Coated cathode materials, their preparation methods and applications

Abstract

This disclosure belongs to the field of lithium-ion battery cathode material technology, and discloses a coated cathode material, its preparation method and application. This disclosure utilizes silicon tetrafluoride gas to react with residual alkali components on the surface of the cathode material to form a Li2SiO3 / LiF composite coating layer on the surface of the cathode material. Then, ammonia gas is introduced to react the residual silicon tetrafluoride gas in the reaction device with the ammonia gas to generate silicon nitride, which is then deposited on the surface of the cathode material after cooling to form a Si3N4 coating layer.

Description

Technical Field

[0001] This disclosure belongs to the field of lithium-ion battery cathode material technology, specifically relating to a coated cathode material, its preparation method, and its application. Background Technology

[0002] With the pursuit of energy conservation and environmental protection, new energy vehicles have rapidly become a hot topic in the automotive market. Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have become a research focus in the new energy industry. The cathode material is the core of a lithium-ion battery and plays a decisive role in its energy density.

[0003] Lithium nickel cobalt manganese oxide ternary cathode materials have advantages such as high specific capacity, high energy density, low price, and environmental friendliness. The discharge capacity of high-nickel ternary materials can reach more than 200 mAh / g. However, because nickel ions are easily reduced and enter the lithium layer, a serious ion mixing phenomenon will occur, lithium is easy to precipitate, and the lithium salt added during sintering will also remain on the material surface in the form of oxides.

[0004] Residual lithium is highly sensitive to moisture, readily absorbing water and carbon dioxide from the air to form lithium hydroxide and lithium carbonate, causing surface degradation of the material. Excessive residual lithium in the material easily leads to a jelly-like consistency in the slurry during battery manufacturing and coating processes, resulting in uneven coating and causing problems such as increased electrode production difficulty and capacity decay. Furthermore, residual lithium has poor conductivity, hindering lithium-ion insertion and extraction and causing electrode polarization. Residual alkali readily reacts with the electrolyte at high temperatures to generate gas, causing battery swelling and posing a serious safety hazard. Therefore, high-nickel ternary cathode materials require more stringent storage and subsequent processing conditions.

[0005] To address these issues, high-nickel materials are typically treated with water washing or surface coating to reduce residual alkali production. However, water washing consumes a large amount of water, and its reaction with the high-nickel ternary cathode material leads to lithium loss, damages the material structure, and ultimately reduces the material's capacity. Solid-phase coatings, on the other hand, have poor surface uniformity and cannot completely prevent the material from contacting H2O and CO2 in the air.

[0006] Chinese patent CN108807969A discloses a method for reducing residual alkali on the surface of layered cathode materials in lithium-ion batteries. This invention reduces surface residual alkali through water washing, followed by rapid removal of residual surface moisture through alcohol washing, and then stabilizes the surface structure by adding nano-zirconia and sintering. This invention effectively reduces surface residual alkali in the cathode material. However, the material structure is damaged after water washing, and despite stabilizing the surface structure by adding nano-zirconia, a significant amount of lithium is still lost during the water washing process. Summary of the Invention

[0007] This disclosure aims to at least address one of the technical problems existing in the prior art. To this end, this disclosure proposes a coated cathode material, its preparation method, and its application.

[0008] According to one aspect of this disclosure, a method for preparing a coated cathode material is provided, comprising the following steps:

[0009] The positive electrode material is placed in a reaction apparatus, silicon tetrafluoride gas is first introduced to heat and react, then ammonia gas is introduced to heat and react, and after the reaction is completed, it is cooled to obtain the coated positive electrode material.

[0010] This disclosure utilizes silicon tetrafluoride gas to react with residual alkaline components (Li2CO3 and LiOH) on the surface of the cathode material to form a Li2SiO3 / LiF composite coating layer on the cathode material surface. Then, ammonia gas is introduced to react the remaining silicon tetrafluoride gas in the reaction apparatus with the ammonia gas to generate silicon nitride, which is then deposited onto the cathode material surface after cooling. The reaction formula is as follows:

[0011] SiF4+6LiOH==Li2SiO3+4LiF+3H2O;

[0012] SiF4+2Li2CO3+2H2O==H4SiO4+4LiF+2CO2;

[0013] 3SiF4 + 4NH3 = Si3N4 + 12HF.

