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-capsules (SGCs) with good dispersibility is rational designed and serves as both the anode and cathode in symmetric LICs. At room temperature, all the half-cells of SGCs exhibit excellent high capacity, outstanding rate performance and ultra-long cycling stability. Furthermore, the assembled SGCs//SGCs LICs shows a 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 −30 °C, It still displays 179.6 W h kg−1 at 1658.2 W kg−1 and 68.8 W h kg−1 at 4755.7 W 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 plays a key role in enhancing the electronic conductivity and Li+ storage capability. Our results offer a promising application reserve force for the next generation energy storage devices in LICs.