The heating and cooling rates of the calcination are 0.5–10 °C / min, preferably 1–5 °C / min;

[0026] Preferably, the parameters for the high-temperature calcination include: a temperature of 850–950°C and a holding time of no more than 30 minutes;

[0027] Preferably, the parameters for the low-temperature calcination include: a temperature of 700–800°C and a holding time of 8–10 hours.

[0028] Preferably, in step (2), when the calcination includes: first a low-temperature calcination, then a high-temperature calcination, and finally a second low-temperature calcination, the parameters of the high-temperature calcination include: a temperature of 800–1000°C and a holding time of no more than 90 min; the parameters of the first low-temperature calcination include: a temperature of 500–900°C and a holding time of 1–10 h; the parameters of the second low-temperature calcination include: a temperature of 500–900°C and a holding time of 1–10 h; and the total time for the first and second low-temperature calcinations is 4–20 h.

[0029] The heating and cooling rates of the calcination are 0.5–10 °C / min, preferably 1–5 °C / min;

[0030] Preferably, the parameters for the high-temperature calcination include: a temperature of 850–950°C and a holding time of no more than 30 minutes;

[0031] Preferably, the parameters for the first low-temperature calcination include: a temperature of 700–800°C and a holding time of 5–6 hours;

[0032] Preferably, the parameters for the secondary low-temperature calcination include: a temperature of 700–800°C and a holding time of 5–6 hours.

[0033] Preferably, in step (2), the calcination atmosphere includes at least one of oxygen, nitrogen, and an inert gas; preferably, the inert gas is argon.

[0034] On the other hand, the present invention provides a P2-type high-temperature phase layered oxide cathode material prepared according to the above method, wherein the P2-type high-temperature phase layered oxide cathode material is an oxide solid powder with a primary particle size of 0.1 to 10 μm, preferably 0.5 to 3 μm.

[0035] In another aspect, the present invention provides a sodium-ion battery, comprising: the above-mentioned P2-type high-temperature phase layered oxide positive electrode material, a negative electrode, and an electrolyte;

[0036] Preferably, the negative electrode includes a hard carbon negative electrode, an alloy negative electrode, or a metallic sodium negative electrode;

[0037] Preferably, the electrolyte is a liquid electrolyte, an organic polymer electrolyte, or an inorganic solid electrolyte.

[0038] The beneficial effects of this invention are:

[0039] (1) Unlike the common high-temperature solid-state method (e.g., 900℃ / 20h) used to prepare P2 type high-temperature phase sodium ion layered cathode materials, the present invention adopts an auxiliary low-temperature calcination strategy to reduce the calcination temperature, shorten the calcination time, reduce energy consumption, and reduce costs while ensuring the high crystallinity of the material, making it suitable for large-scale industrial production.

[0040] (2) The auxiliary low-temperature calcination strategy provided by this invention avoids the problems of particle melting and agglomeration and uneven size and morphology caused by long-term high-temperature calcination. During the heat treatment process, the short high-temperature step promotes the formation of crystal nuclei and ensures high crystallinity; during the low-temperature calcination process, the grains grow uniformly, and the prepared P2-type high-temperature phase sodium ion layered cathode material has a regular shape, uniform size and reduced particle size;

[0041] (3) The resulting uniform and fine primary particles shorten the sodium ion insertion / extraction path, which is beneficial to improving the rate performance of the cathode material; the pulverization phenomenon of secondary particles is alleviated, thereby reducing the formation of cracks during electrochemical cycling, inhibiting the corrosion of active materials by the electrolyte, and improving the cycle stability of the cathode material. Therefore, the P2-type high-temperature phase layered oxide cathode material prepared by this invention has high reversible specific capacity, good rate performance, and long cycle life;

[0042] (4) The solid-phase assisted low-temperature calcination synthesis process provided by the present invention is easy to operate, has a short cycle, low energy consumption, high efficiency, and outstanding electrochemical modification effect, and is suitable for the large-scale development and application of high energy density sodium ion cathode materials. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the calcination process for Example 1 of the present invention;

[0044] Figures 2-3 The image shows the X-ray diffraction (XRD) pattern of the cathode material, which includes Examples 1-2 and Comparative Example 1 (labeled as CTS sample) calcined using conventional solid-state methods. The space group of the layered oxide cathode material prepared in this invention is P63 / mmc, corresponding to a P2 phase structure.

