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 pressure reactor; (b) contacting the plurality of porous particles with a silicon precursor gas under conditions effective to cause deposition of silicon in the pores of the porous particles to provide composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton; and (c) during step (b), recovering exhaust gas from the pressure reactor, wherein the silicon precursor gas is continuously introduced into the pressure reactor.

Description

[Technical field]

[0001] The present invention relates to a method for making silicon-containing composite particles suitable for use as anode active materials 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 generally includes a metal current collector with a layer of an electroactive material, defined herein as a material capable of inserting and releasing lithium ions during charging and discharging of the battery. The terms "cathode" and "anode" are used herein in the sense that the battery is loaded such that the anode is the negative electrode. When the LIB is charged, lithium ions are transported from the cathode through the electrolyte to the anode and inserted into the electroactive material of the anode as inserted lithium atoms. The term "battery" is used herein to refer to both devices containing a single lithium ion battery and devices containing multiple connected lithium ion batteries.

[0003] Since their development in the 1980s and 1990s, LIBs have been widely applied in portable electronic devices. The recent development of electric and hybrid vehicles has created significant new LIB markets, and renewable energy sources are creating additional demand for on-grid energy storage, which can be met, at least in part, by LIB farms. Overall, global production of LIBs is expected to grow from approximately 290 GWh in 2018 to over 2000 GWh in 2028.

[0004] In parallel with the growth of total storage capacity, there is great interest in improving the gravimetric and / or volumetric capacity of rechargeable metal-ion batteries so that the same energy storage is realized with a smaller battery mass and / or a smaller battery volume. Conventional LIBs use graphite as the anode electroactive material. Graphite anodes can accommodate up to one lithium atom for every six carbon atoms, resulting in a maximum theoretical specific capacity of 372 mAh / g in lithium-ion batteries, with practical capacities somewhat lower (approximately 340 mAh / g to 360 mAh / g).

[0005] Silicon is a promising alternative to graphite because of its extremely high capacity relative to lithium (see, for example, Non-Patent Document 1). Silicon has a theoretical maximum specific capacity of about 3600 mAh / g (Li 15 The lithium-ion battery is based on the silicon-based lithium-ion battery (Si4). However, when lithium is intercalated into bulk silicon, the silicon material expands to 400% of its original volume, which can lead to battery failure. Repeated charge-discharge cycling induces significant mechanical stresses, resulting in the fracture and delamination of the silicon. The formation of a solid electrolyte interface (SEI) layer on the silicon surface consumes the electrolyte, and the newly exposed silicon surface on the fractured surface leads to further electrolyte decomposition, an increase in the thickness of the SEI layer, and irreversible lithium consumption. These failure mechanisms collectively result in an unacceptable loss of electrochemical capacity over successive charge-discharge cycles.

[0006] The applicant has previously reported the development of a class of electroactive materials having a composite structure in which an electroactive material, such as silicon, is deposited within the pore network of a highly porous conductive particulate material, such as a porous carbon material (see U.S. Pat. No. 5,399,323 and U.S. Pat. No. 5,499,496). The silicon in these materials is finely divided into individual silicon structures having dimensions on the order of a few nanometers or less, and therefore experiences minimal stress and strain during charging and discharging. The silicon is confined to the pore volume of the porous material, minimizing the exposure of the silicon surface to the electrolyte and effectively limiting the extent of SEI formation. As a result, these materials exhibit good reversible capacity retention over many charge-discharge cycles.

[0007] The materials described in US Pat. No. 5,399,433 and US Pat. No. 5,499,446 are synthesized by chemical vapor infiltration (CVI) in different reactor systems (static, rotating and FBR). Porous conductive particles are contacted with a silicon precursor, typically silane gas, at atmospheric pressure and temperatures between 400° C. and 700° C. Although the reaction rates at these temperatures are high, the silicon precursor molecules must traverse a tortuous path to access the pore spaces, which are only a few nanometers in diameter. This means that to obtain uniform infiltration in such reactor systems, the reaction temperature must be relatively high to avoid mass transfer becoming the rate-limiting step. Furthermore, the silicon precursor generally needs to be used at high dilution in an inert gas. Too high a concentration of silicon precursor leads to rapid and uncontrolled deposition of silicon deposits into the outermost pores, which then blocks access to most of the available pore volume. As a result, the deposited silicon does not have the fine structure associated with deposition into narrow pores, but is rough and exposed, and therefore shows poor cycling behavior. However, the use of low concentrations of silicon precursor means that reaction times to achieve the required silicon loading in the composite particles are relatively long, reducing throughput.

[0008] Systems operated by batch injection of silicon precursor have another disadvantage. To obtain composite particles with the required silicon content, several cycles of CVI deposition are required. At the beginning of each cycle, a certain injection of silicon precursor is introduced into the reactor. Generally, the reactor temperature decreases as the silicon precursor is added, making it necessary to heat the reactor to bring the feedstock back up to the reaction temperature. It is also necessary to remove by-product gases after each cycle. Therefore, the total production time of composite particles is long and the throughput of such systems is insufficient.

[0009] Therefore, these systems are not suitable for scale-up and it is difficult to produce large amounts of material. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2020 / 095067 [Patent Document 2] International Publication No. 2020 / 128495 [Non-patent literature]

[0011] [Non-Patent Document 1] Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al. in Adv. Mater. 1998, 10, No. 10 Summary of the Invention [Problem to be solved by the invention]

[0012] Thus, there is a need in the art for improved methods of preparing silicon-containing composite particles suitable for use as electroactive materials in LIBs, and in particular for methods of preparing such composite particles on a large scale, with high throughput, while maintaining product quality. [Means for solving the problem]

[0013] In a first aspect, the present invention provides a method of preparing a composite particle, the method comprising: (a) providing a plurality of porous particles in a pressure reactor; (b) contacting a plurality of porous particles with a silicon precursor gas under conditions effective to cause deposition of silicon in the pores of the porous particles to provide composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particles; (c) recovering exhaust gas from the pressure reactor during said contacting; wherein a silicon precursor gas is continuously introduced into the pressure reactor.

[0014] The present invention therefore generally relates to a method for preparing a composite particulate material, in which nanoscale silicon domains are deposited in the pore network of a porous particle by a process of chemical vapor infiltration, i.e., by pyrolysis of a silicon-containing precursor compound. The composite particle thus comprises a first component in the form of a porous particle skeleton derived from the porous particle, and a second component in the form of a plurality of nanoscale silicon domains arranged within the pore structure of the porous particle skeleton. As used herein, the term "nanoscale silicon domain" refers to a nanoscale body of elemental silicon having a maximum dimension determined by the location of silicon within the micropores and / or mesopores of the porous particle.

[0015] Operating the pressure reactor under these conditions means that the CVI deposition proceeds under conditions in which new silicon precursor is added before the by-products are completely removed from the system. Thus, as silicon precursor gas is continuously added to the reactor, the silicon precursor gas and the by-products are mixed, resulting in a consistent concentration of silicon precursor. Compared to a system operated by batch injection of silicon precursor gas, the porous particles are exposed to a more consistent concentration of silicon precursor throughout the deposition.

[0016] Since CVI deposition occurs in a consistent but relatively dilute phase, it is expected to occur at a slower rate compared to systems operated by batch injection of silicon precursor gas.However, the pressure and temperature gradients in the pressure reactor are eliminated, and therefore the degree of control over the deposition reaction is enhanced, since the porous particles are exposed to more consistent conditions, including the temperature, pressure and concentration of silicon precursor.Increased control of reaction conditions can lead to better control of the important properties of the composite particles, including silicon content, surface area and amount of crude silicon.

[0017] Additionally, the method is believed to provide increased throughput by reducing production downtime associated with pressure and temperature fluctuations inherent in systems operated by batch input of silicon precursor gas, while also allowing for the processing of large batches of composite particles.

[0018] operation The process is operated continuously for the silicon precursor gas and batchwise for the porous particles, and thus the pressure reactor is operated as a semi-batch reactor.

[0019] In this specification, the term continuous is used to distinguish it from batch type operation. In batch operation, in the first step, a batch of starting material (porous particles) is added to the reactor, the reaction is allowed to proceed for a specified period of time, and then a batch of product (composite particles) is withdrawn from the reactor. In continuous operation, the introduction of starting material (silicon precursor) into the reactor and optionally the withdrawal of product (exhaust gas) are carried out continuously while the reaction is proceeding.

[0020] In principle, continuous operation does not exclude the possibility of bias in the flow rate of silicon precursor gas into the reactor or the exhaust gas from the reactor. For example, a continuous reactor may be operated in a pulsed manner. For example, the flow rate of silicon precursor gas into the pressure reactor may be reduced to assist in the recovery of exhaust gas from the pressure reactor. Alternatively, the silicon precursor gas may be introduced into the pressure reactor at a constant pressure.

[0021] The exhaust gas recovery may be operated continuously, so that both the supply of silicon precursor gas and the recovery of exhaust gas from the reactor may be performed continuously and simultaneously while the reaction is in progress.

[0022] Alternatively, the recovery of exhaust gas from the pressure reactor may be operated semi-continuously, which as used herein means that the exhaust gas is intermittently removed.

[0023] Semi-continuous recovery of exhaust gas from the pressure reactor can be achieved by opening and closing at least one gas outlet of the pressure reactor at a predetermined frequency, for example at least once per minute, or twice per minute. The at least one gas outlet may be operated at a frequency of 20 times per minute or less, or 15 times per minute or less, or 10 times per minute or less.

[0024] Additionally or alternatively, the recovery of exhaust gas from the pressure reactor may be performed by at least one valve that opens when the pressure in the pressure reactor exceeds a predetermined pressure, which may be 15000 kPa, or 10000 kPa, or 5000 kPa, or 2000 kPa, or 1900 kPa, or 1800 kPa, or 1700 kPa, or 1600 kPa, or 1500 kPa, or 1400 kPa, or 1300 kPa, or 1200 kPa, or 1100 kPa, or 1000 kPa, or 900 kPa, or 800 kPa, or 700 kPa, or 600 kPa.

[0025] Additionally or alternatively, the exhaust gas may be recovered from the pressure reactor by a membrane separator that allows at least one by-product gas to preferentially exit the pressure reactor and prevents the silicon precursor from exiting the pressure reactor.

[0026] The method may include controlling the back pressure to the pressure reactor. This can be accomplished using a flow regulating device to regulate the flow rate of the silicon precursor gas. Suitable flow regulating devices include, but are not limited to, back pressure regulators, orifices, or other fast acting mechanisms.

[0027] The space time of the silicon precursor gas in contact with the porous particles in step (b) can be maintained in the range of 1 to 60 minutes, or 2 to 45 minutes, or 3 to 30 minutes, or 4 to 25 minutes, or 5 to 20 minutes. These space times are believed to be significantly longer than the space time of the silicon precursor gas in a fluidized bed reactor process, because in such a process the silicon precursor gas must be supplied at a sufficient rate to fluidize the porous particles. Increasing the space time of the silicon precursor gas in contact with the porous particles is believed to increase the conversion rate of the silicon precursor.

[0028] The space time of the silicon precursor gas in the pressure reactor is calculated as the reactor volume in liters divided by the flow rate of the silicon precursor gas (total gas including the silicon precursor and any dilution gases) into the pressure reactor in 1 / min at the process conditions.

[0029] The space velocity of the silicon precursor relative to the reactor volume during step (b) is at least 0.02 min -1 , or at least 0.025 minutes -1 , or at least 0.03 minutes -1 , or at least 0.035 minutes -1 , or at least 0.04 minutes -1 , or at least 0.045 minutes -1, or at least 0.05 minutes -1 , or at least 0.06 minutes -1 , or at least 0.07 minutes -1 , or at least 0.08 minutes -1 , or at least 0.09 minutes -1 , or at least 0.1 min -1 , or at least 0.15 minutes -1 , or at least 0.2 minutes -1 , or at least 0.25 minutes -1 , or at least 0.3 minutes -1 , or at least 0.35 minutes -1 , or at least 0.4 minutes -1 It may be.

[0030] The space velocity of the silicon precursor relative to the reactor volume during step (b) is 0.8 min -1 Less than or equal to 0.75 minutes -1 Less than or equal to 0.7 minutes -1 Less than or equal to 0.65 minutes -1 Less than or equal to 0.6 minutes -1 Less than or equal to 0.55 minutes -1 Less than or equal to 0.5 minutes -1 These space velocities are believed to be significantly lower than the space velocities of the silicon precursor gas in fluidized bed reactor processes, because in such processes the silicon precursor gas must be supplied at a velocity sufficient to fluidize the porous particles.

[0031] The space velocity of the silicon precursor relative to the reactor volume is calculated as the flow rate of the silicon precursor in 1 / min into the pressure reactor at the process conditions divided by the reactor volume in liters. When the silicon precursor is used as a diluent, the space velocity of the silicon precursor relative to the reactor volume is calculated as the flow rate of the silicon precursor gas (total gas including the silicon precursor and any diluent gas) in 1 / min into the pressure reactor at the process conditions divided by the reactor volume in liters multiplied by the volume fraction (volume %) of the silicon precursor in the silicon precursor gas introduced into the pressure reactor.

[0032] The conditions in step (b) preferably include a combination of controlled space time of the silicon precursor gas in contact with the porous particles and space velocity of the silicon precursor relative to the reactor volume, which defines a set of conditions that increases the time the silicon precursor is in contact with the porous particles (e.g., compared to a fluidized bed reactor) and therefore increases the conversion rate of the silicon precursor.

[0033] The space time of the silicon precursor gas in contact with the porous particles in step (b) can be maintained in the range of 1 minute to 60 minutes, and the space velocity of the silicon precursor relative to the reactor volume in step (b) can be at least 0.02 min -1 It may be.

