Elaborately Designed S-Doped Graphene Nano-Capsules Toward Excellent Low-Temperature Performance in Li-Ion Capacitors

The electrochemical properties of LICs are greatly decreased at a low-temperature condition due to the sluggish Li-ion storage kinetics coupled with poor structural stability. Herein, S-doped graphene nano-capusles (SGCs) with good dispersibility is rational designed and serves as both the anode and cathode in symmetric LICs. At room temperature, SGCs//SGCs shows high gravimetric energy density of 249.9 W h kg-1 at 2116.7 W kg-1 and high volumetric energy density of 172.4 W h L-1 at 1460.5 W L-1 coupled with 95.4% capacity retention for 10000 cycles. Even at 19617 W h kg-1, it delivers high gravimetric energy density of 149.8 W kg-1, and the volumetric energy density is as high as 103.4 W h L-1 at 13535.5 W L-1. At -30 °C, It still displays 179.6 W h kg-1 at 1658.2 W kg-1 and 24755.7 W kg-1 at 68.8 W h kg-1 coupled with 84.3% capacity retention for 10000 cycles. Furthermore, a fabricated density functional theory (DFT) further demonstrates that the doped S atom into graphene framework plays a key role in enhancing the electronic conductivity and Li+ storage capability. Our results offers a promising application reserve force for the next generation energy storage devices in LICs