Plasma-assisted regulation of O3-type layered oxide positive electrode material and preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion battery electrode materials, and particularly relates to a plasma-assisted regulated O3-type layered oxide positive electrode material and a preparation method and application thereof. The method is a high-temperature solid-phase sintering process in a plasma treatment atmosphere, and an O3-type layered oxide positive electrode material is obtained. The plasma treatment atmosphere is obtained by plasma treatment of a mixed gas containing nitrogen and oxygen. The sintering atmosphere is regulated by plasma assistance, and no additional post-cleaning or post-coating step is required. The in-situ optimization of the surface chemical state of the positive electrode material is realized, the surface residual alkali is effectively converted into a nitrate coating layer in-situ, the interface stability of the material is significantly improved, the rate performance and cycle stability are efficiently improved without changing the main structure, the process is simple, scalable, easy to repeat, efficient, and suitable for large-scale preparation of sodium ion battery positive electrode materials.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery electrode material technology, specifically relating to a plasma-assisted controlled O3-type layered oxide cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are considered an important candidate system for large-scale energy storage due to the abundance and low cost of sodium resources. Among them, O3-type layered oxides Na... x TMO2 (TM = Ni, Co, Cu, Fe, Mn, Ti, etc.) has attracted widespread attention due to its high specific capacity and suitable operating voltage. However, O3-type layered oxides still face serious interface problems in practical applications: on the one hand, surface residual alkalis (such as Na2CO3 and NaOH) are easily generated during high-temperature solid-phase synthesis, and due to the high reactivity of Na, its air stability is poor. In subsequent air exposure, it is easy to react with H2O and CO2, further promoting the formation of residual alkalis and deteriorating the surface structure; on the other hand, during charge and discharge, the positive electrode surface undergoes continuous side reactions with the electrolyte, inducing structural degradation, increased interfacial impedance, and decreased cycle life.

[0003] In existing technologies, for O3-type layered oxide cathodes (such as NaNi) 1 / 3 Fe 1 / 3 Mn 1 / 3 The problem of residual alkali on the surface of O2 (NFM) coatings is usually addressed by cleaning and secondary sintering, but these methods do not improve air stability or interfacial stability. Post-treatment coating or surface reconstruction strategies are effective means to solve the problems of residual alkali, interfacial side reactions, and improve air stability, such as carbon coating, inorganic oxide coating, or in-situ conversion coatings of residual alkali. However, these methods often suffer from drawbacks such as complex processes, low efficiency, and difficulty in controlling coating uniformity.

[0004] Therefore, developing a simple, efficient method that can simultaneously remove residual alkali and construct a stable interface layer during the material synthesis stage is of great significance for improving the interface stability, cycle life, and rate performance of O3-type layered oxide materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the rapid synthesis of layered oxide cathode materials for sodium-ion batteries while simultaneously improving the interface. Addressing the interface problems of existing O3-type NFM cathode materials during high-temperature synthesis and electrochemical cycling, such as residual alkali on the surface, severe side reactions, and air stability, this invention improves the material synthesis rate by using plasma-controlled sintering atmosphere, introducing liquid-phase sintering processes and strong oxidation conditions. This achieves in-situ optimization of the surface chemical state of the material, thereby significantly enhancing its rate performance and cycle stability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a plasma-assisted controlled O3-type layered oxide cathode material, wherein the method involves performing a high-temperature solid-state sintering process of a sodium source and a precursor material in a plasma treatment atmosphere to obtain a plasma-assisted controlled O3-type layered oxide cathode material, wherein the plasma treatment atmosphere is obtained by plasma treatment of a mixture of nitrogen and oxygen.

