Silicon-carbon composite material with multilevel structure, and preparation method and preparation device thereof

Abstract

The invention discloses a method and equipment for semi-continuously producing silicon-carbon composite materials in a fluidized bed reactor through a chemical vapor deposition or thermal deposition process. The produced silicon-carbon composite material has a structure in which silicon particles are uniformly dispersed, bonded and embedded into a carbon conductive matrix and form a secondary structure. The produced silicon-carbon composite material can be used as an advanced anode material for lithium batteries and other electrochemical energy storage devices.

Description

Divisional application

[0001] The present application is a divisional application of the Chinese patent application for invention with application number 201680017134.1 and titled "Apparatus and process for semi-continuous and multi-step production of composite materials" filed on April 12, 2016. TECHNICAL FIELD

[0002] The present application relates generally to lithium ion batteries. More specifically, the present application relates to a process for the preparation of a composite material that can be used as an advanced anode material for lithium ion batteries. BACKGROUND

[0003] Lithium ion batteries (LIBs) have a wide prospect as rechargeable power sources for consumer electronics, automotive and energy storage devices. However, there are numerous technical challenges for the use of LIBs in consumer electronics, automotive and energy storage device applications. Further improvements in LIBs require the development of new cathode, anode and electrolyte materials with the required properties.

[0004] Silicon-carbon composite is a very promising anode material for LIBs due to its excellent high capacity and long cycle life. Among the many methods of producing such materials, the incorporation of silicon into a carbon matrix by a chemical vapor deposition (CVD) process results in a uniform material structure and good performance. To achieve the best battery performance, the ratio of silicon to carbon in the composite of the anode should be constant.

[0005] Chemical vapor deposition (CVD) processes are typically used to deposit silicon onto carbon materials using batch reactors such as fluidized bed reactors (FBR reactors), rotary reactors and V-type mixers, and a constant silicon to carbon ratio in the material is achieved by controlling the deposition time, among other things. The efficiency of batch processes is very low when operated at a large scale. For example, batch processing results in large downtime due to cooling and reheating requirements. At the end of each batch, the equipment needs to be cooled (typically to room temperature) before the finished product can be removed from the reaction equipment and new raw materials can be loaded into the equipment. The equipment then needs to be reheated to high temperature for the subsequent batch production. The prior art of heating, cooling and reheating the equipment uses a large amount of energy (electricity) and results in a long downtime.

[0006] Polysilicon is a raw material for the production of solar cells and is produced by a chemical vapor deposition (CVD) process. In this CVD process, a silicon-containing precursor is decomposed on a silicon substrate to form solid silicon. In some cases, the CVD of silicon is carried out in a FBR reactor.

[0007] The efficiency and high throughput of polysilicon production is improved by using a fluidized bed (FBR) based CVD process compared to the traditional Siemens CVD process, which is essentially a batch process. The high efficiency and high throughput is due, at least in part, to the ability of the fluidized bed process to continuously supply the silicon precursor and to continuously separate the final product from the starting silicon seed. In some embodiments, the silicon precursor gas can include one or more of: SiH4(silane), Si2H6(disilane), Si3H8(trisilane), SiH2Cl2(dichlorosilane), SiHCl3(trichlorosilane), SiH2Br2(dibromosilane), SiHBr3(tribromosilane), SiH2I2(diiodosilane), SiHI3(triiodosilane), SiI4(tetraiodosilicon).

[0008] In the FBR-CVD process, small particle silicon seeds are used as the base material for silicon deposition, and solid silicon deposition is supplied by chemical decomposition of the silicon containing precursor onto the small particle silicon seeds. The silicon particles grow in size with silicon deposition, and the large silicon particles can be pneumatically separated from the small silicon seeds in the FBR reactor because the large silicon particles and the small silicon seeds have different particle sizes and weights. The larger silicon particles will settle to the bottom of the FBR chamber and be removed from the chamber. In addition, the larger silicon particles can be removed from the reactor and separated by sieving. Even with these separation techniques, the resulting product has particles that have been in the reactor for different times and have different sizes. The difference in particle size does not affect the application of the polysilicon product because the composition of the product silicon particles and the silicon seeds is not changed. However, for silicon deposition on carbon materials, the different deposition times will result in products having different silicon to carbon ratios, which will not be favorable for the product to be used as an anode material in lithium ion batteries.

[0009] The CVD process for producing silicon carbon composite materials can use a FBR reactor similar to that used for polysilicon production, but faces the additional challenges of maintaining a constant silicon to carbon ratio, and separating the final product from the starting carbon powder. In silicon carbon composite materials, the composite material typically has a size, morphology, and density similar to the starting carbon particles. Therefore, it is difficult to separate the silicon carbon composite material from the carbon powder particles using the same separation process used in the current FBR-CVD process for polysilicon production. In addition, a continuous mode of continuously adding carbon material particles and continuously removing the composite material product will result in inferior products with inconsistent silicon to carbon ratios. Therefore, there is a need to use a modified FBR-CVD process to produce silicon carbon composite materials. SUMMARY

[0010] The present invention is a semi-continuous production of silicon-carbon composite materials by a chemical vapor deposition (CVD) process in a fluidized bed reactor (FBR). The present invention discloses a method that enables continuous production of composite particles with similar density and morphology of the starting materials and the final product. The semi-continuous process and apparatus produces silicon-carbon composite materials with accurate control of the silicon morphology in the carbon material and avoids overgrowth of silicon particles. The silicon-carbon composite materials produced by the present invention have a morphology and properties that are completely different from polycrystalline silicon produced by the FBR-CVD process. The silicon-carbon composite materials also have different applications than polycrystalline silicon.

[0011] The present invention provides production of silicon (Si) composite anode materials by a high temperature fluidized bed reactor (FBR) and related chemical vapor deposition process (CVD) that can be used for anode materials in lithium batteries, which significantly improves the specific capacity of lithium ion battery anodes (2,000 mAh / gr and above) compared to the conventional graphite anode materials (capacity of 375 mAh / gr) used in most lithium batteries today. In the fluidized bed reactor, silicon particles are deposited into, bonded with, and uniformly embedded in multi-layered nanoscale thin layers based on graphite / graphene to form a stable and commercially producible silicon composite anode material. The silicon composite anode material can be used in lithium batteries in consumer electronics, electric vehicles, and renewable energy storage systems. This apparatus, process, and material have shown great potential to significantly improve the energy density, reduce the cell size and weight, and lower the average cost of lithium batteries.

