Method for preparing silicon-containing composite particles

Abstract

The present invention relates to a method for preparing composite particles, the method comprising the steps of: (a) providing a plurality of porous particles in a reactor; (b) contacting the plurality of porous particles with a silicon precursor gas under conditions effective to cause deposition of silicon in pores of the porous particles; (c) measuring the composition of the exhaust gas discharged from the reactor; (d) detecting a change in the composition of the exhaust gas; (e) in response to the detected change in the composition of the exhaust gas, adjusting at least one gas outlet of the reactor to adjust the flow rate of the exhaust gas, thereby increasing the pressure in the reactor and continuing to deposit silicon in the pores of the porous particles at the adjusted pressure; thereby providing composite particles comprising a porous particle skeleton and silicon within pores of the porous particle skeleton; wherein the silicon precursor gas is continuously introduced into the reactor during steps (b) to (e).

Description

Technical Field

[0001] This invention relates to a method for preparing silicon-containing composite particles suitable for use as an anode active material in rechargeable lithium-ion batteries. Background Technology

[0002] A typical lithium-ion battery (LIB) includes an anode, a cathode, and a lithium-containing electrolyte. The anode typically includes a metal current collector with a layer of electroactive material disposed thereon, which is defined herein as a material capable of inserting and releasing lithium ions during the charging and discharging of the battery. The terms "cathode" and "anode" are used herein in the context of connecting the battery to a load such that the anode is the negative electrode. When the LIB is charged, lithium ions are transported from the cathode to the anode via the electrolyte and are inserted into the electroactive material of the anode as intercalated lithium atoms. The term "battery" herein refers both to a device containing a single lithium-ion battery cell and to a device containing multiple interconnected lithium-ion battery cells.

[0003] LIBs were developed in the 1980s and 1990s and have been widely used in portable electronic devices since then. The recent development of electric or hybrid vehicles has created a huge new market for LIBs, and renewable energy is further creating demand for grid-connected energy storage, which can be met at least in part by LIB storage power plants. Overall, global LIB production is projected to grow from approximately 290 GWh in 2018 to over 2,000 GWh by 2028.

[0004] While total storage capacity is increasing, there is significant interest in improving the weight and / or volumetric capacity of rechargeable metal-ion batteries to achieve the same energy storage with less battery mass and / or smaller battery volume. Conventional lithium-ion batteries use graphite as the anode electroactive material. A graphite anode can accommodate up to one lithium atom for every six carbon atoms, resulting in a maximum theoretical specific capacity of 372 mAh / g for lithium-ion batteries, while the actual capacity is slightly lower (approximately 340 to 360 mAh / g).

[0005] Silicon has become a promising alternative to graphite due to its very high lithium capacity (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al., Adv. Mater. 1998, 10, No. 10). Silicon is used in lithium-ion batteries (Li-based... 15Si4 has a theoretical maximum specific capacity of approximately 3,600 mAh / g. However, lithium intercalation into bulk silicon causes the silicon material to expand to 400% of its original volume, which can lead to battery failure. Repeated charge-discharge cycles create significant mechanical stress, leading to silicon breakage and delamination. The formation of a solid electrolyte interphase (SEI) layer on the silicon surface consumes electrolyte, and the newly exposed silicon surface on the cracked surface leads to further electrolyte decomposition, as well as increased SEI layer thickness and irreversible lithium consumption. These destructive mechanisms collectively result in unacceptable electrochemical capacity loss during continuous charge-discharge cycles.

[0006] The applicant has previously reported the development of a class of electroactive materials with composite structures in which the electroactive material, such as silicon, is deposited into a pore network of a highly porous conductive particulate material, such as porous carbon material (see WO 2020 / 095067 and WO 2020 / 128495). In these materials, the silicon is subdivided into individual silicon structures with dimensions on the order of several nanometers or less, thus minimizing stress and strain during charging and discharging. Because the silicon is confined to the pore volume of the porous material, the exposure of the silicon surface to the electrolyte is minimized, effectively limiting the degree of SEI formation. As a result, these materials exhibit good reversible capacity retention over multiple charge-discharge cycles.

[0007] Materials described in WO2020 / 095067 and WO 2020 / 128495 have been synthesized via chemical vapor infiltration (CVI) in various reactor systems (stationary, rotary, and FBR). Porous conductive particles are contacted with silicon-containing precursors (typically silane gases) at atmospheric pressure and temperatures ranging from 400 to 700 °C. The reaction rate is fast at these temperatures; however, silicon precursor molecules need to navigate tortuous paths into pore spaces with diameters of only a few nanometers. This means that relatively high reaction temperatures are required to achieve uniform infiltration in such reactor systems to prevent mass transfer from becoming the rate-limiting step. Furthermore, silicon precursors typically require high dilution in an inert gas. Excessive silicon precursor concentration can lead to rapid and uncontrolled deposition of silicon in the outermost pores, which then blocks entry into most of the available pore volume. As a result, the deposited silicon lacks the fine structure associated with deposition in narrow pores; instead, it is coarse and exposed, thus exhibiting poor cycling behavior. However, the use of low-concentration silicon precursors means that the reaction time to achieve the required silicon loading in the composite particles is relatively long, thus reducing production volume.

[0008] The CVI process can be operated in batch or continuous mode for silicon precursors.

[0009] In systems operating with batch-fed silicon precursors, multiple CVI deposition cycles are required to obtain composite particles with the desired silicon content. At the beginning of each cycle, a feed amount of silicon precursor is introduced into the reactor. The reactor temperature typically decreases with the addition of the silicon precursor, necessitating reactor reheating to bring the feed back to the reaction temperature. Byproduct gases also need to be removed after each cycle. Therefore, the overall production time for composite particles is long, and the yield of such systems is poor. Consequently, these systems are unsuitable for scale-up and struggle to produce large quantities of material.

[0010] Systems operating with batch-fed silicon precursors have additional drawbacks. To obtain composite particles with the desired silicon content, multiple CVI deposition cycles are required. At the beginning of each cycle, a feed amount of silicon precursor is introduced into the reactor. The reactor temperature typically decreases with the addition of the silicon precursor, necessitating reactor reheating to bring the feed back to the reaction temperature. Byproduct gases also need to be removed after each cycle. Therefore, the overall production time for composite particles is long, and such systems have poor throughput.

[0011] Therefore, these systems are not suitable for scaling up and are difficult to produce in large quantities.

[0012] Therefore, there is a need in the art for improved methods for preparing silicon-containing composite particles suitable for use as electroactive materials in LIBs. In particular, there is a need for methods for the large-scale preparation of such composite particles that offer high throughput while maintaining product quality.

[0013] In systems that operate by continuously adding silicon precursors, it has been found that the silicon precursor conversion rate does not remain constant but changes during the CVI reaction, resulting in an unsatisfactory silicon precursor conversion rate and thus inefficient process.

[0014] Silicon precursor conversion can be controlled by balancing the mass transfer requirements of silicon precursor gas and porous particles with reaction kinetics. One way to achieve this balance is to change the temperature of the CVI process during the CVI reaction. However, it has been found that changing the temperature leads to a significant increase in process time due to the time required to heat and cool the reactor. Summary of the Invention

[0015] In a first aspect, the present invention provides a method for preparing composite particles, the method comprising the following steps:

[0016] (a) Providing multiple porous particles in the reactor;

[0017] (b) Contact the plurality of porous particles with the silicon precursor gas under conditions that effectively induce silicon deposition in the pores of the porous particles;

[0018] (c) Measure the composition of the exhaust gas emitted from the reactor;

[0019] (d) Detect changes in the composition of the exhaust gas;

[0020] (e) In response to a detected change in the composition of the exhaust gas, at least one gas outlet of the reactor is adjusted to adjust the flow rate of the exhaust gas, thereby increasing the pressure in the reactor, and silicon is continued to be deposited into the pores of the porous particles under the adjusted pressure;

[0021] This provides composite particles comprising a porous particle framework and silicon within the pores of the porous particle framework.

[0022] During steps (b) to (e), the silicon precursor gas is introduced into the reactor. Detailed Implementation

[0023] Therefore, the present invention generally relates to a method for preparing composite particulate materials, wherein silicon is deposited into a porous network of porous particles via chemical vapor infiltration (CVI) (i.e., by thermal decomposition of a silicon-containing precursor compound). Thus, the composite particles comprise a first component in the form of porous particles forming a framework that supports a second component in the form of a plurality of silicon domains located within the pore structure of the porous particle framework. As used herein, the term "silicon domain" refers to a silicon mass having a maximum size determined by the location of silicon within the pore structure of the porous particles.

[0024] Batch operations can require a relatively long time to complete the permeation of silicon into porous particles. In batch operations, deposition reaction kinetics slow down as the reaction proceeds, for example, due to increased byproduct gas concentrations. Another factor contributing to the long synthesis time in batch operations is that they may involve multiple cycles and inherently involve production downtime due to the loading of silicon precursor gas before the reaction and the release of product gas after the reaction. The method according to the invention is believed to achieve increased production rates by reducing production downtime associated with temperature fluctuations, while also enabling the processing of large batches of composite particles, which are inherent in systems operated by batch feeding of silicon precursor gas and in systems with intentionally altered temperatures. Even when the silicon precursor is supplied at low flow rates, the method according to the invention does not suffer from slowed reaction kinetics because a controlled concentration of silicon precursor gas in the reactor can be maintained. Furthermore, downtime beyond the reaction due to the loading of silicon precursor gas before the reaction and the release of product gas after the reaction (which is necessary for batch operations) is eliminated. In general, the method according to the invention can produce silicon composite particles similar to those of batch operations in half to one-tenth of the total time of batch permeation, or even less.

[0025] The method according to the invention involves adjusting at least one gas outlet of the reactor to adjust the flow rate of the waste gas in response to a detected change in the composition of the waste gas emitted from the reactor, thereby increasing the pressure in the reactor. Silicon is then deposited into the pores of the porous particles under the adjusted pressure, meaning that deposition is not stopped between steps (b) and (e). Increasing the pressure in the reactor increases the residence time of the silicon precursor gas in the reactor. Increasing the residence time of the silicon precursor gas in the reactor optimizes the silicon precursor conversion. The pressure in the reactor can be adjusted more quickly than the reactor temperature, thus adjusting the pressure in the reactor to optimize the silicon precursor conversion achieves a more efficient process. Therefore, the present invention maintains a high silicon precursor conversion while significantly increasing production compared to batch operation.

[0026] Operating the reactor under these conditions means that CVI deposition is carried out with the addition of freshly prepared silicon precursors and then thorough removal of byproducts from the system. Therefore, as the silicon precursor gas is continuously added to the reactor, it mixes with the byproducts. Compared to systems operating with batch-fed silicon precursor gas, the porous particles are in contact with a more consistent concentration of silicon precursor throughout the deposition process.

[0027] Because it reduces the temperature and concentration gradients of the silicon precursor in the reactor, it improves the control over the deposition reaction, allowing porous particles to be exposed to more uniform conditions. This improved control over reaction conditions leads to better control over important properties of the composite particles, including silicon content, surface area, and amount of crude silicon.

[0028] The method according to the invention also achieves an optimal balance between the conversion rate and utilization rate of silicon precursors. The invention can increase pressure while avoiding the introduction of excessive silicon precursor gas into the reactor, because the invention relates to adjusting the flow rate of exhaust gas to increase the pressure in the reactor. While the pressure in the reactor can be increased by increasing the flow rate of silicon precursor gas into the reactor, this change itself would lead to the introduction of excessive silicon precursor gas into the reactor, resulting in a decrease in the utilization rate of the silicon precursor. Furthermore, the ability to control the pressure within the reactor solely through gas input may raise safety concerns.

[0029] operate

[0030] The method operates continuously for silicon precursor gases but in batches for porous particles. Therefore, the reactor operates as a semi-batch reactor.

[0031] The term "continuous" is used in this document to distinguish it from batch operation. In batch operation, a batch of raw material (porous particles) is added to the reactor in the first step, the reaction is allowed to proceed for a specified time, and then a batch of product (composite particles) is removed from the reactor. In continuous operation, the introduction of raw material (silicon precursor) into the reactor and the optional emission of product (exhaust gas) occur continuously as the reaction proceeds.

[0032] In principle, continuous operation does not preclude the possibility of deviations in the flow rates of the silicon precursor gas flowing into the reactor or the exhaust gas flowing out of the reactor. For example, a continuous reactor can be operated in pulse mode. For instance, the flow rate of the silicon precursor gas flowing into the reactor can be reduced to facilitate the venting of exhaust gas from the reactor. Alternatively, the silicon precursor gas can be introduced into the reactor at a constant flow rate.

[0033] The exhaust gas emitted from the reactor contains at least one byproduct gas from the CVI reaction and optionally an unreacted silicon precursor. For example, when the silicon precursor is silane, ethyl silane, or propsilane, the deposition reaction produces hydrogen (H2) as a byproduct. The exhaust gas may contain the silicon precursor, at least one byproduct gas, and optionally other gases such as inert gases (e.g., nitrogen or argon). In a particularly preferred embodiment, the silicon precursor is silane, and the byproduct gas is hydrogen.

[0034] Methods for measuring the composition of exhaust gases emitted from the reactor are known to those skilled in the art and include, but are not limited to, gas chromatography, mass spectrometry, and infrared spectroscopy such as Fourier transform infrared spectroscopy (FT-IR).

[0035] As used herein, “change in the composition of exhaust gas” means a deviation in the concentration of one or more components of the exhaust gas. A deviation in concentration may be a percentage deviation of at least 1%, or at least 2%, or at least 3%, or at least 4%, or at least 5%. A deviation in concentration may be a percentage deviation not exceeding 10%, or not exceeding 9%, or not exceeding 8%, or not exceeding 7%, or not exceeding 6%.

