A lithium ion conductor coated high-nickel ternary positive electrode material constructed in situ by plasma assistance and a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery cathode material, and provides a kind of plasma assisted in-situ construction lithium ion conductor coated high nickel ternary cathode material and its preparation method and application.The application forms oxygen plasma active group by high pressure ionization oxygen, the active group generated interacts with the gas generated by the thermal decomposition of the added solid source, can consume high nickel ternary cathode surface residual alkali and form a thin, continuous and dense lithium ion conductor coating layer on the surface of high nickel ternary cathode material in-situ, which helps to promote the development of high nickel ternary cathode material of lithium ion battery.The high nickel ternary cathode material prepared by the application shows high specific capacity, excellent cycle stability, rate performance and first charge-discharge efficiency.At the same time, the preparation method provided by the application is simple, fast, efficient and convenient, and the cost is low, which can effectively remove the residual alkali on the surface of high nickel ternary cathode material and improve the structural stability of high nickel ternary cathode material.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a high-nickel ternary positive electrode material coated with a lithium ion conductor by means of plasma-assisted in-situ construction, and belongs to the technical field of positive electrode materials of lithium ion batteries. BACKGROUND

[0002] Due to the aggravation of energy crisis and the improvement of environmental awareness, electric vehicles are attracting more and more attention. In the field of electric vehicles, lithium ion batteries are considered to be one of the most ideal power sources due to their long cycle life, high energy density and environmental protection. However, the biggest problem hindering the development of electric vehicles is still the limitation of the cruising range, which requires lithium ion batteries to achieve higher energy density. In lithium ion batteries, the energy density is mainly determined by the positive electrode material. At present, high-nickel ternary positive electrode materials are mainly used as positive electrode materials for lithium ion batteries of electric vehicles, but the development of such materials still faces bottleneck problems, which seriously affect the performance of the batteries. First, due to the thermodynamic instability of H3 phase and the easy reaction with water and carbon dioxide, high-nickel ternary positive electrode materials form surface residual alkali and irreversible rock salt phase. The accumulation of these surface residual alkali and rock salt phase will block the transmission channel of lithium ions, affecting the performance of the material. Secondly, high-nickel ternary materials have anisotropic lattice shrinkage phenomenon during the cycle process, which will cause the instability of the structure, thus producing local stress at the boundary of the material particles and forming micro-cracks. These micro-cracks will allow the electrolyte to penetrate and erode the inside of the material particles, causing serious side reactions, which are the main reason for the degradation of high-nickel positive electrode materials.

[0003] At present, surface coating is an effective modification strategy to solve the above problems, such as coating oxides, fluorides and metal phosphates. For example, CN105470509A discloses a new type of NCA material and a preparation method thereof, which can not only reduce the pH value but also improve the cycle performance of the NCA material. The technical points are as follows: the new type of NCA material is ammonium hexafluorophosphate coated NCA material; the preparation method is as follows: 1) dissolving ammonium hexafluorophosphate in deionized water, stirring until completely dissolved, adding NCA material, and fully mixing and stirring to make the mixture uniform; 2) drying in an oven, sieving, and sintering in a furnace at 400-500 DEG C for 2-4 hours; the mass ratio of ammonium hexafluorophosphate, deionized water and NCA material is 1:20-30:80-120. However, the process is too complicated and involves multiple steps such as dissolving, stirring, drying, sieving and high-temperature sintering, which is relatively complex and increases the production time and cost. Moreover, high-nickel positive electrode materials (such as NCA) are very sensitive to moisture, and exposure to aqueous solution leads to an increase in surface residual alkali and degradation of the material structure. CN201310699033.5 discloses a preparation method of carbon-coated ternary positive electrode material, which dissolves dry ternary positive electrode material and organic carbon source in an organic solvent and then dries, sintering at 240~350 DEG C for 2~4 hours. However, the process is also relatively complex and involves multiple steps such as dissolving, stirring, drying and sintering, which increases the production time and cost.o C heat treatment for 2-8 hours to obtain carbon-coated ternary cathode material. However, most of the coating can solve the problem of residual alkali to some extent, but the adhesion to the surface of the oxide is weak, and it is difficult to achieve thin and uniform, and the over-thick coating layer will hinder the transmission of lithium ions and reduce the performance. And the preparation method of the coating layer in the current field usually has problems of high reaction temperature, too long preparation time, reduction of high-nickel ternary cathode material during coating process, and too high cost of material equipment. Therefore, it is crucial to develop a uniform and dense coating layer technology that can be closely combined with the surface of the cathode material. SUMMARY