[0034] The space time of the silicon precursor gas in contact with the porous particles in step (b) may be maintained in the range of 2 minutes to 45 minutes, and the space velocity of the silicon precursor relative to the reactor volume during step (b) is at least 0.025 minutes. -1 may be also.

[0035] The space time of the silicon precursor gas in contact with the porous particles in step (b) may be maintained in the range of 3 minutes to 30 minutes, and the space velocity of the silicon precursor relative to the reactor volume during step (b) is at least 0.03 minutes. -1 may be also.

[0036] The space time of the silicon precursor gas in contact with the porous particles in step (b) may be maintained in the range of 4 minutes to 25 minutes, and the space velocity of the silicon precursor relative to the reactor volume during step (b) is at least 0.035 minutes. -1 may be also.

[0037] The space time of the silicon precursor gas in contact with the porous particles in step (b) may be maintained in the range of 5 minutes to 20 minutes, and the space velocity of the silicon precursor relative to the reactor volume during step (b) is at least 0.04 min -1 may be also.

[0038] The method may include interrupting the deposition of silicon and recovering the composite particles from the pressure reactor. Interrupting the deposition of silicon may include interrupting the introduction of silicon precursor gas into the pressure reactor and / or reducing the pressure in the pressure 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.

[0039] Step (b) may comprise agitating the porous particles. Preferably, step (b) comprises continuously agitating the porous particles. Preferably, step (b) comprises mechanically agitating the porous particles. Preferably, step (b) comprises continuously mechanically agitating the porous particles. Preferably, the agitation is performed by a high shear mixer.

[0040] The pressure reactor preferably includes an agitator for agitating the porous particles during said contacting. Any suitable agitator can be used, such as a turbine agitator, a paddle agitator, an anchor agitator, a propeller agitator, or a helical agitator. The agitator is preferably a high shear mixer.

[0041] Mechanically stirring the porous particles decouples the supply of silicon precursor gas from the stirring of the porous particles. With a fluidized bed reactor, the stirring of the porous particles can only be achieved by supplying the silicon precursor gas at a rate sufficient to fluidize the porous particles. Therefore, the use of mechanical stirring allows the process to work with a lower rate of silicon precursor gas than the fluidized bed reactor process, and also allows the space time of the silicon precursor to be adjusted independently of the stirring.

[0042] Continuous mechanical agitation allows for an increase in the porous particle loading per liter of reactor while maintaining uniform silicon deposition. In technologies that rely on a relatively high ratio of reactor surface area to porous particle mass, there is a temperature gradient across the thickness of the porous particle bed, thus limiting the effective porous particle bed thickness at which silicon infiltration is uniform. As a result, the maximum powder bed thickness and porous particle loading are limited. In systems with continuous mechanical agitation, the continuous movement and recirculation of the porous particles within the reactor allows a greater number of porous particles to come into contact with the reactor surface, improving the uniformity of heat transfer and reducing the temperature gradient of the porous particles. This allows for a greater loading of porous particles per reactor volume.

[0043] The use of a high shear mixer provides continuous mechanical agitation, effectively breaking down the agglomerates that inevitably form due to the cohesive nature of the porous particles, thus addressing both heat and mass transfer challenges.

[0044] The temperature in the pressure reactor in step (b) is 340°C to 500°C, or 350°C to 500°C, or 350°C to 480°C, or 350°C to 450°C, or 350°C to 420°C, or 340°C to 400°C, or 340°C to 395°C, or 340°C to 390°C, or 345°C to 400°C, or 345°C to 395°C, or 345°C to 390°C, or 350°C to 400°C, or 350°C to 395°C, or 350°C to 390°C, or 350°C to 385°C, or 350°C to 380°C, or 355°C to 400°C, or 355°C to 390°C. 5°C, or 355°C to 390°C, or 355°C to 385°C, or 355°C to 380°C, or 360°C to 400°C, or 360°C to 395°C, or 360°C to 390°C, or 360°C to 385°C, or 360°C to 380°C, or 365°C to 400°C, or 365°C to 395°C, or 365°C to 390°C, or 365°C to 385°C, or 365°C to 380°C, or 370°C to 400°C, or 370°C to 395°C, or 370°C to 390°C, or 370°C to 385°C, or 370°C to 380°C. Operation at higher temperatures in a pressure reactor increases the reaction rate, resulting in faster deposition rates. The temperature in the pressure reactor during step (b) may be at least 340° C., or at least 350° C., or at least 355° C., or at least 360° C. The temperature in the pressure reactor during step (b) may be 500° C. or less, or 480° C. or less, or 450° C. or less, or 420° C. or less, or 400° C. or less, or 395° C. or less, or 390° C. or less, or 385° C. or less, or 380° C. or less.

[0045] The method of the present invention is preferably operated under a regime in which the silicon precursor is fed to the pressure reactor in a high concentration or even in neat form. In order to control the reaction rate and to achieve a controlled penetration of the silicon precursor into the pore network of the porous particles, the reaction temperature in the pressure reactor is preferably 420°C or less, more preferably 410°C or less, more preferably 400°C or less, more preferably 395°C or less. The temperature range of 370°C to 395°C is particularly preferred.

[0046] Unless otherwise specified, all pressure values ​​disclosed herein are absolute pressure. The conditions in step (b) can include pressures in the range of 50 kPa to 15,000 kPa, or 50 kPa to 10,000 kPa, or 120 kPa to 5,000 kPa, or 150 kPa to 2,000 kPa, or 200 kPa to 1,600 kPa, or 250 kPa to 1,500 kPa, or 300 kPa to 1,200 kPa, or 400 kPa to 1,000 kPa, or 500 kPa to 900 kPa, or 600 kPa to 800 kPa.

[0047] The pressure in the pressure reactor during step (b) may be in the range of 50 kPa to 15000 kPa, or 50 kPa to 10000 kPa, or 50 kPa to 5000 kPa, or 50 kPa to 2000 kPa, or 50 kPa to 1600 kPa, or 50 kPa to 1000 kPa, or 50 kPa to 700 kPa, or 100 kPa to 700 kPa, or 100 kPa to 600 kPa.

[0048] The pressure in the pressure reactor in step (b) is preferably in the range of 600 kPa to 15000 kPa, or 600 kPa to 10000 kPa, or 600 kPa to 5000 kPa, or 600 kPa to 2000 kPa, or 600 kPa to 1600 kPa.

[0049] The pressure in the pressure reactor in step (b) is preferably in the range of 700 kPa to 15000 kPa, or 700 kPa to 10000 kPa, or 700 kPa to 5000 kPa, or 700 kPa to 2000 kPa, or 700 kPa to 1600 kPa.

[0050] The pressure in the pressure reactor in step (b) is preferably in the range of 1000 kPa to 15000 kPa, or 1000 kPa to 10000 kPa, or 1000 kPa to 5000 kPa, or 1000 kPa to 2000 kPa, or 1000 kPa to 1600 kPa.

[0051] The pressure in the pressure reactor in step (b) is preferably in the range of 150 kPa to 15,000 kPa, or 150 kPa to 10,000 kPa, or 150 kPa to 5,000 kPa, or 150 kPa to 2,000 kPa, or 150 kPa to 1900 kPa, or 150 kPa to 1800 kPa, or 150 kPa to 1700 kPa, or 150 kPa to 1600 kPa, or 150 kPa to 1500 kPa, or 150 kPa to 1400 kPa, or 150 kPa to 1300 kPa, or 150 kPa to 1200 kPa, or 150 kPa to 1100 kPa, or 150 kPa to 1000 kPa, or 150 kPa to 700 kPa, or 150 kPa to 600 kPa.

[0052] The pressure in the pressure reactor in step (b) is preferably in the range of 200 kPa to 5000 kPa, or 200 kPa to 4000 kPa, or 200 kPa to 3000 kPa, or 200 kPa to 2000 kPa, or 600 kPa to 1800 kPa, or 700 kPa to 1800 kPa.

[0053] The pressure in the pressure reactor in step (b) is preferably in the range of 500 kPa to 3000 kPa, or 600 kPa to 3000 kPa, or 700 kPa to 3000 kPa, or 1000 kPa to 3000 kPa.

[0054] The pressure in the pressure reactor during step (b) is preferably in the range of 1300 kPa to 1700 kPa, or 1400 kPa to 1600 kPa, or 1450 kPa to 1550 kPa, or 1475 kPa to 1525 kPa.

[0055] The pressure in the pressure reactor during step (b) may be at least 50 kPa, or at least 100 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, or at least 700 kPa, or at least 800 kPa, or at least 900 kPa, or at least 1000 kPa. It is preferred that the pressure in the pressure reactor during step (b) is at least 600 kPa, or at least 700 kPa, or at least 1000 kPa.

[0056] The pressure in the pressure reactor during step (b) may be 15000 kPa or less, or 10000 kPa or less, or 5000 kPa or less, or 4000 kPa or less, or 3000 kPa or less, or 2000 kPa or less, or 1900 kPa or less, or 1800 kPa or less, or 1700 kPa or less, or 1600 kPa or less, or 1500 kPa or less, or 1400 kPa or less, or 1300 kPa or less, or 1200 kPa or less, or 1100 kPa or less, or 1000 kPa or less, or 700 kPa or less, or 600 kPa or less. The pressure in the pressure reactor during step (b) is preferably 15000 kPa or less, or 10000 kPa or less, or 5000 kPa or less, or 2000 kPa or less, or 1600 kPa or less.

[0057] The advantage of operating at elevated pressure is that the mass transfer limitation on the reaction rate is reduced, and the silicon precursor gas can easily penetrate into the pore network of the porous particles. Operating at higher pressure also increases the residence time of the silicon precursor gas, thus increasing the conversion of the silicon precursor. The disadvantage of operating at too high pressure is that the pressure negatively affects the thermodynamic equilibrium of silicon decomposition, thus limiting the extent of reaction. The advantage of operating at pressures below 700 kPa is that no specialized equipment is required, thus reducing costs.

[0058] In order to prevent uncontrolled reaction, it is preferable to decrease the temperature in the pressure reactor as the pressure increases. In particular, when the pressure in the pressure reactor exceeds 100 kPa, the reaction temperature in the pressure reactor is preferably 450°C or less, more preferably 430°C or less, more preferably 420°C or less, more preferably 410°C or less, more preferably 400°C or less, more preferably 395°C or less.

[0059] It is preferred that the temperature in the pressure reactor during step (b) is in the range of 340° C. to 500° C., and the pressure in the pressure reactor during step (b) is in the range of 600 kPa to 5000 kPa.

[0060] It is preferred that the temperature in the pressure reactor during step (b) is in the range of 360° C. to 390° C., and the pressure in the pressure reactor during step (b) is in the range of 600 kPa to 2000 kPa.

[0061] It is preferred that the temperature in the pressure reactor during step (b) is in the range of 360° C. to 385° C., and the pressure in the pressure reactor during step (b) is in the range of 700 kPa to 2000 kPa.

[0062] It is preferred that the temperature in the pressure reactor during step (b) is in the range of 360° C. to 380° C., and the pressure in the pressure reactor during step (b) is in the range of 1000 kPa to 2000 kPa.

[0063] During step (b), the molar fraction of the silicon precursor in the pressure reactor can be maintained in the range of 0.2 to 0.8 relative to the total moles of gaseous compounds in the pressure reactor, or 0.3 to 0.7, or 0.4 to 0.6 relative to the total moles of gaseous compounds in the pressure reactor.

[0064] The method may further comprise increasing or decreasing a flow rate of the silicon precursor gas and / or a flow rate of the exhaust gas during said contacting.

[0065] Control over the flow rate of the silicon precursor gas and / or exhaust gas can be achieved using Coriolis flow meters and controllers or other mass flow controllers used to measure mass flow rate and control the gas flow rate. Suitable valves for controlling the flow rate include, but are not limited to, needle valves, diaphragm valves, and globe valves.

[0066] In step (b), the linear gas velocity of the silicon precursor gas in the pressure reactor may be maintained in the range of 0.001 m / min to 0.4 m / min, or 0.005 m / min to 0.4 m / min, or 0.01 m / min to 0.4 m / min, or 0.02 m / min to 0.4 m / min, or 0.03 m / min to 0.4 m / min, or 0.04 m / min to 0.4 m / min, or 0.05 m / min to 0.4 m / min, or 0.06 m / min to 0.4 m / min, or 0.07 m / min to 0.4 m / min.

[0067] The linear gas velocity of the silicon precursor gas is m 3 The flow rate of silicon precursor gas (including silicon precursor and any dilution gas) into the pressure reactor in m / min is defined as 2 It is calculated as the linear gas velocity of the silicon precursor gas divided by the cross-sectional area of ​​the reactor in units, thus giving units of m / min. In a batch system, the silicon precursor gas is not actively flowing through the reactor (flow rate = 0 l / min), so the linear gas velocity of the silicon precursor gas is assumed to be 0 m / min. In a fluidized bed reactor, a linear gas velocity much higher than the above is generally required due to the minimum velocity to fluidize the porous particle bed.

[0068] Step (b) may include reducing the flow rate of the silicon precursor into the pressure reactor.

[0069] Step (b) may include adjusting a flow rate of the silicon precursor into the pressure reactor from an initial flow rate to an adjusted flow rate, where the adjusted flow rate is greater or less than the initial flow rate.

[0070] Step (c) may include measuring a concentration of the silicon precursor in the exhaust gas, detecting a change in the concentration of the silicon precursor in the exhaust gas, and adjusting a flow rate of the silicon precursor into the pressure reactor in step (b) in response to the detected change in the concentration of the silicon precursor in the exhaust gas.