[0036] The pressure in the reactor may be increased in response to the detection of an increase in the concentration of silicon precursor in the exhaust gas. The pressure in the reactor may be increased in response to the detection of an increase in the concentration of silicon precursor in the exhaust gas of at least 1%, or at least 2%, or at least 3%, or at least 4%, or at least 5%. The pressure in the reactor may be increased in response to the detection of an increase in the concentration of silicon precursor in the exhaust gas of not more than 10%, or not more than 9%, or not more than 8%, or not more than 7%, or not more than 6%.

[0037] The pressure in the reactor can be increased in response to a detected decrease in the concentration of by-product gas in the exhaust gas. When the silicon precursor is silane, the by-product gas is hydrogen. The pressure in the reactor can be increased in response to a detected decrease in the concentration of by-product gas in the exhaust gas of at least 1%, or at least 2%, or at least 3%, or at least 4%, or at least 5%. The pressure in the reactor can be increased in response to a detected decrease in the concentration of by-product gas in the exhaust gas of not more than 10%, or not more than 9%, or not more than 8%, or not more than 7%, or not more than 6%.

[0038] It can measure both the concentration of silicon precursors and the concentration of byproduct gases in the exhaust gas, and can increase the pressure in the reactor accordingly.

[0039] Technicians will identify suitable gas outlets, including but not limited to flow control valves and back pressure valves.

[0040] Optionally, the reactor may include more than one outlet for exhaust gases. The use of multiple gas outlets provides further improvement in the airflow dynamics within the reactor. This is particularly useful when the method is carried out on a large scale.

[0041] Optionally, the reactor may include more than one inlet for the silicon precursor gas. The use of multiple inlets for the silicon precursor gas provides further improvement in the dispersion of the silicon precursor throughout the reactor volume, and thus further improvement in the dispersion of the silicon precursor throughout the porous particle agglomerates. This is particularly useful when the method is carried out on a large scale.

[0042] Waste gas can be continuously discharged from the reactor. In this embodiment, the supply of silicon precursor gas and the discharge of waste gas from the reactor occur continuously and simultaneously with the reaction.

[0043] Alternatively, exhaust gases can be discharged from the reactor semi-continuously. As used herein, semi-continuous means intermittent discharge of exhaust gases.

[0044] Semi-continuous emission of exhaust gas from the reactor can be achieved by oscillating at least one gas outlet of the reactor between an open and closed state.

[0045] At least one gas outlet may include a membrane separator that preferentially allows at least one byproduct gas to leave the reactor and prevents silicon precursors from leaving the reactor.

[0046] Flow control devices can be used to regulate the flow rate of the silicon precursor gas introduced into the reactor. Suitable flow control devices include, but are not limited to, reverse pressure controllers, orifices, or other fast-acting mechanisms.

[0047] Those skilled in the art will understand that there are no particular limitations on the unit for measuring the exhaust gas flow rate, provided that the adjustment of the exhaust gas flow rate is sufficient to increase the pressure in the reactor. The exhaust gas flow rate can be either mass flow rate or volumetric flow rate. For example, the exhaust gas flow rate can be defined herein as: grams of silicon in the silicon precursor per minute per kilogram of porous particles (gmin) -1 kg -1 ) and / or silicon precursor silicon grams / minute / liter reactor volume (gmin) -1 / L RV ).

[0048] Step (e) involves continuously depositing silicon into the pores of the porous particles under adjusted pressure. Therefore, the conditions in the reactor in step (e) effectively induce silicon deposition in the pores of the porous particles. This deposition duration can be referred to as the residence period. After the residence period, changes in the composition of the exhaust gas can be detected, and steps (c) through (e) can be repeated. The method may include adjusting at least one gas outlet of the reactor more than once to adjust the exhaust gas flow rate in response to the detected change in the composition of the exhaust gas, thereby increasing the pressure in the reactor. Therefore, the method may include repeating steps (c) through (e) more than once.

[0049] In this way, the pressure in the reactor can be adjusted in response to changes in the composition of the detected exhaust gas throughout the entire duration of the CVI reaction, thereby ensuring optimal silicon precursor conversion.

[0050] As used herein, “conversion rate” as in “silicon precursor conversion rate” typically refers to instantaneous conversion rate. That is, the conversion rate at a given point in time during the synthesis of composite particles, and the given point in time can be a time interval such as 5 seconds, 10 seconds, 30 seconds, or 60 seconds. As used herein, “utilization rate” as in “silicon precursor utilization rate” typically refers to the total conversion rate of the entire synthesis of composite particles.

[0051] Step (d) may also include:

[0052] Calculate the conversion rate of the silicon precursor;

[0053] The calculated silicon precursor conversion rate was compared with the target silicon precursor conversion rate; and

[0054] It is determined that the calculated silicon precursor conversion rate is less than the target silicon precursor conversion rate;

[0055] Step (e) further includes increasing the pressure in the reactor to increase the silicon precursor conversion rate to at least the target silicon precursor conversion rate.

[0056] Methods for calculating the conversion rate of silicon precursors are known to those skilled in the art. For example, the conversion rate of silicon precursors can be based on a known amount of silicon precursor (SP) introduced into the reactor. in ) and measurements of silicon precursors removed from the reactor (SP out The conversion rate can be calculated using (SP). In other words, the conversion rate can be calculated using (SP). in -SP out ) / SP in Calculated as a percentage. The known amount of silicon precursor (SP) introduced into the reactor. in ) and measurements of silicon precursors removed from the reactor (SP out The conversion rate can be measured almost simultaneously to calculate the conversion rate at a given time. The calculated silicon precursor conversion rate can be the arithmetic mean of the conversion rates measured over a period of time (e.g., more than one second or up to one minute).

[0057] The amount of silicon precursor can be measured directly using known methods such as gas chromatography, mass spectrometry, and infrared spectroscopy (e.g., Fourier transform infrared spectroscopy (FT-IR)). The amount of silicon precursor can also be measured indirectly by measuring the amount of byproducts of the silicon deposition reaction (e.g., hydrogen gas when the silicon precursor is silane), because byproduct formation is directly related to the silicon precursor gas in the reaction. For example, in a silicon deposition reaction, one silane molecule reacts to form two hydrogen molecules. The amount of hydrogen can be measured using known methods such as thermal conductivity measurements and / or gas chromatography.

[0058] The target silicon precursor conversion rate is a predetermined target for the silicon precursor conversion rate (i.e., instantaneous conversion rate). The target silicon precursor conversion rate can vary during the synthesis of the composite particles. Alternatively, the target silicon precursor conversion rate can remain constant throughout the entire synthesis of the composite particles. The target silicon precursor conversion rate can be at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97%, or at least 99%, or 100%.

[0059] Unless otherwise specified, all stress values ​​disclosed in this article are absolute stresses.

[0060] The pressure in the reactor can be increased by at least [50 kPa × ΔX], where ΔX represents the difference between the calculated silicon precursor conversion rate (in %) and the target silicon precursor conversion rate (in %). The pressure in the reactor can be increased by at least [60 kPa × ΔX], or at least [70 kPa × ΔX], or at least [80 kPa × ΔX], or at least [90 kPa × ΔX], or at least [100 kPa × ΔX].

[0061] The pressure in the reactor may be increased to no more than [3000 kPa×ΔX], or no more than [2000 kPa×ΔX], or no more than [1000 kPa×ΔX], or no more than [500 kPa×ΔX], or no more than [400 kPa×ΔX], or no more than [300 kPa×ΔX], or no more than [200 kPa×ΔX].

[0062] Step (d) may also include:

[0063] Calculate the partial pressure of the silicon precursor in the reactor;

[0064] The calculated silicon precursor partial voltage is compared with the target silicon precursor partial voltage; and

[0065] It is determined that the calculated partial voltage is less than the partial voltage of the target silicon precursor;

[0066] Step (e) further includes increasing the pressure in the reactor such that the partial pressure of the silicon precursor is increased to at least the target partial pressure of the silicon precursor.

[0067] As used in this article, “calculated partial pressure of silicon precursor in reactor” equals [pressure in reactor × mole fraction of silicon precursor in exhaust gas taken from at least one gas outlet].

[0068] The target silicon precursor partial pressure can be at least 10 kPa, or at least 20 kPa, or at least 30 kPa, or at least 40 kPa, or at least 50 kPa.

[0069] The target silicon precursor partial pressure can be no more than 5000 kPa, or no more than 4000 kPa, or no more than 3000 kPa, or no more than 2000 kPa, or no more than 1600 kPa, or no more than 1500 kPa, or no more than 1200 kPa, or no more than 1000 kPa, or no more than 900 kPa, or no more than 800 kPa, or no more than 700 kPa, or no more than 600 kPa, or no more than 500 kPa, or no more than 400 kPa, or no more than 300 kPa, or no more than 250 kPa, or no more than 200 kPa, or no more than 150 kPa.

[0070] The pressure in step (e) may be at least 10%, or at least 20%, or at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% higher than the pressure in step (b).

[0071] The pressure in step (e) may be no more than 5000%, 4000%, 3000%, 2000%, 1000%, 900%, 800%, 700%, 600%, 500%, 400%, 300%, 175%, 150%, 125%, or 100% higher than the pressure in step (b).

[0072] The method may include the following steps: interrupting silicon deposition; and removing composite particles from the reactor. Interrupting silicon deposition may include: interrupting the introduction of silicon precursor gas into the reactor; and / or reducing the pressure in the reactor to less than 50 kPa, or less than 40 kPa, or less than 30 kPa, or less than 20 kPa, or less than 10 kPa, or less than 5 kPa, or less than 3 kPa, or less than 2 kPa, or less than 1 kPa.

[0073] During steps (b) through (e), the porous particles may be mechanically agitated. As used herein, “mechanical agitation” means using mechanical energy to stir or mix the porous particles in the reactor. Mechanical energy may be provided, for example, by an agitator in the reactor, rotation of the reactor vessel, or mechanical vibration. Reactors suitable for mechanically agitating porous particles include, but are not limited to, stirred tank reactors, rotary tank reactors (e.g., rotary kilns), and vibrating fluidized beds. Other reactors suitable for mechanically agitating porous particles include, but are not limited to, tumbling fluidized beds and rolling-fluidized beds.

[0074] During steps (b) to (e), porous particles can be moved through the reaction zone in the reactor. Suitable reactors include, but are not limited to, moving bed reactors.

[0075] The reactor may be a stirred tank reactor. A stirred tank reactor is particularly preferred when the pressure in the reactor is higher than atmospheric pressure. In one embodiment, the reactor is a stirred tank reactor, and the pressure in step (b) is at least 150 kPa, or at least 200 kPa, or at least 250 kPa, or at least 300 kPa, or at least 400 kPa, or at least 500 kPa, or at least 600 kPa.

[0076] The reactor can be a pressure reactor.

[0077] The porous particles can be continuously mechanically stirred during steps (b) to (e).

[0078] During steps (b) through (e), the porous particles may be mechanically fluidized. As used herein, “mechanical fluidization” means fluidizing the porous particles using mechanical energy. In principle, it is not excluded that the flow of the silicon precursor gas may contribute to the fluidization of the porous particles during mechanical fluidization.

[0079] Preferably, the reactor includes a stirrer for agitating the porous particles during steps (b) to (e). Any suitable stirrer can be used, such as a turbine stirrer, paddle stirrer, anchor stirrer, propeller stirrer, or helical stirrer.

[0080] Mechanical stirring of porous particles decouples the silicon precursor gas supply from the stirring of the porous particles. In the case of a fluidized bed reactor, stirring of porous particles can only be achieved by supplying silicon precursor gas at a rate sufficient to fluidize the porous particles. Therefore, the use of mechanical stirring allows the method to operate at a lower silicon precursor gas rate compared to fluidized bed reactor processes and allows for adjustment of the silicon precursor space-time independently of stirring.

[0081] Continuous mechanical stirring allows for increased porous particle packing per liter of reactor while maintaining uniform silicon deposition. In technologies relying on a relatively high ratio of reactor surface area to porous particle mass, a temperature gradient exists across the porous particle bed thickness, thus limiting the effective porous particle bed thickness for uniform silicon penetration. This, in turn, limits the maximum powder bed thickness and porous particle packing. In a continuous mechanical stirring system, the continuous movement and recirculation of porous particles within the reactor allows for greater contact of porous particles with the reactor surface, improved heat transfer uniformity, and a reduced temperature gradient. This allows for a larger porous particle packing per unit reactor volume.

[0082] Mechanical fluidization of porous particles effectively breaks down naturally occurring aggregates due to the properties of porous particles. This solves both the challenges of heat and mass transfer.

[0083] The temperature may be increased or decreased during steps (b) to (e). Preferably, the temperature range during steps (b) to (e) is no more than 50°C, or no more than 40°C, or no more than 30°C, or no more than 20°C, or no more than 10°C. As used herein, "temperature range during steps (b) to (e)" means a statistical range, i.e., the difference between the lowest and highest temperatures throughout the entire process of steps (b) to (e).

[0084] By controlling the temperature range during steps (b) to (e), time loss due to temperature correction can be reduced.

[0085] The temperature in the reactor during steps (b) to (e) is preferably maintained at 340 to 500°C, or 350 to 500°C, or 350 to 480°C, or 350 to 450°C, or 350 to 420°C, or 340 to 400°C, or 340 to 395°C, or 340 to 390°C, or 345 to 400°C, or 345 to 395°C, or 345 to 390°C, or 350 to 400°C, or 350 to 395°C, or 350 to 385°C, or 350 to 380°C, or 355 to 400°C. The temperatures range from 355 to 395°C, or 355 to 390°C, or 355 to 385°C, or 355 to 380°C, or 360 to 400°C, or 360 to 395°C, or 360 to 390°C, or 360 to 385°C, or 360 to 380°C, or 365 to 400°C, or 365 to 395°C, or 365 to 390°C, or 365 to 385°C, or 365 to 380°C, or 370 to 400°C, or 370 to 395°C, or 370 to 390°C, or 370 to 385°C, or 375 to 385°C. Operating at higher temperatures in the reactor will increase the reaction rate and result in a faster deposition rate. The temperature in the reactor during steps (b) to (e) may be at least 340°C, or at least 350°C, or at least 355°C, or at least 360°C, or at least 365°C, or at least 370°C, or at least 375°C. During step (b), the temperature in the reactor may not exceed 500°C, or 480°C, or 450°C, or 420°C, or 400°C, or 395°C, or 390°C, or 385°C.

