Electroactive composite particles

Abstract

The present invention relates to a particulate material consisting only of a plurality of composite particles, each comprising a porous particle framework and a plurality of nanoscale elemental silicon domains located within the pores of the porous particle framework. The porous particle framework includes micropores and mesopores, and the total volume of the micropores and mesopores in the porous particle framework measured by gas adsorption is 0.5 to 1.8 cm 3 / g. The composite particles contain 30 to 70% by weight of silicon, and at least 30% by weight of the silicon is surface silicon determined by thermogravimetric analysis (TGA). Hydrogen is 1.2 wt% or less; the weight ratio of oxygen to silicon is 0.15 or less. The BET surface area of the composite particles is 40 m 2 / g or less.

Description

Technical Field

[0001] Introduction The present invention relates to composite particles suitable for use as an anode active material of a lithium ion battery. The composite particles include a porous particle framework and a plurality of silicon domains located within the pores of the porous particle framework. The dimensions and chemical composition of the silicon domains are controlled for optimal electrochemical performance.

Background Art

[0002] A lithium ion battery (LIB) generally includes an anode, a cathode, and a lithium-containing electrolyte. The anode generally includes a metal current collector provided with a layer of an electroactive material as defined herein as a material capable of inserting and releasing lithium ions during charging and discharging of the battery. When the LIB is charged, lithium ions are transported from the cathode through the electrolyte to the anode and inserted into the electroactive material of the anode as intercalated lithium atoms. Thus, the terms “cathode” and “anode” are used herein in the sense that the battery is arranged across a load such that the anode is the negative electrode. The term “battery” is used herein to refer to both a device including a single lithium ion cell and a device including a plurality of connected lithium ion cells.

[0003] LIBs were developed in the 1980s and 1990s and have since found wide applications in portable electronic devices. The recent development of electric or hybrid vehicles has created an important new market for LIBs, and renewable energy sources have created a further demand for on-grid energy storage that can be at least partially met by LIB farms. Overall, the global production volume of LIBs is predicted to increase from about 290 GWh in 2018 to over 2,000 GWh in 2028.

[0004] In addition to increasing the total storage capacity, there is great interest in improving the gravimetric and / or volumetric capacity of rechargeable metal-ion batteries such that the same energy storage is achieved with less battery mass and / or less battery volume. Conventional LIBs use graphite as the anode electroactive material. The graphite anode can accommodate a maximum of one lithium atom per six carbon atoms, resulting in a maximum theoretical specific capacity of 372 mAh / g in lithium-ion batteries, with a practical capacity somewhat lower (about 340 - 360 mAh / g).

[0005] Silicon is a promising alternative to graphite due to its very high capacity for lithium (see, for example, Insertion Electrode Materials for Rechargeable Lithium Batteries, Winter, M. et al. in Adv. Mater. 1998, 10, No. 10). Silicon has a theoretical maximum specific capacity of about 3,600 mAh / g in lithium-ion batteries (based on Li 15 Si4). However, such a high ratio of intercalated lithium to silicon results in expansion of the silicon material up to 400% of its original volume. Repeated charge / discharge cycles cause significant mechanical stress in the silicon material, leading to cracking and structural failure. Furthermore, charging of the anode in a LIB results in the formation of a solid electrolyte interphase (SEI) layer. This SEI layer is ion-conductive but insulating and is formed by the reductive decomposition of the electrolyte on the electrode surface exposed during initial charging. In a graphite anode, this SEI layer is relatively stable during subsequent charge / discharge cycles. However, the expansion and contraction of a silicon anode result in cracking and delamination of the SEI layer and exposure of fresh silicon surfaces, leading to further electrolyte decomposition, an increase in the thickness of the SEI layer, and irreversible consumption of lithium. These failure mechanisms collectively result in unacceptable loss of electrochemical capacity over successive charge / discharge cycles.

[0006] The present inventors have previously reported the development of certain electroactive materials having a composite structure in which an electroactive material such as silicon is deposited within the pore network of highly porous particles having a carefully controlled pore size distribution, for example, a porous carbon material. For example, International Publication Nos. 2020 / 095067 and 2020 / 128495 report that the improved electrochemical performance of these materials may be due to the electroactive material forming small domains having dimensions on the order of a few nanometers or less within the pore network of the porous particles and thus functioning as the framework of the composite particles. The fine electroactive structure is considered to be less resistant to elastic deformation and more resistant to fragmentation than a larger electroactive structure, and thus can lithiate and delithiate without excessive structural stress. As a result, the electroactive material exhibits good reversible capacity retention over multiple charge-discharge cycles. Second, by controlling the filling amount of silicon in the porous particle framework such that only a portion of the pore volume is occupied by uncharged silicon, the unoccupied pore volume of the porous particle framework can accommodate a significant amount of silicon expansion internally. Excessive expansion is constrained by the particle framework. Furthermore, the surface area of the electroactive material accessible to the electrolyte is very small, and thus SEI formation is substantially prevented.

[0007] In International Publication No. WO 2022 / 029422, the Applicant reported further developments in which the control of the distribution of electroactive silicon within the pore network of the particle framework leads to further improvement in the electrochemical performance of the composite particles. Specifically, the Applicant showed that the electrochemical performance is optimized such that the length scale of the individual silicon structures in the composite particles is minimized, most of the silicon atoms are in the surface region of the silicon structures, and the proportion of silicon atoms located inside the bulky / coarse silicon structures is relatively small. The Applicant identified an optimized pore structure of the porous particle framework and a set of conditions for the deposition of silicon onto the porous particle framework, enabling an increase in the proportion of this so-called "surface silicon", while ensuring that a large amount of silicon in total is incorporated into the composite particles to meet the overall volumetric energy density requirements. The nanoscale silicon domains formed by the thermal decomposition of the silicon-containing precursor are thought to be in the form of nanoclusters of silicon atoms substantially terminated by silicon-hydrogen bonds (Si-H).

[0008] In the art, there is still a need to further improve the electroactive composite particles of the above type in order to improve the electrochemical performance and lifespan of the material over a plurality of charge-discharge cycles. Here, it has been found that the surface functionality of the nanoscale silicon domains can be modified to obtain improved electrochemical properties.

SUMMARY OF THE INVENTION

[0009] In a first aspect, the present invention is a particulate material consisting only of a plurality of composite particles, wherein the composite particles are (a) a porous particle framework comprising micropores and mesopores, wherein when measured by gas adsorption, the total volume of the micropores and mesopores in the porous particle framework is 0.5 to 1.8 cm 3 / g, the porous particle framework; and (b) a plurality of nanoscale elemental silicon domains located within the pores of the porous particle framework, wherein (i) The composite particles contain 30 to 70% by weight of silicon, (ii) When determined by thermogravimetric analysis (TGA), at least 30% by weight of the silicon is surface silicon, (iii) The hydrogen content of the composite particles is 1.2% by weight or less, (iv) The weight ratio of oxygen to silicon in the composite particles is 0.15 or less, (v) The BET surface area of the composite particles is 40 m 2 / g or less, a plurality of nanoscale elemental silicon domains, and to provide a particulate material.

[0010] Accordingly, the present invention generally relates to composite particles comprising a plurality of nanoscale silicon domains in the pore network of porous particles comprising micropores and mesopores. As used herein, the term "nanoscale silicon domain" refers to a nanoscale body of elemental silicon having a maximum dimension determined by the position of the silicon within the micropores and mesopores of the porous particles.

[0011] The deposition of nanoscale silicon domains in mesoporous and microporous particles is kinetically controlled such that thermal deposition preferentially occurs on the internal pore surfaces of the porous particles. The Applicant has previously demonstrated in International Publication No. WO 2022 / 029422 a method for obtaining composite particles containing a large proportion of so-called "surface silicon", which refers herein to silicon located in the surface region of the silicon microstructure. The silicon within the surface region of the silicon microstructure can be quantified by TGA measurements and thus provides a measure of the fineness of the silicon microstructure.

[0012] The nanoscale silicon domains formed by the pyrolysis of silicon-containing precursors are thought to be in the form of nanoclusters of silicon atoms with a series of different binding interactions on their surfaces, between silicon atoms, and between silicon atoms and the porous particle framework, similar to silicon atoms terminated by silicon-hydrogen bonds (Si-H). The surfaces of these silicon nanoclusters are highly reactive as a result of these unbalanced binding interactions of silicon atoms on the surface of the silicon nanoclusters. In particular, a silicon surface terminated by silicon-hydrogen bonds (Si-H) is highly reactive in a lithium-ion battery when lithium insertion occurs. Therefore, if the composite particles have a high proportion of "surface silicon", but the Si-H bonds are reduced and the Si-Si bonds are maximized, an improvement in stability can be achieved. Accordingly, the present invention provides a particulate material as defined above, wherein at least 30% by weight of the silicon is surface silicon and the hydrogen content of the composite particles is less than 1.2% by weight. In this way, silicon maintains a desirable length scale for effective electrochemical performance while reducing the surface reactivity of silicon.

[0013] In a preferred embodiment of the present invention, the oxygen content of the composite particles is 10% by weight or less. If the oxygen content of the composite particles is too high, too much silicon is trapped as Si-O bonds. Although this is less reactive than Si-H bonds, it can increase the resistivity of the electroactive material, undergo irreversible lithium insertion, and potentially reduce the efficiency of the electroactive material in a lithium-ion battery.

[0014] Accordingly, the particulate material is based on a previous disclosure by the applicant that identified the performance advantages achieved by composite particles containing a high proportion of surface silicon by identifying further beneficial structural features of the composite particles. Thereby, it has been found that the stability of the electroactive material during charge and discharge is improved, and the cycle life of a lithium-ion battery containing the particulate material as an anode active material is improved.

[0015] In a second aspect, the present invention provides a composition comprising the particulate material of the first aspect and at least one other ingredient.

[0016] In a third aspect, the present invention provides an electrode comprising the particulate material of the first aspect or the composition of the second aspect.

[0017] In a fourth aspect, the present invention provides a rechargeable metal-ion battery comprising an electrode of the third aspect. [Brief description of the drawings]

[0018]

Figure 1

Figure 2

[0019] Detailed Description of the Invention The composite particles of the present invention comprise a plurality of nanoscale elemental silicon domains located within the pores of the porous particle framework. The length scale of the nanoscale silicon domains in the particulate materials of the present invention are quantified using TGA analysis. This analytical method relies on the principle that when silicon is oxidized to silicon dioxide (SiO2) in air and at high temperatures, a weight gain is observed. The mechanism by which silicon oxidizes is temperature dependent. Silicon atoms at the surface of a silicon nanostructure are oxidized at a lower temperature than silicon atoms in the bulk of the silicon nanostructure (Reference: Bardet et al., Phys. Chem. Chem. Phys. (2016), 18, 18201). By plotting the weight gain against temperature, it is possible to distinguish and quantify bulk and surface silicon in a sample.