[0071] Step (c) may include detecting an increase in the concentration of the silicon precursor in the exhaust gas and reducing the flow rate of the silicon precursor in step (b) into the pressure reactor in response to the detected increase in the concentration of the silicon precursor in the exhaust gas. The silicon precursor may be a silane.

[0072] Step (c) may include measuring a concentration of the by-product gas in the exhaust gas, detecting a change in the concentration of the by-product gas in the exhaust gas, and adjusting the flow rate of the silicon precursor into the pressure reactor in step (b) in response to the detected change in the concentration of the by-product gas in the exhaust gas.

[0073] Step (c) may include detecting a decrease in the concentration of the by-product gas in the exhaust gas, and reducing the flow rate of the silicon precursor into the pressure reactor in step (b) in response to the detected decrease in the concentration of the by-product gas in the exhaust gas, and optionally, the by-product gas is hydrogen. The by-product gas may be hydrogen. For example, when the silicon precursor is silane, disilane, or trisilane, hydrogen (H2) is produced as a by-product by the deposition reaction.

[0074] Techniques for measuring the concentration of silicon precursor and by-product gases in a gas are known to those skilled in the art, for example, FT-IR can be used.

[0075] Both the concentration of silicon precursor and the concentration of by-product gases in the exhaust gas may be measured, and the flow rate of silicon precursor into the pressure reactor may be adjusted accordingly.

[0076] The flow rate of the silicon precursor into the pressure reactor can be reduced by 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%.

[0077] The flow rate of the silicon precursor into the pressure reactor may be reduced after 50% of the target mass of silicon has been deposited, or after 60% of the target mass of silicon has been deposited, or after 70% of the target mass of silicon has been deposited, or after 80% of the target mass of silicon has been deposited, or after 90% of the target mass of silicon has been deposited.

[0078] The flow rate of the silicon precursor into the pressure reactor can be decreased while the absolute pressure in the reactor is kept constant.

[0079] As silicon CVI progresses, the pore volume available for silicon deposition in the porous particles decreases. It is believed that the deposition of crude silicon is influenced by the ratio of silicon precursor concentration to the pore volume available for deposition. Thus, if the flow rate of silicon precursor is kept constant during silicon CVI, the formation of crude silicon may increase as the available pore volume decreases. Therefore, it is preferable to decrease the flow rate of silicon precursor as silicon CVI progresses.

[0080] The mole fraction of the silicon precursor in the pressure reactor during step (b) may be maintained in the range of 0.2 to 0.8, or 0.3 to 0.7, or 0.4 to 0.6, relative to the total moles of gaseous compounds in the pressure reactor.

[0081] The method may further include controlling the flow rate of the silicon precursor gas into the pressure reactor and / or the flow rate of the exhaust gas recovered from the pressure reactor during the contacting to maintain a mole fraction of the silicon precursor in the pressure reactor in the range of 0.2 to 0.8, relative to the total moles of gaseous compounds in the pressure reactor, or 0.3 to 0.7, or 0.4 to 0.6, relative to the total moles of gaseous compounds in the pressure reactor.

[0082] The method may further include controlling the flow rate of silicon precursor gas into the pressure reactor and / or the flow rate of exhaust gas recovered from the pressure reactor during the contacting to maintain the pressure in the pressure reactor in the range of, optionally, 50 kPa to 15,000 kPa, or 50 kPa to 10,000 kPa, or 50 kPa to 5,000 kPa, or 50 kPa to 2,000 kPa, or 50 kPa to 1,600 kPa, or 50 kPa to 1,000 kPa, or 50 kPa to 700 kPa, or 100 kPa to 700 kPa, or 100 kPa to 600 kPa.

[0083] The method comprises adjusting the pressure in the pressure reactor to 150 kPa to 15,000 kPa, or 150 kPa to 10,000 kPa, or 150 kPa to 5,000 kPa, or 150 kPa to 2,000 kPa, or 150 kPa to 1900 kPa, or 150 kPa to 1800 kPa, or 150 kPa to 1700 kPa, or 150 kPa to 1600 kPa, or 150 kPa to 1500 kPa, or 150 kPa to 1400 kPa, or 15 The method may further include, during the contacting, (i) controlling the flow rate of the silicon precursor gas into the pressure reactor, and / or (ii) controlling the flow rate of the exhaust gas recovered from the pressure reactor to maintain a pressure in the range of 0 kPa to 1300 kPa, or 150 kPa to 1200 kPa, or 150 kPa to 1100 kPa, or 150 kPa to 1000 kPa, or 150 kPa to 700 kPa, or 150 kPa to 600 kPa.

[0084] The method preferably includes a step of controlling the flow rate of the silicon precursor gas into the pressure reactor and / or the flow rate of the exhaust gas recovered from the pressure reactor during the contacting, so as to maintain the pressure in the pressure reactor in the range of 600 kPa to 15,000 kPa, or 600 kPa to 10,000 kPa, or 600 kPa to 5,000 kPa, or 600 kPa to 2,000 kPa, or 600 kPa to 1,600 kPa.

[0085] The method preferably includes a step of controlling the flow rate of the silicon precursor gas into the pressure reactor and / or the flow rate of the exhaust gas recovered from the pressure reactor during the contacting, so as to maintain the pressure in the pressure reactor in the range of 700 kPa to 15,000 kPa, or 700 kPa to 10,000 kPa, or 700 kPa to 5,000 kPa, or 700 kPa to 2,000 kPa, or 700 kPa to 1,600 kPa.

[0086] The method preferably includes a step of controlling the flow rate of the silicon precursor gas into the pressure reactor and / or the flow rate of the exhaust gas recovered from the pressure reactor during the contacting so as to maintain the pressure in the pressure reactor in the range of 1000 kPa to 15000 kPa, or 1000 kPa to 10000 kPa, or 1000 kPa to 5000 kPa, or 1000 kPa to 2000 kPa, or 1000 kPa to 1600 kPa.

[0087] In another embodiment, the method includes controlling the flow rate of silicon precursor gas into the pressure reactor and / or the flow rate of exhaust gas recovered from the pressure reactor during said contacting to maintain a pressure in the pressure reactor in the range of 1300 kPa to 1700 kPa, or 1400 kPa to 1600 kPa, or 1450 kPa to 1550 kPa, or 1475 kPa to 1525 kPa.

[0088] During the contacting, the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to the mass of the porous particles in the pressure reactor in grams may range from 0.006 to 0.7.

[0089] During the contact, the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to the mass of the porous particles in the pressure reactor in grams may be in the range of 0.006 to 0.008. These ratios have the advantage that the conversion of the silicon precursor is higher compared to larger ratios. It is believed that a high level of conversion of the silicon precursor helps to obtain composite particles with a low degree of crude silicon formation. However, a lower ratio leads to unacceptably long reaction times.

[0090] Alternatively, during said contacting, the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to the mass of the porous particles in the pressure reactor in grams may range from 0.01 to 0.7. These ratios have the advantage that an excess of silicon precursor is maintained in the pressure reactor. At equilibrium between the silicon precursor and silicon + by-product(s), the high silicon precursor concentration drives the equilibrium towards silicon deposition. As mentioned above, high pressure in the pressure reactor reduces the silicon deposition rate. By maintaining an excess of silicon precursor in the pressure reactor, the reduced silicon deposition rate at high pressure is offset, thus maintaining the silicon deposition rate while providing the advantage of operating at high pressure. This also helps to reduce the synthesis time.

[0091] During the contact, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute into the pressure reactor to (the mass of the porous particles in the pressure reactor in grams x the internal free volume of the reactor in liters) may be in the range of 0.0002 to 0.025. During the contact, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute into the pressure reactor to (the mass of the porous particles in the pressure reactor in grams x the internal free volume of the reactor in liters) may be in the range of 0.0002 to 0.0003. Alternatively, during the contact, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute into the pressure reactor to (the mass of the porous particles in the pressure reactor in grams x the internal free volume of the reactor in liters) may be in the range of 0.0004 to 0.025. The internal free volume of the reactor refers to the volume that does not include any internal elements.

[0092] The stated ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor to the mass of the porous particles in the pressure reactor, and / or the stated ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (mass of the porous particles in the pressure reactor in grams x internal free volume of the reactor in liters) can be maintained throughout step (b).

[0093] Alternatively, the method comprises: (i) the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to the mass of the porous particles in the pressure reactor in grams; and / or (ii) the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters); The method may further include adjusting the

[0094] The method further comprises, after a predetermined period of time, during said contacting: (i) the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to the mass of the porous particles in the pressure reactor in grams; and / or (ii) the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters); to provide the above ratio.

[0095] The composite particles provided in step (b) may comprise a target amount of silicon occupying 20%-95% of the internal pore volume of the porous particle scaffold and the predetermined period of time may be after the composite particles contain 50%-95%, or 60%-95%, or 70%-95%, or 80%-95%, or 90%-95% of the target amount of silicon. The target amount of silicon may occupy 20%-80%, or 20%-70%, or 30%-70%, or 30%-60% of the internal pore volume of the porous particle scaffold.

[0096] The ratio can be adjusted throughout step (b), for example, by adjusting the flow rate of the silicon precursor gas. For example, step (b) can be operated for a period during which the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor to the mass of the porous particles in the pressure reactor is outside the range of 0.006 to 0.7. Thereafter, during step (b), the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor to the mass of the porous particles in the pressure reactor can be adjusted to be in the range of 0.006 to 0.7.

[0097] It is preferred to operate the pressure reactor such that the silicon precursor is consumed by at least 20%, preferably at least 50%, preferably at least 60%, preferably at least 80%, preferably at least 90%. Alternatively, the pressure reactor may be operated in a low conversion mode such that the silicon precursor is consumed by no more than 20%, preferably no more than 10%, more preferably no more than 5%.

[0098] The composite particles recovered from the pressure reactor may contain between 0.2 grams and 1.8 grams of silicon per gram of porous particle scaffold.

[0099] The composite particles provided in step (b) may comprise silicon in an amount occupying 20% ​​to 95% of the internal pore volume of the porous particle scaffold, or 20% to 80%, or 20% to 70%, or 30% to 70%, or 30% to 60% of the internal pore volume of the porous particle scaffold. The silicon occupancy can be calculated using the equation: 100 x (density of silicon x weight percent of silicon in the composite particle) / pore volume of the porous particle. The density of silicon is, for this purpose, 2.3 g / cm. 3 It is assumed that.

[0100] It is not excluded that unreacted silicon precursor gas may be removed from the exhaust gas recovered from the pressure reactor and recycled into the pressure reactor.

[0101] The exhaust gas from the pressure reactor contains at least one by-product gas from the CVI reaction, and optionally unreacted silicon precursor. The exhaust gas may contain the silicon precursor, at least one by-product gas, and optionally other gases, such as hydrogen or an inert gas such as nitrogen or argon. The content of the silicon precursor in the exhaust gas from the pressure reactor is preferably at least 5%, at least 10% by volume, or at least 15% by volume, or at least 20% by volume, or at least 50% by volume, or at least 85% by volume. The exhaust gas may contain 2.5% to 80% by volume of silicon precursor, or 2.5% to 70% by volume, or 2.5% to 60% by volume, or 2.5% to 50% by volume, or 5% to 80% by volume, or 5% to 70% by volume, or 5% to 60% by volume, or 5% to 50% by volume of silicon precursor. It may be preferable to control the pressure reactor so that the exhaust gas contains unreacted silicon precursor, because this can ensure that a high concentration of silicon precursor is maintained throughout the pressure reactor.When the exhaust gas from the pressure reactor contains a large amount of unreacted silicon precursor, it may be appropriate to remove the unreacted silicon precursor from the exhaust gas and recycle the removed silicon precursor to the pressure reactor.Means for removing the unreacted silicon precursor from the exhaust gas include semi-permeable membrane separation process, pressure swing adsorption process, and cryogenic separation process.

[0102] Optionally, the silicon precursor gas is preheated before being introduced into the pressure reactor. Preferably, the silicon precursor gas is heated to a temperature of (T RZ -200)℃ or higher (in the formula, T RZ is the reaction temperature of the pressure reactor), preferably at (T RZ -100)℃ or higher, preferably (T RZ Preheat to a temperature of at least -50)℃.

[0103] Step (b) may include contacting the plurality of porous particles with a silicon precursor gas under conditions effective to cause deposition of silicon in the pores of the porous particles to provide composite particles comprising 30 wt.% to 70 wt.% silicon based on a total mass of the composite particles.

[0104] The composite particles formed in step (b) may comprise at least 26% by weight silicon, or at least 28% by weight silicon, or at least 30% by weight silicon, or at least 32% by weight silicon, or at least 34% by weight silicon, or at least 36% by weight silicon, or at least 38% by weight silicon, or at least 40% by weight silicon, or at least 42% by weight silicon, or at least 44% by weight silicon.

[0105] The composite particles formed in step (b) may comprise up to 62% by weight silicon, or up to 60% by weight silicon, or up to 58% by weight silicon, or up to 56% by weight silicon, or up to 54% by weight silicon.

