A high-air-stability ternary positive electrode material based on a two-step plasma technology, and a preparation method and application thereof

Abstract

The application belongs to the technical field of positive electrode materials, and relates to a high-air-stability ternary positive electrode material based on a two-step plasma technology and a preparation method and application thereof. The ternary positive electrode material and a zirconium source are sintered under normal pressure in an oxygen plasma atmosphere, efficient and uniform doping of Zr elements into the material bulk phase lattice is promoted, the crystallization process of the material is simultaneously completed, and the bulk phase strengthening of the lattice structure is realized. Subsequently, the obtained Zr-doped ternary material is placed in a vacuum environment, a fluorine source gas such as nitrogen trifluoride is introduced, and plasma is excited to generate surface fluorine lithium (LiF) coating. Through the above two-step plasma technology, the synergistic modification of bulk doping and surface coating is realized. The capacity retention rate, cycle life and rate performance of the prepared ternary positive electrode material after exposure to humid air are significantly improved, and the performance is far superior to that of unmodified materials and single modification samples. It has broad industrial application prospects.

Description

Technical Field

[0001] This invention relates to a high-air-stability ternary cathode material based on two-step plasma technology, its preparation method and application, belonging to the field of lithium-ion battery cathode material technology. Background Technology

[0002] Lithium-ion batteries, as a new generation of green, high-energy chemical power sources, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. Layered ternary cathode material LiNi x Co y Mn Z O2 (NCM), with its high specific capacity and high energy density, is considered a key cathode material for achieving long driving range in electric vehicles. Due to Ni... 3+ / 4+ It has strong oxidizing properties, and it reacts with O. 2- The weak bond energy between the lattice oxygen and the carbon atoms makes the lattice oxygen easily oxidized or even released as oxygen under electrochemical or environmental conditions. This intrinsic thermodynamic instability is the fundamental reason for the material's sensitivity to environmental atmospheres (such as H2O and CO2). During the synthesis and storage of the material, the unstable lattice structure promotes the migration of lithium ions to the particle surface, where they react with water vapor and carbon dioxide in the air to generate residual alkaline species such as Li2CO3 and LiOH. This process not only consumes the active lithium source, causing irreversible capacity loss, but also induces structural defects in the near-surface region. With the continuous loss of lithium and the reconstruction of the transition metal valence state, the layered structure on the surface of the material will undergo an irreversible phase transition, transforming into an electrochemically inert rock salt phase (such as NiO). This rock salt phase acts as a dense insulating barrier, severely hindering the diffusion kinetics of lithium ions at the interface, significantly increasing the interfacial impedance, thereby degrading the rate performance of the material and becoming the core cause of continuous capacity decay and voltage polarization during cycling. Therefore, the production, storage, and electrode preparation of ternary cathode materials require strict low-humidity environmental control, which significantly increases the complexity of the process and the manufacturing cost. To fundamentally improve the air stability of ternary materials, the key lies in enhancing their lattice structure stability, especially strengthening the binding capacity of oxygen in the lattice, thereby inhibiting the occurrence of the aforementioned chain degradation reactions from the source.

[0003] To improve the electrochemical performance and stability of high-nickel ternary materials, the industry generally adopts two modification strategies: bulk doping and surface coating. However, both existing technical approaches have significant shortcomings. For example, CN202211726223.7 authorizes a method for preparing zirconium-doped ternary cathode material, the ternary cathode material and its application; the preparation method is as follows: S1. According to the stoichiometric ratio of each element in the zirconium-doped ternary cathode material, a first precursor is prepared by using soluble nickel salt, soluble cobalt salt and a soluble salt containing element M through a first co-precipitation reaction. The first precursor contains nickel, cobalt and manganese, and the stoichiometric ratio of the first precursor is Ni:Co:Mn = 8:1:1; S2. Zirconium dioxide is deposited on the surface of the first precursor through a second co-precipitation reaction to obtain a second precursor, wherein the particle size of the zirconium dioxide is ≤100nm; S3. According to the stoichiometric ratio of each element in the zirconium-doped ternary cathode material, the second precursor is mixed with a lithium source to obtain a third precursor, which is then heated to 480℃ at a heating rate of 5℃ / min, held for 5 hours, and then heated to 800℃ at a heating rate of 5℃ / min. The zirconium-doped ternary cathode material was prepared by holding the material at ℃ for 20 hours; wherein the zirconium doping content in the zirconium-doped ternary cathode material is 0.5%. The core technology relies solely on a complex multi-step wet process and long-term high-temperature sintering (750-900℃) to achieve single-dimensional bulk zirconium doping. This method is not only energy-intensive, lengthy, and prone to introducing impurities, but also completely fails to solve the key industrialization bottleneck of poor air stability caused by residual lithium on the surface of high-nickel ternary materials. Furthermore, it requires long-term sintering at 750-900℃ (12-24 hours), resulting in extremely high energy consumption. CN202510616815.0 discloses a cathode active material with a lithium fluoride layer, its preparation method, and its application. High-purity LiF is used as the target material. NCM material is placed in a high-vacuum magnetron sputtering device, and LiF target atoms are sputtered out under argon (Ar) plasma bombardment. The sputtered LiF atoms are physically deposited on the surface of NCM particles to form a LiF thin film. However, its modification dimension is singular, only performing surface physical coating without involving the doping and strengthening of the bulk lattice of the material, and thus failing to improve structural stability from the root. Secondly, the process cost and complexity are high, relying on expensive LiF targets, high vacuum equipment and precise parameter control, resulting in low production efficiency and making it difficult to meet the needs of large-scale, low-cost continuous production of electrode materials.

