Silicon-carbon composite material and preparation method and preparation system thereof

Abstract

The invention relates to the field of battery materials, in particular to a silicon-carbon composite material and a preparation method and system thereof.The preparation method comprises the steps that a granular solid silicon source and a gaseous carbon source are premixed and preheated to 300-600 DEG C, then the mixture is fed into a fluidized bed to be subjected to a fluidization reaction, the temperature is controlled to be 300-900 DEG C, the operation pressure is controlled to be 0.05-0.15 MPa (g), and the reaction time is controlled to be 30-60 min; and filtering and separating the reacted gas-solid mixture to obtain the silicon-carbon composite material and tail gas, and feeding the silicon-carbon composite material into a product bin. The preparation system comprises a feeding unit, a fluidized bed and a dust removal unit which are sequentially connected, the bottom of the dust removal unit is connected with a product bin, and a tail gas exhaust port is formed in the top of the dust removal unit; and the bottom of the product bin is connected with the fluidized bed feed pipe through a return pipe. The method disclosed by the invention is simple, low in production and investment cost, capable of realizing continuous production, high in reaction rate, good in product performance and capable of realizing large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a silicon-carbon composite material and a preparation method and a preparation system thereof. Background Art

[0002] Liquid lithium-ion batteries are currently a widely used battery technology, which is believed to have certain advantages in operating voltage, energy density and cycle life. However, in the past one or two years, with the iteration of technology and the society's higher demand for energy storage components, this technology still faces difficulties in further improving energy density and safety performance. Solid-state battery technology can improve battery energy density through methods such as improving the material system, and can achieve intrinsic safety of the battery. It meets the development requirements of lithium-ion battery technology for future portable charging devices, new energy vehicles and artificial intelligence, and is also an important technical direction for future lithium-ion battery upgrades.

[0003] Recently, with the continuous breakthroughs in cathode material technology, the theoretical gram capacity of traditional graphite anodes of power batteries is 372mAh / g, which cannot be well matched with cathode materials. It is urgent to seek a new material with high specific capacity. The theoretical gram capacity upper limit of silicon materials is 10 times higher than that of graphite, up to 4200mAh / g, with obvious gram capacity advantages. However, during the cycle, silicon has poor conductivity, the solid electrolyte interface (SEI) film is repeatedly formed and destroyed, and the volume expansion is serious (~300%), which limits the practical application of silicon. Therefore, effective modification of silicon materials (such as coating, deposition, etc.) has become a hot topic of research, in order to give full play to the performance advantages of silicon and carbon, form new high-energy-density anode materials, effectively match with cathodes, and obtain high-energy-density and safe-performance solid-state battery products.

[0004] For example, CN 113957417 A discloses a CVD fluidized deposition device and a method for preparing silicon-carbon negative electrode materials, which is to deliver carbon-based materials into a reaction chamber, input carrier gas into the reaction chamber through a carrier gas delivery mechanism, fluidize the carbon-based materials in the reaction chamber, deliver silicon source gas and reducing gas into the reaction chamber through a gas phase material delivery mechanism, and perform CVD fluidized deposition of silicon source gas and fluidized carbon-based materials in the reaction chamber, deposit silicon on the surface of the carbon-based materials, and achieve better coating. Its main equipment involves a fluidized bed.

[0005] The above technical solution has the following problems:

[0006] 1) Most existing technologies deposit silicon on solid carbon-based materials to form a coating structure. Due to the complex deposition process, this reaction base will have problems such as unstable product consistency and difficulty in scale-up.

[0007] 2) When the above-mentioned basic reaction is adopted, since the deposition reaction of the gaseous silicon source begins at 100°C, the solid carbon source and the gaseous silicon source cannot be heated and pre-mixed in the equipment before the reaction, otherwise it will cause uneven deposition. Therefore, they can only be introduced into the fluidized bed through different pipelines for heating reaction, resulting in poor mixing effect, low reaction rate, long time and high energy consumption.

[0008] 3) After a stage of reaction in the fluidized bed is completed, the reaction needs to be stopped (stop gas introduction, reduce / adjust temperature), gas replacement, and then a new round of reaction is carried out. This reaction method is time-consuming, has low production efficiency and high cost; the discontinuity of the reaction process will also affect the electrochemical performance of the resulting silicon-carbon negative electrode material.

