Method of preparing a silicon suboxide-carbon composite from silicon-containing biomass

Abstract

The present invention discloses a method of preparing a silicon suboxide-carbon composite from silicon-containing biomass, the method comprising a step of subjecting the silicon-containing biomass to an electrical heating in an inert gas atmosphere thereby forming a silicon suboxide-carbon composite.

Description

[0001] METHOD OF PREPARING A SILICON SUBOXIDE-CARBON COMPOSITE FROM SILICON-CONTAINING BIOMASS

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to preparation of composites from agricultural waste. More particularly, the present invention relates to a method of preparing a silicon suboxide-carbon composite from silicon-containing biomass.

[0004] BACKGROUND OF THE INVENTION

[0005] The utilization of agricultural waste for producing sustainable and eco-friendly materials has garnered significant attention. Among the various agricultural waste, silicon-containing biomass have sparked significant interest in both biological and technological research. The variety of silicon-containing biomass such as rice husks, palm fruit bunch fibres and sugarcanes offer opportunities for sustainable material development, bioengineering, and environmental applications.

[0006] Rice husks stand out due to their abundance and rich silica content. Rice husks, the protective coverings of rice grains, are typically discarded as waste, posing environmental disposal challenges. However, recent advancements in material science have showcased the potential of rice husks as a valuable precursor for producing negative electrode materials for batteries.

[0007] China Patent Publication No. CN 105098183 A discloses a method for preparing a microporous carbon negative electrode material for a lithium-ion battery, comprising the steps of calcining cleaned rice husks at 450 to 650° C for 1 to 5 hours under nitrogen spray to obtain rice husk dry distillate, boiling the rice husk dry distillate in a 0.1M hydrochloric acid solution at 50°C to 70°C for 0.5 to 2.5 hours, washing with distilled water until neutral, and drying to obtain the acid-treated rice husk dry distillate. Na2COs and the acid-treated rice husk carbonized product are mixed in a specific mass ratio of ground evenly, placed in a tubular furnace, and calcined at 850-1000°C for 2-5 hours under nitrogen injection. The obtained product is repeatedlywashed with distilled water until the Na+ions and SiCh2' are removed, and then dried to obtain the lithium ion battery microporous carbon negative electrode material.

[0008] China Patent Publication No. CN117303348A discloses method for preparing a negative electrode material for a battery from rice husk. The method according to this publication comprises the steps of rapidly burning rice hulls at 500-600°C to obtain shell carbon, crushing shell carbon and grinding edges to obtain carbon powder, and sieving carbon powder with a certain particle size range to obtain the negative electrode material.

[0009] Korea Patent Publication No. KR 101527644 B1 discloses a method for producing an active material for a negative electrode of a lithium secondary battery derived from a rice husk. The method according to this publication comprises the steps of subjecting rice husks to an acid treatment and a first heat treatment, followed by mixing with magnesium, and subsequently performing a magnesium heat reduction process as a second heat treatment to produce rice husk-derived silicon.

[0010] International PCT Application No. PCT / US2006 / 038651 (published as WO 2007 / 047094 A2) describes a method for making carbon-silica products. According to this publication, plant matter containing silica is leached in either a single-stage or multi-stage process using a sulfuric acid solution at a controlled temperature for a suitable time. This publication also discloses the use of a pyrolysis reaction for thermally volatilizing the volatile carbon component of the carbon-silica product in a reactor.

[0011] The methods described in the prior art are complex, as they involve multi-step processes such as acid treatment and pyrolysis. These multi-step procedures are time-intensive, demand high energy consumption, and require precise control of temperature, pressure, and atmosphere. Consequently, scaling up these methods for industrial applications is challenging and incurs significant costs. Moreover, the time required for each step reduces overall efficiency, hindering the commercial viability of these approaches.Furthermore, the method described in CN117303348A offers limited flexibility in adjusting the composition of the resulting composite materials, particularly with respect to the carbon and silica content. This lack of precise control over the carbon-to-silicon ratio in the composite material can result in suboptimal electrochemical properties, including reduced energy density, decreased stability, and a shorter cycle life for batteries.

[0012] Another drawback of the methods as disclosed by the prior art is the reliance on harsh chemicals such as those described in WO 2007 / 047094 A2, which can lead to the production of substantial waste byproducts, including excess silica and carbon residues. Handling these byproducts poses environmental challenges and adds to the overall cost of the process, which is not practical for large scale applications.