[0008] By employing the aforementioned technical solution, this invention constructs a high-energy active reaction environment by introducing a plasma-treated N2 / O2 mixed atmosphere during the high-temperature solid-state synthesis process of O3-type layered oxide cathode materials. This environment is rich in ozone (O3) and nitrogen-oxygen reactive species (N... x O y During the sintering process, it can react with the sodium salt on the surface of the positive electrode material and be converted in situ into a stable liquid nitrate species, thereby forming a uniform, dense, and stable coating layer on the particle surface. This coating layer can effectively isolate the positive electrode material from direct contact with the electrolyte, suppress side reactions, and at the same time, it does not affect the Na+ content. + The method of this invention enables reversible insertion and extraction. Furthermore, it significantly improves the sintering efficiency of materials, significantly shortens sintering time, and reduces costs and energy consumption, thus possessing significant economic advantages.

[0009] Preferably, the O3-type layered oxide cathode material is Na. x Ni y Fe z Mn 1-y-z O2, x=0.9-1.2, y=0.2-0.4, z=0.2-0.4, is an NFM cathode material.

[0010] Preferably, the plasma-assisted controlled O3-type layered oxide cathode material is an NFM material containing a sodium nitrate coating layer between 5-20 nm. Conventional post-coating processes typically require a second high-temperature sintering. When nitrate is used as the coating material, it is prone to decomposition at the sintering temperature, thus making it impossible to prepare a nitrate coating layer. This invention utilizes the strong oxidizing properties and high nitrogen oxide concentration atmosphere generated by plasma to suppress the decomposition of in-situ formed nitrate, thereby successfully achieving the effective preparation of a nitrate coating layer.

[0011] Preferably, the method includes the following steps:

[0012] (1) Raw material mixing: Weigh the sodium source and precursor material, mix them evenly to obtain a mixture;

[0013] (2) Plasma treatment atmosphere: A plasma treatment atmosphere is obtained by subjecting a mixture of nitrogen and oxygen to plasma treatment;

[0014] (3) The mixture from step (1) is subjected to a high-temperature solid-state sintering process in a plasma treatment atmosphere to obtain plasma-assisted controlled O3-type layered oxide cathode material.

[0015] Preferably, in step (1), the precursor is Ni. x Fe y Mn 1-x-y (OH)2, x=0.2-0.4, y=0.2-0.4.

[0016] Preferably, in step (1), the sodium source is selected from at least one of common sodium sources such as Na2CO3, NaOH, NaNO3, and NaCl. More preferably, the amount of sodium source fed is in a molar excess of 3-10% based on Na.

[0017] Preferably, in steps (2) and (3), the volume ratio of nitrogen to oxygen in the nitrogen-oxygen mixture is between 1 and 4:1, more preferably 1 to 2:1. More preferably, the flow rate of the nitrogen-oxygen mixture is 150-600 sccm, and even more preferably, the flow rate of N2 is 100-400 sccm and the flow rate of O2 is 50-200 sccm.

[0018] Preferably, in step (2), the plasma generation method includes: dielectric barrier discharge, radio frequency discharge, microwave discharge, atmospheric pressure glow discharge, etc.

[0019] Preferably, in step (2), the excitation power of the plasma treatment is 500-1000W.

[0020] Preferably, in step (3), the high-temperature solid-state sintering process includes a pre-sintering step and a high-temperature sintering step. The pre-sintering step involves a heating rate of 3-15 ℃ min. -1 The sintering temperature is 500-600℃, and the holding time is 0.5-3h; a more preferred sintering temperature is 550℃.

[0021] And / or, high-temperature sintering: heating rate 3-15 ℃ min -1 The sintering temperature is 850-950℃, and the holding time is 3-5h; a more preferred sintering temperature is 930℃.

