CN109950530A

CN109950530A - With the nickelic tertiary cathode material and preparation method thereof for improving electrical property

Info

Publication number: CN109950530A
Application number: CN201711395913.8A
Authority: CN
Inventors: 高智; 朱晓沛; 张家文; 张媛娇; 沙金; 屈兴圆
Original assignee: Tianjin Guoan MGL New Materials Technology Co Ltd
Current assignee: Tianjin Guoan MGL New Materials Technology Co Ltd
Priority date: 2017-12-21
Filing date: 2017-12-21
Publication date: 2019-06-28

Abstract

The present invention relates to having the nickelic tertiary cathode material and preparation method thereof for improving electrical property, the positive electrode is obtained by positive electrode matrix through overpickling and cladding, and the positive electrode matrix is by formula Li (Ni_1‑x‑yCo_xMn_y)O₂It indicates, wherein 0,0.4 > y > 0 of 1-x-y >=0.5,0.4 > x >；The preparation method includes that positive electrode matrix is added in scattered acid solution to carry out pickling, removes dispersing agent, and calcining obtains washing rear positive electrode；It is added in the dispersion liquid containing silane coupling agent, solvent evaporated, is dried in vacuo under different temperatures to get modified tertiary cathode material is arrived rear positive electrode is washed again.The discharge performance for the nickelic tertiary cathode material that the present invention is prepared is good, preparation method of the invention improves water resistance, thermal stability and the mechanical property of material, improve the high rate performance of material, this preparation method condition is simple, controllable, it is low to the device requirement of production, it is the Practical Approach that can be promoted the use of.

Description

High-nickel ternary cathode material with improved electrical property and preparation method thereof

Technical Field

The invention relates to the field of battery anode materials, in particular to a high-nickel anode material with improved electrical property in a lithium ion battery and a preparation method thereof.

Background

The defect of high residual alkali content on the surface of the high-nickel anode material not only puts higher requirements on the environmental humidity of the high-nickel anode material during storage and use, but also causes poor stability of the battery anode material slurry, and easily causes viscosity increase and even jelly phenomenon, thus causing poor coating performance in the manufacturing process of the battery pole piece. The high content of residual alkali on the surface of the high-nickel anode material can also cause low battery capacity and gas generation expansion, thereby causing the reduction of the safety performance of the battery. In order to solve the problems, people use many measures to improve the electrochemical performance of the ternary material, such as ion doping, surface coating, and the use of electrolyte additives, but any method is single, and the improvement effect is difficult to last, for example, alumina coating can effectively improve the interface stability of the material and can improve the cycle performance of the material, however, alumina at the material interface can react with HF in the electrolyte, which is also the reason that the alumina coated material cannot be protected for a longer time. Li (Ni)_0.8Co_0.1Mn_0.1)O₂The nickel content is higher, the pH value of the material is also higher, the water absorption is strong, the material absorbs moisture in the processes of material transportation and slurry mixing, the performance of the battery is reduced rapidly, and the difficulty is caused in the aspects of material storage and industrialization.

Therefore, a method for improving the electrical property of the high-nickel ternary cathode material is needed to ensure that the high-nickel ternary cathode material has good electrical property and simple method, and meets the requirement of industrial production.

Disclosure of Invention

In order to solve the above problems, the present inventors have conducted intensive studies and, as a result, have found that: the high-nickel anode material matrix is firstly washed by protonic acid and then calcined, and then the washed high-nickel anode material is coated by a silane coupling agent, so that the high-nickel ternary anode material with improved electrical property is obtained. The high-nickel anode material prepared by the method has the advantages of good rate capability, good discharge performance and good cycle performance. The preparation method has simple conditions and low requirements on production equipment, thereby completing the invention.

The object of the present invention is to provide the following:

(1) the high-nickel ternary cathode material with the improved electrical property is obtained by pickling and coating a cathode material matrix, wherein the cathode material matrix is prepared from Li (Ni)_1-x-yCo_xMn_y)O₂Wherein 1-x-y is more than or equal to 0.5, 0.4 is more than x and more than 0, 0.4 is more than y and more than 0, preferably, the matrix of the cathode material is Li (Ni)_0.8Co_0.1Mn_0.1)O₂。

(2) A preparation method of a high-nickel ternary cathode material with improved electrical property comprises the following steps:

step 1, adding a positive electrode material matrix into a protonic acid dispersion liquid, stirring, and removing a dispersing agent;

step 2, calcining the system obtained in the step 1 to obtain a washed anode material;

and 3, mixing the washed anode material with a coating agent, and performing post-treatment to obtain a final product.

(3) The high-nickel ternary cathode material prepared by the method in the (2),

the battery prepared from the anode material is charged and discharged at a rate of 1C within a range of 3.0V-4.3V, and the initial discharge specific capacity reaches more than 177 mAh/g; and/or

After the battery prepared from the cathode material is cycled for 200 times at a multiplying power of 1C within the range of 3.0V-4.3V, the coulombic efficiency is more than 85%.

The high-nickel ternary cathode material with the improved electrical property and the preparation method thereof provided by the invention have the following beneficial effects:

1) the battery prepared by the high-nickel ternary cathode material provided by the invention is charged and discharged at a rate of 1C within a range of 3.0V-4.3V, and the initial discharge specific capacity reaches more than 177 mAh/g; and/or

After the battery prepared from the positive electrode material is cycled for 200 times at a multiplying power of 1C within the range of 3.0V-4.3V, the coulombic efficiency is more than 85%;

2) the method provided by the invention adopts the protonic acid to wash and calcine the anode material matrix, is environment-friendly and is convenient to operate and treat; the residual alkali content is effectively reduced, the electrical property is not obviously reduced, a lithium phosphate coating layer is formed on the surface of the ternary material, and the lithium ion de-intercalation passing rate is improved;

3) the coating agent is added after the proton acid washing and calcining, so that not only can the water resistance and the mechanical property of the ternary material be improved, but also the contact between the anode material and the electrolyte can be isolated, the side reaction is reduced, the cycle life of the material is prolonged, and the electrical property of the high-nickel anode material is improved;

4) the whole preparation method has simple process, the used solvent has low price, the requirement on the used production equipment is not high, the operation is easy, the cost is reduced, and the factors are beneficial to the popularization of industrialization.