[0086] The method of the present invention is preferably operated by supplying the silicon precursor to the reactor in a high concentration or even in a pure form. To control the reaction rate and achieve controlled permeation of the silicon precursor into the porous network of porous particles, the reaction temperature in the reactor is preferably no more than 420°C, more preferably no more than 410°C, more preferably no more than 400°C, and even more preferably no more than 395°C. A temperature range of 370 to 395°C is particularly preferred.

[0087] Unless otherwise specified, all stress values ​​disclosed in this article are absolute stresses.

[0088] The pressure in step (b) and / or step (e) may be below atmospheric pressure (approximately 101 kPa), equal to atmospheric pressure, or above atmospheric pressure. Preferably, the pressure in at least step (e) is above atmospheric pressure.

[0089] The pressure in step (b) and / or step (e) may be at least 50 kPa.

[0090] The pressure in step (b) and / or step (e) may be below atmospheric pressure, or not more than 100 kPa, or not more than 95 kPa, or not more than 90 kPa, or not more than 85 kPa, or not more than 80 kPa, or not more than 75 kPa.

[0091] The pressure in step (b) and / or step (e) may be at least atmospheric pressure (about 101 kPa), or at least 105 kPa, or at least 110 kPa, or at least 115 kPa, or at least 120 kPa, or at least 150 kPa, or at least 200 kPa, or at least 250 kPa, or at least 300 kPa, or at least 400 kPa, or at least 500 kPa, or at least 600 kPa.

[0092] The pressure in step (b) and / or step (e) may be at least 200 kPa, or at least 250 kPa, or at least 300 kPa, or at least 400 kPa, or at least 500 kPa, or at least 600 kPa.

[0093] The pressure in step (b) and / or step (e) may not exceed 5000 kPa, or not exceed 4000 kPa, or not exceed 3000 kPa, or not exceed 2000 kPa, or not exceed 1600 kPa, or not exceed 1500 kPa, or not exceed 1200 kPa, or not exceed 1000 kPa, or not exceed 900 kPa, or not exceed 800 kPa.

[0094] The pressure in step (b) and / or step (e) may be in the range of 105 to 5000 kPa, or 110 to 4000 kPa, or 115 to 3000 kPa, or 120 to 2000 kPa, or 150 to 2000 kPa, or 200 to 2000 kPa.

[0095] The pressure in step (b) and / or step (e) may be in the range of 200 to 5000 kPa, or 200 to 4000 kPa, or 200 to 3000 kPa, or 200 to 2000 kPa, or 200 to 1600 kPa, or 200 to 1500 kPa.

[0096] The pressure in step (b) and / or step (e) may be in the range of 250 to 1600 kPa, or 300 to 1500 kPa, or 400 to 1200 kPa, or 500 to 1000 kPa, or 500 to 900 kPa, or 600 to 800 kPa.

[0097] Preferably, the pressure in step (b) and / or step (e) is in the range of 200 to 2000 kPa or 600 to 800 kPa.

[0098] Operating at increased pressure offers several advantages: it reduces mass transfer limitations on the reaction rate, thus facilitating the permeation of silicon precursor gas into the porous network of particles. Higher pressures also increase the residence time of the silicon precursor gas, thereby improving silicon precursor conversion. However, operating at excessively high pressures has the disadvantage that the pressure negatively impacts the thermodynamic equilibrium of silicon decomposition, thus limiting the extent of the reaction. Operating at pressures below 700 kPa offers the advantage of eliminating the need for specialized equipment, thereby reducing costs.

[0099] To prevent uncontrolled reactions, it is preferable to reduce the temperature in the reactor as the pressure increases. In particular, when the pressure in the reactor is higher than atmospheric pressure, the reaction temperature in the reactor is preferably no more than 450°C, more preferably no more than 430°C, more preferably no more than 420°C, more preferably no more than 410°C, more preferably no more than 400°C, and more preferably no more than 395°C.

[0100] Preferably, the temperature in the reactor during steps (b) to (e) is in the range of 340 to 500°C, and the pressure in the reactor during steps (b) to (e) is in the range of 105 to 5000 kPa.

[0101] Preferably, the temperature in the reactor during steps (b) to (e) is in the range of 360 to 390°C, and the pressure in the reactor during steps (b) to (e) is in the range of 110 to 4000 kPa.

[0102] Preferably, the temperature in the reactor during steps (b) to (e) is in the range of 365 to 390°C, and the pressure in the reactor during steps (b) to (e) is in the range of 115 to 3000 kPa.

[0103] Preferably, the temperature in the reactor during steps (b) to (e) is in the range of 375 to 385°C, and the pressure in the reactor during steps (b) to (e) is in the range of 200 to 2000 kPa.

[0104] During steps (b) to (e), the flow rate of the silicon precursor gas flowing into the reactor can be increased or decreased. Preferably, the flow rate of the silicon precursor gas flowing into the reactor is maintained during steps (b) to (e). As used herein, maintaining the flow rate of the silicon precursor gas flowing into the reactor means that the percentage deviation of the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) does not exceed 20%.

[0105] Maintaining the flow rate of silicon precursor gas into the reactor within a small range improves the ability to control conditions in the reactor by adjusting at least one gas outlet.

[0106] The percentage deviation of the flow rate of silicon precursor gas into the reactor shall not exceed 18%, or 15%, or 10%, or 5%, or 3%, or 2%, or 1%.

[0107] As described herein, the present invention is particularly suitable for scale-up and mass production of materials. Therefore, a preferred embodiment of the invention relates to a high porous particle packing in the reactor, which enables high production volumes and reduces synthesis time and cost. Synthesis time is reduced by the high porous particle packing because it minimizes batch-to-batch operations, such as porous particle packing, reactor heating, and preparation of the inert atmosphere. This reduction in batch numbers while maintaining production volume results in less overall time. The porous particle packing in the reactor can be defined herein as: the volume of porous particles per liter of reactor, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor, and / or the bed depth of porous particles in the reactor.

[0108] In step (a), the multiple porous particles in the reactor can be feed-source porous particles with a volume of at least 20 cm³. 3 Reactor volume per liter (cm³) 3 / L RV ), or at least 50 cm 3 / L RV or at least 80 cm 3 / L RV or at least 100 cm 3 / L RV or at least 150 cm 3 / L RV or at least 200 cm 3 / L RV or at least 250 cm 3 / L RV or at least 300 cm 3 / L RV or at least 400 cm 3 / L RV or at least 500 cm 3 / L RV or at least 600 cm 3 / L RV or at least 700 cm 3 / L RV or at least 800 cm 3 / LRV or at least 900 cm 3 / L RV .

[0109] Preferably, the porous particles used in step (a) are at least 500 cm² in size. 3 / L RV In some embodiments, it is optionally sufficient to substantially fill the reactor volume.

[0110] As used herein, the volume of a porous particle refers to its equivalent mass as determined by its tap density. For example, 200 cm³ as defined herein. 3 A porous particle material with a tap density of 1000 g / L is equivalent to 200 g of porous particle material.

[0111] The ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 1 m². 2 / kg, or not exceeding 0.9 m 2 / kg, or not exceeding 0.8 m 2 / kg, or not exceeding 0.7 m 2 / kg, or not exceeding 0.6 m 2 / kg, or not exceeding 0.5 m 2 / kg, or not exceeding 0.4 m 2 / kg, or not exceeding 0.3 m 2 / kg.

[0112] The ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be at least 0.001 m². 2 / kg, or at least 0.002 m 2 / kg, or at least 0.003 m 2 / kg, or at least 0.004 m 2 / kg, or at least 0.006 m 2 / kg, or at least 0.008 m 2 / kg, or at least 0.01 m 2 / kg.

[0113] The bed depth of porous particles in the reactor can be at least 11 cm, or at least 15 cm, or at least 20 cm, or at least 25 cm, or at least 30 cm.

[0114] Preferably, the ratio of the porous particle volume per liter of reactor, the internal surface area of ​​the reactor to the mass of porous particles in the reactor, and / or the bed depth of porous particles in the reactor are combined with continuous stirring as described herein.

[0115] In step (a), the volume of the multiple porous particles in the reactor can be at least 100 cm³. 3 / L RV Furthermore, the bed depth of porous particles in the reactor can be at least 11 cm.

[0116] In step (a), the volume of the multiple porous particles in the reactor can be at least 200 cm³. 3 / L RV Furthermore, the bed depth of porous particles in the reactor can be at least 15 cm.

[0117] In step (a), the volume of the multiple porous particles in the reactor can be at least 300 cm³. 3 / L RV Furthermore, the bed depth of porous particles in the reactor can be at least 20 cm.

[0118] In step (a), the volume of the multiple porous particles in the reactor can be at least 400 cm³. 3 / L RV Furthermore, the bed depth of porous particles in the reactor can be at least 25 cm.

[0119] In step (a), the volume of the multiple porous particles in the reactor can be at least 500 cm³. 3 / L RV Furthermore, the bed depth of porous particles in the reactor can be at least 30 cm.

[0120] In step (a), the volume of the multiple porous particles in the reactor can be at least 100 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 1 m². 2 / kg.

[0121] In step (a), the volume of the multiple porous particles in the reactor can be at least 200 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 0.9 m². 2 / kg.

[0122] In step (a), the volume of the multiple porous particles in the reactor can be at least 300 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 0.8 m². 2 / kg.

[0123] In step (a), the volume of the multiple porous particles in the reactor can be at least 400 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 0.7 m². 2 / kg.

[0124] In step (a), the volume of the multiple porous particles in the reactor can be at least 500 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 0.6 m². 2 / kg.

[0125] In step (a), the volume of the multiple porous particles in the reactor can be at least 600 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can not exceed 0.5 m². 2 / kg.

[0126] A particularly preferred embodiment of the invention combines a high porous particle packing of the reactor with a relatively low flow rate of silicon precursor gas flowing into the reactor. The flow rate of the silicon precursor gas flowing into the reactor can be defined herein as: grams of silicon in the silicon precursor per minute per kilogram of porous particles (g / min). -1 kg -1 ), and / or grams of silicon in the silicon precursor per minute per liter of reactor volume (g / min) -1 / L RV Even when producing large quantities of material, the combination of a high porous particle packing in the reactor and a relatively low flow rate of silicon precursor gas into the reactor allows for better control over material quality. As the silicon precursor gas flow rate increases, the reactor temperature must be increased during the deposition reaction, leading to poorer silicon precursor penetration within the porous network of particles. It is believed that poor silicon precursor penetration within the porous network of particles can increase the amount of crude silicon to undesirable levels, which is detrimental to product quality. This is thought to be because, under high-temperature conditions, the kinetics of the deposition reaction predominate over mass transfer, resulting in poorer silicon precursor penetration within the porous network of particles.

[0127] The flow rate of silicon precursor gas flowing into the reactor, measured in grams of silicon per minute per kilogram of porous particles, can range from 0.2 to 25 g / min. -1 kg -1 or 0.5 to 20 gmin -1 kg -1 or 1 to 15 gmin -1 kg -1or 1 to 14 gmin -1 kg -1 or 1 to 13 gmin -1 kg -1 or 1 to 12 gmin -1 kg -1 or 2 to 12 gmin -1 kg -1 or 3 to 12 gmin - 1 kg -1 or 3 to 11 gmin -1 kg -1 This is the flow rate during steps (b) to (e).

[0128] Preferably, the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e), measured in grams of silicon per minute per kilogram of porous particles in the silicon precursor, is 0.2 to 5 g / min. -1 kg -1 or 0.2 to 4 gmin -1 kg -1 or 0.2 to 3 g min -1 kg -1 .

[0129] The silicon content in the silicon precursor is expressed in grams per minute per liter of reactor volume (g / min). -1 / L RV The flow rate of silicon precursor gas into the reactor during steps (b) to (e), expressed in units of 0.03 to 40 g / min, can be from 0.03 to 40 g / min. -1 / L RV or 0.04 to 35 gmin -1 / L RV or 0.05 to 30 gmin -1 / L RV , or 0.06 to 25 gmin -1 / L RV or 0.07 to 20 gmin -1 / L RV , or 0.08 to 15 gmin -1 / L RV or 0.09 to 10 gmin -1 / L RV or 0.1 to 5 gmin -1 / L RV or 0.1 to 1 gmin -1 / L RV or 0.15 to 1 gmin -1 / L RVor 0.15 to 0.95 gmin -1 / L RV or 0.2 to 0.95 gmin -1 / L RV , or 0.2 to 0.9 gmin -1 / L RV .

[0130] Preferably, the flow rate of silicon precursor gas into the reactor during steps (b) to (e), measured in grams of silicon in the silicon precursor per minute per liter of reactor volume, is 0.03 to 0.55 g / min. -1 / L RV or 0.03 to 0.45 gmin -1 / L RV or 0.03 to 0.35 gmin -1 / L RV .

[0131] The flow rate of exhaust gas can be controlled using Coriolis flow meters and controllers, or other mass flow controllers that measure mass flow and use it to control gas flow. Suitable valves for flow control include, but are not limited to, needle valves, diaphragm valves, and glove valves.

[0132] A particularly preferred embodiment of the invention combines a high porous particle packing of the reactor with a relatively low flow rate of silicon precursor gas into the reactor.

[0133] In step (a), the volume of the multiple porous particles in the reactor can be at least 100 cm³. 3 / L RV Furthermore, the bed depth of the porous particles in the reactor can be at least 11 cm, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 5 g / min. -1 kg -1 .

[0134] In step (a), the volume of the multiple porous particles in the reactor can be at least 200 cm³. 3 / L RV Furthermore, the bed depth of the porous particles in the reactor can be at least 15 cm, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 4 g / min. -1 kg -1 .

[0135] In step (a), the volume of the multiple porous particles in the reactor can be at least 300 cm³. 3 / L RVFurthermore, the bed depth of the porous particles in the reactor can be at least 20 cm, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 3 g / min. -1 kg -1 .