[0020] The determination of the amount of unoxidized surface silicon is derived from the characteristic TGA traces of these materials, as shown in FIGS. 1 and 2. Following an initial mass loss up to about 300 °C, a significant increase in mass is seen from about 400 °C (shown in FIGS. 1 and 2 as the mass decrease from (a) to (b)), reaching a peak between 550 °C and 650 °C (shown in FIGS. 1 and 2 as the mass increase from (b) to (c)). Then, as the porous particle framework is oxidized to CO2 gas, a mass decrease is observed (mass decrease from (c)), and then above about 800 °C, a mass increase corresponding to the continuous conversion of silicon to SiO2 is again observed, which increases towards an asymptote above 1000 °C as the silicon oxidation is completed (mass increase from (d) to (e)). The temperature at which the weight increase occurs is related to the structure of the silicon, with surface silicon being oxidized at lower temperatures and bulk silicon being oxidized at higher temperatures. Thus, the coarser the silicon domains, the more oxidation is observed at higher temperatures.

[0021] Since already oxidized silicon does not cause a mass increase in TGA analysis, any native oxide already formed on the silicon surface exposed to air does not affect the TGA analysis. Thus, the less surface silicon observed by TGA, the more the silicon surface can react with air to form a native oxide. Thus, to avoid misunderstanding, the calculation of "surface silicon" takes into account only the silicon that is not oxidized at the start of the TGA analysis after the material has been passivated by air or another surface passivating agent described herein (i.e., the particulate material is not kept under any special inert conditions prior to the TGA analysis).

[0022] As defined herein, "surface silicon" is calculated from the initial mass increase of the TGA trace from a minimum between 150 °C and 500 °C to the maximum mass measured in the temperature range between 550 °C and 650 °C, where the TGA is performed in air at a temperature gradient rate of 10 °C / min. This mass increase is assumed to be due to the oxidation of the surface silicon, and thus the percentage of surface silicon as a proportion of the total amount of silicon can be determined according to the following formula. Y = 1.875 × [(Mmax - Mmin) / Mf] × 100%

[0023] In the formula, Y is the percentage of surface silicon as the ratio of total silicon in the sample, Mmax is the maximum mass of the sample measured in the temperature range of 550°C to 650°C (mass (c) in FIGS. 1 and 2), Mmin is the minimum mass of the sample above 150°C and below 500°C (mass (b) in FIGS. 1 and 2), and Mf is the mass of the sample at the completion of oxidation at 1400°C (mass (e) in FIGS. 1 and 2). For completeness, it should be understood that 1.875 is the molar mass ratio of SiO2 to O2 (i.e., the mass ratio of the formed SiO2 to the mass increase due to oxygen addition). Typically, the TGA analysis is performed using a sample size of 10 mg ± 2 mg.

[0024] When the surface silicon as determined by the above TGA method is at least 30% by weight of the total amount of silicon in the material, it has been found that an optimal reversible capacity retention rate can be obtained over a plurality of charge / discharge cycles. Preferably, when determined by thermogravimetric analysis (TGA), at least 32% by weight, or at least 35% by weight, or at least 38% by weight, at least 40% by weight, or at least 42% by weight, or at least 45% by weight, or at least 48% by weight, or at least 50% by weight of silicon is surface silicon.

[0025] In addition to the surface silicon content, the particulate material of the present invention preferably has a low content of coarse bulk silicon determined by TGA. Coarse bulk silicon is defined herein as silicon that undergoes oxidation above 800°C as determined by TGA, and the TGA is performed in air at a temperature gradient rate of 10°C / min. This is shown in FIGS. 1 and 2 as the mass increase from (d) to (e). Therefore, the coarse bulk silicon content is determined according to the following formula. Z = 1.875 × [(M f - M 800 ) / M f × 100%

[0026] where Z is the percentage of unoxidized silicon at 800 °C, and M 800 is the mass of the sample at 800 °C (mass (d) in Figures 1 and 2), and M f is the mass of the ash at the completion of oxidation at 1400 °C (mass (e) in Figures 1 and 2). For the purposes of this analysis, any mass increase above 800 °C is assumed to correspond to the oxidation of silicon to SiO2, and the total mass at the completion of oxidation is SiO2.

[0027] Preferably, silicon of 6 wt% or less, or 5 wt% or less, or 4 wt% or less, or 3.5 wt% or less, or 3 wt% or less, or 2.5 wt% or less, or 2 wt% or less, or 1.5 wt% or less is the crude bulk silicon determined by TGA.

[0028] Preferably, at least 35 wt% of the silicon is surface silicon, and 6 wt% or less of the silicon, more preferably 5 wt% or less of the silicon, is the crude bulk silicon, both determined by TGA as defined herein. More preferably, at least 40 wt% of the silicon is surface silicon, and 5 wt% or less of the silicon, more preferably 4 wt% or less of the silicon, is the crude bulk silicon, both determined by TGA as defined herein. More preferably, at least 45 wt% of the silicon is surface silicon, and 4 wt% or less of the silicon, more preferably 3 wt% or less of the silicon, is the crude bulk silicon, both determined by TGA as defined herein. More preferably, at least 50 wt% of the silicon is surface silicon, and 3 wt% or less of the silicon, more preferably 2 wt% or less of the silicon, is the crude bulk silicon, both determined by TGA as defined herein.

[0029] The total volume of micropores and mesopores (i.e., the total pore volume of pores having diameters in the range of 0 - 50 nm) in the porous particle framework is 0.5 - 1.8 cm 3For the avoidance of doubt, references herein to the pore volume of the porous particulate framework (unless indicated to the contrary) relate to the pore volume of the porous particulate framework taken alone, i.e., measured in the absence of any electroactive material (or any other material) occupying the pores of the porous particulate framework.

[0030] Preferably, the total volume of the micropores and mesopores in the porous particle framework is at least 0.55 cm 3 / g, or at least 0.6 cm 3 / g, or at least 0.65 cm 3 / g, or at least 0.7 cm 3 / g, or at least 0.75 cm 3 / g.

[0031] A high pore volume can be advantageous because it allows a larger amount of silicon to be accommodated within the pore structure without compromising the resistance of the porous particulate framework to fracture under compressive stresses during electrode fabrication or expansion stresses due to silicon lithiation. However, if the pore volume is too high, it is not possible to achieve the high levels of surface silicon that characterize the present invention. Thus, the total volume of micropores and mesopores in the porous particulate framework is preferably less than 1.6 cm. 3 / g or less, or 1.4cm 3 / g or less, or 1.3 cm 3 / g or less, or 1.2 cm 3 / g or less, or 1.1cm 3 / g or less.

[0032] For example, the total volume of micropores and mesopores in the porous particle framework is preferably between 0.55 and 1.6 cm 3 / g, or 0.6 to 1.4 cm 3 / g, or 0.65 to 1.3 cm 3 / g, or 0.7 to 1.2 cm 3 / g, or 0.75 to 1.1 cm 3 / g range.

[0033] The common term "PDn The "pore diameter" refers to the volume-based n-percentile pore diameter of the porous particle framework based on the total volume of micropores and mesopores in this specification. For example, the "PD 50 pore diameter" as used in this specification refers to the pore diameter below which 50% of the total micropore and mesopore volume is found. To avoid misunderstanding, the PD n For the purpose of determining the value, the macropore volume (pore diameter exceeding 50 nm) is not considered.

[0034] The PD of the porous particle framework 90 pore diameter is preferably 12 nm or less, or 10 nm or less, or 8 nm or less, or 6 nm or less, or 4 nm or less. Preferably, the PD 90 pore diameter is at least 3 nm. The PD 90 If the value is too high, excessive deposition of coarse silicon and / or excessive natural oxide formation reduces the content of surface silicon. However, if the PD 90 is too low, the penetration of the pore volume by the silicon precursor is hindered, and instead silicon deposits on the outer surface of the porous particle framework.

[0035] The PD of the porous particle framework 50 pore diameter is preferably 2 nm or less, or 1.9 nm or less, or 1.8 nm or less, or 1.7 nm or less, or 1.6 nm or less. Preferably, the PD of the porous particle framework 50 pore diameter is at least 1 nm, or at least 1.1 nm, or at least 1.2 nm. For example, the PD of the porous particle framework 50 pore diameter is preferably in the range of 1 to 2 nm, or 1 to 1.9 nm, or 1.1 to 1.8 nm, or 1.1 to 1.7 nm, or 1.2 to 1.6 nm.

[0036] As used herein, the micropore volume fraction refers to the volume of micropores expressed as a fraction of the total volume of micropores and mesopores. In other words, the micropore volume fraction is the volume fraction of pores having a diameter of 2 nm or less with respect to the total volume of pores having a diameter of up to 50 nm. Preferably, the micropore volume fraction of the porous particle framework is selected within the range of 0.45 to 0.95 in order to obtain a required high level of surface silicon content in the composite particles.

[0037] Preferably, the micropore volume fraction is at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, optionally at least 0.75. Preferably, the micropore volume fraction is 0.9 or less, or 0.85 or less, optionally 0.8 or less.

[0038] The micropore volume fraction may optionally be in the range of 0.5 to 0.9, or 0.5 to 0.85, or 0.55 to 0.80, or 0.55 to 0.75, or 0.6 to 0.7.

[0039] (Determined using nitrogen gas adsorption at 77K as described herein) The total volume of micropores in the porous particle framework is preferably at least 0.32 cm 3 / g, or at least 0.36 cm 3 / g, or at least 0.38 cm 3 / g, at least 0.40 cm 3 / g, at least 0.42 cm 3 / g, or at least 0.5 cm 3 / g, or at least 0.6 cm 3 / g. Since the silicon located within the micropores has a smaller length scale, a higher total micropore volume enables a higher proportion of surface silicon to be accommodated within the porous particle framework, and thus enables a higher weight measurement and volume measurement capacity of the composite particles.

[0040] When the total volume of micropores and mesopores in the porous particle framework is in the range of 0.7 to 1.2 cm 3 / g, the total volume of micropores is preferably in the range of 0.4 to 0.9.

[0041] Any pore volume within the mesopore range is preferably substantially within a smaller range of mesopores. Thus, the fractional volume of pores having a pore diameter of 5 nm or less is preferably at least 0.8, or at least 0.82, or at least 0.84, or at least 0.86, or at least 0.88, or at least 0.9, based on the total volume of micropores and mesopores. Preferably, the fractional volume of pores having a pore diameter of 10 nm or less is preferably at least 0.9, or at least 0.92, or at least 0.94, or at least 0.96, based on the total volume of micropores and mesopores. Preferably, the fractional volume of pores having a pore diameter of 20 nm or less is preferably at least 0.94, or at least 0.96, or at least 0.98, based on the total volume of micropores and mesopores.

