Continuous process for preparing silicon-containing composite particles

Abstract

The present invention relates to a continuous method for preparing composite particles, which is carried out by continuously introducing a porous particle raw material and a silicon precursor gas into a first reaction zone, and continuously withdrawing the composite particles and the exhaust gas from the first reaction zone, wherein the composite particles contain a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton.

Description

[0001] The present invention relates generally to silicon-containing electroactive materials, and more particularly to a continuous process for preparing silicon-containing composite particles suitable for use as anode active materials in rechargeable lithium-ion batteries.

[0002] A typical lithium-ion battery (LIB) includes an anode, a cathode, and a lithium-containing electrolyte. The anode typically includes a metal current collector provided with a layer of an electroactive material, which is 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 following sense: the battery is connected to a load so that the anode is the negative electrode. When the LIB is charged, lithium ions are transferred from the cathode to the anode via the electrolyte and are inserted into the electroactive material of the anode as intercalated lithium atoms. The term "battery" is used herein to refer to both a device comprising a single lithium-ion battery cell and a device comprising a plurality of connected lithium-ion battery cells.

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

[0004] While total storage capacity is growing, there is a strong interest in improving the weight and / or volumetric capacity of rechargeable metal ion batteries so that the same energy storage can be achieved with less battery mass and / or battery volume. Conventional LIBs use graphite as the anode electroactive material. Graphite anodes can accommodate up to one lithium atom per six carbon atoms, resulting in a maximum theoretical specific capacity of 372 mAh / g for lithium ion batteries, while the actual capacity is slightly lower (approximately 340 to 360 mAh / g).

[0005] Silicon is a promising graphite replacement due to its very high lithium capacity (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al., Adv. Mater. 1998, 10, No. 10). 15Si4) has a theoretical maximum specific capacity of about 3,600 mAh / g. However, the insertion of lithium into bulk silicon causes the silicon material to expand to 400% of its original volume, which can lead to battery failure. Repeated charge-discharge cycles cause significant mechanical stress, leading to the breakage and delamination of 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 crack surface leads to additional electrolyte decomposition, as well as increased SEI layer thickness and irreversible consumption of lithium. These damage mechanisms together lead to unacceptable electrochemical capacity loss during continuous charge and discharge cycles.

[0006] The applicant has previously reported the development of a class of electroactive materials with composite structures in which electroactive materials such as silicon are deposited into a pore network of highly porous conductive particulate materials, such as porous carbon materials (see WO 2020 / 095067 and WO 2020 / 128495). The silicon in these materials is subdivided into individual silicon structures with sizes on the order of a few nanometers or less, so that the individual silicon structures are subjected to minimal stress and strain during charge and discharge. Because silicon is limited to the pore volume of the porous material, the exposure of the silicon surface to the electrolyte is minimized, thereby effectively limiting the extent of SEI formation. As a result, these materials exhibit good reversible capacity retention over multiple charge and discharge cycles.

[0007] The materials described in WO2020 / 095067 and WO 2020 / 128495 have been synthesized in different reactor systems (stationary, rotary and FBR) by chemical vapor infiltration (CVI). At atmospheric pressure and at a temperature of 400 to 700°C, porous conductive particles are contacted with a silicon precursor gas flow (typically silane gas). All these reactor configurations work in batch mode for solid carbon supports and in continuous mode for silicon precursor gases. The reaction rate at these temperatures is fast, however, silicon precursor gas molecules need to enter the pore space with a diameter of only a few nanometers through a tortuous path. This means that in order to obtain uniform penetration in such a reactor system, the reaction temperature needs to be relatively high to avoid mass transfer becoming a rate-limiting step. In addition, silicon precursor gases generally need to be used at high dilutions in inert gases. Too high a concentration of silicon precursor gas may result in rapid and uncontrolled deposition of silicon deposited in the outermost pores, which in turn blocks access to most of the available pore volume. As a result, the deposited silicon lacks the fine structure associated with deposition in narrow pores, but is rough and exposed, and therefore exhibits poor cycling behavior. However, the use of low concentration silicon precursor gases means that the reaction times to achieve the desired silicon loading in the composite particles are relatively long, reducing production throughput.

[0008] Another disadvantage of these systems is that good mixing of the solids with the gas is required, otherwise the product batch may contain compositional inhomogeneities. Solids that have been in contact with the dilute silicon precursor gas for a longer time will contain a greater amount of silicon than those that have been in contact with the unreacted silane gas stream for a shorter time; deposition on the powder bed will not be uniform.

[0009] Another disadvantage of these systems is that batch operations are not amenable to scale-up, making it difficult to produce large quantities of material.

[0010] Therefore, there is a need in the art for improved methods for preparing silicon-containing composite particles suitable for use as electroactive materials in LIBs. In particular, there is a need for methods for large-scale preparation of such composite particles with high throughput while maintaining product quality.

[0011] First reaction zone

[0012] In a first aspect, the present invention provides a continuous method for preparing composite particles, the method comprising the following steps:

[0013] (a) providing a chemical vapor permeation unit comprising at least a first reaction zone;

[0014] (b) providing a feedstock comprising porous particles, and continuously introducing the porous particles into the first reaction zone;

[0015] (c) continuously introducing a silicon precursor gas into the first reaction zone;

[0016] (d) providing conditions in the reaction zone effective to cause deposition of silicon in the pores of the porous particles;

[0017] (e) continuously removing composite particles from the first reaction zone, the composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton; and

[0018] (f) continuously removing exhaust gas from the first reaction zone.

[0019] Thus, the present invention generally relates to a continuous process for preparing a composite particulate material, wherein nano-sized silicon domains are deposited into the pore network of porous particles by chemical vapor infiltration (i.e., by thermal decomposition of a silicon-containing precursor compound). Thus, the composite particles comprise: a first component in the form of a porous particle skeleton derived from the porous particle raw material determined in step (b), and a second component in the form of a plurality of nano-sized silicon domains disposed in the pore structure of the porous particle skeleton. As used herein, the term "nano-sized silicon domain" refers to nano-sized elemental silicon bodies whose maximum size is determined by the location of silicon within the micropores and / or mesopores of the porous particles.

[0020] The term continuous is used herein to distinguish the first reaction zone from a batch operation. In a batch reactor, a batch of raw materials is added to the reactor in a first step, the reaction is allowed to proceed for a specified time, and then a batch of product is removed from the reactor. A batch reactor contains the entire stock of reaction materials for the duration of the reaction, and then the entire stock of product is removed. Continuous operation as defined herein refers to a reaction in which the introduction of raw materials into the reaction zone and the removal of product from the reaction zone are both carried out continuously and simultaneously as the reaction proceeds, so that the reaction zone contains only a portion of the stock of reaction materials.

[0021] Continuous reaction can be realized by using a plug flow reactor, wherein the reaction material moves along the path from the reactor inlet to the reactor outlet, so that the moving time limits the residence time of the particles in the reactor. Continuous operation can also be realized with a non-plug flow using a reactor with an inlet and an outlet but without a continuous path between the two, that is, particles are allowed to mix freely in the reaction zone. In the non-plug flow mode, the product taken out from the reaction zone will be a static mixture of materials with a distribution of residence time. The rate at which the raw material is supplied to the reactor, the rate at which the product is taken out, and the size of the reactor limit the average residence time of the material in the reactor. In principle, continuous operation does not exclude the possibility of deviation of the flow rate of the material flowing into the reactor or flowing out of the reactor, for example, a continuous reactor can be operated in a pulse mode. However, as defined herein, the continuous operation of the reactor satisfies the following conditions: the introduction of the raw material into the reaction zone and the removal of the product from the reaction zone are both continuous and carried out simultaneously with the reaction, so that the reaction zone contains only a portion of the reaction material in stock.

[0022] The first reaction zone is preferably operated in a plug flow mode for the particles so that the reactor has an axial direction and the mixing of the particles in the axial direction is limited so that the particle residence time in the reactor has a narrow distribution. Plug flow mode is defined herein as a residence time distribution in which the standard deviation of the residence time does not exceed 30% of the average residence time, more preferably does not exceed 20%, more preferably does not exceed 10%, and more preferably does not exceed 5% of the average residence time. Because the residence time of all particles in the plug flow mode is essentially the same (assuming limited axial mixing), this operating mode results in a composite particle product with a more uniform composition than when the reaction is carried out in a non-plug flow mode.

[0023] For operation in plug flow mode, the reaction zone of the chemical vapor infiltration (CVI) unit is preferably in the form of a continuous tubular reactor having a first end, a second end, and a length, wherein the porous particles are introduced through a particle inlet at the first end of the tubular reactor, and wherein the composite particles are removed through a particle outlet at the second end of the tubular reactor. The cross-section of the tubular reactor can be any suitable shape. For example, the shape of the cross-section of the tubular reactor can be circular, oval, rectangular or square, or irregular.

[0024] The tubular reaction zone can be arranged substantially horizontally over its length, for example with a slope of less than ±20°, preferably less than ±10° relative to the horizontal plane. The density of the porous particles increases as silicon is deposited into the pores, and the horizontal arrangement of the tubular reaction zone prevents the particles from backmixing as they move from the particle inlet to the particle outlet. Alternatively, the tubular reaction zone can be arranged with a negative gradient so that the particle outlet is disposed below the particle inlet. Alternatively, the tubular reaction zone can be arranged vertically so 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.

[0025] The tubular reactor can be operated as a co-current or counter-current reactor. In co-current operation, the silicon precursor gas is introduced through an inlet near the first end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near the second end of the tubular reactor. In counter-current operation, the silicon precursor gas is introduced through an inlet near the second end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near the first end of the tubular reactor.

[0026] More preferably, the silicon precursor gas may be introduced into the tubular reactor through a plurality of inlets spaced apart along the length of the tubular reactor. In this case, the exhaust gas may be removed through one or more gas exhaust outlets disposed at any position along the length of the tubular reactor. For example, in the case where the silicon precursor gas is introduced through a plurality of inlet reservoirs spaced apart along the length of the tubular reactor, the exhaust gas may be removed by: (i) through a gas exhaust outlet proximate to the second end of the tubular reactor; or (ii) through a gas exhaust outlet proximate to the first end of the tubular reactor; or (iii) through a plurality of gas exhaust outlets spaced apart along the length of the tubular reactor.