[0004] In summary, compared with existing single doping or physical coating technologies, the process of this invention overcomes the common industrial challenges of traditional methods, such as limited modification dimensions, complex processes, and high energy consumption. This invention achieves uniform bulk doping of zirconium at relatively low temperatures through plasma activation, and utilizes a highly active fluorine source for in-situ plasma fluorination to form a dense lithium fluoride coating layer. This integrates the bulk structure and surface interface of the ternary cathode material, simultaneously granting it excellent structural stability, electrochemical performance, and crucial air storage stability. This represents a breakthrough direction in the preparation technology of next-generation high-performance cathode materials. Summary of the Invention

[0005] The purpose of this invention is to address the key problems in existing ternary cathode material modification technologies, such as lattice oxygen instability leading to increased air sensitivity, excessively high doping process temperature causing lithium volatilization, and insufficient ionic conductivity of the coating layer restricting rate performance, which affect long-term cycling performance. This invention provides a high-air-stability ternary cathode material based on two-step plasma technology and its preparation method.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] A method for preparing a high-air-stability ternary cathode material based on a two-step plasma technology, the method comprising:

[0008] (1) A mixture of ternary cathode material and zirconium source is placed in an atmospheric pressure plasma sintering apparatus and an oxygen-rich atmosphere is introduced. After atmospheric pressure sintering, zirconium-doped ternary cathode material is obtained.

[0009] (2) The doped ternary cathode material is transferred to a vacuum plasma treatment device, a fluorine source gas is introduced, and plasma treatment is performed to obtain a ternary cathode material with an in-situ lithium fluoride coating layer on the surface.

[0010] By adopting the above technical solution, the method includes the following core steps: First, under atmospheric pressure conditions, commercial ternary cathode materials mixed with zirconium sources are sintered at medium to high temperatures using oxygen plasma, promoting the efficient infiltration of zirconium elements into the bulk lattice, effectively anchoring lattice oxygen by forming strong Zr-O bonds, inhibiting its precipitation and migration, and essentially enhancing the structural integrity and air stability of the material; Subsequently, in a vacuum environment, a fluorine source such as nitrogen trifluoride plasma is introduced to construct a lithium fluoride coating layer with excellent chemical stability. This method has multiple synergistic advantages: On the one hand, Zr bulk doping inhibits oxygen loss and phase transformation during charge and discharge from the lattice level, significantly reducing the degradation rate of the material in air; On the other hand, the LiF coating layer not only effectively isolates the erosion of water vapor and carbon dioxide, greatly reducing the interfacial impedance, thereby simultaneously improving the capacity retention rate, cycle life, and rate performance of the material. Compared with traditional solid-phase doping and wet coating processes, the present invention realizes the dual optimization of the bulk structure and surface interface of the material under mild conditions, achieving significant technological progress and unexpected synergistic effects.

[0011] Preferably, in step (1), the chemical formula of the ternary cathode material is LiNi x Co y Mn z O2; where x + y + z = 1, 0.6 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2; More preferably, the ternary cathode material is high-nickel NCM, and the chemical formula is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0012] Preferably, in step (1), the ternary cathode material and the zirconium source are mixed by wet mixing to obtain a mixture. More preferably, the wet mixing step includes: mixing the ternary cathode material and a certain amount of zirconium source in a solvent by wet mixing, stirring under heating conditions until the solvent is completely volatilized, and then drying the obtained mixture. More preferably, the solvent is preferably ethanol, and the solvent amount is 30 - 100 ml. Other suitable solvents and solvent amounts can also be selected; The heating and stirring temperature is 60 - 100 °C, and the stirring speed is 400 - 800 r / min; More preferably, the ethanol solvent amount is 60 ml, the heating and stirring temperature is 80 °C, and the stirring speed is 650 r / min. More preferably, the drying temperature is 80 o °C, and the time is 12 h.

[0013] Preferably, in step (1), the doping amount of the zirconium source is 0.5 - 2 at% in terms of the atomic percentage of zirconium element in the total metal molar amount of nickel, cobalt, manganese, and zirconium in the ternary cathode material; More preferably, the doping molar ratio of the zirconium source is 1 at%. More preferably, the mass of the ternary cathode material is between 5 - 10 g.