[0042] The portion of pores having a diameter in the larger mesopore range can be advantageous for facilitating electrolyte access to the silicon domain. Thus, pores having a diameter in the range of 10 to 50 nm (i.e., larger mesopores) may, in some cases, constitute 2% or less, or 4% or less, or 6% or less of the total micropore and mesopore volume of the porous particle framework.

[0043] The pore size distribution of the porous particle framework is preferably bimodal or multimodal. As used herein, the term "pore size distribution" relates to the distribution of pore diameter with respect to the cumulative total internal pore volume of the porous particle framework. The proximity between micropores and pores of larger diameter provides the advantage of efficient ion transport to silicon through the porous network, so a bimodal or multimodal pore size distribution may be preferred. As a result, the particulate material has high ion diffusivity and thus improved rate performance.

[0044] The total volume of micropores and mesopores, as well as the pore size distribution of micropores and mesopores, are determined using the quenched solid density functional theory (QSDFT) according to the standard methods described in ISO15901-2 and ISO15901-3, at 77 K up to a relative pressure p / p0 of 10 -6 using nitrogen gas adsorption at 77 K up to a relative pressure p / p0 of -6 . Nitrogen gas adsorption is a technique that characterizes the porosity and pore diameter distribution of a material by condensing the gas inside the pores of the solid. As the pressure increases, the gas first condenses inside the pores with the smallest diameter, and the pressure increases until a saturation point is reached where all the pores are filled with liquid. Then, the pressure of the nitrogen gas is gradually decreased to evaporate the liquid from the system. The analysis of the adsorption and desorption isotherms, as well as the hysteresis between them, makes it possible to determine the pore volume and pore size distribution. Instruments suitable for measuring the pore volume and pore size distribution by nitrogen gas adsorption include the TriStar II and TriStar II Plus porosimeters available from Micromeritics Instrument Corporation, USA, and the Autosorb IQ porosimeter available from Quantachrome Instruments.

[0045] Nitrogen gas adsorption is effective for measuring the pore volume and pore size distribution of pores with diameters up to 50 nm, but is less reliable for pores with much larger diameters. Therefore, for the purposes of the present invention, nitrogen adsorption is used to determine the pore volume and pore size distribution only for pores with diameters of 50 nm or less.

[0046] If the porous particle framework contains macropores, the volume of pores in the range from over 50 nm to 100 nm is measured by mercury porosimetry. As described above, this parameter relates to the pore volume of the porous particle framework when measured alone, i.e., in the absence of silicon or any other material occupying the pores of the porous particle framework. The pore volume measured by mercury porosimetry above 100 nm is assumed to be the interparticle porosity for the purposes of the present invention.

[0047] Mercury porosimetry is a technique for characterizing the porosity and pore diameter distribution of a material by applying various levels of pressure to a sample of the material immersed in mercury. The pressure required to cause mercury to penetrate the pores of the sample is inversely proportional to the size of the pores. The values obtained by the mercury porosimetry described herein are obtained in accordance with ASTM UOP578-11, with the surface tension γ assumed to be 480 mN / m and the contact angle φ assumed to be 140° for mercury at room temperature. The density of mercury is 13.5462 g / cm 3 at room temperature. A number of high-precision mercury porosimetry instruments are commercially available, such as the AutoPoreIV series of automated mercury porosimeters available from Micromeritics Instrument Corporation of the United States. For a complete review of mercury porosimetry, reference can be made to P. A. Webb and C. Orr, "Analytical Methods in Fine Particle Technology", 1997, Micromeritics Instrument Corporation, ISBN 0-9656783-0.

[0048] The volume of macropores is preferably small compared to the volume of micropores and mesopores. The small portion of macropores can be useful for facilitating electrolyte access to the pore network, but the advantages of the present invention are substantially obtained by accommodating silicon in micropores and smaller mesopores.

[0049] Accordingly, according to the present invention, the total volume of macropores in the range of more than 50 nm to 100 nm in the porous particle framework is preferably 0.2 × P 1 or less, or 0.1 × P 1 or less, or 0.05 × P 1 or less, or 0.02 × P 1 or less, or 0.01 × P 1 or less, or 0.005 × P 1 or less, where P 1 represents the total volume of micropores and mesopores in the porous particle framework defined above.

[0050] Invasive techniques such as gas adsorption and mercury porosimetry are understood to be effective only for determining the pore volume of pores accessible to nitrogen or mercury from the outside of the porous particle framework. The porosity values (P 1 and P 2 ) specified herein are to be understood to refer to the volume of open pores, i.e., pores accessible to fluid from the outside of the porous particle framework. Completely enclosed pores that cannot be identified by nitrogen adsorption or mercury porosimetry shall not be considered when specifying the porosity value herein. Similarly, pore volumes located within pores that are so small as to be below the detection limit by nitrogen adsorption are not considered for determining the porosity value.

[0051] The porous particle framework preferably has a BET surface area of 1200 - 3000 m 2 / g. Preferably, the porous particle framework has a BET surface area of at least 1500 m 2 / g, or at least 1700 m 2 / g. Preferably, the porous particle framework has a BET surface area of 2500 m 2 / g or less, or 2000 m 2 / g or less. As used herein, the term "BET surface area" shall be interpreted to refer to the surface area per unit mass calculated from measurements of the physical adsorption of gas molecules on the solid surface using the Brunauer - Emmett - Teller theory in accordance with ISO9277.

[0052] The porous particle framework preferably has a density of at least 0.35, preferably less than 3 g / cm 3 , more preferably less than 2 g / cm 3 , more preferably less than 1.5 g / cm 3 , most preferably 0.35 - 1.2 g / cm 3has a particle density. As used herein, the term "particle density" refers to the "apparent particle density" measured by mercury porosimetry (i.e., the mass of the particles divided by the particle volume, where the particle volume is considered to be the sum of the volume of the solid material and any closed or blind pores (a "blind pore" is a pore that is too small to be measured by mercury porosimetry)). Preferably, the porous particles have at least 0.4 g / cm 3 or at least 0.45 g / cm 3 or at least 0.5 g / cm 3 or at least 0.55 g / cm 3 or at least 0.6 g / cm 3 or at least 0.65 g / cm 3 or at least 0.7 g / cm 3 has a particle density. Preferably, the porous particles have a particle density of 1.15 g / cm 3 or less, or 1.1 g / cm 3 or less, or 1.05 g / cm 3 or less, or 1 g / cm 3 or less, or 0.95 g / cm 3 or less, or 0.9 g / cm 3 or less.

[0053] The porous particle framework preferably contains a conductive material. The use of a conductive porous particle framework is advantageous because the conductive framework within the composite particles facilitates the flow of electrons between the lithium atoms / ions inserted into the electroactive material and the current collector.

[0054] A preferred type of conductive porous particle framework contains, or consists only of, a conductive carbon material, which is referred to herein as a conductive porous carbon particle framework.

[0055] The conductive porous carbon particle framework preferably contains at least 80% by weight of carbon, more preferably at least 85% by weight of carbon, more preferably at least 90% by weight of carbon, more preferably at least 95% by weight of carbon, and optionally at least 98% or at least 99% by weight of carbon. The carbon may be crystalline carbon, amorphous carbon, or a mixture of amorphous carbon and crystalline carbon. The porous carbon particle framework may be either a hard carbon or a soft carbon particle framework.

[0056] As used herein, the term "hard carbon" refers to an irregular carbon matrix in which carbon atoms are mainly in an sp 2 hybridized state (triple bond) in nanoscale polycyclic aromatic domains. The polycyclic aromatic domains are cross-linked by chemical bonds, such as C-O-C bonds. Due to the chemical cross-linking between the polycyclic aromatic domains, hard carbon cannot be converted to graphite at high temperatures. Hard carbon has graphite-like characteristics, as evidenced by a large G band (about 1600 cm -1 ) in the Raman spectrum. However, the carbon is not completely graphite-like, as evidenced by a significant D band (about 1350 cm -1 ) in the Raman spectrum.

[0057] As used herein, the term "soft carbon" also refers to an irregular carbon matrix in which carbon atoms are mainly in an sp 2 hybridized state (triple bond) in polycyclic aromatic domains having dimensions in the range of 5 to 200 nm. In contrast to hard carbon, the polycyclic aromatic domains in soft carbon are associated by intermolecular forces but not cross-linked by chemical bonds. This means that it graphitizes at high temperatures. The porous carbon particles preferably contain at least 50% sp 2 hybridized carbon as measured by XPS. For example, the porous carbon particles suitably contain 50% to 98% sp 2 hybridized carbon, 55% to 95% sp 2 hybridized carbon, 60% to 90% sp2 Hybrid carbon, or 70% - 85% sp 2 hybrid carbon can be included.

[0058] Appropriate porous carbon particles can be prepared by pyrolysis using a variety of different materials. Examples of organic materials that can be used include plant biomass such as lignocellulosic materials (e.g., coconut shells, rice husks, wood, etc.) and fossil carbon sources such as coal. Examples of resins and polymer materials that form porous carbon particles by pyrolysis include phenolic resins, novolac resins, pitch, melamine, polyacrylates, polystyrene, polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and various copolymers containing monomer units of acrylates, styrenes, α - olefins, vinyl pyrrolidone, and other ethylenically unsaturated monomers. Depending on the starting materials and the conditions of the pyrolysis process, a variety of different carbon materials are available in the art. Porous carbon particles of various different specifications are available from commercial suppliers.

[0059] The porous carbon particles can undergo a chemical or gaseous activation process to increase the volume of mesopores and micropores. Suitable activation processes include contacting the pyrolytic carbon with one or more of oxygen, steam, CO, CO2, and KOH at a temperature in the range of 600 - 1000 °C.

[0060] Mesopores can also be obtained by known templating processes using extractable pore - forming agents such as MgO and other colloidal or polymeric templates that can be removed by thermal or chemical means after pyrolysis or activation.

[0061] As an alternative to carbon - based conductive particles, titanium nitride (TiN), titanium carbide (TiC), silicon carbide (SiC), nickel oxide (NiOx), titanium silicon nitride (TiSiN), nickel nitride (Ni3N), molybdenum nitride (MoN), titanium oxynitride (TiO x N 1-x) Porous particles including silicon oxycarbide (SiOC), boron nitride (BN), or vanadium nitride (VN) can be mentioned. Preferably, the porous particles include titanium nitride (TiN), silicon oxycarbide (SiOC), or boron nitride (BN).

[0062] The elemental composition of the composite particles can be determined by elemental analysis. Using elemental analysis, the weight percentages of silicon, hydrogen, and carbon in the composite particles are determined. Optionally, the amounts of nitrogen and oxygen may be determined by elemental analysis.

