Continuous process for preparing silicon-containing composite particles - Patents.com

Abstract

The present invention relates to a continuous process for preparing composite particles, comprising continuously introducing a porous particle feedstock and a silicon precursor gas into a first reaction zone, and continuously withdrawing the composite particles and exhaust gas from the first reaction zone, the composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton.

Description

[Technical field]

[0001] The present invention relates generally to silicon-containing electroactive materials, and more particularly to a continuous process for producing 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 have been synthesized by chemical vapor infiltration (CVI) in different reactor systems (static, rotating and FBR). Porous conductive particles are contacted with a stream of silicon precursor gas, typically silane gas, at atmospheric pressure and temperatures between 400° C. and 700° C. All these reactor configurations work as batch modes for the solid carbon scaffold and continuous modes for the silicon precursor gas. The reaction rates at these temperatures are high, but the silicon precursor gas molecules have to traverse a tortuous path to access the pore spaces that are only a few nanometers in diameter. This means that to obtain uniform infiltration in such reactor systems, the reaction temperature needs to be relatively high to avoid mass transfer becoming the rate-limiting step. Furthermore, the silicon precursor gas generally needs to be used at high dilution in an inert gas. Too high a concentration of silicon precursor gas leads to rapid and uncontrolled deposition of silicon deposits in 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 in narrow pores, but is rough and bare, and therefore exhibits poor cycling behavior. However, the use of low concentrations of silicon precursor gas means that reaction times to achieve the required silicon loading in the composite particles are relatively long, reducing throughput.

[0008] Another drawback of these systems is that good mixing of solids and gases is required, otherwise the product batch may contain compositional non-uniformities: solids that have a longer contact time with the dilute silicon precursor gas will contain more silicon than those that have a shorter contact time with the unreacted silane gas stream, resulting in unequal deposition across the powder bed.

[0009] A further drawback of these systems is that batch operations are not amenable to scale-up and therefore 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] First Reaction Zone In a first aspect, the present invention provides a continuous method for preparing composite particles, the method comprising: (a) providing a chemical vapor infiltration unit including at least a first reaction zone; (b) providing a feedstock comprising porous particles and continuously introducing the porous particles into a first reaction zone; (c) continuously introducing a silicon precursor gas into the first reaction zone; (d) providing conditions in the reaction zone effective to cause deposition of silicon within the pores of the porous particles; (e) continuously recovering composite particles from the first reaction zone, the composite particles comprising a porous particulate skeleton and elemental silicon within the pores of the porous particulate skeleton; (f) continuously recovering exhaust gas from the first reaction zone; Includes.

[0014] The present invention therefore generally relates to a continuous method of preparing a composite particulate material, in which nanoscale silicon domains are deposited within 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 scaffold derived from the porous particle feedstock identified in step (b) and a second component in the form of a plurality of nanoscale silicon domains disposed within the pore structure of the porous particle scaffold. 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 the silicon within the micropores and / or mesopores of the porous particle.

[0015] The term continuous is used herein to distinguish between a first reaction zone and a batch type operation. In a batch reactor, a batch of starting materials is added to the reactor in a first step, the reaction is allowed to proceed for a specified period of time, and then a batch of product is withdrawn from the reactor. A batch reactor contains a full inventory of reactants for the duration of the reaction, and then the full inventory of products is withdrawn. Continuous operation as defined herein refers to a reaction in which both the introduction of starting materials to the reaction zone and the withdrawal of products from the reaction zone are carried out continuously and simultaneously during the course of the reaction, and thus the reaction zone contains only a portion of the inventory of reactants.

[0016] A continuous reaction can be achieved by using a plug-flow type reactor, in which the reacting materials move along a path from the inlet of the reactor to the outlet of the reactor, and thus the movement time defines the residence time of the particles in the reactor. A continuous operation can also be achieved in a non-plug flow manner, in which a reactor is used that has an inlet and an outlet, but there is no continuous path between the inlet and the outlet, i.e., the particles are allowed to mix freely within the reaction zone. In a non-plug flow mode, the product withdrawn from the reaction zone is a statistical mixture of materials with a distribution of residence times. The rate at which the starting materials are fed to the reactor, the rate at which the products are withdrawn, and the size of the reactor define the average residence time of the materials in the reactor. In principle, continuous operation does not exclude the possibility of bias in the flow rate of materials into or out of the reactor, for example, a continuous reactor may be operated in a pulsed manner. However, as defined herein, continuous operation of a reactor means that both the introduction of starting materials to the reaction zone and the withdrawal of products from the reaction zone are carried out continuously and simultaneously during the progress of the reaction, thus providing that the reaction zone contains only a portion of the amount of reactants used.

[0017] The first reaction zone is preferably operated in a plug flow mode with respect to the particles, such that the reactor has an axial direction, with limited axial mixing of the particles, resulting in a narrow distribution of particle residence times in the reactor. Plug flow mode is defined herein as a residence time distribution in which the standard deviation of the residence times is 30% or less of the average residence time, more preferably 20% or less, more preferably 10% or less, more preferably 5% or less of the average residence time. Since in plug flow mode all particles have essentially the same residence time (assuming limited axial mixing), this mode of operation results in a composite particle product that is more uniform in composition than if the reaction were run in a non-plug flow mode.

[0018] For operation in plug flow mode, the reaction zone of the chemical vapor infiltration (CVI) unit preferably has the form of a continuous tubular reactor having a first end, a second end and a length, where the porous particles are introduced through a particle inlet at the first end of the tubular reactor and the composite particles are withdrawn through a particle outlet at the second end of the tubular reactor. The cross section of the tubular reactor may be of any suitable shape. For example, the cross section of the tubular reactor may be circular, elliptical, rectangular or square, or may be irregular in shape.

[0019] The tubular reaction zone can be arranged substantially horizontally over its length, e.g., with an inclination of less than ±20°, preferably less than ±10°, from the horizontal. The porous particles increase in density as silicon is deposited in the pores, and the horizontal arrangement of the tubular reaction zone prevents backmixing of the particles as they move from the particle inlet to the particle outlet. Alternatively, the tubular reaction zone can be arranged to have a negative gradient, such that the particle outlet is located below the particle inlet. Alternatively, the tubular reaction zone can be arranged vertically, such that the particle inlet is at the top of the tubular reaction zone and the particle outlet is at the bottom of the tubular reaction zone.

[0020] The tubular reactor can be operated as a co-current reactor or a counter-current reactor. In co-current operation, the silicon precursor gas is introduced through an inlet proximal to the first end of the tubular reactor, and the exhaust gas is collected through a gas discharge outlet proximal to the second end of the tubular reactor. In counter-current operation, the silicon precursor gas is introduced through an inlet proximal to the second end of the tubular reactor, and the exhaust gas is collected through a gas discharge outlet proximal to the first end of the tubular reactor.

[0021] More preferably, the silicon precursor gas can be introduced into the tubular reactor through multiple inlets spaced apart along the length of the tubular reactor. In this case, the exhaust gas can be collected through one or more gas discharge outlets located at any position along the length of the tubular reactor. For example, when the silicon precursor gas is introduced through multiple inlets spaced apart along the length of the tubular reactor, the exhaust gas can be collected (i) through a gas discharge outlet proximate the second end of the tubular reactor, or (ii) through a gas discharge outlet proximate the first end of the tubular reactor, or (iii) through multiple gas discharge outlets spaced apart along the length of the tubular reactor.