[0013] Additionally, the methods outlined in CN 117303348 and KR 101527644 B1 are primarily designed for producing anode materials specifically for lithium-ion batteries. However, these approaches may lack the versatility required to develop materials compatible with next-generation energy storage systems, such as solid-state or lithium-sulfur batteries.

[0014] Accordingly, there is a need to provide a method for producing anode materials for a battery from silicon-containing biomass including rice husk which can overcome the drawbacks of the methods as described in the prior art.

[0015] SUMMARY OF THE INVENTION

[0016] In a first aspect, the present invention discloses a method of preparing a silicon suboxide-carbon composite from silicon-containing biomass. The method comprises a step of subjecting the silicon-containing biomass to an electrical heating in an inert gas atmosphere thereby forming a silicon suboxide-carbon composite. The silicon suboxide is represented by the formula SiOx, where 0<x<2. The electrical heating is conducted by applying current density ranging from 2 A / cm2to 100 A / cm2.In one embodiment, the electrical heating is conducted for a period ranging from 10 to 100 seconds, and at a temperature ranging from 500°C to 3000°C. The inert gas is selected from argon, nitrogen, or a mixture thereof.

[0017] The silicon-containing biomass used in the method of the present invention may be selected from rice husk, palm fruit bunch fibers, sugarcane, bamboo leaves, corn cob or wheat husk.

[0018] In a second aspect, the present invention discloses a silicon suboxide (SiOx)-carbon composite obtained from the method described in the first aspect. The silicon suboxide (SiOx)-carbon composite has a core-shell structure comprising a silicon core and a carbon shell covering the core.

[0019] In one embodiment, the carbon shell has a thickness ranging from 5 nm to 15 nm and comprises graphitic carbon. The silicon suboxide (SiOx)-carbon composite has a specific surface area ranging from 50 to 150 m2 / g.

[0020] In a third aspect, the present invention discloses use of the silicon suboxide (SiOx)-carbon composite described in the second aspect as anode material in an energy storage device. The energy storage device includes lithium-ion batteries, solid-state batteries, lithium-sulfur batteries, and sodium-ion batteries. The energy storage device can be used in portable electronic devices, electric vehicles, or grid energy storage systems.

[0021] The method of the present invention is advantageous since the method only involves a single step, i.e. the electrical heating step which reduces the complexity, energy consumption and time required to convert silicon-containing biomass into high quality silicon suboxide-carbon composite, hence making the method suitable for industrial applications.

[0022] Moreover, the rapid electrical heating step allows for precise control over the synthesis process, enabling the fine-tuning of carbon and SiOxcontent in the prepared composite. This ensures consistent and optimized material properties, such as high energy density, improved stability, and extended cycle life.It is also an advantage of the present invention to provide a method which is environmentally friendly since it minimizes the use of harsh chemicals and thus reducing production of waste by-products.

[0023] The silicon suboxide-carbon composite obtained by the method of the present invention exhibits enhanced electrochemical properties, including higher energy density, improved stability, and longer cycle life, thus offering various applications in energy storage systems.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 shows an X-ray diffraction pattern of rice husk which is subjected to a method of the present invention (i.e. treated rice husk) and rice husk which is not subjected to any treatment (i.e. untreated rice husk), according to an example of the present invention;

[0026] Fig. 2 shows thermogravimetric analysis (TGA) of treated rice husk and untreated rice husk according to an example of the present invention;

[0027] Fig. 3 shows a scanning electron microscopy (SEM) image of the synthesized silicon suboxide-carbon composite, according to an example of the present invention;

[0028] Fig. 4 illustrates rate capability of two materials, SiOx-carbon composite and graphite, used as electrode materials in lithium-ion batteries, according to an example of the present invention; and

[0029] Fig. 5 illustrates the cyclic charge-discharge performance of two materials, SiOx-carbon composite and graphite, at a current density of 200 mA / g over 300 cycles, according to an example of the present invention.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] In a first aspect, the present invention discloses a method of preparing a silicon suboxide-carbon composite from silicon-containing biomass. Silicon suboxide is aderivative of silicon which is represented by the formula SiOxwhere 0<x<2. The method of the present invention employs a rapid electrical heating, also known as rapid Joule heating, which is conducted by applying rapid and localized electrical energy to generate high temperatures over a short duration. The rapid electrical heating significantly reduces the complexity and time required to convert silicon-containing biomass into a high-quality silicon suboxide-carbon composite.