[0136] In step (a), the volume of the multiple porous particles in the reactor can be at least 400 cm³. 3 / L RV Furthermore, the bed depth of the porous particles in the reactor can be at least 25 cm, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 3 g / min. -1 kg -1 .

[0137] In step (a), the volume of the multiple porous particles in the reactor can be at least 500 cm³. 3 / L RV Furthermore, the bed depth of the porous particles in the reactor can be at least 30 cm, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 3 g / min. -1 kg -1 .

[0138] In step (a), the volume of the multiple porous particles in the reactor can be at least 100 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 1 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 5 g / min. -1 kg -1 .

[0139] In step (a), the volume of the multiple porous particles in the reactor can be at least 200 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 0.9 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be from 0.2 to 4 g / min. -1 kg -1 .

[0140] In step (a), the volume of the multiple porous particles in the reactor can be at least 300 cm³. 3 / L RVFurthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 0.8 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be 0.2 to 3 g / min. -1 kg -1 .

[0141] In step (a), the volume of the multiple porous particles in the reactor can be at least 400 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 0.7 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be 0.2 to 3 g / min. -1 kg -1 .

[0142] In step (a), the volume of the multiple porous particles in the reactor can be at least 500 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 0.6 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be 0.2 to 3 g / min. -1 kg -1 .

[0143] In step (a), the volume of the multiple porous particles in the reactor can be at least 600 cm³. 3 / L RV Furthermore, the ratio of the reactor's internal surface area to the mass of porous particles in the reactor can be no more than 0.5 m². 2 / kg, and the flow rate of the silicon precursor gas flowing into the reactor during steps (b) to (e) can be 0.2 to 3 g / min. -1 kg -1 .

[0144] The composite particles may contain a target silicon content, and in step (b) 5% to 95% of the target silicon content may be deposited. As used herein, "target silicon content" means the amount of silicon in the composite particles prepared according to the method of the present invention.

[0145] The target silicon content can be the amount of silicon occupying 20% ​​to 95% of the internal pore volume of the porous particle framework. Specifically, the target silicon content can occupy 20% to 80%, 20% to 70%, 30% to 70%, or 30% to 60% of the internal pore volume of the porous particle framework.

[0146] The target silicon content may be at least 26% by weight of silicon, or at least 28% by weight of silicon, or at least 30% by weight of silicon, or at least 32% by weight of silicon, or at least 34% by weight of silicon, or at least 36% by weight of silicon, or at least 38% by weight of silicon, or at least 40% by weight of silicon, or at least 42% by weight of silicon, or at least 44% by weight of silicon.

[0147] The target silicon content may be no more than 70% by weight, or no more than 65% by weight, or no more than 62% by weight, or no more than 60% by weight, or no more than 58% by weight, or no more than 56% by weight, or no more than 54% by weight.

[0148] In step (b), at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 45%, or at least 50%, or at least 55%, or at least 60%, or at least 65%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90% of the target silicon content may be deposited.

[0149] In step (b), the target silicon content may be deposited at no more than 90%, or no more than 85%, or no more than 80%, or no more than 75%, or no more than 70%, or no more than 65%, or no more than 60%, or no more than 55%, or no more than 50%, or no more than 45%, or no more than 40%, or no more than 35%, or no more than 30%, or no more than 25%, or no more than 20%, or no more than 15%, or no more than 10%.

[0150] The composite particles prepared by the method according to the present invention may contain 0.2 to 1.8 grams of silicon per gram of porous particle framework.

[0151] The composite particles prepared by the method according to the invention may contain a certain amount of silicon, which occupies 20% to 95% of the internal pore volume of the porous particle framework, or 20% to 80%, 20% to 70%, 30% to 70%, or 30% to 60% of the internal pore volume of the porous particle framework. The silicon occupancy can be calculated using the following formula: 100 × (density of silicon × weight of silicon in the composite particles) / pore volume of the porous particles. For this purpose, the density of silicon is set to 2.3 g / cm³. 3 .

[0152] It is possible that unreacted silicon precursors can be recovered from the exhaust gas emitted from the reactor and recycled back into the reactor.

[0153] When the exhaust gas emitted from the reactor contains a significant amount of unreacted silicon precursors, it may be appropriate to recover the unreacted silicon precursors from the exhaust gas. The recovered silicon precursors can be recycled back into the reactor. Methods for recovering unreacted silicon precursors from exhaust gas include semi-permeable membrane separation processes, pressure swing adsorption processes, and cryogenic separation processes.

[0154] Optionally, prior to step (b), the porous particles in the reactor are flushed with an inert gas. Optionally, the porous particles are heated to the CVI reaction temperature under an inert gas flow, and silicon deposition is initiated by switching the inert gas to a silicon precursor gas.

[0155] Optionally, the porous particles are preheated before being introduced into the reactor. Preferably, the porous particles are preheated to ≥(T) RZ The temperature is -200)℃, where T RZ The temperature of the reactor in step (b) is preferably preheated to ≥ (T RZ A temperature of -100)℃, more preferably preheated to ≥(T)℃ RZ Temperature -50℃.

[0156] Optionally, the silicon precursor gas is preheated before being introduced into the reactor. Preferably, the silicon precursor gas is preheated to ≥(T) RZ The temperature is -200)℃, where T RZ The reaction temperature of the reactor is preferably preheated to ≥ (T). RZ A temperature of -100)℃, more preferably preheated to ≥(T RZ -50)℃ temperature.

[0157] The BET surface area of ​​the composite particles prepared by the method according to the present invention is preferably not more than 100 m². 2 / g, or not exceeding 80 m 2 / g, or not exceeding 60 m 2 / g, or not exceeding 40 m 2 / g, or not exceeding 30 m 2 / g, or not exceeding 25 mg 2 / g, or not exceeding 20 mg 2 / g, or not exceeding 15 m 2 / g, or not exceeding 10 mg 2 / g. Generally, a low BET surface area is preferred to minimize the formation of a solid electrolyte interface (SEI) layer at the surface of the composite particles during the first charge-discharge cycle of the anode. However, an excessively low BET surface area results in unacceptably low charge rates and capacities due to the inaccessibility of the electroactive material bulk to metal ions in the surrounding electrolyte. For example, the BET surface area of ​​the composite particles is preferably at least 0.1 m². 2 / g, or at least 1 m 2 / g, or at least 2 m 2 / g, or at least 5 m 2 / g. For example, the surface area of ​​BET can range from 0.1 to 100 m². 2 / g, or 0.1 to 80 m 2 / g, or 0.5 to 60 m 2 / g, or 0.5 to 40 m 2 / g, or 1 to 30 m 2 / g, or 1 to 25 mg 2 / g, or 2 to 20 mg 2 Within the range of / g. As used herein, the term “BET surface area” should be considered as the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on a solid surface according to ISO 9277 (2022) using the Brunauer-Emmett-Teller principle.

[0158] The composite particles can be characterized by their performance under thermogravimetric analysis (TGA) in air. This analytical method relies on the principle that an increase in weight is observed when an electroactive material is exposed to air and oxidized at elevated temperatures.

[0159] As defined herein, “surface silicon” is calculated from the initial mass increment measured in the TGA trace from a minimum of 150°C to 500°C to a maximum of 550°C to 650°C, where the TGA is performed in air at a heating rate of 10°C / min. This mass increment is considered to be due to oxidation of the surface silicon, thus allowing the percentage of surface silicon as a proportion of the total silicon to be determined according to the following formula:

[0160] Y = 1.875 × [(M max - M min ) / M f ] ×100%

[0161] Where Y is the percentage of surface silicon (the proportion of total silicon in the sample), M max M is the maximum mass of the sample measured within the temperature range of 550℃ to 650℃. minIt is the minimum mass of the sample at temperatures above 150°C and below 500°C, and M f This refers to the mass of the sample after oxidation at 1400℃. For completeness, 1.875 should be understood as the molar mass ratio of SiO2 to O2 (i.e., the mass ratio of the SiO2 formed to the mass increase due to the addition of oxygen). Typically, TGA analysis is performed using a sample amount of 10 mg ± 2 mg.

[0162] It has been found that when the surface silicon content, as measured by the TGA method described above, is at least 20% by weight of the total silicon content in the material, the reversible capacity retention rate is significantly improved with repeated charge / discharge cycles.

[0163] The composite particles provided by the method according to the invention preferably contain at least 20% by weight of surface silicon, which is the total amount of silicon. Alternatively, as determined by TGA, at least 22% by weight, or at least 25% by weight, or at least 30% by weight, or at least 35% by weight, or at least 40% by weight, or at least 45% by weight of silicon are surface silicon.

[0164] As determined by TGA, the composite particles provided by the method according to the invention preferably have a low content of coarse bulk silicon. Coarse bulk silicon is defined herein as silicon oxidized at above 800°C as determined by TGA, wherein the TGA is performed in air at a heating rate of 10°C / min. Therefore, the coarse bulk silicon content is determined according to the following formula:

[0165] Z = 1.875 × [(M f - M 800 ) / M f ] ×100%

[0166] Where Z is the percentage of silicon that was not oxidized at 800℃, and M... 800 The mass of the sample at 800℃, and M f This refers to the mass of ash at the point where oxidation is complete at 1400°C. For the purposes of this analysis, it is assumed that any mass increment above 800°C corresponds to the oxidation of silicon to SiO2, and that the total mass at the point of oxidation is SiO2. Typically, TGA analysis is performed using a sample amount of 10 mg ± 2 mg.

[0167] Silicon oxidized at temperatures above 800°C is less desirable. Preferably, as determined by TGA, silicon comprising no more than 10% by weight, or no more than 8% by weight, or no more than 6% by weight, or no more than 5% by weight, or no more than 4% by weight, or no more than 3% by weight, or no more than 2% by weight, or no more than 1.5% by weight is coarse phase silicon.

[0168] Preferably, at least 20% by weight of silicon is surface silicon, and no more than 10% by weight of silicon is bulk silicon, both determined by TGA. More preferably, at least 30% by weight of silicon is surface silicon, and no more than 10% by weight of silicon is bulk silicon, both determined by TGA. More preferably, at least 35% by weight of silicon is surface silicon, and no more than 8% by weight of silicon is bulk silicon, both determined by TGA. More preferably, at least 40% by weight of silicon is surface silicon, and no more than 5% by weight of silicon is bulk silicon, both determined by TGA. More preferably, at least 45% by weight of silicon is surface silicon, and no more than 2% by weight of silicon is bulk silicon, both determined by TGA.

[0169] Porous particles

[0170] Porous particles can contain micropores and / or mesopores.

[0171] Porous particles can have:

[0172] (i) D in the range of 0.5 to 200 µm 50 Particle size;

[0173] (ii) Between 0.4 and 2.2 cm 3 The total pore volume of micropores and mesopores within the range of / g, measured by gas adsorption; and

[0174] (iii) PD not exceeding 30 nm as measured by gas adsorption 50 Aperture.

[0175] As used herein, the term "particle size" refers to the equivalent sphere diameter (esd), that is, the diameter of a sphere having the same volume as a given particle, where particle volume should be understood to include the volume of any internal pores within the particle. As used herein, the term "D" refers to... 50 "and "D 50 "Particle size" refers to the volume median particle size, that is, the diameter at which 50% of the volume of the particle population is measured to be smaller than a certain diameter. As used in this article, the term "D" is similar. 10 "and "D 10 "Particle size" refers to the 10th percentile volume median particle size, that is, the diameter at which 10% of the particle population by volume is measured to be smaller than a certain diameter. As used in this paper, the term "D" is similar. 90 "and "D 90 "Particle size" refers to the 90th percentile volume median particle size, that is, the diameter at which 90% of the volume of the particle population is measured to be smaller than a certain diameter.

[0176] Particle size and particle size distribution can be determined using standard laser diffraction techniques according to ISO 13320:2009. Laser diffraction relies on the principle that particles scatter light at an angle that varies depending on the particle size, and that an aggregate of particles will produce a scattered light pattern defined by the intensity and angle, which can be correlated with the particle size distribution. Many commercially available laser diffraction instruments are used for the rapid and reliable determination of particle size distribution. Unless otherwise stated, particle size distribution measurements specified or reported herein are performed using instruments from Malvern Instruments. TM The standard Malvern Mastersizer TM Measured using a 3000 particle size analyzer. Malvern Mastersizer TM The 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing particles of interest suspended in an aqueous solution. The light striking the particles is scattered at an angle inversely proportional to the particle size, and a photodetector array measures the intensity of the light at multiple predetermined angles. The particle size distribution is determined by computer processing of the intensities measured at different angles using standard theoretical principles. The laser diffraction values ​​reported in this paper were obtained using a solution containing 5% (v / v) of the surfactant SPAN. TM -40 (sorbitan monopalmitate) particles were obtained as a wet dispersion in 2-propanol. The refractive index of the porous particles was considered to be 2.68, and the refractive index of the composite particles was considered to be 3.50, with a dispersion index of 1.378. The particle size distribution was calculated using the Mie scattering model.

[0177] Typically, the D of porous particles 50 The particle size can range from 0.5 to 200 µm. Optionally, the D of the porous particles... 50 The particle size can be at least 1 µm, or at least 1.5 µm, or at least 2 µm, or at least 2.5 µm, or at least 3 µm, or at least 4 µm, or at least 5 µm. Optionally, the D of the porous particles... 50 The particle size may not exceed 150 µm, or not exceed 100 µm, or not exceed 70 µm, or not exceed 50 µm, or not exceed 40 µm, or not exceed 30 µm, or not exceed 25 µm, or not exceed 20 µm, or not exceed 18 µm, or not exceed 15 µm, or not exceed 12 µm, or not exceed 10 µm, or not exceed 8 µm.