Drawings

FIG. 1 shows SEM images of the raw material NCM811 directly coated with kh560 as compared with the raw material NCM811 in comparative examples 6 to 8;

FIG. 2 is an SEM photograph showing that the starting material NCM811 in examples 1 to 3 was coated with kh560 after being washed with phosphoric acid;

FIG. 3 shows XRD patterns of the raw material NCM811 directly coated with kh560 as compared with those of comparative examples 6 to 8;

FIG. 4 shows XRD patterns of the starting material NCM811 and the starting material NCM811 coated with kh560 after being washed with phosphoric acid in examples 1 to 3;

FIG. 5 shows a graph of rate performance of the raw material NCM811 directly coated with kh560 as compared to comparative examples 6-8;

FIG. 6 is a graph showing rate performance of the starting material NCM811 and the starting material NCM811 coated with kh560 after phosphoric acid washing in examples 1 to 3;

FIG. 7 shows a graph of the cycle performance of the raw material NCM811 directly coating kh560 with the raw material NCM811 in comparative examples 6 to 8;

FIG. 8 is a graph showing the cycle performance of the starting material NCM811 and the starting material NCM811 coated with kh560 after phosphoric acid washing in examples 1 to 3;

FIG. 9 is a TEM image of the starting material NCM811 and the starting material NCM811 in examples 1 to 3 coated with kh560 after phosphoric acid washing;

FIG. 10 shows a graph of the cycle performance of different protonic acid pickling starting materials NCM 811;

FIG. 11 shows the cycle performance curves of the NCM811 coated with kh560 after acid washing with different protonic acids in example 2 and comparative examples 1-2;

FIG. 12 shows the cycle performance curves of different silane coupling agents coating the starting material NCM811 of comparative examples 7, 9 and 10;

FIG. 13 is a graph showing the cycle performance of NCM811 materials after phosphoric acid-coating with different silane coupling agents of example 2 and comparative examples 4 to 5;

FIG. 14 shows the cycle performance profile of the starting material NCM811 from example 2 after pickling with phosphoric acid and the coated kh560 from comparative example 3 after washing with lithium dihydrogen phosphate;

FIG. 15 shows the cycle performance profile of the coated kh560 starting material NCM811 after various amounts of phosphoric acid.

Detailed Description

The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

The invention aims to provide a high-nickel ternary cathode material with improved electrical property, which is obtained by pickling and coating a cathode material matrix of a formula Li (Ni)_1-x-yCo_xMn_y)O₂Wherein 1-x-y is more than or equal to 0.5, 0.4 is more than x and more than 0, and 0.4 is more than y and more than 0; preferably, the positive electrode material matrix is Li (Ni)_0.8Co_0.1Mn_0.1) O₂。

Another object of the present invention is to provide a method for preparing a high nickel tri-positive electrode material with improved electrical properties, comprising the steps of:

Step 1, adding a positive electrode material matrix into the protonic acid dispersion liquid, stirring, and removing the dispersing agent.

In the present invention, the positive electrode material matrix is formed of Li (Ni)_1-x-yCo_xMn_y)O₂Wherein 1-x-y is more than or equal to 0.5, 0.4 is more than x and more than 0, and 0.4 is more than y and more than 0; go toStep one, the matrix of the positive electrode material is Li (Ni)_0.8Co_0.1Mn_0.1)O₂。

In the present invention, the protonic acid is acetic acid, oxalic acid or phosphoric acid, preferably phosphoric acid.

While the nickel-rich material receives a great deal of attention, a large amount of residual lithium compounds like LiOH and Li on the surface thereof₂CO3, which compounds form Li during high-voltage operation of the battery₂O and CO₂These gases reduce the charge and discharge performance of the battery, and also cause the battery to increase in temperature, swell, and even explode. The inventor finds that in the compound for treating the residual lithium on the surface of the high nickel material, a protonic acid is preferably used: phosphoric acid, which can consume 3 Li at a time when reacting with phosphoric acid⁺Formation of Li₃PO₄In addition, phosphoric acid is also a good ion conductor (6 x 10)^-8S/cm). Firstly, the original material Li (Ni)_0.8Co_0.1Mn_0.1)O₂After being washed by protonic acid phosphoric acid, the amount of residual lithium on the surface is reduced, thereby reducing the high-temperature ballooning of the battery and improving the cycle performance of the battery.

The amount of the protonic acid used is such that the mass ratio of the protonic acid to the positive electrode material substrate is (0.001-1): 100, preferably (0.005-0.05): 100, more preferably 0.5:98.5, 1:99, 1.5:98.5 or 2:98, and still more preferably 1: 99.

The inventor finds that when the dosage of the protonic acid is too high, the surface of the anode material is corroded, the morphology of the material is seriously damaged, so that the lithium ions in the anode material are lost, the crystal structure is damaged, the electrical property of the anode material is influenced, the electrical property of the ternary material cannot be improved, and the electrical property of the ternary material is greatly reduced. When the amount of protonic acid used is too small, the residual LiOH and Li cannot be effectively reduced₂CO₃And thus cannot improve the electrical properties of the ternary material, the inventors have found that the amount of protic acid is preferably used in a mass ratio of protic acid to ternary material of 1: 99.

The inventors have found that protic acids are preferredAfter being washed by phosphoric acid, Li is formed on the surface of the ternary material₃PO₄Coating layer of Li₃PO₄The coating layer reduces the solubility of HF to materials in electrolysis, and the battery keeps better stability under high-rate circulation.

In the present invention, the protonic acid dispersion is a dispersion of a protonic acid with a dispersant, and the dispersant is an alcohol, preferably methanol, ethanol, or isopropanol, more preferably ethanol, and even more preferably absolute ethanol. The inventor finds that the concentration of the protonic acid can be effectively reduced by dispersing the protonic acid by using the absolute ethyl alcohol, and the protonic acid is ensured to consume residual LiOH and Li₂CO₃。

In the invention, the temperature for removing the dispersing agent is 70-90 ℃, and the dispersing agent is removed by heating and evaporating at the temperature.

In a preferred embodiment, the temperature for removing the dispersant is 80 ℃. The method for removing the dispersant is not particularly limited, and in the present invention, the dispersant is evaporated off under normal pressure by heating with an oil bath.

And 2, calcining the system obtained in the step 1 to obtain the washed anode material.

