The total use of rice husk to create highly porous silicon and sulfur-doped activated carbon for the fabrication of high-performance silicon-anode lithium-ion capacitors

The promising advantages between the high energy density of lithium-ion batteries and the high power density of supercapacitors are hybridized to construct lithium-ion capacitors (LICs). The high capacity of anode materials is challenging for high-performance LICs. Simultaneously, the quest for sustainable and environmentally friendly energy storage materials has attracted attention. In this work, rice husk was treated with alkaline to separate silica and biochar, followed by magnesiothermic reduction and thermal activation to produce porous silicon (PSi) and sulfur-doped activated carbon (SAC), respectively. The PSi had high porosity for accommodating volumetric expansion during cycling, resulting in outstanding rate capability and cycling stability, whereas the SAC had a high surface area with micro- and mesopores (2511 m2 g−1), a high degree of graphitization, and excellent electrochemical performance. For the fabrication of half-cell lithium-ion batteries, PSi gave a specific capacity of 1005.3 mAh g−1 between 0.01 and 3 V, while SAC provided a specific capacity of 108 mAh g−1 (2.0–4.5 V), and showed a better electrochemical stability than the both commercial silicon and activated carbon. When a full-cell LIC was fabricated, the optimized P-Si//SAC LIC had a high energy density of 107 Wh kg−1 at a power density of 163 W kg−1 and a capacitance retention of 81.3 and 61.8% between a potential range of 2.0–4.5 V after 1000 and 3000 charge-discharge cycles, respectively. This study not only turned agricultural waste into valuable, high-performance LICs but also made significant progress toward the creation of environmentally responsible, long-lasting, and sustainable energy storage systems.