[0014] Preferably, in step (1), the zirconium source includes at least one of zirconium oxychloride, zirconium nitrate, zirconium acetylacetonate, and zirconium silicate; more preferably, the zirconium source is zirconium nitrate.

[0015] Preferably, in step (1), the ternary cathode material is mixed with the zirconium source and then sieved, with the mesh size preferably being 300 mesh.

[0016] Preferably, in step (1), the sintering temperature is 500~750 °C, more preferably 600 °C. The heating rate does not affect the reaction effect, preferably 2~8 °C / min, more preferably 5 °C / min. The ℃ / min setting facilitates efficient energy utilization, and the sintering time is 2~5 h, more preferably 3 h.

[0017] Preferably, in step (1), the volume ratio of oxygen in the oxygen-enriched atmosphere is not less than 80%, more preferably oxygen; the flow rate of the oxygen-enriched atmosphere, measured in terms of oxygen, is 50~200 sccm, more preferably, the oxygen flow rate is 100 sccm.

[0018] Preferably, the fluorine source gas in step (2) is selected from at least one of nitrogen trifluoride, carbon tetrafluoride, carbonyl fluoride, hexafluorobutadiene, and Freon, with nitrogen trifluoride being a more preferred fluorine source gas. A more preferred fluorine source gas flow rate is 30 sccm.

[0019] Preferably, the plasma treatment conditions in step (2) include: a reaction temperature of 200~500 ℃, a reaction time of 4~10 min, a plasma device power of 200~550 W, and a vacuum degree of 30-100 Pa. More preferably, the reaction temperature is 300 ℃, the reaction time is 6 min, the device power is 300 W, and the vacuum degree is 50 Pa.

[0020] Preferably, the thickness of the surface coating layer of the obtained ternary cathode material is 3~10nm, and the Zr doping amount is 1at.

[0021] Preferably, the method specifically includes the following steps:

[0022] (1) The ternary cathode material and a certain amount of zirconium source are mixed in ethanol solvent by wet method, and stirred under heating conditions until the solvent is completely evaporated. Then the resulting mixture is dried.

[0023] (2) The dried mixture is sieved and then placed in an atmospheric pressure oxygen plasma sintering device and oxygen is introduced. Zirconium-doped ternary cathode material is obtained under the set temperature and time conditions.

[0024] (3) The doped ternary cathode material is transferred to a vacuum plasma processing device, a fluorine source gas is introduced and the plasma device is started. By controlling the processing temperature, time and equipment power, a lithium fluoride-based coating layer is generated in situ on the material surface.

[0025] (4) The obtained sample was subjected to electrochemical performance testing and placed in the air for 10 days, and its electrochemical performance was tested again.

[0026] The present invention also provides a high-air-stability ternary cathode material based on two-step plasma technology prepared by any of the above preparation methods.

[0027] This invention also provides an application of the high air stability ternary cathode material prepared by any of the above preparation methods based on two-step plasma technology in the field of batteries, especially in the field of lithium-ion batteries.

[0028] This invention achieves a significant breakthrough in the field of cathode material modification through an innovative two-step plasma technology. First, under ambient pressure, oxygen plasma is used to achieve uniform doping of zirconium in the material, effectively enhancing the stability of the crystal structure and significantly suppressing the precipitation of lattice oxygen. Subsequently, in a vacuum environment, nitrogen trifluoride plasma is used to induce an in-situ fluorination reaction with the material, successfully constructing a lithium fluoride coating layer with superionic conductivity. This synergistic modification strategy of bulk doping and surface coating solves the long-standing technical challenge of "high capacity - low stability" in ternary cathode materials. This invention achieves synergistic modification of bulk doping and surface coating through the aforementioned two-step plasma technology. The prepared ternary cathode material, after exposure to humid air, exhibits significantly improved capacity retention, cycle life, and rate performance, far exceeding the performance of unmodified materials and single-modification samples. In addition, this plasma technology has the advantages of high energy density, fast reaction speed, and green and pollution-free operation. It effectively overcomes the problems of high energy consumption, uneven coating and easy introduction of impurities in traditional high-temperature sintering and wet coating processes, and has broad prospects for industrial application.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) Plasma technology enables the doping and coating processes to be completed at temperatures significantly lower than those of traditional methods, effectively avoiding lithium volatilization and material structure damage caused by high-temperature processing;

[0031] (2) The lithium fluoride coating layer generated in situ forms a strong bond with the substrate material, which greatly reduces the interfacial impedance and improves the ion transport efficiency.

[0032] (3) This technology avoids the problems of impurity introduction and secondary pollution that may be caused by the all-wet process. The ternary cathode material prepared by this invention exhibits excellent structural stability in air exposure tests, and its capacity retention, cycle life and rate performance are significantly improved. This innovative material modification method provides a new technical path for developing lithium-ion battery cathode materials with both high energy density and long cycle life, and has important industrial application value. Attached Figure Description

[0033] Figure 1 The images show the scanning electron microscope (SEM) morphology of Example 1 and Comparative Example 1, and the mapping diagram of Example 1.