[0012] Embodiments can include a method for producing a composite material. The method can include performing a controlled silicon loading on a first batch of carbon base material in a reactor, and then transferring the silicon-carbon composite material from the reactor to a reservoir. While the silicon-carbon composite material is cooling in the reservoir, a controlled silicon loading can be performed on a second batch of carbon base material in the reactor.

[0013] Embodiments can include an apparatus for producing a composite material. The apparatus can include a reactor and a reservoir. The reactor can perform a silicon vapor deposition process to produce a first batch of silicon-carbon composite material. The reservoir can receive the first batch of silicon-carbon composite material, and allow the reactor to perform a second silicon vapor deposition process to produce a second batch of silicon-carbon composite material while the first batch of silicon-carbon composite material is cooling in the reservoir.

[0014] Embodiments can include a composite structure. The composite structure can include a plurality of silicon particles and a plurality of layers of graphene. The plurality of layers of graphene can form two or more gaps, where each gap is formed by an upper graphene layer and a lower graphene layer of the plurality of layers of graphene. The plurality of silicon particles can be embedded within the gaps formed between the plurality of layers of graphene. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a block diagram of an apparatus for producing silicon-carbon composite material.

[0016] Figure 2 is a method for producing silicon-carbon composite material.

[0017] Figure 3 is a block diagram of an apparatus for performing a semi-continuous deposition process.

[0018] Figure 4 is a block diagram of a reactor for performing a semi-continuous deposition process.

[0019] Figure 5 is a block diagram of a reactor with multi-step capability.

[0020] Figure 6 is another block diagram of a reactor with multi-step capability.

[0021] Figure 7A is a silicon-graphene microstructure.

[0022] Figure 7B is a silicon-graphene macrostructure.

[0023] Figure 8A is a photograph of a silicon-graphene composite material produced by an FBR reactor.

[0024] Figure 8B is another photograph of a silicon-graphene composite material produced by an FBR reactor.

[0025] Figure 9 is a block diagram of an operating environment for use with the present invention. DETAILED DESCRIPTION

[0026] The present invention provides for the production of silicon (Si) composite anode material by a high temperature fluidized bed reactor (FBR) and related chemical vapor deposition process (CVD) that can be used for anode material in lithium batteries that significantly improves the specific capacity of lithium ion battery anodes (2,000 mAh / gr and above) compared to the conventional graphite anode material (capacity is 375 mAh / gr) that is used in most lithium batteries today. In the fluidized bed reactor, silicon particles are deposited into, bonded with, and uniformly embedded in multi-layered nano-thin layers based on graphite / graphene to form a stable, and commercially producible silicon composite anode material. The silicon composite anode material can be used in lithium batteries in consumer electronic devices, electric vehicles, and renewable energy storage systems. This apparatus, process, and material has shown great potential to significantly improve the energy density of lithium batteries, reduce cell size and weight, and lower the average cost of lithium batteries.

[0027] The present invention is a semi-continuous production of silicon-carbon composites in a fluidized bed reactor by a chemical vapor deposition process or a thermal deposition process. The present invention discloses a process that semi-continuously produces composite particles with similar density and morphology of the starting material and the final product. The semi-continuous process and apparatus produces silicon-carbon composites and preferentially controls the morphology of silicon deposited on graphite / graphene and its derivatives and avoids excessive growth of silicon particles. The silicon-carbon composites produced by the present invention have a morphology and properties that are completely different from polycrystalline silicon produced by a fluidized bed chemical vapor deposition process and the silicon-carbon composites produced have different applications than polycrystalline silicon.

[0028] Figure 1 A block diagram of an apparatus for producing silicon-carbon composites is shown. The apparatus includes a fluidized bed reactor 120 and a reservoir 150. The reactor 120 includes a reactive gas input 110, a gas purge input 115, a carbon solids input 125, a waste gas output 130, a connection mechanism 135 between the reactor 120 and the reservoir 150, a vacuum line 140, a purge gas input line 145, a composite output 160, a fluidization gas input 165, and a silicon precursor gas input 170. The reactor and the reservoir can implement a semi-continuous process to produce silicon-carbon composites and control the morphology of silicon in graphite / graphene and its derivatives to avoid excessive growth of the resulting silicon particles.

[0029] The reactor 120 and the reservoir 150 can be fully or partially controlled by one or more computer devices. The process performed by the computer that fully or partially controls the reactor 120 and the reservoir 150 is more accurate and more efficient than the process performed completely by a human. Although Figure 1 The reactor 120 and the reservoir 150 can be communicatively coupled and controlled by one or more computers, although this is not shown in the system of FIG. 1. Additionally, the various steps discussed can be performed or controlled by one or more computers that are communicatively coupled and / or control the reactor 120 and the reservoir 150. Figure 2 The various steps discussed can be performed or controlled by one or more computers that are communicatively coupled and / or control the reactor 120 and the reservoir 150.

[0030] Figure 2 A method for producing silicon-carbon composites is shown. The method can semi-continuously produce silicon-carbon composites and can be implemented by the apparatus of Figure 1 In step 210, carbon powder is loaded into the FBR, which can be loaded into the chamber of the FBR by the carbon solids input 125.

[0031] Inert gas can be provided in step 215. Inert gas can be provided through fluidizing gas input 165 to remove any trace amounts of air within the chamber. The FBR can be heated during the inert gas flow in step 220. The heating can be performed to reach a desired temperature of, for example, 800°C to 1000°C. The inert gas flow rate can be increased in step 225. The gas flow rate is increased to fluidize the carbon powder and reach a steady state of fluidization.

[0032] In step 230, reactive gas and silicon precursor gas are introduced. The reactive gas is introduced through reactive gas input 110, while the silicon precursor gas is introduced through silicon precursor gas input 170. The introduced silicon gas precursor decomposes into solid silicon reactant.