[0063] The silicon content is preferably determined by ICP-OES (inductively coupled plasma optical emission spectrometry). Several ICP-OES instruments are commercially available, such as the iCAP (registered trademark) 7000 series ICP-OES analyzers available from ThermoFisher Scientific. The carbon content (and, if necessary, the hydrogen, nitrogen, and oxygen contents) of the composite particles and the porous particle framework alone are preferably determined by combustion and infrared (IR) absorption techniques. A suitable instrument for measuring the contents of carbon, hydrogen, nitrogen, and oxygen is the TruSpec (registered trademark) Micro elemental analyzer available from LECO Corporation.

[0064] The composite particles contain 30 to 70% by weight of silicon. Preferably, the composite particles contain at least 32% by weight of silicon, or at least 35% by weight of silicon, or at least 38% by weight of silicon, or at least 40% by weight of silicon, or at least 42% by weight of silicon, or at least 44% by weight of silicon, or at least 46% by weight of silicon, or at least 48% by weight of silicon, or at least 50% by weight of silicon. Optionally, the composite particles may contain up to 68% by weight of silicon, or up to 65% by weight of silicon, or up to 60% by weight of silicon, or up to 58% by weight of silicon, or up to 55% by weight of silicon. For example, the composite particles may contain 32 to 68% by weight of silicon, or 35 to 66% by weight of silicon, or 38 to 64% by weight of silicon, or 40 to 62% by weight of silicon, or 42 to 60% by weight of silicon, or 44 to 58% by weight of silicon.

[0065] A minimum amount of silicon is required to ensure that the particulate material has a volumetric measurement capacity sufficient for commercial use. However, an excessive amount of silicon deposits silicon on the larger pores and / or surface of the porous particle framework, reducing the surface silicon content and degrading the performance as an electroactive material.

[0066] The amount of silicon in the composite particles of the present invention is selected such that at least about 20% to at most about 78% of the internal pore volume of the porous particle framework (based on micropores and mesopores) is occupied by silicon (in the uncharged state). Generally, the higher the microporosity of the porous particle framework, the greater the amount of silicon that can be used without reducing the percentage of surface silicon.

[0067] Preferably, silicon occupies from about 20% to about 78% of the internal pore volume of the porous particle framework, such as from about 23% to 75%, or from about 26% to 72%, or from about 28% to 70%, or from about 30% to 70%, or from about 35% to 68%, or from about 40% to 65%, or from about 45 to 60% of the internal pore volume of the porous particle framework. Within these preferred ranges, the pore volume of the porous particle framework is effective in accommodating the expansion of silicon during charge and discharge, while avoiding excessive pore volume that does not contribute to the volumetric capacity of the particulate material. However, the amount of silicon is also not so high as to prevent effective lithiation due to insufficient metal ion diffusion rates or insufficient expansion volume resulting in mechanical resistance to lithiation.

[0068] The amount of silicon in the porous particle framework can be correlated with the available pore volume by the requirement that the weight ratio of silicon to the porous particle framework is in the range of [0.50×P 1 ~1.9×P 1 :1, where P 1 represents the total volume of micropores and mesopores in the porous particle framework as defined above. This relationship defines the weight ratio of silicon that is estimated to occupy from about 20% to 78% of the pore volume, taking into account the density of silicon and the pore volume of the porous particle framework. Preferably, the weight ratio of silicon to the porous particle framework is in the range of [0.7×P 1 ~1.8×P 1 :1, which indicates that the pore volume is occupied from about 30% to 78%.

[0069] Preferably, the weight ratio of silicon to the porous particle framework is at least 0.50×P 1 or at least 0.55×P 1 or at least 0.6×P 1 or at least 0.65×P 1 or 0.7×P 1 or at least 0.75×P 1 or at least 0.8×P 1 or at least 0.85×P1 or at least 0.9×P 1 or at least 0.95×P 1 or at least 1×P 1 is. Preferably, the weight ratio of silicon to the porous particle framework is 1.85×P 1 or less, or 1.8×P 1 or less, or 1.75×P 1 or less, or 1.7×P 1 or less, or 1.65×P 1 or less, or 1.6×P 1 or less, or 1.55×P 1 or less, or 1.5×P 1 or less.

[0070] The composite particles of the present invention contain less than 1.2% by weight of hydrogen. Preferably, the composite particles contain at least 0.1% by weight of hydrogen, or at least 0.15% by weight of hydrogen, or at least 0.2% by weight of hydrogen. Preferably, the composite particles contain 1.1% by weight or less of hydrogen, or 1% by weight or less of hydrogen, or 0.95% by weight or less of hydrogen, or 0.9% by weight or less of hydrogen, or 0.85% by weight or less of hydrogen, or 0.8% by weight or less of hydrogen, or 0.75% by weight or less of hydrogen. For example, the composite particles may contain 0.1 to 0.9% by weight of hydrogen, more preferably 0.15 to 0.85% by weight of hydrogen, more preferably 0.15 to 0.8% by weight of hydrogen, more preferably 0.2 to 0.8% by weight of hydrogen.

[0071] Preferably, the ratio of hydrogen to silicon (H wt% / Si wt%×100%) is in the range of 1.0 to 3.0% by weight, more preferably 1.4 to 2.8% by weight.

[0072] The composite particles preferably have a low total oxygen content as determined by elemental analysis. Oxygen can be present in the composite particles, for example, as part of a porous particle framework or as an oxide layer on an exposed silicon surface. Preferably, the composite particles contain 6 wt% or less oxygen, or 5.5 wt% or less oxygen, or 5 wt% or less oxygen, or 4.5 wt% or less oxygen, for example 4 wt% or less oxygen, or 3 wt% or less oxygen, or 2 wt% or less oxygen, or 1 wt% or less oxygen, or 0.5 wt% or less oxygen.

[0073] Preferably, the weight ratio of oxygen to silicon in the composite particles is 0.14 or less, or 0.12 or less, or 0.1 or less, or 0.09 or less, or 0.08 or less.

[0074] Preferably, silicon and carbon together constitute at least 90 wt% of the composite particles, more preferably at least 95 wt% of the composite particles.

[0075] Silicon may optionally contain a small amount of one or more dopants. Suitable dopants include boron and phosphorus, other n-type or p-type dopants, nitrogen, or germanium. Preferably, the dopant is present in a total amount of 2 wt% or less based on the total amount of silicon and dopant.

[0076] Preferably, the total volume of micropores and mesopores in the composite particles (i.e., in the presence of silicon) as measured by nitrogen gas adsorption is 0.15×P 1 or less, or 0.10×P 1 or less, or 0.05×P 1 or less, or 0.02×P 1 or less.

[0077] Preferably, the total volume of micropores and mesopores in the composite particles (i.e., in the presence of silicon) as measured by nitrogen gas adsorption is 0.2 cm 3 / g or less, or 0.15 cm 3 / g or less, or 0.12 cm 3 / g or less, or 0.1 cm3 less than or equal to 0.1 g, or less than or equal to 0.09 cm 3 less than or equal to 0.09 g, or less than or equal to 0.08 cm 3 less than or equal to 0.08 g, or less than or equal to 0.07 cm 3 less than or equal to 0.07 g, or less than or equal to 0.06 cm 3 less than or equal to 0.06 g, or less than or equal to 0.05 cm 3 is less than or equal to 0.05 g.

[0078] Preferably, the total volume of micropores and mesopores in the composite particles measured by nitrogen gas adsorption is less than 0.2 cm 3 / g, preferably less than 0.15 cm 3 / g, or less than 0.1 cm 3 / g, or less than 0.08 cm 3 / g, or less than 0.06 cm 3 / g, or less than 0.04 cm 3 / g, or less than 0.02 cm 3 / g, or less than 0.015 cm 3 / g, or less than 0.012 cm 3 / g, or less than 0.010 cm 3 / g, or less than 0.008 cm 3 is less than 0.008 g.

[0079] As used herein, the term "particle diameter" refers to the equivalent spherical diameter (esd), i.e., the diameter of a sphere having the same volume as a given particle, and the particle volume is understood to include the volume of any internal pores of the particle. As used herein, "D 50 " and "D 50 particle diameter" refer to the volume-based median particle diameter, i.e., the diameter less than 50 volume % of the particle population. As used herein, "D 10 " and "D 10 particle diameter" refer to the 10th percentile volume-based median particle diameter, i.e., the diameter less than 10 volume % of the particle population. As used herein, "D 90 " and "D 90 particle diameter" refer to the 90th percentile volume-based median particle diameter, i.e., the diameter less than 90 volume % of the particle population.

[0080] The term "D" used herein to define the particle diameter distribution n should be distinguished from the term "PD" used herein to define the pore diameter distribution, as described above. n

[0081] The particle diameter and particle size distribution can be determined by routine laser diffraction techniques in accordance with ISO 13320:2009. Unless otherwise specified, the particle size distribution measurements specified or reported herein are those measured by a conventional Malvern Mastersizer (trademark) 3000 particle size analyzer manufactured by Malvern Instruments. The Malvern Mastersizer (trademark) 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 beam hitting the particles is scattered at an angle inversely proportional to the particle size, and an array of photodetectors measures the intensity of the light at several predetermined angles. The intensities measured at different angles are processed by a computer using standard theoretical principles to determine the particle size distribution. The laser diffraction values described herein are obtained using a wet dispersion of the particles in 2-propanol with 5 volume % addition of the surfactant SPAN (trademark)-40 (sorbitan monopalmitate). The particle refractive index is 2.68 for porous particle framework particles and 3.50 for composite particles, and the dispersion index is 1.378. The Mie scattering model is used to calculate the particle size distribution.

[0082] Composite particles can have a D 50 particle diameter in the range of 1 to 30 μm. Preferably, the D 50 particle diameter of the composite particles can be at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm. Optionally, the D 50 particle diameter can be 20 μm or less, or 18 μm or less, or 16 μm or less, or 14 μm or less, or 12 μm or less, or 10 μm or less, or 8 μm or less.

[0083] ​For example, the composite particles may have a D particle diameter in the range of 1 to 20 μm, or 1 to 18 μm, or 1 to 16 μm, or 2 to 16 μm, or 2 to 14 μm, or 2 to 12 μm, or 2 to 10 μm, or 2 to 8 μm. 50 Particles within these size ranges and having the porosity and pore diameter distribution described herein are ideally suitable for use in the anode of a metal ion battery due to their dispersibility in a slurry, structural robustness, capacity retention over repeated charge and discharge cycles, and compatibility for forming a high-density electrode layer of uniform thickness in the conventional range of 20 to 50 μm.

[0084] The D 10 particle diameter of the composite particles is preferably 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. By maintaining the D 10 particle diameter at 0.5 μm or more, the possibility of submicron-sized particles aggregating undesirably is reduced, the dispersibility of the particulate material is improved, and the capacity retention is improved.