[0034] Figure 2 These are TEM images of Example 1 and Comparative Example 1;

[0035] Figure 3 The XRD refinement images are of Example 1 and Comparative Example 1;

[0036] Figure 4 Commercial unmodified LiNi for Example 1 and Comparative Example 1 0.8 Co 0.1 Mn 0.1 CV plot of O2 sample;

[0037] Figure 5 Impedance spectra of Example 1 and Comparative Example 1;

[0038] Figure 6 This is a comparison graph of the electrochemical performance of Example 1 and Comparative Example 1 at different magnification rates;

[0039] Figure 7 This is a comparison graph of the long-cycle electrochemical performance of Example 1 and Comparative Example 1;

[0040] Figure 8 This is a comparison of the long-cycle electrochemical performance of Example 1 and Comparative Example 1 after being left to stand in air for 10 days.

[0041] Figure 9 XPS spectra of Example 1 and Comparative Example 1O 1s, Ni 2P, Zr 3d, F 1s. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] Example 1

[0045] First, 7 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.3 g of zirconium nitrate (equivalent to a Zr doping concentration of 1 at%) were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. The mixture was then dried and sieved. Subsequently, it was placed in an atmospheric pressure oxygen plasma sintering apparatus and heated to 600 °C at maximum power (e.g., 100% power) and an oxygen flow rate of 100 sccm, and held at that temperature for 3 hours. Afterward, the doped material was transferred to a vacuum plasma treatment apparatus and treated for 6 min at 300 °C, a vacuum of 50 Pa, and a power of 300 W under a nitrogen trifluoride atmosphere at a flow rate of 30 sccm. Finally, depending on the testing requirements, the resulting sample can be left to stand in air for 10 days to evaluate its environmental stability and electrochemical performance.

[0046] Example 2-11

[0047] Based on Example 1, the reaction conditions were changed, including the zirconium source mass, the reaction temperature and time in the atmospheric pressure oxygen plasma sintering stage, and the equipment power, reaction temperature and time in the vacuum plasma treatment stage. The specific conditions are shown in Table 1 below:

[0048]

[0049] Comparative Example 1

[0050] Commercialized, unmodified LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) material. Samples can be left to stand in the air for 10 days, depending on testing requirements.

[0051] Comparative Example 2

[0052] First, 7 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.04 g of zirconium nitrate (equivalent to a Zr doping concentration of 0.1 at%) were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. The mixture was then dried and sieved. Subsequently, the precursor was placed in an atmospheric pressure oxygen plasma sintering apparatus, heated to 800 °C at an oxygen flow rate of 100 sccm, and held at that temperature for 3 hours. Finally, depending on the testing requirements, the resulting sample can be left to stand in air for 10 days. This example tests the effect of a low zirconium source content on the results.

[0053] Comparative Example 3

[0054] First, 7 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.2 g of zirconium nitrate were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus and heated to 800 °C at an oxygen flow rate of 100 sccm and held for 6 hours. The doped material was then transferred to a vacuum plasma treatment apparatus and treated at 200 °C and 250 W for 4 min in a carbon tetrafluoride atmosphere. Finally, the resulting sample could be left to stand in air for 10 days, depending on the testing requirements. This example tested the effect of excessively high calcination temperature and time, which may have exacerbated lithium loss and oxygen leakage in the material.

[0055] Comparative Example 4

[0056] First, 5 g of LiNi 0.8 Co 0.1 Mn 0.1O2 and 0.2 g of zirconium nitrate were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus and heated to 400 °C at an oxygen flow rate of 100 sccm and held for 5 hours. The doped material was then transferred to a vacuum plasma treatment apparatus and treated at 200 °C and 200 W for 10 min under a nitrogen trifluoride atmosphere. Finally, the resulting sample could be left to stand in air for 10 days, depending on the testing requirements. This example tested the effect of excessively low calcination temperature; the parameters in the vacuum positive ion treatment stage were too low, resulting in no doping or coating formation.

[0057] Comparative Example 5

[0058] First, 8 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.8 g of zirconium nitrate (equivalent to a Zr doping concentration of 3 at%) were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus and heated to 600 °C at an oxygen flow rate of 100 sccm and held for 4 hours. Afterward, the doped material was transferred to a vacuum plasma treatment apparatus and treated at 350 °C and 300 W for 8 min under a carbonyl fluoride atmosphere. Finally, the resulting sample can be left to stand in air for 10 days, depending on the testing requirements. This example tests the effect of excessively high zirconium source content.