[0033] In step 235, a reaction occurs and reaches a predetermined time period, resulting in a controllable silicon loading and morphology on the solid carbon matrix material. The carbon matrix material can produce a silicon-carbon composite or a tin-carbon composite. In step 240, the reactive gas and silicon precursor gas are removed from the FBR. Removing the gas can include turning off the reactive gas and silicon precursor gas to allow sufficient time to remove all of the reactive gas and silicon-containing gas from the FBR chamber. In step 245, the reservoir is purged to remove air from the reservoir. Vacuum line 140 and purge gas input line 145 are used to purge air from the reservoir. In step 250, the composite is transferred from the FBR to the reservoir. The composite is transferred via connection mechanism 135. The connection mechanism can include a pipe, tubing, or other structure for allowing movement of the composite from the FBR to the reservoir. The transfer is performed by closing the exhaust outlet, pulling the vapor through the vacuum line, and purging through purge lines 115 and 165.

[0034] The FBR is configured for the next use in step 255. The configuration can include closing the connection mechanism after all of the composite has been removed from the FBR chamber. Then, in step 260, the composite is unloaded from the reservoir. The composite can be unloaded after it has cooled to room temperature.

[0035] The present invention utilizes a reservoir to contain the produced high temperature composite and allows it to cool to room temperature under static or fluidized bed inert gas protection. The reservoir allows the FBR chamber to continue to be used to produce composite during the cooling of the composite, which is a lengthy period, without the FBR chamber having to continue to hold the composite.

[0036] Inert gas gas locks can be used to protect the valves and other components that connect the FBR reactor that are exposed to high temperature chlorine-containing gases and need to be moved to open and close.

[0037] In some embodiments, the present application can be used with one or more computing systems. The computing systems can be dedicated to the FBR and reservoirs of the present application and used to provide improved composite materials in a semi-continuous process. For example, the equipment can employ a specially designed monitoring system to observe the fluidization and evacuation of the composite material within the FBR. The computing systems can be implemented by the systems of Figure 3

[0038] In some embodiments, the feed material ("feedstock") can be added semi-continuously to the pressurized vessel as a powder. The feedstock can include graphite / graphene and its derivatives, and it is fluffy, cohesive, and prone to agglomeration. The feedstock is difficult to transport to the pressurized vessel without agglomeration. The present application achieves this goal by using a screw, auger process, pneumatic method, and multi-stage feed container.

[0039] Graphite / graphene, its derivatives, and other graphitic materials suitable for use in the deposition process of the present application have small particles and are considered to be Geldart Type C particles. The particle size of graphene and its derivatives is fluffy, cohesive, and tends to agglomerate when handled. This characteristic makes the use of traditional silicon particle feed mechanisms such as lock hoppers, screw feeders, and rotary feeders prone to clogging when adding graphene and its derivatives to a pressurized reactor. However, the present technology provides new methods for using these mechanisms to add graphene and its derivative materials to a pressurized reactor.

[0040] Prior art screw feeders can be open or closed, where closed feeders have been used to resist pressure gradients by forming a gas-tight, compacted plug. Testing has shown that the formed plug is difficult to open in a fluidized bed. Therefore, this technology cannot be used without additional breakage mechanisms. Because the plug is not needed, both open and closed screw feeders can feed between vessels without the need for a pressure gradient, however this feeder is similar to a rotary feeder that provides flow control rather than pressure sealing.

[0041] Prior art rotary gas lock feeders can be used to provide pressure sealing, but typically have a certain rate of gas leakage. In the production of polysilicon processes, where flammable and toxic gases are present in the reactor when seed silicon is added to the deposition reactor, this leakage rate is not acceptable. In some embodiments of the present application, the deposition reactor of the present technology can be fed between cycles when the reactor is empty and operating under nitrogen. Therefore, a rotary feeder can be used in the equipment and process of the present application. In the present technology, the seal is not provided by a compacted graphite material, but rather by an elastomer, and because the elastomer is temperature sensitive and the reactor of the present application is operated at high temperatures during deposition, design techniques such as cooling, flushing gas flow, and / or additional valves need to be implemented during operation to protect the seal from the hot gases of the reactor.​

[0042] Further, in the prior art, various pneumatic feeders are used to blow solids into a pressurized reactor containing silicon deposition. Such feeders require the use of hydrogen gas compatible with the gases in the reactor, for safety, an additional nitrogen purge gas must be used to remove the hydrogen, then the system can be opened to air for refilling. As mentioned above, in some embodiments, the semi-continuity of the present invention allows for the use of nitrogen only during the filling process, therefore, the pneumatic feeders will not need to supply both hydrogen and nitrogen simultaneously, the pneumatic feeders in the present invention will be easier to use than the feeders in prior art silicon deposition reactors. Such feeders can have a conical bottom section that directs the flow of solids into a pneumatic delivery tube, and the graphite material compresses in the cone, creating a plug. Therefore, when using pneumatic feeders in the present invention, positive feed mechanisms such as screw feeders or rotary feeders can be used.

[0043] Multi-stage feed vessels or lock hoppers are a common means of adding solids to a pressurized reactor, they rely on two gas tight seals: one between the reactor and the reactor feed vessel, and the other between the reactor feed vessel and the solids receiver, which is periodically vented to atmosphere. Maintaining these seals is difficult due to the solids passing and the flammable and / or toxic gases in the reactor. A multiple gas flush system is often required as with pneumatic feeders. The semi-continuous process of the present invention does not require this multiple gas flush system, this is due to the semi-continuous nature of the present invention and the ability to safely open to atmosphere to fill solids while the reactor is in the evacuation portion of the semi-continuous cycle, and under nitrogen fill.

[0044] Figure 3A block diagram of an apparatus for performing a semi-continuous CVD / thermal deposition process is shown. A vessel 301 with a closable opening 302, including a solids feeder 303, a conduit 304, a gas tight valve 305, and a conduit 306 connected to a reactor 310. The reactor 310 also has a gas inlet 311 and a gas outlet 312. The reactor 310 is operated in a semi-continuous manner, with portions of the cycle being beneficial for operating the filling mechanism. This cycle portion occurs when deposition has been stopped and the solid particles in the reactor are fluidized by an inert gas, such as nitrogen, flowing in through inlet 311 and out through outlet 312. At this time, the gas tight valve 305 is closed, the solids feeder 303 is closed, and flushing nitrogen is allowed to flow through line 307 into chamber 301 and out through line 308 to a vent. After flushing the vent line 308 and closing the nitrogen line 307, the top opening 302 is opened and the graphite powder material is injected. The opening 302 is closed, the vent line 308 is opened, and nitrogen flows in through line 307 and out through line 308. Lines 307 and 308 are closed to isolate the chamber 301. Once the reactor has been emptied of product, new material can be placed into the reactor. The gas tight valve 305 is first opened, and then the solids feeder 303 is started to feed the new material into the conduit 306 and reactor at a controlled rate. The solids are controlled to flow through the conduit 306 so as not to cause a blockage of the conduit 306 that can cause a shut down. The maximum solids flow rate depends on the conduit diameter at the smallest restriction.