[0004] The purpose of the present application is to solve the problems of high reaction temperature, too long preparation time, non-uniform and thick coating layer, reduction of high-nickel ternary cathode material during coating process, easy peeling of coating layer, and too high cost of material equipment in the prior art coating of high-nickel ternary cathode material. A plasma-assisted in-situ construction of lithium ion conductor coated high-nickel ternary cathode material and its preparation method and application are provided. The method is to consume the residual alkali on the surface of the high-nickel ternary cathode by the interaction of the high-activity oxygen plasma and the gas generated by the thermal decomposition of the solid source at a certain temperature, and to generate a uniform and dense thin and good-conductivity lithium ion conductor coating layer on the surface of the high-nickel ternary cathode in-situ after a certain time of plasma treatment. This method can effectively solve the problems of too long preparation time, non-uniform coating layer, and high cost in the process of traditional chemical vapor deposition, and can achieve good and uniform coating while effectively improving the performance of the material such as cycle and rate, achieving unexpected technical effects.

[0005] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is:

[0006] The present application provides a preparation method of plasma-assisted in-situ construction of lithium ion conductor coated high-nickel ternary cathode material. The method is to modify the high-nickel ternary cathode material with a solid source and oxygen as plasma source to obtain a plasma-assisted in-situ construction of lithium ion conductor coated high-nickel ternary cathode material. The solid source includes at least one of ammonium hexafluorophosphate, ammonium hexafluorosilicate, ammonium metatungstate, ammonium fluoroborate, urea, and thiourea.

[0007] Preferably, the method comprises the following steps:

[0008] (1) uniformly mix the high-nickel ternary cathode material with the solid source, and then place it in the reaction cavity of the plasma reaction device, the two ends of the plasma reaction device being in communication with a vacuum pump and an oxygen source respectively;

[0009] (2) warm up and vacuumize the reaction cavity of the plasma reaction device, and introduce oxygen;

[0010] (3) Rotate the reaction cavity, start the plasma reaction device, adjust the power after ignition, react for a period of time, and obtain a lithium ion conductor coated high-nickel ternary positive electrode material.

[0011] Preferably, the reaction cavity in step (1) is a special-shaped tube, which can further increase the processing capacity of the sample, facilitate uniform mixing of the sample, and reduce the loss of the sample during vacuum pumping.

[0012] Preferably, the chemical formula of the high-nickel ternary positive electrode material in step (1) is LiNi x Co y Mn Z O2; wherein 0.6≤x<1, 0.01≤y<0.4, 0.01≤z<0.4, and x+y+z=1; more preferably, the chemical formula of the high-nickel ternary positive electrode material is LiNi 0.9 Co 0.05 Mn 0.05 O2.

[0013] Preferably, in step (1), the mass of the solid source accounts for 1% to 10% of the mass of the high-nickel ternary positive electrode material; more preferably, the mass of the solid source is 0.01 to 1 g, and the mass of the high-nickel ternary positive electrode material is 1 to 10 g; more preferably, the mass of the solid source is 0.04 g, and the mass of the high-nickel ternary positive electrode material is 2 g.

[0014] Preferably, in step (1), the solid source includes at least one of ammonium hexafluorophosphate, ammonium hexafluorosilicate, ammonium metatungstate, ammonium fluoroborate, urea, and thiourea; more preferably, the solid source is ammonium hexafluorophosphate.