The calcination temperature is 450-550 ℃, and preferably 500 ℃; the calcination time is 4-6h, preferably 5 h. The purpose of the calcination here is that the protonic acid phosphoric acid forms a layer of Li on the surface of the material and the residual lithium on the surface₃PO₄A layer protecting the bulk material.

A large number of experimental results show that the electrical property of the positive electrode material treated by the protonic acid is not obviously reduced. Without being bound by any theory, it is believed that the protonic acid selected by the invention reacts with the residual alkali and simultaneously is not easy to damage the lattice structure of the cathode material.

The coating agent is a silane coupling agent, preferably kh550, kh560 or kh570, more preferably kh560, and the amount of the silane coupling agent is such that the mass ratio of the silane coupling agent to the washed positive electrode material is (0.001-1): 100, preferably (0.005-0.05): 100, more preferably 0.5:99.5, 1:99 or 2:98, and more preferably 1: 99.

kh560 silane coupling agent, gamma-glycidoxypropyltrimethoxysilane, is an epoxy functional group silane.

Li(Ni_0.8Co_0.1Mn_0.1)O₂The content of nickel in the material is higher, the pH value of the material is also higher, the water absorption is very strong, the material absorbs moisture in the processes of material transportation and slurry mixing, the performance of the battery is reduced rapidly, the storage and industrialization of the material are difficult, the silane coupling agent kh560 is adopted for coating, the moisture absorption phenomenon can be effectively reduced, the water resistance of the material is improved, and the thermal stability and the mechanical stability of the material can be improved.

In a preferred embodiment of the invention, the ternary cathode material after being washed by protonic acid phosphoric acid is coated by a silane coupling agent kh560, so that two coating layers are formed on the surface of the ternary cathode material, wherein one coating layer is Li₃PO₄The coating, one deck is kh560 coating, and the even compact coating that forms has not only effectively blockked electrolyte and the emergence of original material surface matter side reaction, has improved the percent of pass that lithium ion takes off and inlays simultaneously, makes the cyclicity of material promote greatly.

In a preferred embodiment, the silane coupling agent is used in such an amount that the mass ratio of the silane coupling agent to the washed positive electrode material is 1: 99. The coated material exhibits excellent cycling performance, not only cycles at high capacity, but also coulombic efficiency is improved.

The inventors have found that when the amount of the silane coupling agent is low, the low coating amount does not form a dense coating layer, the hydrophobic ability decreases, and the resistance to HF in electrolysis is poor. When the amount of the silane coupling agent is too large, the improvement effect of the thicker coating layer on the cycle performance of the material is not large, which indicates that the thicker coating layer not only hinders the desorption of internal lithium ions, but also reduces the activity of the surface of the battery, so that the material is unstable in structure at the later stage of the cycle and is rapid in capacity attenuation.

In the invention, the post-treatment comprises the steps of firstly dispersing the coating agent by using a dispersing agent II, then adding the weighed washed positive electrode material into the dispersed coating agent, removing the dispersing agent II, drying in vacuum and carrying out heat treatment to obtain the final product.

The dispersant II is alcohol, preferably methanol, ethanol and isopropanol, more preferably ethanol, and further preferably absolute ethanol;

in a preferred embodiment, the silane coupling agent kh560 is dispersed by absolute ethyl alcohol, and ultrasonic dispersion is carried out during dispersion, preferably ultrasonic dispersion is carried out for 2h, so that the silane coupling agent is uniformly distributed, and uniform and compact coating is achieved during coating of the washed ternary material.

The present inventors have found that the mode of removing absolute ethyl alcohol is not particularly limited, and in the present invention, absolute ethyl alcohol is evaporated at normal pressure by heating in an oil bath, and the evaporation temperature is 60 to 80 ℃.

In a preferred embodiment, the evaporation temperature for removing absolute ethanol is 70 ℃.

In the invention, the vacuum drying is 65-85 ℃, preferably 80 ℃, and the vacuum drying time is 3-8 hours, preferably 4-6 hours;

the inventor finds that after the acid-washed ternary material is coated with the silane coupling agent, low-temperature vacuum drying is carried out, the drying temperature is 65-85 ℃, the drying time is preferably 4-6 hours, and residual dispersant ethanol is effectively removed.

In the invention, the heat treatment is vacuum drying, the temperature of the vacuum drying is 100-200 ℃, the time is 2-7 hours, and the preferable time is 3-5 hours.

The inventor finds that the coated ternary material is further subjected to heat treatment after being dried at a low temperature, so that the silane coupling agent is strongly adhered to the positive electrode material at a higher temperature.

The high-nickel ternary cathode material with the improved electrical property is prepared according to the method, a battery prepared from the cathode material is charged and discharged at a rate of 1C within the range of 3.0V-4.3V, and the initial discharge specific capacity reaches more than 177 mAh/g; and/or

In a preferred embodiment of the invention, two coating layers are formed on the surface of the prepared high-nickel ternary cathode material with the improved electrical property, and one coating layer is Li₃PO₄The coating, one deck is kh560 coating, and the even compact coating that forms has not only effectively blockked the emergence of electrolyte and the surperficial material side reaction of original material, has improved the percent of pass that lithium ion takes off and inlays simultaneously, makes the cyclicity ability of material promote greatly, has effectively improved the electrical property.

Examples

The present invention is further described below by way of specific examples. However, these examples are only illustrative and do not set any limit to the scope of the present invention.

Example 1

0.05g of phosphoric acid was dispersed in 10mL of absolute ethanol at room temperature, and stirred for 0.5 h. Then Li (Ni)_0.8Co_0.1Mn_0.1)O₂Slowly pouring 5g of powder (the mass ratio of the anode material matrix to the phosphoric acid is 99:1) into the dispersed solution, stirring and evaporating at the constant temperature of 80 ℃ in an oil bath, calcining the powder subjected to proton acid washing in the air at the constant temperature of 500 ℃ for 5 hours after all the ethanol is evaporated, and cooling to obtain about 5.02g of a system with the number of NCM-a 1;

transferring 0.025g of kh560 (according to the mass ratio of the acid-washed ternary cathode material to the kh560 of 99.5:0.5) by using a liquid transfer gun, adding the kh560 into 15ml of absolute ethyl alcohol, dispersing for 2h by using ultrasonic waves, transferring the mixture into a container, pouring 5.02g of the weighed system obtained in the step 1 into a volumetric flask, stirring and evaporating the weighed system to dryness in an oil bath at 60-80 ℃, and drying the coated material in a vacuum drying oven for 5 hours at 80 ℃;

the obtained mixture is thermally treated for 4h in a vacuum drying box at the temperature of 100-_0.8Co_0.1Mn_0.1)O₂And the ternary cathode material is numbered NCM-a1-k 0.5.