[0014] In some embodiments of this disclosure, the cathode material is a high-nickel ternary cathode material or a lithium iron phosphate material.

[0015] In some embodiments of this disclosure, the chemical formula of the high-nickel ternary cathode material is LiNi. x Co y Mn z O2, 0.7≤x≤0.9, 0.05≤y≤0.15, 0.05≤z≤0.15, and x+y+z=1.

[0016] In some embodiments of this disclosure, the average particle size D50 of the cathode material is 2-15 μm.

[0017] In some embodiments of this disclosure, the temperature at which the silicon tetrafluoride gas is introduced to heat the reaction is 500-600°C.

[0018] In some embodiments of this disclosure, the flow rate of the silicon tetrafluoride gas is 0.05-0.15 L / min.

[0019] In some embodiments of this disclosure, the time for introducing the silicon tetrafluoride gas and heating the reaction is 2-4 hours.

[0020] In some embodiments of this disclosure, the reaction apparatus is a tubular furnace; the positive electrode material is packed in the reaction apparatus at a volume ratio of 5%-15%.

[0021] In some embodiments of this disclosure, after the positive electrode material is placed in the reaction apparatus, a protective gas is first introduced to expel oxygen, the temperature is increased to the reaction temperature at a rate of 2-10°C / min, and then the silicon tetrafluoride gas is introduced to carry out the reaction.

[0022] In some embodiments of this disclosure, the temperature at which the ammonia gas is introduced to heat the reaction is 500-600°C.

[0023] In some embodiments of this disclosure, the flow rate of the ammonia gas is 0.01-0.1 L / min.

[0024] In some embodiments of this disclosure, the ammonia gas is introduced and the heating reaction is carried out for 0.5-2 hours. The amount of Si3N4 coating is controlled by controlling the flow rate of ammonia gas and the reaction time.

[0025] This disclosure also provides a coated cathode material, prepared by the aforementioned method, wherein the coated cathode material is sequentially coated with a Li2SiO3 / LiF composite coating layer and a Si3N4 coating layer from the inside out.

[0026] In some embodiments of this disclosure, the Si3N4 coating layer has a coating amount of 0.2%-1% of the mass of the cathode material.

[0027] This disclosure also provides the application of the described coated cathode material in lithium-ion batteries.

[0028] This disclosure has at least the following beneficial effects:

[0029] 1. This disclosure employs a vapor-phase coating method to ensure sufficient contact between SiF4 and the surface of the cathode material. SiF4 does not damage the ternary material structure and reacts with residual alkali components (Li2CO3 and LiOH), reducing the amount of residual alkali on the material surface without causing lithium loss, thus forming a conductive Li2SiO3 / LiF composite coating layer. After the residual alkali has completely reacted, NH3 is introduced to react with the remaining SiF4, generating Si3N4 which is deposited on the surface of the cathode material, making the coating layer more uniform and complete, thereby improving the cycle life, cycle stability, and safety of the cathode material.

[0030] 2. By using a gas-solid reaction, the damage to the cathode material structure and the loss of lithium caused by liquid immersion are avoided. It can also effectively avoid the problem of uneven solid-phase grinding. The gas-solid contact makes the residual alkali removal more complete and the resulting coating layer has high uniformity. It can avoid direct contact between the cathode material and the electrolyte. Si3N4 has the characteristics of high hardness, wear resistance, corrosion resistance and high thermal stability. As a coating layer, it can effectively enhance the strength of the cathode material and stabilize the material structure.

[0031] 3. The Li2SiO3 / LiF composite coating is selectively formed at the residual alkali site. Si3N4 can increase the uniformity of the coating and enhance its protective effect. The Si3N4 coating is non-conductive, while the Li2SiO3 / LiF composite coating is lithium-ion conductive. The synergistic effect of the two can enhance the strength of the material without reducing its lithium-ion conductivity. Detailed Implementation

[0032] The following will describe the concept and technical effects of this disclosure clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this disclosure.

[0033] Example 1

[0034] This embodiment prepares a coated ternary cathode material, the specific process of which is as follows:

[0035] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 10 μm. 0.8 Co 0.1 Mn 0.1 O2 powder is placed in a tube furnace;

[0036] (2) A protective gas is introduced into the tube furnace to completely remove oxygen. The temperature is raised to 600°C at a rate of 10°C / min. Then, silicon tetrafluoride gas is introduced at a flow rate of 0.15 L / min. The reaction time is 2 h. The residual alkali is converted into a Li2SiO3 / LiF composite coating layer.