[0015] Preferably, in step (2), the temperature of the temperature rise is 100 to 600 o C, and more preferably, the temperature of the temperature rise is 300 o C. The temperature rise rate does not affect the reaction effect, and preferably, the temperature rise rate is 2 to 8 o C / min, and more preferably, the temperature rise rate is 5 o C / min, which facilitates efficient use of energy.

[0016] Preferably, in step (2), the oxygen flow rate is 10 to 100 sccm, and the vacuum degree after the oxygen is introduced is 10 to 200 Pa; more preferably, the oxygen flow rate is 30 sccm, and the vacuum degree after the oxygen is introduced is 50 Pa.

[0017] Preferably, the rotation speed of the reaction cavity in step (3) is 30-200 r / min, the reaction time is 3-30 min, the equipment power is 50-500 W, and the reaction temperature is 100-600 DEG C, more preferably, the rotation speed of the special-shaped tube is 150 r / min, the reaction time is 10 min, the equipment power is 200 W, and the reaction temperature is 300 DEG C. The rotating reaction cavity can further promote the uniform reaction.

[0018] Preferably, the surface coating layer of the obtained lithium ion conductor coated high-nickel ternary positive electrode material is 3-5 nm thick.

[0019] The application also provides a high-nickel ternary positive electrode material with a lithium ion conductor coating layer constructed in situ by plasma assistance, which is prepared by any one of the preparation methods.

[0020] The application also provides application of the high-nickel ternary positive electrode material with a lithium ion conductor coating layer constructed in situ by plasma assistance in the field of batteries, in particular in the field of lithium ion batteries.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] The method for constructing a lithium ion conductor coated high-nickel ternary positive electrode material by plasma provided by the application realizes multiple technical breakthroughs through innovative process design: under a certain temperature, high-activity oxygen plasma and the gas generated by the thermal decomposition of the added solid source react with each other, consume the residual alkali on the surface of the high-nickel ternary positive electrode material, and generate a lithium ion conductor on the surface of the positive electrode material in situ. This technology breaks through the construction of a dense and uniform ion conductive network on the surface of the high-nickel ternary positive electrode material, successfully solves the long-existing technical paradox of 'high capacity-low life' of the high-nickel ternary material, and provides an innovative solution for the synergistic improvement of the energy density and service life of power batteries. Moreover, the high-nickel ternary positive electrode material prepared by the application exhibits high specific capacity, excellent cycle stability, rate performance and first charge-discharge efficiency.

[0023] The preparation method of the high-nickel ternary positive electrode material with a lithium ion conductor coating layer constructed in situ by plasma assistance provided by the application and the application thereof have the advantages of the traditional 500-700 o The lithium ion conductor coated high-nickel ternary positive electrode material obtained by the method such as CVD has the advantage of lower process temperature, can better maintain the original characteristics of the positive electrode material, and avoid performance degradation of the positive electrode material caused by high temperature. The preparation method provided by the application is simple, fast, efficient, convenient and low in cost, can effectively remove the residual alkali on the surface of the high-nickel ternary positive electrode material, and improve the structural stability of the high-nickel ternary positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1SEM morphology of Example 1 and Comparative Example 1;

[0025] Figure 2 mappping of Example 1;

[0026] Figure 3 XRD refinement of Example 1;

[0027] Figure 4 CV of Example 1 and Comparative Example 1 commercial unmodified LiNi 0.9 Co 0.05 oMn 0.05 CV of Example 1 and Comparative Example 1 commercial unmodified LiNi

[0028] Figure 5 Electrochemical performance of Example 1 and Comparative Example 1 at different rates;

[0029] Figure 6 Long cycle electrochemical performance of Example 1 and Comparative Example 1;

[0030] Figure 7 C 1s XPS of Example 1 and Comparative Example 1;