[0032] The method of preparing a silicon suboxide (SiOx)-carbon composite from silicon-containing biomass according to the present invention comprises a step of subjecting the silicon-containing biomass to an electrical heating in an inert gas atmosphere to form a silicon suboxide (SiOx)-carbon composite. The electrical heating is conducted by applying current density ranging from 2 A / cm2to 100 A / cm2. The range of the current density is a key factor in determining the efficiency of the SiOxconversion and the formation of the carbon component from the silicon-containing biomass. This range is necessary to achieve high temperatures required for carbothermal reduction without the materials.

[0033] The electrical heating is conducted for a short period of time, particularly for 10 to 100 seconds in order to control the reaction kinetics and to ensure silica is completely converted to silicon suboxide (SiOx) while forming the carbon component. A short, controlled burst of heat within 10 to 100 seconds allows formation of high quality SiOx-carbon composite. The selection of time period depends on the desired siliconcarbon ratio.

[0034] The electrical heating is conducted at a high temperature to facilitate the carbothermal reduction of silica and the formation of the carbon component. In one embodiment, the electrical heating is conducted at a temperature ranging from 500°C to 3000°C. The temperature is carefully controlled to prevent excessive volatilization or material degradation.

[0035] Upon formation of the silicon suboxide (SiOx)-carbon composite, the composite may be subjected to a controlled, gradual cooling stabilize the composite structure and prevent the formation of internal stresses or defects.The electrical heating is conducted in an inert gas atmosphere wherein the inert gas may be selected from argon, nitrogen, or a mixture thereof. The inert gas atmosphere is required to prevent further oxidation of the SiOxand carbon components during the high-temperature heating process. An oxygen-deficient environment is crucial for maintaining the purity and quality of the SiOx-carbon composite.

[0036] The silicon-containing biomass used in the method of the present invention may include, but not limited to, rice husk, palm fruit bunch fibers, sugarcane, bamboo leaves, corn cob and wheat husk.

[0037] According to a preferred example, rice husks containing 15-20% silica are firstly cleaned and pre-treated with an acid wash. The rice husks are then subjected to an electrical heating (i.e. rapid Joule heating) in an argon atmosphere, wherein current density at 50 A / cm2is applied for 20 second, thereby forming the SiOx-carbon composite. The SiOx-carbon composite obtained thereof demonstrates no capacity degradation after 300 cycles and a coulombic efficiency of 99%.

[0038] By employing the single-step rapid electrical heating, the method of the present invention significantly reduces the complexity and time required to convert silicon-containing biomass into a high-quality SiOx-carbon composite. Since the method of the present invention does not require multiple processing steps and complex acid treatments, the synthesis of SiOx-carbon composite is significantly simplified therefore increasing production efficiency, reducing energy consumption and lowering operational costs, making the method suitable for large-scale industrial production.

[0039] Moreover, the electrical heating step allows for precise control over the SiOx-carbon ratio in the composite, which is necessary to meet specific electrochemical performance criteria.

[0040] Additionally, the method of the present invention is environmentally friendly as it minimizes the use of harsh chemicals and reduces the generation of waste byproducts.In a second aspect, the present invention discloses a silicon suboxide (SiOx)-carbon composite obtained from the method as described in the first aspect. The silicon suboxide (SiOx)-carbon composite has a core-shell structure comprising a silicon core and a carbon shell covering the core. The core-shell structure enhances the stability and performance of the composite in energy storage application, particularly in mitigating silicon expansion during cycling. The carbon shell comprises graphitic carbon and has a thickness ranging from 5 nm to 15 nm. The presence of graphitic carbon enhances electrical conductivity and strengthens structural integrity. Moreover, the thickness of the carbon shell ensures high structural stability and minimizes silicon expansion during cycling. Further, the silicon suboxide (SiOx)-carbon composite has a specific surface area ranging from 50 to 150 m2 / g, which enhances the electrochemical performance of the composite.

[0041] The SiOx-carbon composite of the present invention is subjected to extensive electrochemical testing, including cyclic voltammetry, galvanostatic charge-discharge cycles, and capacity retention analysis. Based on the tests, the SiOx-carbon composite of the present invention shows stable redox peaks indicative of good electrochemical reversibility. Moreover, the SiOx-carbon composite exhibits a capacity retention of at least 85% after 100 charge-discharge cycles and coulombic efficiency of 99% during cycling tests.

