CN108039461A - A kind of silicium cathode material of coated and preparation method thereof - Google Patents

Abstract

The invention discloses a kind of silicium cathode material of coated, and the silicium cathode material is using silicon grain as core, and using alumina doped Zinc oxide film as shell, certain space is left between silicon grain and shell.The problems such as this space is in order to adapt to volumetric expansion of the silicon grain after embedding lithium, avoid dusting and the decline of electric conductivity.Present invention also offers the preparation method of the negative material, and in one layer of PMMA of silicon grain outer wrapping, one layer of alumina doped zinc-oxide film is then deposited on PMMA, finally removes PMMA and obtains the silicon grain negative material wrapped up with film.Silicium cathode material specific capacity provided by the invention is high, has extended cycle life.

Description

A kind of wrapped silicon negative electrode material and preparation method thereof

technical field

The invention relates to the field of electrochemical technology, in particular to the field of lithium ion batteries, in particular to a method for preparing a packaged silicon material used as a lithium battery negative electrode material.

Background technique

In today's pursuit of energy saving and environmental protection, the development and utilization of clean and renewable energy is particularly important. Among them, lithium-ion batteries, which have the advantages of high operating voltage, large specific capacity, high energy density, and long cycle life, have received extensive attention. At present, lithium-ion batteries are used in electric vehicles, electrostatic storage and portable electronic communication equipment and other fields. With the continuous improvement of the performance of lithium-ion batteries, it is also believed that lithium-ion batteries will play an indispensable role in human life in the future. Therefore, electrode materials that play a decisive role in the performance of lithium-ion batteries have been vigorously developed.

Silicon-based materials have the world's largest theoretical specific capacity of 4200mAh/g, which is 10 times that of commercial graphite anodes. In addition, silicon is the second largest element on the earth, with abundant reserves and no pollution to the environment. Therefore, silicon-based materials are considered to be the most promising anode materials for lithium-ion batteries.

However, as an anode material for lithium-ion batteries, silicon-based materials have two serious problems. During the continuous charge and discharge process of lithium-ion batteries, the volume of silicon will expand violently, resulting in structural damage and silicon pulverization. In addition, the electrolyte is reduced to form a solid electrolyte film on the silicon surface. The instability of the silicon volume can also lead to the damage of the solid electrolyte membrane. After many charge-discharge cycles, the film on the surface of the silicon becomes thicker and thicker, which not only weakens the conductivity of the electrode, but also makes lithium ions in the negative electrode material The transfer efficiency in is reduced.

In recent years, people have focused on researching and improving the performance of silicon anode materials. First, people improve the performance of silicon-based materials by changing the material structure. The structure of silicon-based materials enables the transition from thin films to nanowires or nanoparticles. The naturally occurring spaces in nanowires or nanoparticles moderate the volume expansion caused by lithium ion intercalation. In addition to the change in the structure of the silicon-based material itself, the combination of the silicon-based material and other materials also greatly improves the cycle life of the negative electrode material. For example, carbon and silicon-based materials can form core-shell structures. The space reserved between the carbon shell and the silicon particles acts as a buffer against volume expansion. The carbon shell also has a certain inhibitory effect on it.

Contents of the invention

The technical problem to be solved by the present invention is that the silicon-based negative electrode material of the lithium-ion battery is prone to pulverization, which leads to unstable cycle performance of the battery.

The first aspect of the present invention provides a method for preparing a packaged silicon negative electrode material, comprising the following steps:

A. Cover the surface of the silicon particles with a coupling agent to obtain silicon particles with a surface modified by the coupling agent;

B. then add PMMA monomer, emulsifier, buffering agent, initiator, crosslinking agent and dispersion medium to react, form PMMA film on silicon particle surface, obtain the silicon particle that PMMA wraps;

C. soak the silicon particles wrapped by PMMA in the reaction solution containing zinc source and aluminum source, and stir, and the reaction generates a layer of aluminum oxide-doped zinc oxide film covering the outer surface of PMMA film;

D. PMMA is removed at high temperature in an argon atmosphere, and finally the silicon negative electrode material for lithium-ion batteries is obtained. The silicon negative electrode material has silicon particles as the core, aluminum oxide doped zinc oxide film as the shell, and is between the silicon particles and the shell. There is a certain amount of space.