[0085] The D1 particle size of the composite particles is preferably at least 0.5 μm, or at least 0.8 μm, or at least 1.0 μm, or at least 1.2 μm, or at least 1.4 μm, or at least 1.5 μm.

[0086] The D 90 particle diameter of the composite particles is preferably 50 μm or less, or 40 μm or less, or 30 μm or less, or 25 μm or less, or 20 μm or less, or 15 μm or less. The presence of very large particles results in non-uniform formation and filling of the particles within the electrode active layer, thus disturbing the formation of a high-density electrode layer, particularly an electrode layer having a thickness in the range of 20 to 50 μm. Therefore, the D 90 particle diameter is preferably up to 40 μm, and more preferably even smaller.

[0087] The composite particles preferably have a narrow size distribution span. For example, the particle size distribution span ((D 90 - D 10 ) / D 50) is preferably 5 or less, more preferably 4 or less, still more preferably 3 or less, even more preferably 2 or less, and most preferably 1.5 or less. By maintaining a narrow size distribution span, more efficient packing of particles into the high-density electrode layer can be more easily achieved.

[0088] The composite particles preferably have a positive asymmetry in the volume-based distribution, for example, such that the volume-based distribution has a longer tail on the right side with left-right asymmetry. The positive asymmetry in the volume-based particle size distribution is advantageous for providing a higher-density electrode because it results in a higher natural packing rate than when all particles are the same size, thereby reducing the need for calendaring or other physical densification processes. Preferably, D 50 The composite particle diameter is less than the volume-based average (D[4.3]) of the particle diameter distribution. Preferably, the asymmetry of the composite particle size distribution (measured by a Malvern Mastersizer™ 3000 analyzer) is 5 or less, or 3 or less.

[0089] The composite particles can have an average sphericity (as defined herein) of at least 0.5, or at least 0.55. Preferably, the average sphericity is at least 0.65, or at least 0.7, or at least 0.75, or at least 0.8.

[0090] High-precision two-dimensional projections of micron-scale particles can be obtained by scanning electron microscopy (SEM) or dynamic image analysis using a digital camera to record the shadow projected by the particles. The term "sphericity" as used herein is understood to be the ratio of the area of the particle projection (obtained from 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 follows.

Equation

Number

[0091] The composite particles of the present invention preferably have a BET surface area of 35 m 2 / g or less, or 30 m 2 / g or less, or 25 m 2 / g or less, or 20 m 2 / g or less, or 15 m 2 / g or less, or 10 m 2 / g or less.

[0092] Generally, a low BET surface area is preferred to minimize the formation of the solid electrolyte interface (SEI) layer on the surface of the composite particles during the first charge-discharge cycle of the anode containing the particulate material of the present invention. However, if the BET surface area is too small, the bulk of the electroactive material cannot access the metal ions in the surrounding electrolyte, resulting in unacceptable low charge rates and capacity limitations. For example, the BET surface area is preferably at least 0.1 m 2 / g, or at least 1 m 2 / g, or at least 2 m 2 / g, or at least 5 m 2 / g. For example, the BET surface area may be in the range of 1 m 2 / g to 25 m 2 / g, more preferably in the range of 2 to 15 m 2 / g.

[0093] The composite particles are measured using a Quantachrome (trademark) Autotap in accordance with ISO 3953 and ISO787 (measurement of the tapped volume and apparent density after tapping) and are greater than 0.7 g / cm 3 or at least 0.8 g / cm 3, or at least 0.85 g / cm 3 , or at least 0.9 g / cm 3 Preferably, it has a tap density of. The drop height of the device is 3 mm, and the tap frequency of the device is fixed at 250 - 265 taps / min. The sample is tapped at least 5,000 times. If a change in the sample volume is still observed after 5,000 taps, additional increments of 1,250 taps are applied until no further volume change is observed.

[0094] The particulate material of the present invention typically has a specific charge capacity of 900 - 2300 mAh / g during the first lithiation. Preferably, the particulate material of the present invention has a specific charge capacity of at least 1200 mAh / g, or at least 1400 mAh / g during the first lithiation.

[0095] The particulate material of the present invention may optionally include a silicon surface treated with a passivating agent. As will be described in more detail below, a passivating agent is defined herein as a compound that can modify the surface of an electroactive material so as to inhibit or prevent the formation of surface oxides.

[0096] The composite particles of the present invention may optionally be coated with a lithium-ion permeable coating. The coating may at least partially cover the outer surface of the particles, preferably completely cover the outer surface of the particles. As used herein, the term "lithium-ion permeable" refers to an ion-conductive material that enables the transport of lithium ions from the outside of the composite particles to the nanoscale electroactive material domains. Preferably, the lithium-ion permeable coating is impermeable to liquids such as the solvent of a liquid electrolyte. Preferably, the lithium-ion permeable filler material is electrochemically stable at less than 0.1 V vs. Li / Li + and is electrochemically stable at less than 0.1 V vs. Li / Li.

[0097] Optionally, the coating may be a conductive carbon coating. Suitably, the conductive carbon coating can be obtained by chemical vapor deposition (CVD). CVD is a method well known in the art and involves the pyrolysis of a volatile carbon-containing gas (such as ethylene) onto the surface of a particulate material. Alternatively, the carbon coating may be formed by depositing a solution of a carbon-containing compound onto the surface of the particulate material and subsequently pyrolyzing it. The conductive carbon coating has sufficient permeability to allow lithium access into the composite particles without excessive resistance so as not to degrade the rate performance of the composite particles. For example, the thickness of the carbon coating may suitably be in the range of 2 to 50 nm, such as 2 to 30 nm. Optionally, the carbon coating may be porous and / or may only partially cover the surface of the composite particles.

[0098] Alternatively, the coating may include a lithium ion permeable solid electrolyte. Examples of suitable lithium permeable solid electrolytes include garnet-type solid electrolytes (such as "LLZO" electrolytes including Li7La3Zr2O 12 and Li 6.5 La3Ti 0.5 Zr 1.5 O 12 etc.); perovskite-type solid electrolytes (such as "LLTO" electrolytes including Li 0.33 La 0.57 TiO3 etc.); LISICON-type solid electrolytes, NaSICON-type solid electrolytes (such as Li 1.3 Al 0.3 Ti 1.7 (PO4)3 etc.); lithium oxynitride phosphate (LiPON) solid electrolytes; Li3N-type solid electrolytes; lithium phosphate (Li3PO4) solid electrolytes, lithium titanate (Li4Ti5O 12 ) solid electrolytes; lithium tantalate (LiTaO3) solid electrolytes; sulfide-type solid electrolytes; alginate-type solid electrolytes; and anti-perovskite-type solid electrolytes. Modifications (such as including dopants) and combinations of these electrolyte types are also included.

[0099] The coating has the advantage of further reducing the BET surface area of the particulate material by smoothing any surface defects and filling any remaining surface micropores, thereby further reducing the first cycle loss. The use of a conductive coating such as a carbon coating improves the conductivity of the surface of the composite particles, improves the rate performance of the particulate material when used as an electroactive material in a lithium ion battery, and / or reduces the need for a conductive additive in the electrode composition, creating an improved surface for the formation of a stable SEI layer and improving the capacity retention rate during cycling, and is thus particularly advantageous. When the composite particles include a coating, the silicon content of the particles in weight percent is determined based on the weight of the particles including the coating.

[0100] A preferred particulate material according to the present invention, when measured by gas adsorption, has a total volume of micropores and mesopores in the porous particle framework of 0.6 to 1.4 cm 3 / g, the micropore volume fraction relative to the total volume of micropores and mesopores in the porous particle framework is 0.5 or more and 0.9 or less, the silicon content of the composite particles is 40 to 70% by weight, and when determined by thermogravimetric analysis (TGA), at least 30% by weight of the silicon is surface silicon, and when determined by thermogravimetric analysis (TGA), 5% by weight or less of the silicon is coarse bulk silicon, and the hydrogen content of the composite particles is 0.4 to 0.9% by weight.

[0101] A more preferred particulate material according to the present invention, when measured by gas adsorption, has a total volume of micropores and mesopores in the porous particle framework of 0.65 to 1.3 cm 3 / g, the micropore volume fraction relative to the total volume of micropores and mesopores in the porous particle framework is 0.55 or more and 0.9 or less, the silicon content of the composite particles is 42 to 68% by weight, and when determined by thermogravimetric analysis (TGA), at least 35% by weight of the silicon is surface silicon, and when determined by thermogravimetric analysis (TGA), 4% by weight or less of the silicon is coarse bulk silicon, and the hydrogen content of the composite particles is 0.45 to 0.85% by weight.

[0102] A more preferred particulate material according to the present invention, when measured by gas adsorption, has a total volume of micropores and mesopores in the porous particle framework of 0.7 to 1.2 cm 3 / g, the micropore volume fraction with respect to the total volume of micropores and mesopores in the porous particle framework is 0.6 or more and 0.85 or less, the silicon content of the composite particles is 44 to 66% by weight, and when determined by thermogravimetric analysis (TGA), at least 40% by weight of the silicon is surface silicon, and when determined by thermogravimetric analysis (TGA), 3% by weight or less of the silicon is coarse bulk silicon, and the hydrogen content of the composite particles is 0.5 to 0.8% by weight.

[0103] A more preferred particulate material according to the present invention, when measured by gas adsorption, has a total volume of micropores and mesopores in the porous particle framework of 0.75 to 1.1 cm 3 / g, the micropore volume fraction with respect to the total volume of micropores and mesopores in the porous particle framework is 0.65 or more and 0.85 or less, the silicon content of the composite particles is 46 to 64% by weight, and when determined by thermogravimetric analysis (TGA), at least 45% by weight of the silicon is surface silicon, and when determined by thermogravimetric analysis (TGA), 2% by weight or less of the silicon is coarse bulk silicon, and the hydrogen content of the composite particles is 0.55 to 0.75% by weight.

[0104] The composite particles of the present invention are suitably prepared by chemical vapor infiltration (CVI) of a silicon-containing precursor into the pore structure of the porous particle framework. As used herein, CVI refers to a process in which a gaseous silicon-containing precursor is thermally decomposed on the surface to form elemental silicon and gaseous by-products on the surface.

[0105] A preferred CVI process is (a) providing a plurality of porous particles in a pressure reactor; (b) continuously introducing a silicon precursor gas into the pressure reactor; (c) Under conditions effective for depositing silicon within the pores of the porous particles, contacting a plurality of porous particles with a silicon precursor gas to provide composite particles comprising a porous particle framework and elemental silicon within the pores of the porous particle framework; (d) During said contacting, drawing off effluent gas from the pressure reactor.