[0009] CN 117867464 A discloses a method for continuously preparing silicon-carbon negative electrode materials, wherein silicon deposition and carbon coating are carried out in two sets of fluidized beds. After the previous stage is completed, it can be directly transported to the next stage through a pipeline, thereby realizing continuous production, improving the production efficiency of silicon-carbon negative electrode materials, and reducing production costs. On the one hand, this technical solution requires two sets of fluidized beds, which increases the investment cost; on the other hand, it still does not solve the technical problems of the above-mentioned points 1) and 2). Summary of the invention

[0010] The purpose of the present invention is to solve the above technical problems and to provide a method for preparing a silicon-carbon composite material with simple process, low production and investment costs, continuous production, high reaction rate, good product performance and large-scale production.

[0011] The present invention also provides a silicon-carbon composite material prepared by the above method, which has the excellent characteristics of low cost, excellent rate performance and fast charging performance, and easy scale-up.

[0012] The present invention also provides a preparation system for the silicon-carbon composite material prepared by the above method, which has low production and investment costs, high efficiency, and can be operated for a long time, continuously, and stably.

[0013] The preparation method of the silicon-carbon composite material of the present invention comprises the following steps: premixing a granular solid silicon source and a gaseous carbon source and preheating them to 300-600°C, and then feeding them into a fluidized bed for fluidized reaction, wherein the temperature is controlled to be 300-900°C and the operating pressure is 0.05-0.15MPa(g). The gas-solid mixture after the reaction is separated by filtration to obtain a silicon-carbon composite material and tail gas, and the silicon-carbon composite material is fed into a product silo.

[0014] The silicon source is a single substance of silicon including crystal and amorphous silicon.

[0015] The silicon element containing crystals and amorphous materials is metallic silicon powder, polycrystalline silicon or single crystal silicon powder.

[0016] The particle size of the silicon source is 5-100 nm, preferably 5-65 nm, and more preferably 10-50 nm.

[0017] The carbon source is a mixed gas containing hydrocarbons, wherein the volume ratio of the hydrocarbons to the mixed gas is 3%-100%, preferably 3%-45%, and more preferably 3%-30%.

[0018] In the mixed gas containing hydrocarbons, the hydrocarbons are at least one of methane, ethane, propane, ethylene and propylene, and the gas other than hydrocarbons is at least one of hydrogen, nitrogen or inert gas.

[0019] The gaseous carbon source is divided into two streams, one of which is premixed with the solid silicon source and then fed into the nozzle at the bottom of the fluidized bed, and the other is directly fed into the nozzle at the bottom of the fluidized bed.

[0020] The mixing mass ratio of the solid silicon source and the gaseous carbon source in the fluidized bed is controlled to be 1:1-10, more preferably 1:2-6.

[0021] The silicon-carbon composite material in the product silo is tested. When it does not meet the product performance requirements, the silicon-carbon composite material in the product silo is circulated back to the nozzle at the bottom of the fluidized bed to be sprayed out to continue reacting. When it meets the product performance requirements, the silicon-carbon composite material in the product silo is cooled and then led out as a qualified product.

[0022] The tail gas obtained after filtering and dust removal is used for indirect preheating of the gaseous carbon source.

[0023] When the silicon-carbon composite material in the product silo needs to be circulated back to the nozzle at the bottom of the fluidized bed, the exhaust gas obtained after filtering and dust removal is introduced into the product silo as a carrier gas and circulated back to the bottom of the fluidized bed together with the silicon-carbon composite material.

[0024] A preparation system for a silicon-carbon composite material used in the above-mentioned preparation method comprises a feeding unit, a fluidized bed and a dust removal unit connected in sequence, wherein the bottom of the dust removal unit is connected to a product silo, and the top of the dust removal unit has an exhaust gas outlet; the bottom of the product silo is connected to the fluidized bed feeding pipe via a return pipe.

[0025] The feeding unit is connected to the feeding pipe of the fluidized bed via a mixing silo, and both the mixing silo and the product silo are provided with temperature control devices.

[0026] A plurality of feed nozzles are evenly arranged at the bottom of the fluidized bed along the circumferential direction, and a built-in cyclone separator is arranged at the top.

[0027] The feed nozzle is a two-channel or multi-channel nozzle, at least one channel is fed with the mixed material from the mixing silo, and at least another channel is fed with the gaseous carbon source.

[0028] The tail gas outlet at the top of the dust removal unit is respectively connected to the tail gas inlet of the raw material preheater and the carrier gas inlet of the product silo; the carbon source outlet of the raw material preheater is respectively connected to the mixing silo and the feed nozzle of the fluidized bed.