[0022] The use of multiple inlets spaced along the length of the tubular reactor for silicon precursor gas can be advantageous to ensure that the concentration of silicon precursor gas is substantially uniform along the length of the reaction zone. When the reactor is operated in a simple co-current or counter-current manner, the concentration of silicon precursor gas in the reactor decreases from the inlet to the exhaust gas outlet. As a result, the reaction rate increases in the part of the reaction zone adjacent to the silicon precursor gas inlet, and decreases in the remaining part of the length of the reaction zone. Depending on the reactor conditions, an excessive reaction rate adjacent to the silicon precursor gas inlet can result in the uncontrolled type of deposition described above, where the high rate of deposition quickly blocks the pore space, thus preventing the silicon precursor gas from penetrating the fine pore structure, and instead silicon is deposited as coarse domains that exhibit poor circulation behavior that is unacceptable in LIBs.

[0023] The tubular reactor preferably includes a means for conveying particles from its first end to its second end. The means for conveying particles from the first end to the second end of the tubular reactor may include at least one helix, defined herein as a rotating shaft having a helical form arranged axially within the reactor, such that the rotation of the shaft conveys the porous particles along the length of the tubular reactor. Optionally, the device for conveying particles from the first end to the second end of the tubular reactor includes a pair of cooperating helices, where the helices of each helical are arranged to overlap. As a result of this paired helical arrangement, the particles are interchanged from the path of one helical to the path of the other, thereby facilitating radial mixing and heat transfer within the particles as they are conveyed through the tubular reaction zone.

[0024] Optionally, the tubular reactor preferably includes both a device for conveying particles from its first end to its second end, and an internal mixing element, e.g., a paddle for radial mixing of the particles. For example, the device for conveying particles may include the above-mentioned helix, where the helix is ​​provided with additional mixing elements and / or blade modifications that provide radial mixing. Alternatively, the reactor wall may include geometric features that provide radial mixing.

[0025] Optionally, the tubular reactor includes both a geometric feature that rotates and conveys the particles from its first end to its second end, e.g., a helical blade, and an internal mixing geometric element, e.g., a paddle for radial mixing of the particles. For example, the particle conveying device may include a helical blade with additional mixing elements and / or blade modifications that provide radial mixing.

[0026] Optionally, the tubular reactor includes a moving interior that conveys the powder from its first end to its second end, where the moving interior optionally includes a moving belt conveyor, bucket conveyor, or tube chain conveyor, or a vertical conveyor. For example, the particle conveying device may include a vertical bucket conveyor or several vertical bucket conveyors, or a vertical conveyor belt within the heated reactor vessel, providing a means for continuous introduction of porous particles and continuous withdrawal of composite particles.

[0027] Optionally, the tubular reactor preferably comprises a vertically vibrating screw conveyor furnace.

[0028] The tubular reactor may include a vibrating surface as an alternative means of conveying the particles from its first end to its second end. In this embodiment, the porous particles are conveyed through the tubular reactor from its first end to its second end by vibration. Preferably, the amplitude of the vibration is 0.01 mm to 10 cm, more preferably 0.1 mm to 10 cm, more preferably 1 cm to 10 cm. The frequency of the vibration is suitably 0.01 Hz to 100 Hz, more preferably 0.1 Hz to 10 Hz.

[0029] The temperature in the first reaction zone is preferably in the range of 340° C. to 500° C., more preferably 350° C. to 480° C., more preferably 350° C. to 450° C., more preferably 350° C. to 420° C., more preferably 350° C. to less than 400° C., more preferably 355° C. to 395° C., more preferably 360° C. to 390° C., more preferably 365° C. to 385° C., more preferably 370° C. to 385° C., for example, 370° C. to 395° C. Alternatively, the temperature in the first reaction zone may be in the range of 400° C. to 500° C., or 400° C. to 490° C., or 400° C. to 480° C., or 400° C. to 470° C., or 400° C. to 460° C.

[0030] The method of the present invention is preferably operated under a regime of supplying silicon precursor gas to the first reaction zone in high concentration or even neat form. In order to control the reaction rate and to achieve controlled penetration of the silicon precursor gas into the pore network of the porous particles, the reaction temperature in the first reaction zone is 420°C or less, more preferably 410°C or less, more preferably 400°C or less, more preferably 395°C or less.

[0031] The pressure in the first reaction zone is preferably in the range of 1 kPa to 10,000 kPa, or 10 kPa to 6,000 kPa, or 20 kPa to 4,000 kPa, or 50 kPa to 2,000 kPa, or 80 kPa to 1,500 kPa, or 90 kPa to 1,000 kPa, or 90 kPa to 600 kPa, or about 100 kPa.

[0032] Optionally, the first reaction zone may be operated at a pressure above atmospheric pressure, for example, from 110 kPa to 10,000 kPa, or from 120 kPa to 5,000 kPa, or from 150 kPa to 2000 kPa, or from 200 kPa to 1800 kPa, or from 200 kPa to 1600 kPa, or from 250 kPa to 1500 kPa, or from 300 kPa to 1200 kPa, or from 400 kPa to 1000 kPa, or from 500 kPa to 900 kPa, or from 600 kPa to 800 kPa.

[0033] The pressure in the first reaction zone may be 650 kPa or less, or 600 kPa or less, or 500 kPa or less. For example, the pressure may be in the range of 100 kPa to 600 kPa. The pressure in the first reaction zone may be 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. Operating at elevated pressure has the advantage of reducing mass transfer limitations on the reaction rate and facilitating penetration of the silicon precursor gas into the pore network of the porous particles. However, to prevent uncontrolled reaction, it is preferred to reduce the temperature in the reaction zone as the pressure increases. In particular, when the pressure in the first reaction zone is greater than 100 kPa, the reaction temperature in the first reaction zone is preferably no greater than 450° C., more preferably no greater than 430° C., more preferably no greater than 420° C., more preferably no greater than 410° C., more preferably no greater than 400° C., more preferably no greater than 395° C. Unless otherwise specified, all pressure values ​​disclosed herein are absolute pressures.

[0034] The average residence time of the particles in the first reaction zone between the introduction of the porous particles in step (b) to the first reaction zone and the withdrawal of the composite particles from the first reaction zone in step (e) is preferably from 10 minutes to 300 minutes, or from 15 minutes to 240 minutes, or from 20 minutes to 180 minutes, or from 30 minutes to 120 minutes, or from 40 minutes to 90 minutes. The average residence time can typically be calibrated for any given reactor based on the dimensions of the reactor and the operating speed of any mechanical equipment conveying the particles through the reaction zone.

[0035] As mentioned above, the first reaction zone is preferably operated in an essentially plug flow manner with respect to the particles. Bias in the particle residence time resulting in a broadening of the particle residence time distribution can be prevented by using a reaction vessel with an interior that prevents axial mixing. For example, in the above-mentioned tubular reactors that include at least one helix that conveys the particles through the reaction zone, the pitch of the screw of the helix can determine the degree of axial mixing. Preferably, the pitch of the helix blades used in the tubular reactor according to the invention is not more than 1.5 times the outer diameter of the helix blades, more preferably not more than 1.2 times the outer diameter of the helix blades, more preferably not more than 1.0 times the outer diameter of the helix blades. Preferably, the first reaction zone has a length of at least 5 times the pitch of the helix blades, more preferably at least 8 times the pitch of the helix blades, more preferably at least 10 times the pitch of the helix blades.

[0036] The volume of the first reaction zone in liters (L) is (0.003 L g -1 ×F PP ×RT)~(0.06L g -1 ×F PP × RT), where F PP is the rate at which the porous particles are fed into the first reaction zone in grams per minute, and RT is the average residence time of the particles in the first reaction zone in minutes. In other words, the first reaction zone can accommodate 3 cm of porous particles per gram of porous particles introduced into the reactor per residence time interval. 3 ~60cm 3 For example, to input 100 g / hour of porous particles and set the average residence time to 1 hour, a reactor volume of 0.3 L to 6 L is required. Preferably, the volume of the first reaction zone in liters (L) is less than (0.05 L g -1 ×F PP ×RT), more preferably less than (0.04 L g -1 ×F PP ×RT), more preferably less than (0.03 L g -1×F PP ×RT), more preferably less than (0.02 L g -1 ×F PP ×RT), more preferably less than (0.01 L g -1 ×F PP ×RT), more preferably less than (0.009 L g -1 ×F PP ×RT), more preferably less than (0.008 L g -1 ×F PP ×RT), more preferably less than (0.007 L g -1 ×F PP ×RT), more preferably less than (0.006 L g -1 ×F PP × RT). The small reactor volume relative to the mass of particles fed into the reactor is advantageous in that it can reduce axial mixing of the particles, thus allowing the reactor to more closely approximate an ideal plug flow reactor.

