Method for spray coating lithium cobalt oxide positive electrode material and its application

Abstract

The invention discloses a method for spray coating a lithium cobalt oxide positive electrode material and its application, comprising preparing an ether solution of organosilicon, adding a surfactant and a combustion aid to obtain a mixed solution, adding lithium cobalt oxide to the mixed solution to obtain a mixed material, adding the mixed material to a spray combustion device, the mixed material enters a combustion chamber through a carrier gas flow for combustion, and after the reaction is completed, solid materials are collected to obtain lithium cobalt oxide coated with silicon dioxide. The invention uses combustible organosilicon as a coating source, after evenly mixing ether with a lithium cobalt oxide positive electrode material, igniting in a spray combustion device, generating a silicon dioxide coating layer, coating the surface of the lithium cobalt oxide positive electrode material, further generating lithium silicate at high temperature, and reducing the alkalinity of the material surface.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials, and specifically relates to a method for spray coating a lithium cobalt oxide positive electrode material and an application thereof. Background Art

[0002] Among lithium-ion cathode materials, lithium cobalt oxide is widely used due to its high operating voltage and energy density, easy synthesis, and fast charge and discharge. In recent years, with the further miniaturization and multifunctionalization of electronic products, higher requirements have been placed on the energy density of battery output. The application of conventional lithium cobalt oxide at high voltage still has many problems and challenges, especially the structural phase change at the interface with the electrolyte, transition metal dissolution, oxygen precipitation, and continuous oxidation and decomposition of the electrolyte, which seriously limit its application in high energy density lithium batteries.

[0003] In view of the above problems, in the prior art, a coating layer can be formed on the surface of the material to optimize the structural properties and electrochemical properties of the particles, improve the corrosion resistance of the material, and reduce the side reactions between the material and the electrolyte.

[0004] On the other hand, lithium cobalt oxide is mainly prepared by the high-temperature solid phase method. Solid lithium sources such as LiOH and Li2CO3 are volatile at high temperatures, so an excess of lithium source is added when the raw materials are mixed to compensate for the lithium loss during the high-temperature process. However, the amount of lithium volatilization during the sintering process is difficult to control, so it is inevitable that excess lithium source will remain on the surface of the material after the high-temperature solid phase reaction is completed. Excess lithium source generally exists in the form of Li2O, which can easily combine with H2O and CO2 in the air to form LiOH and Li2CO3 attached to the surface of the material, resulting in a high alkalinity of the material, which makes it easy for the slurry to form a "jelly" form during the slurry adjustment process of electrode production, making slurry adjustment difficult.

[0005] In order to remove the excess Li2O on the surface of the material, researchers have done a lot of work. The simplest and most effective method is water washing. However, the positive electrode material is very sensitive to water, and it is easy to undergo chemical delithiation reaction in water, causing the lithium ions in the lattice to dissolve into the water in the form of LiOH, destroying the structure and electrochemical properties of the material. Summary of the invention

[0006] 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 spray coating a lithium cobalt oxide positive electrode material and its application, wherein the method comprises mixing the lithium cobalt oxide positive electrode material with an organic silicon liquid, and then spraying and burning the mixture to remove residual lithium and obtain a lithium cobalt oxide material coated with silicon dioxide.

[0007] According to one aspect of the present invention, a method for spray coating a lithium cobalt oxide positive electrode material is provided, comprising the following steps:

[0008] S1: preparing an ether solution of organic silicon, and adding a surfactant and a combustion aid to obtain a mixed solution;

[0009] S2: adding lithium cobalt oxide to the mixed solution to obtain a mixed material;

[0010] S3: adding the mixed material into a spray combustion device, and the mixed material enters a combustion chamber through a carrier gas flow and is burned. After the reaction is completed, the solid material in the combustion chamber is collected to obtain lithium cobalt oxide coated with silicon dioxide.

[0011] In some embodiments of the present invention, in step S1, the organosilicon is at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane or dodecamethylcyclohexasiloxane.

[0012] In some embodiments of the present invention, in step S1, the surfactant is at least one of lauryl alcohol polyoxyethylene ether or nonylphenol polyoxyethylene ether.

[0013] In some embodiments of the present invention, in step S1, the combustion improver is at least one of alkyl nitroanisole, nitrophenylhydrazine, alkoxy nitroaniline or nitrobenzophenone.

[0014] In some embodiments of the present invention, in step S1, the ratio of the organosilicon, ether, surfactant and combustion aid is (1.0-10.0) mL: (100-300) mL: (0.5-1.0) g: (1.0-2.0) g.

[0015] In some embodiments of the present invention, in step S2, the solid-to-liquid ratio of the lithium cobalt oxide to the mixed solution is 1 g: (1.0-3.0) mL.

[0016] In some embodiments of the present invention, in step S3, the nozzle aperture of the spray combustion device is 30-50 μm, and the spray pressure is 0.8-1.5 MPa.