[0027] Using multiple inlets spaced apart along the length of the tubular reactor for the silicon precursor gas can advantageously ensure that the concentration of the silicon precursor gas is substantially uniform along the length of the reaction zone. In the case where the reactor is operated in a simple co-current or countercurrent mode, the concentration of the silicon precursor gas in the reactor decreases from the inlet to the exhaust gas outlet. As a result, the reaction rate in the portion of the reaction zone adjacent to the silicon precursor gas inlet is increased, and the reaction rate is reduced for the rest of the length of the reaction zone. Depending on the reactor conditions, excessive reaction rates adjacent to the silicon precursor gas inlet may lead to the above-mentioned uncontrolled deposition type, wherein the high deposition rate leads to rapid blockage of the pore space, so that the silicon precursor gas may no longer penetrate into the fine pore structure, and instead, silicon is deposited as a coarse domain, which exhibits unacceptably poor circulation behavior in LIBs.

[0028] The tubular reactor preferably includes a device for conveying particles from its first end to the second end. The device for conveying particles from the first end of the tubular reactor to the second end may include at least one auger (the auger is defined herein as a rotating shaft axially disposed in the reactor and having a spiral form) so 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 of the tubular reactor to the second end includes a pair of mating augers, wherein the helical lines of each augers are arranged overlappingly. As a result, in this double auger arrangement, the particles are exchanged from the path of one auger to the path of another auger, which is conducive to radial mixing and heat transfer within the particles when the particles are conveyed through the tubular reaction zone.

[0029] 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, such as a paddle for radial mixing of the particles. For example, the device for conveying particles may include an auger as described above, wherein the auger has additional mixing elements and / or blade modifications that enable radial mixing. Alternatively, the reactor wall may include geometric features that enable radial mixing.

[0030] Optionally, the tubular reactor rotates and includes both geometric features for conveying particles from its first end to its second end (e.g., a spiral scraper) and internal mixing geometric elements, such as paddles for radial mixing of particles. For example, the means for conveying particles may include a spiral scraper with additional mixing elements and / or blade modifications to achieve radial mixing.

[0031] Optionally, the tubular reactor comprises a moving internal member for conveying the powder from its first end to its second end, wherein the moving internal member optionally comprises a moving belt conveyor, a bucket conveyor, or a tube chain conveyor, or a vertical conveyor. For example, the means for conveying the particles may comprise a vertical bucket conveyor or several vertical bucket conveyors, or a vertical conveyor belt in a heated reaction vessel, thereby providing a means for continuously introducing the porous particles and continuously removing the composite particles.

[0032] Optionally, the tubular reactor preferably consists of a vertical vibrating screw conveyor furnace.

[0033] As an alternative means for transporting particles from its first end to the second end, the tubular reactor may include a vibrating surface. In this embodiment, the porous particles are transported through the tubular reactor from the first end to the second end of the tubular reactor by vibration. Preferably, the amplitude of the vibration is from 0.01 mm to 10 cm, more preferably from 0.1 mm to 10 cm, more preferably from 1 cm to 10 cm. The frequency of the vibration is suitably from 0.01 to 100 Hz, more preferably from 0.1 to 10 Hz.

[0034] The temperature in the first reaction zone is preferably in the range of 340 to 500° C., more preferably 350 to 480° C., more preferably 350 to 450° C., more preferably 350 to 420° C., more preferably 350 to below 400° C., more preferably 355 to 395° C., more preferably 360 to 390° C., more preferably 365 to 385° C., more preferably 370 to 385° C., for example 370 to 395° C. Alternatively, the temperature in the first reaction zone may be in the range of 400 to 500° C., or 400 to 490° C., or 400 to 480° C., or 400 to 470° C., or 400 to 460° C.

[0035] The method of the present invention is preferably operated under a scheme in which the silicon precursor gas is supplied to the first reaction zone in high concentration or even in pure form. In order to control the rate of the reaction 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 preferably not more than 420° C., more preferably not more than 410° C., more preferably not more than 400° C., more preferably not more than 395° C.

[0036] The pressure in the first reaction zone is preferably in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or is about 100 kPa.

[0037] Optionally, the first reaction zone can be operated at a pressure above atmospheric pressure, for example, at a pressure of 110 to 10000 kPa, or 120 to 5000 kPa, or 150 to 2000 kPa, or 200 to 1800 kPa, or 200 to 1600 kPa, or 250 to 1500 kPa, or 300 to 1200 kPa, or 400 to 1000 kPa, or 500 to 900 kPa, or 600 to 800 kPa.

[0038] The pressure in the first reaction zone may not exceed 650 kPa, or not exceed 600 kPa, or not exceed 500 kPa. For example, the pressure may be in the range of 100 to 600 kPa. The pressure in the first reaction zone may be 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa. Operation under elevated pressure has the following advantages: mass transfer limitations on the reaction rate are reduced, thereby facilitating the penetration of silicon precursor gas into the pore network of the porous particles. However, in order to prevent uncontrolled reactions, it is preferred to reduce the temperature in the reaction zone as the pressure increases. In particular, in the case where the pressure in the first reaction zone is higher than 100 kPa, the reaction temperature in the first reaction zone is preferably not more than 450 ° C, more preferably not more than 430 ° C, more preferably not more than 420 ° C, more preferably not more than 410 ° C, more preferably not more than 400 ° C, more preferably not more than 395 ° C. Unless otherwise indicated, all pressure values ​​disclosed herein are absolute pressures.

[0039] The average residence time of the particles in the first reaction zone between step (b) introducing the porous particles into the first reaction zone and step (e) removing the composite particles from the first reaction zone is preferably from 10 to 300 minutes, or from 15 to 240 minutes, or from 20 to 180 minutes, or from 30 to 120 minutes, or from 40 to 90 minutes. For any given reactor, the average residence time can be calibrated based on the size of the reactor and the operating speed of any mechanical device used to transport the particles through the reaction zone.

[0040] As described above, the first reaction zone is preferably operated essentially in a plug flow mode for the particles. Deviations in the residence time of the particles that lead to a broadening of the particle residence time distribution can be prevented by using a reaction vessel with internal components that prevent axial mixing. For example, in a tubular reactor comprising at least one auger that transports the particles through the reaction zone as described above, the pitch of the auger thread can determine the degree of axial mixing. Preferably, the pitch of the auger blade used in the tubular reactor according to the present invention does not exceed 1.5 times the outer diameter of the auger blade, more preferably does not exceed 1.2 times the outer diameter of the auger blade, more preferably does not exceed 1.0 times the outer diameter of the auger blade. Preferably, the length of the first reaction zone is at least 5 times the pitch of the auger blade, more preferably at least 8 times the pitch of the auger blade, more preferably at least 10 times the pitch of the auger blade.

[0041] The volume of the first reaction zone (in liters (L)) is preferably between (0.003 L·g -1 ×F PP x RT) to (0.06L·g -1 ×F PP x RT), where F PP is the feed rate of porous particles to the first reaction zone (in g / min), and where RT is the average residence time of the particles in the first reaction zone (in minutes). In other words, the reactor volume of the first reaction zone is: 3 cm 3 Up to 60cm 3 / gram of porous particles introduced into the reactor / residence time interval. For example, a charge of 100 g / h of porous particles and an average residence time of 1 h would require a reactor volume of 0.3 L to 6 L. Preferably, the volume of the first reaction zone (in liters (L)) is less than (0.05 L·g -1 ×F PP x RT), more preferably less than (0.04 L·g -1 ×F PP x RT), more preferably less than (0.03 L·g -1 ×F PP x RT), more preferably less than (0.02 L·g -1 ×F PP x RT), more preferably less than (0.01 L·g -1 ×F PP x RT), more preferably less than (0.009 L·g -1 ×F PP x RT, more preferably less than (0.008 L g -1 ×F PP x RT, more preferably less than (0.007 L·g-1 ×F PP x RT, more preferably less than (0.006L·g -1 ×F PP A low reactor volume relative to the mass of particles loaded into the reactor is advantageous because it reduces axial mixing of the particles, making the reactor very close to an idealized plug flow reactor.

[0042] The ratio of the feed rate of the silicon precursor gas to the first reaction zone to the feed rate of the porous particles to 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, during the residence time of the particles in the first reaction zone, 0.25 to 2 grams of silicon (in the form of silicon precursor gas) is introduced into the reactor per gram of porous particles.

[0043] Preferably, the first reaction zone is operated so that the consumption of the 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 so that the consumption of the silicon precursor gas does not exceed 99%, or does not exceed 98%. Low levels of unreacted silicon precursor gas in the exhaust gas can be used as an indication of the controlled reaction rate.

[0044] Preferably, the composite particles removed from the first reaction zone contain from 0.2 to 1.8 grams of silicon per gram of porous particle skeleton.

[0045] The ratio of the feed rate of the silicon precursor gas to the first reaction zone to the feed rate of the porous particles is based on the fresh feed of the silicon precursor gas. It is not excluded that the unreacted silicon precursor gas can be recovered from the exhaust gas taken out from the first reaction zone in step (f) and recycled to the first reaction zone. The silicon precursor gas recycled to the first reaction zone in this way is not included in the above feed ratio.

[0046] The exhaust gas from the first reaction zone contains byproduct gases from the CVI reaction and optionally unreacted silicon precursor gas. In the case where the exhaust gas from the first reaction zone contains a significant amount of unreacted silicon precursor gas, it may be appropriate to recover the unreacted silicon precursor gas from the exhaust gas and recycle the recovered silicon precursor gas to the first reaction zone. Means for recovering unreacted silicon precursor gas from the exhaust gas include semi-permeable membrane separation processes, pressure swing adsorption processes, and cryogenic separation processes.

[0047] Optionally, the silicon precursor gas is preheated before being introduced into the first reaction zone. Preferably, the silicon precursor gas is preheated to ≥(TRZ –200)℃, where T RZ is the reaction temperature of the first reaction zone, preferably preheated to ≥(T RZ –100)℃, preferably preheated to ≥(T RZ –50)℃ temperature.

[0048] The process as defined in steps (a) to (f) is preferably operated under steady state conditions to ensure uniformity over time of the composite particles withdrawn from the first reaction zone in step (e).