[0037] The ratio of the rate at which the silicon precursor gas is pumped into the first reaction zone to the rate at which the porous particles are pumped into the first reaction zone is preferably 0.25 to 2, or 0.4 to 1.9, or 0.6 to 1.8, or 0.7 to 1.7, or 0.8 to 1.6, or 0.9 to 1.6, or 1 to 1.5, based on grams of silicon in the silicon precursor gas per gram of porous particles. In other words, between 0.25 grams and 2 grams of silicon (in the form of silicon precursor gas) are introduced into the reactor per gram of porous particles during the residence time of the particles in the first reaction zone.

[0038] The first reaction zone is preferably operated such that the consumption of silicon precursor gas is at least 20%, preferably at least 50%, preferably at least 60%, preferably at least 80%, preferably at least 90%. Optionally, the first reaction zone is operated such that the consumption of silicon precursor gas is 99% or less, or 98% or less. A low level of unreacted silicon precursor gas in the exhaust gas can be used as an indicator of a controlled reaction rate.

[0039] The composite particles recovered from the first reaction zone preferably contain from 0.2 grams to 1.8 grams of silicon per gram of porous particle skeleton.

[0040] The ratio of the rate at which the silicon precursor gas is fed into the first reaction zone to the rate at which the porous particles are fed is based on the silicon precursor gas that is freshly fed. It is not excluded that the unreacted silicon precursor gas can be taken from the exhaust gas recovered from the first reaction zone in step (f) and recycled into the first reaction zone. The silicon precursor gas that is recycled in the first reaction zone is not included in the above-mentioned feeding ratio.

[0041] The exhaust gas from the first reaction zone includes by-product gas from the CVI reaction, and optionally unreacted silicon precursor gas.When the exhaust gas from the first reaction zone contains a significant amount of unreacted silicon precursor gas, it may be appropriate to remove the unreacted silicon precursor gas from the exhaust gas, and recycle the removed silicon precursor gas to the first reaction zone.Means for removing the unreacted silicon precursor gas from the exhaust gas include semi-permeable membrane separation process, pressure swing adsorption process, and cryogenic separation process.

[0042] Optionally, the silicon precursor gas is preheated prior to being introduced into the first reaction zone. 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 first reaction zone), preferably at a temperature of (T RZ -100)℃ or higher, preferably (T RZ Preheat to a temperature of at least -50)℃.

[0043] To ensure that the composite particles recovered from the first reaction zone in step (e) are uniform over time, it is preferred to operate the process defined in steps (a) to (f) under steady state conditions.

[0044] The method of the present invention optionally further includes monitoring the partial pressure of the silicon precursor gas in the exhaust gas recovered from the first reaction zone, and optionally adjusting one or more of the temperature in the first reaction zone, the pressure in the first reaction zone, or the rate at which the silicon precursor gas is delivered to the first reaction zone in response to a measured deviation of the partial pressure of the silicon precursor gas from a steady state partial pressure.

[0045] Preheat Zone Preferably, step (b) comprises pretreating the porous particles prior to introduction into the first reaction zone. In particular, step (b) preferably further comprises preheating the feedstock comprising the porous particles in a preheating zone and then introducing the preheated feedstock into the first reaction zone. The feedstock comprising the porous particles is then subjected to a preheating process in a preheating zone, followed by introduction of the preheated feedstock into the first reaction zone. RZ -50)℃ or higher, preferably (T RZ -30)℃ or higher, preferably (T RZ It is preferable to preheat the substrate to a temperature of at least T RZ is the reaction temperature of the first reaction zone.

[0046] The preheat zone may optionally take the form of a tubular vessel having a first end, a second end and a length, where the porous particles are introduced through a particle inlet at the first end of the tubular vessel and the composite particles are withdrawn through a particle outlet at the second end of the vessel reactor. One or more heating elements are disposed along the length of the tubular vessel, and the tubular vessel preferably includes a conveying means for transporting the porous particles from the particle inlet to the particle outlet.

[0047] During preheating of the porous particles, it is preferred to flush the preheating zone with an inert gas, for example, an inert gas selected from nitrogen and argon. Optionally, the preheating zone may be operated under vacuum. For example, the pressure of the preheating zone may be less than 100 kPa, or less than 80 kPa, or less than 60 kPa, or less than 40 kPa, or less than 20 kPa.

[0048] Second Reaction Zone The CVI unit optionally comprises at least a first reaction zone and a second reaction zone, and thus the CVI reaction is carried out in at least two stages. When the CVI unit comprises a first reaction zone and a second reaction zone, the first reaction zone may be as defined above, and the method comprises: (g) continuously introducing the composite particles recovered from the first reaction zone in step (e) into a second reaction zone; (h) continuously introducing a silicon precursor gas into the second reaction zone; (i) providing conditions in a second reaction zone effective to cause deposition of silicon within the pores of the porous particles; (j) continuously recovering composite particles from the second reaction zone, the composite particles comprising a porous particulate skeleton and elemental silicon within the pores of the porous particulate skeleton; (k) continuously recovering exhaust gas from the second reaction zone; Further includes:

[0049] One advantage of a staged CVI process using two or more reaction zones is that different CVI reaction conditions can be applied in each of the reaction zones. For example, the bulk of the silicon deposition can take place in a first reaction zone, while a second reaction zone can be operated under conditions that ensure finer control of the later stages of deposition, by which point the available pore volume has been depleted and uncontrolled deposition can result in the undesirable deposition of coarse silicon domains, especially on the outer surfaces of the porous particles.

[0050] The second reaction zone is preferably operated in a plug flow mode with respect to the particles as described above.

[0051] The second reaction zone may optionally comprise a tubular reactor having any of the features of the tubular reactor described in relation to the first reaction zone. In particular, the first reaction zone and the second reaction zone may comprise respective tubular reactors having means in step (g) for conveying the composite particles recovered from the first reaction zone in step (e) to the second reaction zone.

[0052] The tubular reactor of the second reaction zone can be operated as a co-current or counter-current reactor. More preferably, the silicon precursor gas can be introduced into the tubular reactor of the second reaction zone through multiple inlets spaced along the length of the tubular reactor. In this case, the exhaust gas from the second reaction zone can be collected through one or more gas discharge outlets located anywhere along the length of the tubular reactor, as described for the first reaction zone.

[0053] The tubular reactor of the second reaction zone preferably includes a device for conveying particles from its first end to its second end, e.g., at least one helix, optionally a pair of cooperating helices arranged such that the helices of each helix overlap.

[0054] Optionally, the tubular reactor preferably includes geometric features, such as helical blades, that rotate and convey the particles from a first end to a second end thereof, and internal mixing geometric elements, such as paddles for radial mixing of the particles. For example, the particle conveying device may include helical blades with additional mixing elements and / or blade modifications that provide radial mixing.

[0055] Optionally, the tubular reactor includes a moving interior that conveys the powder from its first end to its second end, where the moving interior optionally includes a moving belt conveyor, bucket conveyor, or tube chain conveyor, or a vertical conveyor. For example, the particle conveying device may include a vertical bucket conveyor or several vertical bucket conveyors, or a vertical conveyor belt within the heated reactor vessel, providing a means for continuous introduction of porous particles and continuous withdrawal of composite particles.