[0042] Overall, the SiOx-carbon composite of the present invention exhibits enhanced electrochemical properties, including higher energy density, improved stability, and longer cycle life, making it suitable for energy storage applications.

[0043] In a third aspect, the present invention discloses use of the silicon suboxide (SiOx)-carbon composite as described in the second aspect. The SiOx-carbon composite is suitable for use as anode material in an energy storage device, which includes but not limited to, lithium-ion batteries, solid-state batteries or lithium-sulfur batteries.

[0044] In one example, the silicon suboxide (SiOx)-carbon composite of the present invention is used as anode materials in lithium-ion batteries. The core-shell structure enhances energy density, improves stability, and extends the cycle life of the batteries. These enhanced properties make the batteries ideal for high-performanceapplications such as electric vehicles (EVs), portable electronics (smartphones, laptops, etc.), and renewable energy storage systems.

[0045] In another example, the silicon suboxide (SiOx)-carbon composite of the present invention may be applied in the production of solid-state batteries, where the siliconcarbon composites contribute to higher capacity and improved stability. These batteries are crucial for next-generation energy storage technologies that require safer and more efficient energy solutions. The use of solid electrolytes in conjunction with the SiOx-carbon composite anodes results in batteries with greater safety, longevity, and energy density.

[0046] In yet another example, the silicon suboxide (SiOx)-carbon composite of the present invention may also be used as anode materials in lithium-sulfur batteries, which are known for their high theoretical capacity. The core-shell structure helps mitigate issues such as the polysulfide shuttle effect, thereby improving battery performance. Lithium-sulfur batteries with enhanced anode materials could offer a more sustainable and cost-effective solution for high-energy applications, including electric vehicles and large-scale energy storage.

[0047] Batteries comprising the SiOx-carbon composite of the present invention as anode materials may be used in electronics devices including but not limited to smartphones, tablets and wearable devices such as smartwatches and fitness trackers. The improved battery performance resulting from the SiOx-carbon composite can extend battery life enhance charge retention and enable faster charging in the electronics devices, thus enabling these devices to operate for extended periods without frequent recharging, making them more user-friendly.

[0048] Further, batteries comprising the SiOx-carbon composite of the present invention as anode materials may also be used in electric vehicles (EVs), since the increased energy density provided by the SiOx-carbon composite in the battery anodes can significantly extend the driving range of electric vehicles and reduce the frequency of recharging. This advancement supports the broader adoption of EVs by making them more competitive with traditional gasoline-powered vehicles in terms of range and convenience. The enhanced battery stability and performance allow for fastercharging times in EVs, make EVs more convenient for everyday use and longdistance travel.

[0049] The SiOx-carbon composite of the present invention is also suitable for grid energy storage systems that support the integration of renewable energy sources like solar and wind. The high capacity and long cycle life of the silicon-carbon composites make them ideal for stabilizing the grid and balancing supply and demand. Improved grid storage systems facilitate the adoption of renewable energy, helping to reduce reliance on fossil fuels and lower greenhouse gas emissions.

[0050] In addition, batteries comprising the SiOx-carbon composite of the present invention may be used for backup power systems in residential, commercial, and industrial settings. High-capacity, long-lasting batteries are essential as backup power systems to ensure uninterrupted power supply during outages.

[0051] Other potential applications of the SiOx-carbon composite of the present invention include high-energy density batteries and portable power supply in aerospace and defense sectors, implantable devices and wearable health monitors in healthcare sectors, backup power for communication towers in telecommunication sector, and power tools and Uninterruptible Power Supplies (UPS) for industrial applications.

[0052] The SiOx-carbon composite of the present invention may also be applicable for supercapacitors, catalysis, composite materials, photovoltaics, sensors and agriculture.

[0053] EXAMPLE

[0054] Silicon suboxide (SiOx)-carbon composite is prepared in accordance with the method described in the first aspect of the present invention. The silicon-containing biomass used for this example is rice husk.

[0055] Rice husk which is subjected to electrical heating as described in the method of the present invention is hereinafter referred as “treated rice husk”. As a comparativeexample, rice husk which is not subjected to any treatment is also provided (hereinafter referred as “untreated rice husk”).

[0056] The synthesized SiOx-carbon composite is characterized using X-ray diffraction (XRD) to confirm the crystalline phases and scanning electron microscopy (SEM) to visualize the composite structure.