[0049] The method of the present invention optionally also includes: monitoring the partial pressure of the silicon precursor gas in the exhaust gas taken out from the first reaction zone, and optionally, in response to the deviation of the measured partial pressure of the silicon precursor gas from the steady-state partial pressure, adjusting one or more of the following items: the temperature in the first reaction zone, the pressure in the first reaction zone, or the feed rate of the silicon precursor gas to the first reaction zone.

[0050] Preheating area

[0051] Step (b) preferably comprises preheating the porous particles before introducing the porous particles into the first reaction zone. In particular, step (b) preferably further comprises preheating the feedstock containing the porous particles in the preheating zone and then introducing the preheated feedstock into the first reaction zone. Preferably, the feedstock containing the porous particles is preheated to ≥ (T RZ –50)℃, where T RZ is the reaction temperature of the first reaction zone, preferably preheated to ≥(T RZ –30)℃, preferably preheated to ≥(T RZ –20)℃ temperature.

[0052] The preheating zone may optionally take the form of a tubular vessel having a first end, a second end, and a length, wherein the porous particles are introduced via a particle inlet at the first end of the tubular vessel, and wherein the composite particles are removed via a particle outlet at the second end of the vessel reactor. One or more heating elements are arranged along the length of the tubular vessel, and the tubular vessel preferably includes a conveying device for conveying the porous particles from the particle inlet to the particle outlet.

[0053] Preferably, the preheating zone is flushed with an inert gas, such as an inert gas selected from nitrogen and argon, during preheating of the porous particles. Optionally, the preheating zone may be operated under vacuum. For example, the pressure in 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.

[0054] Second reaction zone

[0055] The CVI unit optionally comprises at least a first reaction zone and a second reaction zone, so that the CVI reaction is carried out in at least two stages. In the case where 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 further comprises:

[0056] (g) continuously introducing the composite particles removed from the first reaction zone in step (e) into the second reaction zone;

[0057] (h) continuously introducing a silicon precursor gas into the second reaction zone;

[0058] (i) providing conditions in the second reaction zone effective to cause deposition of silicon in the pores of the porous particles;

[0059] (j) continuously removing composite particles from the second reaction zone, the composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton; and

[0060] (k) continuously removing exhaust gas from the second reaction zone.

[0061] One of the advantages of a staged CVI process using more than one reaction zone is that different CVI reaction conditions can be applied in each reaction zone. For example, the bulk of the silicon deposition can be performed in the first reaction zone, and the second reaction zone can be operated under conditions that ensure fine control of the later stages of deposition, when the available pore volume is exhausted and uncontrolled deposition can lead to the deposition of undesirable coarse silicon domains, particularly on the outer surfaces of the porous particles.

[0062] As noted above, the second reaction zone is preferably operated in plug flow mode with respect to the particles.

[0063] The second reaction zone may optionally include 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 include respective tubular reactors each having a means for transporting the composite particles removed from the first reaction zone in step (e) to the second reaction zone in step (g).

[0064] The tubular reactor of the second reaction zone may be operated as a co-current or counter-current reactor. More preferably, the silicon precursor gas may be introduced into the tubular reactor through a plurality of inlets spaced apart along the length of the tubular reactor of the second reaction zone. In this case, exhaust gas from the second reaction zone may be removed through one or more gas exhaust outlets disposed at any position along the length of the tubular reactor, as described with respect to the first reaction zone.

[0065] The tubular reactor of the second reaction zone preferably comprises means for conveying particles from a first end to a second end thereof, such as at least one auger, optionally a pair of mating augers in which the helices of the augers are arranged overlapping.

[0066] Optionally, the tubular reactor preferably rotates and includes geometric features for conveying particles from its first end to the second end, such as a spiral scraper, and internal mixing geometric elements, such as paddles for radial mixing of particles. For example, the means for conveying particles may include a spiral scraper with additional mixing elements and / or blade modifications to achieve radial mixing.

[0067] Optionally, the tubular reactor comprises a moving internal member for conveying the powder from its first end to its second end, wherein the moving internal member optionally comprises a moving belt conveyor, a bucket conveyor, or a tube chain conveyor, or a vertical conveyor. For example, the means for conveying the particles may comprise a vertical bucket conveyor or several vertical bucket conveyors, or a vertical conveyor belt in a heated reaction vessel, thereby providing a means for continuously introducing the porous particles and continuously removing the composite particles.

[0068] Optionally, the reactor preferably consists of a vertical vibrating screw conveyor furnace.

[0069] As an alternative means for transporting particles from its first end to its second end, the tubular reactor may include a vibrating surface. In this embodiment, the porous particles are transported through the tubular reactor from the first end to the second end of the tubular reactor by vibration. Preferably, the amplitude of the vibration is from 0.01 mm to 10 cm, more preferably from 0.1 mm to 10 cm, more preferably from 1 cm to 10 cm. The frequency of the vibration is suitably from 0.01 to 100 Hz, more preferably from 0.1 to 10 Hz.

[0070] The temperature in the second reaction zone is preferably in the range of 350 to 450°C, or 350 to 420°C, or 350 to below 400°C, or 355 to 395°C, or 360 to 390°C, or 365 to 385°C, or 370 to 385°C, for example 370 to 395°C.

[0071] The pressure in the second reaction zone is preferably in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or is about 100 kPa.

[0072] Optionally, the second reaction zone can be operated above atmospheric pressure, for example, at a pressure of 110 to 10000 kPa, or 120 to 5000 kPa, or 150 to 2000 kPa, or 200 to 1800 kPa, or 200 to 1600 kPa, or 250 to 1500 kPa, or 300 to 1200 kPa, or 400 to 1000 kPa, or 500 to 900 kPa, or 600 to 800 kPa.

[0073] The pressure in the second reaction zone may be no more than 650 kPa, or no more than 600 kPa, or no more than 500 kPa. For example, the pressure may be in the range of 100 to 600 kPa. The pressure in the second reaction zone may be 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa. In the case where the pressure in the second reaction zone is higher than 100 kPa, the reaction temperature in the second reaction zone is preferably no more than 450 ° C, more preferably no more than 430 ° C, more preferably no more than 420 ° C, more preferably no more than 410 ° C, more preferably no more than 400 ° C, more preferably no more than 395 ° C.

[0074] In order to control the rate of the reaction and 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 preferably not more than 420°C, more preferably not more than 410°C, more preferably not more than 400°C, more preferably not more than 395°C.

[0075] Preferably, the operation of the first reaction zone and the second reaction zone differs in one or more of reaction temperature, reaction pressure, particle residence time and feed rate of silicon precursor gas. In particular, it is preferred that the second reaction zone is operated under the following conditions: the silicon deposition rate in the second reaction zone is reduced 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.

[0076] For example, the reaction temperature in the second reaction zone is optionally 5 to 50°C lower, or 10 to 20°C lower, than the reaction temperature in the first reaction zone.

[0077] Between step (g) of introducing the composite particles into the second reaction zone and step (j) of removing the composite particles from the second reaction zone, the average residence time of the particles in the second reaction zone is preferably from 2 to 60 minutes, or from 5 to 30 minutes, or from 10 to 20 minutes. Preferably, the average residence time of the particles in the second reaction zone is less than the average residence time of the particles in the first reaction zone.

[0078] As noted above, the second reaction zone is preferably operated in plug flow mode.

[0079] The volume of the second reaction zone (in liters (L)) is preferably between (0.001 L·g -1 ×F CP x RT) to (0.02L g -1 ×F CP x RT), where F CP is the feed rate of composite particles to the second reaction zone in grams of porous particle skeleton per minute, and wherein 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 x RT), more preferably less than (0.008 L·g -1 ×F CP x RT), more preferably less than (0.007 L·g -1 ×F CP x RT), more preferably less than (0.006L·g -1 ×F CP xRT), more preferably less than (0.005L·g -1 ×F CP x RT), more preferably less than (0.004 L·g -1 ×F CP x RT).

[0080] To facilitate comparison between the first reaction zone and the second reaction zone, the mass of the composite particles in the second reaction zone and the reaction parameters defined with reference to the mass of the composite particles in the second reaction zone are normalized to the mass of the porous particle skeleton. Thus, the mass of silicon added to the composite particles per gram of porous particle feedstock in each of the first reaction zone and the second reaction zone can be directly compared.

[0081] The ratio of the feed rate of the silicon precursor gas to the second reaction zone to the feed rate of the composite particles to the second reaction zone is preferably 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 grams of silicon in the silicon precursor gas per gram of porous particle skeleton. In other words, during the residence time of the particles in the second reaction zone, 0.02 to 0.3 grams of silicon atoms (in the form of silicon precursor gas) are introduced into the reactor per gram of porous particle skeleton.

[0082] Preferably, the second reaction zone is operated so that the consumption of the 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 so that the consumption of the silicon precursor gas does not exceed 99%, or does not exceed 98%. Low levels of unreacted silicon precursor gas in the exhaust gas can be used as an indication of the controlled reaction rate.

[0083] In another embodiment, the first reaction zone is operated such that the consumption of the silicon precursor gas does not exceed 90%, or does not exceed 80%, or does not exceed 60%, or does not exceed 60%, and the exhaust gas from the first reaction zone is used as at least a portion of the silicon precursor gas feed to the second reaction zone.

[0084] The composite particles removed from the second reaction zone contain silicon deposited in the first reaction zone, and preferably contain from 0.016 to 0.024 grams of silicon deposited in the second reaction zone per gram of porous particle skeleton.

[0085] More preferably, 0.2 to 1.6 grams of silicon per gram of porous particle skeleton is deposited in the first reaction zone, and 0.016 to 0.024 grams of silicon per gram of porous particle skeleton is deposited in the second reaction zone.

[0086] As discussed above, the ratio of the feed rate of the silicon precursor gas to the second reaction zone to the feed rate of the composite particles to the second reaction zone is calculated based on the fresh feed of the silicon precursor gas. The unreacted silicon precursor gas can be recovered from the exhaust gas withdrawn from the second reaction zone in step (k) and recycled to the second reaction zone. The silicon precursor gas recycled to the second reaction zone in this manner is not included in the above feed ratio.