In the technical scheme of the present invention, the concrete method of step A is as follows:

A-1. Mix the silicon nanoparticles with an appropriate amount of ethanol, stir with a magnetic stirrer,

A-2. Mix the coupling agent, deionized water, and ethanol, and ultrasonically mix,

A-3. Slowly drop the mixed solution in step A-2 into the silicon nanoparticle solution in step A-1, and stir until uniformly mixed to obtain a solution containing silicon particles whose surface has been modified by a coupling agent.

In the method of the above step A, the coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane (MPS), and the particle size of the silicon nanoparticles is 100nm-5um.

In the technical solution of the present invention, the thickness of the PMMA film wrapped outside the silicon particles is 100-500nm.

In the technical scheme of the present invention, the concrete method of step B is as follows:

B-1. Centrifuge the silicon particle solution with the surface modified by the coupling agent, then ultrasonically clean with alcohol and then centrifuge, repeat several times, and finally dry in vacuum.

B-2. Put the vacuum-dried silicon particles and deionized water into the reaction vessel after mixing, and stir evenly;

B-3. Then add PMMA monomer, emulsifier, buffer, initiator, cross-linking agent, and in a nitrogen atmosphere, in a water bath environment of 50-90 ° C, magnetically stir for a period of time, and finally get a mixture containing PMMA on the surface Thin films of silicon particles in solution.

In the method of the above-mentioned step B-3, methyl methacrylate (MMA), sodium dodecylbenzene carbonate, sodium bicarbonate, potassium persulfate, and triaminotriphenylmethane (BVA) were added for reaction.

In the technical scheme of the present invention, the concrete method of step C is as follows:

C-1. The solution containing the silicon particles covered with PMMA film is centrifuged, then ultrasonically cleaned with deionized water and then centrifuged, repeated several times, and finally vacuum-dried;

C-2. Put the dried silicon particles into deionized water, stir magnetically in a water bath environment at 50-90°C, and adjust the pH value of the solution to 8-11;

C-3. Then, add zinc acetate and aluminum chloride to the solution, and adjust the pH value of the solution to 8-11 with sodium hydroxide solution, and stir it magnetically for a period of time in a water bath environment at 50-90°C; then centrifuge the solution, Ultrasonic cleaning with deionized water and centrifugation, repeated several times, and finally vacuum drying;

C-4. The solid particles obtained in the above C-3 are annealed in an argon atmosphere at 300°C-400°C to remove PMMA, and finally a structure in which silicon particles are wrapped with aluminum oxide-doped zinc oxide film is obtained.

In the technical solution of the present invention, in steps C-2 and C-3, the pH value of the solution is adjusted to 8.5.

In the technical solution of the present invention, the silicon nanoparticles are silicon nanoparticles with a particle diameter of 100nm-5um.

The second aspect of the present invention provides a silicon negative electrode material with good cycle performance and large specific capacity that can be used in lithium-ion batteries. A packaged silicon negative electrode material, the silicon negative electrode material uses silicon particles as the core, aluminum oxide doped zinc oxide film as the shell, and there is a certain space between the silicon particles and the shell.

In the technical solution of the present invention, the diameter of the silicon particles is 100nm-5um.

In the technical solution of the present invention, the thickness of the aluminum oxide-doped zinc oxide film is 100-500 nm, and the doping concentration of the aluminum oxide-doped zinc oxide film is 2-10%.

The third aspect of the present invention provides a lithium-ion battery, which includes: battery positive and negative electrode housings, diaphragms, electrolyte, shrapnel, steel sheets, positive and negative current collectors, positive and negative electrode materials, and the negative electrode materials are the aforementioned Wrapped silicon anode material.

The silicon negative electrode material of the lithium ion battery prepared by the present invention has a silicon particle as a core, an aluminum oxide-doped zinc oxide film as a shell, and a certain space between the silicon particle and the shell. In order to adapt to the volume expansion of silicon particles after lithium intercalation, this space avoids problems such as pulverization, conductivity decline, and solid electrolyte membrane instability.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and become a part of the description, explain the present invention together with the embodiments of the present invention, and do not limit the present invention. In the attached picture,

Fig. 1 is one of the flow charts for preparing the wrapped silicon negative electrode material of the present invention. In the figure, 1 is a silicon particle, 2 is PMMA, and 3 is a zinc oxide-doped aluminum oxide film.