[0022] Preferably, the method specifically includes the following steps:

[0023] (1) Raw material mixing: Weigh out the sodium source (Na2CO3, NaOH, NaNO3, NaCl, etc.) and the precursor (Ni) according to the stoichiometric ratio. x Fe y Mn 1-x-y(OH)2, x=0.2-0.4, y=0.2-0.4), where the molar ratio of Na is 3-10% excess, and it is thoroughly mixed using conventional methods such as ball milling / grinding / stirring;

[0024] (2) Sintering atmosphere (plasma treatment atmosphere): N2 and O2 are introduced into a mixing tank, where the flow rate of N2 is 100-400 sccm and the flow rate of O2 is 50-200 sccm, and the N2:O2 ratio is maintained between 1-4:1. The N2 and O2 mixture is introduced into the plasma device, and the plasma excitation power is set to 500-1000W to form a sintering atmosphere rich in O3 and N2. x O y The high-energy mixed atmosphere is introduced into a tube furnace, and subsequent pre-sintering, high-temperature sintering, and cooling steps are carried out in the plasma-treated atmosphere.

[0025] (3) Pre-sintering: Place 5-20g of the mixture in a corundum boat and put it in a tube furnace. The heating rate is 3-15 ℃min. -1 The temperature was raised to 550℃ under certain conditions and held in a high-energy mixed atmosphere of plasma treatment for 0.5-3 hours.

[0026] (4) High-temperature sintering: Continue to heat to 930℃ at the same heating rate as pre-sintering, and hold at the temperature for 3-5 hours under the same atmosphere to complete the formation of the crystal structure;

[0027] (5) Cooling and storage: After sintering, the sample was naturally cooled to 150-200 °C, then removed, ground, and sieved. It was then quickly transferred to a glove box filled with argon gas for storage to obtain plasma-assisted synthesized Na. x Ni y Fe z Mn 1-y-z O2 (x=0.9-1.2, y=0.2-0.4, z=0.2-0.4, NFM) cathode material.

[0028] The present invention also provides a plasma-assisted controlled O3-type layered oxide cathode material prepared by any of the above preparation methods.

[0029] The present invention also provides an application of plasma-assisted controlled O3-type layered oxide cathode material prepared by any of the above preparation methods in the field of sodium-ion batteries.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: by controlling the sintering atmosphere with plasma assistance, no additional post-cleaning or post-coating steps are required, thus achieving in-situ optimization of the surface chemical state of the cathode material, effectively converting residual alkali on the surface into a nitrate coating layer in situ, and significantly improving the interfacial stability of the material; without changing the phase and morphology, it efficiently improves the rate performance and cycle stability. The process is simple, highly scalable, easy to repeat, and highly efficient, and is suitable for the large-scale preparation of sodium-ion battery cathode materials. Attached Figure Description

[0031] Figure 1 These are SEM images of Embodiment 1 and Comparative Example 1 of the present invention;

[0032] Figure 2 These are the XRD patterns of Embodiment 1 and Comparative Example 1 of the present invention;

[0033] Figure 3 These are the FT-IR images of Embodiment 1 and Comparative Example 1 of the present invention;

[0034] Figure 4 These are TEM images of Embodiment 1 and Comparative Example 1 of the present invention;

[0035] Figure 5 The following are the rate performance diagrams for Examples 1-3 and Comparative Example 1 of the present invention;

[0036] Figure 6 The diagram shows the cyclic performance of Embodiments 1-3 and Comparative Example 1 of the present invention. Detailed Implementation

[0037] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0039] Example 1

[0040] This embodiment provides a method for preparing O3-type NaNi using plasma-assisted controlled sintering atmosphere. 1 / 3 Fe 1 / 3 Mn 1 / 3 Methods for using O2 cathode materials.

[0041] First, weigh out Na₂CO₃ and Ni according to a stoichiometric ratio of 1.05:1. 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)2 precursor is prepared with Na added in 5% excess of the theoretical amount to compensate for the loss of sodium through volatilization during high-temperature sintering. After thoroughly mixing the above raw materials, 10g of each is placed in a corundum boat and sintered in a tube furnace.

