METHOD FOR THE PRODUCE OF COMPOUND ELECTRODE PARTICLES; COATED WITH A GRANULAR SILICON STRUCTURE; A CARBON LAYER AND ZINC OXIDE

Abstract

A process for producing composite electrode particles coated with a granular silicon structure, a carbon layer, and zinc oxide, comprising the following steps: introducing several first silicon particles, a macromolecular material, bitumen, and an alcohol solution into a grinding mill for mixing to cause some of the first silicon particles to form several composite silicon particles; then introducing several porous carbon particles into the grinding mill for mixing to form a first mixture; then introducing the first mixture into a rotary evaporator to obtain several mixed powders; then introducing the mixed powders into a sintering furnace to perform atmospheric sintering to obtain several first composite particles coated with the carbon layer that incorporates the first silicon particles and the composite silicon particles;and then the introduction of several zinc oxide particles and the first composite particles into a roller mixer for mixing in order to obtain the composite electrode particles.

Description

AREA OF INVENTION The invention relates to battery electrode material and in particular a method for producing composite electrode particles coated with a granular silicon structure, a carbon layer and zinc oxide. BACKGROUND OF THE INVENTION A typical battery comprises a positive and a negative electrode. The negative electrode of a solid-state or semi-solid-state battery consists of a negative electrode substrate and a negative electrode mass layer. The negative electrode mass layer comprises a negative electrode mass and a variety of negative electrode particles. The negative electrode particles must be either additionally conductive or electrically conductive so that free electrons can migrate through the negative electrode mass without sacrificing too much energy due to internal resistance. The negative electrode particles are distributed throughout the negative electrode mass, and an outer surface of each negative electrode particle is coated with silicon particles. During the battery's chemical reaction, lithium ions penetrate the silicon particles and expand their size, potentially increasing by up to 400 times their original size. This dramatic change in the size of the negative electrode particles can damage them, leading to a deterioration in battery performance. SUMMARY OF THE INVENTION To overcome the aforementioned shortcomings of the current state of the art, the object of the invention is to provide a method for producing composite electrode particles coated with a granular silicon structure, a carbon layer, and zinc oxide, wherein the carbon layer, along with the silicon particles, is applied to the outer surface of the porous carbon particle. The silicon particles coated with the silicon oxide layer have a lower coefficient of thermal expansion and a high bond strength, which inhibits the expansion of the composite electrode particle and thus prevents it from bursting. The carbon layer exhibits high conductivity and serves to inhibit the expansion of the composite electrode particle, thereby preventing it from bursting due to volume expansion once the lithium ions fill the composite electrode particle.The outer surface of the carbon layer is also coated with a zinc oxide layer, which exhibits high conductivity and ductility comparable to metals. Once the lithium ions fill the silicon particles and thus increase their size, the zinc oxide layer serves to protect the internal structure through its high ductility. As a result of the multilayer coating structure described above, the fracture rate of the composite electrode particles can be significantly reduced. BRIEF DESCRIPTION OF THE IMAGES Fig. 1 shows a flowchart illustrating the process of the invention. Fig. 2 shows a flowchart illustrating steps 500 to 530 of the invention. Fig. 3 shows a flowchart illustrating steps 540 to 550 of the invention. Fig. 4 shows a cross-sectional view illustrating the structure of the composite electrode particle of the invention. Fig. 5 shows a schematic view illustrating the porous carbon particle of the invention. Fig. 6 shows a schematic view illustrating the complete structure and a partial structure of the composite electrode particle of the invention. Fig. 7 shows a schematic view illustrating the silicon particles and the silicon oxide layer of the invention. Fig. 8 shows a schematic view illustrating the composite electrode particle of the invention coated with carbon nanotubes. Fig. 9 shows a schematic view illustrating an application of the invention. DETAILED DESCRIPTION OF THE INVENTION With reference to Figures 1, 2, 3, 4, 5, 6, 7, 8 to 9, the invention provides a method for producing composite electrode particles 40 coated with a granular silicon structure, a carbon layer, and zinc oxide. The composite electrode particles 40 are used in a negative (-) electrode 10 of a solid-state or semi-solid-state battery. With reference to Figure 9, the negative electrode 10 comprises a negative electrode substrate 11 as a support for the material of the negative electrode 10 and a negative electrode mass layer 13 applied to the negative electrode substrate 11. The negative electrode mass layer 13 comprises a plurality of composite electrode particles 40 and a negative electrode mass 12 with a binder. The weight fraction of the composite electrode particles 40 in the negative electrode mass layer 13 is 90 wt.