[0029] The feeding unit comprises a silicon source silo, a silicon source weighing hopper and a silicon powder rotary feeder which are connected in sequence.

[0030] The silicon-carbon composite material of the present invention is prepared by the above method.

[0031] In view of the problems existing in the background technology, the inventor has made the following improvements:

[0032] 1) Using the principle of CVD deposition, a solid silicon source and a gaseous carbon source are reacted in a fluidized state to generate a new type of silicon-carbon composite material. The silicon source here is a silicon element containing crystals and amorphous materials, which can effectively improve the specific capacity of the composite material. The hydrocarbons in the mixed gas containing hydrocarbons can be cracked at high temperature to form a carbon coating on the surface of the silicon source. The silicon-carbon composite material generated by this reaction has good consistency, excellent rate performance and fast charging performance, and can maintain a high specific capacity at high current density. As a solid-state battery negative electrode material, it can improve the energy density and endurance of the battery.

[0033] 2) Based on the above reaction principle, the problem that the raw materials cannot be premixed and heated before the fluidized reaction is overcome. The solid silicon source and the gaseous carbon source can be mixed and preheated before entering the fluidized bed. This mixed preheating method has multiple effects: a. After the raw materials are preheated and then sent to the fluidized bed, they can be quickly heated to the reaction temperature, the material temperature uniformity is good, and the reaction rate is improved; b. Premixing is conducive to the homogenization of the gas and solid phases, and the ratio is adjustable, the feed temperature can be maintained, and the operation is flexible, ensuring continuous, efficient and stable operation of the reaction. c. The gaseous carbon source can be heated by tail gas, and the high-temperature gaseous carbon source can directly preheat the solid silicon source in the mixing bin, and the temperature control device provided in the mixing bin is used for insulation, so as to achieve the purpose of waste heat recovery and energy saving and consumption reduction. d. The gaseous carbon source can also be used as a carrier gas to transport the solid silicon source. The preheating temperature should be controlled at 300-600℃ here. The specific temperature control is based on the reaction starting temperature of the specific selected reaction raw materials as a reference, and the preheating temperature should not exceed the starting temperature of the fluidized reaction.

[0034] 3) The heated gaseous carbon source is divided into two streams, one of which is premixed with the solid silicon source and then fed into the nozzle at the bottom of the fluidized bed, and the other is directly fed into the nozzle at the bottom of the fluidized bed. Here, the nozzle preferably adopts a two-channel or multi-channel nozzle, at least one channel is fed into the mixture from the mixing bin, and at least another channel is fed into the gaseous carbon source, so that the mixture is uniformly mixed with the gaseous carbon source again while being ejected, further improving the mixing efficiency and uniformity, and improving the reaction efficiency. Since the gas-solid phase has good mixing uniformity in the fluidized bed, there is no need to set up complex components such as distribution plates in the fluidized bed, so there is no clogging problem caused by this.

[0035] 4) The product silo has two outlets, one of which is connected to the nozzle at the bottom of the fluidized bed. When the silicon-carbon composite material in the product silo fails the test, part of the tail gas can be introduced into the product silo. While heating the silicon-carbon composite material, it is also circulated back to the bottom of the fluidized bed as a carrier gas and ejected from the nozzle in the cycle to continue the reaction and return to the bed until the silicon-carbon composite material in the product silo passes the test. At this time, the tail gas delivery and return to the bed can be stopped, and the qualified product can be led out for packaging after cooling. The setting of the return to bed process makes the production not limited by the reaction time. By circulating the return to the bed, the process is continuous, which overcomes the various problems caused by traditional intermittent operation and greatly improves production efficiency. Here, the control device of the product silo can heat and keep the unqualified silicon-carbon composite material warm when it returns to the bed, and cool it before the qualified silicon-carbon composite material is led out.

[0036] The preparation method of the present invention is simple, easy to operate, has low production and investment costs, can achieve continuous and stable production, has a high reaction rate, and has good product performance; the system of the present invention has a simple structure, is not easy to clog, has high efficiency, can operate for a long time, continuously, and stably, has high equipment production capacity, and meets the needs of large-scale development of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a system diagram of the present invention.

[0038] Among them, 1-feeding unit, 1.1-silicon source silo, 1.2-silicon source weighing hopper, 1.3-silicon powder rotary feeder, 1.4-silicon powder filter, 2-mixing silo, 3-fluidized bed, 3.1-cyclone separator, 3.2-feeding nozzle, 4-dust removal unit, 5-product silo, 6-raw material preheater. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0040] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatuses.