[0017] In some embodiments of the present invention, in step S3, the carrier gas flow is air or oxygen, and the carrier gas flow rate is 100-150 L / h.

[0018] In some embodiments of the present invention, in step S3, the temperature of the combustion chamber is 750-1000°C.

[0019] The invention also provides application of the method in preparing lithium ion batteries.

[0020] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved:

[0021] 1. The present invention uses combustible organosilicon as a coating source, and after evenly mixing ether with the lithium cobalt oxide positive electrode material, ignites it in a spray combustion device to generate a silicon dioxide coating layer, which is coated on the surface of the lithium cobalt oxide positive electrode material. And at high temperature, silicon dioxide further reacts with the lithium remaining on the surface of the lithium cobalt oxide to generate lithium silicate, which reduces the alkalinity of the material surface and avoids the problem of lattice lithium precipitation caused by washing to remove residual lithium. Not only does it achieve the coating of silicon dioxide on the surface of lithium cobalt oxide, but it also further eliminates the slurry adjustment problem caused by residual lithium, killing two birds with one stone. The reaction equation is as follows:

[0022] xLi2O+ySiO2→xLi2O·ySiO2.

[0023] 2. In the process of spray pyrolysis, the flammability of silicone is utilized and ether is used as solvent for fire coating, thus avoiding the problem of lattice lithium precipitation caused by wet methods such as hydrothermal coating. At the same time, in order to reduce the viscosity of droplets generated in the spraying process, organic surfactants are added to improve the dispersion of the spray, so that the lithium cobalt oxide particles and the liquid can be sprayed at the same time without adhesion, thereby improving the combustion and coating effects. In order to avoid the problem of cobalt reduction caused by incomplete combustion, nitro-based combustion aids are added to ensure that all liquids can be fully burned, thus ensuring the stability of the lithium cobalt oxide material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0025] Figure 1 This is a SEM image of lithium cobalt oxide coated with silicon dioxide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments 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.

[0027] Example 1

[0028] A method for spray coating a lithium cobalt oxide positive electrode material, the specific process is:

[0029] Step 1, preparing an ether solution of hexamethylcyclotrisiloxane, adding lauryl alcohol polyoxyethylene ether as a surfactant and nitrophenylhydrazine as a combustion aid, mixing evenly to obtain a mixed solution, wherein the ratio of each material is: organosilicon: ether: surfactant: combustion aid = 5mL: 200mL: 0.8g: 1.5g;

[0030] Step 2, adding the sintered lithium cobalt oxide positive electrode material to the mixed solution in step 1 according to a solid-liquid ratio of 1 g:2.0 mL to obtain a mixed material;

[0031] Step 3, adding the mixed material obtained in step 2 into a spray combustion device, setting the nozzle aperture to 40 μm, the spray pressure to 1.2 MPa, using oxygen as a carrier gas flow under constant stirring, setting the flow rate to 120 L / h, and entering the combustion chamber through the carrier gas flow for combustion, and controlling the combustion chamber temperature to 900° C.;

[0032] Step 4: After the reaction is completed, the solid material in the combustion chamber is collected to obtain lithium cobalt oxide spray-coated with silicon dioxide.

[0033] Example 2

[0034] A method for spray coating a lithium cobalt oxide positive electrode material, the specific process is:

[0035] Step 1, preparing an ether solution of octamethylcyclotetrasiloxane, adding nonylphenol polyoxyethylene ether as a surfactant and alkoxy nitroaniline as a combustion aid, mixing evenly to obtain a mixed solution, wherein the ratio of each material is: ether: surfactant: combustion aid = 1 mL: 100 mL: 0.5 g: 1.0 g;

[0036] Step 2, adding the sintered lithium cobalt oxide positive electrode material to the mixed solution in step 1 at a solid-liquid ratio of 1 g:1.0 mL to obtain a mixed material;

[0037] Step 3, adding the mixed material obtained in step 2 into a spray combustion device, setting the nozzle aperture to 30 μm, the spray pressure to 0.8 MPa, using air as a carrier gas flow under constant stirring, setting the flow rate to 100 L / h, and entering the combustion chamber through the carrier gas flow for combustion, and controlling the combustion chamber temperature to 1000° C.;

[0038] Step 4: After the reaction is completed, the solid material in the combustion chamber is collected to obtain the spray-coated lithium cobalt oxide positive electrode material.