[0087] The exhaust gas from the second reaction zone comprises byproduct gas from the CVI reaction and optional unreacted silicon precursor gas. Preferably, the content of silicon precursor gas in the exhaust gas from the second reaction zone is at least 1 volume %, or at least 2 volume %, or at least 5 volume %, or at least 10 volume %, or at least 15 volume %. As described above with respect to the first reaction zone, the silicon precursor gas can be recovered and recycled. Optionally, the unreacted silicon precursor gas in the exhaust gas from the first reaction zone and the second reaction zone can be recovered with a combined recovery process, such as a semi-permeable membrane separation process, a pressure swing adsorption process, or a cryogenic separation process.

[0088] The second reaction zone is preferably operated in-line with the first reaction zone so that the composite particles taken out from the first reaction zone in step (e) continuously enter the second reaction zone. The particles taken out from the first reaction zone in step (e) can be introduced into the second reaction zone by an airlock valve in step (g), and the airlock valve is defined as a valve capable of separating the gas flow in the first reaction zone from the gas flow in the second reaction zone and particularly capable of separating the pressure difference between the two reaction zones. A preferred form of the airlock valve for processing particles is a rotary valve (also referred to as a rotary airlock feeder in the art). Alternatively, particles can be introduced into the second reaction zone by a ball valve, a dome valve, a piston valve or a screw feeder in step (g).

[0089] The process as defined in steps (g) to (k) is preferably operated under steady state conditions to ensure uniformity over time of the composite particles withdrawn from the first reaction zone in step (j).

[0090] The method of the present invention optionally also includes: monitoring the partial pressure of the silicon precursor gas in the exhaust gas taken out from the second reaction zone, and optionally, in response to the deviation of the measured partial pressure of the silicon precursor gas from the steady-state partial pressure, adjusting one or more of the following items: the temperature in the second reaction zone, the pressure in the second reaction zone, or the feed rate of the silicon precursor gas to the second reaction zone.

[0091] raw material

[0092] The porous particles preferably have:

[0093] (i) D in the range of 0.5 to 200 μm 50 Particle size;

[0094] (ii) 0.4 to 2.2 cm 3 The total pore volume of micropores and mesopores measured by gas adsorption in the range of 1000 g / min; and

[0095] (iii) PD measured by gas adsorption not exceeding 30 nm 50 Aperture.

[0096] 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, wherein the particle volume is understood to include the volume of any intraparticle pores. As used herein, the term "D 50 ” and “D 50 The term "particle size" as used herein refers to the volume median particle size, i.e., the diameter below which 50% of the volume of the particle population is measured. 10 ” and “D 10The term "particle size" as used herein refers to the 10th percentile volume median particle size, i.e., the diameter at which 10% of the volume of the particle population is below a certain diameter. 90 ” and “D 90 The term "particle size" refers to the 90th percentile volume median particle size, i.e., the diameter below which 90% of the volume of the particle population is measured.

[0097] Particle size and particle size distribution can be determined by standard laser diffraction techniques according to ISO 13320:2009. Laser diffraction relies on the principle that particles will scatter light at angles that vary depending on the size of the particle, and that a collection of multiple particles will produce a scattered light pattern defined by intensity and angle that can be related to the particle size distribution. A wide variety of laser diffraction instruments are commercially available for rapid and reliable determination of particle size distribution. Unless otherwise stated, particle size distribution measurements indicated or reported herein were obtained by a laser diffraction analyzer from Malvern Instruments. TM The regular Malvern Mastersizer TM Measured by Malvern Mastersizer 3000 particle size analyzer. TM The 3000 particle size analyzer operates by projecting a helium-neon gas laser beam through a transparent cell containing the particles of interest suspended in an aqueous solution. The light impinging on the particles is scattered through angles inversely proportional to the particle size, and an array of photodetectors measures the intensity of the light at a number of predetermined angles, and the measured intensities at different angles are processed by computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values ​​reported herein were calculated using an aqueous solution with 5% by volume of the surfactant SPAN added. TM The particle wet dispersion of 1,4-dihydro- ...

[0098] Usually, the D of porous particles 50 The particle size is in the range of 0.5 to 200 μm. Optionally, the 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 50The particle size may be no more than 150 μm, or no more than 100 μm, or no more than 70 μm, or no more than 50 μm, or no more than 40 μm, or no more than 30 μm, or no more than 25 μm, or no more than 20 μm, or no more than 18 μm, or no more than 15 μm, or no more than 12 μm, or no more than 10 μm, or no more than 8 μm.

[0099] For example, the D 50 The particle size may be in the range of 0.5 to 150 μm, or 0.5 to 100 μm, or 0.5 to 50 μm, or 0.5 to 30 μm, or 1 to 25 μm, or 1 to 20 μm, or 2 to 25 μm, or 2 to 20 μm, or 2 to 18 μm, or 2 to 15 μm, or 2 to 12 μm, or 2.5 to 15 μm, or 2.5 to 12 μm, or 2 to 10 μm, or 3 to 20 μm, or 3 to 18 μm, or 3 to 15 μm, or 4 to 18 μm, or 4 to 15 μm, or 4 to 12 μm, or 5 to 15 μm, or 5 to 12 μm, or 5 to 10 μm, or 5 to 8 μm. Particles within these size ranges and having the porosity and pore size distribution described herein are ideally suited for making composite particles suitable for use in anodes of metal ion batteries by the CVI process.

[0100] 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 The particle size is maintained above 0.2 μm, reducing the possibility of undesirable agglomeration of submicron-sized particles and improving the dispersibility of the formed composite particles.

[0101] D of porous particles 90 The particle size is preferably no more than 300 μm, or no more than 250 μm, or no more than 200 μm, or no more than 150 μm, or no more than 100 μm, or no more than 80 μm, or no more than 60 μm, or no more than 40 μm, or no more than 30 μm, or no more than 25 μm, or no more than 20 μm.

[0102] The porous particles preferably have a narrow size distribution span. For example, the particle size distribution span (defined as (D 90 -D 10 ) / D 50 ) is preferably 5 or less, more preferably 4 or less, more preferably 3 or less, more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, efficient filling of particles into a continuous reactor can be more easily achieved.

[0103] The average sphericity (as defined herein) of the porous particles may exceed 0.5. Preferably, their average sphericity is at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8, or at least 0.85. Spherical particles are believed to aid in uniformity of deposition and facilitate denser packing of particles in continuous reactors and in the final product after incorporation into an electrode.

[0104] Highly accurate two-dimensional projections of micrometer-scale particles can be obtained by scanning electron microscopy (SEM) or by dynamic image analysis, where a digital camera is used to record the shadow of the particle projection. The term "sphericity" as used herein is understood to be the ratio of the area of ​​the particle projection (obtained by such imaging techniques) 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:

[0105]

[0106] Among them A m is the measured area of ​​the particle projection, and C m is the measured circumference of the particle projection. As used herein, the average sphericity S of a plurality of particles av is defined as:

[0107]

[0108] wherein n represents the number of particles in the population. The average sphericity of the plurality of particles is preferably calculated from two-dimensional projections of at least 50 particles.

[0109] The porous particles include a three-dimensional interconnected open pore network including micropores and / or mesopores and optionally small volumes of macropores. According to conventional IUPAC terminology, the term "micropore" is used herein to refer to pores with a diameter less than 2 nm, the term "mesopore" is used herein to refer to pores with a diameter of 2-50 nm, and the term "macroporous" is used to refer to pores with a diameter greater than 50 nm.

[0110] References herein to the volumes of micropores, mesopores and macropores in porous particles and any reference to the distribution of pore volumes within porous particles relate to the internal pore volume of the porous particles used as the raw material in step (a) of the claimed method (i.e., before silicon is deposited into the pore volume in step (c)).

[0111] The porous particles are characterized by a 3 / g range of micropores and mesopores (i.e., the total pore volume in the range of 0 to 50 nm). Typically, the porous particles include both micropores and mesopores. However, it is not excluded that porous particles including micropores but not mesopores or porous particles including mesopores but not micropores can be used.

[0112] More preferably, the total volume of the micropores and mesopores in the porous particles is at least 0.45 cm 3 / g, or at least 0.5cm 3 / g, or at least 0.55cm 3 / g, or at least 0.6cm 3 / g, or at least 0.65cm 3 / g, or at least 0.7cm 3 / g, or at least 0.75cm 3 / g, or at least 0.8cm 3 / g, or at least 0.85cm 3 / g, or at least 0.9cm 3 / g, or at least 0.95cm 3 / g, or at least 1cm 3 The use of high porosity conductive particles can be advantageous because it enables a larger amount of silicon to be accommodated within the pore structure.

[0113] The internal pore volume of the porous particles is suitably limited to a value at which the increased fragility of the porous particles outweighs the advantages of the increased pore volume to accommodate a greater amount of silicon. Preferably, the combined volume of micropores and mesopores in the porous particles does not exceed 2 cm 3 / g, or not more than 1.8cm 3 / g, or not more than 1.6cm 3 / g, or not more than 1.5cm 3 / g, or not more than 1.45cm 3 / g, or not more than 1.4cm 3 / g, or not more than 1.35cm 3 / g, or not more than 1.3cm 3 / g, or not more than 1.25cm 3 / g, or not more than 1.2cm 3 / g, or not more than 1.1, or not more than 1, or not more than 0.95.

[0114] In some examples, the total volume of the micropores and mesopores of the porous particles can be between 0.45 and 2.2 cm 3 / g, or 0.5 to 2cm 3 / g, or 0.55 to 2cm 3 / g, or 0.6 to 1.8 cm 3 / g, or 0.65 to 1.8 cm 3 / g, or 0.7 to 1.6 cm 3 / g, or 0.75 to 1.6 cm 3 / g, or 0.8 to 1.5 cm 3 / g range.

[0115] In other examples, the total volume of the micropores and mesopores of the porous particles can be between 0.55 and 1.4 cm 3 / g, or 0.6 to 1.4 cm 3 / g, or 0.6 to 1.3 cm 3 / g, or 0.65 to 1.3 cm 3 / g, or 0.65 to 1.2 cm 3 / g, or 0.7 to 1.2 cm 3 / g, or 0.7 to 1.1 cm 3 / g, or 0.7 to 1cm 3 / g, or 0.75 to 0.95 cm 3 / g range.