[0042] During the sintering process, a high-energy active atmosphere is continuously introduced into the tubular furnace. This mixed atmosphere, composed of N2 and O2 with a flow ratio of 2:1 and a total gas flow rate of 300 sccm, is obtained by treating the mixed atmosphere with a plasma generator. The mixed gas is then introduced into a dielectric barrier discharge (DBD) plasma generator, which consists of a DBD generation chamber, a power supply system, and a cooling system. The plasma excitation power is set to 1000W via the power supply system. After plasma treatment, the high-energy active atmosphere is rich in O3 and N2. x O y (Including N2O, NO, NO2, N2O3, N2O4, N2O5, N2O2, N4O, NO3, etc.), thereby creating a high-energy active reaction environment inside the furnace.

[0043] Subsequently, under the aforementioned high-energy active atmosphere, at 10°C min... -1 The mixture was heated to 550℃ at a controlled heating rate and held for 1 hour to complete the pre-sintering process. Then, the temperature was increased to 930℃ at the same rate and held for 3 hours to form a stable O3-type layered crystal structure. After sintering, the sample was allowed to cool naturally in the furnace to approximately 200℃, ground, sieved, and then quickly transferred to an argon-filled glove box for storage, yielding plasma-assisted synthesized O3-type NaNi.1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cathode material.

[0044] Example 2

[0045] The N2 to O2 flow rate ratio is 2:1, and the total gas flow rate is 600 sccm.

[0046] Example 3

[0047] The N2 to O2 flow rate ratio is 1:1, and the total gas flow rate is 400 sccm.

[0048] Example 4

[0049] The mixed atmosphere introduced into the plasma generator consists of compressed air with a gas flow rate of 500 sccm.

[0050] Example 5

[0051] The plasma excitation power is 500W.

[0052] Example 6

[0053] The amount of Na added was 10% more than the theoretical value.

[0054] Example 7

[0055] The heating rate is 5°C / min. -1 .

[0056] Example 8

[0057] The heat preservation time is 2 hours at 550℃ and 5 hours at 930℃.

[0058] Example 9

[0059] The precursor is Ni 0.4 Fe 0.2 Mn 0.4 (OH)2, with other conditions remaining unchanged, finally yielded O3-type NaNi synthesized by plasma assistance. 0.4 Fe 0.2 Mn 0.4 O2 cathode material.

[0060] Comparative Example 1

[0061] In contrast, a traditional high-temperature solid-state synthesis method for O3-type NaNi is provided. 1 / 3 Fe 1 / 3 Mn 1 / 3 The preparation method of O2 cathode material involves using a traditional solid-state method under normal air atmosphere, employing a heating temperature of 550℃ for 5 hours and then 930℃ for 12 hours to prepare untreated samples. Details are as follows:

[0062] First, weigh out Na₂CO₃ and Ni according to a stoichiometric ratio of 1.05:1. 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor, wherein the amount of Na added is 5% excess compared to the theoretical value, to compensate for the loss of sodium through volatilization during high-temperature sintering. After the above raw materials are thoroughly mixed, 10g is placed in a corundum boat and sintered in a tube furnace. This step is the same as in Example 1.

[0063] During the sintering process, both ends of the tubular furnace are open. Under air atmosphere conditions, the sintering temperature is 5°C for 5 minutes. -1 The mixture was heated to 550°C at a controlled heating rate and held for 5 hours to complete the pre-sintering process. The temperature was then further increased to 930°C and held at this temperature for 12 hours to obtain an O3-type layered structure. After sintering, the sample was allowed to cool naturally in the furnace to approximately 200°C, ground, sieved, and then rapidly transferred to an argon-filled glove box for storage, yielding O3-type NaNi synthesized via a conventional high-temperature solid-state method. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 cathode material.

[0064] Comparative Example 2

[0065] Take 5g of the product from Comparative Example 1 into a beaker, add 20ml of deionized water, stir for 5min, filter, and then vacuum dry at 80℃ for 12h to wash away residual alkali on the surface.