[0106] The composite particles provided in step (b) are 2 / g or less, or 80m 2 / g or less, or 60m 2 / g or less, or 40m 2 / g or less, or 30m 2 / g or less, or 25m 2 / g or less, or 20m 2 / g or less, or 15m 2 / g or less, or 10m 2 It is preferred that the composite particles have a BET surface area of ​​at least 0.1 m / g. Generally, a low BET surface area is preferred to minimize the formation of a solid electrolyte interfacial (SEI) layer on the surface of the composite particles during the first charge-discharge cycles of the anode. However, an excessively low BET surface area will result in unacceptably low charge rates and capacities due to the inaccessibility of the metal ions of the bulk electroactive material in the surrounding electrolyte. For example, the BET surface area of ​​the composite particles is preferably at least 0.1 m 2 / g, or at least 1m2 / g, or at least 2m 2 / g, or at least 5m 2 / g. For example, the BET surface area is 0.1 m 2 / g~100m 2 / g, or 0.1m 2 / g~80m 2 / g, or 0.5m 2 / g~60m 2 / g, or 0.5m 2 / g~40m 2 / g, or 1m 2 / g~30m 2 / g, or 1m 2 / g~25m 2 / g, or 2m 2 / g~20m 2 The term "BET surface area" as used herein should be taken to refer to the surface area per unit mass calculated from measurements of the physical adsorption of gas molecules on a solid surface using the Brunauer-Emmett-Teller theory and in accordance with ISO 9277.

[0107] The composite particles may be characterized by their performance under thermogravimetric analysis (TGA) in air, which is based on the principle that when an electroactive material is oxidized in air and at elevated temperature, a weight gain is observed.

[0108] As defined herein, "surface silicon" is calculated from the initial mass increase in a TGA trace from a minimum of 150°C-500°C to a maximum mass measured in the temperature range of 550°C-650°C, the TGA being performed in air at a heating rate of 10°C / min. This mass increase is assumed to result from oxidation of the surface silicon and is therefore calculated according to the following formula: Y = 1.875 × [(M max -M min ) / M f ]×100% where Y is the percentage of surface silicon as a proportion of the total silicon in the sample, and M max is the maximum mass of the sample measured in the temperature range between 550°C and 650°C, and M minis the minimum mass of the sample at temperatures greater than 150°C and less than 500°C, and M f The percentage of surface silicon as a proportion of the total amount of silicon can be determined according to (where 1.875 is the mass of the sample at the completion of oxidation at 1400°C). For completeness, it will be understood that 1.875 is the molar mass ratio of SiO2 to O2 (i.e., the mass ratio of SiO2 formed to the mass increase due to the addition of oxygen). Typically, TGA analysis is performed using a sample size of 10 mg ± 2 mg.

[0109] It has been found that reversible capacity retention over several charge / discharge cycles is significantly improved when the surface silicon, as determined by the TGA method described above, is at least 20% by weight of the total amount of silicon in the material.

[0110] The composite particles provided in step (b) preferably comprise at least 20% by weight of the total amount of silicon as surface silicon, alternatively at least 22% by weight of the silicon, or at least 25% by weight, at least 30% by weight, or at least 35% by weight of the silicon, or at least 40% by weight of the silicon, or at least 45% by weight of the silicon is surface silicon as determined by TGA.

[0111] The composite particles provided in step (b) preferably have a low content of crude bulk silicon, as determined by TGA. Crude bulk silicon is defined herein as silicon that undergoes oxidation above 800° C., as determined by TGA, where the TGA is performed in air at a heating rate of 10° C. / min. Thus, the crude bulk silicon content is calculated according to the following formula: Z = 1.875 × [(M f -M 800 ) / M f ]×100% (where Z is the percentage of unoxidized silicon at 800°C, M 800 is the mass of the sample at 800 °C, M fis the mass of ash at completion of oxidation at 1400°C). For the purposes of this analysis, any mass increase above 800°C corresponds to the oxidation of silicon to SiO2, and it is assumed that the total mass at completion of oxidation is SiO2. Typically, TGA analysis is performed using a sample size of 10 mg ± 2 mg.

[0112] Silicon that undergoes oxidation above 800° C. is less desirable. Preferably, no more than 10% by weight of the silicon is crude bulk silicon, 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, as determined by TGA.

[0113] Preferably, at least 20% by weight of the silicon is surface silicon and not more than 10% by weight of the silicon is crude bulk silicon, both determined by TGA. More preferably, at least 30% by weight of the silicon is surface silicon and not more than 10% by weight of the silicon is crude bulk silicon, both determined by TGA. More preferably, at least 35% by weight of the silicon is surface silicon and not more than 8% by weight of the silicon is crude bulk silicon, both determined by TGA. More preferably, at least 40% by weight of the silicon is surface silicon and not more than 5% by weight of the silicon is crude bulk silicon, both determined by TGA. More preferably, at least 45% by weight of the silicon is surface silicon and not more than 2% by weight of the silicon is crude bulk silicon, both determined by TGA.

[0114] In step (a), the plurality of porous particles in the pressure reactor are at least 20 g per liter of reactor volume (g / L RV ), or at least 50 g / L RV , or at least 80 g / 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 The porous particles may be a loading amount having a volume of

[0115] Preferably, the loading of the porous particles used in step (a) is at least 500 cm 3 / L RV and in some embodiments, optionally sufficient to substantially fill the reactor volume of the pressure reactor.

[0116] As used herein, the volume of a porous particle refers to the equivalent mass of the porous particle as determined from the tap density. For example, as defined herein, a particle volume of 200 cm of a porous particulate material having a tap density of 1000 g / L is 3 is equivalent to 200 g of porous particulate material.

[0117] The flow rate of silicon precursor gas into the pressure reactor is in grams of silicon per minute per kilogram of porous particles, 0.2 g min -1 kg -1 ~25g portion -1 kg -1 , or 0.5g -1 kg -1 ~20g portion -1 kg -1 , or 1g -1 kg -1 ~15g portion -1 kg-1 , or 1g -1 kg -1 ~14g portion -1 kg -1 , or 1g -1 kg -1 ~13g -1 kg -1 , or 1g -1 kg -1 ~12g portion -1 kg -1 , or 2g -1 kg -1 ~12g portion -1 kg -1 , or 3g -1 kg -1 ~12g portion -1 kg -1 , or 3g -1 kg -1 ~11g portion -1 kg -1 It may be.

[0118] The flow rate of silicon precursor gas into the pressure reactor is expressed in grams of silicon per minute per liter of reactor volume (gmin -1 / L RV ) for 0.03g -1 / L RV ~40g portion -1 / L RV , or 0.04g -1 / L RV ~35g portion -1 / L RV , or 0.05g -1 / L RV ~30g portion -1 / L RV , or 0.06g -1 / L RV ~25g portion -1 / L RV , or 0.07g -1 / L RV ~20g portion -1 / L RV , or 0.08g -1 / L RV ~15g portion -1 / L RV , or 0.09g -1 / L RV~10g portion -1 / L RV , or 0.1g -1 / L RV ~5g portion -1 / L RV , or 0.1g -1 / L RV ~1g -1 / L RV , or 0.15g -1 / L RV ~1g -1 / L RV , or 0.15g -1 / L RV ~0.95g min -1 / L RV , or 0.2g -1 / L RV ~0.95g min -1 / L RV , or 0.2g -1 / L RV ~0.9g -1 / L RV It may be.

[0119] The ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 1 m 2 / kg or less, or 0.9m 2 / kg or less, or 0.8m 2 / kg or less, or 0.7m 2 / kg or less, or 0.6m 2 / kg or less, or 0.5m 2 / kg or less, or 0.4m 2 / kg or less, or 0.3m 2 / kg or less.

[0120] The ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is at least 0.001 m 2 / kg, or at least 0.002m 2 / kg, or at least 0.003m 2 / kg, or at least 0.004m 2 / kg, or at least 0.006m 2 / kg, or at least 0.008m 2 / kg, or at least 0.01m 2 / kg.

[0121] The bed depth of the porous particles in the pressure reactor may 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.

[0122] The above-mentioned porous particle volume per liter of pressure reactor, ratio of internal surface area of ​​the pressure reactor to mass of porous particles in the pressure reactor, and / or bed depth of porous particles in the pressure reactor are preferably combined with continuous agitation as described herein.

[0123] In step (a), the plurality of porous particles in the pressure reactor are at least 100 cm 3 / L RV and the bed depth of the porous particles in the pressure reactor may be at least 11 cm.

[0124] In step (a), the plurality of porous particles in the pressure reactor are at least 200 cm 3 / L RV and the bed depth of the porous particles in the pressure reactor may be at least 15 cm.

[0125] In step (a), the plurality of porous particles in the pressure reactor are at least 300 cm 3 / L RV and the bed depth of the porous particles in the pressure reactor may be at least 20 cm.

[0126] In step (a), the plurality of porous particles in the pressure reactor are at least 400 cm 3 / L RV and the bed depth of the porous particles in the pressure reactor may be at least 25 cm.

[0127] In step (a), the plurality of porous particles in the pressure reactor are at least 500 cm3 / L RV and the bed depth of the porous particles in the pressure reactor may be at least 30 cm.

[0128] In step (a), the plurality of porous particles in the pressure reactor are at least 100 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 1 m 2 / kg or less.

[0129] In step (a), the plurality of porous particles in the pressure reactor are at least 200 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 0.9 m 2 / kg or less.

[0130] In step (a), the plurality of porous particles in the pressure reactor are at least 300 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 0.8 m 2 / kg or less.

[0131] In step (a), the plurality of porous particles in the pressure reactor are at least 400 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 0.7 m 2 / kg or less.

[0132] In step (a), the plurality of porous particles in the pressure reactor are at least 500 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 0.6 m 2 / kg or less.

[0133] In step (a), the plurality of porous particles in the pressure reactor are at least 600 cm 3 / L RV and the ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 0.5 m 2 / kg or less.

[0134] porous particles The porous particles may contain micropores and / or mesopores.

[0135] The porous particles are (i) D in the range of 0.5 μm to 200 μm 50 Particle size, (ii) 0.4 cm 3 / g~2.2cm 3 / g range of total pore volume of micropores and mesopores as measured by gas adsorption, and (iii) PDs of 30 nm or less, measured by gas adsorption 50 pore diameter, may have

[0136] As used herein, the term "particle size" refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, where the volume of the particle is understood to include the volume of the pores within the particle. 50 " and "D 50 The term "particle size" refers to the median particle size on a volume basis, i.e., the diameter below which 50% by volume of the particle population lies. 10 " and "D 10 The term "particle size" refers to the 10th percentile median particle size on a volume basis, i.e., the diameter below which 10% by volume of the particle population lies. 90 " and "D 90 The term "particle size" refers to the volume-based 90th percentile median particle size, i.e., the diameter below which 90% of the particle population falls, by volume.

[0137] Particle size and size distribution can be determined by standard laser diffraction techniques according to ISO 13320:2009. Laser diffraction is based on the principle that particles scatter light at angles that vary with the size of the particle, and a collection of particles produces a scattered light pattern defined by intensity and angle that can be correlated to particle size distribution. Many laser diffraction instruments are commercially available for quickly and reliably determining particle size distribution. Unless otherwise stated, particle size distribution measurements specified or reported herein are measured by a conventional Malvern Mastersizer™ 3000 particle size analyzer manufactured by Malvern Instruments™. The Malvern Mastersizer™ 3000 particle size analyzer works by projecting a helium neon gas laser beam through a transparent cell containing particles of interest suspended in an aqueous solution. The light that strikes the particles is scattered at angles that are inversely proportional to the particle size, and a photodetector array measures the light intensity at several predetermined angles, and the intensities measured at the various angles are processed by a computer using standard theoretical principles to determine the particle size distribution. Laser diffraction values ​​as reported herein are obtained using a wet dispersion of particles in 2-propanol with the addition of 5% by volume of the surfactant SPAN™-40 (sorbitan monopalmitate). The particle refractive index is taken to be 2.68 for porous particles and 3.50 for composite particles, and the dispersant refractive index is taken to be 1.378. The Mie scattering model is used to calculate the particle size distribution.

[0138] Generally, porous particles have a D in the range of 0.5 μm to 200 μm. 50 Optionally, the porous particles may have a particle size D 50 The particle size may 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 50The particle size may be 150 μm or less, or 100 μm or less, or 70 μm or less, or 50 μm or less, or 40 μm or less, or 30 μm or less, or 25 μm or less, or 20 μm or less, or 18 μm or less, or 15 μm or less, or 12 μm or less, or 10 μm or less, or 8 μm or less.

[0139] For example, the porous particles may have a diameter of 0.5 μm to 150 μm, or 0.5 μm to 100 μm, or 0.5 μm to 50 μm, or 0.5 μm to 30 μm, or 1 μm to 25 μm, or 1 μm to 20 μm, or 2 μm to 25 μm, or 2 μm to 20 μm, or 2 μm to 18 μm, or 2 μm to 15 μm, or 2 μm to 12 μm, or 2.5 D in the range of μm to 15 μm, or 2.5 μm to 12 μm, or 2 μm to 10 μm, or 3 μm to 20 μm, or 3 μm to 18 μm, or 3 μm to 15 μm, or 4 μm to 18 μm, or 4 μm to 15 μm, or 4 μm to 12 μm, or 5 μm to 15 μm, or 5 μm to 12 μm, or 5 μm to 10 μm, or 5 μm to 8 μm 50 Particles within these size ranges and having porosities and pore size distributions as set forth herein are ideally suited for the preparation of composite particles for use in anodes for metal ion batteries by the CVI process.

[0140] 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. 10 Maintaining particle size above 0.2 μm reduces the potential for undesirable agglomeration of submicron sized particles and improves dispersibility of the composite particles.

[0141] D of porous particles 90 The particle size is preferably 300 μm or less, or 250 μm or less, or 200 μm or less, or 150 μm or less, or 100 μm or less, or 80 μm or less, or 60 μm or less, or 40 μm or less, or 30 μm or less, or 25 μm or less, or 20 μm or less.

[0142] The porous particles preferably have a narrow particle size distribution span. For example, the particle size distribution span (D 90 -D 10 ) / D 50 (defined as) 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 particle size distribution span, efficient packing of particles in a continuous reactor can be more easily achieved.