[0178] For example, the D of porous particles 50The particle size can be in the range of 0.5 to 150 µm, or 0.5 to 100 µm, or 0.5 to 50 µm, or 0.5 to 30 µm, or 1 to 25 µm, or 1 to 20 µm, or 2 to 25 µm, or 2 to 20 µm, or 2 to 18 µm, or 2 to 15 µm, or 2 to 12 µm, or 2.5 to 15 µm, or 2.5 to 12 µm, or 2 to 10 µm, or 3 to 20 µm, or 3 to 18 µm, or 3 to 15 µm, or 4 to 18 µm, or 4 to 15 µm, or 4 to 12 µm, or 5 to 15 µm, or 5 to 12 µm, or 5 to 10 µm, or 5 to 8 µm. Particles within these size ranges and having the porosity and pore size distribution described herein are ideally suited for use as composite particles in the anode of metal-ion batteries, prepared via the CVI process.

[0179] D of porous particles 10 The particle size is preferably at least 0.2 µm, or at least 0.5 µm, or at least 0.8 µm, or at least 1 µm, or at least 1.5 µm, or at least 2 µm. This is achieved by using D... 10 Maintaining a particle size above 0.2 µm reduces the likelihood of unwanted submicron particle aggregation and improves the dispersibility of the resulting composite particles.

[0180] D of porous particles 90 The particle size is preferably no more than 300 µm, or no more than 250 µm, or no more than 200 µm, or no more than 150 µm, or no more than 100 µm, or no more than 80 µm, or no more than 60 µm, or no more than 40 µm, or no more than 30 µm, or no more than 25 µm, or no more than 20 µm.

[0181] Porous particles preferably have a narrow size distribution span. For example, the particle size distribution span (defined as (D...) 90 -D 10 ) / D 50 The particle size distribution is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, it is easier to achieve efficient particle filling into a continuous reactor.

[0182] Preferably, the D1 particle size of the porous particles is at least 0.8 µm, or at least 1.0 µm, or at least 1.2 µm, or at least 1.4 µm, or at least 1.5 µm, or at least 1.6 µm, or at least 1.8 µm, or at least 2.0 µm, or at least 2.2 µm, or at least 2.4 µm, or at least 2.5 µm, or at least 2.6 µm, or at least 2.8 µm, or at least 3.0 µm. It should be understood that the D1 particle size of the porous particles provides a measure of the fine particle content in the porous particles of the feed. It has been found that substantially eliminating fine particles in porous particles provides improved silicon deposition, particularly by increasing the content of “surface silicon” in the composite particles. The “surface silicon” content of the composite particles is discussed in more detail below.

[0183] Preferably, the D1 particle size is in the range of 1.5 to 4.5 µm, or 2 to 4 µm, or 2.5 to 3.5 µm, or 11 to 13 µm.

[0184] D of porous particles 98 The particle size is preferably no more than 35 µm, or no more than 30 µm, or no more than 25 µm, or no more than 20 µm, or no more than 18 µm, or no more than 16 µm.

[0185] D of porous particles 100 The particle size is preferably no more than 40 µm, or no more than 35 µm, or no more than 30 µm, or no more than 25 µm, or no more than 20 µm.

[0186] Preferably, the D of porous particles 98 The difference between particle size and D1 particle size (D 98 -D1) Not exceeding 18 µm, or not exceeding 16 µm, or not exceeding 15 µm, or not exceeding 14 µm, or not exceeding 13 µm, or not exceeding 12 µm.

[0187] Preferably, the D of porous particles 98 The ratio of particle size to D1 particle size (D 98 / D1) not exceeding 12, or not exceeding 10, or not exceeding 8, or not exceeding 6, or not exceeding 5.

[0188] Preferably, (D) 98 -D1) / D 50 Not exceeding 2.2, or not exceeding 2, or not exceeding 1.9, or not exceeding 1.8, or not exceeding 1.7, or not exceeding 1.6.

[0189] The average sphericity (as defined herein) of the porous particles can exceed 0.5. Preferably, their average sphericity is at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85. Spherical particles are considered to contribute to the uniformity of deposition and are advantageous for simultaneously packing the particles more densely into the continuous reactor and into the final product when incorporated into the electrodes.

[0190] Highly accurate two-dimensional projections of micrometer-scale particles can be obtained using scanning electron microscopy (SEM) or dynamic image analysis, where a digital camera is used to record the shadow of the particle projection. As used herein, the term "sphericity" should be understood as the ratio of the area of ​​the particle projection (obtained by such imaging techniques) to the area of ​​a circle, wherein the particle projection and the circle have the same circumference. Therefore, for an individual particle, the sphericity S can be defined as:

[0191]

[0192] Where A m It is the measured area of ​​the particle projection, and C m This is the measured perimeter of the particle's projection. For example, the average sphericity S of multiple particles used in this paper... av Defined as:

[0193]

[0194] Where n represents the number of particles in the swarm. The average sphericity of the particle swarm is preferably calculated by a two-dimensional projection of at least 50 particles.

[0195] Porous particles comprise a three-dimensional interconnected open network, which includes micropores and / or mesopores, as well as optional macropores with small volumes. According to standard IUPAC terminology, the term "micropore" is used herein to refer to pores with a diameter less than 2 nm, the term "mesopore" is used herein to refer to pores with a diameter between 2 and 50 nm, and the term "macropore" is used herein to refer to pores with a diameter greater than 50 nm.

[0196] The volume of micropores, mesopores and macropores mentioned in this article, as well as any mention of the distribution of pore volume within porous particles, refers to the internal pore volume of the porous particles used as raw material in step (a) of the claimed method (i.e., before silicon is deposited into the pore volume in step (c)).

[0197] Porous particles can range in size from 0.4 to 2.2 cm. 3The total volume of micropores and mesopores in the range of / g (i.e., the total pore volume in the range of 0 to 50 nm). Typically, porous particles contain both micropores and mesopores. However, it is not excluded that porous particles containing micropores but not mesopores or porous particles containing mesopores but not micropores may be used.

[0198] More preferably, the total volume of micropores and mesopores in the porous particles is at least 0.45 cm³. 3 / g, or at least 0.5 cm 3 / g, or at least 0.55 cm 3 / g, or at least 0.6 cm 3 / g, or at least 0.65 cm 3 / g, or at least 0.7 cm 3 / g, or at least 0.75cm 3 / g, or at least 0.8 cm 3 / g, or at least 0.85 cm 3 / g, or at least 0.9 cm 3 / g, or at least 0.95 cm 3 / g, or at least 1cm 3 / g. The use of highly porosity conductive particles can be advantageous because it allows for the inclusion of larger amounts of silicon within porous structures.

[0199] The internal pore volume of the porous particles is suitably limited to a value at which the increased brittleness of the porous particles outweighs the advantage of the increased pore volume gained from accommodating a larger amount of silicon. Preferably, the total volume of micropores and mesopores in the porous particles does not exceed 2 cm³. 3 / g, or not exceeding 1.8 cm 3 / g, or not exceeding 1.6 cm 3 / g, or not exceeding 1.5 cm 3 / g, or not exceeding 1.45 cm 3 / g, or not exceeding 1.4 cm 3 / g, or not exceeding 1.35 cm 3 / g, or not exceeding 1.3 cm 3 / g, or not exceeding 1.25 cm 3 / g, or not exceeding 1.2 cm 3 / g, or not exceeding 1.1 cm 3 / g, or not exceeding 1 cm 3 / g, or not exceeding 0.95cm 3 / g.

[0200] In some instances, the total volume of micropores and mesopores in porous particles can range from 0.45 to 2.2 cm³. 3 / g, or 0.5 to 2 cm 3 / g, or 0.55 to 2 cm 3 / g, or 0.6 to 1.8 cm 3 / g, or 0.65 to 1.8 cm 3 / g, or 0.7 to 1.6 cm 3 / g, or 0.75 to 1.6 cm 3 / g, or 0.8 to 1.5 cm 3 Within the range of / g.

[0201] In other examples, the total volume of micropores and mesopores in porous particles can range from 0.55 to 1.4 cm³. 3 / g, or 0.6 to 1.4 cm 3 / g, or 0.6 to 1.3 cm 3 / g, or 0.65 to 1.3 cm 3 / g, or 0.65 to 1.2 cm 3 / g, or 0.7 to 1.2cm 3 / g, or 0.7 to 1.1 cm 3 / g, or 0.7 to 1 cm 3 / g, or 0.75 to 0.95 cm 3 Within the range of / g.

[0202] In other examples, the total volume of micropores and mesopores in porous particles can range from 0.4 to 0.75 cm³. 3 / g, or 0.4 to 0.7 cm 3 / g, or 0.4 to 0.65 cm 3 / g, 0.45 to 0.75 cm 3 / g, or 0.45 to 0.7 cm 3 / g, or 0.45 to 0.65cm 3 / g, or 0.45 to 0.6 cm 3 Within the range of / g.

[0203] In other examples, the total volume of micropores and mesopores in porous particles can range from 0.6 to 2 cm³. 3 / g, or 0.6 to 1.8 cm 3 / g, or 0.7 to 1.8 cm 3 / g, or 0.7 to 1.6 cm 3 / g, or 0.8 to 1.6 cm 3 / g, or 0.8 to 1.5 cm 3 / g, or 0.8 to 1.4 cm 3 / g, or 0.9 to 1.5 cm 3 / g, or 0.9 to 1.4 cm 3 / g, or 1 to 1.4 cm 3 Within the range of / g.

[0204] PD of porous particles 50 The pore size may not exceed 30 nm, and optionally not exceed 25 nm, or not exceed 20 nm, or not exceed 15 nm, or not exceed 12 nm, or not exceed 10 nm, or not exceed 8 nm, or not exceed 6 nm, or not exceed 5 nm, or not exceed 4 nm, or not exceed 3 nm, or not exceed 2.5 nm, or not exceed 2 nm, or not exceed 1.5 nm. The term "PD" as used herein... 50 "Pore diameter" refers to the volume median pore diameter based on the total volume of micropores and mesopores (i.e., the pore diameter at which 50% of the total volume of micropores and mesopores is lower than a certain pore diameter). Therefore, according to the present invention, at least 50% of the total volume of micropores and mesopores is preferably in the form of pores with a diameter of less than 30 nm.

[0205] To avoid ambiguity, and to determine PD 50 Values, without considering any large pore volume (pore diameter greater than 50 nm).

[0206] The volume ratio of micropores to mesopores in porous particles can generally be in the range of 100:0 to 0:100. Preferably, the volume ratio of micropores to mesopores is 90:10 to 55:45, or 90:10 to 60:40, or 85:15 to 65:35.

[0207] Based on the total volume of micropores and mesopores of the porous particles, the micropore volume fraction is preferably at least 0.4, or at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6.

[0208] Based on the total volume of micropores and mesopores of porous particles, the micropore volume fraction is preferably no more than 0.85, or no more than 0.8.

[0209] For example, based on the total volume of micropores and mesopores in porous particles, the micropore volume fraction can be in the range of 0.4 to 0.85, or in the range of 0.45 to 0.85, or in the range of 0.5 to 0.8, or in the range of 0.55 to 0.8, or in the range of 0.6 to 0.8. Alternatively, based on the total volume of micropores and mesopores in porous particles, the micropore volume fraction can be greater than 0.8, or greater than 0.85, or greater than 0.9, or greater than 0.95, or greater than 0.98.

[0210] The pore size distribution of porous particles can be unimodal, bimodal, or multimodal. As used herein, the term "pore size distribution" refers to the distribution of the pore size of porous particles relative to the cumulative total internal pore volume. Bimodal or multimodal pore size distributions may be preferred because the close proximity between micropores and pores with larger diameters provides the advantage of efficient ion transport to silicon through the porous network.

[0211] Following the standard method described in ISO 15901-2:2022, using quenched solid density functional theory (QSDFT), nitrogen adsorption was applied at 77 K, and the density decreased to 0.8 × 10⁻⁶. -6 The relative pressure p / p0 is used to determine the total volume of micropores and mesopores, as well as the pore size distribution of micropores and mesopores. Nitrogen adsorption is a technique that characterizes the porosity and pore size distribution of a material by condensing a gas within the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases until a saturation point is reached, at which point all pores are filled with liquid. The nitrogen pressure is then gradually decreased to allow the liquid to evaporate from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them allows for the determination of pore volume and pore size distribution. Suitable instruments for measuring pore volume and pore size distribution by nitrogen adsorption include the TriStar II and TriStar II Plus porosity analyzers (available from Micromeritics Instrument Corporation, USA) and the Autosorb IQ porosity analyzer (available from Quantachrome Instruments).

[0212] Nitrogen adsorption is effective for measuring pore volume and pore size distribution of pores with a maximum diameter of 50 nm, but it is less reliable for pores with much larger diameters. For the purposes of this invention, nitrogen adsorption is therefore used only for pores with a maximum diameter of 50 nm (inclusive) (i.e., only for micropores and mesopores) to determine pore volume and pore size distribution. PD 50 Similarly, it is determined only relative to the total volume of micropores and mesopores.

[0213] Due to limitations in available analytical techniques, it is impossible to measure pore volume and pore size distribution across the entire range of micropores, mesopores, and macropores using a single technique. In the case of porous particles including macropores, the volume of pores with diameters greater than 50 nm and not exceeding 100 nm can be measured by mercury porosimetry, and preferably not exceeding 0.3 cm³. 3 / g, or not exceeding 0.20 cm 3 / g, or not exceeding 0.1 cm 3 / g, or not exceeding 0.05 cm 3 / g. Although a small number of macropores can be useful in facilitating the entry of electrolytes into the porous network, the advantages of the present invention are primarily achieved by accommodating silicon in micropores and smaller mesopores.

[0214] Any pore volume below 50 nm measured by mercury porosimetry (as described above, using nitrogen adsorption to characterize mesopores and micropores) is ignored. For the purposes of this invention, pore volumes above 100 nm measured by mercury porosimetry are assumed to be interparticle porosity and are ignored.