[0039] Example 3

[0040] A method for spray coating a lithium cobalt oxide positive electrode material, the specific process is:

[0041] Step 1, prepare an ether solution of decamethylcyclopentasiloxane, add lauryl alcohol polyoxyethylene ether as a surfactant and nitrobenzophenone as a combustion aid, mix well, and obtain a mixed solution, wherein the ratio of each material is: organosilicon: ether: surfactant: combustion aid = 10 mL: 300 mL: 1.0 g: 2.0 g;

[0042] Step 2, adding the sintered lithium cobalt oxide positive electrode material to the mixed solution in step 1 according to a solid-liquid ratio of 1 g:3.0 mL to obtain a mixed material;

[0043] Step 3, adding the mixed material obtained in step 2 into a spray combustion device, setting the nozzle aperture to 50 μm, the spray pressure to 1.5 MPa, using oxygen as a carrier gas flow under constant stirring, setting the flow rate to 150 L / h, and entering the combustion chamber through the carrier gas flow for combustion, and controlling the combustion chamber temperature to 750°C;

[0044] Step 4: After the reaction is completed, the solid material in the combustion chamber is collected to obtain the spray-coated lithium cobalt oxide positive electrode material.

[0045] The sintered lithium cobalt oxide positive electrode material used in step 2 of Example 1-3 is prepared as follows: cobalt oxide and lithium carbonate are mixed to control the molar ratio of Li:Co to 1.06, and placed in a push plate kiln for high-temperature solid-phase sintering. The sintering temperature is 1000°C and the sintering time is 12h to obtain a lithium cobalt oxide positive electrode material, and this lithium cobalt oxide positive electrode material is used as Comparative Example 1.

[0046] Take 500 ml of deionized water, maintain the water temperature at 30°C under stirring, add 500 g of lithium cobalt oxide positive electrode material (Comparative Example 1) into the deionized water, and stir at a speed of 400 r / min. After 10 minutes, use suction filtration to separate the material and water, and dry the material at 120°C for 10 hours to obtain the washed and dried lithium cobalt oxide positive electrode material, which is used as Comparative Example 2.

[0047] Test example

[0048] The residual lithium in the coated lithium cobalt oxide material obtained in the example and the lithium cobalt oxide in the comparative example was detected.

[0049] The coated lithium cobalt oxide material obtained in the embodiment and the comparative example lithium cobalt oxide are used as raw materials, acetylene black is used as a conductive agent, and PVDF is used as a binder. The active material, conductive agent, and binder are weighed in a ratio of 92:4:4, and a certain amount of organic solvent NMP is added. After stirring, they are coated on aluminum foil to make a positive electrode sheet. The negative electrode uses a metal lithium sheet and is made into a CR2430 button battery in an argon-filled glove box. The electrical performance test was carried out in a CT2001A blue electric test system. Test conditions: 3.0-4.48V, current density 1C=180mAh / g, and the test temperature is 25±1°C. The test results are shown in Table 1.

[0050] Table 1

[0051]

[0052] As can be seen from Table 1, the amount of residual lithium in the lithium cobalt oxide treated by spray coating in Example 1 is significantly lower than that in Comparative Example 1, and the amount of residual lithium removed is comparable to that in Comparative Example 2 by ordinary water washing. However, the discharge capacity and cycle performance of the material in Comparative Example 2 are significantly inferior to those in Example 1. This is because during the water washing process in Comparative Example 2, the material undergoes a chemical delithiation reaction in water, causing the lithium ions in the lattice to dissolve into water in the form of LiOH, destroying the structure of the material and resulting in reduced electrochemical performance.

[0053] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for spray coating a lithium cobalt oxide positive electrode material, characterized in that: The following steps are involved: S1: preparing an ether solution of organic silicon, and adding a surfactant and a combustion aid to obtain a mixed solution; S2: adding lithium cobalt oxide containing residual lithium on the surface into the mixed solution to obtain a mixed material; S3: adding the mixed material into a spray combustion device, and the mixed material enters a combustion chamber through a carrier gas flow and burns. After the reaction is completed, the solid material in the combustion chamber is collected to obtain lithium cobalt oxide coated with silicon dioxide; In step S1, the surfactant is at least one of lauryl alcohol polyoxyethylene ether or nonylphenol polyoxyethylene ether; the combustion improver is at least one of alkyl nitroanisole, nitrophenylhydrazine, alkoxy nitroaniline or nitrobenzophenone; the ratio of the organosilicon, ether, surfactant and combustion improver is (1.0-10.0) mL: (100-300) mL: (0.5-1.0) g: (1.0-2.0) g; In step S3, the temperature of the combustion chamber is 750-1000°C.

2. The method according to claim 1, characterized in that In step S1, the organosilicon is at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane or dodecamethylcyclohexasiloxane.

3. The method according to claim 1, characterized in that In step S2, the solid-liquid ratio of the lithium cobalt oxide to the mixed solution is 1 g: (1.0-3.0) mL.

4. The method according to claim 1, characterized in that: In step S3, the nozzle aperture of the spray combustion device is 30-50 μm, and the spray pressure is 0.8-1.5 MPa.

5. The method according to claim 1, characterized in that In step S3, the carrier gas flow is air or oxygen, and the carrier gas flow rate is 100-150 L / h.

6. Use of the method according to any one of claims 1 to 5 in the preparation of lithium ion batteries.

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