% to 99 wt.%.Each of the composite electrode particles 40 has a size of 5 µm to 12 µm. With reference to Figures 1, 2 to 3, the method of the invention comprises the following steps: Step 500: Introducing a plurality of first silicon particles 321, a macromolecular material 323, a bitumen 324, and an alcohol solution 325 into a grinding mill 100 for mixing and grinding. The grinding mill 100 is a wet grinding mill. The grinding time by the grinding mill 100 is four to six hours. The grinding speed of the grinding mill 100 is 2,600 to 3,000 rpm. Preferably, the alcohol solution 325 consists of isopropyl alcohol or ethanol. The macromolecular material 323 is selected from at least one of the following substances: sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), a linear macromolecule with carboxyl groups, and phenol-formaldehyde resin (PF). Before mixing and grinding in step 500, the ratio of the weight of the first silicon particles 321, the weight of the macromolecular material 323, and the weight of the bitumen 324 is 80-90 : 2-10 : 2-10. The ratio of the weight of a solid formed from the first silicon particles 321, the macromolecular material 323, and the bitumen 324 to the weight of the alcohol solution 325 is 4:6. With reference to Fig. 7, during mixing and grinding in the mill 100, a portion of the first silicon particles 321 are disproportionated to form a plurality of composite silicon particles 32. Each of the composite silicon particles 32 comprises a first silicon particle 321 and a silicon oxide layer 322, which is formed from SiOx, where 0 < x ≤ 2. The silicon oxide layer 322 is formed by disproportionation and is deposited on an outer surface of the respective first silicon particle 321. The size of each of the composite silicon particles 32 ranges from 10 nm to 30 nm. The thickness of the silicon oxide layer 322 is less than 3 nm. The conductivity of the silicon oxide layer 322 is lower than that of the first silicon particle 321. As soon as the lithium ions pass through the first silicon particles 321 and expand their size, this enormous expansion will damage the final electrode particle. The coefficient of thermal expansion is lower than that of the silicon oxide layer 322, and the bonding capacity of the silicon oxide layer 322 is better than that of the first silicon particle 321, which inhibits the expansion of the composite electrode particle 40 and prevents it from shattering. Step 510: A large number of porous carbon particles 30 are introduced into the grinding mill 100 for continuous mixing and grinding with the first silicon particles 321, the macromolecular material 323, the bitumen 324, and the alcohol solution 325 to form an initial mixture. The mixing and grinding time in the grinding mill 100 is between half an hour and two hours. The grinding speed of the grinding mill 100 is 1,800 to 2,200 rpm. The ratio of the total weight of the porous carbon particles 30 to the total weight of the first silicon particle 321 is 80 to 95:5 to 20. Each of the porous carbon particles 30 has a plurality of holes 31 to accommodate the expanded first silicon particles 321. After mixing and grinding in step 510, the size of each of the porous carbon particles 30 is 5 to 10 µm. Step 520: The first mixture is removed from the mill 100 after mixing and grinding and then placed in a rotary evaporator 150 to remove the alcohol solution 325, thus obtaining a variety of powder mixtures 50. The rotary evaporator 150 is a water bath-assisted rotary evaporator, and the water bath temperature of the rotary evaporator 150 is 20°C to 45°C. Step 530: The powder mixtures 50 are introduced into a sintering furnace 200 to carry out atmospheric sintering of the powder mixtures 50, in order to cause the porous carbon particles 30 to form a plurality of first composite particles 361. The sintering temperature of the sintering furnace 200 is 980°C to 1100°C. The sintering time of the sintering furnace 200 is six to eight hours. With reference to Fig. 4, Fig. 5 to Fig. 6, during atmospheric sintering, an outer surface of each of the porous carbon particles 