[0059] Comparative Example 6

[0060] First, 4 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.16 g of zirconium nitrate were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus, heated to 650 °C at an oxygen flow rate of 100 sccm, and held for 4 hours. The doped material was then transferred to a vacuum plasma treatment apparatus and treated at 500 °C and 600 W for 7 min under a carbonyl fluoride atmosphere. Finally, the resulting sample could be left to stand in air for 10 days, depending on the testing requirements. This example and Comparative Example 8 demonstrate the effect of excessively high parameters in the vacuum plasma treatment stage; power and treatment time can cause some damage to the material structure.

[0061] Comparative Example 7

[0062] First, 4 g of LiNi 0.8Co 0.1 Mn 0.1 O2 and 0.2 g of zirconium nitrate were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus, heated to 650 °C at an oxygen flow rate of 100 sccm, and held for 4 hours. The doped material was then mixed with 0.2 g of ammonium fluoride (NH4F) in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an oxygen sintering apparatus, heated to 600 °C at an oxygen flow rate of 100 sccm, and held for 4 hours. Finally, depending on the testing requirements, the resulting sample can be left to stand in air for 10 days. This example tests the effect of plasma zirconium source doping versus conventional coating on product performance.

[0063] Comparative Example 8

[0064] First, 6 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 0.3 g of zirconium nitrate were stirred in 60 mL of ethanol at 80 °C and 650 r / min until the solvent was completely evaporated. After drying and sieving, the material was placed in an atmospheric pressure oxygen plasma sintering apparatus and heated to 650 °C at an oxygen flow rate of 100 sccm and held for 4 hours. The doped material was then transferred to a vacuum plasma treatment apparatus and treated at 400 °C and 600 W for 15 min in a hexafluorobutadiene atmosphere. Finally, the resulting sample can be left to stand in air for 10 days, depending on the testing requirements.

[0065] Comparative Example 9

[0066] First, 7 g of LiNi 0.8 Co 0.1 Mn 0.1 The O2 material is transferred to a vacuum plasma treatment apparatus and treated for 12 minutes at 400 °C and 400 W under a nitrogen trifluoride atmosphere. Finally, the resulting sample can be left to stand in air for 10 days, depending on the testing requirements.

[0067] Performance testing

[0068] The ternary cathode materials prepared in Examples 1-11 and Comparative Examples 1-9 were assembled into coin half-cells for electrochemical testing. The electrolyte was 1 mol / L LiPF6 in DEC:EC:EMC = 1:1:1 vol% (DEC: diethyl carbonate, EC: ethylene carbonate, EMC: methyl ethyl carbonate), and the separator was a PP separator. The batteries were assembled in the order of positive electrode shell, positive electrode sheet, electrolyte, separator, lithium sheet, and negative electrode shell, and then sealed using a sealing machine. The positive electrode sheet was prepared by adding high-nickel ternary cathode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1, along with an appropriate amount of N-methylpyrrolidone. The mixture was stirred in a homogenizer for 40 min to form a slurry, which was then uniformly coated onto bright aluminum foil and vacuum dried at 120 °C for 12 h. Finally, the electrode sheet was cut into circular electrode sheets with a diameter of 12 mm. The active material loading of each electrode sheet was 2–3 mg cm⁻¹. -2 After the battery was left to stand for 24 hours, electrochemical tests were performed using the Xinwei testing system and the Chenhua electrochemical workstation.

[0069] Electrochemical tests were conducted under a constant temperature of 30℃, primarily consisting of constant current charge-discharge tests. These tests included initial discharge capacity (0.1C), rate performance, initial charge-discharge efficiency, and cycle life. Rate performance was tested at current densities of 0.1, 0.3, 0.5, 1, 2, 5, and 0.1C. The constant current charge-discharge test procedure was: 5 min rest - constant current discharge - 5 min rest - constant current charging, with 5 cycles at each rate. Long-cycle performance was tested at a 1C current density. The constant current charge-discharge test procedure was: 5 min rest - constant current discharge - 5 min rest - constant current charging, with 200 cycles. The results are shown in Tables 2-4.

[0070]

[0071] Table 2 shows the rate performance test results of the various embodiments and comparative examples. It can be seen that the ternary cathode material optimized by the two-step plasma technology described in this invention in Example 1 exhibits a high specific capacity of over 202 mAh / g at a current density of 0.1 C. Furthermore, the above materials not only maintain high reversible specific capacity at low rates of 0.1, 0.3, and 0.5 C, but also can still perform reversible charge-discharge at a high rate of 5 C, demonstrating excellent rate performance and kinetic characteristics. Conversely, the ternary cathode materials in Comparative Examples 1-9 have low initial capacities (below 200 mAh / g) at a low current density of 0.1 C, and their reversible specific capacities at 1 and 5 C rates are far lower than those in Examples 1-11. Experiments show that when the zirconium source content, calcination temperature deviates from the preferred range of this invention, or when the vacuum plasma treatment parameters (such as power and time) are too high, the electrochemical performance of the material will decrease. In particular, excessively high vacuum plasma energy will damage the main structure of the material, causing capacity decay and kinetic deterioration. The above results fully demonstrate that the two-step plasma technology and its optimized process conditions adopted in this invention can achieve synergistic effects of bulk doping and surface modification without damaging the material's bulk structure, thereby significantly improving the overall electrochemical performance of the ternary cathode material and verifying the effectiveness of this technical route.