[0056] Optionally, the reactor preferably comprises a vertically vibrating screw conveyor furnace.

[0057] The tubular reactor may include a vibrating surface as an alternative means of conveying the particles from its first end to its second end. In this embodiment, the porous particles are conveyed through the tubular reactor from its first end to its second end by vibration. Preferably, the amplitude of the vibration is 0.01 mm to 10 cm, more preferably 0.1 mm to 10 cm, more preferably 1 cm to 10 cm. The frequency of the vibration is suitably 0.01 Hz to 100 Hz, more preferably 0.1 Hz to 10 Hz.

[0058] The temperature in the second reaction zone is preferably in the range of 350°C to 450°C, or 350°C to 420°C, or 350°C to less than 400°C, or 355°C to 395°C, or 360°C to 390°C, or 365°C to 385°C, or 370°C to 385°C, for example, 370°C to 395°C.

[0059] The pressure in the second reaction zone is preferably in the range of 1 kPa to 10,000 kPa, or 10 kPa to 6,000 kPa, or 20 kPa to 4,000 kPa, or 50 kPa to 2,000 kPa, or 80 kPa to 1,500 kPa, or 90 kPa to 1,000 kPa, or 90 kPa to 600 kPa, or about 100 kPa.

[0060] Optionally, the second reaction zone may be operated at a pressure above atmospheric pressure, for example, from 110 kPa to 10,000 kPa, or from 120 kPa to 5000 kPa, or from 150 kPa to 2000 kPa, or from 200 kPa to 1800 kPa, or from 200 kPa to 1600 kPa, or from 250 kPa to 1500 kPa, or from 300 kPa to 1200 kPa, or from 400 kPa to 1000 kPa, or from 500 kPa to 900 kPa, or from 600 kPa to 800 kPa.

[0061] The pressure in the second reaction zone may be 650 kPa or less, or 600 kPa or less, or 500 kPa or less. For example, the pressure may be in the range of 100 kPa to 600 kPa. The pressure in the second reaction zone may be 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. When the pressure in the second reaction zone is greater than 100 kPa, the reaction temperature in the second reaction zone 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.

[0062] To control the reaction rate and to achieve controlled penetration of the silicon precursor gas into the pore network of the porous particles, the reaction temperature in the second reaction zone is 420° C. or less, more preferably 410° C. or less, more preferably 400° C. or less, more preferably 395° C. or less.

[0063] The operation of the first reaction zone and the operation of the second reaction zone preferably differ with respect to one or more of the reaction temperature, reaction pressure, particle residence time, and the rate at which the silicon precursor gas is delivered. In particular, the second reaction zone is preferably operated under conditions such that the silicon deposition rate is reduced in the second reaction zone compared to the first reaction zone and / or the total mass of silicon deposited in the second reaction zone is less than the total mass of silicon deposited in the first reaction zone.

[0064] For example, the reaction temperature of the second reaction zone is optionally 5° C. to 50° C. lower, or 10° C. to 20° C. lower than the reaction temperature of the first reaction zone.

[0065] The average residence time of the particles in the second reaction zone from the introduction of the composite particles to the second reaction zone in step (g) to the withdrawal of the composite particles from the second reaction zone in step (j) is preferably from 2 to 60 minutes, or from 5 to 30 minutes, or from 10 to 20 minutes. The average residence time of the particles in the second reaction zone is preferably shorter than the average residence time of the particles in the first reaction zone.

[0066] The second reaction zone is preferably operated in plug flow mode as described above.

[0067] The volume of the second reaction zone in liters (L) is (0.001 L g -1 ×F CP ×RT)~(0.02L g -1 ×F CP × RT), where F CP is the rate at which the composite particles are pumped into the second reaction zone, based on grams of porous particle scaffold per minute, and RT is the average residence time of the particles in the second reaction zone, in minutes. Preferably, the volume of the second reaction zone in liters (L) is less than (0.01 L g -1 ×F CP ×RT), more preferably less than (0.008 L g -1 ×F CP ×RT), more preferably less than (0.007 L g -1 ×F CP ×RT), more preferably less than (0.006 L g -1 ×F CP ×RT), more preferably less than (0.005 L g -1 ×F CP ×RT), more preferably less than (0.004 L g -1 ×F CP × RT).

[0068] To facilitate comparison between the first and second reaction zones, the mass of the composite particles in the second reaction zone, and reaction parameters defined by reference to the mass of the composite particles in the second reaction zone, are normalized to the mass of the porous particle scaffold, so that the mass of silicon added to the composite particles per gram of porous particle feedstock in each of the first and second reaction zones can be directly compared.

[0069] The ratio of the rate at which the silicon precursor gas is pumped into the second reaction zone to the rate at which the composite particles are pumped into the second reaction zone is preferably 0.02-0.3, or 0.03-0.25, or 0.04-0.2, or 0.05-0.18, or 0.06-0.15, based on grams of silicon in the silicon precursor gas per gram of porous particle scaffold. In other words, during the residence time of the particles in the second reaction zone, 0.02 grams to 0.3 grams of silicon atoms (in the form of silicon precursor gas) are introduced into the reactor per gram of porous particle scaffold.

[0070] The second reaction zone is preferably operated such that the consumption of silicon precursor gas is at least 50%, preferably at least 80%, preferably at least 90%, preferably at least 95%. Optionally, the second reaction zone is operated such that the consumption of silicon precursor gas is 99% or less, or 98% or less. A low level of unreacted silicon precursor gas in the exhaust gas can be used as an indicator of the controlled reaction rate.

[0071] In another embodiment, the first reaction zone is operated such that the consumption of silicon precursor gas is 90% or less, or 80% or less, or 60% or less, and exhaust gas from the first reaction zone is used as at least a portion of the silicon precursor gas fed to the second reaction zone.

[0072] The composite particles recovered from the second reaction zone contain silicon deposited in the first reaction zone, and preferably the silicon deposited in the second reaction zone is between 0.016 grams and 0.024 grams per gram of porous particle skeleton.

[0073] More preferably, between 0.2 grams and 1.6 grams of silicon are deposited per gram of porous particulate scaffold in the first reaction zone and between 0.016 grams and 0.024 grams of silicon are deposited per gram of porous particulate scaffold in the second reaction zone.

[0074] As described above, the ratio of the rate at which the silicon precursor gas is fed to the second reaction zone to the rate at which the composite particles are fed to the second reaction zone is based on the silicon precursor gas that is freshly fed. Unreacted silicon precursor gas can be taken from the exhaust gas recovered from the second reaction zone in step (k) and recycled into the second reaction zone. The silicon precursor gas that is recycled to the second reaction zone in this manner is not included in the above-mentioned feeding ratio.

[0075] The exhaust gas from the second reaction zone comprises by-product gas from the CVI reaction and optionally unreacted silicon precursor gas. The content of silicon precursor gas in the exhaust gas from the second reaction zone is preferably at least 1 vol.%, or at least 2 vol.%, or at least 5 vol.%, or at least 10 vol.%, or at least 15 vol.%. As described above for the first reaction zone, the unreacted silicon precursor gas can be taken out and recycled. Optionally, the unreacted silicon precursor gas in the exhaust gas from the first reaction zone and the second reaction zone can be taken out in a combined take-out process, such as a semi-permeable membrane separation process, a pressure swing adsorption process, or a cryogenic separation process.

[0076] The second reaction zone is preferably operated in series with the first reaction zone such that the composite particles recovered from the first reaction zone in step (e) are continuously transferred to the second reaction zone. In step (g), the particles recovered from the first reaction zone in step (e) can be introduced into the second reaction zone through an airlock valve, which is defined herein as a valve capable of separating the gas flow in the first reaction zone from the gas flow in the second reaction zone, and in particular, capable of separating the pressure difference between these two reaction zones. A preferred form of airlock valve for handling particles is a rotary valve (also known in the art as a rotary airlock feeder). Alternatively, in step (g), the particles may be introduced into the second reaction zone through a ball valve, a dome valve, a piston valve, or a screw feeder.