[0041] System Example:

[0042] The system of the present invention comprises a feed unit 1, a mixing silo 2, a fluidized bed 3 and a dust removal unit 4 connected in sequence, wherein the bottom of the dust removal unit 4 is connected to a product silo 5, and the bottom of the product silo 5 is connected to the feed pipe of the fluidized bed 3 via a return pipe. The tail gas outlet at the top of the dust removal unit 4 is respectively connected to the tail gas inlet of the raw material preheater 6 and the carrier gas inlet of the product silo 5; the carbon source outlet of the raw material preheater 5 is respectively connected to the mixing silo 3 and the feed nozzle 3.2 of the fluidized bed 3. The mixing silo 3 and the product silo 5 are both provided with a temperature control device.

[0043] The feeding unit 1 comprises a silicon source silo 1.1, a silicon source weighing hopper 1.2 and a silicon powder rotary feeder 1.3 which are connected in sequence, and the gas phase outlet at the top of the silicon source silo 1.1 is connected to a silicon powder filter 1.4.

[0044] The bottom of the fluidized bed 3 is evenly provided with a plurality of feed nozzles 3.2 along the circumferential direction, and the top is provided with a built-in cyclone separator 3.1. The feed nozzle 3.1 is a two-channel or multi-channel nozzle, at least one channel of which is fed with the mixed material from the mixing silo 3, and at least another channel of which is fed with the gaseous carbon source from the raw material preheater 5.

[0045] According to the reaction requirements, the fluidized bed 3 can be one or multiple fluidized beds connected in series.

[0046] Working process:

[0047] The silicon source silo 1.1 is used to receive and store granular solid silicon sources (particle size 5-100nm). The solid silicon sources in the silicon source silo 1.1 fall into the silicon source weighing silo 1.2 under the action of gravity. When the weight of the silicon source weighing silo 1.2 reaches the set value, the inlet valve is closed, and the outlet valve of the silicon source weighing silo 1.2 and the silicon source rotary feeder 1.3 are opened. By adjusting the speed of the silicon source rotary feeder 1.3, the silicon source is fed to the mixing silo 2 of the mixing unit according to the set value. At the same time, the heated gaseous carbon source enters the mixing silo 2 and is fully mixed with the solid silicon source and preheated to 300-600°C (the preheating temperature should be lower than the reaction temperature in the fluidized bed). The outlet valve of the mixing silo 2 is opened, and the mixed material is sent to the feed pipe of the fluidized bed 3 through the feed main pipe, and is ejected through the feed nozzle 3.2 to form a vortex (controlling the mixed mass of the silicon source and the gaseous carbon source in the fluidized bed 3). The amount ratio is 1:1-10, and a full reaction is achieved (temperature is 300-900°C, operating pressure is 0.05-0.15MPa(g)). A part of the solid material is intercepted by the expansion section of the fluidized bed 3 itself and the interception effect of the cyclone separator 3.1. The gas phase is passed from the top of the fluidized bed 3 into the dust removal unit 4 (such as a primary or multi-stage cyclone separator or an online filter). After filtering and dust removal, the solid material falls into the product silo 5, and the high-temperature tail gas enters the raw material preheater 6 to preheat the gaseous carbon source with high-temperature waste heat. The gaseous carbon source out of the raw material preheater 6 is divided into two streams, one of which is sent to the mixing silo 2 to be fully mixed with the solid silicon source for preheating, and the other is sent to the feed pipe of the fluidized bed 3 and sprayed out through the feed nozzle 3.2. The mixed material from the preheater 6 is passed into one channel of the feed nozzle 3.2, and the other gaseous carbon source is passed into another channel of the feed nozzle 3.2.

[0048] The solid material in the product silo 5 (the silicon-carbon composite material obtained after the reaction) is sampled and tested in stages. If the product index requirements are not met, the valve of the return pipe is opened, and part of the tail gas of the dust removal unit 4 is drawn out as a carrier gas, and the temperature control device of the product silo 5 is started for heating and heat preservation. The solid material is returned to the fluidized bed 3 for further reaction, so that the solid material is returned to the bed;

[0049] If the test meets the product index requirements, the return pipe valve is closed, the tail gas is stopped, the control device of the product silo 5 is started to cool down, and after the temperature drops to the set packaging temperature, the packaging outlet valve is opened to complete the product packaging. The above process is a continuous operation.