[0037] (3) Maintain the temperature of step (2) and introduce ammonia gas into the tubular furnace at a flow rate of 0.1 L / min for a reaction time of 0.5 h.

[0038] (4) After naturally cooling to room temperature, Si3N4 is deposited on the surface of the cathode material to form a uniform coating layer. The mass of the Si3N4 coating layer is 1% of the mass of the high-nickel ternary cathode material.

[0039] Example 2

[0040] This embodiment prepares a coated ternary cathode material, the specific process of which is as follows:

[0041] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 2.7 μm 0.7 Co 0.1 Mn 0.2 O2 powder is placed in a tube furnace;

[0042] (2) A protective gas is introduced into the tube furnace to completely remove oxygen. The temperature is increased to 550°C at a rate of 5°C / min. Then, silicon tetrafluoride gas is introduced at a flow rate of 0.1L / min. The reaction time is 2.5h. The residual alkali is converted into a Li2SiO3 / LiF composite coating layer.

[0043] (3) Maintain the temperature of step (2), and introduce ammonia gas into the tubular furnace at a flow rate of 0.05 L / min for a reaction time of 0.5 h.

[0044] (4) After natural cooling to room temperature, Si3N4 is deposited on the surface of the cathode material to form a uniform coating layer. The mass of the Si3N4 coating layer is 0.5% of the mass of the high-nickel ternary cathode material.

[0045] Example 3

[0046] This embodiment prepares a coated ternary cathode material, the specific process of which is as follows:

[0047] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 14.3 μm was used. 0.9 Co 0.05 Mn 0.05 O2 powder is placed in a tube furnace;

[0048] (2) A protective gas is introduced into the tube furnace to completely remove oxygen. The temperature is raised to 500°C at a rate of 2°C / min. Then, silicon tetrafluoride gas is introduced at a flow rate of 0.05 L / min. The reaction time is 4 h. The residual alkali is converted into a Li2SiO3 / LiF composite coating layer.

[0049] (3) Maintain the temperature of step (2), introduce ammonia into the tubular furnace at a flow rate of 0.01 L / min, and react for 2 hours;

[0050] (4) After natural cooling to room temperature, Si3N4 is deposited on the surface of the cathode material to form a uniform coating layer. The mass of the Si3N4 coating layer is 0.2% of the mass of the high-nickel ternary cathode material.

[0051] Comparative Example 1

[0052] This comparative example prepared a low-alkali ternary cathode material. The difference from Example 1 is that the high-nickel ternary material LiNi was directly removed by water washing. 0.8 Co 0.1Mn 0.1 Residual alkali on the O2 surface. The specific process is as follows:

[0053] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 10 μm. 0.8 Co 0.1 Mn 0.1 O2 powder was dispersed in 2 kg of clean water and stirred for 10 min at a stirring speed of 1000 r / min at a washing temperature of 35℃.

[0054] (2) After washing, the ternary material is separated from the water by filtration and vacuum drying at 100°C for 4 hours to obtain the water-washed low-alkali ternary cathode material.

[0055] Comparative Example 2

[0056] This embodiment prepares a coated ternary cathode material, the specific process of which is as follows:

[0057] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 10 μm. 0.8 Co 0.1 Mn 0.1 O2 and 10g Al2O3 are mixed and ground together;

[0058] (2) Place it in a tube furnace for calcination at a temperature of 600℃ for 5 hours;

[0059] (3) Cool to room temperature and grind to obtain Al2O3-coated LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0060] Comparative Example 3

[0061] This embodiment prepares a coated ternary cathode material. The difference from Example 1 is that ammonia gas is not introduced for the reaction. The specific process is as follows:

[0062] (1) 1 kg of high-nickel ternary cathode material LiNi with an average particle size D50 of 10 μm. 0.8 Co 0.1 Mn 0.1 O2 powder is placed in a tube furnace;

[0063] (2) A protective gas is introduced into the tube furnace to completely remove oxygen. The temperature is increased to 600°C at a rate of 10°C / min. Then, silicon tetrafluoride gas is introduced at a flow rate of 0.15 L / min. The reaction time is 2 h.