[0077] To ensure that the composite particles recovered from the first reaction zone in step (j) are uniform over time, it is preferred to operate the process defined in steps (g) through (k) under steady state conditions.

[0078] The method of the present invention optionally further comprises monitoring the partial pressure of the silicon precursor gas in the exhaust gas recovered from the second reaction zone, and optionally adjusting one or more of the temperature in the second reaction zone, the pressure in the second reaction zone, or the rate at which the silicon precursor gas is delivered to the second reaction zone in response to a measured deviation of the partial pressure of the silicon precursor gas from a steady state partial pressure.

[0079] feedstock 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 adsorption50 pore diameter, It is preferred that the compound has the formula:

[0080] 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.

[0081] 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.

[0082] Generally, porous particles have a D in the range of 0.5 μm to 200 μm. 50 Optionally, the porous particles have a 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] PD of porous particles 50 The pore size is 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] Any pore volume measured by mercury porosimetry 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 porosimetry above 100 nm is assumed to be interparticle porosity for purposes of this invention, and this pore volume is also disregarded.

[0106] Mercury intrusion 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 intrusion 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, see PA Webb and C. Orr, "Analytical Methods in Fine Particle Technology", 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] Mesopores can also be obtained by known templating processes using extractable pore formers such as MgO and other colloidal or polymeric templates, which can be removed by thermal or chemical means after pyrolysis or activation.

[0114] 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:

[0115] 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.

[0116] 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:

[0117] 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:

[0118] Silicon precursor gas 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. Examples of suitable silicon precursor gases include silane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane, dimethylsilane, and chlorosilane, and mixtures thereof. The silicon precursor gas is preferably selected from silane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane, and dimethylsilane. Silane (SiH4) is the most preferred silicon-containing precursor gas.

[0119] 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.

[0120] The silicon precursor gas can be used undiluted (undiluted) or as a diluent containing at least 20% by volume of silicon precursor gas, the remainder being selected from hydrogen and an inert gas, where optionally the inert gas is selected from nitrogen and argon. Preferably, the silicon precursor gas contains at least 50% by volume, more preferably at least 60% by volume, more preferably at least 70% by volume, more preferably at least 80% by volume, more preferably at least 90% by volume, more preferably at least 95% by volume, more preferably at least 98% by volume, more preferably at least 99% by volume of silicon precursor gas.

[0121] Carbon Coating The method of the invention optionally further comprises: (l) providing a carbon deposition unit comprising at least one reaction zone; (m) introducing into the reaction zone a feedstock comprising the composite particles recovered from the chemical vapor infiltration unit in step (e) or step (j); (n) introducing a carbon precursor gas into the reaction zone; (o) providing conditions within the reaction zone effective to cause deposition of carbon within the pores and / or on the surfaces of the composite particles; (p) recovering from the reaction zone composite particles comprising a porous particulate skeleton, elemental silicon within the pores of the porous particulate skeleton, and carbon within the pores and / or on an exterior surface thereof; Further includes:

[0122] The carbon deposited in step (o) 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.

[0123] Steps (l) through (p) are preferably operated as a continuous process such that the introduction of the composite particles and carbon precursor gas into the reaction zone in steps (m) and (n), and the withdrawal of the composite particles from the reaction zone in step (p), are each carried out continuously.

[0124] The carbon deposition unit is preferably operated in series with the CVI unit such that the composite particles recovered from the CVI unit in step (e) or (j) are continuously transferred to the carbon deposition unit in step (m).

[0125] The reaction zone of the carbon deposition unit preferably has the form of a tubular reactor having a first end, a second end and a length, where particles are introduced through a particle inlet at the first end of the tubular reactor and composite particles including the deposited carbon are withdrawn through a particle outlet at the second end of the tubular reactor.

[0126] The tubular reactor may be operated as a co-current reactor, where the carbon precursor gas is introduced through an inlet proximal to the first end of the tubular reactor and the exhaust gas is collected through a gas discharge outlet proximal to the second end of the tubular reactor. Alternatively, the tubular reactor may be operated as a counter-current reactor, where the carbon precursor gas is introduced through an inlet proximal to the second end of the tubular reactor and the exhaust gas is collected through a gas discharge outlet proximal to the first end of the tubular reactor.

[0127] Alternatively, the carbon precursor gas may be introduced into the tubular reactor through multiple inlets spaced along the length of the tubular reactor. In this case, the exhaust gas may be collected through one or more gas discharge outlets located anywhere along the length of the tubular reactor. For example, the exhaust gas may be collected (i) through a gas discharge outlet proximate the second end of the tubular reactor, or (ii) through a gas discharge outlet proximate the first end of the tubular reactor, or (iii) through multiple gas discharge outlets spaced along the length of the tubular reactor.

[0128] The tubular reactor of the carbon deposition zone preferably comprises at least one device for conveying particles from its first end to its second end, for example a spiral as defined above.

[0129] Step (o) is suitably carried out at a temperature in the range of 350° C. to 700° C., or 400° C. to 700° C. The temperature in step (o) is preferably 680° C. or less, or 660° C. or less, or 640° C. or less, or 620° C. or less, or 600° C. or less, or 580° C. or less, or 560° C. or less, or 540° C. or less, or 520° C. or less, or 500° C. or less.

[0130] The minimum temperature of step (o) depends on the type of carbon precursor used. Preferably, the temperature of step (o) is at least 300°C, or at least 350°C, or at least 400°C.

[0131] Step (o) is suitably carried out at 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.

[0132] The average residence time of the particles in the reaction zone of the carbon deposition unit, between the introduction of the composite particles into the reaction zone in step (m) and the recovery of the composite particles from the reaction zone in step (p), is preferably from 2 minutes to 60 minutes, or from 5 minutes to 30 minutes, or from 10 minutes to 20 minutes.

[0133] The reaction zone of the carbon deposition unit is preferably operated in a plug flow regime with respect to the particles, as described above.

[0134] The volume of the reaction zone in liters (L) is (0.001 L g -1 ×F PP ×RT)~(0.02L g -1 ×F PP × RT), where F PP is the rate at which the composite particles are pumped into the reaction zone, based on grams of porous particle scaffold per minute, and RT is the average residence time of the particles in the first reaction zone, in minutes. Preferably, the volume of the second reaction zone in liters (L) is less than (0.01 L g -1 ×F CP ×RT), more preferably less than (0.008 L g -1 ×F CP ×RT), more preferably less than (0.05 L g -1 ×F CP × RT).

[0135] As described above, the mass of the composite particles in the carbon deposition unit and the reaction parameters defined by reference to the mass of the composite particles in the carbon deposition unit are normalized to the mass of the porous particle skeleton, so that the mass of carbon added to the composite particles per gram of porous particle feedstock can be directly compared to the mass of silicon added in each of the first and second reaction zones.

[0136] The ratio of the rate at which the carbon precursor gas is fed into the reaction zone to the rate at which the composite particles are fed into the reaction zone is preferably 0.02-2, or 0.03-1, or 0.04-0.5, or 0.04-0.2, or 0.04-0.1, based on grams of carbon in the carbon-containing gas per gram of porous particle skeleton. In other words, during the residence time of the particles in the second reaction zone, 0.02-2 grams of carbon atoms (in the form of carbon precursor gas) are introduced into the reactor per gram of porous particle skeleton. The reaction zone of the carbon deposition unit is preferably operated such that the consumption of the carbon precursor gas is essentially 100%, and thus the composite particles recovered from the reaction zone preferably contain 0.02 grams to 0.06 grams, more preferably 0.02 grams to 0.05 grams, more preferably 0.03 grams to 0.04 grams of carbon derived from the carbon precursor gas per gram of porous particle skeleton.