[0050] The parameters of Examples 1-5 using the above preparation process are shown in the following table:

[0051]

[0052] The properties of the products of Examples 1-5 prepared are shown in the following table:

[0053]

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The granular solid silicon source and the gaseous carbon source are premixed and preheated to 300-600°C, and then sent into a fluidized bed for fluidized reaction. The temperature is controlled to be 300-900°C and the operating pressure is 0.05-1.5MPa(g). The gas-solid mixture after the reaction is separated by filtration to obtain a silicon-carbon composite material and tail gas, and the silicon-carbon composite material is sent to a product silo.

2. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The silicon source is a single substance of silicon including crystal and amorphous silicon.

3. The method for preparing the silicon-carbon composite material according to claim 2, characterized in that: The silicon element containing crystals and amorphous materials is metallic silicon powder, polycrystalline silicon or single crystal silicon powder.

4. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The particle size of the silicon source is 5-100 nm.

5. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The carbon source is a mixed gas containing hydrocarbons, wherein the hydrocarbons account for 3% to 100% of the volume of the mixed gas.

6. The method for preparing the silicon-carbon composite material according to claim 5, characterized in that: In the mixed gas containing hydrocarbons, the hydrocarbons are at least one of methane, ethane, propane, ethylene and propylene, and the gas other than hydrocarbons is at least one of hydrogen, nitrogen or inert gas.

7. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The gaseous carbon source is divided into two streams, one of which is premixed with the solid silicon source and then fed into the nozzle at the bottom of the fluidized bed, and the other is directly fed into the nozzle at the bottom of the fluidized bed.

8. The method for preparing the silicon-carbon composite material according to any one of claims 1 to 7, characterized in that: The mixing mass ratio of the silicon source and the gaseous carbon source in the fluidized bed is controlled to be 1:1-10.

9. The method for preparing the silicon-carbon composite material according to claim 1, characterized in that: The silicon-carbon composite material in the product silo is tested. When it does not meet the product performance requirements, the silicon-carbon composite material in the product silo is circulated back to the nozzle at the bottom of the fluidized bed to be sprayed out to continue reacting. When it meets the product performance requirements, the silicon-carbon composite material in the product silo is cooled and then led out as a qualified product.

10. The method for preparing the silicon-carbon composite material according to claim 1 or 9, characterized in that: The tail gas obtained after filtering and dust removal is used for indirect preheating of the gaseous carbon source.

11. The method for preparing the silicon-carbon composite material according to claim 10, characterized in that: When the silicon-carbon composite material in the product silo needs to be circulated back to the nozzle at the bottom of the fluidized bed, the exhaust gas obtained after filtering and dust removal is introduced into the product silo as a carrier gas and circulated back to the bottom of the fluidized bed together with the silicon-carbon composite material.

12. A system for preparing a silicon-carbon composite material for use in the preparation method of any one of claims 1 to 11, comprising a feeding unit, a fluidized bed and a dust removal unit connected in sequence, characterized in that: The bottom of the dust removal unit is connected to the product silo, and the top of the dust removal unit is provided with an exhaust gas outlet; the bottom of the product silo is connected to the fluidized bed feed pipe via a return pipe.

13. The system for preparing the silicon-carbon composite material according to claim 12, characterized in that: The feeding unit is connected to the feeding pipe of the fluidized bed via a mixing silo, and both the mixing silo and the product silo are provided with temperature control devices.

14. The system for preparing the silicon-carbon composite material according to claim 12 or 13, characterized in that: A plurality of feed nozzles are evenly arranged at the bottom of the fluidized bed along the circumferential direction, and a built-in cyclone separator is arranged at the top.

15. The system for preparing the silicon-carbon composite material according to claim 14, characterized in that: The feed nozzle is a two-channel or multi-channel nozzle, at least one channel is fed with the mixed material from the mixing silo, and at least another channel is fed with the gaseous carbon source.

16. The system for preparing the silicon-carbon composite material according to claim 14, characterized in that: The tail gas outlet at the top of the dust removal unit is respectively connected to the tail gas inlet of the raw material preheater and the carrier gas inlet of the product silo; the carbon source outlet of the raw material preheater is respectively connected to the mixing silo and the feed nozzle of the fluidized bed.

17. The system for preparing the silicon-carbon composite material according to claim 12, characterized in that: The feeding unit comprises a silicon source silo, a silicon source weighing hopper and a silicon powder rotary feeder which are connected in sequence.

18. A silicon-carbon composite material, characterized in that: Prepared by the method according to any one of claims 1 to 11.

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