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

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journal contribution
posted on 29.09.2020, 16:33 by Yu-Shun Luo, Dah-Shyang Tsai, Chien-Chen Wang, Chun-Wei Chiang
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 LiNO3 than the general-purpose electrolyte of LiPF6. On the positive electrode, a nitrogen-doped carbon, KPN900, is prepared in-house with a high Brunauer–Emmett–Teller (BET) surface area of 3280 m2 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 LiPF6 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.