[0137] 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.

[0138] The carbon precursor used in step (o) 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.

[0139] passivation The silicon deposited in the CVI reaction zone has a hydride-terminated silicon surface that is highly reactive towards oxygen, therefore the process of the present invention preferably includes a passivation step in which the composite particles are subjected to a controlled oxidation with an oxygen-containing gas to form a passivated material that is stable in air.

[0140] Therefore, the method of the present invention comprises: (q) providing a passivation unit comprising at least one reaction zone; (r) introducing into the reaction zone a feedstock comprising the composite particles recovered from the chemical vapor infiltration unit in step (e) or step (j) or recovered from the carbon deposition unit in step (p); (s) introducing an oxygen-containing gas into the reaction zone; (t) recovering the passivated composite particles from the reaction zone; (u) recovering exhaust gas from the reaction zone; It is preferred that the compound further comprises:

[0141] Steps (q) to (u) are preferably operated as a continuous process such that the introduction of the composite particles and oxygen-containing gas into the reaction zone in steps (r) and (s), and the recovery of the composite particles and exhaust gas from the reaction zone in steps (t) and (u), respectively, are carried out continuously.

[0142] Step (s) is suitably carried out at 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 in step (s) is preferably 150° C. or lower.

[0143] Step (s) is suitably carried out at 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.

[0144] The passivation unit is preferably operated in series with the CVI unit or any carbon deposition unit such that the composite particles recovered from the CVI unit in step (e) or step (j), or from the optional carbon deposition unit in step (p), are continuously transferred to the passivation unit in step (r).

[0145] It is preferred that the reaction zone of the passivation unit comprises the form of a tubular reactor having a first end, a second end and a length, in which in step (r) the composite particles are introduced into the first end of the tubular reactor and in step (t) the passivated composite particles are withdrawn from the second end of the tubular reactor.

[0146] The tubular reactor may be operated as a co-current reactor, where the oxygen-containing precursor gas is introduced through an inlet proximal to the first end of the tubular reactor and the exhaust gas is collected through a gas discharge outlet proximal to the second end of the tubular reactor, or alternatively, the tubular reactor may be operated as a counter-current reactor, where the oxygen-containing gas is introduced through an inlet proximal to the second end of the tubular reactor and the exhaust gas is collected through a gas discharge outlet proximal to the first end of the tubular reactor.

[0147] More preferably, the oxygen-containing gas may be introduced into the tubular reactor through multiple inlets spaced apart along the length of the tubular reactor. In this case, the exhaust gas may be collected through one or more gas discharge outlets located anywhere along the length of the tubular reactor. For example, the exhaust gas may be collected (i) through a gas discharge outlet proximate the second end of the tubular reactor, or (ii) through a gas discharge outlet proximate the first end of the tubular reactor, or (iii) through multiple gas discharge outlets spaced apart along the length of the tubular reactor.

[0148] More preferably, the plurality of inlets spaced apart along the length of the tubular reactor are assigned to two or more inlet groups spaced apart along the length of the reactor, each inlet group comprising one or more inlets. For example, the plurality of inlets may be assigned to 2 to 10 inlet groups, each inlet group independently comprising 1 to 10 inlets. The oxygen concentration in the oxygen-containing gas is increased in successive inlet groups such that the oxygen-containing gas fed to the inlet group closest to the first end of the tubular reactor has a relatively low concentration of oxygen and the oxygen-containing gas fed to the inlet group closest to the second end of the tubular reactor has a relatively high concentration of oxygen. For example, the concentration of oxygen in the oxygen-containing gas fed to the inlet group closest to the first end of the tubular reactor is 0.5% to 5% by volume, and the concentration of oxygen in the oxygen-containing gas fed to the inlet group closest to the second end of the tubular reactor is 15% to 21% by volume, optionally air.

[0149] By arranging the inlets in groups of increasing oxygen content, the composite particles are continually exposed to increasing concentrations of oxygen as they pass through the tubular reaction zone. When the composite particles first enter the passivation unit, they react most extensively with oxygen. Thus, the oxygen-containing gas provided to the group of inlets closest to the first end of the tubular reactor contains a relatively low oxygen content that inhibits the reaction rate. As the passivation reaction progresses and the composite particles become less reactive, the concentration of oxygen in the oxygen-containing gas can be increased to drive the passivation reaction toward completion. As a result, the reaction of oxygen with the reactive silicon surfaces is controlled in such a way that large exotherms that could be detrimental to the composite particle structure are avoided.

[0150] cooling The method of the present invention optionally further comprises the step of cooling the composite particles to ambient temperature. Cooling of the particles can be accomplished by any convenient method, but one preferred method is to pass the composite particles through a tubular cooling vessel provided with cooling means. The particles are introduced through a particle inlet at a first end of the tubular cooling vessel and collected through a particle outlet at a second end of the tubular cooling vessel.

[0151] The cooling means may comprise a cooling jacket supplied with a liquid coolant (eg water) or a cooling gas (eg air) in contact with the composite particles within the cooling vessel.

[0152] The cooled particles can be collected, optionally sorted to remove oversized and / or fine particles, and transferred to containers for storage and subsequent delivery to downstream processes in lithium ion battery manufacturing.

[0153] The invention will now be further described with reference to the accompanying drawings. [Brief description of the drawings]

[0154] [Figure 1]1 is a schematic diagram of a chemical vapor infiltration (CVI) reaction zone apparatus operated in accordance with one embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a passivation reaction zone apparatus operated in accordance with one embodiment of the present invention. [Diagram 3] 2 is a flow chart of a method according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0155] Referring to Figure 1, there is shown a CVI reaction zone 1 comprising a continuous tubular reactor 10 having a first end 11 and a second end 12 and a length. In the embodiment of Figure 1, the tubular reactor 10 is oriented horizontally. The tubular reactor comprises a particle inlet 13 at the first end, where porous particles are introduced into the tubular reactor via an airlock valve 13a, and a particle outlet 14 at the second end, where the porous particles are withdrawn from the tubular reactor.

[0156] The tubular reactor includes a gas inlet 15 at a first end of the tubular reactor for introducing silicon precursor gas, and a gas outlet 16 at a second end of the tubular reactor for withdrawing exhaust gas. Optionally, the CVI reaction zone includes a plurality of further gas inlets 17 spaced along the length of the tubular reactor. The CVI reaction zone preferably includes a gas heater 18 for preheating the silicon precursor gas.

[0157] The tubular reactor 10 further comprises a device for conveying particles from its first end to its second end, which is in the form of a spiral 19 powered by an electric motor 20. An electric heater 21 is provided to control the internal temperature of the tubular reactor.

[0158] Referring to Figure 2, there is shown a passivation unit 30 comprising a continuous tubular reactor 31 having a first end 32, a second end 33 and a length. In the embodiment of Figure 2, the tubular reactor is oriented horizontally. The tubular reactor comprises a particle inlet 34 at the first end, where porous particles are introduced into the tubular reactor via an airlock valve 34a, and a particle outlet 35 at the second end, where the porous particles are withdrawn from the tubular reactor.

[0159] The tubular reactor includes a number of gas inlets arranged along the length of the tubular reactor for introducing oxygen-containing gas. As shown, the number of gas inlets is allocated into four inlet groups 36, 37, 38, 39, each of which includes three gas inlets. The oxygen concentration of the oxygen-containing gas is lowest in the gas supplied to the inlet group 36 closest to the first end 32 of the tubular reactor. In each successive inlet group 37, 38, 39, the oxygen concentration of the oxygen-containing gas is increased. The oxygen concentration in the oxygen-containing gas supplied to the inlet group 39 closest to the second end 33 of the tubular reactor is preferably approximately the same as the oxygen concentration in air. Optionally, the gas supplied to the inlet group 39 may be air. A gas outlet 40 is provided at the second end of the tubular reactor for collecting exhaust gas.