[0066] Comparative Example 3

[0067] Take 5g of the product of Comparative Example 1 into a beaker, add 20ml of ethanol, stir for 5min, filter, and then vacuum dry at 80℃ for 12h to wash away residual alkali on the surface.

[0068] Comparative Example 4

[0069] Based on Example 1, the flow ratio of N2 to O2 is 1:4, and the total gas flow rate is 500 sccm.

[0070] Comparative Example 5

[0071] Based on Example 1, the flow ratio of N2 to O2 is 1:0, and the total gas flow rate is 400 sccm.

[0072] Comparative Example 6

[0073] Based on Example 1, the flow ratio of N2 to O2 is 0:1, and the total gas flow rate is 400 sccm.

[0074] Comparative Example 7

[0075] Based on Example 1, the plasma excitation power is 0W.

[0076] Comparative Example 8

[0077] Based on Example 1, the heat preservation time is 550℃ for 5 hours and 930℃ for 12 hours.

[0078] Appendix Figure 1 These are SEM images of Example 1 and Comparative Example 1. Comparative Example 1 has a blocky secondary particle morphology with a large amount of residual alkali on the surface. Example 1 has the same structural characteristics, but its surface is smooth and there is no residual alkali. This indicates that the plasma-assisted control strategy can remove residual alkali from the surface during the synthesis process.

[0079] Appendix Figure 2 These are the XRD patterns of Example 1 and Comparative Example 1, illustrating that the plasma-assisted control strategy can generate a new sodium nitrate phase in situ during the synthesis process without changing the layered oxide phase.

[0080] Appendix Figure 3 The FT-IR results showed that, compared to Comparative Example 1, which was synthesized using conventional high-temperature solid-state methods, Example 1 did not involve CO3. 2- The relevant characteristic peaks were observed, and a significant NO3- concentration was also present. - The characteristic peaks indicate that the sodium nitrate originates from the in-situ conversion of residual alkali on the surface by a high-energy active atmosphere.

[0081] Appendix Figure 4 TEM observation showed that the particles in Example 1 had a uniform and continuous 5 nm uniform coating layer on their surface. This layer was tightly bonded to the main crystal lattice, and no obvious phase separation or structural damage was observed. In contrast, the surface of Comparative Example 1 was covered by a thick and unevenly distributed sodium carbonate layer.

[0082] Test case

[0083] Finally, the cathode materials from the above embodiments and comparative examples were assembled into sodium-ion half-cells, and the electrochemical behavior of the materials was evaluated through rate performance testing and cycle performance testing. Specific tests and results are as follows:

[0084] Half-cells were assembled using the positive electrode materials of each example: Each example was mixed with acetylene black and PVDF in an 8:1:1 ratio, and an appropriate amount of NMP was added to prepare a slurry. This slurry was then coated onto carbon-coated aluminum foil, vacuum dried at 100°C for 12 hours, and then cut into 12mm round pieces. The active material loading was 2.5~3.5 mg / cm³. -1Using NaClO4 electrolyte (1.0 M NaClO4 in DEC:EC = 1:1 vol % with 5% FEC), the positive electrode was then assembled in a glove box in the following order: positive electrode shell, positive electrode sheet, electrolyte, glass fiber separator, electrolyte, sodium sheet, stainless steel gasket, stainless steel spring sheet, and negative electrode shell. The assembly was then pressed into a button half-cell under a pressure of 50 MPa and allowed to stand at room temperature of 25°C for 12 hours before electrochemical testing.

[0085] Specific methods and conditions for electrochemical performance testing: Test temperature 25℃, voltage range 2.0-4.0V, nominal specific capacity 130 mAh g. -1 Cycle 5 times at each of the following rates: 0.1, 0.2, 0.5, 1, 2, 5, 10, and 0.2C. Compare rate performance using specific capacity at 10C as the indicator. Activate 5 times at 0.1C, then cycle 200 times at 1C. Compare cycle performance using capacity retention as the indicator.