[0106] Operating the pressure reactor under these conditions means that CVI deposition proceeds under conditions where fresh silicon precursor is added before by-products are completely removed from the system. Thus, when silicon precursor gas is continuously added to the reactor, it mixes with the by-products and provides a consistent concentration of silicon precursor. Compared to a system operated by batch charging of the silicon precursor gas, the porous particles are in contact with a more consistent concentration of silicon precursor throughout the deposition.

[0107] This process is continuous with respect to the silicon precursor gas and batch-operated with respect to the porous particles. Thus, the process operates as a semi-continuous process.

[0108] The term continuous is used herein to distinguish from batch-type operations. In batch operations, a batch of starting materials (porous particles and silicon-containing precursor) is added to the reactor in a first step, the reaction is allowed to proceed for a specific period, and then a batch of product (composite particles) is removed from the reactor along with the by-products. In semi-continuous operations, the introduction of starting material (silicon precursor) into the reactor and, optionally, the removal of product (effluent gas) are carried out continuously along with the ongoing reaction.

[0109] In principle, continuous operation does not rule out the possibility of bias in the flow rate of the silicon precursor to the reactor or the flow rate of the effluent gas from the reactor. For example, a continuous reactor can operate in a pulsed mode. For example, the flow rate of the silicon precursor gas to the pressure reactor can be decreased to assist in the removal of the effluent gas from the pressure reactor. Alternatively, the silicon precursor gas may be introduced into the pressure reactor at a constant pressure.

[0110] The extraction of the effluent gas may be continuously operated such that the supply of the silicon precursor gas and the extraction of the effluent gas from the reactor occur continuously and simultaneously with the ongoing reaction.

[0111] Alternatively, the extraction of the effluent gas from the pressure reactor may be semi - continuously operated. Here, semi - continuous means intermittently removing the effluent gas.

[0112] Semi - continuous extraction of the effluent gas from the pressure reactor can be achieved by vibrating at least one gas outlet of the pressure reactor between an open state and a closed state at a predetermined frequency such as at least 1 min⁻¹ or 2 min⁻¹.

[0113] Suitable gaseous silicon - containing precursors include silane (SiH₄), silane derivatives (e.g., disilane, trisilane, and tetrasilane), and trichlorosilane (SiHCl₃). The silicon - containing precursor can be used in pure form or as a diluted mixture with a carrier gas, and the carrier gas is selected from nitrogen or an inert gas such as nitrogen or argon.

[0114] Preferably, the concentration of the silicon - containing precursor in the diluted mixture in the feed stream to the CVI reaction vessel is at least 60% by volume, or at least 70% by volume, or at least 80% by volume, or at least 90% by volume, or at least 95% by volume, or at least 98% by volume, or at least 99% by volume, based on the total amount of the silicon - containing precursor gas and the inert carrier gas. Preferably, the concentration of the silicon - containing precursor gas is 100% (i.e., no inert carrier gas is used).

[0115] Preferably, the silicon - containing precursor is chlorine - free. Being chlorine - free means that the silicon - containing precursor contains less than 1% by weight, preferably less than 0.1% by weight, preferably less than 0.01% by weight of chlorine - containing compounds.

[0116] The temperature suitable for the CVI process ranges from 350 to 500 °C, such as 350 to 450 °C, or 360 to 430 °C, or 370 to 420 °C, or 370 to 400 °C. Preferably, since temperature fluctuations may cause non-uniformity of the product, the specified temperature is maintained throughout the CVI process.

[0117] The pressure in the pressure reactor during step (c) is preferably in the range of 50 to 15000 kPa, or 100 to 10000 kPa, or 150 to 5000 kPa, or 200 to 2000 kPa, or 500 to 1800 kPa, or 800 to 1500 kPa, or 1000 to 1400 kPa. Operating at high pressure has the advantage of reducing the mass transfer limitation on the reaction rate and promoting the penetration of the silicon precursor gas into the pore network of the porous particles. Operating at a higher pressure also increases the residence time of the silicon precursor gas, and thus increases the conversion of the silicon precursor. To prevent an uncontrolled reaction, the temperature in the pressure reactor preferably decreases as the pressure increases. In particular, when the pressure in the pressure reactor exceeds 100 kPa, the reaction temperature in the pressure reactor is preferably 450 °C or lower, more preferably 430 °C or lower, more preferably 420 °C or lower, more preferably 410 °C or lower, more preferably 400 °C or lower, more preferably 395 °C or lower.

[0118] During step (c), the molar fraction of the silicon precursor in the pressure reactor can range from 0.2 to 0.8 based on the total number of moles of gaseous compounds in the pressure reactor, or from 0.3 to 0.7 based on the total number of moles of gaseous compounds in the pressure reactor, or 0.4 to 0.6.

[0119] The conditions within the CVI reactor should also be as uniform as possible. Stirring or fluidizing the porous carbon particles ensures that the silicon precursor gas can penetrate the particles uniformly and also ensures that the temperature within the reactor is uniform throughout the particle bed. Thus, by carefully selecting the porous particles in conjunction with the use of the controlled CVI conditions described herein, it is possible to obtain particulate materials with a very high surface silicon content and a low content of coarse bulk silicon, indicating that a high proportion of the silicon exists in the form of ultrafine silicon nanostructures.

[0120] During said contact, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams can be in the range of 0.006 to 0.7.

[0121] During said contact, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams can be in the range of 0.006 to 0.008. These ratios have the advantage of a higher conversion rate of the silicon precursor compared to larger ratios. A high level of conversion of the silicon precursor is thought to help obtain composite particles with less coarse silicon formation. However, at lower ratios, the reaction time is unacceptably long.

[0122] Alternatively, during the contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams may be in the range of 0.01 to 0.7. These ratios have the advantage that an excess of silicon precursor is maintained in the pressure reactor. In the equilibrium between the silicon precursor and silicon + by-products, a high silicon precursor concentration pushes the equilibrium towards silicon deposition. As described above, at higher pressures in the pressure reactor, the silicon deposition rate decreases. By maintaining an excess of silicon precursor in the pressure reactor, the decrease in the silicon deposition rate at higher pressures is compensated for, and thus the advantages of operating at higher pressures while maintaining the silicon deposition rate are obtained. This also helps to shorten the synthesis time.

[0123] During the contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) may be in the range of 0.0002 to 0.025. During the contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) may be in the range of 0.0002 to 0.0003. Alternatively, during the contacting, the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) may be in the range of 0.0004 to 0.025. The internal free volume of the reactor refers to the volume excluding internal elements.

[0124] The ratio of the flow rate of silicon in the silicon precursor gas to the mass of the porous particles in the pressure reactor and / or the ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) may be maintained throughout step (c).

[0125] Alternatively, the process further (i) The ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams, and / or (ii) The ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) can include a step of adjustment.

[0126] This process, after a predetermined period, during said contact, (i) The ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to the mass of the porous particles in the pressure reactor in grams, and / or (ii) The ratio of the flow rate of silicon in the silicon precursor gas in grams per minute to (the mass of the porous particles in the pressure reactor in grams × the internal free volume of the reactor in liters) can include a step of adjustment.

[0127] The composite particles provided in step (c) may include a target amount of silicon that occupies 20% to 95% of the internal pore volume of the porous particle framework, and the predetermined period may be after the composite particles contain 50% to 95%, or 60% to 95%, or 70% to 95%, or 80% to 95%, or 90 to 95% of the amount of silicon. The target amount of silicon may occupy 20% to 80%, or 20% to 70%, or 30% to 70%, or 30% to 60% of the internal pore volume of the porous particle framework.

[0128] The ratio can be adjusted throughout step (c), for example, by adjusting the flow rate of the silicon precursor gas. For example, step (c) may be operated for a period when the ratio of the flow rate of silicon in the silicon precursor gas to the mass of the porous particles in the pressure reactor is outside the range of 0.006 to 0.7. Thereafter, in step (c), the ratio of the flow rate of silicon in the silicon precursor gas to the mass of the porous particles in the pressure reactor may be adjusted to be within the range of 0.006 to 0.7.

[0129] Preferably, the pressure reactor is operated such that the consumption rate of the silicon precursor is at least 20%, preferably at least 50%, preferably at least 60%, preferably at least 80%, preferably at least 90%. Alternatively, the pressure reactor may be operated in a low conversion mode where the consumption rate of the silicon precursor is 20% or less, preferably 10% or less, more preferably 5% or less.

[0130] The composite particles removed from the pressure reactor may contain 0.2 to 1.8 grams of silicon per gram of the porous particle framework.

[0131] Optionally, step (c) may include two or more deposition stages, during which the supply of the silicon-containing precursor gas is interrupted and the by-products are removed from the reactor volume. The removal of the by-products may include flushing the reactor volume with an inert gas and / or hydrogen gas. More preferably, the removal of the by-products includes reducing the pressure in the pressure reactor to less than 50 kPa, or less than 40 kPa, or less than 30 kPa, or less than 20 kPa, or less than 10 kPa, or less than 5 kPa, or less than 3 kPa, or less than 2 kPa, or less than 1 kPa. Then, the supply of the silicon-containing precursor gas is resumed to continue the silicon deposition. Preferably, the number of deposition stages is 5 or less, more preferably 3 or less.

[0132] The surface of the electroactive material deposited by CVI is reactive towards oxygen and forms a native oxide layer when exposed to atmospheric oxygen. Therefore, the particles formed by CVI can be contacted with a passivating agent before exposing the particles to atmospheric oxygen. The passivating agent is defined herein as a compound capable of modifying the surface of the electroactive material so as to inhibit or prevent the formation of surface oxides. Suitable passivating agents and passivation conditions are disclosed in the applicant's International Publication No. WO 2022 / 029422. Optionally, the intermediate passivation step may be performed during the silicon deposition stage when the silicon deposition is interrupted as described above.

[0133] The hydrogen content of the composite particles can be adjusted by heat treatment (annealing) in the presence of an inert gas at a temperature of at least 400 °C. The heat treatment of the composite particles is thought to promote the desorption of hydrogen and the solid rearrangement of silicon atoms, thereby reducing the density of unstable and reactive Si-H bonds and promoting the formation of more thermodynamically stable Si-Si bonds.

[0134] The rearrangement of silicon atoms further contributes to the volume-measured shrinkage of the silicon domains. One result of this is that the pore spaces that were previously blocked or sealed by the silicon nanostructures are reopened so that the passivation gas and other functional gases can access the remaining pore volume. The increased access of the passivation gas to the residual pore space enables more extensive passivation of the silicon surface, while the removal of hydrogen from the silicon nanostructures in the pore spaces that were previously inaccessible reduces the generation of hydrogen during charge and discharge.