[0143] The porous particles may have an average sphericity (as defined above) of greater than 0.5. Preferably, the porous particles have an average sphericity of 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. It is believed that spherical particles aid in the uniformity of deposition and promote dense packing of the particles in the final product both in the continuous reactor and when incorporated into the electrode.

[0144] Highly accurate two-dimensional projections of micron-scale particles can be obtained by scanning electron microscopy (SEM) or dynamic image analysis, where the shadows cast by the particles are recorded using a digital camera. The term "sphericity" as used herein is to be understood as the ratio of the area of ​​the particle projection (obtained from such imaging technique) to the area of ​​a circle, where the particle projection and the circle have the same circumference. Thus, for an individual particle, the sphericity S can be defined as:

number

number

[0145] Porous particles contain a three-dimensionally interconnected open pore network that includes micropores and / or mesopores, and optionally a small amount of macropores. In accordance with conventional IUPAC terminology, the term "micropores" is used herein to refer to pores with a diameter of less than 2 nm, the term "mesopores" is used herein to refer to pores with a diameter of 2 nm to 50 nm, and the term "macropores" is used herein to refer to pores with a diameter of more than 50 nm.

[0146] References herein to the volume of micropores, mesopores and macropores in a porous particle, and any references to the distribution of pore volume within the porous particle, similarly relate to the internal pore volume of the porous particle used as starting material for step (a) of the claimed method, i.e. prior to the deposition of silicon in the pore volume in step (c).

[0147] The porous particles are 0.4 cm 3 / g~2.2cm 3 / g (i.e. total pore volume in the range of 0 nm to 50 nm). Typically the porous particles contain both micropores and mesopores. However, it is not excluded that porous particles containing micropores and no mesopores, or mesopores and no micropores, can be used.

[0148] The total volume of the micropores and mesopores in the porous particles is at least 0.45 cm 3 / g, or at least 0.5 cm 3 / g, 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 0.75 cm 3 / g, or at least 0.8 cm 3 / g, 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 1 cm 3 / g, more preferably. The use of highly porous conductive particles can be advantageous as it allows for a greater amount of silicon to be accommodated within the pore structure.

[0149] The internal pore volume of the porous particles is appropriately limited such that the increased fragility of the porous particles outweighs the benefit of the increased pore volume that accommodates more silicon. The total volume of micropores and mesopores in the porous particles is less than 2 cm 3 / g or less, or 1.8 cm 3 / g or less, or 1.6 cm 3 / g or less, or 1.5cm 3 / g or less, or 1.45 cm 3 / g or less, or 1.4cm 3 / g or less, or 1.35 cm 3 / g or less, or 1.3 cm 3 / g or less, or 1.25 cm 3 / g or less, or 1.2 cm 3 / g or less, or 1.1cm 3 / g or less, or 1cm 3 / g or less, or 0.95 cm 3 It is preferable that the molecular weight is not more than 1 / g.

[0150] In some embodiments, the total volume of the micropores and mesopores in the porous particles is less than or equal to 0.45 cm 3 / g~2.2cm 3 / g, or 0.5 cm 3 / g~2cm 3 / g, or 0.55 cm 3 / g~2cm 3 / g, or 0.6 cm 3 / g~1.8cm 3 / g, or 0.65 cm 3 / g~1.8cm 3 / g, or 0.7 cm 3 / g~1.6cm 3 / g, or 0.75 cm 3 / g~1.6cm 3 / g, or 0.8 cm 3 / g~1.5cm 3 / g.

[0151] In another embodiment, the total volume of the micropores and mesopores in the porous particle is less than or equal to 0.55 cm 3 / g~1.4cm 3 / g, or 0.6 cm 3 / g~1.4cm 3 / g, or 0.6 cm 3 / g~1.3cm 3 / g, or 0.65 cm 3 / g~1.3cm 3 / g, or 0.65 cm 3 / g~1.2cm 3 / g, or 0.7 cm 3 / g~1.2cm 3 / g, or 0.7 cm 3 / g~1.1cm 3 / g, or 0.7 cm 3 / g~1cm 3 / g, or 0.75 cm 3 / g~0.95cm 3 / g.

[0152] In another embodiment, the total volume of the micropores and mesopores in the porous particle is less than or equal to 0.4 cm 3 / g~0.75cm 3 / g, or 0.4 cm 3 / g~0.7cm 3 / g, or 0.4 cm 3 / g~0.65cm 3 / g, or 0.45 cm 3 / g~0.75cm 3 / g, or 0.45 cm 3 / g~0.7cm 3 / g, or 0.45 cm 3 / g~0.65cm 3 / g, or 0.45 cm 3 / g~0.6cm 3 / g.

[0153] In another embodiment, the total volume of the micropores and mesopores in the porous particle is less than or equal to 0.6 cm 3 / g~2cm 3 / g, or 0.6 cm 3 / g~1.8cm 3 / g, or 0.7 cm 3 / g~1.8cm 3 / g, or 0.7 cm 3 / g~1.6cm 3 / g, or 0.8 cm 3 / g~1.6cm 3 / g, or 0.8 cm 3 / g~1.5cm 3 / g, or 0.8 cm 3 / g~1.4cm 3 / g, or 0.9 cm 3 / g~1.5cm 3 / g, or 0.9 cm 3 / g~1.4cm 3 / g or 1cm 3 / g~1.4cm 3 / g.

[0154] PD of porous particles 50 The pore size may be 30 nm or less, optionally 25 nm or less, or 20 nm or less, or 15 nm or less, or 12 nm or less, or 10 nm or less, or 8 nm or less, or 6 nm or less, or 5 nm or less, or 4 nm or less, or 3 nm or less, or 2.5 nm or less, or 2 nm or less, or 1.5 nm or less. 50 The term "pore size" refers to the median pore size on a volumetric basis relative to the total volume of micropores and mesopores (i.e. the pore size below which 50% of the total volume of micropores and mesopores are found). Thus, according to the present invention, it is preferred that at least 50% of the total volume of micropores and mesopores is in the form of pores having a diameter of less than 30 nm.

[0155] For the avoidance of doubt, any macropore volume (pore diameters greater than 50 nm) is not included in the PD 50 It is not taken into account for the purpose of calculating the value.

[0156] The volume ratio of micropores to mesopores in the porous particles may in principle be in the range of 100:0 to 0:100. The volume ratio of micropores to mesopores is preferably 90:10 to 55:45, or 90:10 to 60:40, or 85:15 to 65:35.

[0157] The pore size distribution of the porous particles may be unimodal, bimodal or multimodal. The term "pore size distribution" as used herein refers to the distribution of pore sizes relative to the cumulative total internal pore volume of the porous particle. A bimodal or multimodal pore size distribution may be preferred, since the proximity of the micropores to the larger diameter pores provides the advantage of efficient transport of ions through the porous network to the silicon.

[0158] The total volume of micropores and mesopores, and the pore size distribution of micropores and mesopores were determined using quenched solid-state density functional theory (QSDFT) according to standard methodologies specified in ISO 15901-2 and ISO 15901-3, with a relative pressure p / p of at least 10 at 77 K. -6 The pore volume and pore size distribution are determined using nitrogen gas adsorption. Nitrogen gas adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing a gas in the pores of a solid. As the pressure is increased, the gas condenses initially in the pores with the smallest diameter, and the pressure is increased until a saturation point is reached where all pores are filled with liquid. The nitrogen gas pressure is then reduced in stages to allow the liquid to evaporate from the system. The pore volume and pore size distribution can be determined by analysis of the adsorption and desorption isotherms and the hysteresis between them. Suitable instruments for measuring the pore volume and pore size distribution by nitrogen gas 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.

[0159] Nitrogen gas adsorption is effective for measuring the pore volume and pore size distribution of pores with diameters up to 50 nm, but is less reliable for pores with much larger diameters. Therefore, for the purposes of the present invention, nitrogen adsorption is used to determine the pore volume and pore size distribution of only pores with diameters up to 50 nm (i.e., only micropores and mesopores). Similarly, PD 50 is determined for the total volume of micropores and mesopores only.

[0160] Given the limitations of available analytical techniques, it is not possible to measure the pore volume and pore size distribution over the full range of micropores, mesopores and macropores using a single technique. When a porous particle contains macropores, the volume of pores with diameters greater than 50 nm and ranging up to 100 nm can be measured by mercury intrusion porosimetry, which measures the volume of pores with diameters greater than 50 nm and ranging up to 100 nm in 0.3 cm. 3 / g or less, or 0.20 cm 3 / g or less, or 0.1cm 3 / g or less, or 0.05 cm 3 / g or less. Although a small proportion of macropores can be useful to facilitate electrolyte access into the pore network, the advantages of the present invention are substantially obtained by containing the silicon in the micropores and smaller mesopores.

[0161] Any pore volume measured by mercury intrusion at pore diameters of 50 nm or less is disregarded (as described above, nitrogen adsorption is used to characterize mesopores and micropores). Pore volume measured by mercury intrusion above 100 nm is assumed to be interparticle porosity for purposes of this invention, and this pore volume is also not considered.

[0162] Mercury porosimetry is a technique for characterizing the porosity and pore size distribution of a material by applying various levels of pressure to a sample of the material immersed in mercury. The pressure required to force mercury into the pores of the sample is inversely proportional to the pore size. Mercury porosimetry values ​​reported herein were obtained according to ASTM UOP578-11, with a surface tension of mercury at room temperature, γ, of 480 mN / m and a contact angle, φ, of 140°. The density of mercury at room temperature is 13.5462 g / cm 3 There are many high-precision mercury intrusion instruments available commercially, such as the AutoPore IV series of automated mercury intrusion meters available from Micromeritics Instrument Corporation, USA. For a complete review of mercury intrusion methods, refer to "Analytical Methods in Fine Particle Technology, 1997, Micromeritics Instrument Corporation" by PA Webb and C. Orr (ISBN 0-9656783-0).

[0163] It will 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 exterior of the porous particle. The porosity values ​​defined herein should be understood to refer to the open pores, i.e., the volume of pores accessible to fluids from the exterior of the porous particle. Completely enclosed pores that cannot be identified by nitrogen adsorption or mercury porosimetry shall not be considered in determining the porosity values ​​herein. Similarly, any pore volume located within pores that are small enough to be below the detection limit by nitrogen adsorption shall not be considered.

[0164] The porous particles are preferably porous conductive particles. A preferred type of porous conductive particle is a porous carbon particle. The porous carbon particles preferably comprise at least 80% by weight carbon, more preferably at least 90% by weight carbon, more preferably at least 95% by weight carbon, optionally at least 98% by weight or at least 99% by weight carbon. The carbon may be crystalline carbon, or amorphous carbon, or a mixture of amorphous and crystalline carbon. The porous carbon particles may be either hard or soft carbon particles.

[0165] As used herein, the term "hard carbon" refers to carbon atoms that are primarily distributed in nanoscale polyaromatic domains. 2 It refers to a disordered carbon matrix that adopts a hybridized (three-way bond) state. The polyaromatic domains are cross-linked by chemical bonds, e.g., COC bonds. Because the polyaromatic domains are chemically cross-linked, the hard carbon cannot be converted to graphite at high temperatures. The high G band (approx. 1600 cm) in the Raman spectrum -1 ), hard carbon has graphite-like properties. However, the high D band in the Raman spectrum (approximately 1350 cm -1 ), carbon is not completely graphitic. The graphiticity of a carbon material can be assessed by monitoring the ratio of the peak intensities of the D band and the G band (ID / IG). The porous carbon particles may comprise an ID / IG of 0.84 or less, or 0.75 or less.

[0166] The term "soft carbon" as used herein also refers to carbon atoms that are primarily dispersed in polyaromatic domains having dimensions in the range of 5 nm to 200 nm. 2 It refers to a disordered carbon matrix that adopts a hybridized (three-way bond) state. In contrast to hard carbon, the polyaromatic domains in soft carbon are not cross-linked by chemical bonds but are held together by intermolecular forces; that is, at high temperatures, soft carbon can be graphitized. The porous carbon particles preferably have at least 50% sp 2For example, the porous carbon particles preferably contain 50% to 98% sp 2 Hybrid carbon, 55%-95% sp 2 Hybrid carbon, 60%-90% sp 2 Hybrid carbon, or 70% to 85% sp 2 It may contain hybridized carbon.

[0167] A variety of different materials can be used to create suitable porous carbon scaffolds. Examples of organic materials that can be used include plant biomass, including lignocellulosic materials (coconut shells, rice husks, wood, etc.), and fossil carbon sources such as coal. Examples of resins and polymeric materials that form porous carbon particles upon pyrolysis include phenolic resins, novolac resins, pitch, melamine, polyacrylates, polystyrene, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and various copolymers that contain monomer units of acrylates, styrene, α-olefins, vinylpyrrolidone, and other ethylenically unsaturated monomers. Depending on the starting materials and the conditions of the pyrolysis process, a variety of different carbon materials are available in the art. A variety of different specifications of porous carbon particles are available from suppliers.

[0168] To increase the mesopore and micropore volume, the porous carbon particles can be subjected to a chemical or gas activation process. Suitable activation processes include contacting the pyrolyzed carbon with one or more of oxygen, steam, CO, CO2, and KOH at temperatures ranging from 600°C to 1000°C.

[0169] Mesopores can also be obtained by known templating processes using extractable 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.