[0086] The test results are shown in Table 1 below:

[0087]

[0088] The data in the table shows that:

[0089] A comparison of Example 1 and Comparative Example 1 shows that simply replacing traditional air sintering with a high-energy active atmosphere treated with plasma can significantly shorten the material synthesis time and improve the rate performance and cycle stability of the material. This indicates that plasma control of the sintering atmosphere is the core factor in achieving the technical effects of this invention.

[0090] A comparison of Example 1 with Comparative Examples 2 and 3 reveals that even after post-treatment of the traditional sintered samples by means of water washing or alcohol washing, their overall performance is still significantly lower than that of Example 1. This indicates that post-treatment methods that simply remove residual alkali from the surface are insufficient to construct a stable interface structure from the synthesis stage and cannot achieve the technical effect of the present invention.

[0091] A comparison of Examples 1 and 5 with Comparative Example 7 shows that when the plasma excitation power is reduced but still remains in the excited state, the material can still maintain good electrochemical performance; while when the plasma excitation power is zero, the material performance decreases significantly, further illustrating that plasma excitation is an indispensable key technical feature.

[0092] A comparison of Examples 1 and 8 with Comparative Example 8 reveals that, under the condition of extending the traditional pre-sintering and high-temperature sintering holding time, the material properties did not achieve the same improvement as the sample in the examples. This indicates that the effect of the present invention does not come from simply extending the heat treatment time, but from the synergistic control of the sintering atmosphere under plasma excitation conditions.

[0093] A comparison of Examples 1–4 and Comparative Examples 4–6 shows that when a suitable mixed atmosphere (N2:O2 = 1–4:1) is used under plasma excitation conditions, the resulting material exhibits relatively stable electrochemical performance. However, when the gas ratio deviates significantly from this range, or when only a single gas is introduced, the material performance deteriorates significantly even with plasma treatment. This comparison demonstrates that the technical effect of the present invention does not solely originate from the plasma treatment itself, but rather relies on the synergistic effect formed by N2 and O2 under plasma conditions.

[0094] Comparing Example 1 with Example 9 reveals that the plasma-assisted control strategy employed in this invention can still function effectively even when the proportion of transition metals is changed, and the resulting material maintains good electrochemical performance. This indicates that the method of this invention is not limited to a specific Ni / Fe / Mn ratio, but has broader applicability.

[0095] A comparison of Example 1 and Example 7 shows that the material properties did not deteriorate significantly under the condition of reducing the heating rate, indicating that the present invention does not rely on a specific heating rate curve and its technical effect is not dominated by the slight difference in the thermal history.

[0096] Comparing Example 1 with Example 6 reveals that the material properties remain stable even when the excess proportion of sodium source is increased. This indicates that the present invention has a certain degree of process tolerance for the raw material ratio, and its performance improvement does not depend on the strictly limited amount of sodium source added.

[0097] Appendix Figure 5 and 6 This is a comprehensive display of the electrochemical test results of some examples and comparative examples. Examples 1-3 can still maintain a high capacity output under 10C rate conditions, indicating that their Na+... + Transport dynamics are improved. Furthermore, [the following text is incomplete and likely refers to a separate point:] ...attached... Figure 6 In the 200-cycle test at 1C, Examples 1-3 showed a more stable capacity retention rate, indicating that the removal of residual alkali on the surface and the in-situ formed surface coating layer effectively suppressed interfacial side reactions and delayed structural degradation.

[0098] In summary, this invention achieves an overall improvement in the electrochemical performance of materials by controlling the sintering atmosphere through plasma, without relying on the optimization of a single process parameter. This improvement effect cannot be expected by conventional process adjustments in existing technologies, fully demonstrating the significant advancement of the technical solution of this invention.