[0031] Figure 8 TEM of Example 1 and Comparative Example 1 after cycling. DETAILED DESCRIPTION

[0032] In order to better clarify and understand the purpose, process scheme and advantages of the present application, the technical scheme and implementation of the present application are further clearly, completely and specifically described below by specific examples, and combined with the drawings. It should be known that the described examples of the present application are implemented on the premise of the technical scheme of the present application, and give detailed implementation and specific operation process, but only part of the examples of the present application, not all examples. The described specific implementation is limited to the description and explanation of the present application, and does not limit the present application. Based on the examples in the present application, all other implementation ways obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0033] The experimental methods and conditions used in the examples of the present application are conventional methods and conventional conditions, and the materials, reagents or instrument devices used in the examples, unless otherwise specified, are conventional substances or devices known to those skilled in the art and can be obtained from commercial channels or prepared by conventional methods. The reaction conditions embodied in the content of the present application can realize the described reaction and obtain the expected effect product. Due to the limitation of the length, the following part of the examples are listed to further illustrate the advantages of the technical scheme of the present application.

[0034] Example 1

[0035] 0.04 g of ammonium hexafluorophosphate was uniformly ground with 2 g of LiNi 0.9 C 0.05 oMn 0.05 O2(NCM90) into a mortar, the mixture was placed into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to an oxygen gas circuit, the oxygen flow rate was adjusted to 30 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM90 mixture was entirely in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma equipment were connected to the two ends of the special-shaped tube, respectively. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 300°C and kept, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to be 150 r / min to make the powder in the special-shaped tube roll uniformly. The plasma equipment was started, the power was adjusted to 200 W, and the reaction was carried out for 10 min to obtain LiF / Li3PO4 double lithium ion conductor coated NCM90 positive electrode material.

[0036] Examples 2-11

[0037] On the basis of Example 1, the reaction conditions were changed, including solid source and its content, high-nickel ternary positive electrode material, reaction temperature, reaction time, equipment power, oxygen flow rate, etc., and the specific conditions are shown in Table 1.

[0038]

[0039] Comparative Example 1

[0040] Commercial LiNi 0.9 C 0.05 oMn 0.05 O2(NCM90) material without any modification.

[0041] Comparative Example 2

[0042] 0.02 g of ammonium hexafluorophosphate was uniformly ground with 2 g of LiNi 0.9 C 0.05 oMn 0.05O2 (NCM90) was put into a mortar and uniformly ground. The mixture was put into a rotatable special-shaped tube. The gas outlet of the special-shaped tube was connected to a vacuum pump, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM90 was entirely in the temperature zone of the heating furnace. The two ends of the special-shaped tube were respectively connected to the positive and negative electrode lines of a plasma device. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 150 ℃, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma device was started, the power was adjusted to 100 W, and the reaction was performed for 10 min.

[0043] Comparative Example 3

[0044] 0.3 g of ammonium hexafluorophosphate was mixed with 3 g of LiNi 0.9 Co 0.05 oMn 0.05 O2 (NCM90) was put into a mortar and uniformly ground. The mixture was put into a rotatable special-shaped tube. The gas outlet of the special-shaped tube was connected to a vacuum pump, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM90 was entirely in the temperature zone of the heating furnace. The two ends of the special-shaped tube were respectively connected to the positive and negative electrode lines of a plasma device. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 100 ℃, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma device was started, the power was adjusted to 150 W, and the reaction was performed for 20 min.

[0045] Comparative Example 4

[0046] 0.05 g of thiourea was mixed with 5 g of LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM90) was put into a mortar and uniformly ground. The mixture was put into a rotatable special-shaped tube. The gas outlet of the special-shaped tube was connected to a vacuum pump, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM90 was entirely in the temperature zone of the heating furnace. The two ends of the special-shaped tube were respectively connected to the positive and negative electrode lines of a plasma device. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 100 ℃, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma device was started, the power was adjusted to 150 W, and the reaction was performed for 20 min.