Example 2

The experimental procedure was the same as in example 1, except that kh560 was used in an amount of 0.0507g (mass ratio to the ternary positive electrode material after pickling 1:99) and numbered NCM-a1-k 1.

Example 3

The experimental procedure was the same as in example 1, except that 0.1024g of kh560 (mass ratio to the ternary positive electrode material after pickling: 2:98) was used, and the numbering was NCM-a1-k 2.

Example 4

The experimental procedure was the same as in example 1, except that 0.07614g of phosphoric acid was used (mass ratio to the ternary positive electrode material substrate was 1.5:98.5), and 0.055g of the silane coupling agent Kh560 (mass ratio to the ternary positive electrode material after acid washing was 1:99), and was numbered NCM-a1.5-k 1.

Example 5

The experimental procedure was the same as in example 1 except that the amount of phosphoric acid used was 0.0251g (mass ratio to the ternary cathode material substrate was 0.5:99.5), and the silane coupling agent Kh560 was 0.0507g (mass ratio to the ternary cathode material after acid washing was 1:99) and was numbered NCM-a0.5-k 1.

Comparative example

Comparative example 1

0.05g of oxalic acid is firstly dispersed in 10mL of absolute ethyl alcohol at room temperature and stirred for 0.5 h. Then Li (Ni)_0.8Co_0.1Mn_0.1)O₂Slowly pouring 5g of powder (the mass ratio of the anode material matrix to the oxalic acid is 99:1) into the dispersed solution, stirring and evaporating at the constant temperature of 80 ℃ in an oil bath, calcining the proton acid-washed powder in the air at the constant temperature of 500 ℃ for 5 hours after all the ethanol is evaporated, and cooling to obtain an acid-washed ternary material, wherein the serial number of the acid-washed ternary material is NCM (oxalic acid);

transferring kh560 (0.0507 g) (the mass ratio of NCM (oxalic acid) to kh560 is 99:1) by using a liquid transfer gun to obtain kh560, adding the kh560 into 5ml of absolute ethyl alcohol, dispersing for 2h by using ultrasonic waves, transferring the mixture into a container, pouring 5.02g of weighed NCM (oxalic acid) into a volumetric flask, stirring and evaporating the mixture in an oil bath at 60-80 ℃ to dryness, and drying the coated material in a vacuum drying oven at 80 ℃ for 5 hours;

the obtained mixture is thermally treated for 4h in a vacuum drying box at the temperature of 100-_0.8Co_0.1Mn_0.1)O₂And the ternary cathode material is numbered NCM-oxalic acid-k 1.

Comparative example 2

0.05g of acetic acid was dispersed in 10mL of absolute ethanol at room temperature and stirred for 0.5 h. Then Li (Ni)_0.8Co_0.1Mn_0.1)O₂Slowly pouring 5g of powder (the mass ratio of the anode material matrix to the acetic acid is 99:1) into the dispersed solution, stirring and evaporating at the constant temperature of 80 ℃ in an oil bath, calcining the proton acid-washed powder in the air at the constant temperature of 500 ℃ for 5 hours after all the ethanol is evaporated, and cooling to obtain an acid-washed ternary material, wherein the serial number of the acid-washed ternary material is NCM (acetic acid);

transferring kh560 (0.0507 g is carried out by a liquid transferring gun according to the mass ratio of NCM (acetic acid) to kh560 being 99:1), adding into 5ml absolute ethyl alcohol, dispersing for 2h by ultrasonic, transferring into a container, pouring 5.02g weighed NCM (acetic acid) into a volumetric flask, stirring in an oil bath at 60-80 ℃ and drying by distillation, and drying the coated material in a vacuum drying oven at 80 ℃ for 5 hours;

the obtained mixture is thermally treated for 4h in a vacuum drying box at the temperature of 100 ℃ and 200 ℃ to obtain the final product of Li (Ni) coated by the silane coupling agent kh560_0.8Co_0.1Mn_0.1)O₂And the ternary cathode material is numbered as NCM-acetic acid-k 1.

Comparative example 3

0.05g of lithium dihydrogen phosphate was dispersed in 10mL of absolute ethanol at room temperature, and the mixture was stirred for 0.5 h. Then Li (Ni)_0.8Co_0.1Mn_0.1)O₂Slowly pouring 5g of powder (the mass ratio of the positive electrode material matrix to the lithium dihydrogen phosphate is 99:1) into the dispersed solution, stirring and evaporating at the constant temperature of 80 ℃ in an oil bath, calcining the powder subjected to proton acid washing in the air at the constant temperature of 500 ℃ for 5 hours after all the ethanol is evaporated, and cooling to obtain a washed ternary material, wherein the serial number of the ternary material is NCM (lithium dihydrogen phosphate);

transferring kh560 (0.0507 g is carried out (the mass ratio of NCM (lithium dihydrogen phosphate) to kh560 is 99:1) by using a liquid transfer gun, adding into 5ml of absolute ethyl alcohol, dispersing for 2h by using ultrasonic waves, transferring into a container, pouring 5.02g of weighed NCM (lithium dihydrogen phosphate) into a volumetric flask, stirring and evaporating at 60-80 ℃ in an oil bath, and drying the coated material for 5 hours at 80 ℃ in a vacuum drying oven;

the obtained mixture is thermally treated for 4h in a vacuum drying box at the temperature of 100 ℃ and 200 ℃ to obtain the final product of Li (Ni) coated by the silane coupling agent kh560_0.8Co_0.1Mn_0.1)O₂And the ternary cathode material is numbered NCM-lithium dihydrogen phosphate-k 1.

Comparative example 4

The experimental procedure was the same as in example 2, except that kh550 was used as the coating agent in an amount of 0.0507g (1: 99 by mass of ternary positive electrode material matrix) and numbered NCM-a1-k 550.

Comparative example 5

The experimental procedure was the same as in example 2, except that the coating agent used was kh570, which was used in an amount of 0.0507g (mass ratio to the ternary positive electrode material matrix of 1:99) and was numbered NCM-a1-k 570.