[0072] The electrochemical performance test results of the examples and comparative examples in Tables 3 and 4 show that the charge-discharge efficiency of the ternary cathode materials optimized by the two-step plasma technology in Examples 1-11 is all above 88%, which is a significant improvement compared to the charge-discharge efficiency of the ternary cathode materials in Comparative Examples 1-9. This performance improvement can be attributed to the synergistic effect of zirconium doping and the surface LiF coating: on the one hand, the Zr introduced by the oxygen plasma... 4+ Doping effectively suppressed lithium-nickel mixing and stabilized the layered structure; on the other hand, the LiF coating layer generated in situ by nitrogen trifluoride plasma, as a highly efficient lithium-ion conductor, optimized the interfacial dynamics and promoted Li... + Rapid migration at the interface jointly enhances the initial coulombic efficiency of the material. Furthermore, the half-cell of the high-nickel ternary cathode material optimized by plasma technology retains no less than 80% capacity after 200 cycles at a current density of 1 C. Compared to the lower capacity retention of 49-58% for the half-cells of the high-nickel ternary cathodes in Comparative Examples 1-9, the modification effect is significant. This further demonstrates the crucial role of synergistic modification of the bulk phase and surface: Zr doping strengthens the bulk structure of the material, mitigating lattice strain and microcrack formation during cycling; while the uniform and dense LiF layer on the surface effectively blocks direct contact between the electrolyte and the cathode active material, significantly suppressing interfacial side reactions and transition metal dissolution. The combination of these two factors systematically improves the long-cycle structural and chemical stability of the material.

[0073] Figure 1 The images show a comparison of the SEM morphology of the ternary cathode materials of Comparative Example 1 and Example 1 at magnifications of 6k and 30k, and an elemental distribution diagram of Example 1. All cathode materials exhibit a spherical morphology with an average particle size of approximately 4-6 μm. The SEM image of Comparative Example 1 shows a smooth surface, while the surface smoothness of the ternary cathode material after two-step plasma technology treatment decreases, and continuous dot-like particles are present, indicating the presence of a continuous and dense nano-coating layer on the surface. The elemental distribution diagram of Example 1 shows that Ni, CO, Mn, O, Zr, and F are all distributed on the surface of the material particles.

[0074] Figure 2 The images show TEM images of Comparative Example 1 and Example 1, respectively. In Comparative Example 1, the particles have clear edges, a clean surface, and no obvious covering layer. In contrast, a continuous, uniform, and dense nanoscale amorphous coating layer with a thickness of approximately 5-8 nm can be observed on the surface of the particles in Example 1. This coating layer has a clear interface and tight bonding with the substrate, directly confirming that a structurally complete lithium fluoride (LiF) protective layer was formed in situ on the material surface through nitrogen trifluoride plasma treatment.

[0075] Figure 3 The XRD patterns of Example 1 and Comparative Example 1 are shown in the refined XRD patterns. The XRD peaks of Example 1 exhibit a typical α-NaFeO2 layered structure with space group R-3 m, and no other impurity peaks are observed. Further refined analysis reveals that the Li... + / Ni 2+ The mixing degree decreased significantly from 4.38% in Comparative Example 1 to 2.21%. This confirms that the crystal structure of the high-nickel ternary cathode material after plasma treatment remains intact, and the lower ordered structural defects provide a smoother channel for the rapid insertion and extraction of lithium ions. This explains the excellent initial capacity and rate performance exhibited in Example 1 from the perspective of crystal structure.

[0076] Figure 4 The cyclic voltammetry (CV) curves for the first three cycles of Comparative Example 1 and Example 1 show similar oxidation / reduction peaks for both samples in the voltage range of 2.7–4.4 V, indicating that the two-step plasma treatment did not alter the Li-C of the ternary cathode material. + Storage behavior. It is noteworthy that, in Example 1, the voltage difference (ΔV) between the oxidation and reduction peaks in the first cycle was only 0.085 V, significantly lower than the ΔV value (0.283 V) of Comparative Example 1. This significant reduction in ΔV directly reflects a substantial alleviation of electrode polarization. This is primarily attributed to the synergistic effect of the two-step plasma technology of this invention: on the one hand, the uniformly doped Zr in the bulk phase… 4+The stabilized crystal structure facilitated bulk lithium-ion diffusion. Furthermore, the dense LiF coating layer formed in situ on the surface, acting as an excellent ion conductor, significantly optimized the interfacial lithium-ion transport kinetics. Together, these two factors effectively reduced electrochemical polarization during charge and discharge, thus providing crucial kinetic assurance for the material to achieve excellent rate performance and cycle stability.