Detailed ways

The specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

Referring to FIG. 1 , a packaged silicon negative electrode material includes silicon particles 1 , PMMA 2 , and zinc oxide-doped aluminum oxide film 3 from the inside to the outside. The silicon particle diameter of the invention is 100nm-5um, the thickness of the aluminum oxide-doped zinc oxide film is 100-500nm, and the doping concentration of the aluminum oxide-doped zinc oxide film is 2-10%. First wrap the silicon particles with a PMMA film, then deposit a zinc oxide-doped aluminum oxide film on the PMMA surface, and finally remove the PMMA at high temperature in an argon atmosphere to leave a certain gap between the silicon particles and the zinc oxide-doped aluminum oxide film. space.

The present invention also provides a preparation method of the negative electrode material, the specific steps comprising:

(1) Mix 0.1-2g of silicon nanoparticles with a diameter of 100nm-5um and 100-500mL of ethanol, and stir with a magnetic stirrer for 1-30 minutes.

(2) Mix 0.001-0.5g coupling agent, 1-10g deionized water, and 1-20g ethanol, and then sonicate for 1-30 minutes.

(3) Slowly drop the mixed solution obtained in step (2) into the silicon particle solution obtained in step 1), and magnetically stir for 1-24 hours at a temperature of 1-100° C., and finally obtain the surface modified with a coupling agent. silicon particles.

(4) Centrifuge the solution obtained in step (3), then ultrasonically clean it with ethanol, and then centrifuge again. Repeat this step 1-3 times.

(5) Put the surface-modified silicon particles obtained by centrifuging in step (4) into a vacuum drying oven, and vacuum-dry for 1-24 hours at an environment of 1-100° C.

(6) Mix the vacuum-dried silicon particles in step (5) with 1-500 mL of deionized water, put them into a three-necked flask, and stir with a magnetic stirrer for 1-30 minutes.

(7) Pour 0.1-10mL PMMA monomer, 0.1-1g emulsifier, 0.1-1g buffer, 0.1-1g initiator, 0.1-1g cross-linking agent into a three-necked flask, and in nitrogen atmosphere, in 1- Stir with magnetic force at 100°C for 1-24 hours, and finally obtain silicon particles covered with a PMMA film.

(8) Centrifuge the solution obtained in step (7), then ultrasonically clean it with deionized water, and then centrifuge again. Repeat this step 1-3 times.

(9) Put the solid obtained in step (8) into a vacuum drying oven, and dry it under vacuum for 1-24 hours under the environment of 1-100°C.

(10) Put the dried solid in step (9) into 50-500mL deionized water, stir magnetically for 1-5 hours in a water bath environment at 1-100°C, and adjust the pH value of the solution to 8-11 with ammonia water , and then, 0.2-5g of zinc acetate and 0.2-5g of aluminum chloride are added to the solution, and the pH of the solution is adjusted to 8-11 with sodium hydroxide solution, and magnetic stirring is maintained for 1-24 hours.

(11) The solution obtained in step (10) is centrifuged, then ultrasonicated with ethanol, and then centrifuged again. Repeat this step 1-3 times.

(12) Put the solid obtained in step (11) into a vacuum drying oven, and dry it under vacuum for 1-24 hours under the environment of 1-100°C.

(13) annealing the solid particles obtained in step (12) at 350° C. in an argon atmosphere to remove PMMA. Finally, a structure in which silicon particles are wrapped with aluminum oxide-doped zinc oxide films is obtained.

(14) Mix and dissolve the material obtained in step (13) with a binder and a conductive agent in a dispersant to make a slurry, and the mass of the active material accounts for 60-90% of the entire slurry.

(15) Coating the slurry prepared in step (14) on the copper foil with a coating machine, and drying in vacuum for 1-24 hours, the thickness of the negative electrode film is 10-1000um.

(16) Use a punch with a diameter of 13-18um to punch the negative electrode film into pole pieces, and weigh each pole piece.