Comparative example 6

Transferring kh560 (0.0251 g (according to the mass ratio of the original materials NCM811 to kh560 is 99.5:0.5) by using a liquid transfer gun, adding the kh560 into 5ml of absolute ethyl alcohol, dispersing for 2h by using ultrasonic waves, transferring to a capacity, pouring 5g of weighed untreated NCM811 into a volumetric flask, stirring and evaporating to dryness in an oil bath at 60-80 ℃, and drying the coated material for 5 hours at 80 ℃ in a vacuum drying oven;

the obtained mixture is thermally treated for 4h in a vacuum drying box at the temperature of 100 ℃ and 200 ℃ to obtain the final product of Li (Ni) coated by the silane coupling agent kh560_0.8Co_0.1Mn_0.1)O₂And the number of the ternary cathode material is NCM-k 0.5.

Comparative example 7

The procedure is as in comparative example 6, except that 0.0505g (99: 1 by mass) of kh560, numbered NCM-k1, is used.

Comparative example 8

The procedure is as in comparative example 6, except that 0.101g (in a mass ratio of 99:2) of kh560, numbered NCM-k2, are used.

Comparative example 9

Transferring kh550 of 0.0505g (according to the mass ratio of the original material NCM811 to the kh550 of 99:1) by using a liquid transfer gun, adding the kh550 into 5ml of absolute ethyl alcohol, dispersing for 2h by using ultrasonic waves, transferring the mixture into a container, pouring 5g of weighed untreated NCM811 into a volumetric flask, stirring and evaporating the mixture in an oil bath at 60-80 ℃ to dryness, and baking the coated material in a vacuum drying oven at 80 ℃ for 5 hours;

the resulting mixture was placed in a vacuum oven 100Heat treatment at-200 deg.c for 4 hr to obtain final product Li (Ni) coated with silane coupling agent kh550_0.8Co_0.1Mn_0.1)O₂And the ternary cathode material is numbered as NCM-k 550.

Comparative example 10

The procedure is as in comparative example 9, except that 0.0505g of kh570 (99: 1 by mass of starting material NCM811 to kh 570) is used, numbered NCM-k 570.

The "(ternary) positive electrode material substrate" mentioned in this application has the same meaning as the "starting material".

Examples of the experiments

Experimental example 1 SEM images of different materials

FIG. 1 is an SEM image of a raw material NCM811 coated with different amounts of kh560 than a raw material NCM 811; the latter results from the products of comparative examples 6 to 8.

FIG. 2 is an SEM image of NCM811 coated with varying amounts of kh560 treated with 1% phosphoric acid. The materials used in FIG. 2 are from the products of examples 1 to 3.

In the context of figure 1 of the drawings,

811 shows an SEM image of the raw material NCM 811;

0.5% shows the SEM image of NCM-k0.5 made in comparative example 6;

1% shows the SEM image of NCM-k1 from comparative example 7;

2% shows the SEM image of NCM-k2 from comparative example 8;

in the context of figure 2, it is shown,

k-0.5% shows the SEM image of NCM-a1-k0.5 obtained in example 1;

k-1% shows the SEM image of NCM-a1-k1 prepared in example 2;

k-2% shows the SEM image of NCM-a1-k2 prepared in example 3.

As can be seen from fig. 1, the primary particles of the raw material NCM811 material which was untreated were thick flakes, and at a coating amount of 0.5%, it was observed from fig. 1 that the surface flakes became finer, and at an enlargement of 5k times, individual particles were coated, while the morphology of other particles was not changed, indicating that at a coating amount of 0.5%, only individual particles had a coating layer. When the coating amount is increased to 1%, it is obvious from fig. 1 that the surface of the primary particles becomes dense and uniform, and the surface is covered with a layer of binding material, and after the magnification is reduced, most of the surfaces of the spherical particles are covered with a layer of dense coating layer. When the coating amount is 2%, the primary particles are observed to be less flaky in fig. 1, but many particles are found to be agglomerated together like a layer of jelly, but the sphericity of the particles is intact at all different coating amounts, which indicates that the coating only changes the morphology of the particle surface and does not affect the structure.

As can be seen from FIG. 2, when the NCM811 material treated by 1% phosphoric acid is coated with the silane coupling agent kh560, the material still maintains good sphericity, the particle size is about 12 μm, the particles are uniformly dispersed, the surface becomes smooth and compact, no excessive impurities are generated, and the surface presents a colloidal coating layer.

Experimental example 2 XRD patterns of different materials

Figure 3 shows XRD patterns of raw material NCM811 clad with different amounts of kh560 material than raw material NCM 811.

Figure 4 shows XRD patterns of different amounts of kh560 material coated with the virgin NCM811 and the pickled NCM 811.

In the context of figure 3, it is shown,

a shows the XRD profile of NCM-k0.5 prepared in comparative example 6;

b shows the XRD profile of NCM-k1 prepared in comparative example 7;

c shows the XRD profile of NCM-k2 prepared in comparative example 8;

d shows the XRD profile of the starting material NCM 811.

In the context of figure 4, it is shown,

a shows the XRD profile of NCM-a1-k0.5 prepared in example 1;

b shows the XRD profile of NCM-a1-k1 prepared in example 2;

c shows the XRD profile of NCM-a1-k2 prepared in example 3;

d shows the XRD profile of the starting material NCM 811.

As can be seen from FIG. 3, the positions of the respective peaks before and after the cladding were not changed, indicating that the clad material did not change the structure of the raw material and each had good α -NaFeO₂The layered structure belongs to an R-3m space point group. The two pairs of peaks, which are clearly separated by the layered structure (018/110), (006/102), remain clear, indicating that the crystallinity of the material before and after coating is good, see table 1 (where a, c represent unit cell parameters of the material).

TABLE 1 lattice parameters of NCM811 and materials of varying coating amounts

Material	a	c	c/a	I003/I104
					NCM811	2.8775	14.2434	4.949	1.36
NCM-k0.5	2.8776	14.2532	4.9531	1.34
					NCM-k1	2.8773	14.2547	4.9541	1.35
NCM-k2	2.878	14.2573	7.9538	1.33

It can be seen from fig. 4 that the four materials still belong to hexagonal layered structure, and the R-3m space group, 006/102 and 018/110, have good bimodal division degree, which indicates that the coated material still maintains good layered structure. No diffraction peaks were observed for the silane coupling agent, either because kh560 was amorphous and because the amount of coating was too small to reach the lowest detection line. The data measured by XRD can be refined by software to obtain the values of a and c, and the value of I003/I104 can be calculated by software to judge the cation mixing degree. The data obtained are compiled in Table 2. As can be seen from the table, the coated material has a higher a, c value than the original material.