30 is coated with a carbon layer 36, which is formed from the macromolecular material 323 and the bitumen 324. The carbon layer 36 comprises a plurality of corresponding first silicon particles 321 and a plurality of corresponding composite silicon particles 32. Each of the porous carbon particles 30 coated with the carbon layer 36 forms a first composite particle 361.Excess non-carbon elements are removed by atmospheric sintering. Atmospheric sintering can occur under an atmosphere of argon (Ar) or nitrogen (N2). The macromolecular material 323 and the bitumen 324 support each of the first silicon particles 321 and the composite silicon particles 32 in adhering to a corresponding porous carbon particle 30. The first silicon particles 321 and the composite silicon particles 32 on each of the first composite particles 361 form a discontinuous structure, wherein in each of the first composite particles 361 the first silicon particles 321 and the composite silicon particles 32 form an island-like structure with several protruding sections on an outer surface of the corresponding carbon layer 36, the first silicon particles 321 and the composite silicon particles 32 are attached to the outer surface of the corresponding porous carbon particle 30 on an inner surface of the corresponding carbon layer 36, and the first silicon particles 321 and the composite silicon particles 32 are suspended between the outer surface and the inner surface of the corresponding carbon layer 36 in the corresponding carbon layer 36 without touching the corresponding porous carbon particle 30. The carbon layer 36 has a high conductivity and serves to prevent expansion of the generated electrode particle in order to avoid the electrode particle tearing due to volume expansion once the lithium ions fill the electrode particle. Step 540: A plurality of zinc oxide particles 38 and the first composite particles 361 are introduced into a roller mixer 300 for mixing, in order to coat an outer surface of each of the first composite particles 361 with a zinc oxide layer 37 formed by the zinc oxide particles 38. The first composite particles 361 coated with the zinc oxide layer 37 form the composite electrode particles 40 of the invention. Referring to Figures 4 and 6, the zinc oxide particles 38 on each of the first composite particles 361 form an island-like structure with several protruding sections. The mixing time of the roller mixer 300 is from half an hour to two hours. The rotational speed of the roller mixer 300 is 200 to 350 rpm. The roller mixer 300 has a plurality of zirconium spheres.The fill level of the zirconium spheres is 30-50%, which corresponds to the ratio of the total volume of the zirconium spheres to the mixing volume of the 300 mm roller mixer. The size of each zirconium sphere is 1.2-2 mm. The zinc oxide layer 37 exhibits high conductivity and a specific ductility identical to that of metals. As the lithium ions fill the first silicon particles 321 and increase their size, the zinc oxide layer 37 serves to protect the internal structure through its high ductility and to maintain the integrity of the composite electrode particle 40. With reference to Figures 3 and 8, the method of the invention further comprises the following step: Step 550: Introducing the composite electrode particles 40 and a plurality of carbon nanotubes 42 into a dry mixer 250 for mixing and stirring to cause an outer surface of each of the composite electrode particles 40 to be coated with carbon nanotubes 42. The composite electrode particles 40 coated with the carbon nanotubes 42 form a plurality of carbon nanotube-coated composite electrode particles 45. The size of each of the carbon nanotubes 42 is less than 5 µm. In each of the carbon nanotube-coated composite electrode particles 45, the ratio of the weight of the carbon nanotubes 42 to the weight of the composite electrode particle 40 is 1:99 to 0.2:99.8. The carbon nanotubes 42 exhibit high conductivity. Each of the composite electrode particles 45 coated with carbon nanotubes has a yarn-like structure (as shown in Fig. 5). The carbon nanotubes 42 serve to increase the electrical conductivity so that the electrons on the composite electrode particle 40 become conductive. The carbon nanotubes 42 also serve to conduct the lithium ions so that the lithium ions can be conducted between different composite electrode particles 40 in the electrode, which increases the electrical conductivity and the ionic conductivity of the electrode. In describing the invention, it is obvious that it can be varied in many ways. Such variations are not to be considered a departure from the spirit and scope of the invention, and all such modifications, which would be obvious to a person skilled in the art, are to fall within the scope of the following claims.