[0099] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a plasma-assisted controlled O3-type layered-oxide cathode material, characterized in that, The method involves a high-temperature solid-state sintering process of a sodium source and a precursor material in a plasma treatment atmosphere to obtain a plasma-assisted controlled O3-type layered oxide cathode material. The plasma treatment atmosphere is obtained by plasma treatment of a mixture of nitrogen and oxygen. The precursor is Ni. x Fe y Mn 1-x-y (OH)₂, x = 0.2-0.4, y = 0.2-0.4; the plasma-assisted controlled O₃-type layered oxide cathode material contains a 5-20 nm sodium nitrate coating layer; the method includes the following steps: (1) Raw material mixing: Weigh the sodium source and precursor material, mix them evenly to obtain a mixture; (2) Plasma treatment atmosphere: A plasma treatment atmosphere is obtained by subjecting a mixture of nitrogen and oxygen to plasma treatment; (3) The mixture is subjected to a high-temperature solid-state sintering process in a plasma treatment atmosphere to obtain plasma-assisted controlled O3-type layered oxide cathode material; In step (2), the volume ratio of nitrogen to oxygen in the mixed gas containing nitrogen and oxygen is 1-4:1; the excitation power of the plasma treatment is 500-1000W. In step (3), the high-temperature solid-phase sintering process includes a pre-sintering and a high-temperature sintering step, the pre-sintering: the heating rate is 3-15 ℃min -1 , the sintering temperature is 500-600℃, and the holding time is 0.5-3h; high temperature Sintering: heating rate 3-15 °C min -1 sintering temperature 850-950 °C, holding time 3-5 h.

2. The method for preparing a plasma-assisted controlled O3-type layered oxide cathode material according to claim 1, characterized in that, The O3-type layered oxide cathode material is Na. x Ni y Fe z Mn 1-y-z O2, x=0.9-1.2, y=0.2-0.4, z=0.2-0.

4.

3. The method for preparing a plasma-assisted controlled O3-type layered oxide cathode material according to claim 1, characterized in that, In step (1), the sodium source is selected from at least one of Na2CO3, NaOH, NaNO3 or NaCl; and / or, the amount of sodium source fed is 3-10% excess in molar ratio based on Na.

4. The method for preparing a plasma-assisted controlled O3-type layered oxide cathode material according to claim 1, characterized in that, In step (2), the flow rate of the mixture containing nitrogen and oxygen is 150-600 sccm; And / or, in a mixture of nitrogen and oxygen, the flow rate of nitrogen is 100-400 sccm and the flow rate of oxygen is 50-200 sccm.

5. The method for preparing a plasma-assisted controlled O3-type layered oxide cathode material according to claim 1, characterized in that, The method specifically includes the following steps: (1) Raw material mixing: Weigh out sodium source and precursor Ni according to stoichiometric ratio. x Fe y Mn 1-x-y (OH)2, x=0.2-0.4, y=0.2-0.4, wherein the molar ratio of Na is 3-10% excess, and the mixture is thoroughly mixed to obtain a mixture; (2) Plasma treatment atmosphere: N2 and O2 are introduced into the mixing tank, where the flow rate of N2 is 100-400 sccm and the flow rate of O2 is 50-200 sccm. The ratio of N2:O2 is maintained between 1-4:

1. The N2 and O2 mixture is introduced into the plasma device, and the plasma excitation power is set to 500-1000W to form a high-energy mixed atmosphere, which is then connected to the tube furnace. (3) pre-sintering: the mixture is placed in a tube furnace, heated to 550°C at a heating rate of 3-15°C / min -1 and held for 0.5-3h in a plasma treatment atmosphere; (4) High-temperature sintering: continue heating to 930℃, keep warm for 3-5 hours under the same atmosphere, and cool naturally after sintering to obtain plasma-assisted synthesized cathode material.

6. A plasma-assisted controlled O3-type layered oxide cathode material prepared by the preparation method according to any one of claims 1-5.

7. The application of a plasma-assisted controlled O3-type layered oxide cathode material prepared by the preparation method according to any one of claims 1-5 in the field of sodium-ion batteries.

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