[0047] Comparative Example 5

[0048] 0.08 g of ammonium fluoroborate was uniformly ground with 2 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) into a mortar, the mixture was placed into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM811 was entirely in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma equipment were connected to the two ends of the special-shaped tube. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube from being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 200°C, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to be 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma equipment was started, the power was adjusted to 100 W, and the reaction was performed for 20 min.

[0049] Comparative Example 6

[0050] 0.5 g of ammonium fluoroborate was uniformly ground with 4 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) into a mortar, the mixture was placed into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM811 was entirely in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma equipment were connected to the two ends of the special-shaped tube. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube from being sucked away due to sudden change in suction. The temperature of the tube furnace was adjusted to 300°C, the vacuum degree in the special-shaped tube was controlled to reach 50 Pa, the rotating device was turned on, and the rotating speed was controlled to be 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma equipment was started, the power was adjusted to 200 W, and the reaction was performed for 15 min.

[0051] Comparative Example 7

[0052] 0.2 g of ammonium metatungstate was uniformly ground with 5 g of LiNi 0.92 Co 0.04 Mn 0.04O2 (NCM92) was put into a mortar and ground evenly, the mixture was put into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM92 was all in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma equipment were connected to the two ends of the special-shaped tube respectively. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid that the material in the special-shaped tube was sucked away due to sudden change of suction. The temperature of the tube furnace was adjusted to 300 ℃, the vacuum degree in the special-shaped tube was controlled to 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 60 r / min to make the powder in the special-shaped tube roll uniformly. The plasma equipment was started, the power was adjusted to 150 W, and the reaction was carried out for 10 min.

[0053] Comparative Example 8

[0054] 0.01 g of ammonium tungstate was mixed with 1 g of LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM92) was put into a mortar and ground evenly, the mixture was put into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM92 was all in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma equipment were connected to the two ends of the special-shaped tube respectively. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid that the material in the special-shaped tube was sucked away due to sudden change of suction. The temperature of the tube furnace was adjusted to 450 o C, the vacuum degree in the special-shaped tube was controlled to 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma equipment was started, the power was adjusted to 300 W, and the reaction was carried out for 15 min.

[0055] Comparative Example 9

[0056] 0.07 g of ammonium hexafluorosilicate was mixed with 1 g of LiNi 0.83 Co 0.06 Mn 0.01O2(NCM83) was put into a mortar and ground evenly, the mixture was put into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM83 was all in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma device were connected to the two ends of the special-shaped tube respectively. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change of suction. The temperature of the tube furnace was adjusted to 250 ℃, the vacuum degree in the special-shaped tube was controlled to 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma device was started, the power was adjusted to 300 W, and the reaction was carried out for 10 min.

[0057] Comparative Example 10

[0058] 0.9 g of ammonium hexafluorosilicate was mixed with 8 g of LiNi 0.83 Co 0.06 Mn 0.01 O2(NCM83) was put into a mortar and ground evenly, the mixture was put into a rotatable special-shaped tube, the gas outlet of the special-shaped tube was connected to a vacuum pump, the gas inlet was connected to oxygen, the oxygen flow rate was 50 sccm, and the center part of the special-shaped tube was placed on a heating furnace to ensure that the NCM83 was all in the temperature zone position of the heating furnace. The positive and negative electrodes of the plasma device were connected to the two ends of the special-shaped tube respectively. The vacuum pump was turned on, and the suction was gradually turned to the maximum through the knob of the vacuum pump to avoid the material in the special-shaped tube being sucked away due to sudden change of suction. The temperature of the tube furnace was adjusted to 300 o C, the vacuum degree in the special-shaped tube was controlled to 50 Pa, the rotating device was turned on, and the rotating speed was controlled to 100 r / min to make the powder in the special-shaped tube roll uniformly. The plasma device was started, the power was adjusted to 150 W, and the reaction was carried out for 20 min.