[0116] In other examples, the total volume of the micropores and mesopores of the porous particles can be between 0.4 and 0.75 cm 3 / g, or 0.4 to 0.7 cm 3 / g, or 0.4 to 0.65cm 3 / g, 0.45 to 0.75 cm 3 / g, or 0.45 to 0.7 cm 3 / g, or 0.45 to 0.65cm 3 / g, or 0.45 to 0.6 cm 3 / g range.

[0117] In other examples, the total volume of the micropores and mesopores of the porous particles can be between 0.6 and 2 cm 3 / g, or 0.6 to 1.8 cm 3 / g, or 0.7 to 1.8 cm 3 / g, or 0.7 to 1.6 cm 3 / g, or 0.8 to 1.6 cm 3 / g, or 0.8 to 1.5 cm 3 / g, or 0.8 to 1.4 cm 3 / g, or 0.9 to 1.5cm 3 / g, or 0.9 to 1.4 cm 3 / g, or 1 to 1.4cm 3 / g range.

[0118] PD of porous particles 50The pore size is no more than 30 nm, and optionally no more than 25 nm, or no more than 20 nm, or no more than 15 nm, or no more than 12 nm, or no more than 10 nm, or no more than 8 nm, or no more than 6 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3 nm, or no more than 2.5 nm, or no more than 2 nm, or no more than 1.5 nm. As used herein, the term "PD 50 "Pore diameter" refers to the volume median pore diameter calculated based on the total volume of micropores and mesopores (i.e., the pore diameter at which 50% of the total micropore and mesopore volume is measured to be lower than a certain pore diameter). Therefore, according to the present invention, at least 50% of the total volume of micropores and mesopores is preferably in the form of pores with a diameter of less than 30 nm.

[0119] For the avoidance of doubt, in order to determine the PD 50 value, without taking into account any macropore volume (pores larger than 50 nm).

[0120] The volume ratio of micropores to mesopores in the porous particles can in principle be in the range of 100:0 to 0: 100. Preferably, the volume ratio of micropores to mesopores is 90:10 to 55:45, or 90:10 to 60:40, or 85:15 to 65:35.

[0121] The pore size distribution of the porous particles may be unimodal, bimodal or multimodal. As used herein, the term "pore size distribution" relates to the distribution of pore sizes of the porous particles relative to the cumulative total internal pore volume. Bimodal or multimodal pore size distributions may be preferred because the close proximity between micropores and pores with larger diameters provides the advantage of efficient ion transport from the porous network to the silicon.

[0122] The quenched solid density functional theory (QSDFT) was used according to the standard method described in ISO 15901-2 and ISO 15901-3, using nitrogen adsorption at 77 K down to 10 -6The relative pressure p / p0 of pore volume is used to determine the total volume of micropores and mesopores and the pore size distribution of micropores and mesopores. Nitrogen 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 increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases until a saturation point is reached, at which all pores are filled with liquid. The nitrogen pressure is then gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms and the hysteresis between them enables the determination of the pore volume and pore size distribution. Suitable instruments for measuring pore volume and pore size distribution by nitrogen adsorption include TriStar II and TriStar IIPlus porosity analyzers (which are available from Micromeritics Instrument Corporation in the United States), and Autosorb IQ porosity analyzer (which is available from Quantachrome Instruments).

[0123] Nitrogen adsorption is effective for measuring pore volume and pore size distribution for pores up to 50 nm in diameter, but is less reliable for pores with much larger diameters. For the purposes of the present invention, therefore, pore volume and pore size distribution are determined using nitrogen adsorption only for pores up to and including 50 nm in diameter (i.e., only for micropores and mesopores). 50 Likewise it is determined only relative to the total volume of micropores and mesopores.

[0124] Given the limitations of available analytical techniques, it is not possible to measure pore volume and pore size distribution over the entire range of micropores, mesopores and macropores using a single technique. Where the porous particles include macropores, the volume of pores with diameters in the range of greater than 50 nm to 100 nm can be measured by mercury intrusion porosimetry, and preferably not more than 0.3 cm 3 / g, or not more than 0.20cm 3 / g, or not more than 0.1cm 3 / g, or not more than 0.05cm 3 Although a small fraction of macropores may be useful in facilitating the entry of electrolyte into the pore network, the advantages of the present invention are substantially obtained by accommodating silicon in micropores and smaller mesopores.

[0125] Any pore volume measured by mercury porosimetry for pore sizes below 50 nm is not considered (as described above, nitrogen adsorption is used to characterize mesopores and micropores). For the purposes of this invention, the pore volume measured by mercury porosimetry above 100 nm is assumed to be interparticle porosity and is also not considered.

[0126] Mercury intrusion porosimetry is a technique for characterizing the porosity and pore size distribution of a material by applying varying levels of pressure to a sample of the material immersed in mercury. The pressure required to cause mercury to penetrate into the pores of the sample is inversely proportional to the size of the pores. The values ​​obtained by mercury intrusion porosimetry reported herein are obtained according to ASTM UOP578-11, where for mercury at room temperature, the surface tension γ is 480 mN / m and the contact angle is is 140°. The density of mercury at room temperature is 13.5462 g / cm 3 A variety of high-precision mercury intrusion instruments are commercially available, such as the AutoPore IV series of automated mercury porosimeter, which is available from Micromeritics Instrument Corporation in the United States. For a complete overview of mercury intrusion, reference can be made to "Analytical Methods in Fine Particle Technology" by PA Webb and C. Orr, 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0127] It should be understood that intrusion techniques such as gas adsorption and mercury intrusion are only valid for determining the pore volume of pores accessible to nitrogen or mercury from outside the porous particle. The porosity values ​​specified herein should be understood to refer to the volume of open pores (i.e., pores accessible to fluid from outside the porous particle). In this context, completely enclosed pores that cannot be identified by nitrogen adsorption or mercury intrusion should not be considered when determining porosity values. Likewise, any pore volume located in pores so small as to be below the detection limit of nitrogen adsorption is also not considered.

[0128] The porous particles are preferably porous conductive particles. A preferred type of porous conductive particles are porous carbon particles. The porous carbon particles preferably contain at least 80% by weight carbon, more preferably at least 90% by weight carbon, more preferably at least 95% by weight carbon, and 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 carbon and crystalline carbon. The porous carbon particles may be hard carbon particles or soft carbon particles.

[0129] As used herein, the term "hard carbon" refers to a disordered carbon matrix in which the carbon atoms are found primarily as sp 2 Hybrid state (trigonal bond). The polyaromatic domains are cross-linked using chemical bonds such as C-O-C bonds. Due to the chemical cross-linking between the polyaromatic domains, hard carbon cannot be converted into graphite at high temperatures. Hard carbon has graphite-like properties, which is reflected by the large G band (~1600 cm) in the Raman spectrum. -1However, the carbon is not completely graphitic, as evidenced by the distinct D band (~1350 cm -1 ) is proved. The graphitic properties of the carbon material can be evaluated by monitoring the peak intensity ratio of the D band to the G band (ID / IG). The porous carbon particles may contain an ID / IG of no more than 0.84, or no more than 0.75.

[0130] As used herein, the term "soft carbon" also refers to a disordered carbon matrix in which carbon atoms are found primarily in sp 2 The polyaromatic domains in the hybrid state (triangular bonds) are in the size range of 5 to 200 nm. Compared with hard carbon, the polyaromatic domains in soft carbon are associated by intermolecular forces rather than cross-linked by chemical bonds. This means that they will graphitize at high temperatures. The porous carbon particles preferably contain at least 50% sp 2 Hybridized carbon (measured by XPS). For example, the porous carbon particles may suitably contain 50% to 98% sp 2 Hybridized carbon, 55% to 95% sp 2 Hybridized carbon, 60% to 90% sp 2 Hybridized carbon, or 70% to 85% sp 2 Hybridized carbon.

[0131] A variety of different materials can be used to prepare suitable porous carbon skeletons. Examples of organic materials that can be used include: plant biomass, which includes lignocellulosic materials (such as coconut shells, rice husks, wood, etc.), and fossil carbon sources, such as coal. Examples of resins and polymer materials that form porous carbon particles during pyrolysis include: phenolic resins, novolac resins, asphalt, melamine materials, polyacrylate materials, polystyrene materials, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and various copolymers of monomer units comprising acrylic ester monomers, styrene monomers, α-olefins, vinyl pyrrolidone and other ethylenically unsaturated monomers. Depending on the raw materials and conditions of the pyrolysis process, various carbon materials can be obtained in the art. Porous carbon particles of various specifications can be obtained from commercial suppliers.

[0132] The porous carbon particles may be subjected to a chemical or gas activation process to increase the volume of the mesopores and micropores. Suitable activation processes include contacting the pyrolytic carbon with one or more of oxygen, water vapor, CO, CO2 and KOH at a temperature in the range of 600 to 1000°C.

[0133] Mesopores can also be obtained by known templating processes using removable pore formers such as MgO and other colloidal or polymer templates that can be removed by thermal or chemical means after pyrolysis or activation.

[0134] Alternatives to carbon-based conductive particles include porous metal oxides, such as those having the formula TiO x An oxide of titanium, wherein the value of x is greater than 1 and less than 2.

[0135] The BET surface area of ​​the porous particles is preferably at least 750 m 2 / g, or at least 1,000m 2 / g, or at least 1,250m 2 / g, or at least 1,500m 2 / g. The term "BET surface area" as used herein should be taken to mean the surface area per unit mass calculated from the measurement results of the physical adsorption of gas molecules on the solid surface using the Brunauer-Emmett-Teller principle according to ISO 9277. Preferably, the BET surface area of ​​the porous particles does not exceed 4,000 m 2 / g, or not more than 3,500m 2 / g, or not more than 3,250m 2 / g, or not more than 3,000m 2 / g, or not more than 2,500m 2 / g, or not more than 2,000m 2 / g. For example, the BET surface area of ​​a porous particle can be 750m 2 / g to 4,000m 2 / g, or 1,000m 2 / g to 3,500m 2 / g, or 1,250m 2 / g to 3,250m 2 / g, or 1,500m 2 / g to 3,000m 2 / g range.