[0045] After performing the semi-continuous CVD process, the resulting silicon-carbon composite material product can be removed and separated from the starting material. The resulting silicon-carbon composite material has a physical morphology similar to the starting graphene, and thus, it is nearly impossible to separate the resulting silicon-carbon composite material from the starting graphene using methods similar to those used in the production of polysilicon.

[0046] After deposition of the silicon, the silicon-carbon composite material has silicon distributed throughout its interior, but the external morphology and particle diameter are substantially unchanged. In contrast, the prior art silicon is continuously deposited on the silicon particles, and the seed silicon particles, which are in the reactor for a long time, can be separated into large and small silicon particles by particle size-based separation techniques, such as sieving or selective fluidization methods, because the silicon particles become large as they receive a large amount of silicon deposition. An example of sieving in the prior art is described in U.S. Patent No. 6,827,786 ('786 Patent), entitled "Machine for production of granular silicon," which shows a silicon sieve as item 14 in Figure 1 of that patent (the '786 Patent) Figure 1 An example of fluidization separation is shown in U.S. Patent No. 4,818,495 ('495 Patent), entitled "Reactor for fluidized bed silane decomposition," which shows a fluidized bed as item 1 in Figure 1 of that patent (the '495 Patent) Figure 4A separator 18 and collector 20 are shown.

[0047] These separation techniques are not suitable for the resulting silicon-graphene composite material, as there is no useful correlation between silicon deposition and composite particle size in the reactor of the present invention. The useful properties of the silicon composite depend on the ratio of silicon to graphene in individual particles, not in bulk material. Therefore, the silicon deposition of each particle must be carefully controlled to avoid large variations between particles, which would result in problems with the use of silicon-carbon particles in electrodes. Therefore, when performing batch processing of graphite / graphene and derivatives, the particles should be given the same deposition time.

[0048] The present technology involves removing the product from the FBR. Methods for removing product from the FBR include, but are not limited to, blowing out from the apparatus, using a pulse of gas to discharge from the bottom, and using a specialized valve manufactured by SML, Inc. of Encinitas, CA.

[0049] The prior art uses a variety of ways to remove silicon particles when depositing silicon on the particles. These can be divided into techniques that remove the entire bed of particles and techniques that remove a portion of the bed. Since batch processing of graphene and derivatives is required, only the techniques that remove the entire bed can be used to remove the silicon-graphene composite material.

[0050] In some embodiments, the FBR can include a reactor, one or more inlet coolers, a bead and gas heater, and a bead cooler. The resulting product can be removed from the bottom through the bead cooler into a silicon sieve. Since the removal occurs at the bottom, the entire bed of particles can be removed through the bead cooler. In some embodiments, it is not desirable to selectively remove a portion of the bed and recycle it, so the sieve is detrimental and can be removed. Similarly, the product can also be removed from the bottom, but it is not desirable to only selectively remove the large particles of the bed as product, so the separator can also be removed. Thus, the prior art FBR that provides for removal of silicon product from the bottom or near the bottom of the chamber can also be used to remove the silicon-graphene composite material, for example by removing the entire bed of material.

[0051] Certain techniques for removing silicon particles from the top or near the top of the FBR are not suitable for removing the silicon-graphene product as part of a continuous process. The continuous top removal technique cannot be modified to provide continuous complete bed removal. However, with the semi-continuous method of the present invention, a semi-continuous overhead removal design can be used by removing the fines during the deposition portion of the cycle and processing them separately from the product, then purging at the end of the deposition by a large short-term increase in fluidization gas.

[0052] While the concept of bottom removal is common in silicon deposition, the actual removal of silicon-graphene composite is significantly different from that of silicon product due to the different properties of the silicon-graphene composite. In particular, the silicon-graphene composite has greater cohesion, agglomeration tendency and lower density. Therefore, the silicon-graphene composite behaves differently from silicon deposition and cannot be effectively removed by separation techniques designed for silicon particles. Therefore, typical FBR bottom removal mechanisms, as well as top removal mechanisms, are not suitable for separating silicon-graphene composite.

[0053] Any bottom product removal requires a conduit at the bottom of the FBR chamber, through which it is connected to some type of container. The conduit must have an upward gas flow sufficient to prevent the downward flow of solids during deposition, but when removal is required, the upward gas flow can be reduced to facilitate the downward flow of solids. Various solutions have been proposed, including providing a tube for the inlet of the reaction gas and the removal of the particle product, and using an annular removal device and a separate tube with upward flowing non-reactive hydrogen. The upward flowing gas must be heated in some way and diluted with the reaction gas in the reactor. Therefore, it is desirable to use the smallest diameter and still be able to obtain the flow of solids. Other attempts to remove silicon-graphene composite, such as through the product removal conduit, have resulted in clogging of the conduit.

[0054] The control of the outlet flow can be achieved by the opening and closing of the pulse gas and the control of its flow. It is most desirable to close the reactor during deposition, but due to the problem of attrition of silicon particles, special precautions such as gas purging and special modifications are required (to the reactor). The prior art also limits the use of metal materials (for the reactor) due to the requirements for the purity of the silicon material, so ceramics such as quartz are used more often.

[0055] By cooling, the temperature of the silicon-graphene composite can be reduced in the reservoir of the present invention, unlike the silicon deposition technology of the prior art, which does not have a reservoir. Cooling can be achieved using an annular removal device that exchanges heat with the incoming silicon reaction gas through the inner wall of the annulus, thereby achieving cooling. Cooling can also be achieved by heat exchange with a water-cooled jacket. Because the incoming silicon deposition gas is close to the bead removal tube, both of these methods can be used to cool the product as it leaves the settling chamber to the reservoir. Final cooling of the beads from the reservoir can be more easily achieved using the water-cooled jacket method.

