Lithium-Ion Hybrid Capacitor with a Scaffold Electrode of Tin Sulfide and Tin Metal and Its Electrolyte Issue

In an effort to exploit low-cost tin and sulfur as active materials in lithium-ion hybrid capacitors, we prepare a SnS–Sn/carbon nanotube (CNT) negative electrode through molten slag coating of acidified carbon nanotubes (CNTs) with a minimum level of surface oxidation. The capacity of this sulfur-containing electrode behaves more reversibly and less decaying in an ether-based electrolyte of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and LiNO 3 than the general-purpose electrolyte of LiPF 6 . On the positive electrode, a nitrogen-doped carbon, KPN900, is prepared in-house with a high Brunauer–Emmett–Teller (BET) surface area of 3280 m 2 g –1 to increase the capacitance of microporous carbon. Intriguingly, the rate performance of the KPN900 electrode is slowed down by the LiTFSI electrolyte, compared with the LiPF 6 electrolyte, since a part of its capacitive component is switched to the diffusive component, while its total double-layer capacitance remains the same. Soaked in the LiTFSI electrolyte, a hybrid capacitor of KPN900//SnS–Sn/CNT, with a capacity of 97.5 mAh g –1, is capable of storing an energy of 143 Wh kg –1 with a retrieving power of 148 W kg –1, when the charging voltage is 3.8 V. The stability test of this cell, in a 4:1 mass ratio, shows a capacity retention of 78.8% after 2400 cycles of charging and discharging at 1.0 A g –1 .