A method for removing residual alkali and coating high-nickel ternary positive electrode material and its application

Abstract

The present invention discloses a method for removing residual alkali and coating a high-nickel ternary cathode material and its application. The sintered and crushed high-nickel ternary cathode material is placed in a reaction device, ozone is introduced and heated for reaction, an inert gas is then introduced to expel the ozone, titanium tetrachloride gas is introduced under heating conditions for reaction, and oxygen is introduced and heated for reaction to obtain a coated high-nickel ternary cathode material. The present invention utilizes the strong oxidizing property of ozone to oxidize residual lithium into lithium peroxide, which is subsequently reacted with titanium tetrachloride to form lithium titanate to neutralize the residual lithium on the surface. The titanium tetrachloride and oxygen are then subjected to a vapor deposition reaction to obtain a titanium dioxide coating layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery positive electrode materials, and in particular relates to a method for removing residual alkali and coating a high-nickel ternary positive electrode material. Background Art

[0002] Ternary lithium-ion batteries are widely used in portable electronic devices such as mobile phones, power banks, and laptops due to their safety, high energy density, environmental friendliness, and excellent electrochemical performance. Furthermore, with the continuous development of the new energy vehicle industry, market demand for lithium-ion batteries is also expanding. Currently, the pursuit of high specific energy density is a key research direction for lithium-ion power batteries and a key focus for future R&D and industrialization.

[0003] As we all know, with the increase of nickel content in ternary materials, energy density has also been improved. However, its residual alkali content has also been getting higher and higher. This is also an important reason why high-nickel materials have not been able to be industrialized. When the material is exposed to air, the structure, morphology and composition of the powder material change, and the electrochemical performance gradually decreases, especially when exposed to humid air. It is easy to generate alkaline products Li2CO3 and LiOH. The high residual alkali content will cause the slurry to absorb water during preparation. After absorbing water, the slurry will easily form "jelly", which is difficult to coat, resulting in poor processing performance of the positive electrode sheet. In addition, the residual alkali will react with the electrolyte to generate gas, causing the battery to bloat, affecting safety performance.

[0004] At present, the means to reduce the excessive alkalinity of the surface of high nickel ternary materials mainly start from several aspects:

[0005] (1) During the mixed lithium sintering stage, the lithium salt ratio is reduced and the sintering system is adjusted to allow lithium to diffuse quickly into the crystal. However, reducing the lithium ratio will lead to a decrease in capacity.

[0006] (2) Wash the material with water, and then sinter it twice to reduce the residual alkali content on the surface. The commonly used method for washing high nickel positive electrode materials is to stir them for a certain time according to a certain water-to-material ratio, then filter or filter press, and finally put them into the oven for drying. There are also some methods to add some additives to the water, such as HF, boric acid, etc. However, the washing process can easily cause the Li in the surface lattice of the material to + Dissolution generates NiO with no electrochemical activity, destroying the surface structure of the material and affecting the electrochemical properties of the material. Moreover, the material needs to be dried after washing. There is still a lot of water left on the surface of the material. Lithium is hydrophilic, and the drying process is equivalent to giving Li + The precipitation provides a "drag force", causing the material to lose discharge capacity.

[0007] CN201810371980.4 discloses a method for reducing residual alkali on the surface of layered positive electrode materials for lithium-ion batteries. The invention reduces the residual alkali on the surface by washing with water, then quickly removes the residual surface moisture by washing with alcohol, and finally stabilizes the surface structure by adding nano-zirconia sintering. This invention effectively reduces the residual alkali on the surface of the positive electrode material. However, the material structure is destroyed after washing with water. Although the surface structure is stabilized by adding nano-zirconia, the amount of lithium loss during the washing process is still high.

[0008] Therefore, there is an urgent need for a method that can reduce the high residual alkali content of high-nickel ternary materials while protecting the structure of the high-nickel ternary materials from being destroyed. Summary of the Invention

[0009] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for removing residual alkali and coating a high-nickel ternary cathode material. This method can reduce the residual alkali on the surface of the high-nickel material, protect the internal structure of the high-nickel ternary material, and ensure the material's processing performance, safety performance, and electrochemical performance.

[0010] According to one aspect of the present invention, a method for removing residual alkali and coating a high-nickel ternary positive electrode material is proposed, comprising the following steps:

[0011] S1: Place the sintered and crushed high-nickel ternary cathode material in a reaction device and introduce ozone for heating reaction;

[0012] S2: After the reaction in step S1 is completed, an inert gas is introduced to expel ozone, and then titanium tetrachloride gas is introduced under heating to react;

[0013] S3: introducing oxygen so that the reaction equipment contains titanium tetrachloride and oxygen at the same time, heating for reaction, releasing the pressure after the reaction is completed, and introducing protective gas for airflow washing to obtain a coated high-nickel ternary positive electrode material.