[0215] Mercury intrusion porosimetry (MIP) is a technique for characterizing the porosity and pore size distribution of a material sample by applying varying levels of pressure to the sample immersed in mercury. The pressure required to allow mercury to penetrate the pores of the sample is inversely proportional to the pore size. The values ​​obtained by MIP reported in this paper are based on ASTM UOP578-11, where the surface tension γ is 480 mN / m and the contact angle φ is 140° for mercury at room temperature. The density of mercury at room temperature is 13.5462 g / cm³. 3 A variety of high-precision mercury porosimetry instruments are commercially available, such as the AutoPore IV series automated mercury porosimeter, which is available from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury porosimetry, see PA Webb and C. Orr, "Analytical Methods in Fine Particle Technology," 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0216] It should be understood that intrusion techniques such as gas adsorption and mercury porosimetry are only effective for determining the pore volume of pores accessible to nitrogen or mercury from the outside of porous particles. The porosity values ​​indicated herein should be understood as referring to the volume of open pores (i.e., pores accessible to fluid from the outside of porous particles). In determining porosity values ​​herein, completely encapsulated pores that cannot be identified by nitrogen adsorption or mercury porosimetry should not be considered. Similarly, any pore volume located in pores as small as or below the detection limit of nitrogen adsorption should not be considered.

[0217] The porous particles are preferably porous conductive particles. A preferred type of porous conductive particle is porous carbon particles. The porous carbon particles preferably contain at least 80% by weight of carbon, more preferably at least 90% by weight of carbon, even more preferably at least 95% by weight of carbon, and optionally at least 98% by weight or at least 99% by weight of carbon. The carbon can be crystalline carbon or amorphous carbon, or a mixture of amorphous and crystalline carbon. The porous carbon particles can be hard carbon particles or soft carbon particles.

[0218] As used in this paper, the term "hard carbon" refers to a disordered carbon matrix in which carbon atoms are found to be primarily sp(s) in nanoscale polyaromatic domains. 2 Hybridized state (trigonal bond). Polyaromatic domains are cross-linked using chemical bonds such as COC bonds. Due to the chemical cross-linking between polyaromatic domains, hard carbon cannot be converted to graphite at high temperatures. Hard carbon exhibits graphitic properties, as evidenced by the large G band (~1600 cm⁻¹) in its Raman spectrum. -1 This is evidenced by the fact that the carbon is not entirely graphitic, as evidenced by the distinct D band (~1350 cm⁻¹) in the Raman spectrum. -1 The graphite properties of carbon materials can be evaluated by monitoring the peak intensity ratio of the D-band to the G-band (ID / IG). Porous carbon particles can contain an ID / IG ratio not exceeding 0.84 or 0.75.

[0219] As used in this paper, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are found to be primarily sp(s) in polyaromatic domains in the 5 to 200 nm size range. 2 Hybridization (triangular bonding). Compared to hard carbon, the polyaromatic domains in soft carbon are associated through intermolecular forces rather than cross-linked by chemical bonds. This means they will graphitize at high temperatures. Porous carbon particles preferably contain at least 50% sp. 2 Hybridized carbon (measured by XPS). For example, porous carbon particles can suitably contain 50% to 98% sp. 2 Hybridized carbon, 55% to 95% sp 2 Hybridized carbon, 60% to 90% sp 2 Hybridized carbon, or 70% to 85% sp 2 Hybridized carbon.

[0220] A wide variety of materials can be used to prepare suitable porous carbon frameworks. Examples of usable organic materials include plant biomass, including lignocellulosic materials (such as coconut shells, rice husks, wood, etc.), and fossil carbon sources such as coal. Examples of resins and polymers that form porous carbon particles upon pyrolysis include phenolic resins, phenolic varnish resins, bitumen, melamine-based materials, polyacrylate-based materials, polystyrene-based materials, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers containing monomer units of acrylate monomers, styrene monomers, α-olefins, vinylpyrrolidone, and other olefinically unsaturated monomers. Depending on the raw materials and conditions of the pyrolysis process, a wide variety of carbon materials are available in the art. Porous carbon particles of various sizes are available from commercial suppliers.

[0221] Porous carbon particles can undergo chemical or gas-based activation processes to increase the volume of mesopores and micropores. Suitable activation processes include contacting pyrolytic carbon with one or more of oxygen, water vapor, CO, CO2, and KOH at temperatures ranging from 600 to 1000°C.

[0222] Mesoporous structures can also be obtained using known template-based processes, employing removable pore-forming agents such as MgO and other colloidal or polymeric templates (which can be removed by thermal or chemical means after pyrolysis or activation).

[0223] Alternatives to carbon-based conductive particles include porous metal oxides, such as TiO₂. x Oxides of titanium, wherein the value of x is greater than 1 and less than 2.

[0224] The BET surface area of ​​porous particles is preferably at least 750 m². 2 / g, or at least 1,000 m 2 / g, or at least 1,250 m 2 / g, or at least 1,500 m 2 / g. As used herein, the term "BET surface area" should be understood to refer to the surface area per unit mass calculated from the measurement of the physical adsorption of gas molecules on a solid surface according to ISO 9277 using the Brunauer-Emmett-Teller principle. Preferably, the BET surface area of ​​the porous particles does not exceed 4,000 m². 2 / g, or not exceeding 3,500m 2 / g, or not exceeding 3,250 m 2 / g, or not exceeding 3,000 m 2 / g, or not exceeding 2,500 m 2 / g, or not exceeding 2,000 m 2 / g. For example, the BET surface area of ​​porous particles can be as high as 750 m². 2 / g to 4,000 m 2 / g, or 1,000 m 2 / g to 3,500 m 2 / g, or 1,250 m 2 / g to 3,250 m 2 / g, or 1,500 m 2 / g to 3,000 m 2 Within the range of / g.

[0225] The particle density of the porous particles is preferably at least 0.35 and more preferably less than 3 g / cm³. 3 More preferably less than 2 g / cm 3 More preferably less than 1.5 g / cm3 The optimal value is 0.35 to 1.2 g / cm³. 3 As used herein, the term "particle density" refers to the "apparent particle density" (i.e., the mass of a particle divided by its volume, where the particle volume is considered as the sum of the volumes of the solid material and any closed or blind pores ("blind pores" are pores too small to be measured by mercury porosimetry)) as measured by mercury porosimetry. Typically, the particulate additives used in this invention have a low BET surface area and therefore a relatively low open-pore volume. Thus, the apparent density measured by mercury porosimetry is close to the "effective particle density" (whose calculation includes the volume of open pores). Preferably, the particle density of the porous particles is at least 0.4 g / cm³. 3 or at least 0.45 g / cm 3 or at least 0.5 g / cm 3 or at least 0.55 g / cm 3 or at least 0.6 g / cm 3 or at least 0.65 g / cm 3 or at least 0.7 g / cm 3 Preferably, the particle density of the porous particles does not exceed 1.15 g / cm³. 3 or not exceeding 1.1 g / cm 3 or not exceeding 1.05 g / cm 3 or not exceeding 1 g / cm 3 or not exceeding 0.95 g / cm 3 or not exceeding 0.9 g / cm 3 .

[0226] The preferred porous particles used in this invention include those that satisfy the following conditions:

[0227] (i) D 50 The particle size ranges from 0.5 to 30 µm;

[0228] (ii) The total pore volume of micropores and mesopores, measured by gas adsorption, is between 0.5 and 1.5 cm³. 3 Within the range of / g;

[0229] (iii) PD measured by gas adsorption 50 The pore size does not exceed 5 nm;

[0230] Silicon precursor gas

[0231] The silicon precursor gas contains a silicon precursor. The silicon precursor is a silicon compound or mixture of silicon compounds that is gaseous at the temperature of the CVI process and can be thermally decomposed to form elemental silicon and a byproduct gas. The silicon precursor gas optionally contains other gases, such as inert gases. Examples of suitable silicon precursors include silane (SiH4), disilane (Si2H6), propane (Si3H8), methylsilane, dimethylsilane, and chlorosilane, and mixtures thereof. Preferably, the silicon precursor is selected from silane (SiH4), disilane (Si2H6), propane (Si3H8), methylsilane, and dimethylsilane. Siane (SiH4) is the most preferred silicon precursor.

[0232] Preferably, the silicon precursor gas is chlorine-free, for example, containing less than 1% by weight, preferably less than 0.1% by weight, and preferably less than 0.01% by weight of a chlorine-containing compound.

[0233] The silicon precursor can be used undiluted (pure) or diluted, such that the silicon precursor gas contains at least 5% by volume of silicon precursor and the balance of a gas selected from hydrogen and inert gases, optionally wherein the inert gas is selected from nitrogen and argon.

[0234] During steps (b) to (e), the concentration of silicon precursor in the silicon precursor gas introduced into the reactor can be increased or decreased. Preferably, the concentration range of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is no more than 20% by volume, or no more than 10% by volume, or no more than 5% by volume, or no more than 3% by volume, or no more than 2% by volume, or no more than 1% by volume. As used herein, "concentration range of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e)" means a statistical range, i.e., the difference between the minimum and maximum concentrations throughout the entire process of steps (b) to (e).

[0235] The silicon precursor gas may contain at least 10% by volume, or at least 20% by volume, or at least 30% by volume, or at least 40% by volume, or at least 50% by volume, or at least 60% by volume, or at least 70% by volume, or at least 80% by volume, or at least 90% by volume, or at least 95% by volume, or at least 98% by volume, or at least 99% by volume, or at least 99.9% by volume, or at least 100% by volume of silicon precursor. Preferably, the silicon precursor gas contains at least 50% by volume, or at least 60% by volume, or at least 70% by volume, or at least 80% by volume, or at least 90% by volume, or at least 90% by volume, or at least 95% by volume, or at least 98% by volume, or at least 99% by volume, or at least 99.9% by volume, or at least 99.99% by volume, or at least 100% by volume of silicon precursor. The volume percentage of silicon precursor refers to the concentration of silicon precursor as a proportion of the total gas (silicon precursor gas) introduced into the reactor.

[0236] Preferably, the concentration of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is no more than 20% by volume, and the percentage deviation of the flow rate of the silicon precursor gas into the reactor during steps (b) to (e) is no more than 20%. In addition, the temperature during steps (b) to (e) can be no more than 50°C.

[0237] Preferably, the concentration of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is no more than 10% by volume, and the percentage deviation of the flow rate of the silicon precursor gas into the reactor during steps (b) to (e) is no more than 18%. In addition, the temperature during steps (b) to (e) can be no more than 40°C.

[0238] Preferably, the concentration of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is no more than 10% by volume, and the percentage deviation of the flow rate of the silicon precursor gas into the reactor during steps (b) to (e) is no more than 15%. In addition, the temperature during steps (b) to (e) can be no more than 30°C.

[0239] Preferably, the concentration of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is no more than 5% by volume, and the percentage deviation of the flow rate of the silicon precursor gas into the reactor during steps (b) to (e) is no more than 10%. In addition, the temperature during steps (b) to (e) can be no more than 20°C.

[0240] carbon coating

[0241] The method of the present invention optionally further includes the step of contacting the composite particles with a carbon precursor gas under conditions that effectively induce carbon deposition in the pores and / or on the surface of the composite particles.

[0242] The deposited carbon is a pyrolytic carbon material formed through the thermal decomposition of carbon-containing gases (such as ethylene). It offers several performance advantages. It further reduces the BET surface area of ​​the composite particles by smoothing any surface defects and filling any residual surface micropores, thereby reducing initial cycle loss. It also improves the surface conductivity of the composite particles, thus reducing the need for conductive additives in the electrode composition. Additionally, it produces an optimal surface for forming a stable SEI layer, resulting in improved capacity retention during cycling.

[0243] Conditions that effectively induce carbon deposition may include temperatures in the range of 350 to 700°C or 400 to 700°C. Preferably, the temperature does not exceed 680°C, or 660°C, or 640°C, or 620°C, or 600°C, or 580°C, or 560°C, or 540°C, or 520°C, or 500°C.

[0244] The minimum temperature will depend on the type of carbon precursor used. Preferably, the temperature is at least 300°C, or at least 350°C, or at least 400°C.

[0245] Conditions that can effectively induce carbon deposition may include pressures ranging from 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa.

[0246] Suitable carbon precursor gases include:

[0247] (i) C2-C 10 Hydrocarbons, optionally selected from alkanes, alkenes, alkynes, cycloalkanes, cycloolefins and aromatic hydrocarbons, such as methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, α-terpinene and acetylene;

[0248] (ii) a dicyclic monoterpene, optionally wherein the dicyclic monoterpene is selected from camphor, borneol, eucalyptol, camphene, carene, sapinene, limonene, and pinene; and

[0249] (iii) A polycyclic hydrocarbon comprising 10 to 25 carbon atoms and optionally 1 to 3 heteroatoms, wherein the polycyclic aromatic hydrocarbon is optionally selected from naphthalene, substituted naphthalene (e.g., dihydroxynaphthalene), anthracene, tetraphenylene, pentaphenylene, fluorene, acenaphthene, phenanthrene, fluoranthene, pyrene, β-carbamate, perylene, benzoxene, fluorenone, anthraquinone, anthrone, and their alkyl-substituted derivatives.

[0250] The carbon precursor used can be used in pure form or as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the carbon precursor can be used in amounts ranging from 0.1 vol% to 100 vol%, or 20 vol% to 95 vol%, or 50 vol% to 90 vol%, or 60 vol% to 85 vol%, based on the total volume of the precursor and the inert carrier gas.

[0251] passivation

[0252] The silicon deposited in CVI deposition has a hydride-terminated silicon surface that is highly reactive to oxygen. Therefore, the method of the present invention preferably includes a passivation step, through which the composite particles can be passivated in a controlled manner to form a passivation material stable in air.

[0253] The passivation described herein can be carried out in the same reactor as steps (b)-(e). Alternatively, the composite particles formed in step (e) can be removed from the reactor after step (e) and transferred to a post-treatment vessel under inert conditions, where passivation can then be performed.

[0254] Therefore, the method of the present invention may further include the step of contacting the composite particles with a passivating agent under conditions that effectively passivate the composite particles. As defined herein, a passivating agent is a compound or mixture of compounds capable of reacting with the surface of deposited silicon to form a modified surface. The composite particles may be contacted with the passivating agent in a reactor or may be conveyed to a separate container for contact with the passivating agent. The composite particles may be contacted with a first passivating agent in the reactor, and subsequently conveyed to a separate container and contacted with a second passivating agent, wherein the first and second passivating agents may be the same or different. Preferably, the composite particles are contacted with the passivating agent at least in the reactor.