[0160] The tubular reactor 31 further comprises a device for conveying particles from its first end to its second end, which is in the form of a spiral 41 powered by an electric motor 42. An electric heater 43 is provided to control the internal temperature of the tubular reactor.

[0161] FIG. 3 shows a flow chart of one embodiment of the method of the present invention. The method includes a particle pretreatment step 50, in which the porous particle feedstock is pretreated, preferably by preheating under an inert gas. The pretreated particles are introduced into a CVI unit 60, which includes a first CVI reaction zone 65 for steps (a)-(f) and a second CVI reaction zone 70 for steps (g)-(k). The composite particles recovered from the second CVI reaction zone in step (k) may be transferred directly to a passivation unit 80 for steps (q)-(u). Alternatively, the particles recovered from the reaction zone in step (k) may be transferred to a carbon deposition unit 75 for steps (l)-(p), and then the composite particles recovered from the carbon deposition unit in step (p) may be transferred to a passivation unit 80 for steps (q)-(u). Finally, the passivated particles recovered from the passivation unit 80 in step (u) are transferred to a cooling unit 90.

Claims

1. A continuous method for preparing composite particles, (a) A step of providing a chemical vapor impregnation unit including at least a first reaction zone, (b) A step of preparing a supply material containing porous particles and continuously introducing the porous particles into the first reaction zone, (c) A step of continuously introducing a silicon precursor gas into the first reaction zone, (d) A step of providing conditions within the reaction zone that are effective in causing silicon to deposit into the pores of the porous particles, (e) A step of continuously recovering composite particles, which include a porous particle skeleton and elemental silicon in the pores of the porous particle skeleton, from the first reaction zone, (f) A step of continuously recovering the exhaust gas from the first reaction zone, Methods that include...

2. The method according to claim 1, wherein the first reaction zone includes a tubular reactor having a first end, a second end and length, wherein porous particles are introduced through a particle inlet at the first end of the tubular reactor, and composite particles are recovered through a particle outlet at the second end of the tubular reactor.

3. The method according to claim 2, wherein the cross-sectional shape of the tubular reactor is selected from circular, elliptical, rectangular, or square.

4. (i) The silicon precursor gas is introduced through an inlet located near the first end of the tubular reactor, and the exhaust gas is recovered through a gas outlet located near the second end of the tubular reactor, or (ii) The silicon precursor gas is introduced through an inlet located near the second end of the tubular reactor, and the exhaust gas is recovered through a gas outlet located near the first end of the tubular reactor. The method according to claim 2 or 3.

5. The silicon precursor gas is introduced through a plurality of inlets that are spaced apart along the length of the tubular reactor, and the exhaust gas is (i) A gas outlet located near the second end of the tubular reactor, (ii) A gas outlet located near the first end of the tubular reactor, (iii) Multiple gas outlets located at intervals along the length of the tubular reactor, The method according to claim 2 or 3, which is recovered through

6. The method according to claim 2, wherein the tubular reactor includes means for transporting particles from a first end to a second end.

7. The method according to claim 6, wherein the means for transporting particles from a first end to a second end of the tubular reactor includes at least one helical section, a moving belt conveyor, a bucket conveyor, a tube chain conveyor, or a vertical conveyor.

8. The method according to claim 6, wherein the means for transporting particles from the first end to the second end includes a vibrating surface.

9. The method according to claim 1, wherein the conditions within the first reaction zone include a reaction temperature in the range of 340°C to 500°C, or 350°C to 480°C, or 350°C to 450°C, or 350°C to 420°C, or 350°C to less than 400°C, or 355°C to 395°C, or 360°C to 390°C, or 365°C to 385°C, or 370°C to 380°C, or 370°C to 385°C, or 370°C to 395°C.

10. The method according to claim 1, wherein the conditions in the first reaction zone include a reaction temperature in the range of 400°C to 500°C, or 400°C to 490°C, or 400°C to 480°C, or 400°C to 470°C, or 400°C to 460°C.

11. The method according to claim 1, wherein the conditions within the first reaction zone include a pressure in the range of 1 kPa to 10,000 kPa, or 10 kPa to 6,000 kPa, or 20 kPa to 4,000 kPa, or 50 kPa to 2,000 kPa, or 80 kPa to 1,500 kPa, or 90 kPa to 1,000 kPa, or 90 kPa to 600 kPa, or about 100 kPa.

12. The method according to claim 1, wherein the conditions within the first reaction zone include a pressure in the range of 110 kPa to 10000 kPa, or 120 kPa to 5000 kPa, or 150 kPa to 2000 kPa, or 200 kPa to 1800 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.

13. The method according to claim 1, wherein the average residence time of the particles in the first reaction zone from the introduction of porous particles into the first reaction zone in step (b) to the recovery of composite particles from the first reaction zone in step (e) is 10 minutes to 300 minutes, or 15 minutes to 240 minutes, or 20 minutes to 180 minutes, or 30 minutes to 120 minutes, or 40 minutes to 90 minutes.

14. The volume of the first reaction zone in liters is (0.003 L·g) －１ ×F ＰＰ × RT)~(0.06L・g －１ ×F ＰＰ It is within the range of ×RT), F ＰＰ The method according to claim 1, wherein is the rate at which porous particles are introduced into the first reaction zone, in units of grams per minute, and RT is the average residence time of the particles in the first reaction zone, in units of minutes.

15. The method according to claim 1, wherein the ratio of the rate at which the silicon precursor gas is introduced into the first reaction zone to the rate at which the porous carbon particles are introduced into the first reaction zone is 0.25 to 2, or 0.4 to 1.9, or 0.6 to 1.8, or 0.7 to 1.7, or 0.8 to 1.6, or 0.9 to 1.6, or 1 to 1.5, based on the number of grams of silicon in the silicon precursor gas per gram of porous carbon particles.

16. The method according to claim 1, further comprising step (b) preheating the feed material containing the porous particles in a preheating zone, and then introducing the preheated feed material into the first reaction zone.

17. The supply material containing the porous particles (T ＲＺ Preheat to a temperature of -50°C or higher, T ＲＺ The method according to claim 16, wherein the reaction temperature is that of the first reaction zone.

18. The chemical vapor phase penetration unit includes at least a first reaction zone and a second reaction zone, wherein the first reaction zone is a reaction zone as defined in claim 1, and the method is (g) Continuously introducing the composite particles recovered from the first reaction zone in step (e) into the second reaction zone, (h) Continuously introducing silicon precursor gas into the second reaction zone, (i) To provide conditions within the second reaction zone that are effective in causing silicon to deposit into the pores of the porous particles, (j) Continuously recovering composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton from the second reaction zone, (k) Continuously recovering the exhaust gas from the second reaction zone, The method according to claim 1, further comprising:

19. The method according to claim 18, wherein the second reaction zone includes a tubular reactor having a first end portion, a second end portion and length, and composite particles recovered from the first reaction zone are introduced into the first end portion of the tubular reactor, and the composite particles are recovered from the second end portion of the tubular reaction zone.

20. (i) The silicon precursor gas is introduced through an inlet located near the first end of the tubular reactor, and the exhaust gas is recovered through a gas outlet located near the second end of the tubular reactor, or (ii) The silicon precursor gas is introduced through an inlet located near the second end of the tubular reactor, and the exhaust gas is recovered through a gas outlet located near the first end of the tubular reactor. The method according to claim 19.

21. The silicon precursor gas is introduced through a plurality of inlets that are spaced apart along the length of the tubular reactor, and the exhaust gas is (i) A gas outlet located near the second end of the tubular reactor, (ii) A gas outlet located near the first end of the tubular reactor, (iii) Multiple gas outlets located at intervals along the length of the tubular reactor, The method according to claim 19, which is recovered through

22. The method according to claim 19, wherein the tubular reactor includes at least one helical portion for transporting particles from a first end to a second end.