[0170] As an alternative to carbon-based conductive particles, porous metal oxides, e.g., of the formula TiOx (wherein x has a value greater than 1 and less than 2) is an example of an oxide of titanium having the formula:

[0171] The porous particles are at least 750 m 2 / g, or at least 1000m 2 / g, or at least 1250m 2 / g, or at least 1500m 2 It is preferred that the porous particles have a BET surface area of ​​4000 m / g. The term "BET surface area" as used herein should be taken to refer to the surface area per unit mass calculated from measurements of the physical adsorption of gas molecules on a solid surface using the Brunauer-Emmett-Teller theory and in accordance with ISO 9277. The BET surface area of ​​the porous particles is preferably 4000 m 2 / g or less, or 3500m 2 / g or less, or 3250m 2 / g or less, or 3000m 2 / g or less or 2500m 2 / g or less, or 2000m 2 For example, the porous particles preferably have a particle size of 750 m 2 / g~4000m 2 / g, or 1000m 2 / g~3500m 2 / g, or 1250m 2 / g~3250m 2 / g, or 1500m 2 / g~3000m 2 / g.

[0172] The porous particles preferably have a density of at least 0.35 g / cm 3 and preferably 3 g / cm 3 less than 2 g / cm 3 less than 1.5 g / cm 3 less than 0.35 g / cm 3 ~1.2g / cm 3The term "particle density" as used herein refers to the "apparent particle density" measured by mercury porosimetry (i.e., particle mass divided by particle volume, where particle volume is taken to be the sum of the volume of solid material and any closed or blocked pores ("blocked pores" are pores that are too small to be measured by mercury porosimetry). In general, the particulate additives used in the present invention have a low BET surface area and therefore a relatively low volume of open pores. Thus, the apparent density measured by mercury porosimetry is an approximation of the "effective particle density" (the calculation includes the volume of open pores). The porous particles have a density of 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 The porous particles preferably have a particle density of 1.15 g / cm 3 or less than 1.1g / cm 3 or less than 1.05g / cm 3 or less than 1g / cm 3 or less than 0.95g / cm 3 or less than 0.9g / cm 3 It is preferred to have a particle density of:

[0173] Preferred porous particles for use in accordance with the present invention include: (i)D 50 Particle size ranges from 0.5 μm to 30 μm; (ii) The total pore volume of micropores and mesopores measured by gas adsorption is less than 0.5 cm 3 / g~1.5cm 3 / g range; (iii) PD measured by gas adsorption 50 The pore size is 5 nm or less; Some examples include:

[0174] Silicon Precursor Gas The silicon precursor gas includes 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 by-product gases. The silicon precursor gas optionally includes other gases, such as inert gases. Examples of suitable silicon precursors include silane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane, dimethylsilane, and chlorosilane, and mixtures thereof. The silicon precursor is preferably selected from silane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane, and dimethylsilane. Silane (SiH4) is the most preferred silicon precursor.

[0175] The silicon precursor gas is preferably chlorine-free, e.g., contains less than 1 wt. %, preferably less than 0.1 wt. %, preferably less than 0.01 wt. % chlorine-containing compounds.

[0176] The silicon precursor can be used undiluted (undiluted) or as a diluent such that the silicon precursor gas comprises at least 5% by volume of the silicon precursor, with the remainder being selected from hydrogen and an inert gas, where optionally the inert gas is selected from nitrogen and argon. The silicon precursor gas may comprise 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 99.99% by volume of the silicon precursor. The silicon precursor gas preferably comprises 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 99.99% by volume of silicon precursor. The volume percent of silicon precursor refers to the concentration of silicon precursor as a ratio to the total gas (silicon precursor gas) introduced into the pressure reactor.

[0177] Preferably, the silicon precursor gas comprises at least 50% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may range from 600 kPa to 15000 kPa.

[0178] Preferably, the silicon precursor gas comprises at least 60% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 600 kPa to 5000 kPa.

[0179] Preferably, the silicon precursor gas comprises at least 70% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 600 kPa to 2000 kPa.

[0180] Preferably, the silicon precursor gas comprises at least 80% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 700 kPa to 2000 kPa.

[0181] Preferably, the silicon precursor gas comprises at least 90% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 1000 kPa to 2000 kPa.

[0182] Preferably, the silicon precursor gas comprises at least 95% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 1000 kPa to 1600 kPa.

[0183] Preferably, the silicon precursor gas comprises at least 99.9% by volume of silicon precursor, and the pressure in the pressure reactor during step (b) may be in the range of 1000 kPa to 1600 kPa.

[0184] Carbon Coating The method of the present invention optionally further comprises the step of contacting the composite particles with a carbon precursor gas under conditions effective to cause deposition of carbon within the pores and / or on the surfaces of the composite particles.

[0185] The deposited carbon is a pyrolytic carbon material formed by the pyrolysis of a carbon-containing gas (e.g., ethylene). The carbon deposition provides several performance advantages. It reduces the BET surface area of ​​the composite particles by smoothing out any surface defects and filling any remaining surface microporous structure, thereby further reducing first cycle losses. It also improves the electrical conductivity of the composite particle's surface, reducing the need for conductive additives in the electrode composition. Additionally, it creates an optimal surface for the formation of a stable SEI layer, thereby improving capacity retention during cycling.

[0186] Effective conditions for causing carbon deposition can include temperatures in the range of 350° C. to 700° C., or 400° C. to 700° C. Preferably, the temperature is no greater than 680° C., or no greater than 660° C., or no greater than 640° C., or no greater than 620° C., or no greater than 600° C., or no greater than 580° C., or no greater than 560° C., or no greater than 540° C., or no greater than 520° C., or no greater than 500° C.

[0187] The minimum temperature depends 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.

[0188] Conditions effective to cause carbon deposition may include pressures in the range of 1 kPa to 600 kPa, or 10 kPa to 500 kPa, or 20 kPa to 200 kPa, or 50 kPa to 150 kPa, or 80 kPa to 120 kPa, or about 100 kPa.

[0189] Suitable carbon precursor gases include: (i) C2~C 10 Hydrocarbons, optionally the hydrocarbons are selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, and arenes, such as methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, α-terpinene, and acetylene; (ii) a bicyclic monoterpenoid, optionally the bicyclic monoterpenoid is selected from camphor, borneol, eucalyptol, camphene, carene, sabinene, thujene and pinene; and (iii) Polycyclic hydrocarbons, optionally polycyclic aromatic hydrocarbons, containing 10 to 25 carbon atoms and, optionally, 1 to 3 heteroatoms, are selected from naphthalene, substituted naphthalenes, such as dihydroxynaphthalene, anthracene, tetracene, pentacene, fluorene, acenaphthene, phenanthrene, fluoranthene, pyrene, chrysene, perylene, coronene, fluorenone, anthraquinone, anthrone, and alkyl-substituted derivatives thereof.

[0190] The carbon precursor used can be used in pure form or as a dilute mixture with an inert carrier gas, such as nitrogen or argon. For example, the carbon precursor can be used in an amount ranging from 0.1% to 100% by volume, or from 20% to 95% by volume, or from 50% to 90% by volume, or from 60% to 85% by volume, based on the total volume of the precursor and the inert carrier gas.

[0191] passivation The silicon deposited in CVI deposition has a hydride-terminated silicon surface that is highly reactive towards oxygen, therefore the method of the present invention preferably includes a passivation step in which the composite particles undergo controlled passivation to form a passivated material that is stable in air.

[0192] Thus, the method of the present invention may further comprise contacting the composite particles with a passivation agent under conditions effective to passivate the composite particles. As defined herein, a passivation agent is a compound or mixture of compounds capable of reacting with the surface of the deposited silicon to form a modified surface. The composite particles may be contacted with the passivation agent in a pressure reactor or transferred to another vessel for contacting with the passivation agent. The composite particles may be contacted with a first passivation agent in a pressure reactor and then transferred to another vessel and contacted with a second passivation agent, where the first and second passivation agents may be the same or different. It is preferred to contact the composite particles with at least one passivation agent in a pressure reactor.

[0193] The method of the present invention may also include the steps of interrupting the deposition of silicon to form intermediate composite particles, contacting the intermediate composite particles with a passivating agent under conditions effective to 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 effective to cause deposition of silicon within the pores of the passivated intermediate composite particles to provide composite particles.

[0194] The composite particles, which have been contacted with a carbon precursor gas under conditions effective to cause carbon deposition within the pores and / or on the surface of the composite particles, can then be contacted with a passivating agent under conditions effective to passivate the composite particles.

[0195] The passivating agent can be selected from (i) an oxygen-containing gas; (ii) ammonia; (iii) a gas containing ammonia and oxygen; and (iv) phosphine.

[0196] The passivating agent can be an oxygen-containing gas. In this case, the conditions effective to passivate the composite particles can include a temperature in the range of 20°C to 300°C, or 20°C to 200°C, or 25°C to 200°C, or 25°C to 180°C, or 50°C to 160°C. The temperature is preferably 150°C or less. Further, the conditions effective to passivate the composite particles can include a pressure in the range of 1 kPa to 600 kPa, or 10 kPa to 500 kPa, or 20 kPa to 200 kPa, or 50 kPa to 150 kPa, or 80 kPa to 120 kPa, or about 100 kPa. The oxygen-containing gas can be air. When the oxygen-containing gas is air, optionally, as the composite particles are cooled to a temperature below 50°C, the concentration of oxygen contacting the composite particles during the passivation process can be increased over a period of time.

[0197] The passivating agent can be ammonia or another nitrogen-containing molecule. In this case, the passivation layer may contain 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°C to 700°C, preferably 400°C to 700°C, more preferably 400°C to 600°C. If necessary, the temperature can be raised to the range of 500°C to 1000°C to form a nitride surface (e.g., a silicon nitride surface of the formula SiN x (where x ≤ 4 / 3)). A stoichiometric nitride (e.g., SiN x(where 0 < x ≦ 4 / 3)) is conductive, so the nitride intermediate layer functions as a conductive network that enables faster charging and discharging of the electroactive material.

[0198] Phosphine can also be used as a passivating agent as a phosphorus analog of ammonia.

[0199] The passivating agent may include ammonia (or another nitrogen-containing molecule) and oxygen gas. In this case, the passivating layer may contain 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 containing ammonia (or another nitrogen-containing molecule) and oxygen gas.

[0200] Other suitable passivating agents include compounds containing an alkene, alkyne or carbonyl functional group, more preferably a terminal alkene, terminal alkyne, aldehyde or ketone group.

[0201] Preferred passivating agents include the following formulas: (i) R 1 -CH=CH-R 1 , (ii) R 1 -C≡C-R 1 , and, (iii) O=CR 1 R 1 (where each R 1 independently represents H, or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, or two R 1 groups form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring).

[0202] Particularly preferred passivating agents include the following formulas: (i) CH2=CH-R 1, and (ii) HC≡CR 1 (In the formula, R 1 is as defined above. 1 is non-substitutive.

[0203] Examples of suitable passivators 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 passivators can also be used.

[0204] Passivating agents containing an alkene, alkyne or carbonyl group are believed to undergo an insertion reaction with M-H groups (where M represents an atom of the electroactive material) on the surface of the electroactive material to form a covalently passivated surface that is resistant to oxidation by air. When silicon is the electroactive material, the passivating reaction between the silicon surface and the passivating agent can be understood as a form of hydrosilylation as shown diagrammatically below. [ka]

[0205] Other suitable passivation agents include compounds that contain an active hydrogen atom bonded to oxygen, nitrogen, sulfur, or phosphorus. For example, the passivation agent may be an alcohol, an amine, a thiol, or a phosphine. It is understood that the reaction of the -XH group with a hydride group on the electroactive material surface results in the elimination of H2 and the formation of a direct bond between X and the electroactive material surface.

[0206] Suitable passivators in this category include those having the following formula: (iv) HX-R 2 , and (v) HX-C(O)-R 1 (wherein X is O, S, NR 1 Or PR1 Each R 1 are independently as defined above, and R 2 represents an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, or R 1 and R 2 taken together form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring.

[0207] Preferably, X represents O or NH.

[0208] Preferably, R 2 represents an optionally substituted aliphatic or aromatic group having from 2 to 10 carbon atoms. Amine groups may also be incorporated into 4- to 10-membered aliphatic or aromatic ring structures, such as in pyrrolidine, pyrrole, imidazole, piperazine, indole, or purine.

[0209] The contact of the composite particles with the passivating agent may be carried out at a temperature in the range of 25°C to 700°C, preferably 50°C to 500°C, and more preferably 100°C to 300°C.

[0210] Gas Separation Unit The method may experience low silicon precursor conversion during CVI deposition due to the recovery of exhaust gas (including silicon precursor) during the reaction. While the method beneficially maintains the concentration of silicon precursor during the reaction, low conversion would negatively impact operating costs. Thus, the exhaust gas may include silicon precursor and at least one by-product gas, and the method includes: directing at least a portion of the exhaust gas into a gas separation unit; operating the gas separation unit such that the silicon precursor is separated from at least one by-product gas; It may further include.

[0211] The silicon precursor and at least one by-product gas are separated to provide at least one enriched gas stream and at least one waste gas stream, where the enriched gas stream is enriched in the silicon precursor compared to the exhaust gas and the waste gas stream is depleted in the silicon precursor compared to the exhaust gas.

[0212] The enriched gas stream may contain at least one by-product gas from the exhaust gas, but the amount of at least one by-product gas is preferably minimal. For example, the enriched gas stream may contain at least 60% by volume of silicon precursor, or at least 70% by volume of silicon precursor, or at least 80% by volume of silicon precursor, or at least 90% by volume of silicon precursor, or at least 95% by volume of silicon precursor, or at least 98% by volume of silicon precursor. The waste gas stream may contain silicon precursor, but the amount of silicon precursor is preferably minimal. For example, the waste gas stream may contain less than 40% by volume of silicon precursor, or less than 30% by volume of silicon precursor, or less than 20% by volume of silicon precursor, or less than 10% by volume of silicon precursor, or less than 5% by volume of silicon precursor.