Claims

A method for producing composite electrode particles coated with a granular silicon structure, a carbon layer, and zinc oxide comprises the following steps: Step A: Introducing a plurality of first silicon particles, a macromolecular material, a bitumen, and an alcohol solution into a mill for mixing and grinding; wherein, during mixing and grinding in the mill, a portion of the first silicon particles undergoes disproportionation to form a plurality of composite silicon particles; wherein each of the composite silicon particles comprises a first silicon particle and a silicon oxide layer formed from SiOx, where 0 < x ≤ 2; and the silicon oxide layer is formed by disproportionation and deposited onto an outer surface of the respective first silicon particle;Step B: Introducing a plurality of porous carbon particles into the mill for continuous mixing and grinding with the first silicon particles, the macromolecular material, the bitumen, and the alcohol solution to form an initial mixture; wherein each of the porous carbon particles has a plurality of holes to accommodate the expanded first silicon particles; Step C: Removing the initial mixture from the mill after mixing and grinding and subsequently introducing the initial mixture into a rotary evaporator to remove the alcohol solution in order to obtain a plurality of powder mixtures; Step D: Introducing the powder mixtures into a sintering furnace to perform atmospheric sintering on the powder mixtures to cause the porous carbon particles to form a plurality of initial composite particles;wherein in atmospheric sintering an outer surface of each of the porous carbon particles is coated with the carbon layer formed by the macromolecular material and the bitumen; the carbon layer comprises a plurality of corresponding first silicon particles and a plurality of corresponding silicon composite particles; each of the porous carbon particles coated with the carbon layer forms a first composite particle;The first silicon particles and the composite silicon particles on each of the first composite particles form a discontinuous structure, wherein in each of the first composite particles the first silicon particles and the composite silicon particles on an outside of the corresponding carbon layer form an island-like structure with several protruding sections, the first silicon particles and the composite silicon particles on an inside of the corresponding carbon layer are attached to the outer surface of the corresponding porous carbon particle, and the first silicon particles and the composite silicon particles are suspended between the outside and the inside of the corresponding carbon layer in the corresponding carbon layer without touching the corresponding porous carbon particle;Step E: Placing a large number of zinc oxide particles and the first composite particles in a roller mixer for mixing to cause an outer surface of each of the first composite particles to be coated with a zinc oxide layer formed by the zinc oxide particles; wherein the first composite particles coated with the zinc oxide layer form the composite electrode particles; and wherein the zinc oxide particles on each of the first composite particles form an island-like structure with several protruding sections; and wherein the silicon oxide layer serves to prevent expansion of the composite electrode particles in order to avoid breakup of the composite electrode particles. A method according to claim 1, wherein the size of each of the composite electrode particles is 5 µm to 12 µm. A method according to claim 1, wherein in step A the grinding mill is a wet grinding mill; the grinding time of the grinding mill is four to six hours; and the grinding speed of the grinding mill is 2,600 to 3,000 rpm. A method according to claim 1, wherein the alcohol solution consists of isopropyl alcohol or ethanol. A method according to claim 1, wherein the macromolecular material is selected from at least one of the following substances: sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), linear macromolecule with carboxyl groups and phenol-formaldehyde resin (PF). A method according to claim 1, wherein, prior to mixing and grinding in step A, the ratio of the weight of the first silicon particles, the weight of the macromolecular material and the weight of the bitumen is 80-90 : 2-10 : 2-10. A method according to claim 1, wherein, prior to mixing and grinding in step A, the ratio of the weight of a solid formed from the first silicon particles, the macromolecular material and the bitumen, to the weight of the alcohol solution is 4:

6. A method according to claim 1, wherein after mixing and grinding step A the size of each of the composite silicon particles is 10 nm to 30 nm; and the thickness of the silicon oxide layer is less than 3 nm. A method according to claim 1, wherein in step B the mixing and grinding time of the mill is half an hour to two hours; and the grinding speed of the mill is 1800 to 2200 rpm. A method according to claim 1, wherein in step B the ratio of the total weight of the porous carbon particles to the total weight of the first silicon particle is 80 to 95: 5 to 20. A method according to claim 1, wherein after mixing and grinding in step B the size of each of the porous carbon particles is 5 to 10 µm. A method according to claim 1, wherein in step D the sintering temperature of the sintering furnace is 980°C-1,100°C; and the sintering time of the sintering furnace is six to eight hours. A method according to claim 1, wherein the atmospheric sintering is a sintering under an atmosphere formed by argon (Ar) or by nitrogen (N2). A method according to claim 1, wherein in step E the mixing time of the roller mixer is half an hour to two hours; the rotational speed of the roller mixer is 200-350 rpm; the roller mixer has a plurality of zirconium spheres inside; a filling ratio of the zirconium spheres is 30-50%, which is a ratio of the total volume of the zirconium spheres to the mixing volume of the roller mixer; and the size of each of the zirconium spheres is 1.2 mm to 2 mm. A method according to claim 1, further comprising the following step: Step F: placing the composite electrode particles and a plurality of carbon nanotubes in a dry mixer for mixing and stirring to cause an outer surface of each of the composite electrode particles to be enveloped by the carbon nanotubes; wherein the carbon nanotube-enveloped composite electrode particles form a plurality of carbon nanotube-coated composite electrode particles; and each of the carbon nanotube-coated composite electrode particles has a yarn-like structure. A method according to claim 15, wherein the size of each of the carbon nanotubes is less than 5 µm. A method according to claim 15, wherein in each of the composite electrode particles coated with carbon nanotubes the ratio of a weight of the carbon nanotubes to a weight of the composite electrode particle is 1:99 to 0.2:99.8.

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