23. The method according to claim 18, wherein the conditions in the second reaction zone include a reaction temperature in the range of 350°C to 450°C, or 350°C to 420°C, or 350°C to less than 400°C, or 355°C to 395°C, or 360°C to 390°C, or 365°C to 385°C, or 370°C to 380°C, or 370°C to 385°C, or 370°C to 395°C.

24. The method according to claim 18, wherein the conditions within the second reaction zone include a pressure in the range of 1 kPa to 10,000 kPa, or 10 kPa to 6,000 kPa, or 20 kPa to 4,000 kPa, or 50 kPa to 2,000 kPa, or 80 kPa to 1,500 kPa, or 90 kPa to 1,000 kPa, or 90 kPa to 600 kPa, or about 100 kPa.

25. The method according to claim 18, wherein the conditions within the first reaction zone include a pressure in the range of 110 kPa to 10000 kPa, or 120 kPa to 5000 kPa, or 150 kPa to 2000 kPa, or 200 kPa to 1800 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.

26. The method according to claim 18, wherein the first reaction zone and the second reaction zone differ with respect to one or more of the reaction temperature, the reaction pressure, the particle residence time, and the rate at which the silicon precursor gas is introduced.

27. The method according to claim 18, wherein the reaction temperature of the second reaction zone is 5°C to 50°C lower, or 10°C to 20°C lower, than the reaction temperature of the first reaction zone.

28. The method according to claim 18, wherein the average residence time of the particles in the second reaction zone from the introduction of the composite particles into the second reaction zone in step (g) to the recovery of the composite particles from the second reaction zone in step (j) is 2 minutes to 60 minutes, or 5 minutes to 30 minutes, or 10 minutes to 20 minutes.

29. The volume of the second reaction zone in liters is (0.001 L·g －１ ×F ＣＰ ×RT) to (0.02 L·g －１ ×F ＣＰ ×RT), where F ＣＰ is the rate at which the composite particles are fed into the second reaction zone in units of grams per minute, and RT is the residence time of the particles in the second reaction zone in units of minutes. The method according to claim 18

30. The method according to claim 18, wherein the ratio of the rate at which the silicon precursor gas is introduced into the second reaction zone to the rate at which the composite carbon particles are introduced into the second reaction zone is 0.02 to 0.3, or 0.03 to 0.25, or 0.04 to 0.2, or 0.05 to 0.18, or 0.06 to 0.15, based on the number of silicon atoms per gram of porous composite particles.

31. The method according to claim 18, wherein in step (e), the composite particles recovered from the first reaction zone are introduced into the second reaction zone via an airlock valve in step (g).

32. 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 11, comprising:

33. The porous particles are in the range 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 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 The method according to claim 32, having a particle size.

34. The porous conductive particles are 0.45 cm ３ / g ~ 2.2cm ３ / g, or 0.5cm ３ / g to 2cm ３ / g, or 0.55cm ３ / g to 2cm ３ / g, or 0.6cm ３ / g to 1.8cm ３ / g, or 0.65cm ３ / g to 1.8cm ３ / g, or 0.7cm ３ / g ~ 1.6cm ３ / g, or 0.75cm ３ / g ~ 1.6cm ３ / g, or 0.8cm ３ / g to 1.5cm ３ The method according to claim 32 or 33, having a total volume of micropores and mesopores in the range of / g.

35. The porous conductive particles PD ５０ The method according to claim 32, wherein the pore size is 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.

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

37. (l) To provide a carbon deposition unit including at least one reaction zone, (m) Introducing a supply material containing composite particles recovered from the chemical vapor impregnation unit in step (e) or step (j) into the reaction zone, (n) Introducing a carbon precursor gas into the reaction zone, (o) To provide conditions within the reaction zone that are effective in causing carbon to deposit within the pores and / or on the surface of the composite particles, (p) Recovering composite particles containing a porous particle skeleton, elemental silicon in the pores of the porous particle skeleton, and carbon in and / or on the outer surface thereof from the reaction zone, The method according to claim 1, further comprising:

38. The method according to claim 37, wherein the reaction zone of the carbon deposition unit includes a tubular reactor having a first end, a second end and length, the particles are introduced through a particle inlet at the first end of the tubular reactor, and the composite particles containing deposited carbon are recovered through a particle outlet at the second end of the tubular reactor.

39. The method according to claim 37, wherein step (o) is performed at a temperature in the range of 300°C to 700°C, or 350°C to 700°C, or 400°C to 700°C, or 400°C to 680°C, or 400°C to 660°C, or 400°C to 640°C, or 400°C to 620°C, or 400°C to 600°C, or 400°C to 580°C, or 400°C to 560°C, or 400°C to 540°C, or 400°C to 520°C, or 400°C to 500°C.

40. The method according to claim 37, wherein step (o) is performed at 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 at a pressure of about 100 kPa.

41. The method according to claim 37, wherein the carbon precursor gas comprises one or more of the following: (i) C2 to C10 hydrocarbons; (ii) Bicyclic monoterpenoids; and, (iii) 10 to 25 carbon atoms.

42. The method according to claim 37, wherein the average residence time of the particles in the reaction zone of the carbon deposition unit from the introduction of the composite particles into the reaction zone in step (m) to the recovery of the composite particles from the reaction zone in step (p) is 2 minutes to 60 minutes, or 5 minutes to 30 minutes, or 10 minutes to 20 minutes.

43. The carbon precursor gas is introduced into the tubular reactor through a plurality of inlets that are spaced apart along the length of the tubular reactor, and the exhaust gas is (i) A gas outlet located near the second end of the tubular reactor, (ii) A gas outlet located near the first end of the tubular reactor, (iii) Multiple gas outlets located at intervals along the length of the tubular reactor, The method according to claim 38, which is recovered through

44. The method according to claim 38, wherein the tubular reactor includes a device for transporting particles from its first end to its second end.

45. (q) To provide a passivation unit including at least one reaction zone, (r) Introducing a feedstock containing composite particles recovered from the chemical vapor impregnation unit in step (e) or step (j), or recovered from the carbon deposition unit in step (p), into the reaction zone. (s) Introducing an oxygen-containing gas into the reaction zone, (t) Recovering the passivated composite particles from the reaction zone, (u) Continuously recovering the exhaust gas from the reaction zone The method according to claim 1, further comprising:

46. The method according to claim 45, wherein the at least one reaction zone includes a tubular reactor having a first end portion, a second end portion and length, the composite particles are introduced into the first end portion of the tubular reactor in step (r), and the passivated composite particles are recovered from the second end portion of the tubular reactor in step (t).

47. The oxygen-containing gas is introduced through a plurality of inlets that are spaced apart along the length of the tubular reactor, and the exhaust gas is (i) A gas outlet located near the second end of the tubular reactor, (ii) Multiple gas outlets located at intervals along the length of the tubular reactor, The method according to claim 46, which is recovered through

48. (i) The plurality of entrances are assigned to groups of 2 to 10 entrances, (ii) Each group of entrances independently contains 1 to 10 entrances, The inlet groups are spaced apart along the length of the tubular reactor such that the proximal inlet group is close to the first end of the tubular reactor and the distal inlet group is close to the second end of the tubular reactor, thereby increasing the oxygen concentration in the oxygen-containing gas from the proximal inlet group to the distal inlet group. The method according to claim 47.

49. The method according to claim 48, wherein the oxygen concentration in the oxygen-containing gas supplied to the proximal inlet group is 0.5% by volume to 5% by volume.

50. The method according to claim 48 or 49, wherein the oxygen concentration in the oxygen-containing gas supplied to the distal inlet group is 15% by volume to 21% by volume.

51. The method according to claim 1, further comprising the step of cooling the composite particles to ambient temperature.

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