[0056] In some embodiments, the present application uses a reservoir to cool the product in a separate fluidized bed. The present application has several advantages over the prior art disclosed, which is generally limited in cooling speed, because the surface area of a flowing solid is limited compared to a fluid, and because of its much larger heat capacity and high internal thermal conduction impedance, which makes cooling difficult. In cooling a flowing solid, it is common to find very high temperatures in the center, but low temperatures at the walls, because of the low thermal conduction between the solid particles and the particles. In contrast, a fluidized bed has much higher thermal conductivity to the solid particles, because the cold gas directly contacts all the external areas of the solid particles, and the particles physically move and contact the reactor walls. Therefore, the present application uses a fluidized bed cooling approach in a separate, discrete reservoir, with the fast cooling characteristics of a fluidized bed per se, and can use conventional fluidized bed heat exchange technology, such as cooling walls and cooling internals, which are typically coils. Because the silicon-graphene composite is not sensitive to metal contamination, the reservoir can be made of metal, which greatly simplifies the structure and reduces the cost of the FBR. The reservoir can be designed with cooling walls or cooling internal parts, which also protect the walls from the high temperature silicon-graphene composite from the deposition reactor. It is feasible to recover valuable heat from this system, even if the cooling is semi-continuous, by using storage of a heat medium, or by operating multiple reactor storage systems in phase with each other. In prior art silicon-on-silicon deposition systems, heat recovery is considered desirable, but difficult to achieve. In prior art systems, the product can be transferred to a cyclone cooler, but removing the heat is challenging, because the purity limitations of the silicon product require the cyclone cooler to use ceramics such as quartz, but such ceramics do not have sufficient strength to be used as a pressure vessel.

[0057] However, for silicon-graphene composite, the wear is greatly reduced, and metal corrosion is not an issue, so conventional valves can be used. In some embodiments, if the upward gas flow is completely closed by the valve, to avoid plugging of the valve and the inlet line to the valve, two valves can be used, with a gas flow purge between them. The top valve can be a solid control valve, which allows upward gas flow, but prevents downward solid flow. The second valve can seal the gas flow. This allows the product container to be safely removed from under the product reservoir while the reservoir is at operating pressure. Various valves can be suitable for solid flow control, such as slide valves, pinch valves or rotary valves. The gas control valve can be chosen from a range of similar valves, such as plugs and ball valves, which allow the solids to pass through the valve and flow freely when the valve is open, and seal the gas pressure when closed. Ball valves with elastomer seats have been found to be a good choice.

[0058] In some embodiments, the formed composite material has similar density and morphology to the starting solid material, making it difficult to separate the product from the starting material by methods used in polysilicon production.

[0059] Figure 4 is a block diagram of a reactor used to perform a semi-continuous deposition process. Deposition reactor 400 is a vessel containing a particle bed 401 with a solids inlet 402, a gas outlet 403, a gas inlet 404, a gas distributor 405, and a solids outlet 406. Deposition reactor 400 is heated by external heaters 408. Operation of deposition reactor 400 is cyclical. At the beginning of a cycle, an inert gas flow (e.g. nitrogen) is initiated through gas inlet 404, which then flows up through gas distributor 405 into the vessel. An additional gas flow is directed up through solids outlet 406 from solids purge line 407 to prevent solids from falling out of the solids outlet. Solids are introduced into deposition reactor 400 through solids inlet 402 to form particle bed 401. Once the bed is formed, solids feed is stopped and the two inert gas flows are switched to hydrogen at sufficient flow rates to fluidize particle bed 401, and heaters 408 are used to raise the bed temperature to the desired deposition temperature of 800-1000°C. As the bed temperature is raised, the initial hydrogen flow is reduced to maintain fluidization at the desired level of agitation.

[0060] After the deposition temperature and hydrogen flow are established, a silicon deposition gas, such as monosilane, SiH4, or trichlorosilane, SiHCl3, is added to the hydrogen 404 flow through the gas inlet. Deposition is then performed for a sufficient time to obtain the desired amount of silicon deposition. Deposition can be performed, for example, for half to five hours. To terminate deposition, the silicon deposition gas is removed from the hydrogen 404 through the gas inlet, and additional hydrogen is added as needed to maintain fluidization. The material in the particle bed has now been deposited with silicon and is ready to be moved to storage 420. Prior to this transfer occurring, a cooling flow must be established through outlet shroud cooler 409, which can be done by flowing a coolant through coolant inlet 410 in and through coolant outlet 411 out.

[0061] The reservoir 420 is a vessel containing a bed of particles 421 which has a solids inlet 422, a gas outlet 423, a gas inlet 424, a gas distributor 425 and a solids outlet 426. It is cooled by an outer jacket 428 and an inner coil 431. The operation of the reservoir 420 is also cyclical. At the beginning of the cycle, a flow of non-reactive gas, such as hydrogen, argon or nitrogen, is initiated through the gas inlet 424, then flows up through the gas distributor 425 into the vessel 420 via the gas inlet 424. Further gas flow is initiated up through the solids outlet 426 from the valve purge line 427 to prevent solids from falling from the solids outlet. Prior to this solids transfer, a coolant must be flowed in through the coolant inlet 429 and out through the coolant outlet 430 and the reservoir inner coil 431 to establish a cooling flow through the reservoir jacket cooler 428, in through the inlet 432 and out through the coolant outlet 433.