[0045] Figure 4 This is a transmission electron microscope (TEM) image of the PLTS sample in Example 1;

[0046] Figure 5 The images show scanning electron microscope (SEM) images of the PLTS sample in Example 1 and the comparative example 1 calcined using the conventional solid-state method. The layered oxide cathode material prepared in this invention is a solid powder with a particle size of 1-5 μm.

[0047] Figure 6 The first cycle curves of the PLTS sample in Example 1 and the comparative example 1 calcined by conventional solid-state method are shown.

[0048] Figure 7 The diagram shows a comparison of the cycle stability of the cathode materials, which include Example 1 and Comparative Example 1, which is calcined by conventional solid-state method.

[0049] Figure 8 This is a ratio comparison chart of the cathode materials, which includes Example 1 and Comparative Example 1 calcined by conventional solid-state method;

[0050] Figure 9 The diagram shows the cycling stability of the full cell assembled with the PLTS sample matched with the pre-sodiumized SnSb@CN / CNT anode in Example 1.

[0051] Figure 10 The comparison shows the cycle stability of various cathode materials prepared by one low-temperature calcination, then high-temperature calcination, and finally two low-temperature calcinations in Example 2.

[0052] Figure 11 The graph shows a comparison of the rate performance of the cathode prepared under the calcination mode of 750℃-5h-950℃-1min-750℃-5h in Example 2 with that of the comparative CTS cathode. Detailed Implementation

[0053] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0054] In this invention, a brief high-temperature calcination step is introduced in the early or middle stage of the low-temperature short-time calcination process to effectively avoid the particle melting and agglomeration phenomenon in traditional heat treatment. The principle is that high temperature promotes crystal nucleation, ensuring high crystallinity of the material; the low-temperature holding process results in uniform particle growth. The prepared particles are uniform and fine, shortening the sodium ion transport path and reducing crack formation, thereby improving cycle and rate performance. This method is convenient to operate, simple in principle, and easy to scale up for production. Half-cells and full-cells assembled using the cathode material prepared by the above method exhibit excellent overall performance.

[0055] Specifically, the core of this invention lies in the solid-state heat treatment process. By controlling parameters such as calcination temperature, holding time, temperature change rate, and calcination atmosphere during calcination, production energy consumption is reduced while ensuring high crystallinity, thus preparing uniform and fine layered oxide cathode particles.

[0056] This invention proposes an assisted calcination technique to reduce the synthesis temperature of P2-type high-temperature layered oxide cathode materials. The technical solution of this invention includes three steps: grinding and mixing, drying and pre-processing, and calcination. The assisted low-temperature calcination strategy involves introducing a brief (1-60 min) high-temperature (800-1000℃) calcination step during the initial or middle stage of a low-temperature (700-800℃) and short-time (8-15 h) calcination. This brief high-temperature step promotes crystal nucleation, ensures high crystallinity, and reduces particle melting and agglomeration; the low-temperature calcination process is beneficial for uniform grain growth. The material prepared using the technique of this invention has high crystallinity, uniform and fine particles, and a regular shape. More specifically, to better understand this invention, the following detailed description is provided in conjunction with specific embodiments.

[0057] The molecular formula of the P2-type high-temperature phase layered oxide cathode material prepared by the assisted low-temperature calcination method in this invention is Na. x Li y TM 1-y O2, where TM refers to a transition metal, which is one or a combination of Mn, Ni, Fe, Mg, Ca, Al, Co, etc.; 0.6≤x≤0.8, 0≤y≤0.3. The sodium source, lithium source, and transition metal source include at least one or a combination of carbonates, oxides, or hydroxides as raw materials. P2-Na, a P2-type high-temperature phase cathode material, is preferred. 0.72 Li 0.24 Mn 0.76 O2.