[0014] In some embodiments of the present invention, in step S1, the reaction equipment is a vapor deposition equipment, and the filling rate of the high-nickel ternary positive electrode material in the reaction chamber of the vapor deposition equipment is 2-8%.

[0015] In some embodiments of the present invention, in step S1, the ozone gas flow rate is 10-100 sccm.

[0016] In some embodiments of the present invention, in step S1, the heating reaction process is: first heating to 500-800°C, reacting for 4-7 hours, then cooling to 100-120°C, reacting for 1-2 hours.

[0017] In some embodiments of the present invention, in step S2, the reaction temperature is 140-160°C. Specifically, after the ozone is discharged in step S2, the temperature is first raised to 140-160°C, and then titanium tetrachloride gas at 140-160°C is introduced to carry out the reaction. Furthermore, the reaction time is 0.5-1 hour.

[0018] In some embodiments of the present invention, in step S2, the inert gas is at least one of nitrogen or argon.

[0019] In some embodiments of the present invention, in step S2, after the titanium tetrachloride gas is introduced, the total gas pressure in the reaction equipment is 0.1-1.0 MPa, and the titanium tetrachloride gas partial pressure is 0.1-1.0 MPa.

[0020] In some preferred embodiments of the present invention, before proceeding to step S3, the operations of steps S1-S2 may be repeated multiple times to further reduce the residual alkali. Specifically, after the reaction in step S2 is completed, nitrogen is introduced to replace the titanium tetrachloride, and then ozone is introduced to proceed to the reaction in step S1, and steps S1-S2 are repeated according to the above operation.

[0021] In some embodiments of the present invention, in step S3, after the oxygen is introduced, the molar ratio of titanium tetrachloride to oxygen is 1:(5-20).

[0022] In some embodiments of the present invention, in step S3, the reaction temperature is 550-1100° C. Further, the reaction time is 2-60 min.

[0023] In some embodiments of the present invention, in step S3, the shielding gas is at least one of nitrogen, argon or oxygen, and the inlet rate of the shielding gas is 5-50 sccm.

[0024] The present invention also provides application of the method in preparing lithium ion batteries.

[0025] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0026] 1. The present invention first further sintered the sintered and crushed high-nickel ternary positive electrode material with ozone. On the one hand, under the strong oxidizing conditions of ozone, the residual alkali further reacts and combines with the incompletely oxidized divalent nickel. At the same time, the extremely small amount of lithium hydroxide and lithium carbonate in the residual lithium will gradually decompose into lithium oxide. On the other hand, the residual lithium is further oxidized, and the lithium remaining on the surface is oxidized into lithium peroxide. Subsequently, the lithium peroxide reacts with titanium tetrachloride to generate lithium titanate to neutralize the residual lithium on the surface of the high-nickel ternary positive electrode material. Finally, a titanium dioxide particle coating layer is deposited on the surface of the high-nickel ternary positive electrode material through a vapor deposition reaction between titanium tetrachloride and oxygen. The reaction principle is as follows:

[0027] O3+3Li2O→3Li2O2;

[0028] 2Li2O2+TiCl4→Li2TiO3+Li2O+2Cl2;

[0029] O2+TiCl4→TiO2+2Cl2.

[0030] 2. The high-nickel ternary cathode material is further sintered by ozone, and the residual lithium on the surface is oxidized. After neutralization with titanium tetrachloride, lithium titanate is formed, which solves the problems of water absorption and "jelly" caused by residual alkali, reduces the alkalinity of the material surface, and avoids the problem of lattice lithium precipitation caused by washing to remove residual lithium; on the other hand, vapor deposition coating is carried out to coat the surface of the material with titanium dioxide. The entire process uses titanium tetrachloride as a raw material, avoiding the process troubles caused by raw material replacement. The present invention can reduce the residual alkali on the surface of the high-nickel material, and protect the internal structure of the high-nickel ternary material through the titanium dioxide coating layer, ensuring the processing performance, safety performance and electrochemical performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0032] Figure 1 This is an SEM image of the titanium dioxide-coated high-nickel ternary positive electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for removing residual alkali and coating high-nickel ternary positive electrode materials, the specific process is as follows:

[0036] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) was placed in the reaction chamber of a vapor deposition device, the filling rate of the high-nickel ternary cathode material was 5%, and ozone gas was introduced at a flow rate of 50 sccm. The temperature was first raised to 700°C, reacted for 5 hours, and then cooled to 110°C and continued for 1.5 hours;