[0136] The particle density of the porous particles is preferably at least 0.35 and preferably less than 3 g / cm 3 , more preferably less than 2g / cm 3 , more preferably less than 1.5 g / cm 3 , most preferably 0.35 to 1.2 g / cm 3As used herein, the term "particle density" refers to the "apparent particle density" as measured by mercury intrusion (i.e., the mass of a particle divided by the particle volume, where the particle volume is taken to be the sum of the volume of the solid material and any closed pores or blind pores ("blind pores" are pores that are too small to be measured by mercury intrusion)). Typically, the particulate additives used in the present invention have a low BET surface area and therefore a relatively low open pore volume. Thus, the apparent density measured by mercury intrusion is close to the "effective particle density" (the calculation of which includes the volume of the open pores). Preferably, the porous particles have a particle density of at least 0.4 g / cm 3 , or at least 0.45g / cm 3 , or at least 0.5g / cm 3 , or at least 0.55g / cm 3 , or at least 0.6g / cm 3 , or at least 0.65g / cm 3 , or at least 0.7g / cm 3 Preferably, the particle density of the porous particles does not exceed 1.15 g / cm 3 , or not more than 1.1g / cm 3 , or not more than 1.05g / cm 3 , or not more than 1g / cm 3 , or not more than 0.95g / cm 3 , or not more than 0.9g / cm 3 .

[0137] Preferred porous particles for use according to the present invention include those that satisfy the following conditions:

[0138] (i)D 50 Particle size ranges from 0.5 to 30 μm;

[0139] (ii) The total pore volume of micropores and mesopores measured by gas adsorption is between 0.5 and 1.5 cm 3 / g range;

[0140] (iii) PD measured by gas adsorption 50 The pore size does not exceed 5nm;

[0141] The silicon precursor gas is a silicon compound or a mixture of silicon compounds that is gaseous at the temperature of the CVI process and can be thermally decomposed to form elemental silicon and byproduct gases. Examples of suitable silicon precursor gases include monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane, dimethylsilane and chlorosilane, and mixtures thereof. Preferably, the silicon precursor gas is selected from monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8), methylsilane and dimethylsilane. Monosilane (SiH4) is the most preferred silicon-containing precursor gas.

[0142] Preferably, the silicon precursor gas contains no chlorine, for example contains less than 1 wt. %, preferably less than 0.1 wt. %, preferably less than 0.01 wt. % of chlorine-containing compounds.

[0143] The silicon precursor gas can be used undiluted (pure) or diluted, and comprises at least 20% by volume of a silicon precursor gas and the remainder of a gas selected from hydrogen and an inert gas, optionally wherein the inert gas is selected from nitrogen and argon. Preferably, the silicon precursor gas comprises 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 a silicon precursor gas.

[0144] Carbon coating

[0145] The method of the present invention optionally further comprises the following steps:

[0146] (1) providing a carbon deposition unit comprising at least one reaction zone

[0147] (m) introducing a feedstock comprising the composite particles removed from the chemical vapor infiltration unit in step (e) or (j) into the reaction zone;

[0148] (n) introducing a carbon precursor gas into the reaction zone;

[0149] (o) providing conditions in the reaction zone effective to cause deposition of carbon within the pores and / or on the surfaces of the composite particles;

[0150] (p) removing from the reaction zone composite particles comprising a porous particle skeleton, elemental silicon within the pores of the porous particle skeleton, and carbon within the pores and / or on the external surface thereof.

[0151] The carbon deposited in step (o) is a pyrolytic carbon material formed by the thermal decomposition of a carbon-containing gas (such as ethylene). It provides a variety of performance advantages. It further reduces the BET surface area of ​​the composite particles by smoothing any surface defects and filling any residual surface micropores, thereby further reducing the first cycle loss. It also improves the conductivity of the surface of the composite particles, thereby reducing the need for conductive additives in the electrode composition. In addition, it produces an optimal surface for forming a stable SEI layer, thereby obtaining an improved capacity retention rate during cycling.

[0152] Steps (l) to (p) are preferably operated as a continuous process such that introducing the composite particles and carbon precursor gas into the reaction zone in steps (m) and (n) and removing the composite particles from the reaction zone in step (p) each occur continuously.

[0153] Preferably, the carbon deposition unit is operated as a CVI unit, such that the composite particles removed from the CVI unit in step (e) or (j) continuously enter the carbon deposition unit in step (m).

[0154] The reaction zone of the carbon deposition unit is preferably in the form of a tubular reactor having a first end, a second end and a length, wherein particles are introduced through a particle inlet at the first end of the tubular reactor, and wherein composite particles comprising deposited carbon are removed through a particle outlet at the second end of the tubular reactor.

[0155] The tubular reactor can be operated as a co-current reactor, wherein the carbon precursor gas is introduced through an inlet near a first end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near a second end of the tubular reactor. Alternatively, the tubular reactor can be operated as a counter-current reactor, wherein the carbon precursor gas is introduced through an inlet near the second end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near the first end of the tubular reactor.

[0156] Alternatively, the carbon precursor gas may be introduced into the tubular reactor through a plurality of inlets spaced apart along the length of the tubular reactor. In this case, the exhaust gas may be removed through one or more gas exhaust outlets disposed at any position along the length of the tubular reactor. For example, the exhaust gas may be removed by: (i) through a gas exhaust outlet proximate the second end of the tubular reactor; or (ii) through a gas exhaust outlet proximate the first end of the tubular reactor; or (iii) through a plurality of gas exhaust outlets spaced apart along the length of the tubular reactor.

[0157] The tubular reactor of the carbon deposition zone preferably comprises means as defined above for transporting particles from a first end to a second end thereof, such as at least one auger.

[0158] Step (o) is suitably carried out at a temperature in the range of 350 to 700° C., or 400 to 700° C. Preferably, the temperature in step (o) is no more than 680° C., or no more than 660° C., or no more than 640° C., or no more than 620° C., or no more than 600° C., or no more than 580° C., or no more than 560° C., or no more than 540° C., or no more than 520° C., or no more than 500° C.

[0159] The minimum temperature in step (o) will depend on the type of carbon precursor used. Preferably, the temperature in step (o) is at least 300°C, or at least 350°C, or at least 400°C.

[0160] Step (o) is suitably carried out at a pressure in the range of 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa.

[0161] The average residence time of the particles in the reaction zone of the carbon deposition unit between step (m) of introducing the composite particles into the reaction zone and step (p) of removing the composite particles from the reaction zone is preferably from 2 to 60 minutes, or from 5 to 30 minutes, or from 10 to 20 minutes.

[0162] As mentioned above, the reaction zone of the carbon deposition unit is preferably operated in plug flow mode with respect to the particles.

[0163] The volume of the reaction zone (in liters (L)) is preferably between (0.001 L·g -1 ×F PP x RT) to (0.02L g -1 ×F PP x RT), where F PP is the feed rate of composite particles to the reaction zone in grams of porous particle skeleton per minute, and wherein 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 x RT), more preferably less than (0.008 L·g -1 ×F CP x RT), more preferably less than (0.05 L·g -1 ×F CP x RT).

[0164] As described above, the mass of the composite particles in the carbon deposition unit and the reaction parameters defined with reference to the mass of the composite particles in the carbon deposition unit are normalized to the mass of the porous particle skeleton. Thus, 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 to each of the first reaction zone and the second reaction zone.

[0165] The ratio of the feed rate of the carbon precursor gas to the reaction zone to the feed rate of the composite particles to the reaction zone is preferably from 0.02 to 2, or from 0.03 to 1, or from 0.04 to 0.5, or from 0.04 to 0.2, or from 0.04 to 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 to 2 grams of carbon atoms (in the form of carbon precursor gas) are introduced into the reactor per gram of porous particle skeleton. Preferably, the reaction zone of the carbon deposition unit is operated so that the consumption of the carbon precursor gas is substantially 100%, so that the composite particles removed from the reaction zone preferably contain 0.02 to 0.06 grams, more preferably 0.02 to 0.05 grams, more preferably 0.03 to 0.04 grams of carbon derived from the carbon precursor gas per gram of porous particle skeleton.

[0166] Suitable carbon precursor gases include:

[0167] (i) C2-C 10 a hydrocarbon, optionally wherein the hydrocarbon is selected from alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes and aromatic hydrocarbons, such as methane, ethylene, propylene, limonene, styrene, cyclohexane, cyclohexene, alpha-terpinene and acetylene;

[0168] (ii) a bicyclic monoterpene, optionally wherein the bicyclic monoterpene is selected from camphor, borneol, eucalyptol, camphene, carene, sabinene, limonene and pinene; and

[0169] (iii) a polycyclic hydrocarbon containing 10 to 25 carbon atoms and optionally 1 to 3 heteroatoms, optionally wherein the polyaromatic hydrocarbon is selected from naphthalene, substituted naphthalenes (such as dihydroxynaphthalene), anthracene, tetracene, pentacene, fluorene, acenapthene, phenanthrene, fluoranthene, pyrene, Perylene, corone, fluorenone, anthraquinone, anthrone and their alkyl substituted derivatives.

[0170] The carbon precursor used in step (o) can be used in pure form or as a mixture diluted with an inert carrier gas such as nitrogen or argon. For example, the carbon precursor can be used in 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.

[0171] Passivation

[0172] The silicon deposited in the CVI reaction zone has a hydride-terminated silicon surface that is highly reactive toward oxygen. Therefore, the method of the present invention preferably includes a passivation step by which the composite particles can undergo controlled oxidation by an oxygen-containing gas to form a passivated material that is stable in air.

[0173] Therefore, the method of the present invention preferably further comprises the following steps:

[0174] (q) providing a passivation unit comprising at least one reaction zone;

[0175] (r) introducing a feedstock comprising the composite particles removed from the chemical vapor infiltration in step (e) or (j) or the composite particles removed from the carbon deposition unit in step (p) into the reaction zone;

[0176] (s) introducing an oxygen-containing gas into the reaction zone;

[0177] (t) removing the passivated composite particles from the reaction zone; and

[0178] (u) removing exhaust gas from the reaction zone.

[0179] 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 removal of the composite particles and exhaust gas from the reaction zone in steps (t) and (u) are each performed continuously.

[0180] Step (s) is suitably carried out at a temperature in the range of 20 to 300°C, or 20 to 200°C, or 25 to 200°C, or 25 to 180°C, or 50 to 160°C. Preferably, the temperature in step (s) does not exceed 150°C.