[0059] Performance test

[0060] The high-nickel ternary positive electrode materials prepared in the above Examples 1-11 and Comparative Examples 1-10 were assembled into button 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: ethyl methyl carbonate), and the separator was a PP separator. The cells were assembled in the order of positive electrode shell, positive electrode sheet, electrolyte, separator, lithium sheet, and negative electrode shell, and were tightly sealed with a packaging machine, wherein the positive electrode sheet of the cell was prepared by adding the high-nickel ternary positive electrode material of each example, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1, adding an appropriate amount of N-methyl pyrrolidone, stirring in a homogenizer for 40 min to prepare a slurry, then uniformly coating the slurry on a bright aluminum foil, vacuum drying at 100 °C for 12 h, and finally cutting the electrode sheet into a circular electrode sheet with a diameter of 12 mm. The loading of active material of each electrode sheet was 2-3 mg cm -2 After the cells were left to stand for 24 hours, electrochemical testing was performed using a Neware test system and a Chenhua electrochemical workstation.

[0061] The electrochemical tests were all performed under constant temperature conditions at 30 °C, and mainly included constant current charge-discharge tests. In the constant current charge-discharge tests, the main indicators included the first discharge capacity (0.1C), rate performance, first charge-discharge efficiency, and cycle life. The rate performance of the battery was tested at current densities of 0.1, 0.2, 0.5, 1, 2, and 5, and 0.1C. The process of the constant current charge-discharge test was: standing for 5 min - constant current discharge - standing for 5 min - constant current charging, and each cycle was repeated 5 times at different rates. The long cycle performance of the battery was tested at a current density of 1C. The process of the constant current charge-discharge test was: standing for 5 min - constant current discharge - standing for 5 min - constant current charging, and the cycle was repeated 300 times.

[0062]

[0063]

[0064] From the rate performance test results of each example and comparative example in Table 2, it can be found that the high-nickel ternary positive electrode materials of Example 1 optimized by the plasma technology described in the application all exhibit high specific capacity of 229 mAh / g or more at a current density of 0.1 C. In addition, the above-mentioned materials not only maintain high reversible specific capacity at small rates of 0.1, 0.2 and 0.5 C, but also can still perform reversible charging and discharging at a high rate of 5 C, and the rate performance is very excellent. In contrast, the high-nickel ternary positive electrode materials in Comparative Examples 1-10 have low initial capacity, all lower than 215.6 mAh / g at a small rate current density of 0.1 C, and the reversible specific capacity at rates of 1 and 5 C is much lower than that of Example 1-11. It can be seen that when the parameter range of the plasma technology is too low, the plasma energy is not enough to form a coating layer on the surface of the material, so the performance is poor. When the parameter is too high, the energy of the plasma is too high, which destroys the structure of the material and leads to a decrease in performance. Therefore, it is proved that the plasma technology and its conditions of the application are very effective for improving the performance of high-nickel positive electrode materials.

[0065] From the electrochemical performance test results of each example and comparative example in Table 3, it can be found that the high-nickel ternary positive electrode materials of Example 1-11 optimized by the plasma technology all have a charge-discharge efficiency of 88.8% or more, which is obviously improved compared with the charge-discharge efficiency of the high-nickel ternary positive electrode materials of Comparative Examples 1-10. This may be because the high-nickel ternary positive electrode material modified by the plasma technology forms a lithium ion conductor coating layer on the surface which is easy for lithium ion transmission, which can promote the transmission of Li+. In addition, the half-cell of the high-nickel ternary positive electrode material optimized by the plasma technology has a capacity retention of not less than 80% after 300 cycles at a current density of 1 C, which is significantly improved compared with the capacity retention of 50-62% of the half-cell of the high-nickel ternary positive electrode of Comparative Examples 1-10. The modification effect is remarkable because the existence of the double coating layer on the surface can effectively prevent the contact between the electrolyte and the surface of the ternary positive electrode material, reduce the side reaction between the material and the electrolyte, and improve the cycle stability of the material.