[0057] X-ray Diffraction (XRD)

[0058] Fig. 1 shows an X-ray diffraction pattern of treated rice husk and untreated rice husk.

[0059] Peak at 22°:

[0060] Untreated Rice Husk: As shown in Fig. 1, the broad peak observed around 22° in the XRD pattern of the untreated rice husk suggests the presence of amorphous silica (SiC>2). This peak is typical of natural silica found in biological materials like rice husk, where silica exists in a disordered, non-crystalline form. The broad nature of the peak indicates a lack of long-range order, consistent with the amorphous structure of silica interspersed within organic components such as cellulose and lignin in the untreated husk.

[0061] Treated Rice Husk: In the treated rice husk, the peak at 22° is less pronounced and more diffuse, suggesting that the thermal treatment process has altered the silica structure. During thermal treatment, the organic materials such as cellulose, hemicellulose, and lignin are decomposed, leaving behind silica in a more uniform, less crystalline state. The reduction in peak intensity at 22° indicates that some of the original amorphous silica has been transformed or modified due to this high-temperature exposure.

[0062] Peak at 45°:

[0063] Treated Rice Husk: Still referring to Fig. 1, a notable feature appears around 45° in the treated rice husk, which is not present in the untreated rice husk. This peak is indicative of SiOxphases, where x is greater than 0 and less than 2 (0<x<2). SiOxrepresents partially oxidized silicon, which can form when silica (SiC>2) undergoes thermal decomposition or partial reduction at high temperatures. The presence of thispeak suggests a transition from pure amorphous silica to a partially reduced, more ordered SiOxstructure. The thermal treatment, conducted at elevated temperatures, facilitates the removal of oxygen atoms from the silica network, leading to the formation of these SiOxphases.

[0064] Absence in Untreated Rice Husk: The untreated rice husk lacks this peak at 45°, confirming that the material predominantly contains amorphous silica with minimal SiOxformation. This absence aligns with the natural state of rice husk, where silica remains largely unaltered and lacks any crystalline or sub-stoichiometric silicon oxide phases.

[0065] Distinction Between Silica (SiOa) and SiOx:

[0066] Silica (SiO2): The broad peak at 22° is characteristic of amorphous silica, where there is a lack of long-range crystallinity. In the untreated rice husk, this peak reflects the natural disordered state of silica mixed within organic matrices. After thermal treatment, the reduction of this peak suggests a decrease in the typical amorphous silica structure as organic materials are removed.

[0067] SiOx: The peak at 45° in the treated rice husk indicates the formation of SiOx, a partially reduced form of silica. SiOxcontains varying ratios of silicon and oxygen (where x < 2), resulting in a more ordered structure than amorphous silica but not fully crystalline. The thermal treatment process at high temperatures leads to partial deoxygenation, creating these SiOxphases with different physical and chemical properties.

[0068] Summary of Structural Changes:

[0069] The transition from a broad peak at 22° to a more defined feature at 45° indicates that thermal treatment alters the silica in rice husk, transforming some of it into SiOxphases. This change implies that the treated material may have enhanced properties, such as higher reactivity and a more tailored structure for applications like battery anodes.

[0070] Fig. 2 shows thermogravimetric analysis (TGA) of treated rice husk and untreated rice husk.Residual Weight Percentage at 1000°C:

[0071] As shown in Fig. 2, both treated rice husk (-represented by solid line) and untreated rice husk (represented by dotted line) have a residual weight of approximately 30% at 1000°C.

[0072] Interpretation of Residual Weight:

[0073] The 30% residual weight in both samples represents the silica (SiC>2) content remaining after the complete thermal decomposition of organic matter.

[0074] Although the initial weight loss profiles differ due to varying organic content, the final residual weight suggests that the silica content in both treated and untreated rice husk is similar, indicating that the majority of the mass remaining after thermal processing is due to silica (SiC>2).

[0075] Impact of Thermal Treatment:

[0076] The treated rice husk (solid line) shows less weight loss between 200°C and 400°C, indicating that the initial thermal treatment removed a significant portion of the organic components, such as cellulose and lignin, prior to the TGA analysis.

[0077] The untreated rice husk (dotted line) exhibits a more pronounced weight loss in the same temperature range, reflecting the decomposition of its organic materials during the TGA process.

[0078] Despite these differences in the decomposition process, both samples stabilize at approximately 30% residual weight, indicating that the thermal treatment's primary effect is the removal of organic content rather than altering the final silica content.