[0255] The method of the present invention may further include the following steps: interrupting silicon deposition to form intermediate composite particles; contacting the intermediate composite particles with a passivating agent under conditions that effectively passivate the intermediate composite particles to provide passivated intermediate composite particles; and contacting the passivated intermediate composite particles with a silicon precursor gas under conditions that effectively induce silicon deposition in the pores of the passivated intermediate composite particles to provide composite particles.

[0256] Composite particles that have already been contacted with carbon precursor gas under conditions that effectively induce carbon deposition in the pores and / or on the surface of the composite particles can be subsequently contacted with a passivating agent under conditions that effectively passivate the composite particles.

[0257] The passivating agent may be selected from: (i) oxygen-containing gas; (ii) ammonia; (iii) a gas containing ammonia and oxygen; and (iv) phosphine.

[0258] The passivating agent can be an oxygen-containing gas. In this case, the conditions for effectively passivating the composite particles can include temperatures in the range of 20 to 300°C, or 20 to 200°C, or 25 to 200°C, or 25 to 180°C, or 50°C to 160°C. Preferably, the temperature does not exceed 150°C. Additionally, the conditions for effectively passivating the composite particles can include pressures in the range of 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa. The oxygen-containing gas can be air. When the oxygen-containing gas is air, the concentration of oxygen in contact with the composite particles during the passivation step can increase over time, optionally as the composite particles cool to a temperature below 50°C.

[0259] The passivating agent can be ammonia or other nitrogen-containing molecules. In this case, the passivation layer can comprise a silicon nitride of the formula SiN x where 0 < x ≤ 4 / 3. The silicon nitride is preferably amorphous silicon nitride. The nitride layer can be formed by contacting the composite particles with ammonia at a temperature in the range of 200 - 700 °C, preferably 400 - 700 °C, more preferably 400 - 600 °C. Then, the temperature can be raised to the range of 500 to 1,000 °C if necessary to form a nitride surface (e.g., a silicon nitride surface of the formula SiNx where x ≤ 4 / 3). Since sub-stoichiometric nitrides (such as SiN x where 0 < x ≤ 4 / 3) are conductive, the nitride interlayer functions as a conductive network that allows for more rapid charge and discharge of the electroactive material.

[0260] As a phosphorus analogue of ammonia, phosphine can also be used as a passivating agent.

[0261] The passivating agent can comprise ammonia (or other nitrogen-containing molecules) and oxygen. In this case, the passivation layer can comprise a silicon oxynitride of the formula SiO x N y where 0 < x < 2, 0 < y < 4 / 3, and 0 < (2x + 3y) ≤ 4). The silicon nitride is preferably amorphous silicon oxynitride. The oxynitride layer can be formed by contacting the composite particles with a passivating agent comprising ammonia (or other nitrogen-containing molecules) and oxygen.

[0262] Other suitable passivating agents include: compounds containing olefin, alkyne or carbonyl functional groups, more preferably compounds containing terminal olefin, terminal alkyne, aldehyde or ketone groups.

[0263] Preferred passivating agents include one or more compounds of the following formulae:

[0264] (i) R 1 -CH=CH-R 1 ;

[0265] (ii) R 1 -C≡C-R 1 ; and

[0266] (iii) O=CR 1 R 1 ;

[0267] where each R 1 independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or where two R 1 groups form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring.

[0268] Particularly preferred passivating agents include one or more compounds of the following formula:

[0269] (i) CH2=CH-R 1 ;as well as

[0270] (ii) HC≡CR 1 ;

[0271] Where R 1 As defined above. Preferably, R 1 It is not replaced.

[0272] Examples of suitable passivating agents include: ethylene, propylene, 1-butene, butadiene, 1-pentene, 1,4-pentadiene, 1-hexene, 1-octene, styrene, divinylbenzene, acetylene, phenylacetylene, norbornene, norbornadiene, and bicyclo[2.2.2]oct-2-ene. Optionally, mixtures of different passivating agents may also be used.

[0273] It is believed that passivating agents containing olefin, alkyne, or carbonyl groups undergo an insertion reaction with MH groups (where M represents atoms of the electroactive material) on the surface of the electroactive material to form a covalently passivated surface resistant to air oxidation. When silicon is the electroactive material, the passivation reaction between the silicon surface and the passivating agent can be understood as a form of hydrosilylation, as illustrated below.

[0274]

[0275] Other suitable passivating agents include compounds containing active hydrogen atoms bonded to oxygen, nitrogen, sulfur, or phosphorus. For example, passivating agents can be alcohols, amines, thiols, or phosphine. The reaction of the -XH group with the hydride group on the surface of the electroactive material is understood to result in the elimination of H2 and the formation of a direct bond between X and the surface of the electroactive material.

[0276] Suitable passivating agents of this class include compounds having the following formula:

[0277] (iv) HX-R 2 ,as well as

[0278] (v) HX-C(O)-R 1 ,

[0279] Where X represents O, S, and NR. 1 or PR 1 ; Each R 1 Independently as defined above; and R 2 It represents an unsubstituted or substituted aliphatic or aromatic hydrocarbon group having 1 to 20 carbon atoms, or R 1 and R2 Together they form unsubstituted or substituted ring structures containing 3 to 8 carbon atoms in the ring.

[0280] Preferably, X represents O or NH.

[0281] Preferably, R 2 This indicates an optionally substituted aliphatic or aromatic group having 2 to 10 carbon atoms. An amino group may also be incorporated into a 4-10 member aliphatic or aromatic ring structure, as in pyrrolidine, pyrrole, imidazole, piperazine, indole, or purine.

[0282] The contact between the composite particles and the passivating agent can be carried out at a temperature ranging from 25 to 700°C, preferably from 50 to 500°C, and more preferably from 100 to 300°C.

[0283] Other suitable passivating agents are selected from liquid water and water vapor, preferably wherein the silicon-containing composite particles from step (e) are contacted with liquid water or water vapor at a temperature in the range of 40 to 400°C, or 100 to 350°C, or 120 to 300°C, or 140 to 280°C.

[0284] Gas separation unit

[0285] The method may also include the following steps:

[0286] Feeding at least a portion of the waste gas into a gas separation unit; and

[0287] Operate a gas separation unit to separate silicon precursors from at least one byproduct gas.

[0288] The silicon precursor is separated from at least one byproduct gas to provide at least one enriched gas stream and at least one waste gas stream, wherein the enriched gas stream is richer in silicon precursor compared to the waste gas stream, and wherein the waste gas stream contains less silicon precursor compared to the waste gas stream.

[0289] The enriched gas stream may contain at least one by-product gas from the exhaust gas, but it is preferred to minimize the amount of at least one by-product gas. For example, the enriched gas stream may contain at least 60 vol% of silicon precursor, or at least 70 vol% of silicon precursor, or at least 80 vol% of silicon precursor, or at least 90 vol% of silicon precursor, or at least 95 vol% of silicon precursor, or at least 98 vol% of silicon precursor. The exhaust gas stream may contain silicon precursor, but it is preferred to minimize the amount of silicon precursor. For example, the exhaust gas stream may contain less than 40 vol% of silicon precursor, or less than 30 vol% of silicon precursor, or less than 20 vol% of silicon precursor, or less than 10 vol% of silicon precursor, or less than 5 vol% of silicon precursor.

[0290] For example, CVI deposition of silane produces hydrogen as a byproduct, and a gas separation unit can be used to separate unreacted silane from the silane / hydrogen mixture in the exhaust gas to provide a silane-rich gas stream compared to the exhaust gas and a hydrogen-containing exhaust gas stream with reduced silane content compared to the exhaust gas.

[0291] The enriched gas stream containing the silicon precursor can be recycled back into the reactor, for example, as part of step (b), thereby minimizing its replenishment. Therefore, the method may include the following steps:

[0292] At least a portion of the enriched gas flow is introduced (recirculated) into the reactor.

[0293] The enriched gas stream can be mixed with the silicon precursor gas introduced in step (b), and the mixture can be introduced into the reactor through one or more identical gas inlets. Alternatively, the enriched gas stream can be introduced into the reactor through one or more gas inlets different from the gas inlets used to introduce the silicon precursor gas in step (b). Alternatively, the enriched gas stream containing the silicon precursor can be stored. Similarly, the waste gas stream containing byproduct gases such as hydrogen can be stored.

[0294] Step (b) may include mixing at least a portion of the enriched gas stream with the silicon precursor gas and then introducing it into the reactor. Alternatively or additionally, the method may further include the step of separately introducing at least a portion of the enriched gas stream and the silicon precursor gas into the reactor. Alternatively or additionally, the method may further include the step of collecting at least a portion of the enriched gas stream and / or the waste gas stream for storage. Alternatively or additionally, at least a portion of the enriched gas stream may be further processed to purify the silicon precursor gas.

[0295] At least a portion of the waste gas stream can be further treated to recover energy and / or purify byproduct gases. At least a portion of the waste gas stream can be purified. Alternatively or additionally, at least a portion of the waste gas stream can be treated to recover energy from it. Alternatively or additionally, at least a portion of the waste gas stream can be fed into a feed network. Alternatively or additionally, at least a portion of the waste gas stream can be used as feedstock for further treatment.

[0296] A portion of the exhaust gas can bypass the gas separation unit as a bypass stream. Therefore, the method may further include the step of allowing a portion of the exhaust gas to bypass the gas separation unit as a bypass stream. Step (b) may include mixing at least a portion of the bypass stream with the silicon precursor gas and then introducing it into the reactor. Alternatively or additionally, at least a portion of the bypass stream may be introduced into the reactor separately from the silicon precursor gas. The method may include separating the bypass stream from the effluent stream and recycling the bypass stream back into the reactor without separating the silicon precursor gas from the byproduct gas in the bypass stream.

[0297] The exhaust gas may contain 5% to 80% by volume of silicon precursor, or 5% to 70% by volume, or 5% to 60% by volume, or 5% to 50% by volume of silicon precursor.

[0298] The byproduct gas may contain hydrogen, and the gas separation unit may be a hydrogen (H2) selective membrane. Alternatively, the byproduct gas may contain hydrogen, and the gas separation unit may be a hydrogen (H2)-silane selective membrane.

[0299] The exhaust gas may contain an inert gas, and the method may include the following steps: separating the inert gas and the silicon precursor and / or at least one by-product gas using a gas separation unit. The inert gas, silicon precursor, and at least one by-product gas may be separated sequentially. For example, the silicon precursor may be separated from the inert gas and at least one by-product gas, and then the at least one by-product gas may be separated from the inert gas. In this case, the gas separation unit may include two or more systems for separating the gases.

[0300] Gas separation units may include membrane separation systems such as polymer membrane separation systems and / or metal alloy membrane separation systems, pressure swing adsorption systems, cryogenic separation systems, gas distillation systems, or combinations thereof. Gas separation units may include membrane separation systems and pressure swing adsorption systems.

[0301] The separation unit may include a heat exchanger to cool the exhaust gas to or near ambient temperature, such as below 70°C or below 50°C, and then separate the exhaust gas into a enriched gas stream and an exhaust gas stream. Therefore, the method may include the following steps: cooling the exhaust gas to or near ambient temperature, such as below 70°C or below 50°C. Attached Figure Description

[0302] The invention is further described with reference to the accompanying drawings, wherein:

[0303] Figure 1 This is an illustration of a method of operation according to one embodiment of the present invention.

[0304] Figure 2 This is an illustration of a method of operation according to one embodiment of the present invention.

[0305] Figure 3 This is an illustration of a method of operation according to one embodiment of the present invention.

[0306] Figure 4 This is an illustration of a method of operation according to one embodiment of the present invention.

[0307] Figure 5 This is an illustration of a method of operation according to one embodiment of the present invention.

[0308] Figure 6 This is an illustration of a method of operation according to one embodiment of the present invention.

[0309] Figure 7 This is an illustration of a method of operation according to one embodiment of the present invention.

[0310] Figure 8 This is an illustration of a method of operation according to one embodiment of the present invention.

[0311] Figure 9 This is an illustration of a method of operation according to one embodiment of the present invention.

[0312] Figure 10 This is an illustration of a method of operation according to one embodiment of the present invention.

[0313] exist Figure 1 and 2 In this process, under conditions that effectively induce silicon deposition within the pores of porous particles, a silicon precursor is injected into the reactor, and the pressure is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 20% ​​of the target silicon content, the calculated silicon precursor conversion rate remains at the target silicon precursor conversion rate. After depositing 60% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 80% of the target silicon content, the calculated silicon precursor conversion rate remains at the target silicon precursor conversion rate. After depositing 90% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate until 100% of the target silicon content is deposited.

[0314] exist Figure 3 and 4 In this process, under conditions that effectively induce silicon deposition within the pores of porous particles, a silicon precursor is injected into the reactor, and the pressure is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 5% of the target silicon content, the calculated silicon precursor conversion rate remains at the target silicon precursor conversion rate. After depositing 60% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 90% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate until 100% of the target silicon content is deposited.

[0315] exist Figure 5 and 6 In this process, under conditions that effectively induce silicon deposition within the pores of porous particles, a silicon precursor is injected into the reactor, and the pressure is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 5% of the target silicon content, the calculated silicon precursor conversion rate remains at the target silicon precursor conversion rate. After depositing 60% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate until 100% of the target silicon content is deposited.

[0316] exist Figure 7 and 8 In this process, under conditions that effectively induce silicon deposition within the pores of porous particles, a silicon precursor is injected into the reactor, and the pressure is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 5% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate until 100% of the target silicon content is deposited.