[0037] Step 2: introducing nitrogen to expel ozone and heating to 150°C;

[0038] Step 3: introduce titanium tetrachloride gas at a temperature of 150°C, set the total gas pressure in the reaction chamber to 0.5 MPa, the titanium tetrachloride gas partial pressure to 0.2 MPa, maintain the reaction temperature at 150°C, and continue for 1 hour;

[0039] Step 4: introducing oxygen to make the molar ratio of titanium tetrachloride to oxygen 1:10, and heating to 800°C, and reacting in a sealed container for 30 minutes;

[0040] Step 5: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in a nitrogen flow at an air inlet rate of 25 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material with residual alkali removed and coated with titanium dioxide.

[0041] Example 2

[0042] A method for removing residual alkali and coating high-nickel ternary positive electrode materials, the specific process is as follows:

[0043] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) was placed in the reaction chamber of a vapor deposition device, the filling rate of the high nickel ternary cathode material was 2%, and ozone gas was introduced at a flow rate of 10 sccm. The temperature was first raised to 500°C, reacted for 7 hours, and then cooled to 100°C and continued for 2 hours;

[0044] Step 2: introduce nitrogen to expel ozone and heat to 140°C;

[0045] Step 3: introduce titanium tetrachloride gas at a temperature of 140°C, set the total gas pressure in the reaction chamber to 1.0 MPa, the titanium tetrachloride gas partial pressure to 0.1 MPa, and maintain the reaction temperature at 140°C for 1 hour;

[0046] Step 4: introducing oxygen to make the molar ratio of titanium tetrachloride to oxygen 1:20, and heating to 550°C, and reacting in a sealed container for 60 minutes;

[0047] Step 5: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in an argon flow at an air inlet rate of 5 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material with residual alkali removed and coated with titanium dioxide.

[0048] Example 3

[0049] A method for removing residual alkali and coating high-nickel ternary positive electrode materials, the specific process is as follows:

[0050] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) was placed in the reaction chamber of a vapor deposition device, the filling rate of the high nickel ternary cathode material was 8%, and ozone gas was introduced at a flow rate of 100 sccm. The temperature was first raised to 800°C, reacted for 4 hours, and then cooled to 120°C and continued for 1 hour;

[0051] Step 2: introducing nitrogen to expel ozone and heating to 160°C;

[0052] Step 3: introduce titanium tetrachloride gas at a temperature of 160°C, set the total gas pressure in the reaction chamber to 1.0 MPa, the titanium tetrachloride gas partial pressure to 0.8 MPa, maintain the reaction temperature at 160°C, and continue for 0.5 h;

[0053] Step 4: introducing oxygen to make the molar ratio of titanium tetrachloride to oxygen 1:5, and heating to 1100°C, and reacting in a sealed container for 2 minutes;

[0054] Step 5: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in an oxygen flow at an air inlet rate of 50 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material with residual alkali removed and coated with titanium dioxide.

[0055] Comparative Example 1

[0056] A method for coating a high-nickel positive electrode material, which differs from Example 1 in that ozone is not introduced and vapor deposition is performed directly. The specific process is as follows:

[0057] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) is placed in the reaction chamber of the vapor deposition equipment, and the filling rate of the high-nickel ternary positive electrode material is 5%;

[0058] Step 2: introducing titanium tetrachloride gas at a partial pressure of 0.2 MPa and oxygen to a molar ratio of titanium tetrachloride to oxygen of 1:10, and heating to 800°C and reacting in a sealed container for 30 minutes;

[0059] Step 3: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in a nitrogen flow at an air inlet rate of 25 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material coated with titanium dioxide.

[0060] Comparative Example 2

[0061] A method for coating a high-nickel positive electrode material, which differs from Example 2 in that ozone is not introduced and vapor deposition is performed directly. The specific process is as follows:

[0062] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) is placed in the reaction chamber of the vapor deposition equipment, and the filling rate of the high-nickel ternary positive electrode material is 2%;

[0063] Step 2: introducing titanium tetrachloride gas at a partial pressure of 0.1 MPa and oxygen to a molar ratio of titanium tetrachloride to oxygen of 1:20, and heating to 550°C and conducting a closed reaction for 60 minutes;

[0064] Step 3: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in an argon flow at an air inlet rate of 5 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material coated with titanium dioxide.