[0079] Treated Rice Husk retains approximately 30% of its initial mass as silica (SiO2) after thermal treatment, with most organic matter removed before TGA analysis.

[0080] Untreated Rice Husk also retains approximately 30% of its initial mass as silica (SiO2), but loses more organic material during the TGA process itself.The TGA results indicate that while thermal treatment effectively reduces the organic content of the treated rice husk, it does not significantly alter the silica content, as both samples ultimately retain 30% silica (SiC>2). This makes the treated and untreated rice husk suitable for various applications that require high silica content, such as battery anodes.

[0081] Fig. 3 shows a scanning electron microscopy (SEM) image of the synthesized SiOx-carbon composite.

[0082] Morphology: The SEM image as shown in Fig. 3 reveals a porous, interconnected network structure composed of agglomerated nanoparticles. The particles appear to be clustered together, forming a three-dimensional structure with a high surface area.

[0083] Particle Size: The individual particles seem to have a size range of tens to a few hundred nanometers, forming larger aggregates. The precise size distribution is not easily discernible due to the dense clustering.

[0084] Surface Texture: The surface of the material appears rough and uneven, with numerous small protrusions and voids between the particles, which contribute to the porous nature of the structure.

[0085] Porosity: The visible spaces between the particle clusters suggest a high degree of porosity, which is characteristic of materials designed for applications like electrode materials in energy storage systems.

[0086] This morphology is typical of materials such as silica, and carbon composites, which are often used in applications where a high surface area is desirable, such as electrode materials in energy storage systems. The porous structure enhances surface interactions with reactants or electrolytes, making it suitable for applications in chemical reactions or electrochemical processes.

[0087] Fig. 4 illustrates rate capability of two materials, SiOx-carbon composite and graphite, used as electrode materials in lithium-ion batteries. The graph plots specific capacity(mAh / g) against cycles at various current densities ranging from 50 mA / g to 600 mA / g.

[0088] Comparison of Specific Capacity:

[0089] At each current density, the SiOx-carbon composite consistently shows a higher specific capacity compared to graphite. This suggests that the SiOx-carbon composite has a better performance in terms of storing energy at various rates.

[0090] For instance, at the lower current density of 50 mA / g, the SiOx-carbon composite achieves a specific capacity of approximately 250 mAh / g, whereas graphite exhibits a capacity closer to 150 mAh / g. This indicates that the SiOx-carbon composite can store significantly more charge than graphite under low-current conditions.

[0091] Effect of Increasing Current Density:

[0092] As the current density increases from 50 mA / g to 600 mA / g, the specific capacity of both materials decreases, which is expected as higher current densities typically lead to faster charge / discharge rates, reducing the efficiency of lithium-ion intercalation.

[0093] However, the SiOx-carbon composite maintains a higher specific capacity across all tested current densities. Even at 600 mA / g, where high-rate performance is tested, the SiOx-carbon composite retains a capacity of around 100 mAh / g, while graphite falls to below 80 mAh / g.

[0094] Rate Capability Stability:

[0095] The specific capacity of both materials decreases gradually with increasing cycles, which suggests a stable rate capability. However, the SiOx-carbon composite shows a relatively stable capacity retention across different current densities compared to graphite, indicating better structural integrity and durability during high-rate cycling.

[0096] The relatively consistent performance of the SiOx-carbon composite across varying rates makes it a promising candidate for applications requiring high-rate charge / discharge capabilities, such as in high-power batteries or fast-charging devices.Potential Application and Advantages:

[0097] The superior rate capability of the SiOx-carbon composite over traditional graphite suggests that it could be a more efficient anode material in lithium-ion batteries. Its ability to maintain higher specific capacities at varying rates could be particularly advantageous for applications requiring rapid energy delivery or absorption, such as electric vehicles and portable electronics.

[0098] Additionally, utilizing the SiOx-carbon composite as a precursor for battery materials offers environmental and economic benefits due to its abundance and low cost, making it a sustainable alternative to conventional graphite.

[0099] The graph demonstrates that the SiOx-carbon composite exhibits better rate capability and specific capacity compared to graphite, maintaining higher charge storage even at increased current densities. This suggests that rice husk could serve as a high-performance, sustainable alternative to graphite in energy storage applications, especially where fast charging and high power output are critical.

