Flexible quasi-solid-state lithium-ion capacitors employing amorphous SiO₂ nanospheres encapsulated in nitrogen-doped carbon shell as a high energy anode

Lithium-ion hybrid capacitors (LICs) take the advantage of simultaneous high energy – power output, and become increasingly important for next generation applications. Developing a high performing LICs with high energy-power-cycle combination remains a significant challenge due to low capacity intercalation electrodes, and kinetically sluggish alloying type electrodes. A strategy employing fast pseudocapacitive lithium ion storage in high-capacity alloying type anode, rather than a bulk storage, can output kinetically superior LICs with high energy even at high power conditions. Herein, we demonstrate a highly interconnected 3-dimensional (3D) SiO₂ nanospheres embedded Nitrogen-doped carbon shell with fast lithium ion storage kinetics as high performing anode for LICs. As a result, LIC with a high energy (139 Wh kg⁻¹), high power density (42 kW kg⁻¹), and super stability (20,000 cycles) is obtained, outperforming previously studied alloying type metal oxide and sulfide anodes. A flexible LICs is further demonstrated which shows good stability under different bending conditions. The current research promotes the practical utilization of earth-abundant material as a high capacity and high rate electrode for the next-generation flexible and wearable devices.