[0135] The inert gas can, in principle, be any gas that does not undergo a reaction during the heat treatment (annealing) of the composite particles. Preferably, the inert gas is selected from nitrogen and noble gases, especially argon. Optionally, the inert gas may contain hydrogen.

[0136] The temperature of the heat treatment step may be at least 450 °C, or at least 500 °C, or at least 510 °C, or at least 520 °C, or at least 540 °C, or at least 560 °C, or at least 580 °C, or at least 600 °C. Preferably, the temperature of the heat treatment step is 800 °C or less, or 750 °C or less, or 700 °C or less, or 680 °C or less, or 660 °C or less, or 650 °C or less. For example, a suitable heat treatment temperature can be in the range of 510 °C to 800 °C, or 520 °C to 750 °C, or 540 °C to 700 °C, or 560 °C to 680 °C, or 580 °C to 660 °C, or 600 °C to 650 °C.

[0137] The duration of step (c) is preferably at least 1 minute, or at least 2 minutes, or at least 5 minutes, or at least 10 minutes, or at least 15 minutes, or at least 20 minutes, or at least 30 minutes, or at least 45 minutes, or at least 1 hour, or at least 2 hours. Preferably, the duration of step (c) is 72 hours or less, or 48 hours or less, or 24 hours or less, or 12 hours or less, or 6 hours or less, or 5 hours or less, or 4 hours or less, or 3 hours or less.

[0138] In a second aspect of the present invention, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component. In particular, there is provided a composition comprising the particulate material according to the first aspect of the present invention and at least one other component selected from (i) a binder, (ii) a conductive additive, and (iii) an additional particulate electroactive material. The composition according to the second aspect of the present invention is useful as an electrode composition and can thus be used to form the active layer of an electrode.

[0139] The particulate material used to prepare the composition of the second aspect of the present invention can have any of the features described as preferred or optional with respect to the first aspect of the present invention.

[0140] The composition may be a hybrid electrode composition comprising the particulate material according to the first aspect of the present invention and at least one additional particulate electroactive material. Examples of additional particulate electroactive materials include graphite, hard carbon, silicon, tin, germanium, aluminum, and lead. At least one additional particulate electroactive material is preferably selected from graphite and hard carbon, and most preferably at least one additional particulate electroactive material is graphite.

[0141] In the case of a hybrid electrode composition, the composition may contain at least 5 wt%, or at least 8 wt%, or at least 10 wt%, or at least 12 wt%, or at least 15 wt% of the composite particles according to the second aspect of the present invention, based on the total dry weight of the composition. Optionally, the hybrid electrode composition may contain up to 60 wt%, or up to 50 wt%, or up to 40 wt%, or up to 30 wt%, or up to 25 wt% of the composite particles according to the second aspect of the present invention, based on the total dry weight of the composition.

[0142] Preferably, the hybrid electrode composition contains 3 to 60 wt%, or 3 to 50 wt%, or 5 to 40 wt%, or 10 to 30 wt%, or 15 to 25 wt% of the particulate material according to the first aspect of the present invention, based on the total dry weight of the composition.

[0143] The at least one additional particulate electroactive material is suitably present in an amount of 20 to 95 wt%, or 25 to 90 wt%, or 30 to 75 wt% of the at least one additional particulate electroactive material.

[0144] The at least one additional particulate electroactive material is preferably selected from carbon-containing particles, graphite particles and / or hard carbon particles, and the graphite and hard carbon particles have a D 50 particle diameter in the range of 10 to 50 μm. Even more preferably, the at least one additional particulate electroactive material is selected from graphite particles, and the graphite particles have a D 50 particle diameter in the range of 10 to 50 μm.

[0145] The composition may also be a non-hybrid (or "high loading") electrode composition that substantially does not contain additional particulate electroactive material. In this regard, the term "substantially does not contain additional particulate electroactive material" means that the composition contains, based on the total dry weight of the composition, less than 15 wt%, preferably less than 10 wt%, preferably less than 5 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, and even more preferably less than 0.5 wt% of any additional electroactive material (i.e., additional material capable of inserting and releasing metal ions during charging and discharging of the battery).

[0146] This type of "high loading" electrode composition preferably contains, based on the total dry weight of the composition, at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt% of the particulate material according to the first aspect of the present invention.

[0147] The composition may optionally contain a binder. The binder functions to adhere the composition to the current collector and maintain the integrity of the composition. Examples of binders that can be used according to the present invention include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginate and its alkali metal salts, styrene-butadiene rubber (SBR), and polyimide. The composition may contain a mixture of binders. Preferably, the binder contains a polymer selected from polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, SBR, and CMC.

[0148] The binder may be suitably present in an amount of 0.5 to 20 wt%, preferably 1 to 15 wt%, preferably 2 to 10 wt%, and most preferably 5 to 10 wt% based on the total dry weight of the composition.

[0149] The binder may optionally be present in combination with one or more additives that modify the properties of the binder, such as a crosslinking accelerator, a coupling agent, and / or an adhesion promoter.

[0150] The composition may optionally include one or more conductive additives. Preferred conductive additives are non-electroactive materials included to improve the conductivity between the electroactive components of the composition and between the electroactive components of the composition and the current collector. The conductive additives can be appropriately selected from carbon black, carbon fiber, carbon nanotubes, graphene, acetylene black, ketjen black, metal fibers, metal powders, and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes.

[0151] One or more conductive additives may appropriately be present in a total amount of 0.5 to 20% by weight, preferably 1 to 15% by weight, preferably 2 to 10% by weight, and most preferably 5 to 10% by weight based on the total dry weight of the composition.

[0152] In a third aspect, the present invention provides an electrode comprising a particulate material as defined with reference to the first aspect of the present invention. Generally, the electrode includes a particulate material as the electroactive material and a current collector, and the particulate material is in electrical contact with the current collector. The particulate material used to prepare the electrode of the third aspect of the present invention may have any of the features described as preferred or optional with respect to the first aspect of the present invention.

[0153] As used herein, the term current collector refers to any conductive substrate capable of conducting current with the electroactive particles in the composition. Materials that can be used as the current collector include copper, aluminum, stainless steel, nickel, titanium, sintered carbon, and the like. Copper is a preferred material. The current collector is typically in the form of a foil or mesh having a thickness between 3 and 500 μm. The particulate material of the present invention may preferably be applied to one or both sides of the current collector up to a thickness in the range of 10 μm to 1 mm, such as 20 to 500 μm, or 50 to 200 μm.

[0154] Preferably, the electrode is in electrical contact with a current collector and includes a composition as defined with reference to the second aspect of the present invention. The composition may have any of the features described as preferred or optional with respect to the second aspect of the present invention.

[0155] The electrode of the third aspect of the present invention can be suitably manufactured by combining the particulate material of the present invention (optionally in the form of the composition of the present invention) with a solvent and optionally one or more viscosity modifying additives to form a slurry. The slurry is then cast onto the surface of the current collector, and the solvent is removed to form an electrode layer on the surface of the current collector. Further steps such as heat treatment to cure any binder and / or calendaring of the electrode layer can be carried out as required. The electrode layer suitably has a thickness in the range of 20 μm to 2 mm, preferably 20 μm to 1 mm, preferably 20 μm to 500 μm, preferably 20 μm to 200 μm, preferably 20 μm to 100 μm, preferably 20 μm to 50 μm.

[0156] Alternatively, the slurry may be formed into a free-standing film or mat containing the particulate material of the present invention, for example by casting the slurry onto a suitable mold, removing the solvent, and then removing the casting mold. The resulting film or mat may then be bonded to the current collector by known methods in the form of an aggregated self-standing mass.

[0157] The electrode of the third aspect of the present invention may be used as the anode of a metal ion battery. Thus, in a fourth aspect, the present invention provides a rechargeable metal ion battery comprising the electrode of the third aspect of the present invention. In particular, the present invention provides a rechargeable metal ion battery comprising an anode, the anode comprising an electrode as described above, a cathode comprising a cathode active material capable of releasing and reabsorbing metal ions, and an electrolyte between the anode and the cathode.

[0158] The metal ion is preferably a lithium ion. More preferably, the rechargeable metal ion battery of the present invention is a lithium ion battery, and the cathode active material can release and accept lithium ions.

[0159] The cathode active material is preferably a metal oxide-based composite. Examples of suitable cathode active materials include LiCoO2, LiCo 0.99 Al 0.01 O2, LiNiO2, LiMnO2, LiCo 0.5 Ni 0.5 O2, LiCo 0.7 Ni 0.3 O2, LiCo 0.8 Ni 0.2 O2, LiCo 0.82 Ni 0.18 O2, LiCo 0.8 Ni 0.15 Al 0.05 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2 and LiNi 0.33 Co 0.33 Mn 0.34 O2. The cathode current collector generally has a thickness between 3 and 500 μm. Materials that can be used as the cathode current collector include aluminum, stainless steel, nickel, titanium, sintered carbon, and the like.

[0160] The electrolyte is preferably a non-aqueous electrolyte containing a metal salt, such as a lithium salt, and may include, but is not limited to, non-aqueous electrolyte solutions, solid electrolytes, and inorganic solid electrolytes. As the non-aqueous electrolyte solution, aprotic organic solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, etc. can be used.

[0161] Examples of organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate esters, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociating groups.

[0162] Examples of inorganic solid electrolytes include nitrides, halides, and sulfides of lithium salts such as Li5NI2, Li3N, LiI, LiSiO4, Li2SiS3, Li4SiO4, LiOH, and Li3PO4.

[0163] The lithium salt is suitably soluble in a selected solvent or mixture of solvents. Examples of suitable lithium salts include LiCl, LiBr, LiI, LiClO4, LiBF4, LiBC4O8, LiPF6, LiCF3SO3, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and CF3SO3Li.

[0164] When the electrolyte is a non-aqueous organic solution, the metal ion battery preferably includes a separator interposed between the anode and the cathode. The separator is typically formed of an insulating material having high ion permeability and high mechanical strength. The separator typically has a pore diameter between 0.01 and 100 μm and a thickness between 5 and 300 μm. Examples of suitable electrode separators include microporous polyethylene films.

[0165] The separator may be replaced with a polymer electrolyte material. In such a case, the polymer electrolyte material is present in both the composite anode layer and the composite cathode layer. The polymer electrolyte material can be a solid polymer electrolyte or a gel-type polymer electrolyte.

Example

[0166] Example 1 Composite particles were prepared using a porous particle framework having the characteristics shown in Table 1.

Table 1

[0167] To evaluate the influence of various composite particle characteristics on the electrochemical performance, composite particles were prepared under various CVI reaction conditions. The composite particles according to the present invention were prepared according to the preferred reaction conditions disclosed above. The comparative composite particles were prepared under modified reaction conditions including one or more of an increase in the CVI reaction temperature (resulting in a decrease in the surface silicon content, an increase in the coarse silicon content, and an increase in the hydrogen content), a decrease in particle agitation or a static bed (resulting in an increase in the coarse silicon and hydrogen contents), and faster air passivation (resulting in a higher oxygen content, a higher BET, and a decrease in the chemical stability of the particle surface).