[0062] The next step is to introduce solids from the deposition reactor 400 through the solids inlet 422 to form the bed of particles 421. Once the deposition reactor 400 is empty, the solids feed is stopped and the two inert gas flows are transferred to a sufficient flow rate to fluidize the bed of particles 421 and the cooling jacket 428 and cooling coil 429 are used to reduce the bed temperature to the desired outlet temperature of 10°C to 150°C. The initial gas flow is increased as the bed temperature is reduced to maintain fluidization at the desired level of agitation. Once the desired temperature is reached, the solids are ready to be transferred to the product vessel 440. Prior to this transfer, a cooling flow must be established through the outlet jacket cooler 434 by flowing coolant in through the coolant inlet 435 and out through the coolant outlet 436 and the product vessel 440 must be ready to receive the solids. The product vessel 440 is a gas tight vessel containing a bed of particles 441 which has a solids inlet 442, a gas outlet 443, a gas inlet 444. To receive the solids from the beginning of the cycle, an inert gas flow such as argon or nitrogen is initiated through the gas inlet 424 which then flows up through the vessel 440 and out from the outlet 443. The solids flow through the opening of the air tight valve 438, then the solids valve 437 and the solids isolation valve 445 if provided. The solids flow into the product vessel 440 until the desired amount has been transferred, then the solids valve 437 is closed, then the air tight valve 438 is closed. The product material can then be purged of the inert gas by flowing it through the gas inlet 444 and out from the gas outlet 443 for a period of time. If it is desired to keep the material under an inert gas blanket, isolation valves are provided on the vessel. Such valves are shown as the solids isolation valve 445, the gas outlet isolation valve 446 and the gas inlet isolation valve 447. These valves 445, 446 and 447 are then closed, the connections to the valves are broken, the product vessel is removed and replaced with an empty vessel.

[0063] In some embodiments, the semi-continuous process can be implemented as a multi-step process, which can be implemented in various ways. The initial pair of deposition and storage vessels can be followed by one or more pairs of deposition and storage vessels. In such an operation, a portion of the deposition will occur in the first vessel, then the initial product will be cooled in the storage, transferred to a second deposition reactor to continue deposition, and the second storage cools the material. The transfer between vessels results in mixing and some breaking up of the agglomerates that will benefit in more uniform fluidization and deposition in the subsequent steps. In some embodiments, additional devices, such as a screen between the vessels, can be provided to provide more de-agglomeration of the agglomerated particles and a more uniform release of the particles. Some types of devices for accomplishing de-agglomeration of the agglomerated particles can require cooling of the material, so will be placed after the initial storage.

[0064] Figure 5 is a block diagram of a vessel with multi-step capability. For purposes of illustration and example, the vessel of Figure 5 is shown without all of the components normally within such a vessel, such as Figure 4 the inlet and outlet connections shown in the block diagram of

[0065] Vessel 501 is a first deposition reactor and is connected by pipe 502 to a first storage vessel 503. The first storage vessel 503 has an outlet pipe 504. Vessels 501, 503 and pipes 502 and 504 are similar to the semi-continuous block diagram of Figure 4 Unlike the product vessel shown in Figure 4 , the vessel of Figure 5 includes a de-agglomeration device 505. The de-agglomeration device includes a sifter or any other device capable of opening the agglomerated particles that can form during deposition and processing. The de-agglomeration device can act to disperse the particles and also will mix the solids. The de-agglomerated and mixed solids then pass through conduit 506 into a second deposition reactor 507. Further deposition occurs in the second deposition reactor. The solids then pass through conduit 508 into a second storage vessel 509, where final cooling occurs, and then pass through conduit 510 to a product vessel 511.

[0066] The vessel for multi-step deposition has the advantage of de-agglomerating and re-mixing the silicon-graphene composite material prior to further deposition, which improves the quality control of the deposition, particularly the silicon to graphite ratio and silicon particle control. This is particularly advantageous for making silicon-graphene composite materials with high silicon-carbon ratios, which have important applications for battery electrode performance.

[0067] In a multi-step deposition design, the initial deposition step is used only to deposit a fraction of the total amount of silicon set. The partially silicon-deposited composite material is transferred to a storage reservoir and then fed to another deposition reactor for further deposition. This multi-step approach has the advantage of better control of the deposition process and approaches a more continuous process, which is beneficial for scale-up production.

[0068] The storage reservoir of the first stage can also be used as the deposition reactor of the second stage. The hot silicon-graphene composite material produced by multiple deposition stages can be provided to a single storage reservoir. In such a design, the means to provide agglomerate dispersion after deposition will have to function at high temperature. This multi-stage system can be a multi-stage reactor integrated into a single vessel followed by a final product storage reservoir. Figure 6 is a schematic of the two possibilities.

[0069] Figure 6 is a block diagram of a back-up vessel with multi-step capability. Other different combinations with a basic semi-continuous process are also possible, which maintain the quality advantage of batch deposition but provide a more continuous production of the cooled silicon-graphene composite material product. While it is not possible to illustrate all possible combinations, the following two basic combinations are shown, from which the skilled person can derive other combinations. Figure 6 Two basic combinations are shown, from which the skilled person can derive other combinations.

[0070] Figure 6 is a schematic of a multi-step application of the semi-continuous process using a high-temperature de-agglomeration device. The high-temperature de-agglomeration device is located between two deposition reactors in series. The high-temperature de-agglomeration device replaces the cooled storage reservoir and the low-temperature de-agglomeration device used in Figure 5 is a schematic of a multi-step application of the semi-continuous process using a high-temperature de-agglomeration device. The high-temperature de-agglomeration device is located between two deposition reactors in series. The high-temperature de-agglomeration device replaces the cooled storage reservoir and the low-temperature de-agglomeration device used in Figure 6 The vessels are shown without listing all the necessary input and output connections shown in Figure 5 is a schematic of a multi-step application of the semi-continuous process using a high-temperature de-agglomeration device. The high-temperature de-agglomeration device is located between two deposition reactors in series. The high-temperature de-agglomeration device replaces the cooled storage reservoir and the low-temperature de-agglomeration device used in

[0071] Container 610 is the first deposition reactor, connected via conduit 611 to a first deagglomeration device 612 having an outlet conduit 613. This step opens up the agglomerates and mixes the solid particles without the cooling typically provided by the storage tank. The deagglomerated and mixed solid particles then enter the second deposition reactor 614 via conduit 613 for further deposition. The solid particles then enter container 630 via conduit 615. After final cooling in storage tank 630, the solid particles are conveyed to product container 640 via conduit 631. Connected in parallel with these deposition reactors are a third deposition reactor 620, a second deagglomeration device 622, and a fourth deposition reactor 624. Deposition reactor 620 is the third deposition reactor, connected via conduit 621 to the first deagglomeration device 622 having an outlet conduit 623. This step opens up the agglomerated particles and mixes the solids without the cooling provided by the storage tank. The deagglomerated and mixed solid particles then enter the fourth deposition reactor 624 via conduit 623 for further deposition. The solid then enters the storage container 630 through conduit 625 and is finally cooled there, before being transported to the product container 640 through conduit 631.