[0213] For example, CVI deposition of silane produces hydrogen gas as a by-product, and the unreacted silane can be separated from the silane / hydrogen mixture in the exhaust gas using a gas separation unit to provide an enriched gas stream that is enriched in silane compared to the exhaust gas, and a waste gas stream that contains hydrogen and is depleted in silane compared to the exhaust gas.

[0214] The enriched gas stream containing the silicon precursor can be recycled back into the pressure reactor, for example as part of step (b), thus minimizing its replenishment. introducing (recycle) at least a portion of the enriched gas stream into the pressure reactor; may include:

[0215] The enriched gas stream can be mixed with the silicon precursor gas introduced in step (b) and the mixture can be introduced into the pressure reactor through the same gas inlet(s). Alternatively, or in addition, the enriched gas stream can be introduced into the pressure reactor through a gas inlet(s) different from the silicon precursor gas introduced in step (b). Alternatively, or in addition, the enriched gas stream containing the silicon precursor can be stored. Similarly, the waste gas stream containing by-product gas such as hydrogen can be stored.

[0216] Step (b) may include combining at least a portion of the enriched gas stream with the silicon precursor gas prior to introduction into the pressure reactor. Alternatively, or in addition, the method may further include introducing at least a portion of the enriched gas stream into the pressure reactor separately from the silicon precursor gas. Alternatively, or in addition, the method may further include collecting at least a portion of the enriched gas stream and / or the waste gas stream for storage. Alternatively, or in addition, at least a portion of the enriched gas stream may be subjected to further processing to purify the silicon precursor gas.

[0217] At least a portion of the waste gas stream may be subjected to further processes to extract energy and / or purify by-product gases. At least a portion of the waste gas stream may be purified. Alternatively, or in addition, at least a portion of the waste gas stream may be treated to extract energy. Alternatively, or in addition, at least a portion of the waste gas stream may be fed into a supply grid. Alternatively, or in addition, at least a portion of the waste gas stream may be used as a feedstock in further processes.

[0218] A portion of the exhaust gas may be bypassed around the gas separation unit as a bypass stream. Thus, the method may further include the step of bypassing a portion of the exhaust gas around the gas separation unit as a bypass stream. Step (b) may include combining at least a portion of the bypass stream with the silicon precursor gas prior to introduction into the pressure reactor. Alternatively, or in addition, at least a portion of the bypass stream may be introduced into the pressure reactor separately from the silicon precursor gas. The method may include separating the bypass stream from the exhaust stream and recycling the bypass stream into the pressure reactor without separating the silicon precursor in the bypass stream from the by-product gas in the bypass stream.

[0219] The exhaust gas may contain 5% to 80% by volume of the silicon precursor, or 5% to 70% by volume, or 5% to 60% by volume, or 5% to 50% by volume of the silicon precursor.

[0220] The by-product gas may include hydrogen and the gas separation unit may be a hydrogen (H2) selective membrane.The by-product gas may include hydrogen and the gas separation unit may be a hydrogen (H2)-silane selective membrane.

[0221] The exhaust gas may include an inert gas, and the method may include a step of separating the inert gas and the silicon precursor and / or at least one by-product gas using a gas separation unit. The inert gas, the 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 gases.

[0222] The gas separation unit may include a membrane separation system, such as a polymeric membrane separation system and / or an alloy membrane separation system, a pressure swing adsorption system, a cryogenic separation system, a gas distillation system, or a combination thereof. The gas separation unit may include a membrane separation system and a pressure swing adsorption system.

[0223] The separation unit may comprise a heat exchanger for cooling the exhaust gas to ambient or near ambient temperature, for example below 70° C., or below 50° C., prior to separating the exhaust gas into the enriched and waste gas streams. Thus, the method may comprise the step of cooling the exhaust gas to ambient or near ambient temperature, for example below 70° C., or below 50° C.

[0224] When a gas separation unit is used in the method, it is preferred that during said contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams is in the range of 0.009 to 0.03.

[0225] When a gas separation unit is used in the method, it is preferred that during said contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams x the internal free volume of the reactor in liters) is in the range of 0.0003 to 0.001.

[0226] By operating the process at these conditions, high silicon precursor concentrations are maintained in the pressure reactor while minimizing silicon precursor loss.

[0227] The invention will now be further described with reference to the accompanying drawings. [Brief description of the drawings]

[0228] [Figure 1] FIG. 1 is a schematic diagram of a pressure reactor apparatus operated in accordance with certain embodiments of the present invention. [Diagram 2]FIG. 1 is a schematic diagram of a pressure reactor apparatus operated in accordance with certain embodiments of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. [Diagram 5] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. [Figure 6] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. [Figure 7] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram of an apparatus for performing CVI operated in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0229] Referring to FIG. 1, there is shown a CVI apparatus 1 consisting of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, and exhaust gas 14 recovered from the pressure reactor.

[0230] Referring to Figure 2, a CVI apparatus 1 is shown that is comprised of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, and exhaust gas 14 recovered from the pressure reactor. The silicon precursor gas supply flow passes through a means for determining the flow rate of silicon precursor gas 30, then through a feedback control valve 40, then through a means for determining the pressure of silicon precursor gas 50, and then into the pressure reactor. Feedback is provided from the means for determining the pressure of silicon precursor gas to a feedback control valve that can be changed between an open and closed state to control the pressure within the pressure reactor. A gas release valve 60 controls the flow rate of the exhaust gas recovered from the pressure reactor.

[0231] Referring to FIG. 3, a CVI apparatus 1 is shown, which is composed of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, an exhaust gas 14 recovered from the pressure reactor to a gas separation unit 15, a bypass stream 16 recovered from the pressure reactor bypassing the gas separation unit, an enriched gas stream 17 recovered from the gas separation unit and then combined with the silicon precursor gas and introduced into the pressure reactor, and a waste gas stream 18 recovered from the gas separation unit. The bypass stream may be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream may be introduced into a storage unit for storing gases derived from the waste gas stream and optionally gases derived from the bypass stream. Alternatively or additionally, the waste gas stream may be purified. Alternatively or additionally, the waste gas stream may be treated to extract energy. Alternatively, or in addition, a waste gas stream may be fed into the supply grid.

[0232] Referring to FIG. 4, a CVI apparatus 1 is shown, which is composed of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, an exhaust gas 14 recovered from the pressure reactor in a gas separation unit 15, a bypass stream 16 recovered from the pressure reactor bypassing the gas separation unit, an enriched gas stream 17 recovered from the gas separation unit which is introduced into the pressure reactor separately from the silicon precursor gas, and a waste gas stream 18 recovered from the gas separation unit. The bypass stream may be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream may be introduced into a storage unit for storing gases derived from the waste gas stream and optionally gases derived from the bypass stream. Alternatively or additionally, the waste gas stream may be purified. Alternatively or additionally, the waste gas stream may be treated to extract energy. Alternatively, or in addition, a waste gas stream may be fed into the supply grid.

[0233] Referring to FIG. 5, a CVI apparatus 1 is shown, which is composed of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, exhaust gas 14 recovered from the pressure reactor in a gas separation unit 15, a bypass stream 16 recovered from the pressure reactor bypassing the gas separation unit, an enriched gas stream 17 recovered from the gas separation unit and introduced into a storage unit 20, a storage unit for storing gases derived from the enriched gas stream, and a waste gas stream 18 recovered from the gas separation unit. The bypass stream may be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream may be introduced into a storage unit for storing gases derived from the waste gas stream and optionally the bypass stream. Alternatively or additionally, the waste gas stream may be purified. Alternatively or additionally, the waste gas stream may be treated to extract energy. Alternatively, or in addition, a waste gas stream may be fed into the supply grid.

[0234] 6, a CVI apparatus 1 is shown, which is composed of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, exhaust gas 14 recovered from the pressure reactor in a gas separation unit 15, a bypass stream 16 bypassing the gas separation unit and recovered from the pressure reactor, an enriched gas stream 17a recovered from the gas separation unit, optionally combined with silicon precursor gas and introduced into the pressure reactor, an enriched gas stream 17b recovered from the gas separation unit and introduced into a storage unit 20, a storage unit for storing gases derived from the enriched gas stream, and a waste gas stream 18 recovered from the gas separation unit. The bypass stream may be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream can be introduced into a storage unit for storing gases from the waste gas stream and optionally from the bypass stream. Alternatively or additionally, the waste gas stream can be purified. Alternatively or additionally, the waste gas stream can be treated to extract energy. Alternatively or additionally, the waste gas stream can be fed into a supply grid.

[0235] 7, a CVI apparatus 1 is shown, which comprises a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, exhaust gas 14 recovered from the pressure reactor in a gas separation unit 15, a bypass stream 16 recovered from the pressure reactor bypassing the gas separation unit, an enriched gas stream 17a recovered from the gas separation unit, optionally combined with the silicon precursor gas and introduced into the pressure reactor, an enriched gas stream 17b recovered from the gas separation unit and introduced into a storage unit 20, a storage unit for storing gases derived from the enriched gas stream, and a waste gas stream 18 recovered from the gas separation unit. At least a portion 21 of the bypass stream is combined with the silicon precursor gas before being introduced into the pressure reactor. Alternatively, or in addition, at least a portion of the bypass stream may be introduced into the reaction zone / pressure reactor separately from the silicon precursor gas, as indicated by the dashed line between the portion of the bypass stream and the pressure reactor. At least a portion of the bypass stream may be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream may be introduced into a storage unit for storing gases from the waste gas stream and, optionally, gases from the bypass stream. Alternatively, or in addition, the waste gas stream may be purified. Alternatively, or in addition, the waste gas stream may be treated to extract energy. Alternatively, or in addition, the waste gas stream may be fed into a supply grid.

[0236] Referring to FIG. 8, a CVI apparatus 1 is shown, which is composed of a pressure reactor 10, a supply of silicon precursor gas 11 to the pressure reactor, a supply of porous particles 12 to the pressure reactor, composite particles 13 recovered from the pressure reactor, an exhaust gas 14 in fluid communication with the pressure reactor and a gas separation unit 15, a bypass stream 16 recovered from the pressure reactor bypassing the gas separation unit, and a waste gas stream 18 recovered from the gas separation unit. At least a portion of the bypass stream can be combined with the waste gas stream, as indicated by the dashed line between the bypass stream and the waste gas stream. The waste gas stream may be subjected to further processing 19. For example, the waste gas stream may be introduced into a storage unit for storing gases derived from the waste gas stream and optionally gases derived from the bypass stream. Alternatively or additionally, the waste gas stream may be purified. Alternatively or additionally, the waste gas stream may be treated to extract energy. Alternatively or additionally, the waste gas stream may be fed into a supply grid. This configuration differs from the configurations shown in Figures 3 to 7 in that the gas separation unit prevents the silicon precursor from passing, so that the silicon precursor remains in the pressure reactor, and at least one by-product gas is separated from the silicon precursor as a waste gas stream. In this configuration, a higher degree of conversion of the silicon precursor is possible, since the silicon precursor remains available for reaction in the pressure reactor while at the same time at least one by-product gas is recovered from the pressure reactor. In this configuration, the gas separation unit may consist of a membrane separation system. EXAMPLES

[0237] Modeling was used to determine the total CVI deposition time for the comparative method operated as a batch for the silicon precursor gas input and as a batch for the porous particle input. Modeling was also used to determine the total CVI deposition for the inventive method operated semi-continuously for the silicon precursor gas input and as a batch for the porous particle input. The results are shown in the table below.

[0238] Operation of the pressure reactor according to the present invention resulted in a reduction in CVI deposition time of 13.7 hours, a reduction of approximately 65%. Additionally, reactor productivity was increased by approximately 286%.

[0239] [Table 1]

Claims

1. A method for preparing composite particles, (a) A step of providing a plurality of porous particles in a pressure reactor, (b) A step of bringing the plurality of porous particles and a silicon precursor gas into contact under conditions effective for causing the deposition of silicon in the pores of the porous particles to provide a composite particle comprising a porous particle framework and elemental silicon in the pores of the porous particle framework, (c) During step (b), a step of recovering the exhaust gas from the pressure reactor, A method comprising continuously introducing the silicon precursor gas into the pressure reactor.

2. The method according to claim 1, wherein in step (b), the spatial time of the silicon precursor gas in contact with the porous particles is maintained in the range of 1 to 60 minutes, 2 to 45 minutes, 3 to 30 minutes, 4 to 25 minutes, or 5 to 20 minutes.

3. In step (b), the space velocity of the silicon precursor with respect to the reactor volume is at least 0.02 min －１ or at least 0.025 min －１ or at least 0.03 min －１ or at least 0.035 min －１ or at least 0.04 min －１ or at least 0.045 min －１ or at least 0.05 min －１ or at least 0.06 min －１ or at least 0.07 min －１ or at least 0.08 min －１ or at least 0.09 min －１ or at least 0.1 min －１ or at least 0.15 min －１ or at least 0.2 min －１ or at least 0.25 min －１ or at least 0.3 min －１ or at least 0.35 min －１ or at least 0.4 min －１ The method according to claim 1, wherein it is

4. During step (b), the space velocity of the silicon precursor relative to the reactor volume is 0.8 min⁻¹ －１ The following, or 0.75 minutes －１ The following, or 0.7 minutes －１ The following, or 0.65 minutes －１ The following, or 0.6 minutes －１ The following, or 0.55 minutes －１ The following, or 0.5 minutes －１ The method according to claim 1, which is as follows.

5. The method according to claim 1, wherein in step (b), the linear velocity of the silicon precursor gas in the pressure reactor is maintained in the range of 0.001 m / min to 0.4 m / min, or 0.005 m / min to 0.4 m / min, or 0.01 m / min to 0.4 m / min, or 0.02 m / min to 0.4 m / min, or 0.03 m / min to 0.4 m / min, or 0.04 m / min to 0.4 m / min, or 0.05 m / min to 0.4 m / min, or 0.06 m / min to 0.4 m / min, or 0.07 m / min to 0.4 m / min.