[0168] Example 2 - Electrochemical Test A test coin cell was fabricated using a negative electrode containing the composite particles shown in Table 2 below. A dispersion of Carbon Super P (conductive carbon) in a CMC binder was mixed with a Thinky (trademark) mixer. The composite particles were added to the mixture and mixed for 30 minutes. The slurry was further mixed with a Thinky (trademark) mixer for 30 minutes and then coated on a copper substrate (current collector) with a thickness of 10 μm, dried at 50 °C for 10 minutes, and further dried at 110 °C for 12 hours to form an electrode containing an active layer on the copper substrate.

[0169] The coin-type half-cell was fabricated using a porous polyethylene separator, a lithium foil as the counter electrode, and a circular electrode with a radius of 0.8 cm cut from an electrode having an electrolyte containing 1 M LiPF6 in a 7:3 solution of EC / FEC (ethylene carbonate / fluoroethylene carbonate) containing 3 wt% vinylene carbonate.

[0170] Using these half-cells, the first lithiation capacity (DC0) and the first lithium desorption capacity (DC1, also referred to as the first discharge capacity) of the active layer and the first cycle loss (FCL) were measured. DC0 and DC1 are defined in units of mAh per gram of electroactive material in the electrode, and FCL is defined as (1 - (DC1 / DC0)) × 100%. The half-cell was tested by applying a constant current of C / 25 (where "C" represents the specific capacity of the electrode in mAh units and "25" refers to 25 hours) to lithiate the electrode containing porous particles at a cut-off voltage of 10 mV. When the cut-off is reached, a constant voltage of 10 mV is applied at a cut-off current of C / 100. Then, the cell is rested in the lithiated state for 10 minutes. Then, the electrode is delithiated at a constant current of C / 25 at a cut-off voltage of 1 V, and then the cell is rested for 10 minutes. Then, a constant current of C / 25 is applied to lithiate the cell a second time at a cut-off voltage of 10 mV, followed by applying a constant voltage of 10 mV at a cut-off current of C / 100 and leaving it for 5 minutes.

[0171] The effects of the present invention are shown in Table 2. Specifically, it was found that when the composite particles lack one or more of the characteristics described in claim 1, the first discharge capacity (DC1) decreases and the first cycle loss (FCL) of the active material increases.

Table 2

Claims

1. A particulate material consisting only of a plurality of composite particles, wherein the composite particles are (a) a porous particle framework containing micropores and mesopores, When measured by gas adsorption, the total volume of micropores and mesopores in the porous particle framework is 0.5 to 1.8 cm ３ / g, a porous particle framework, and (b) a plurality of nanoscale elemental silicon domains located within the pores of the porous particle framework, (i) the composite particles contain 30 to 70% by weight of silicon, (ii) when determined by thermogravimetric analysis (TGA), at least 30% by weight of the silicon is surface silicon, (iii) the hydrogen content of the composite particles is 1.2% by weight or less, (iv) the weight ratio of oxygen to silicon in the composite particles is 0.15 or less, (v) The BET specific surface area of the composite particles is 40 m ２ / g or less, a plurality of nanoscale elemental silicon domains; and a particulate material comprising

2. When determined by thermogravimetric analysis (TGA), at least 32% by weight of the silicon, or at least 35% by weight of the silicon, or at least 38% by weight of the silicon, or at least 40% by weight of the silicon, or at least 42% by weight of the silicon, or at least 45% by weight of the silicon, or at least 48% by weight of the silicon, or at least 50% by weight of the silicon is surface silicon, the particulate material according to claim 1.

3. When determined by thermogravimetric analysis (TGA), 6% by weight or less of the silicon, or 5% by weight or less of the silicon, or 4% by weight or less of the silicon, or 3.5% by weight or less of the silicon, or 3% by weight or less of the silicon, or 2.5% by weight or less of the silicon, or 2% by weight or less of the silicon, or 1.5% by weight or less of the silicon is crude bulk silicon, the particulate material according to claim 1 or claim 2.

4. When measured by gas adsorption, the total volume of micropores and mesopores in the porous particle framework is at least 0.55 cm ３ / g, or at least 0.6 cm ３ / g, or at least 0.65 cm ３ / g, or at least 0.7 cm ３ / g, or at least 0.75 cm ３ / g, the particulate material according to any one of the preceding claims.

5. When measured by gas adsorption, the total volume of micropores and mesopores in the porous particle framework is 1.6 cm ３ / g or less, or 1.4 cm ３ / g or less, or 1.3 cm ３ / g or less, or 1.2 cm ３ / g or less, or 1.1 cm ３ / g or less, the particulate material according to any one of the preceding claims.

6. PD of the porous particle framework ９０ The particulate material according to any one of the preceding claims, wherein the pore diameter is 12 nm or less, or 10 nm or less, or 8 nm or less, or 6 nm or less, or 4 nm or less.

7. PD of the porous particle framework ５０ The particulate material according to any one of the preceding claims, wherein the pore diameter of the porous particle framework is 2 nm or less, or 1.9 nm or less, or 1.8 nm or less, or 1.7 nm or less, or 1.6 nm or less.

8. PD of the porous particle framework ５０ The particulate material according to any one of the preceding claims, wherein the pore diameter is at least 1 nm, or at least 1.1 nm, or at least 1.2 nm.

9. The micropore volume fraction of the porous particle framework is at least 0.45, or at least 0.5, or at least 0.55, or at least 0.6, or at least 0.65, or at least 0.7, or at least 0.75 based on the total volume of the micropores and mesopores, the particulate material according to any one of the preceding claims.

10. The micropore volume fraction of the porous particle framework is 0.95 or less, or 0.9 or less, or 0.85 or less, or 0.8 or less based on the total volume of the micropores and mesopores, the particulate material according to any one of the preceding claims.

11. The total volume of micropores in the porous particle framework is at least 0.36 cm ３ / g, or at least 0.38 cm ３ / g, at least 0.40 cm ３ / g, at least 0.42 cm ３ / g, and the particulate material according to any one of the preceding claims.

12. The particulate material according to any one of the preceding claims, wherein the porous particle framework has a bimodal or multimodal pore size distribution. **Claim 13** The total volume of pores having a diameter within the range of 50 nm to 100 nm is 0.2 × P １ or less, or 0.1 × P １ or less, or 0.05 × P １ or less, or 0.02 × P １ or less, or 0.01 × P １ or less, or 0.005 × P １ or less, and P １ represents the total volume of micropores and mesopores in the porous particle framework, the particulate material according to any one of the preceding claims. **Claim 14** The particulate material according to any one of the preceding claims, wherein the porous particle framework has a BET surface area of 1200 to 3000 m ２ / g. **Claim 15** The particulate material according to any one of the preceding claims, wherein the porous particle framework is a conductive porous particle framework, preferably a conductive porous carbon particle framework, more preferably a conductive porous carbon particle framework containing at least 80 wt% carbon, or at least 85 wt% carbon, or at least 90 wt% carbon, or at least 95 wt% carbon. **Claim 16** The particulate material according to any one of the preceding claims, wherein the composite particles contain at least 32 wt% silicon, or at least 35 wt% silicon, or at least 38 wt% silicon, or at least 40 wt% silicon, or at least 42 wt% silicon, or at least 44 wt% silicon, or at least 46 wt% silicon, or at least 48 wt% silicon, or at least 50 wt% silicon. **Claim 17** The particulate material according to any one of the preceding claims, containing up to 68 wt% silicon, or up to 65 wt% silicon, or up to 60 wt% silicon, or up to 58 wt% silicon, or up to 55 wt% silicon. **Claim 18** The particulate material according to any one of the preceding claims, wherein the composite particles contain at least 0.1 wt% hydrogen, or at least 0.15 wt% hydrogen, or at least 0.2 wt% hydrogen. **Claim 19** The particulate material according to any one of the preceding claims, wherein the composite particles contain 1.1 wt% or less hydrogen, or 1 wt% or less hydrogen, or 0.95 wt% or less hydrogen, or 0.9 wt% or less hydrogen, or 0.85 wt% or less hydrogen, or 0.8 wt% or less hydrogen, or 0.75 wt% or less hydrogen. **Claim 20** The particulate material according to any one of the preceding claims, wherein the composite particles contain 6 wt% or less oxygen, or 5.5 wt% or less oxygen, or 5 wt% or less oxygen, or 4.5 wt% or less oxygen. **Claim 21** The particulate material according to any one of the preceding claims, wherein the weight ratio of oxygen to silicon in the composite particles is 0.14 or less, or 0.12 or less, or 0.1 or less, or 0.09 or less, or 0.08 or less. **Claim 22** The composite particles have a D of at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm ５０ The particulate material according to any one of the preceding claims, having a particle diameter **Claim 23** The composite particles have a D particle diameter of 20 μm or less, or 18 μm or less, or 16 μm or less, or 14 μm or less, or 12 μm or less, or 10 μm or less, or 8 μm or less, and are the particulate material according to any one of the preceding claims. ５０ ​ **Claim 24** The composite particles have a D of 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 particulate material according to any one of the preceding claims, having a particle diameter **Claim 25** The composite particles have a D particle size of at least 0.5 μm, or at least 0.8 μm, or at least 1.0 μm, or at least 1.2 μm, or at least 1.4 μm, or at least 1.5 μm １ The particulate material according to any one of the preceding claims. **Claim 26** The composite particles have a D particle diameter of 30 μm or less, or 25 μm or less, or 20 μm or less, or 15 μm or less, of the particulate material according to any one of the preceding claims. ９０ having a particle diameter. **Claim 27** The composite particles have a BET surface area of 35 m ２ / g or less, or 30 m ２ / g or less, or 25 m ２ / g or less, or 20 m ２ / g or less, or 15 m ２ / g or less, or 10 m ２ / g or less, and are the particulate material according to any one of the preceding claims. **Claim 28** The composite particles are at least 0.1 m ２ / g, or at least 1 m ２ / g, or at least 2 m ２ / g, or at least 5 m ２ / g and have a BET surface area, and the particulate material according to any one of the preceding claims.

29. The particulate material according to any one of the preceding claims, wherein the composite particles are obtained by chemical vapor infiltration (CVI) of a silicon-containing precursor into the pore structure of a porous carbon framework.

30. A composition comprising the particulate material according to any one of claims 1 to 29 and at least one other component.

31. An electrode comprising the particulate material according to any one of claims 1 to 29 or the composition according to claim 30.

32. A rechargeable metal-ion battery comprising the electrode according to claim 31.

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