[0072] like Figure 6 As shown and discussed, embodiments of the invention divide the deposition process into two or more reactors connected in series. These deposition reactors may be connected to a deagglomeration device and then to a storage tank for cooling the silicon-graphene composite product. Embodiments of the invention may also have two or more deposition reactors connected in parallel, each producing the same silicon-graphene composite product, which is then transported to a common storage tank for cooling. If the circulation of the parallel reactors is controlled to occur at different times, the composite material can be cross-delivered to the storage tank for cooling, thus achieving stable heat recovery and continuous product cooling. In some embodiments, the cooler of the storage tank may be divided into more than one container, which may facilitate heat recovery.

[0073] In multi-stage reactors used for polycrystalline silicon production, the first reactor typically deposits polycrystalline silicon at a low temperature (600°C to 700°C), followed by post-processing at a high temperature in a second-stage reactor to crystallize the silicon. Heat treatment can reduce the hydrogen content in the polycrystalline silicon. This method is commonly used to process bead-like polycrystalline silicon particles produced by chemical vapor deposition in a fluidized bed. The heat treatment process is preferably carried out at a temperature of 1020°C to 1200°C for approximately 6 hours to approximately 1 hour, which is sufficient to reduce the hydrogen content without causing agglomeration of the treated particles. To reduce the tendency for particle aggregation at the processing temperature, it is necessary to maintain bed movement during the dehydrogenation process. Products produced by this method can have a hydrogen content of 30 ppma or lower. These improved products can be used to manufacture monocrystalline silicon for the production of semiconductor devices.

[0074] Figure 7A A microstructure of a silicon-graphene composite is shown. Figure 7A The microstructure includes graphene layers 710 and silicon particles 720. Silicon island particles (i.e., silicon particles) can be embedded within interstices formed by the graphene layers. The silicon particles can be uniformly dispersed, bonded, and embedded in a graphene matrix formed by the graphene layers 710. The silicon particles can have a size of 2 nm to 2 microns long. Thus, the composite structure includes a nanocomposite. The plurality of graphene layers and the plurality of silicon particles form an embedded conductive matrix. In Figure 7A In the microstructure of FIG. 8, the illustrated portion of the microstructure can be about 10 microns long. In some embodiments, the size of the agglomerates or other portions of the silicon-graphene microstructure can be in the range of 0.05-40 microns long. The illustration of the silicon particles between the graphene layers is not to scale, and the size can be less than or equal to Figure 7A the size shown. Figure 7A The silicon-graphene composite microstructure of FIG. 8 and Figure 7B The macrostructure of FIG. 9 can be formed from the fluidized bed reactor and can be used in electrochemical devices, such as batteries, battery cells, or other power sources.

[0075] The silicon-graphene microstructure can form a macrostructure as shown in Figure 7B The silicon-graphene macrostructure is a secondary structure that forms an agglomerated silicon-graphene composite. In some embodiments, the silicon-graphene macrostructure can be formed into a spherical shape or agglomerate having a diameter of 5-100 microns. In some embodiments, the silicon-graphene macrostructure can be formed into a spherical shape or agglomerate having a diameter of 2-40 microns. The plurality of graphene layers with embedded silicon particles can form one or more agglomerates of coupled and conductive material. The silicon-graphene macrostructure can be formed from large two-dimensional silicon-graphene sheets rolled into a spherical structure or agglomerate. The composite structure is formed into an agglomerated silicon-graphene composite particle.

[0076] In some embodiments, the unique silicon-graphene composite described herein has a strong bond between the silicon particles and the matrix. The particles in the matrix can include silicon, or can also be one or more of Sn, Pb, Al, Au, Pt, Zn, Cd, Ag, Mg, or Mo. The matrix material can be a conductive material that is stable in a lithium battery environment, including but not limited to carbonaceous, exfoliated sheets.

[0077] Figure 8A is a schematic of a silicon-graphene composite material produced by the FBR reactor. The silicon-graphene composite material is in the form of a crystal 810 formed from the silicon-graphene microstructure. The microstructure includes silicon particles that are uniformly dispersed, bonded, and embedded in a graphene matrix. Figure 8AThe macrostructure of the silicon-graphene composite of FIG. 8A also shows the rolling of two-dimensional silicon graphene sheets into a spherical structure. FIG. 8B shows another silicon-graphene composite produced by the FBR reactor. Figure 8B The silicon-graphene composite of FIG. 8A shows visible silicon particles 820 within the graphene 830 layers.

[0078] Figure 9 An exemplary computing system 900 that can be used to implement a computing device for use with the present technology is shown. The computing device can be used with a container to produce particles and to automatically control processes related to Figure 1 to 8B the described processes. Figure 9 The computing system 900 includes one or more processors 910 and memory 920. The main memory 920 stores, in part, instructions and data for execution by the processor(s) 910. The main memory 920 can store the executable code Figure 9 The system 900 further includes a mass storage device 930, portable storage medium drive(s) 940, output devices 950, user input devices 960, graphics display 970, and peripheral devices 980.

[0079] Figure 9 The components shown in FIG. 9 are depicted as being connected via a single bus 990. However, the components can be connected through one or more data transport means. For example, the processor unit 910 and the main memory 920 can be connected via a local microprocessor bus, and the mass storage device(s) 930, peripheral device(s) 980, portable storage device(s) 940, and display system 970 can be connected via one or more input / output (I / O) buses.

[0080] The mass storage device 930, which can be implemented with a magnetic disk drive or optical disk drive, is a non-volatile storage device for storing data and instructions for use by the processor unit(s) 910. The mass storage device 930 can store the system software used to implement embodiments of the present application for loading into the main memory 920.

[0081] The portable storage device 940 operates in conjunction with a portable non-volatile storage medium, such as a floppy disk, compact disk, or digital video disk, to input and output data and code to and from the computer system 900. The system software for implementing embodiments of the present application can be stored on such a portable medium and input to the computer system 900 via the portable storage device 940. Figure 9

[0082] The input devices 960 provide a portion of the user interface. The input devices 960 can include an alpha-numeric input keyboard for inputting alphanumeric and other Figure 9 ​The illustrated system 900 includes output devices 950. Examples of suitable output devices include speakers, printers, network interfaces, and monitors.