[0058] The positive electrode sheet, after uniform mixing, drying, and pressure application, undergoes heat treatment. The calcination temperature and holding time are subject to limitations. The temperature of the brief high-temperature calcination step needs to be slightly higher than the material's phase formation temperature; otherwise, crystallinity will be poor. The holding time should not be too long, otherwise, it will lead to particle melting and agglomeration. The brief high-temperature calcination step can be introduced in the early or middle stage of the material synthesis process. The temperature of the high-temperature calcination step is 800-1000℃, and the holding time is 1-90 min. Preferably, the temperature of the high-temperature calcination step is 850-950℃, and the holding time is 1-30 min. The temperature of the low-temperature calcination process is 501-900℃, the holding time is 4-20 h, and the heating rate is 0.5-10℃ / min. Preferably, the temperature of the low-temperature calcination process is 700-800℃, the holding time is 8-10 h, and the heating rate is 1-5℃ / min.

[0059] In this invention, the P2-type high-temperature phase layered oxide cathode material prepared using this technology exhibits high reversible specific capacity, good rate performance, and long cycle life. The solid-state assisted low-temperature calcination synthesis process provided by this invention is easy to operate, has a short cycle time, low energy consumption, and high efficiency, making it suitable for the large-scale development and application of high-energy-density sodium-ion cathode materials. Sodium-ion batteries assembled from layered oxide cathodes prepared using the assisted low-temperature calcination method demonstrate excellent electrochemical performance. Half-cell Na / / P2-Na 0.72 Li 0.24 Mn 0.76 O2 at 1.5–4.5V, 200mA g -1 After 100 cycles at high current density, it has a capacity of 131.8 mAh g. -1 High discharge specific capacity, at 1000mA g -1 It still maintains high rate performance (107.8mAh g) -1 Full cell SnSb@CN / CNT / / P2-Na 0.72 Li 0.24 Mn 0.76 O2 at 1.0–4.4V, 200mA g -1 After 50 cycles at high current density, it has a capacity of 124.6 mAh g. -1 The specific discharge capacity.

[0060] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0061] Example 1

[0062] Preparation of P2-Na by Assisted Low-Temperature Calcination Strategy 0.72 Li 0.24 Mn 0.76 O2:

[0063] (1) Weigh out sodium carbonate (2wt% excess), lithium hydroxide monohydrate (2wt% excess) and manganese dioxide according to the stoichiometric ratio, place them in a grinding jar, add an appropriate amount of anhydrous ethanol for wet grinding, ball mill at 300 rpm for 5 hours and then dry at 100℃.

[0064] (2) After manually grinding the dried powder evenly, take an appropriate amount and put it into a mold. Pre-press it into a sheet under a mechanical pressure of 50 MPa to promote the uniform diffusion of each element during the heat treatment process.

[0065] (3) Calcination was carried out under normal pressure in an air atmosphere with a heating / cooling rate of 5℃ / min: the temperature was first raised to 950℃ and held for 1 min, then lowered to 700℃, 750℃, 800℃ or 850℃, and held for 10 h or 12 h respectively. Finally, the temperature was lowered to 700℃ and cooled to room temperature in the furnace. The best performance was obtained by comparing 950℃-1min-750℃-12h. The time at 950℃ was further extended to 15 min, 30 min and 45 min respectively. The best performance was obtained by comparing 950℃-30min-750℃-12h, which was marked as PLTS sample.

[0066] Table 1 shows the preparation parameters of the P2-type high-temperature phase layered oxide cathode material in Example 1:

[0067]

[0068]

[0069] Example 2

[0070] Preparation of P2-Na by Assisted Low-Temperature Calcination Strategy 0.72 Li 0.24 Mn 0.76 O2:

[0071] Steps (1)-(2) are the same as steps (1)-(2) in Example 1;

[0072] (3) Calcination under normal pressure in air atmosphere, with a heating and cooling rate of 5℃ / min: first heat to 700℃, 750℃, 800℃ or 850℃ and hold for 5h, then continue heating to 950℃ and hold for 1min, then cool to 700℃, 750℃, 800℃ or 850℃ and hold for 5h. After cooling to 700℃, cool to room temperature with the furnace.