TABLE 2 lattice parameters of NCM811 and materials with different coating amounts after pickling

Material	a	c	c/a	I003/I104
					NCM811	2.8763	14.2436	4.9521	1.38
NCM-a1-k0.5	2.8775	14.2534	4.9534	1.36
					NCM-a1-k1	2.8771	14.2537	4.9542	1.33
NCM-a1-k2	2.8777	14.2572	4.9544	1.34

By calculation, c/a of the four materialsThe values are 4.9521, 4.9534, 4.9542, 4.9544, respectively, and it can be seen that as the amount of cladding increases, the unit cell volume of the material increases. In addition, I003/I104 was greater than 1.2 before and after coating, indicating Li in the structure⁺And Ni²⁺The degree of migration between the layers is relatively small, but the I003/I104 is larger than the cation-mixed degree of the original material after coating.

Experimental example 3 Rate Performance curves for different materials

Fig. 5 shows the rate performance curves for untreated virgin material NCM811 with different amounts of kh560 clad with virgin material NCM 811. And (3) packaging the obtained coating material and the original material into a battery, performing electrochemical test at normal temperature, and testing the rate capability under the conditions of 0.1C,0.5C,1C,2C,3C and 5C within the voltage range of 3.0-4.3V respectively.

In the context of figure 5, it is shown,

a shows the rate performance curve of NCM-k0.5 prepared in comparative example 6;

b shows the rate performance curve of NCM-k1 prepared in comparative example 7;

c shows the rate performance curve of NCM-k2 prepared in comparative example 8;

d shows the rate performance curve of the starting material NCM 811.

FIG. 6 shows rate performance curves for untreated virgin NCM811 and pickled NCM811 coated with different amounts of kh 560. When the multiplying power performance test is carried out, the four materials are firstly activated for three times at 0.1C, and are subjected to constant current discharge under the conditions of 0.5C,1C,2C,3C and 5C respectively, and the circulation is carried out for 5 times at each multiplying power.

In the context of figure 6, it is shown,

a shows the rate performance curve of NCM-a1-k0.5 prepared in example 1;

b shows the rate performance curve of NCM-a1-k1 prepared in example 2;

c shows the rate performance curve of NCM-a1-k2 prepared in example 3;

d shows the rate performance curve of the starting material NCM 811.

As can be seen from fig. 5, when the coating amount is 0.5%, the specific capacity under different discharge rates is similar to the specific discharge capacity of the original material and is not improved, and it is analyzed that the coating amount is too small, so that the coating unevenness does not play a role of a coating layer, and when 5C is discharged, the specific capacity is rather lower than that of the original material, and the coating layer which may be uneven is analyzed by combining an SEM picture, so that the deintercalation of lithium ions under high rates is hindered, and the electrochemical performance is reduced.

When the coating amount is 1%, the rate performance is highest, the rates under 0.1C, O.5C,1C,2C,3C and 5C respectively reach 198.11mAh/g,183.53mAh/g,175.64mAh/g,165.02mAh/g,155.65 mAh/g and 137.33mAh/g, and the capacities are higher than those of the original material, and the three-dimensional network structure is formed by bonding and crosslinking macromolecular chains of the silane coupling agent, so that the water resistance, the thermal stability and the mechanical property of the material are improved, the inert coating layer has a certain inhibiting effect on HF acid in the electrolyte, and the rate performance of the material is improved.

In fig. 6, four materials are activated three times at 0.1C, and are subjected to constant current discharge under the conditions of 0.5C,1C,2C,3C and 5C, respectively, and the discharge specific capacities of the original materials at current densities of 0.1C,0.5C,1C,2C,3C and 5C are 185mAh/g, 175mAh/g, 167mAh/g, 156mAh/g, 146mAh/g and 130mAh/g, respectively, and are cycled 5 times at each rate. The material with the coating capacity of 1% shows the best rate performance, and the specific discharge capacities under 0.1C,0.5C,1C,2C,3C and 5C are respectively 208mAh/g, 193mAh/g, 185mAh/g, 174mAh/g, 165mAh/g and 146mAh/g, which shows that 1% of the coating capacity can enable-Si-O-C-bond, -C-O-C-bond and epoxy bond in the silane coupling agent kh560 to form a layer of net-shaped coating structure, so that the conductivity of lithium ions is improved, and in addition, the hydrophobicity of the silane coupling agent can reduce the water absorption degree of the material in the homogenization process, so that the material can release higher specific discharge capacity under high current density. By testing the electrochemical performance of the materials with the coating amount of 0.5% and 2%, although the performance is improved compared with that of the original material, the performance of the material with the coating amount of 2% is reduced rapidly along with the increase of the current density, which indicates that the coating is too thick, and the lithium ion extraction is hindered. The specific discharge capacity of the material with the coating amount of 0.5 percent is not improved too much compared with that of the material after acid washing, which indicates that the coating layer is too thin, so that the material cannot form a uniform and compact coating layer, and the advantages of the silane coupling agent cannot be exerted.

Experimental example 4 cycle performance curves of different materials

FIG. 7 shows the cycle performance curves for raw material NCM811 coated with different amounts of kh560 than raw material NCM 811;

FIG. 8 shows the cycle performance curves for different amounts of kh560 coated with virgin NCM811 and pickled NCM 811.

In the context of figure 7 of the drawings,

a shows the cycle performance curve of NCM-k0.5 prepared in comparative example 6;

b shows the cycle performance curve of NCM-k1 prepared in comparative example 7;

c shows the cycle performance curve of NCM-k2 prepared in comparative example 8;

d shows the cycle performance curve of the starting material NCM 811.

In fig. 7, the a and d curves substantially coincide and are located below the b curve.

In the context of figure 8 of the drawings,

a shows the cycle performance curve of NCM-a1-k0.5 prepared in example 1;

b shows the cycling performance curve for NCM-a1-k1 made in example 2;

c shows the cycling performance curve for NCM-a1-k2 made in example 3;

d shows the cycle performance curve of the starting material NCM 811.