(17) Assemble and press the battery according to the sequence of positive electrode case, pole piece, separator, lithium sheet, steel sheet, shrapnel and negative electrode case. During assembly, add 1-10 drops of electrolyte.

The method of the present invention improves the volume expansion of the silicon negative electrode material and the instability of the solid electrolyte, thereby well improving the charging and discharging efficiency of the battery and the cycle performance of the battery.

Example

(1) Mix 0.4 g of silicon nanoparticles with 200 mL of ethanol, and stir for 15 minutes with a magnetic stirrer.

(2) Mix 0.35g of coupling agent, 7g of deionized water, and 13g of ethanol, and then sonicate for 10 minutes.

(3) Slowly drop the mixed solution obtained in step (2) into the silicon particle solution obtained in step 1), and magnetically stir at 80° C. for 12 hours. Finally, silicon particles whose surface has been modified with a coupling agent are obtained.

(4) Centrifuge the solution obtained in step (3), then ultrasonically clean it with ethanol, and then centrifuge again, repeating this step 3 times.

(5) Put the surface-modified silicon particles obtained by centrifuging in step (4) into a vacuum drying oven, and vacuum-dry for 12 hours at 60° C.

(6) Mix the vacuum-dried silicon particles in step (5) with 150 mL of deionized water, put them into a three-necked flask, and stir for 5 minutes with a magnetic stirrer.

(7) Add 0.019g sodium dodecylbenzene carbonate (SDBS), 0.24g sodium bicarbonate (NaHCO3), 0.006g potassium persulfate (KPS), 6mL methyl methacrylate (MMA), 0.12g triaminotris Benzene methane (BVA) was poured into a three-necked flask and magnetically stirred at 80° C. for 4 hours in a nitrogen atmosphere. Finally, silicon particles covered with PMMA film are obtained.

(8) Centrifuge the solution obtained in step (7), then use ethanol to sonicate, and then centrifuge again. Repeat this step 3 times.

(9) Put the solid obtained in step (8) into a vacuum drying oven, and dry it under vacuum for 12 hours under the environment of 60°C.

(10) Put the dried solid in step (9) into 100 mL of deionized water, stir magnetically for 1.5 hours in an 80° C. Zinc acetate and 0.05 g of aluminum chloride hexahydrate were added to the solution, and the pH value of the solution was adjusted to 8.5 with sodium hydroxide solution, and magnetic stirring was maintained for 18 hours.

(11) The solution obtained in step (10) is centrifuged, then ultrasonicated with ethanol, and then centrifuged again. Repeat this step 3 times.

(12) Put the solid obtained in step (11) into a vacuum drying oven, and dry it under vacuum for 12 hours under the environment of 60°C.

(13) The solid particles obtained in step (12) were annealed at 350° C. for 2 hours in an argon atmosphere to remove PMMA. Finally, a structure in which silicon particles are wrapped with aluminum oxide-doped zinc oxide films is obtained.

(14) The material obtained in step (13) is mixed with polyvinylidene fluoride (PVDF), carbon black and dissolved in N-methylpyrrolidone (NMP) to make a slurry, active material, adhesive and conductive agent The mass ratio is 7:1:2, and the mass of NMP is 10 times that of the active substance.

(15) Coating the slurry prepared in step (14) on the copper foil with a coater. And vacuum-dried at 120°C for 8 hours, the average thickness of the negative electrode film is 100-160um.

(16) Use a punch with a diameter of 13um to punch the negative electrode film into pole pieces, and weigh each pole piece.

(17) Assemble and press the battery in the order of positive electrode case, pole piece, diaphragm, lithium sheet, steel sheet, shrapnel and negative electrode case. During the assembly process, add 5 drops of electrolyte.