6. The method according to claim 1, wherein the concentration of the silicon precursor as the ratio of the silicon precursor gas introduced into the reactor is at least 20 volume%, or at least 30 volume%, or at least 40 volume%, or at least 50 volume%, or at least 60 volume%, or at least 70 volume%, or at least 80 volume%, or at least 90 volume%, or at least 95 volume%, or at least 98 volume%, or at least 99 volume%, or at least 99 volume%, or at least 99.9 volume%, or at least 99.99 volume%.

7. The flow rate of the silicon precursor gas to the pressure reactor is 0.2 g / min of silicon per kilogram of porous particles per minute. －１ kg －１ ~25g portion －１ kg －１ , or 0.5g －１ kg －１ ~20g portion －１ kg －１ , or 1g portion －１ kg －１ ~15g portion －１ kg －１ , or 1g portion －１ kg －１ ~14g portion －１ kg －１ , or 1g portion －１ kg －１ ~13g portion －１ kg －１ , or 1g portion －１ kg －１ ~12g portion －１ kg －１ , or 2g －１ kg －１ ~12g portion －１ kg －１ , or 3g －１ kg －１ ~12g portion －１ kg －１ , or 3g －１ kg －１ ~11g portion －１ kg －１ The method according to claim 1.

8. The flow rate of the silicon precursor gas into the pressure reactor is in the unit of grams of silicon per minute per liter of reactor volume (g min －１ / L ＲＶ ), and is 0.03 g min －１ / L ＲＶ to 40 g min －１ / L ＲＶ , or 0.04 g min －１ / L ＲＶ to 35 g min －１ / L ＲＶ , or 0.05 g min －１ / L ＲＶ to 30 g min －１ / L ＲＶ , or 0.06 g min －１ / L ＲＶ to 25 g min －１ / L ＲＶ , or 0.07 g min －１ / L ＲＶ to 20 g min －１ / L ＲＶ , or 0.08 g min －１ / L ＲＶ to 15 g min －１ / L ＲＶ , or 0.09 g min －１ / L ＲＶ to 10 g min －１ / L ＲＶ , or 0.1 g min －１ / L ＲＶ to 5 g min －１ / L ＲＶ , or 0.1 g min －１ / L ＲＶ to 1 g min －１ / L ＲＶ , or 0.15 g min －１ / L ＲＶ to 1 g min －１ / L ＲＶ , or 0.15 g min －１ / L ＲＶ to 0.95 g min －１ / L ＲＶ , or 0.2 g min －１ / L ＲＶ to 0.95 g min －１ / L ＲＶ , or 0.2 g min －１ / L ＲＶ to 0.9 g min －１ / L ＲＶ The method according to claim 1.

9. In step (a), the ratio of the mass of the porous particles to the volume of the pressure reactor is at least 20 g (g / L) per liter of reactor volume. ＲＶ ), or at least 50 g / L ＲＶ , or at least 80 g / L ＲＶ , or at least 100 g / L ＲＶ , or at least 150 g / L ＲＶ , or at least 200 g / L ＲＶ , or at least 250 g / L ＲＶ The method according to claim 1.

10. The method according to claim 1, wherein the mole fraction of the silicon precursor in the pressure reactor during step (b) is maintained in the range of 0.2 to 0.8, 0.3 to 0.7, or 0.4 to 0.6 with respect to the total number of moles of gaseous compounds in the pressure reactor.

11. The method according to claim 1, wherein, during the contact, the ratio of the flow rate of silicon in the silicon precursor gas into the pressure reactor in grams per minute to (mass of the porous particles in the pressure reactor in grams × internal free volume of the reactor in liters) is in the range of 0.0002 to 0.025, or 0.0002 to 0.0003, or 0.0004 to 0.

025.

12. The conditions in step (b) are 340°C to 500°C, or 350°C to 500°C, or 350°C to 480°C, or 350°C to 450°C, or 350°C to 420°C, or 340°C to 400°C, or 340°C to 395°C, or 340°C to 390°C, or 345°C to 400°C, or 345°C to 395°C, or 345°C to 390°C, or 350°C to 400°C, or 350°C to 395°C, or 350°C to 390°C, or 355°C to 385°C, or 355°C to 400°C, or 355°C to 395°C, or 35 The method according to claim 1, comprising a reaction temperature in the range of 5°C to 390°C, or 355°C to 385°C, or 355°C to 380°C, or 360°C to 400°C, or 360°C to 395°C, or 360°C to 390°C, or 360°C to 385°C, or 360°C to 380°C, or 365°C to 400°C, or 365°C to 395°C, or 365°C to 390°C, or 365°C to 385°C, or 365°C to 380°C, or 370°C to 400°C, or 370°C to 395°C, or 370°C to 390°C, or 370°C to 385°C, or 370°C to 380°C.

13. The method according to claim 1, wherein the conditions in step (b) include a pressure in the range of 50 kPa to 15000 kPa, or 50 kPa to 10000 kPa, or 120 kPa to 5000 kPa, or 150 kPa to 2000 kPa, or 200 kPa to 1600 kPa, or 250 kPa to 1500 kPa, or 300 kPa to 1200 kPa, or 400 kPa to 1000 kPa, or 500 kPa to 900 kPa, or 600 kPa to 800 kPa.

14. The method according to claim 1, wherein the porous particles include micropores and / or mesopores.

15. The porous particles (i) D in the range of 0.5 μm to 200 μm ５０ Particle size, (ii) 0.4 cm ３ / g ~ 2.2cm ３ The total pore volume of micropores and mesopores measured by gas adsorption in the range of / g, and (iii) PD measured by gas adsorption with a wavelength of 30 nm or less ５０ pore diameter, The method according to claim 1, comprising:

16. The silicon precursor is silane (SiH ４ ), disilane (Si ２ H ６ ), trisilane (Si ３ H ８ The method according to claim 1, wherein the method is selected from methylsilane, dimethylsilane, and chlorosilane.

17. The method according to claim 1, wherein step (b) includes stirring the porous particles, mechanically stirring the porous particles, or continuously mechanically stirring the porous particles.

18. The method according to claim 17, wherein the stirring is performed by a high-shear mixer.

19. Step (c) is, (i) Continuously recovering the exhaust gas from the pressure reactor, (ii) Recovering the exhaust gas semi-continuously from the pressure reactor, The method according to claim 1, including the method described in claim 1.

20. The method according to claim 1, wherein the composite particles formed in step (b) contain 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.

21. The method according to claim 1, wherein the composite particles formed in step (b) contain 62% by weight or less of silicon, or 60% by weight or less of silicon, or 58% by weight or less of silicon, or 56% by weight or less of silicon, or 54% by weight or less of silicon.

22. The method according to claim 1, wherein the composite particles formed in step (b) contain 30% to 70% by weight of silicon.

23. The method according to claim 1, wherein step (b) includes adjusting the flow rate of the silicon precursor into the pressure reactor from an initial flow rate to an adjusted flow rate, wherein the adjusted flow rate is greater than or less than the initial flow rate.

24. The method according to claim 23, wherein step (c) includes measuring the concentration of a silicon precursor in the exhaust gas, detecting a change in the concentration of a silicon precursor in the exhaust gas, and adjusting the flow rate of the silicon precursor into the pressure reactor in step (b) according to the detected change in the concentration of a silicon precursor in the exhaust gas.

25. The method according to claim 24, wherein step (c) includes detecting an increase in the concentration of silicon precursor in the exhaust gas, and reducing the flow rate of the silicon precursor into the pressure reactor in step (b) in accordance with the detected increase in the concentration of silicon precursor in the exhaust gas.

26. The method according to claim 24, wherein step (c) includes detecting a decrease in the concentration of a byproduct gas in the exhaust gas and reducing the flow rate of the silicon precursor into the pressure reactor in step (b) in accordance with the detected decrease in the concentration of the byproduct gas in the exhaust gas, wherein the byproduct gas is optionally hydrogen.

27. The method according to claim 25 or 26, wherein the flow rate of the silicon precursor into the pressure reactor is reduced by at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%.

28. The method according to claim 27, wherein the flow rate of the silicon precursor into the pressure reactor is reduced after 50% of the target mass of silicon has been deposited, or after 60% of the target mass of silicon has been deposited, or after 70% of the target mass of silicon has been deposited, or after 80% of the target mass of silicon has been deposited, or after 90% of the target mass of silicon has been deposited.

29. The method according to claim 25 or 26, wherein the absolute pressure in the reactor is kept constant while the flow rate of the silicon precursor into the pressure reactor is reduced.

30. The method according to claim 1, wherein the exhaust gas contains 2.5% to 80% by volume of silicon precursor, or 2.5% to 70% by volume, or 2.5% to 60% by volume, or 2.5% to 50% by volume, or 5% to 80% by volume, or 5% to 70% by volume, or 5% to 60% by volume, or 5% to 50% by volume of silicon precursor.

31. In step (c), the exhaust gas recovered from the reactor contains a silicon precursor and at least one by-product gas, and the method is A step of sending at least a portion of the exhaust gas to a gas separation unit, A step of operating the gas separation unit so that the silicon precursor is separated from the at least one byproduct gas, thereby providing an enriched gas stream in which the silicon precursor is enriched compared to the exhaust gas and a waste gas stream in which the silicon precursor is depleted compared to the exhaust gas, The method according to claim 1, further comprising:

32. The method according to claim 31, further comprising the step of reusing at least a portion of the enriched gas flow in the pressure reactor.

33. The method according to claim 31, further comprising separating the bypass flow from the discharge flow and reusing the bypass flow in the pressure reactor without separating the silicon precursor in the bypass flow from the by-product gas in the bypass flow.

34. The method according to claim 31, wherein the gas separation unit includes a membrane separation system, for example, a polymer membrane separation system and / or an alloy membrane separation system, a pressure swing adsorption system, a cryogenic separation system, a gas distillation system, or a combination thereof.

35. The method according to claim 34, wherein the gas separation unit includes a membrane separation system and a pressure swing adsorption system.

36. The by-product gas contains hydrogen, and the gas separation unit contains hydrogen (H ２ The method according to claim 34, comprising a selective membrane.

37. The ratio of the internal surface area of ​​the pressure reactor to the mass of the porous particles in the pressure reactor is 1 m ２ / kg or less, or 0.9m ２ / kg or less, or 0.8m ２ / kg or less, or 0.7m ２ / kg or less, or 0.6m ２ / kg or less, or 0.5m ２ / kg or less, or 0.4m ２ / kg or less, or 0.3m ２ The method according to claim 1, wherein the amount is less than or equal to / kg.

38. The ratio of the internal surface area of ​​the pressure reactor to the mass of porous particles in the pressure reactor is at least 0.001 m². ２ / kg, or at least 0.002m ２ / kg, or at least 0.003m ２ / kg, or at least 0.004m ２ / kg, or at least 0.006m ２ / kg, or at least 0.008m ２ / kg, or at least 0.01m ２ The method according to claim 1, wherein the amount is / kg.

39. The method according to claim 1, wherein the bed depth of the porous particles in the pressure reactor 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.

40. The method according to claim 1, further comprising the step of bringing the composite particles and a passivating agent into contact under conditions effective for passivating the composite particles.

41. A step of interrupting silicon deposition to form intermediate composite particles; A step of bringing intermediate composite particles and a passivating agent into contact under conditions effective for passivating the intermediate composite particles and providing the passivated intermediate composite particles; A process of bringing passivated intermediate composite particles and a silicon precursor gas into contact under conditions effective for providing composite particles by causing silicon to deposit into the pores of the passivated intermediate composite particles. The method according to claim 40, which includes the following.

42. The method according to claim 40, wherein the composite particles and the passivating agent are brought into contact in a pressure reactor.

43. The method according to claim 42, wherein the composite particles are then transferred to another container and brought into contact with a second passivating agent, wherein the first passivating agent and the second passivating agent may be the same or different.

44. The method according to claim 40, wherein the passivating agent is selected from oxygen-containing gases, ammonia, gases containing ammonia and oxygen, phosphine, alcohols, amines, and thiols.

45. The passivating agent is of the following formula: (i) HX-R 2, and (ii) HX-C(O)-R 1 The method according to claim 40, comprising a compound of the formula (wherein X represents O, S, NR1 or PR1, each R1 independently represents H or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, R2 represents an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, or R1 and R2 together form an unsubstituted or substituted ring structure having 3 to 8 carbon atoms in the ring).

46. The method according to claim 40, wherein the passivating agent is selected from an alkene, an alkyne, or a compound containing a carbonyl functional group.

47. The passivating agent is of the following formula: (i) R 1 -CH=CH-R 1 , (ii) R 1 - C ≡ C - R 1, and, (iii) O=CR 1 R 1 (i) CH₂ = CH₁-R₁, and, (ii) HC≡CR 1 The method according to claim 40, comprising one or more compounds of the formula (wherein each R1 independently represents H, or an unsubstituted or substituted aliphatic or aromatic hydrocarbyl group having 1 to 20 carbon atoms, or two R1 groups form an unsubstituted or substituted ring structure containing 3 to 8 carbon atoms in the ring).

48. The method according to claim 1, further comprising the step of bringing composite particles and a carbon precursor gas into contact under conditions effective for causing carbon deposition in the pores and / or on the surface of the composite particles.

49. The method according to claim 1, further comprising the step of controlling the flow rate of silicon precursor gas into the pressure reactor and / or the flow rate of exhaust gas recovered from the pressure reactor during the contact, in order to maintain the pressure in the pressure reactor in the range of 50 kPa to 15,000 kPa.

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