In fig. 7, under the 1C circulation condition, the primary material and the coating amount are 0.5%, 1% and 2% of the first discharge specific capacity of 168.61mAh/g, 167.2mAh/g, 174.67mAh/g and 166.61mAh/g, and the capacities after 200 circulations are 142.7656mAh/g, 141.2253 mAh/g, 146.3617mAh/g and 140.7656mAh/g, respectively, and the circulation efficiency is 84.67%, 84.46%, 83.79% and 84.49%. From the data, it can be seen that the specific capacity of the 1C cycle is improved only when the coating amount is 1%, but from the view of cycle efficiency, the slope of the capacity decay of the coated material is similar to that of the original material, and in the cycle, kh560 reacts with the residual water in the electrolyte at the beginning to generate intermolecular dehydration reaction, and the reaction equation is as follows:

however, as the reaction proceeds, especially under a large current, the temperature of the battery rises, so that the kh560 itself also undergoes a dehydration condensation reaction, namely, the kh560 self-crosslinking reaction reduces the resistance of the kh560 to HF of the electrolyte, which causes the residual LiOH and LiCO3 on the surface of the high-nickel material to react with HF acid of the electrolyte, so that the temperature of the battery rises faster, and the rate of the kh560 self-crosslinking reaction is proportional to the reaction temperature, forming a vicious circle.

In fig. 8, when a cycle performance test of four materials is performed, a voltage range is 3.0-4.3V, the materials are activated for 3 cycles at a current density of 0.1C, the materials are cycled for 200 times at 1C, the initial discharge specific capacity of the original material at 1C is 169mAh/g, the discharge specific capacity after 200 cycles is 143 mAh/g, the coulombic efficiency is 84.54%, the initial discharge specific capacities of the materials with the coating capacities of 0.5%, 1% and 2% at 1C are 179mAh/g, 186mAh/g and 177mAh/g, the discharge specific capacities after 200 cycles are 163mAh/g, 174mAh/g and 151mAh/g, and the coulombic efficiencies are 91.28%, 93.42% and 85.32%, respectively. After the material after acid washing is coated with the silane coupling agent, the cycle performance of the material is improved, wherein the material with the coating amount of 1% exerts excellent cycle performance, and not only can be cycled under high capacity, but also the material can be recycledThe efficiency is also improved when the coating amount is 0.5%. The cycling stability is enhanced, but the specific capacity is not high when the coating amount is 1 percent, which indicates that a compact coating layer is not formed at the lower coating amount, the hydrophobic capability is reduced, the HF resistance capability in electrolysis is poor, but Li formed on the surface after phosphoric acid washing is performed₃PO₄The coating layer reduces the solubility of HF to materials in electrolysis, and the battery keeps better stability under high-rate circulation. When the coating amount is 2%, the coating layer has little effect on improving the cycle performance of the material, and the excessively thick coating layer not only hinders the desorption of internal lithium ions, but also reduces the activity of the surface of the battery, so that the material is unstable in structure at the later stage of the cycle and is rapid in capacity decay.

The data obtained from fig. 7 and 8 are made as follows:

table 3 comparison table of specific discharge capacity and cycle efficiency data of different materials

As can be seen from fig. 7, fig. 8 and table 3, after the raw material NCM811 is washed with 1% phosphoric acid and then coated with the silane coupling agent kh560, the cycle performance of the battery is greatly improved, and particularly, the cycle efficiency of the NCM-a1-k1 prepared in example 2 is improved by about 10%.

Experimental example 5 TEM image of ternary material NCM-a1-k1

FIG. 9 shows a TEM image of NCM-a1-k1 obtained after 1% phosphoric acid washing of NCM811 and coating with 1% of a silane coupling agent kh 560. Wherein,

fig. 9(a) shows a TEM image of the raw material NCM 811;

FIG. 9(b) shows a TEM image of NCM-a1-k1 obtained in example 2.

As seen from FIG. 9(b), a layer of about 5nm Li₃PO₄A coating layer and a 5nm kh560 coating layer. The uniform and compact coating layer effectively blocks the electrolyte and the original materialThe side reaction of surface substances, and the passing rate of lithium ion deintercalation are improved, so that the cycle performance of the material is improved.

Experimental example 6 cycle performance curves of different proton-pickled NCM811 materials and coated kh560 after pickling

Figure 10 shows a graph of the cycling performance of the same amount of different protonic acid pickled NCM811 materials. Wherein,

a shows the cycle performance curve of NCM-a1 obtained in step 1 of example 1 (example 2);

b shows the cycle performance curve of the NCM-oxalic acid prepared in step 1 of comparative example 1;

c shows the cycle performance curve of the NCM-acetic acid prepared in step 1 of comparative example 2.

FIG. 11 shows the cycle performance curves for different proton acid washes of NCM811 post-clad Kh560

Wherein,

a shows the cycle performance curve of NCM-a1-k1 prepared in example 2;

b shows the cycle performance curve of NCM-oxalic acid-k 1 prepared in comparative example 1;

c shows the cycle performance curve of NCM-acetic acid-k 1 prepared in comparative example 2.

As can be seen from the cycle data of 50 cycles of high-temperature cycle in FIG. 10 and FIG. 11, the cycle performance of oxalic acid pickling is the worst, and phosphoric acid pickling is the best; the material cycle performance of 1% phosphoric acid pickling NCM811 material coating kh560 is the best, and acetic acid is used as the oxalic acid is too acidic, so that the material surface is corroded strongly; phosphoric acid on the other hand with LiOH and Li₂CO₃Can consume 3 Li at one time during reaction⁺Formation of Li₃PO₄Is a good ion conductor (6 x 10)^-8S/cm) to effectively protect the bulk material from corrosion by HF in the electrolyte. And the product which is washed by phosphoric acid and coated with kh560 can form two coating layers, namely, one coating layer and the other coating layer on the surface of the NCM811 materialLayer of about 5nm Li₃PO₄A coating layer and a 5nm kh560 coating layer. The uniform and compact coating layer effectively prevents the side reaction of the electrolyte and the surface substances of the original material, and simultaneously improves the lithium ion deintercalation passing rate, so that the cycle performance of the material is improved.

Experimental example 7 cycle performance curves of different silane coupling agent-coated virgin NCM811 and pickled NCM811

FIG. 12 shows the cycle performance curves for different silane coupling agent coated NCM 811;

wherein,

a shows the cycle performance curve of NCM-k1 prepared in comparative example 7;

b shows the cycle performance curve of NCM-k550 prepared in comparative example 9;

c shows the cycle performance curve of NCM-k570 prepared in comparative example 10.