[0066] Figure 1 The SEM morphology contrast chart of the high-nickel ternary positive electrode materials of Comparative Example 1 and Example 1 at magnifications of 8k and 30k. All the positive electrode materials exhibit spherical morphology, and the average particle size is about 4-6 μm. The SEM image of Comparative Example 1 shows that its surface is smooth, while the surface smoothness of the high-nickel ternary positive electrode material treated by the plasma technology decreases, and there are continuous point-like particles, indicating that there is a continuous and dense nano-coating layer on the surface.

[0067] Figure 2 The element distribution chart of Example 1 shows that the Ni, CO, Mn, O, P and F elements are distributed on the surface of the material particles.

[0068] Figure 3 The XRD peaks of Example 1 exhibit a typical a-NaFe02layered structure with space group R-3m and other impurity peaks are not observed, confirming that the crystal structure of the high-nickel ternary cathode material after plasma treatment is intact, and has a lower Li + / Ni 2+ mixing degree.

[0069] Figure 4 For the cyclic voltammetry (CV) curves of Comparative Example 1 and Example 1 for the first three cycles, both samples exhibit similar oxidation / reduction peaks in the voltage range of 2.7-4.4 V, indicating that the plasma treatment does not change the Li + storage behavior of the high-nickel ternary cathode material. Notably, Example 1 exhibits a AV value of 0.154 V in the first cycle, which is significantly smaller than that of Comparative Example 1 (0.269 V), indicating that the polarization of Comparative Example 1 has been effectively inhibited by the plasma treatment.

[0070] Figure 5 For the high-nickel ternary cathode materials of Comparative Example 1 and Example 1, the rate performance comparison chart at 0.1, 0.2, 0.5, 1, 2, 5, 0.1 C current density, it can be found in the rate performance comparison chart that compared with the unmodified commercial high-nickel ternary cathode material, the high-nickel ternary cathode material after plasma treatment has a greater improvement in rate performance at different current densities, the first charge-discharge efficiency is maintained above 92% and can be stably charged and discharged at 5 C current density, which is due to the formation of a uniform and dense coating layer on the surface of the high-nickel ternary cathode material after modification by plasma technology, which is beneficial to improve the interface stability and lithium ion transport kinetics during the material cycle.

[0071] Figure 6 For the high-nickel ternary cathode materials of Comparative Example 1 and Example 1, the long cycle performance comparison chart of half-cell at 1 C (1 C = 200 mAh / g) current density, the significant improvement in cycle stability of Example 1 compared to Comparative Example 1 almost 30% capacity retention proves the advantage of modification by plasma. This is because the interaction of high-activity oxygen plasma and gas produced by the decomposition of ammonium hexafluorophosphate forms a Li / Li3PO4 double lithium ion conductor coating layer on the surface of the high-nickel ternary material, and it is precisely because of the existence of the coating layer that Example 1 has superior long cycle performance.

[0072] Figure 7 For the C 1s spectra of Comparative Example 1 and Example 1, the peak at 289.8 eV is attributed to the surface CO3 2-The peak at 284.8 eV is derived from C-C / C-H on the surface. It is clear that the intensity of the peak at 289.8 eV of Example 1 is significantly weaker than that of Comparative Example 1 after plasma treatment, which indicates that the residual alkali on the surface of Example 1 is significantly reduced after modification.

[0073] Figure 8 The TEM pictures of the cycled positive electrode of Comparative Example 1 and Example 1 show that the surface of the particles of the cycled positive electrode of Comparative Example 1 and Example 1 both have a certain degree of rock salt structure, but the thickness of the rock salt phase of Comparative Example 1 is significantly higher than that of Example 1. This indicates that the structure of the sample treated by plasma is better protected and can effectively hinder the growth of the rock salt phase.