[0077] Figure 5 Comparing the impedance spectra of Example 1 and Example 1, the interfacial impedance of Example 1 is significantly lower than that of Comparative Example 1. On one hand, the uniformly doped Zr in the bulk phase... 4+ The crystal structure was stabilized, and the lithium-ion diffusion channels were broadened. On the other hand, the dense LiF coating layer generated in situ on the surface, as an excellent lithium-ion conductor, significantly optimized the interfacial lithium-ion transport dynamics.

[0078] Figure 6 The chart shows a comparison of the rate performance of the ternary cathode materials in Comparative Example 1 and Example 1 at current densities of 0.1, 0.3, 0.5, 1, 2, 5, and 0.1 C. The chart reveals that compared to the unmodified commercial ternary cathode material, the ternary cathode material treated with the two-step plasma technology exhibits significantly improved rate performance at different current densities. The initial charge-discharge efficiency remains above 92%, and it can stably charge and discharge at a current density of 5 C. This superior rate performance is mainly attributed to the bulk-interface synergistic optimization brought about by the two-step plasma technology: on the one hand, the uniform doping of zirconium ions (Zr) in the bulk phase... 4+ The process widens the lithium interlayer spacing, stabilizes the crystal structure, and improves the bulk diffusion rate of lithium ions. On the other hand, the uniform and dense lithium fluoride (LiF) coating layer formed in situ on the surface not only promotes the interfacial transport of lithium ions as a high ionic conductivity interface layer, but also effectively suppresses interfacial side reactions and increased polarization at high rates.

[0079] Figure 7 The graph shows a comparison of the long-term cycling performance of the ternary cathode materials of Comparative Example 1 and Example 1 at a current density of 1 C (1 C = 200 mAh / g). The significant improvement in cycling stability and almost 30% capacity retention of Example 1 compared to Comparative Example 1 demonstrates the advantages of plasma technology modification. This is because the two-step plasma technology described in this invention achieves synergistic enhancement of the bulk structure and surface interface. On one hand, Zr introduced through oxygen plasma... 4+Bulk doping stabilizes the layered crystal framework of the material, effectively suppressing lattice distortion, phase transformation, and microcrack formation caused by repeated lithium-ion insertion / extraction during cycling, thus improving the structural durability of the material itself. On the other hand, the dense and uniform lithium fluoride (LiF) coating layer constructed in situ by nitrogen trifluoride plasma acts as a stable physicochemical barrier, greatly preventing direct contact between the electrolyte and the active material, thereby significantly reducing the occurrence of harmful interfacial side reactions.

[0080] Figure 8 The graph shows a comparison of the long-cycle performance of the ternary cathode materials of Comparative Example 1 and Example 1 after being exposed to air for 10 days and then subjected to a current density of 1 C (1 C = 200 mAh / g). After exposure to the same environment, the cycle stability and capacity retention of Example 1 are significantly better than those of Comparative Example 1. Specifically, Example 1 retains 84% ​​of its capacity after 100 cycles, while Comparative Example 1 retains only 43%. Further comparison of the performance of Examples 2 and 3 after air exposure: Example 2 (only Zr bulk doping, no surface LiF coating) retains 66% of its capacity after 100 cycles after being exposed to air for 10 days, which is better than the unmodified Comparative Example 1 but lower than Example 1; Example 3 (only surface LiF coating, no bulk Zr doping) retains 70% of its capacity under the same conditions, also lower than Example 1. In terms of capacity decay, the capacity decay of Comparative Example 1 and Examples 1-3 is 17%, 6%, 13%, and 10%, respectively. This result clearly demonstrates that while a single modification strategy (doping or coating only) can improve the air stability of materials to some extent, its effect is limited. Only by achieving synergistic modification of bulk doping and surface coating through the two-step plasma technology described in this invention (Example 1) can the degradation caused by air exposure be effectively suppressed while maintaining high performance, thereby obtaining the best overall air stability. This is because the dense lithium fluoride (LiF) coating layer generated in situ on the surface can effectively isolate moisture and carbon dioxide in the air, greatly mitigating the process of residual lithium compounds on the material surface reacting with moisture to form LiOH / Li2CO3, thus avoiding surface degradation caused by air exposure; at the same time, bulk zirconium doping strengthens the crystal structure, enabling the material to maintain structural integrity even under exposure conditions.

[0081] Figure 9 The XPS spectra of O 1s, Ni 2p, Zr 3d, and F 1s for Comparative Example 1 and Example 1 are shown. The peak at 531.8 eV is attributed to surface-adsorbed oxygen, and the peak at 529.5 eV originates from lattice oxygen. Clearly, the lattice oxygen peak intensity of Example 1, modified using a two-step plasma technology, is significantly stronger than that of Comparative Example 1, indicating that Zr… 4+Successful doping enhanced metal-oxygen bonding, stabilized lattice oxygen, and suppressed oxygen loss, thereby improving the structural stability of the material. The Ni peak at 856.2 eV... 3+ ， The peak at 529.5 eV originates from Ni. 2+ Ni from Example 1, modified using a two-step plasma technology 3+ The higher peak content compared to Comparative Example 1 reduces lithium-nickel mixing and improves reversible capacity. In the Zr 3d spectrum, Example 1 exhibits clear Zr 3d peaks at 183.8 eV and 181.4 eV, directly confirming the successful introduction of zirconium into the bulk phase of the material as a dopant. In the F 1s spectrum, Example 1 shows a distinct characteristic peak at 685 eV, attributed to LiF, confirming the in-situ formation of a LiF coating layer on the material surface through nitrogen trifluoride plasma treatment.