The method of the invention improves the volume expansion of the silicon negative electrode material and the stability of the solid electrolyte.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned examples. What are described in the above-mentioned examples and descriptions are only to illustrate the principles of the present invention. The present invention also has various changes without departing from the spirit and scope of the present invention. These changes and improvements all fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. A method for preparing a packaged silicon negative electrode material, comprising the steps of: A. Cover the surface of the silicon particles with a coupling agent to obtain silicon particles with a surface modified by the coupling agent; B. then add PMMA monomer, emulsifier, buffering agent, initiator, crosslinking agent and dispersion medium to react, form PMMA film on silicon particle surface, obtain the silicon particle that PMMA wraps; C. soak the silicon particles wrapped by PMMA in the reaction solution containing zinc source and aluminum source, and stir, and the reaction generates a layer of aluminum oxide-doped zinc oxide film covering the outer surface of PMMA film; D. PMMA is removed at high temperature in an argon atmosphere, and finally the silicon negative electrode material for lithium-ion batteries is obtained. The silicon negative electrode material has silicon particles as the core, aluminum oxide doped zinc oxide film as the shell, and is between the silicon particles and the shell. There is a certain amount of space. 2. preparation method according to claim 1, is characterized in that, step A specifically comprises as follows: A-1. Mix silicon nanoparticles with an appropriate amount of ethanol and stir with a magnetic stirrer; A-2. Mix the coupling agent, deionized water and ethanol, and ultrasonically mix; A-3. Slowly drop the mixed solution in step A-2 into the silicon nanoparticle solution in step A-1, and stir until uniformly mixed to obtain a solution containing silicon particles whose surface has been modified by a coupling agent. 3. preparation method according to claim 1, is characterized in that, step B specifically comprises as follows: B-1. Centrifuge the silicon particle solution with the surface modified by the coupling agent, then ultrasonically clean with alcohol and then centrifuge, repeat several times, and finally dry in vacuum; B-2. Put the vacuum-dried silicon particles and deionized water into the reaction vessel after mixing, and stir evenly; B-3. Then add PMMA monomer, emulsifier, buffer, initiator, cross-linking agent, and in a nitrogen atmosphere, in a water bath environment of 50-90 ° C, magnetically stir for a period of time, and finally get a mixture containing PMMA on the surface Thin films of silicon particles in solution. 4. preparation method according to claim 3 is characterized in that, in above-mentioned steps B-3, adds methyl methacrylate (MMA), sodium dodecylbenzene carbonate, sodium bicarbonate, potassium persulfate, Triaminotriphenylmethane (BVA) for the reaction. 5. preparation method according to claim 1, is characterized in that, step C specifically comprises as follows: C-1. The solution containing the silicon particles covered with PMMA film is centrifuged, then ultrasonically cleaned with deionized water and then centrifuged, repeated several times, and finally vacuum-dried; C-2. Put the dried silicon particles into deionized water, stir magnetically in a water bath environment at 50-90°C, and adjust the pH of the solution to 8-11 with ammonia water; C-3. Then, add zinc acetate and aluminum chloride to the solution, and adjust the pH value of the solution to 8-11 with sodium hydroxide solution, and stir it magnetically for a period of time in a water bath environment at 50-90°C; then centrifuge the solution, Then wash with deionized water and centrifuge again, repeat several times, and finally vacuum dry; C-4. The solid particles obtained in the above C-3 are annealed in an argon atmosphere at 300°C-400°C to remove PMMA, and finally a structure in which silicon particles are wrapped with aluminum oxide-doped zinc oxide film is obtained. 6. The preparation method according to claim 5, characterized in that, in steps C-2 and C-3, the pH value of the solution is adjusted to 8.5. 7. A packaged silicon negative electrode material prepared according to any one of claims 1-6, characterized in that the silicon negative electrode material takes silicon particles as the core and aluminum oxide-doped zinc oxide film as the shell. There is a certain space between the silicon particles and the shell. 8. The encapsulated silicon negative electrode material according to claim 7, characterized in that the diameter of the silicon particles is 100nm-5um. 9. The packaged silicon negative electrode material according to claim 7, characterized in that, the thickness of the aluminum oxide-doped zinc oxide film is 100-500 nm, and the doping concentration of the aluminum oxide-doped zinc oxide film is 2 —10%. 10. A lithium-ion battery, comprising: battery positive and negative housings, separators, electrolyte, shrapnel, steel sheets, positive and negative current collectors, positive and negative materials, characterized in that the negative materials are right The encapsulated silicon negative electrode material described in any one of claims 7-9 or the encapsulated silicon negative electrode material prepared by the method described in any one of claims 1-6.