FIG. 13 shows the cycle performance curves of NCM811 after coating with different silane coupling agents and pickling. Wherein,

a shows the cycle performance curve of NCM-a1-k1 prepared in example 2;

b shows the cycle performance curve of NCM-a1-k550 prepared in comparative example 4;

c shows the cycle performance curve of NCM-a1-k570 prepared in comparative example 5.

From fig. 12 and fig. 13, it can be seen that the cycle performance of the material coated with the silane coupling agent kh560 is the best whether the raw material NCM811 is coated or the acid-washed NCM811 is coated, and the kh550 is the next place, which indicates that the kh560 plays a good role in physical barrier, increases the coating strength, and enhances the high-temperature stability of the material.

Experimental example 8 cycle performance curves of phosphoric acid pickling and lithium dihydrogen phosphate washing NCM811 and coating kh560

In the context of figure 14, it is shown,

a shows the cycle performance curve of NCM-a1-k1 prepared in example 2;

b shows the cycle performance curve of NCM-lithium dihydrogen phosphate-k 1 prepared in comparative example 3.

It can be seen from FIG. 14 that the cycle performance of the material after pickling with phosphoric acid is significantly better than that of the material with lithium dihydrogen phosphate, and the capacity is relatively high. Shows that phosphoric acid reduces residual alkali on the surface of the material after acid cleaning, and generates Li with free lithium on the surface of the material₃PO₄Effectively protecting the NCM811 material.

Experimental example 9 cycle performance curves for different amounts of phosphoric acid washed NCM811 coated with kh560

Fig. 15 shows the cycle performance curves for different amounts of phosphoric acid washed NCM811 coated kh560, wherein,

a shows the cycle performance curve of NCM-a1-k1 prepared in example 2;

b shows the cycle performance curve of NCM-a0.5-k1 from example 5;

c shows the cycle performance curve of NCM-a1.5-k1 from example 4.

As can be seen from FIG. 15, the cycle performance of the material coated with kh560 after 1% phosphoric acid washing of NCM811 is the best, with 0.5% phosphoric acid. This shows that when the amount of phosphoric acid is too high, the surface of the anode material is corroded, and the morphology of the material is seriously damaged, so that the lithium ions in the anode material are lost, the crystal structure is damaged, the electrical property of the anode material is affected, and the electrical property of the ternary material cannot be improved but is greatly reduced. When the amount of phosphoric acid is too small, the residual LiOH and Li cannot be effectively reduced₂CO₃And thus cannot improve the electrical properties of the ternary material.

Therefore, the high-nickel ternary cathode material with improved electrical property prepared by the method has better electrical property compared with the original high-nickel cathode material; meanwhile, after being treated by the coating agent, the high-nickel cathode material is hydrophobicThe sexual performance is improved better. Preferably pickling with phosphoric acid and coating kh560, to form uniform and dense Li₃PO₄And the kh560 double-layer coating layer effectively prevents the side reaction of the electrolyte and the surface substance of the original material, and simultaneously improves the lithium ion de-intercalation passing rate, so that the cycle performance of the material is improved, and the electrical performance of the high-nickel anode material is effectively improved.

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims

1. The high-nickel ternary cathode material with the improved electrical property is characterized in that the cathode material is obtained by pickling and coating a cathode material matrix.

2. The high-nickel ternary cathode material according to claim 1, wherein the cathode material matrix is formed from Li (Ni)_1-x-yCo_xMn_y)O₂Wherein 1-x-y is more than or equal to 0.5, 0.4 is more than x and more than 0, 0.4 is more than y and more than 0, preferably, the matrix of the cathode material is Li (Ni)_0.8Co_0.1Mn_0.1)O₂。

3. The preparation method of the high-nickel ternary cathode material with improved electrical property is characterized by comprising the following steps:

4. The method according to claim 3, wherein in step 1, the positive electrode material matrix is made of Li (Ni)_1-x- _yCo_xMn_y)O₂Wherein 1-x-y is not less than 0.5, 0.4 > x > 0, 0.4 > y > 0, and the matrix of the positive electrode material is preferably Li (Ni)_0.8Co_0.1Mn_0.1)O₂。

5. A process according to claim 3, wherein in step 1, the protic acid is acetic acid, oxalic acid or phosphoric acid, preferably phosphoric acid;

the mass ratio of the protonic acid to the positive electrode material substrate is (0.001-1): 100, preferably (0.005-0.05): 100, more preferably 0.5:99.5, 1:99, 1.5:98.5 or 2:98, and still more preferably 1: 99.

6. The method according to claim 3, wherein in step 1, the protonic acid dispersion is obtained by dispersing protonic acid with a dispersant, and the dispersant is alcohol, preferably methanol, ethanol or isopropanol, more preferably ethanol, and further preferably absolute ethanol;

the temperature for removing the dispersing agent is 70-90 ℃.

7. The method according to claim 3, wherein in step 2, the calcination temperature is 450-550 ℃, preferably 500 ℃,

the calcination time is 4-6h, preferably 5 h.

8. A method according to claim 3, characterized in that in step 3, the coating agent is a silane coupling agent, preferably kh550, kh560 or kh570, further preferably kh560,

the amount of the silane coupling agent is such that the mass ratio of the silane coupling agent to the washed positive electrode material is (0.001-1): 100, preferably (0.005-0.05): 100, more preferably 0.5:99.5, 1:99 or 2:98, and even more preferably 1: 99.

9. The method as claimed in claim 3, wherein in step 3, the post-treatment comprises dispersing the coating agent with a dispersing agent II, adding the weighed and washed positive electrode material into the dispersed coating agent, uniformly mixing, removing the dispersing agent II, vacuum drying, and performing heat treatment to obtain the final product.

10. The method according to claim 9, wherein the dispersant II is an alcohol, preferably methanol, ethanol, isopropanol, more preferably ethanol, further preferably absolute ethanol;

the vacuum drying is 65-85 ℃, preferably 80 ℃, the vacuum drying time is 3-8 hours, preferably 4-6 hours;

the heat treatment is vacuum drying, the temperature of the vacuum drying is 100-200 ℃, the time is 2-7 hours, and the preferable time is 3-5 hours.