[0064] (3) After natural cooling to room temperature, LiNi with Li2SiO3 / LiF composite coating is obtained. 0.8 Co0.1 Mn 0.1 O2.

[0065] Test case

[0066] 1. The residual lithium of the high-nickel ternary cathode materials obtained in the examples and comparative examples was tested, and the results are shown in Table 1.

[0067] 2. To test the electrochemical performance of the high-nickel ternary cathode material, the materials prepared in the examples and comparative examples were made into cathode sheets: the high-nickel ternary material, binder PVDF, and conductive agent SP were dissolved in NMP at a mass ratio of 8:1:1, stirred to form a slurry, the slurry was coated on aluminum foil, dried, assembled into coin cells, and charged-discharge and cycle tests were performed. The results are shown in Table 1.

[0068] Table 1. Lithium residue and electrochemical performance tests of the examples and comparative examples.

[0069]

[0070] As shown in Table 1, the residual lithium in Comparative Example 1 was similar to that in Example 1, but its discharge capacity and cycle performance were lower. This is because Comparative Example 1 used a water washing method to remove residual lithium, which damaged the material structure to some extent, leading to a decrease in material capacity and cycle performance. The discharge capacity and cycle performance of Comparative Example 2 were also somewhat lower than those of Example 1. This is because Comparative Example 2 used solid-phase coating, and the surface uniformity of the coating layer was poor, which could not completely block the material from contacting H2O and CO2 in the air. Comparative Example 3 introduced silicon tetrafluoride gas to react with residual alkali, achieving a good effect in reducing residual alkali, but because it was not coated with silicon nitride, its electrochemical performance was still not as good as that of Example 1.

Claims

1. A method for preparing a coated cathode material, characterized in that, Includes the following steps: The positive electrode material is placed in a reaction apparatus, silicon tetrafluoride gas is first introduced to heat and react, then ammonia gas is introduced to heat and react, and after the reaction is completed, it is cooled to obtain the coated positive electrode material. The cathode material is a high-nickel ternary cathode material or a lithium iron phosphate material; The temperature at which the silicon tetrafluoride gas is introduced to heat the reaction is 500-600℃; The temperature at which the ammonia gas is introduced to heat the reaction is 500-600℃; The coated cathode material is coated with a Li2SiO3 / LiF composite coating layer and a Si3N4 coating layer from the inside out.

2. The preparation method according to claim 1, characterized in that, The chemical formula of the high-nickel ternary cathode material is LiNi. x Co y Mn z O2, 0.7≤x≤0.9, 0.05≤y≤0.15, 0.05≤z≤0.15, and x+y+z=1.

3. The preparation method according to claim 1, characterized in that, The average particle size D50 of the cathode material is 2-15 μm.

4. The preparation method according to claim 1, characterized in that, The flow rate of the silicon tetrafluoride gas is 0.05-0.15 L / min.

5. The preparation method according to claim 1, characterized in that, The time for heating the reaction by introducing the silicon tetrafluoride gas is 2-4 hours.

6. The preparation method according to claim 1, characterized in that, The reaction apparatus is a tubular furnace; the positive electrode material is loaded into the reaction apparatus at a volume ratio of 5%-15%.

7. The preparation method according to claim 1, characterized in that, After placing the positive electrode material in the reaction apparatus, a protective gas is first introduced to expel oxygen, and the temperature is increased to the reaction temperature at a rate of 2-10℃ / min. Then, the silicon tetrafluoride gas is introduced to carry out the reaction.

8. The preparation method according to claim 1, characterized in that, The ammonia gas flow rate is 0.01-0.1 L / min.

9. The preparation method according to claim 1, characterized in that, The ammonia gas is introduced and the reaction is heated for 0.5-2 hours.

10. A coated cathode material, characterized in that, The coated cathode material is prepared by the preparation method according to any one of claims 1-9, wherein the coated cathode material is coated with a Li2SiO3 / LiF composite coating layer and a Si3N4 coating layer from the inside to the outside.

11. The coated cathode material according to claim 10, characterized in that, The Si3N4 coating layer has a coating amount of 0.2%-1% of the mass of the cathode material.

12. The application of the coated cathode material as described in claim 10 in lithium-ion batteries.

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