[0317] exist Figure 9 and 10 In this process, under conditions that effectively induce silicon deposition within the pores of porous particles, silicon precursors are injected into the reactor at a pressure where the calculated silicon precursor conversion rate reaches the target silicon precursor conversion rate. After depositing 70% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate. After depositing 90% of the target silicon content, the calculated silicon precursor conversion rate is lower than the target silicon precursor conversion rate, and the pressure in the reactor is increased to raise the calculated silicon precursor conversion rate to the target silicon precursor conversion rate until the target silicon content is deposited to 100%.

Claims

1. A method for preparing composite particles, the method comprising the following steps: (a) Providing multiple porous particles in the reactor; (b) Contact the plurality of porous particles with the silicon precursor gas under conditions that effectively induce silicon deposition in the pores of the porous particles; (c) Measure the composition of the exhaust gas emitted from the reactor; (d) Detect changes in the composition of the exhaust gas; (e) In response to a detected change in the composition of the exhaust gas, at least one gas outlet of the reactor is adjusted to adjust the flow rate of the exhaust gas, thereby increasing the pressure in the reactor, and silicon is deposited in the pores of the porous particles under the adjusted pressure. This provides composite particles comprising a porous particle framework and silicon within the pores of the porous particle framework. During steps (b) to (e), the silicon precursor gas is continuously introduced into the reactor.

2. The method of claim 1, wherein the pressure in the reactor is increased in response to the detection of an increase in the concentration of silicon precursor in the exhaust gas.

3. The method according to any of the preceding claims, wherein in response to detecting a decrease in the concentration of byproduct gas in the exhaust gas, the pressure in the reactor is increased, optionally wherein the byproduct gas is hydrogen.

4. The method according to any of the preceding claims, wherein the porous particles are mechanically agitated during steps (b) to (e), preferably wherein the porous particles are continuously mechanically agitated during steps (b) to (e), and more preferably wherein the porous particles are mechanically fluidized during steps (b) to (e).

5. The method according to any of the preceding claims, wherein step (d) further comprises: Calculate the conversion rate of the silicon precursor; The calculated silicon precursor conversion rate is compared with the target silicon precursor conversion rate; as well as It is determined that the calculated silicon precursor conversion rate is less than the target silicon precursor conversion rate; Step (e) further includes increasing the pressure in the reactor to increase the silicon precursor conversion rate to at least the target silicon precursor conversion rate.

6. The method of claim 5, wherein the target silicon precursor conversion rate is at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97%, or at least 99%, or 100%.

7. The method according to claim 5 or 6, wherein the pressure in the reactor is increased by at least [50 kPa × ΔX], where ΔX represents the difference between the calculated silicon precursor conversion rate in percentage and the target silicon precursor conversion rate in percentage, or the pressure in the reactor is increased by at least [60 kPa × ΔX], or the pressure in the reactor is increased by at least [70 kPa × ΔX], or the pressure in the reactor is increased by at least [80 kPa × ΔX], or the pressure in the reactor is increased by at least [90 kPa × ΔX], or the pressure in the reactor is increased by at least [100 kPa × ΔX].

8. The method according to any one of claims 5 to 7, wherein the pressure in the reactor is increased by no more than [3000 kPa × ΔX], where ΔX represents the difference between the calculated silicon precursor conversion rate in percentage and the target silicon precursor conversion rate in percentage, or the pressure in the reactor is increased by no more than [2000 kPa × ΔX], or the pressure in the reactor is increased by no more than [1000 kPa × ΔX], or the pressure in the reactor is increased by no more than [500 kPa × ΔX], or the pressure in the reactor is increased by no more than [400 kPa × ΔX], or the pressure in the reactor is increased by no more than [300 kPa × ΔX], or the pressure in the reactor is increased by no more than [200 kPa × ΔX].

9. The method according to any of the preceding claims, wherein step (d) further comprises: Calculate the partial pressure of the silicon precursor in the reactor; The calculated silicon precursor partial voltage is compared with the target silicon precursor partial voltage. as well as It is determined that the calculated partial voltage is less than the partial voltage of the target silicon precursor; Furthermore, step (e) also includes increasing the pressure in the reactor such that the partial pressure of the silicon precursor is increased to at least the target partial pressure of the silicon precursor.

10. The method of claim 9, wherein the target silicon precursor partial pressure is at least 10 kPa, or at least 20 kPa, or at least 30 kPa, or at least 40 kPa, or at least 50 kPa.

11. The method according to claim 9 or 10, wherein the target silicon precursor partial pressure is no more than 5000 kPa, or no more than 4000 kPa, or no more than 3000 kPa, or no more than 2000 kPa, or no more than 1600 kPa, or no more than 1500 kPa, or no more than 1200 kPa, or no more than 1000 kPa, or no more than 900 kPa, or no more than 800 kPa, or no more than 700 kPa, or no more than 600 kPa, or no more than 500 kPa, or no more than 400 kPa, or no more than 300 kPa, or no more than 250 kPa, or no more than 200 kPa, or no more than 150 kPa.

12. The method according to any of the preceding claims, wherein the pressure in step (e) is at least 10%, or at least 20%, or at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% higher than the pressure in step (b).

13. The method according to any of the preceding claims, wherein the pressure in step (e) is not more than 5000%, or not more than 4000%, or not more than 3000%, or not more than 2000%, or not more than 1000%, or not more than 900%, or not more than 800%, or not more than 700%, or not more than 600%, or not more than 500%, or not more than 400%, or not more than 300%, or not more than 175%, or not more than 150%, or not more than 125%, or not more than 100% higher than the pressure in step (b).

14. The method according to any of the preceding claims, wherein the pressure in step (b) and / or step (e) is at least atmospheric pressure (about 101 kPa), or at least 105 kPa, or at least 110 kPa, or at least 115 kPa, or at least 120 kPa, or at least 150 kPa, or at least 200 kPa, or at least 250 kPa, or at least 300 kPa, or at least 400 kPa, or at least 500 kPa, or at least 600 kPa.

15. The method according to any of the preceding claims, wherein the pressure in step (b) and / or step (e) is not more than 5000 kPa, or not more than 4000 kPa, or not more than 3000 kPa, or not more than 2000 kPa, or not more than 1600 kPa, or not more than 1500 kPa, or not more than 1200 kPa, or not more than 1000 kPa, or not more than 900 kPa, or not more than 800 kPa.

16. The method according to claim 14 or 15, wherein the pressure in steps (b) and (d) is at least 150 kPa, and the reactor is a stirred tank reactor.

17. The method according to any of the preceding claims, wherein the composite particles comprise a target silicon content, and 5% to 95% of the target silicon content is deposited in step (b).

18. The method of claim 17, wherein the target silicon content is at least 26% by weight of silicon, or at least 28% by weight of silicon, or at least 30% by weight of silicon, or at least 32% by weight of silicon, or at least 34% by weight of silicon, or at least 36% by weight of silicon, or at least 38% by weight of silicon, or at least 40% by weight of silicon, or at least 42% by weight of silicon, or at least 44% by weight of silicon.

19. The method according to claim 17 or 18, wherein the target silicon content is no more than 70% by weight of silicon, or no more than 65% by weight of silicon, or no more than 62% by weight of silicon, or no more than 60% by weight of silicon, or no more than 58% by weight of silicon, or no more than 56% by weight of silicon, or no more than 54% by weight of silicon.

20. The method according to any one of claims 17 to 19, wherein in step (b) at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 45%, or at least 50%, or at least 55%, or at least 60%, or at least 65%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90% of the target silicon content is deposited.

21. The method according to any one of claims 17 to 20, wherein in step (b) the content of the target silicon deposited is not more than 90%, or not more than 85%, or not more than 80%, or not more than 75%, or not more than 70%, or not more than 65%, or not more than 60%, or not more than 55%, or not more than 50%, or not more than 45%, or not more than 40%, or not more than 35%, or not more than 30%, or not more than 25%, or not more than 20%, or not more than 15%, or not more than 10%.

22. The method according to any of the preceding claims, wherein the ratio of the volume of the porous particles to the volume of the reactor in step (a) is at least 20 cm³. 3 Reactor volume per liter (cm³) 3 / L RV ), or at least 50 cm 3 / L RV or at least 80 cm 3 / L RV or at least 100 cm 3 / L RV or at least 150 cm 3 / L RV or at least 200 cm 3 / L RV or at least 250 cm 3 / L RV or at least 300 cm 3 / L RV or at least 400 cm 3 / L RV or at least 500 cm 3 / L RV or at least 600 cm 3 / L RV or at least 700 cm 3 / L RV or at least 800 cm 3 / L RV or at least 900 cm 3 / L RV .

23. The method according to any of the preceding claims, wherein the bed depth of the porous particles in the reactor in step (a) is at least 11 cm, or at least 15 cm, or at least 20 cm, or at least 25 cm, or at least 30 cm.

24. The method according to any of the preceding claims, wherein the ratio of the inner surface area of ​​the reactor to the mass of the porous particles in the reactor in step (a) is not more than 1 m². 2 / kg, or not exceeding 0.9 m 2 / kg, or not exceeding 0.8 m 2 / kg, or not exceeding 0.7 m 2 / kg, or not exceeding 0.6 m 2 / kg, or not exceeding 0.5 m 2 / kg, or not exceeding 0.4 m 2 / kg, or not exceeding 0.3 m 2 / kg.

25. The method according to any of the preceding claims, wherein the flow rate of the silicon precursor gas into the reactor is maintained during steps (b) to (e).

26. The method of claim 25, wherein the percentage deviation of the flow rate of the silicon precursor gas into the reactor is no more than 18%, or no more than 15%, or no more than 10%, or no more than 5%, or no more than 3%, or no more than 2%, or no more than 1%.

27. The method according to any of the preceding claims, wherein during steps (b) to (e), the flow rate of the silicon precursor gas flowing into the reactor, measured in grams of silicon per minute per kilogram of porous particles in the silicon precursor, is 0.2 to 25 g / min. -1 kg -1 or 0.5 to 20 gmin -1 kg -1 or 1 to 15 gmin -1 kg -1 or 1 to 14 gmin -1 kg -1 or 1 to 13 gmin -1 kg -1 or 1 to 12 gmin -1 kg -1 or 2 to 12 gmin -1 kg -1 or 3 to 12 gmin -1 kg -1 or 3 to 11 gmin - 1 kg -1 .

28. The method of claim 27, wherein during steps (b) to (e), the flow rate of the silicon precursor gas flowing into the reactor, measured in grams of silicon per minute per kilogram of porous particles in the silicon precursor, is 0.2 to 5 g / min. - 1 kg -1 or 0.2 to 4 gmin -1 kg -1 or 0.2 to 3 gmin -1 kg -1 .

29. The method according to any of the preceding claims, wherein during steps (b) to (e), the silicon content in the silicon precursor is measured in grams per minute per liter of reactor volume (g / min). -1 / L RV The flow rate of the silicon precursor gas flowing into the reactor, expressed in units of 0.03 to 40 g / min, is [missing information]. -1 / L RV , or 0.04 to 35 gmin -1 / L RV or 0.05 to 30 gmin -1 / L RV , or 0.06 to 25 gmin -1 / L RV or 0.07 to 20 gmin -1 / L RV , or 0.08 to 15 gmin -1 / L RV or 0.09 to 10 gmin -1 / L RV or 0.1 to 5 gmin -1 / L RV or 0.1 to 1 gmin -1 / L RV or 0.15 to 1 gmin -1 / L RV or 0.15 to 0.95 gmin -1 / L RV , or 0.2 to 0.95 gmin -1 / L RV , or 0.2 to 0.9 gmin -1 / L RV .

30. The method according to any of the preceding claims, wherein the temperature during steps (b) to (e) is in the range of not more than 50°C, or not more than 40°C, or not more than 30°C, or not more than 20°C, or not more than 10°C.

31. The method according to any of the preceding claims, wherein the temperature during steps (b) to (e) is maintained at 340 to 500°C, or 350 to 500°C, or 350 to 480°C, or 350 to 450°C, or 350 to 420°C, or 340 to 400°C, or 340 to 395°C, or 340 to 390°C, or 345 to 400°C, or 345 to 395°C, or 345 to 390°C, or 350 to 400°C, or 350 to 395°C, or 350 to 390°C, or 350 to 385°C, or 350 to 380°C, or 350 to 380°C, or 3 The temperature range is 55 to 400°C, or 355 to 395°C, or 355 to 390°C, or 355 to 385°C, or 355 to 380°C, or 360 to 400°C, or 360 to 395°C, or 360 to 390°C, or 360 to 385°C, or 360 to 380°C, or 365 to 400°C, or 365 to 395°C, or 365 to 390°C, or 365 to 385°C, or 365 to 380°C, or 370 to 400°C, or 370 to 395°C, or 370 to 390°C, or 370 to 385°C, or 375 to 385°C.

32. The method according to any of the preceding claims, wherein the concentration of silicon precursor in the silicon precursor gas introduced into the reactor during steps (b) to (e) is in the range of not more than 20% by volume, or not more than 10% by volume, or not more than 5% by volume, or not more than 3% by volume, or not more than 2% by volume, or not more than 1% by volume.

33. The method according to any of the preceding claims, wherein the silicon precursor gas introduced into the reactor during steps (b) to (e) comprises at least 20 vol% silicon precursor, or comprises at least 30 vol%, or at least 40 vol%, or at least 50 vol%, or at least 60 vol%, or at least 70 vol%, or at least 80 vol%, or at least 90 vol%, or at least 95 vol%, or at least 98 vol%, or at least 99 vol%, or at least 99 vol%, or at least 99.9 vol%, or at least 99.99 vol%, or 100 vol% silicon precursor.

34. The method according to any of the preceding claims, wherein the silicon precursor is selected from silane (SiH4), silane (Si2H6), propane (Si3H8), methylsilane, dimethylsilane, and chlorosilane.

35. The method according to any of the preceding claims, wherein steps (c) to (e) are repeated more than once.

36. The method according to any one of the preceding claims, the method further comprising: The composite particles are brought into contact with the carbon precursor gas under conditions that effectively induce carbon deposition within the pores and / or on the surface of the composite particles.

37. The method according to any one of the preceding claims, the method further comprising: The composite particles are brought into contact with the passivating agent under conditions that effectively passivate the composite particles.

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