[0074] The plasma technology optimizes the treatment of high-nickel ternary positive electrode materials to obtain a stable surface structure, which combines a lithium ion conductor coating layer, inhibits the surface degradation of the nickel cathode, and can effectively remove the residual alkali on the surface of the high-nickel ternary positive electrode material. The surface co-coating effectively prevents the spread of the rock salt structure to the bulk positive electrode. It has broad application prospects in the fields of small mobile electronic devices, electric vehicles, solar power generation, and aerospace.

[0075] The above-described embodiments are only the preferred schemes of the present application, and do not limit the present application in any form. Other variants and modifications can be made without departing from the technical solutions recited in the claims.

Claims

1. A method for preparing a lithium-ion conductor-coated high-nickel ternary cathode material by plasma-assisted in-situ construction, characterized in that, The method is to modify the high-nickel ternary positive electrode material with a solid source and oxygen as a plasma source, to obtain a high-nickel ternary positive electrode material with a lithium ion conductor coating layer constructed in-situ with plasma assistance, the solid source includes at least one of ammonium hexafluorophosphate, ammonium hexafluorosilicate, ammonium metatungstate, ammonium fluoroborate, urea, and thiourea, the mass of the solid source accounts for 1-10% of the mass of the high-nickel ternary positive electrode material, during the modification process, the oxygen flow rate is 20-40 sccm, and the plasma equipment power is 200-400 W.

2. The method according to claim 1, wherein the method is characterized by: The method includes the following steps: (1) uniformly mixing the high-nickel ternary positive electrode material with the solid source and then placing the mixture in a reaction cavity of a plasma reaction device, the two ends of the plasma reaction device are respectively connected with a vacuum pump and an oxygen source; (2) performing temperature rising and vacuumizing treatment on the reaction cavity of the plasma reaction device, and introducing oxygen; (3) rotating the reaction cavity, starting the plasma reaction device, adjusting the power after ignition, and reacting for a period of time to obtain a high-nickel ternary positive electrode material coated with a lithium ion conductor.

3. The method according to claim 2, wherein the method is characterized by: The chemical formula of the high-nickel ternary positive electrode material in step (1) is LiNi x Co y Mn Z O2; wherein, 0.6≤x<1, 0.01≤y<0.4, 0.01≤z<0.4, and x+y+z = 1. And / or, the mass of the high-nickel ternary positive electrode material in step (1) is 1-10 g, and the mass of the solid source is 0.01-1 g.

4. The method according to claim 3, wherein the method is characterized by, The high-nickel ternary positive electrode material has a chemical formula of LiNi 0.9 Co 0.05 Mn 0.05 O2; and / or the solid source is ammonium hexafluorophosphate.

5. The method of claim 3, wherein the method is characterized by: The mass of the high-nickel ternary positive electrode material is 2 g, and the mass of the solid source is 0.04 g.

6. The method of claim 2, wherein the method is characterized by: The temperature in step (2) is 100-600 o C; And / or, the vacuum degree after introducing the oxygen in step (2) is 10-200 Pa; And / or, the reaction time in step (3) is 3-30 min; And / or, the rotation speed of the reaction cavity in step (3) is 30-200 r / min.

7. The method of claim 6, wherein the method is characterized by: The temperature in step (2) is 300 o C; And / or, the oxygen flow rate in step (2) is 30 sccm, and the vacuum degree after introducing the oxygen is 50 Pa; And / or, the reaction time in step (3) is 10 min, and the equipment power is 200 W; And / or, the rotation speed of the reaction cavity in step (3) is 150 r / min.

8. The method of claim 2, wherein the method is characterized by: The thickness of the coating layer on the surface of the high-nickel ternary positive electrode material is 3-8 nm.

9. A high-nickel ternary positive electrode material coated with a lithium ion conductor constructed in-situ with plasma assistance, which is prepared by the preparation method according to any one of claims 1-8.

10. Application of the high-nickel ternary positive electrode material coated with a lithium ion conductor constructed in-situ with plasma assistance according to claim 9 in the field of batteries.

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