[0065] Comparative Example 3

[0066] A method for coating a high-nickel positive electrode material, which differs from Example 3 in that ozone is not introduced and vapor deposition is performed directly. The specific process is as follows:

[0067] Step 1: sinter and crush the high nickel ternary cathode material (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2) is placed in the reaction chamber of the vapor deposition equipment, and the filling rate of the high-nickel ternary positive electrode material is 8%;

[0068] Step 2: introducing titanium tetrachloride gas at a partial pressure of 0.8 MPa and oxygen to a molar ratio of titanium tetrachloride to oxygen of 1:5, and heating to 1100°C and reacting in a sealed container for 2 minutes;

[0069] Step 3: After the reaction is completed, the pressure is released to normal pressure and cooled to room temperature in an oxygen flow with an air inlet rate of 50 sccm. The high-nickel ternary positive electrode material is washed with air flow to avoid residual titanium tetrachloride, thereby obtaining a high-nickel ternary positive electrode material coated with titanium dioxide.

[0070] Comparative Example 4

[0071] A method for removing residual alkali from high-nickel positive electrode materials, the specific process is as follows:

[0072] Take 500ml of deionized water and keep the water temperature at 30℃ under stirring; add 500g of high nickel ternary positive electrode material (NCM811, chemical formula is LiNi 0.8 Co 0.1 Mn 0.1 O2) was added into deionized water with a stirring speed of 400 r / min. After 15 minutes, the material and water were separated by filtration; the material was dried at 120° C. for 10 hours to obtain a washed and dried high-nickel ternary positive electrode material.

[0073] The above examples and comparative examples all use the same batch of high nickel ternary positive electrode materials (NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2).

[0074] Test example

[0075] The high-nickel ternary positive electrode materials obtained in the examples and comparative examples and the residual lithium in the raw materials were detected.

[0076] The high-nickel ternary cathode materials obtained in the Examples and Comparative Examples, along with the selected raw materials, were used as active materials to prepare button-type lithium-ion battery cells for electrochemical performance testing. The specific steps were as follows: The cathode active material was uniformly mixed with acetylene black and PVDF in a mass ratio of 8:1:1 using N-methylpyrrolidone as the solvent. The mixture was then coated onto aluminum foil and dried with forced air at 80°C for 8 hours, followed by vacuum drying at 120°C for 12 hours. The cells were assembled in an argon-protected glove box with a lithium metal sheet as the negative electrode, a polypropylene membrane as the separator, and a 1M LiPF6-EC / DMC (1:1, v / v) electrolyte. The charge and discharge cutoff voltages ranged from 2.7 to 4.3 V. The specific capacity and cycling performance at a current density of 0.1C were tested, and the results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As shown in Table 1, the total amount of residual lithium in the examples is significantly lower than that in the comparative examples, and the discharge capacity and cycle performance are also improved. Comparative Examples 1-3, due to the titanium dioxide coating, have slightly higher electrochemical performance than the uncoated Comparative Example 4 and the raw materials. However, due to the still high residual lithium content, exposure to air can easily cause changes in the material structure. Furthermore, the residual lithium absorbs water, which reacts with the electrolyte to produce hydrogen fluoride, which corrodes the material. This combined effect leads to a decrease in electrochemical performance.

[0080] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A method for removing residual alkali and coating high-nickel ternary positive electrode materials, characterized in that: The following steps are involved: S1: Place the sintered and crushed high-nickel ternary cathode material in a reaction device and introduce ozone for heating reaction; S2: After the reaction in step S1 is completed, an inert gas is introduced to expel ozone, and then titanium tetrachloride gas is introduced under heating to react; S3: introducing oxygen so that titanium tetrachloride and oxygen are simultaneously contained in the reaction equipment, heating for reaction, releasing the pressure after the reaction is completed, and passing protective gas for airflow washing to obtain a coated high-nickel ternary positive electrode material; In step S1, the ozone gas flow rate is 10-100 sccm; the heating reaction process is: first heating to 500-800°C, reacting for 4-7 hours, then cooling to 100-120°C, reacting for 1-2 hours; In step S2, the reaction temperature is 140-160° C.; after the titanium tetrachloride gas is introduced, the total gas pressure in the reaction equipment is 0.1-1.0 MPa, and the titanium tetrachloride gas partial pressure is 0.1-1.0 MPa; In step S3, after the oxygen is introduced, the molar ratio of titanium tetrachloride to oxygen is 1:(5-20); and the reaction temperature is 550-1100°C.

2. The method according to claim 1, characterized in that In step S1, the reaction equipment is a vapor deposition equipment, and the filling rate of the high-nickel ternary positive electrode material in the reaction chamber of the vapor deposition equipment is 2-8%.

3. The method according to claim 1, characterized in that In step S3, the protective gas is at least one of nitrogen, argon or oxygen, and the inlet rate of the protective gas is 5-50 sccm.

4. Use of the method according to any one of claims 1 to 3 in the preparation of lithium-ion batteries.

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