[0082] The two-step plasma modification technology provided by this invention significantly improves the overall performance of ternary cathode materials through precise bulk and surface synergistic modification. In terms of bulk modification, zirconium doping assisted by oxygen plasma effectively enhances the binding energy of lattice oxygen, significantly improving the intrinsic air stability of the material. In terms of surface modification, the superionic conductor inner layer constructed using nitrogen trifluoride gas plasma technology forms a dense protective layer. The ternary cathode material treated with this technology exhibits excellent comprehensive performance: maintaining excellent structural stability in an air environment, possessing superior cycle life and rate performance, while effectively suppressing interfacial side reactions. This innovative material modification method provides reliable technical support for the development of high-performance lithium-ion batteries and has broad application prospects in new energy vehicles, portable electronic devices, and energy storage systems.

[0083] 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 high-air-stability ternary cathode material based on two-step plasma technology, characterized in that, Includes the following steps: (1) Place the mixture of the ternary cathode material and the zirconium source in a plasma sintering device, and introduce an oxygen-rich atmosphere. After sintering, a zirconium-doped ternary cathode material is obtained; the chemical formula of the ternary cathode material is LiNi x Co y Mn z O2; where x + y + z = 1, 0.6 ≤ x < 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2; the doping amount of the zirconium source is 0.5 - 2 at% in terms of the atomic percentage of zirconium element in the total metal molar amount of nickel, cobalt, manganese, and zirconium; the sintering temperature is 500 - 750 °C, and the sintering time is 2 - 5 h; (2) The doped ternary cathode material is transferred to a vacuum plasma treatment device, a fluorine source gas is introduced, and plasma treatment is performed to obtain a ternary cathode material with an in-situ lithium fluoride-based coating layer on the surface; the fluorine source gas is selected from at least one of nitrogen trifluoride, carbon tetrafluoride, carbonyl fluoride, hexafluorobutadiene, and Freon; the thickness of the coating layer on the surface of the ternary cathode material is 3~10 nm; the plasma treatment conditions include: reaction temperature of 200~500 ℃, reaction time of 4~10 min, and plasma device power of 200~550 W.

2. The method for preparing a high-air-stability ternary cathode material based on two-step plasma technology according to claim 1, characterized in that, In step (1), a wet mixing method is used to mix the ternary cathode material and the zirconium source to obtain a mixture. The wet mixing step includes: mixing the ternary cathode material and the zirconium source in a solvent by wet mixing, stirring under heating conditions until the solvent is completely evaporated, and then drying the resulting mixture. And / or, the amount of ethanol solvent is 30-100 ml, the heating and stirring temperature is 60-100 ℃, and the stirring speed is 400-800 r / min; And / or, the amount of ethanol solvent is 60 ml, the heating and stirring temperature is 80 ℃, and the stirring speed is 650 r / min.

3. The method for preparing a high-air-stability ternary cathode material based on two-step plasma technology according to claim 1, characterized in that, In step (1), the zirconium source includes at least one of zirconium oxychloride, zirconium nitrate, zirconium acetylacetonate, zirconium oxychloride, and zirconium silicate; And / or, the oxygen volume ratio in the oxygen-enriched atmosphere is not less than 80%, and the flow rate of the oxygen-enriched atmosphere, measured in oxygen meters, is 50~200 sccm.

4. The method for preparing a high-air-stability ternary cathode material based on two-step plasma technology according to claim 3, characterized in that, The zirconium source is zirconium nitrate; And / or, the doping amount of the zirconium source is 1 at% as an atomic percentage of zirconium in the total molar mass of nickel, cobalt, manganese, and zirconium. And / or, the oxygen-enriched atmosphere is oxygen, with an oxygen flow rate of 100 sccm; And / or, the sintering temperature is 600℃ and the sintering time is 3h.

5. The method for preparing a high-air-stability ternary cathode material based on two-step plasma technology according to claim 1, characterized in that, The fluorine source gas is nitrogen trifluoride, and / or the plasma treatment conditions include: reaction temperature 300℃, reaction time 6 min, and equipment power 300 W.

6. A high-air-stability ternary cathode material prepared by the preparation method according to any one of claims 1 to 5, based on two-step plasma technology.

7. The application of the high air stability ternary cathode material based on two-step plasma technology as described in claim 6 in the field of batteries.

Images