[0073] Table 2 shows the preparation parameters of the P2-type high-temperature phase layered oxide cathode material in Example 2:

[0074] One-time low-temperature calcination High-temperature calcination Secondary low-temperature calcination Example 2-1 700℃ / 5h 950℃ / 1min 700℃ / 5h Example 2-2 750℃ / 5h 950℃ / 1min 750℃ / 5h Example 2-3 800℃ / 5h 950℃ / 1min 800℃ / 5h Examples 2-4 800℃ / 6h 950℃ / 1min 800℃ / 6h Examples 2-5 850℃ / 5h 950℃ / 1min 850℃ / 5h .

[0075] Comparative Example 1

[0076] Traditional solid-state calcination method for preparing P2-Na 0.72 Li 0.24 Mn 0.76 O2:

[0077] (1)-(2) are the same as steps (1)-(2) in Example 1;

[0078] (3) Calcination was carried out under normal pressure in an air atmosphere at a heating / cooling rate of 5℃ / min: the temperature was first raised to 900℃ and held for 12h. Then the temperature was lowered to 700℃ and cooled to room temperature in the furnace. The samples were marked as CTS samples.

[0079] 2025 button cells were fabricated using the PLTS sample from Example 1, all samples from Example 2, and the comparative example 1CTS sample. The sample, Super P, and PVDF were mixed uniformly in an 8:1:1 ratio and dissolved in an appropriate amount of NMP solution to prepare a slurry. This slurry was uniformly coated onto aluminum foil, dried, and then cut into circular electrode sheets with a diameter of 12 mm. Using the electrode sheets as the working electrode and sodium foil as the counter and reference electrode, the button cells were assembled in an argon-filled glove box. The electrolyte was 1M NaClO4 + EC / PC + 5% vol. FEC (V EC :V PC =1:1). Electrochemical performance was tested at room temperature, with a voltage window of 1.5-4.5V.

[0080] Figure 2-3 The X-ray diffraction (XRD) pattern of the positive electrode is shown. The X-ray diffraction peaks of the materials obtained in different embodiments match well with the standard card (PDF#54-0894), belonging to the hexagonal crystal system with space group P63 / mmc.

[0081] Figure 4 The TEM image of the PLTS cathode is shown, corresponding to the (100) crystal plane of the hexagonal crystal system, confirming the layered structure of the P2 phase.

[0082] Figure 5 The images show SEM images of the PLTS cathodes in Comparative Example 1 and Example 1. Compared to Comparative Example 1 synthesized by conventional solid-state method, the particles prepared by low-temperature calcination are more uniform and finer, with regular shapes and reduced melt agglomeration.

[0083] Figure 6 The first-cycle charge-discharge curves of the PLTS sample and the comparative CTS cathode in Example 1 are shown. Compared to the CTS sample synthesized by conventional solid-state method, the charge-discharge specific capacity of the PLTS cathode prepared by low-temperature calcination is increased by approximately 20 mAh g⁻¹. -1 At the same time, the charging voltage decreases and the discharging voltage increases, indicating that the electrochemical polarization decreases.

[0084] Figure 7 This shows a comparison of the cycle stability of the PLTS sample and the comparative CTS cathode in Example 1. Electrochemical cycling test results indicate that the cathode material prepared by low-temperature calcination exhibits a significant improvement in cycle stability. The above cathode material showed improved cycle stability at 200 mA g / g. -1 Under the test conditions, after 100 cycles, the discharge specific capacity of the PLTS sample in Experiment 1 was 131.8 mAh g.-1 The discharge specific capacity of Comparative Example 1 was 99.9 mAh g. -1 This fully demonstrates that the low-temperature calcination modification method can improve the reversible specific capacity of cathode materials.

[0085] Figure 8 This chart shows a rate comparison between the PLTS sample and the comparative CTS cathode in Example 1. The results indicate that at 1000 mAg... -1 At high rates, the discharge specific capacity of the PLTS sample in Example 1 was 107.8 mAh g. -1 In contrast, the discharge specific capacity of Comparative Example 1 was only 27.8 mAh g. -1 This fully demonstrates that the low-temperature calcination modification method can improve the cycle stability and rate performance of P2-type high-temperature phase sodium ion layered cathode materials.