[0181] Step (s) is suitably carried out at a pressure in the range of 1 to 600 kPa, or 10 to 500 kPa, or 20 to 200 kPa, or 50 to 150 kPa, or 80 to 120 kPa, or about 100 kPa.

[0182] Preferably, the passivation unit is operated in accordance with the CVI unit or the optional carbon deposition unit, so that the composite particles removed from the CVI unit in step (e) or step (j) or alternatively the composite particles removed from the optional carbon deposition unit in step (p) continuously enter the passivation unit in step (r).

[0183] The reaction zone of the passivation unit is preferably in the form of a tubular reactor having a first end, a second end and a length, wherein in step (r) the composite particles are introduced into the first end of the tubular reactor and wherein in step (t) the composite particles are removed from the second end of the tubular reactor.

[0184] The tubular reactor can be operated as a co-current reactor, wherein the oxygen-containing precursor gas is introduced through an inlet near the first end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near the second end of the tubular reactor. Alternatively, the tubular reactor can be operated as a countercurrent reactor, wherein the oxygen-containing gas is introduced through an inlet near the second end of the tubular reactor, and the exhaust gas is removed through a gas exhaust outlet near the first end of the tubular reactor.

[0185] More preferably, the oxygen-containing gas may be introduced into the tubular reactor through a plurality of inlets spaced apart along the length of the tubular reactor. In this case, the exhaust gas may be removed through one or more gas exhaust outlets disposed at any position along the length of the tubular reactor. For example, the exhaust gas may be removed by: (i) through a gas exhaust outlet proximate the second end of the tubular reactor; or (ii) through a gas exhaust outlet proximate the first end of the tubular reactor; or (iii) through a plurality of gas exhaust outlets spaced apart along the length of the tubular reactor.

[0186] Still more preferably, multiple inlets spaced apart along the length of tubular reactor are assigned to more than two inlet groups spaced apart along the length of reactor, wherein each inlet group includes one or more inlets.For example, multiple inlets can be assigned to 2 to 10 inlet groups, wherein each inlet group independently includes 1 to 10 inlets.The oxygen concentration in the oxygen-containing gas increases in a continuous inlet group, so that the oxygen-containing gas fed to the first end closest to tubular reactor has a relatively low oxygen concentration, and the oxygen-containing gas fed to the inlet group closest to the second end of tubular reactor has a relatively high oxygen concentration.For example, the oxygen concentration in the oxygen-containing gas supplied to the inlet group closest to the first end of tubular reactor is 0.5 volume % to 5 volume %, and the oxygen concentration in the oxygen-containing gas supplied to the inlet group closest to the second end of tubular reactor is 15 volume % to 21 volume %, and optionally can be air.

[0187] By arranging the inlets as groups with gradually increasing oxygen content, the composite particles are stably exposed to oxygen with gradually increasing concentrations as they pass through the tubular reaction zone. When the composite particles first enter the passivation unit, they are most reactive to oxygen. Therefore, the oxygen-containing gas supplied to the inlet group closest to the first end of the tubular reactor contains a relatively low oxygen content to limit the reaction rate. As the passivation reaction proceeds and the composite particles become less reactive, the oxygen concentration in the oxygen-containing gas can be increased to drive the passivation reaction to completion. As a result, the reaction of oxygen with the reactive silicon surface is controlled, thereby avoiding a large amount of heat release that may have an adverse effect on the composite particle structure.

[0188] cool down

[0189] The method of the present invention optionally also includes the step of cooling the composite particles to ambient temperature. The cooling of the particles can be carried out by any conventional method. However, a suitable method includes sending the composite particles to a tubular cooling container provided with a cooling device. The particles are introduced through the particle inlet at the first end of the tubular cooling container and are removed through the particle outlet at the second end of the tubular cooling container.

[0190] The cooling means may comprise a cooling jacket supplied with a liquid coolant (eg water) or a coolant gas, and / or a coolant gas (eg air) in contact with the composite particles in the cooling vessel.

[0191] The cooled particles may be collected, optionally classified to remove oversized particles and / or fines, and sent to containers for storage and subsequent delivery to downstream processes for making lithium-ion batteries.

[0192] The present invention is further described with reference to the accompanying drawings, in which:

[0193] Figure 1 is a schematic diagram of an apparatus for a chemical vapor infiltration (CVI) reaction zone operated in accordance with one embodiment of the present invention.

[0194] Figure 2 is a schematic diagram of an apparatus for passivating a reaction zone operated in accordance with one embodiment of the present invention.

[0195] Figure 3 A flow chart of a method according to the present invention is depicted.

[0196] Reference Figure 1 , shows a CVI reaction zone (1) comprising a continuous tubular reactor (10) having a first end (11) and a second end (12) and a length. Figure 1In an embodiment of the present invention, the tubular reactor (10) is oriented horizontally. The tubular reactor comprises: a particle inlet (13) at a first end, through which porous particles are introduced into the tubular reactor via an airlock valve (13a), and a particle outlet (14) at a second end, through which porous particles are removed from the tubular reactor.

[0197] The tubular reactor comprises: 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 removing exhaust gas. Optionally, the CVI reaction zone comprises a plurality of additional gas inlets (17) spaced along the length of the tubular reactor. The CVI reaction zone preferably comprises a gas heater (18) for preheating the silicon precursor gas.

[0198] The tubular reactor (10) further comprises means for transporting particles from its first end to its second end in the form of an auger (19) driven by a motor (20). An electric heater (21) is provided to control the internal temperature of the tubular reactor.

[0199] Reference Figure 2 , a passivation unit (30) is shown, which includes a continuous tubular reactor (31) having a first end (32), a second end (33) and a length. Figure 2 In an embodiment of the present invention, the tubular reactor is oriented horizontally. The tubular reactor comprises: a particle inlet (34) at a first end, through which porous particles are introduced into the tubular reactor via an airlock valve (34a), and a particle outlet (35) at a second end, through which porous particles are removed from the tubular reactor.

[0200] The tubular reactor comprises a plurality of gas inlets for introducing oxygen-containing gas arranged along the length of the tubular reactor. As shown, a plurality of gas inlets are allocated to four inlet groups (36, 37, 38, 39), and each inlet group comprises three gas inlets. In the gas supplied to the inlet group (36) of the first end (32) closest to the tubular reactor, the oxygen concentration of the oxygen-containing gas is the lowest. In each continuous inlet group (37, 38, 39), the oxygen concentration of the oxygen-containing gas increases successively. The oxygen concentration in the oxygen-containing gas supplied to the inlet group (39) of the second end (33) closest to the tubular reactor is preferably almost the same as the oxygen concentration in the air. Optionally, the gas supplied to the inlet group (39) can be air. A gas outlet (40) is arranged at the second end of the tubular reactor for taking out exhaust gas.

[0201] The tubular reactor (31) also includes means for transporting particles from its first end to its second end in the form of an auger (41) driven by a motor (42). An electric heater (43) is provided to control the internal temperature of the tubular reactor.

[0202] Figure 3 A flow chart of an embodiment of the method of the present invention is shown. The method includes a particle pretreatment step (50) in which the porous particle feedstock is preheated, preferably by preheating under an inert gas. The preheated particles are introduced into a CVI unit (60) comprising a first CVI reaction zone (65) for steps (a) to (f) and a second CVI reaction zone (70) for steps (g) to (k). The composite particles removed from the second CVI reaction zone in step (k) can be directly sent to a passivation unit (80) for steps (q) to (u). Alternatively, the particles removed from the reaction zone in step (k) can be sent to a carbon deposition unit (75) for steps (l) to (p), and then the composite particles removed from the carbon deposition unit in step (p) are sent to a passivation unit (80) for steps (q) to (u). Finally, the passivated particles removed from the passivation unit (80) in step (u) are sent to a cooling unit (90).

Claims

1. A continuous method for preparing composite particles, the method comprising the following steps: (a) providing a chemical vapor permeation unit comprising at least a first reaction zone; (b) providing a feedstock comprising porous particles, and continuously introducing the porous particles into the 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 in the pores of the porous particles; (e) continuously removing composite particles from the first reaction zone, the composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton; and (f) continuously removing exhaust gas from the first reaction zone.

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

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

4. The method according to claim 2 or 3, wherein: (i) introducing the silicon precursor gas through an inlet proximate a first end of the tubular reactor, and wherein the exhaust gas is removed through a gas exhaust outlet proximate a second end of the tubular reactor; or (ii) introducing the silicon precursor gas through an inlet proximate the second end of the tubular reactor, and wherein the exhaust gas is removed through a gas exhaust outlet proximate the first end of the tubular reactor.

5. The method of claim 2 or 3, wherein the silicon precursor gas is introduced through a plurality of inlets spaced apart along the length of the tubular reactor, and wherein the exhaust gas is removed through the following gas exhaust outlets: (i) a gas discharge outlet proximate to the second end of the tubular reactor; or (ii) a gas discharge outlet proximate to the first end of the tubular reactor; or (iii) a plurality of gas exhaust outlets spaced along the length of the tubular reactor.

6. A process according to any one of claims 2 to 5, wherein the tubular reactor comprises means for transporting particles from a first end to a second end thereof.

7. The method of claim 6, wherein the means for conveying particles from the first end to the second end of the tubular reactor comprises at least one auger, a moving belt conveyor, a bucket conveyor, a tube chain conveyor or a vertical conveyor, optionally wherein the means comprises a double auger.

8. A process according to any preceding claim, wherein the conditions in the first reaction zone comprise a temperature in the range of 340 to 500°C, or 350 to 480°C, or 350 to 450°C, or 350 to 420°C, or 350 to less than 400°C, or 355 to 395°C, or 360 to 390°C, or 365 to 385°C, or 370 to 380°C.

9. A process according to any preceding claim, wherein the conditions in the first reaction zone comprise a pressure in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or about 100 kPa.

10. The process of any one of claims 1 to 9, wherein the conditions in the first reaction zone comprise a pressure in the range of 110 to 10000 kPa, or 120 to 5000 kPa, or 150 to 2000 kPa, or 200 to 1800 kPa, or 200 to 1600 kPa, or 250 to 1500 kPa, or 300 to 1200 kPa, or 400 to 1000 kPa, or 500 to 900 kPa, or 600 to 800 kPa.