[0100] Fig. 5 illustrates the cyclic charge-discharge performance of two materials, SiOx-carbon composite and graphite, at a current density of 200 mA / g over 300 cycles. The vertical axis represents the specific capacity (mAh / g), while the horizontal axis represents the number of cycles.

[0101] Initial Specific Capacity:

[0102] At the beginning of the test (Cycle 0), the SiOx-carbon composite shows a specific capacity of around 280 mAh / g, while graphite starts at approximately 200 mAh / g. This indicates that the SiOx-carbon composite has a higher initial capacity for storing charge compared to traditional graphite.

[0103] Capacity Retention Over Cycles:

[0104] As the cycles progress, the SiOx-carbon composite exhibits a gradual increase in specific capacity, reaching about 393 mAh / g by the end of 300 cycles. This suggests an improvement in the material's electrochemical performance with continuous cycling, which could be attributed to factors like better electrode activation or improved ionic conductivity within the structure.In contrast, the graphite shows a slight decrease in capacity over the same period, stabilizing at around 175 mAh / g. This decline indicates a typical capacity fade that occurs due to electrode degradation, loss of active material, or increased internal resistance during the charge-discharge process.

[0105] Overall Performance Comparison:

[0106] The SiOx-carbon composite outperforms graphite throughout the entire 300-cycle range, showing both higher capacity and better stability. The capacity increase observed in rice husk material suggests that it might be undergoing structural changes or further electrolyte penetration that enhances lithium-ion intercalation over time.

[0107] Graphite, while commonly used as an anode material in lithium-ion batteries, shows relatively limited capacity and a slight decline, demonstrating less adaptability to sustained cycling compared to the rice husk-derived material.

[0108] Implications for Battery Applications:

[0109] The significantly higher specific capacity and stable performance of the SiOx-carbon composite make it a promising candidate for high-capacity lithium-ion batteries, particularly for applications where maintaining high capacity over many chargedischarge cycles is critical.

[0110] The ability of the rice husk-derived material to improve its capacity overtime suggests potential advantages in applications like electric vehicles and energy storage systems, where consistent and improving performance can enhance the lifespan and efficiency of the battery.

[0111] The use of the SiOx-carbon composite, an agricultural waste product, also presents economic and environmental benefits over graphite, aligning with sustainability goals in the development of energy storage materials.

[0112] Fig. 5 clearly demonstrates the superior cyclic stability and higher specific capacity of the SiOx-carbon composite compared to graphite at 200 mA / g. The ability of the SiOx-carbon composite to achieve a capacity of 393 mAh / g after 300 cycles highlightsits potential for use as a sustainable and high-performance anode material in lithium-ion battery technology, offering advantages in terms of both performance and sustainability.

Claims

CLAIMS1. A method of preparing a silicon suboxide-carbon composite from silicon-containing biomass, the method comprising a step of subjecting the silicon-containing biomass to an electrical heating in an inert gas atmosphere, thereby forming a silicon suboxide-carbon composite,wherein the silicon suboxide is represented by the formula SiOx, where 0<x<2, andwherein the electrical heating is conducted by applying current density ranging from 20 A / cm2to 100 A / cm2.

2. The method of claim 1 , wherein the electrical heating is conducted for a period ranging from 10 to 100 seconds.

3. The method of claim 1, wherein the electrical heating is conducted at a temperature ranging from 500°C to 3000°C.

4. The method of claim 1 , wherein the inert gas is selected from argon, nitrogen, or a mixture thereof.

5. The method of claim 1, wherein the silicon-containing biomass is selected from rice husk, palm fruit bunch fibers, sugarcane, bamboo leaves, corn cob or wheat husk.

6. A silicon suboxide (SiOx)-carbon composite obtained from the method of claim 1, characterized in that,the silicon suboxide (SiOx)-carbon composite having a core-shell structure comprising a silicon core and a carbon shell covering the core, wherein the carbon shell having a thickness ranging from 5 nm to 15 nm and the carbon shell comprises graphitic carbon.

7. The silicon suboxide (SiOx)-carbon composite of claim 6 having a specific surface area ranging from 50 to 150 m2 / g.

8. Use of the silicon suboxide (SiOx)-carbon composite of claim 6 as anode material in an energy storage device.

9. The use of claim 8, wherein the energy storage device includes lithium-ion batteries, solid-state batteries, lithium-sulfur batteries and sodium-ion batteries.

10. The use of claim 8 in portable electronic devices, electric vehicles or grid energy storage systems.

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