[0086] Figure 9 This demonstrates the assembly of a full cell using a PLTS sample matched with a pre-sodiumized SnSb@CN / CNT anode in Example 1. The full cell is SnSb@CN / CNT / / P2-Na. 0.72 Li 0.24 Mn 0.76 O2 at 1.0-4.4V, 200mA g -1 After 50 cycles at high current density, it has a capacity of 124.6 mAh g. -1 The specific discharge capacity.

[0087] Figure 10 This section compares the cycle stability of various cathode materials prepared in Example 2 through a single low-temperature calcination, followed by a high-temperature calcination, and finally a second low-temperature calcination. Electrochemical cycle test results show that the cathode prepared in Example 2 under the calcination mode of 750℃-5h-950℃-1min-750℃-5h exhibits better electrochemical cycle stability. The above cathode materials show good electrochemical cycle stability at 200 mAg. -1 Under the test conditions, it has 147.3 mAh g after 40 cycles. -1 The discharge specific capacity was significantly higher than that of the CTS cathode sample under the same conditions, which only had a discharge specific capacity of 119.4 mAh g⁻¹. -1 The discharge specific capacity fully demonstrates that the low-temperature calcination modification method can improve the reversible specific capacity of the cathode material.

[0088] Figure 11 The graph shows a comparison of the rate performance of the cathode prepared under the calcination mode of 750℃-5h-950℃-1min-750℃-5h in Example 2 with that of the comparative CTS cathode. The results indicate that the above cathode achieves a rate performance of [missing information - likely a specific value] at 1000 mA g / g. -1Under high-rate conditions, the discharge specific capacity of the cathode prepared in the calcination mode of 750℃-5h-950℃-1min-750℃-5h in step 2 was 51.6 mAh g. -1 In contrast, the discharge specific capacity of Comparative Example 1 was only 27.8 mAh g. -1 This fully demonstrates that the low-temperature calcination modification method can improve the cycle stability and rate performance of P2-type high-temperature phase sodium ion layered cathode materials.

[0089] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing P2-type high-temperature phase layered oxide cathode material for sodium-ion batteries using assisted low-temperature calcination, characterized in that, The method includes: using a P2-type high-temperature phase layered oxide cathode material for sodium-ion batteries with the chemical formula Na... x Li y TM 1-y O2, where TM is the transition metal element Mn, 0.6≤x≤0.8, 0<y≤0.3; according to the chemical formula of P2 type high-temperature phase layered oxide cathode material Na x Li y TM 1-y O2 is weighed, sodium source, lithium source and transition metal source are mixed evenly and pressed into shape to obtain a preform; the obtained preform is calcined under normal pressure in air atmosphere to obtain the P2 type high temperature phase layered oxide cathode material; the calcination is first held at 950℃ for 30 min, and then held at 750℃ for 12 h.

2. The method according to claim 1, characterized in that, The sodium source is selected from at least one of sodium carbonate, sodium oxide, and sodium hydroxide; the lithium source is selected from at least one of lithium carbonate, lithium oxide, and lithium hydroxide; and the transition metal source is selected from at least one of carbonates, oxides, and hydroxides of the transition metal Mn.

3. The method according to claim 1, characterized in that, The mixing method is grinding; the grinding speed is 100-1500 rpm, the grinding time is 15 min-6 h, and the solvent used is deionized water, anhydrous ethanol, or isopropanol; the grinding includes manual grinding, ball milling, or sand milling; the parameters for ball milling include: a speed of 200-300 rpm, a time of 2-4 h, and the solvent used is deionized water, anhydrous ethanol, or isopropanol; the parameters for sand milling include: a speed of 500-1000 rpm, a time of 30 min-2 h, and the solvent used is deionized water, anhydrous ethanol, or isopropanol.

4. The method according to claim 1, characterized in that, The sodium source is used in excess of 1 wt% to 15 wt% based on the stoichiometric ratio; the lithium source is used in excess of 1 wt% to 15 wt% based on the stoichiometric ratio.

5. The method according to claim 1, characterized in that, The heating rate and cooling rate of the calcination are 1 to 5 °C / min, respectively.

6. The method according to claim 1, characterized in that, The P2-type high-temperature phase layered oxide cathode material is an oxide solid powder with a primary particle size of 0.1–10 μm.

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