11. A method according to any preceding claim, wherein between step (b) introducing the porous particles into the first reaction zone and step (e) removing the composite particles from the first reaction zone, the average residence time of the particles in the first reaction zone is 10 to 300 minutes, or 15 to 240 minutes, or 20 to 180 minutes, or 30 to 120 minutes, or 40 to 90 minutes.

12. A process according to any preceding claim, wherein the volume of the first reaction zone in litres is between (0.003 L·g -1 ×F PP x RT) to (0.06L·g -1 ×F PP x RT), where F PP is the feed rate of porous particles to the first reaction zone in grams per minute, and wherein RT is the average residence time of the particles in the first reaction zone in minutes.

13. A method according to any preceding claim, wherein the ratio of the feed rate of the silicon precursor gas to the first reaction zone to the feed rate of the porous carbon particles to 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.

14. A method according to any preceding claim, wherein step (b) further comprises: The feedstock including the porous particles is preheated in a preheating zone, and then the preheated feedstock is introduced into the first reaction zone.

15. The method according to claim 14, wherein the raw material containing the porous particles is preheated to ≥ (T RZ –50)℃, where T RZ is the reaction temperature of the first reaction zone.

16. A method according to any preceding claim, wherein the chemical vapor permeation unit comprises at least a first reaction zone and a second reaction zone, wherein the first reaction zone is a reaction zone as defined in any preceding claim, and wherein the method further comprises: (g) continuously introducing the composite particles removed from the first reaction zone in step (e) into the second reaction zone; (h) continuously introducing a silicon precursor gas into the second reaction zone; (i) providing conditions in the second reaction zone effective to cause deposition of silicon in the pores of the porous particles; (j) continuously removing composite particles from the second reaction zone, the composite particles comprising a porous particle skeleton and elemental silicon within the pores of the porous particle skeleton; and (k) continuously removing exhaust gas from the second reaction zone.

17. The method of claim 16, wherein the second reaction zone comprises a tubular reactor having a first end, a second end, and a length, wherein the composite particles removed from the first reaction zone are introduced into the first end of the tubular reactor, and wherein the composite particles are removed from the second end of the tubular reaction zone.

18. The method of claim 17, wherein: (i) introducing the silicon precursor gas through an inlet proximate a first end of the tubular reactor, and wherein the exhaust gas is removed through a gas exhaust outlet proximate a second end of the tubular reactor; or (ii) introducing the silicon precursor gas through an inlet proximate the second end of the tubular reactor, and wherein the exhaust gas is removed through a gas exhaust outlet proximate the first end of the tubular reactor.

19. The method of claim 17, wherein the silicon precursor gas is introduced through a plurality of inlets spaced along the length of the tubular reactor, and wherein the exhaust gas is removed through a gas exhaust outlet as follows: (i) a gas discharge outlet proximate to the second end of the tubular reactor; or (ii) a gas discharge outlet proximate to the first end of the tubular reactor; or (iii) a plurality of gas exhaust outlets spaced along the length of the tubular reactor.

20. A process according to any one of claims 17 to 19, wherein the tubular reactor comprises at least one auger to transport particles from a first end to a second end thereof.

21. The process of any one of claims 16 to 20, wherein the conditions in the second reaction zone comprise a reaction temperature in the range of 350 to 450°C, or 350 to 420°C, or 350 to less than 400°C, or 355 to 395°C, or 360 to 390°C, or 365 to 385°C, or 370 to 380°C.

22. The process of any one of claims 16 to 21, wherein the conditions in the second reaction zone comprise a pressure in the range of 1 to 10000 kPa, or 10 to 6000 kPa, or 20 to 4000 kPa, or 50 to 2000 kPa, or 80 to 1500 kPa, or 90 to 1000 kPa, or 90 to 600 kPa, or about 100 kPa.

23. The process of any one of claims 16 to 21, wherein the conditions in the first reaction zone comprise a pressure in the range of 110 to 10000 kPa, or 120 to 5000 kPa, or 150 to 2000 kPa, or 200 to 1800 kPa, or 200 to 1600 kPa, or 250 to 1500 kPa, or 300 to 1200 kPa, or 400 to 1000 kPa, or 500 to 900 kPa, or 600 to 800 kPa.

24. The method of any one of claims 16 to 23, wherein the first reaction zone and the second reaction zone differ in one or more of: reaction temperature, reaction pressure, particle residence time, and feed rate of the silicon precursor gas.

25. The process of any one of claims 16 to 24, wherein the reaction temperature in the second reaction zone is 5 to 50°C lower, or 10 to 20°C lower, than the reaction temperature in the first reaction zone.

26. The method of any one of claims 16 to 25, wherein between step (g) of introducing the composite particles into the second reaction zone and step (j) of removing the composite particles from the second reaction zone, the average residence time of the particles in the second reaction zone is 2 to 60 minutes, or 5 to 30 minutes, or 10 to 20 minutes.

27. The process according to any one of claims 16 to 26, wherein the volume of the second reaction zone in liters is between (0.001 L·g -1 ×F CP x RT) to (0.02L g -1 ×F CP x RT), where F CP is the feed rate of composite particles to the second reaction zone in grams per minute, and wherein RT is the residence time of the particles in the second reaction zone in minutes.

28. The method according to any one of claims 16 to 27, wherein the ratio of the feed rate of the silicon precursor gas to the second reaction zone to the feed rate of the composite carbon particles to 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 grams of silicon atoms per gram of porous composite particles.

29. The method according to any one of claims 16 to 28, wherein the composite particles removed from the first reaction zone in step (e) are introduced into the second reaction zone in step (g) through an airlock valve, preferably a rotary airlock valve.

30. A method according to any preceding claim, wherein the porous particles have: (i) D in the range of 0.5 to 200 μm 50 Particle size; (ii) 0.4 to 2.2 cm 3 The total pore volume of micropores and mesopores measured by gas adsorption in the range of 1000 g / min; and (iii) PD measured by gas adsorption not exceeding 30 nm 50 Aperture.

31. The method of claim 30, wherein the porous particles have a D 50 The particle size is in the range of 0.5 to 150 μm, or 0.5 to 100 μm, or 0.5 to 50 μm, or 0.5 to 30 μm, or 1 to 25 μm, or 1 to 20 μm, or 2 to 25 μm, or 2 to 20 μm, or 2 to 18 μm, or 3 to 20 μm, or 3 to 18 μm, or 3 to 15 μm, or 4 to 18 μm, or 4 to 15 μm, or 4 to 12 μm, or 5 to 15 μm, or 5 to 12 μm, or 5 to 10 μm, or 5 to 8 μm.

32. The method according to claim 30 or claim 31, wherein the total volume of micropores and mesopores of the porous conductive particles is between 0.45 and 2.2 cm 3 / g, or 0.5 to 2cm 3 / g, or 0.55 to 2cm 3 / g, or 0.6 to 1.8 cm 3 / g, or 0.65 to 1.8 cm 3 / g, or 0.7 to 1.6 cm 3 / g, or 0.75 to 1.6 cm 3 / g, or 0.8 to 1.5 cm 3 / g range.

33. The method according to any one of claims 30 to 32, wherein the PD of the porous conductive particles 50 The pore diameter is no more than 25nm, or no more than 20nm, or no more than 15nm, or no more than 12nm, or no more than 10nm, or no more than 8nm, or no more than 6nm, or no more than 5nm, or no more than 4nm, or no more than 3nm, or no more than 2.5nm, or no more than 2nm, or no more than 1.5nm.

34. A method according to any preceding claim, wherein the silicon precursor is selected from monosilane (SiH4), disilane (Si2H6), trisilane (Si3H8) methylsilane, dimethylsilane and chlorosilane.

35. A method according to any preceding claim, further comprising: (1) providing a carbon deposition unit comprising at least one reaction zone (m) introducing a feedstock comprising the composite particles removed from the chemical vapor infiltration unit in step (e) or (j) into the reaction zone; (n) introducing a carbon precursor gas into the reaction zone; (o) providing conditions in the reaction zone effective to cause deposition of carbon within the pores and / or on the surfaces of the composite particles; (p) removing from the reaction zone composite particles comprising a porous particle skeleton, elemental silicon within the pores of the porous particle skeleton, and carbon within the pores and / or on the external surface thereof.

36. A method according to any preceding claim, further comprising: (q) providing a passivation unit comprising at least one reaction zone; (r) introducing a feedstock comprising the composite particles removed from the chemical vapor infiltration in step (e) or (j) or the composite particles removed from the carbon deposition unit in step (p) into the reaction zone; (s) introducing an oxygen-containing gas into the reaction zone; (t) removing the passivated composite particles from the reaction zone; and (u) continuously removing exhaust gas from the reaction zone.

37. The process of claim 36, wherein the at least one reaction zone comprises a tubular reactor having a first end, a second end, and a length, wherein in step (r) the composite particles are introduced into the first end of the tubular reactor, and wherein in step (t) the passivated composite particles are removed from the second end of the tubular reactor.

38. The process of claim 37, wherein the oxygen-containing gas is introduced through a plurality of inlets spaced along the length of the tubular reactor, and wherein the exhaust gas is withdrawn through a gas exhaust outlet: (i) a gas discharge outlet proximate to the second end of the tubular reactor; or (ii) a plurality of gas exhaust outlets spaced along the length of the tubular reactor.

39. The method of claim 38, wherein: (i) the plurality of entrances are allocated into 2 to 10 entrance groups; (ii) each inlet group independently comprises 1 to 10 inlets; wherein the inlet groups are spaced apart along the length of the tubular reactor such that a proximal inlet group is proximate a first end of the tubular reactor and a distal inlet group is proximate a second end of the tubular reactor, and wherein the oxygen concentration in the oxygen-containing gas increases from the proximal inlet group to the distal inlet group.

40. The method of claim 39, wherein the oxygen concentration in the oxygen-containing gas supplied to the proximal inlet set is from 0.5 vol% to 5 vol%.

41. A method according to claim 39 or claim 40, wherein the oxygen concentration in the oxygen-containing gas supplied to the remote inlet set is from 15% to 21% by volume, optionally wherein the oxygen-containing gas supplied to the remote inlet set is air.

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