[0083] The display system 970 can include a liquid crystal display (LCD) or other suitable display device. The display system 970 receives textual and graphical information, and processes the information for output to a display device.

[0084] The peripheral devices 980 can include any type of computer support device to add additional functionality to the computer system. For example, the peripheral devices 980 can include a modem or a router.

[0085] The components contained in the computer system 900 of Figure 9 The components contained in the computer system 900 of Figure 9 The computer system 900 of can be a personal computer, a handheld computing device, a telephone, a mobile computing device, a workstation, a server, a minicomputer, a mainframe computer, or any other computing device. The computer can also include different bus configurations, network platforms, multiprocessor platforms, etc. Various operating systems can be used, including Unix, Linux, Windows, Android operating systems, iOS, and other suitable operating systems.

[0086] The foregoing detailed description of the technology has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the technology to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the technology and its practical application, to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. The scope of the invention is defined by the claims.

Claims

1. A silicon-carbon composite material, characterized in that, include: Graphene layers and silicon particles, with the silicon particles embedded in the gaps formed by the graphene layers, or the silicon particles combined with and embedded in the graphene matrix formed by the graphene layers. Silicon particles have a size ranging from 2 nanometers to 2 micrometers in length.

2. The silicon-carbon composite material according to claim 1, characterized in that, The macroscopic structure of the silicon-graphene is a secondary structure formed by the aggregation of silicon-graphene composite materials.

3. The silicon-carbon composite material according to claim 2, characterized in that, The macroscopic structure of the silicon-graphene is formed as a spherical shape or agglomerate with a diameter of 5-100 micrometers, or as a spherical shape or agglomerate with a diameter of 2-40 micrometers.

4. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The composite material is prepared by chemical vapor deposition, and the deposition process is carried out in a fluidized bed reactor.

5. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The silicon particles in the composite material are replaced with one or more of Sn, Pb, Al, Au, Pt, Zn, Ag, Mg, or Mo.

6. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The silicon particles are formed by chemical vapor deposition, and the silicon precursor gas includes one or more of the following: SiH4, Si2H6, Si3H8, SiH2Cl2, SiHCl3, SiH2Br2, SiHBr3, SiH2I2, SiHI3, and SiI4.

7. The silicon-carbon composite material according to any one of claims 1 to 3, characterized in that, The composite material is used as an anode material for lithium batteries, which are used in lithium batteries for consumer electronics, electric vehicles, and renewable energy storage systems.

8. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 7, characterized in that, Includes the following steps: Controlled silicon loading was performed on the first batch of carbon-based material in the reactor; The reactor is a fluidized bed reactor in which silicon-carbon composite materials are produced semi-continuously through chemical vapor deposition or thermal deposition processes. The fluidized bed process continuously supplies silicon precursors and continuously separates the final product from the starting silicon seed crystals. The silicon precursor gas contains one or more of the following: SiH4, Si2H6, Si3H8, SiH2Cl2, SiHCl3, SiH2Br2, SiHBr3, SiH2I2, SiHI3, SiI4, preferably SiHCl3. The carbon matrix material is transferred from the reactor to a storage container; and While the first batch of carbon matrix material is cooled in the reservoir, controlled silicon loading is performed on the second batch of carbon matrix material in the reactor.

9. The preparation method according to claim 8, characterized in that, Specifically, the following steps are included: The carbon powder is loaded into the FBR container; Inert gas is introduced; The FBR is heated during the inert gas flow. Increase the inert gas flow rate; Reactive gases and silicon precursors are introduced into the FBR; The reaction process reaches a predetermined time period to obtain controllable silicon loading and morphology on the carbon substrate; Reactive gases and silicon precursor gases are removed from the FBR; Flush the reservoir to remove air from it; Transfer the silicon-carbon composite from the FBR to the storage device; Prepare FBR for next use; The complex is unloaded from the storage.

10. The method according to claim 8, characterized in that, Includes the following steps: Controlled silicon loading is performed on a first carbon matrix material in a first deposition reactor to produce a first silicon-carbon composite material; The first silicon-carbon composite material is transferred from the first deposition reactor to the first storage tank for cooling; The cooled first silicon-carbon composite material is transferred to a deagglomeration device to disperse and remix the particles; The deagglomerated and remixed particles are transferred to a second deposition reactor for further deposition to obtain a first silicon-carbon composite material after further deposition; The first silicon-carbon composite material, which has undergone further deposition, is transferred from the second deposition reactor to the second storage tank for final cooling to obtain the final silicon-carbon composite material product; The final silicon-carbon composite product, after final cooling, is discharged into the product container; In this process, while the first silicon-carbon composite material is cooled in the first storage tank, a controlled silicon loading is performed on the second carbon matrix material in the first deposition reactor to produce the second silicon-carbon composite material, thereby realizing the production of silicon-carbon composite material in a semi-continuous manner. The semi-continuous process is realized as a multi-step process.

11. An apparatus for preparing the silicon-carbon composite material according to any one of claims 1 to 7, characterized in that, The device includes: A reactor and a storage tank are provided, wherein the reactor performs a silicon vapor deposition process to produce a first batch of carbon matrix material, the storage tank receives the first batch of carbon matrix material and allows the reactor to perform a second batch of silicon vapor deposition process to produce a second batch of carbon matrix material, while the first batch of carbon matrix material is cooled in the storage tank; the vapor deposition uses a gas, the gas comprising at least one reactive precursor gas that decomposes on or inside the carbon matrix and becomes a solid, and at least one gas that does not decompose or become a solid during the reaction.

12. The apparatus according to claim 11, characterized in that, The first deposition reactor is connected to the first storage container via a pipe. The first storage container has an outlet pipe connected to a deagglomeration device. The deagglomeration device is connected to the second deposition reactor via a conduit. The second deposition reactor is connected to the second storage container via a conduit. The second storage container is connected to the product container via a conduit.

13. The apparatus according to claim 11, characterized in that, The first deposition reactor is connected via a conduit to a first deagglomeration device with an outlet pipe, and the first deagglomeration device is connected via a conduit to a second deposition reactor; the third deposition reactor is connected via a conduit to the second deagglomeration device with an outlet pipe, and the second deagglomeration device is connected via a conduit to a fourth deposition reactor; the second and fourth deposition reactors are respectively connected via conduits to a storage container, and the storage container is connected via a conduit to a product container.

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