One-step MXene selenization-conversion into carbon-scaffold-anchored TiSe2 nanosheets enabling interlayer- and vacancy-mediated ion transport mechanisms for fast lithium-ion storage

Lithium-ion capacitors (LICs) have attracted growing attention in energy storage applications. However, the sluggish Li kinetics in battery-type anodes has significantly restricted the rate capability. Herein we propose a novel one-step MXene selenization-conversion into carbon-scaffold-anchored TiSe2 nanosheets (TiSe2@CSA), which enables interlayer- and vacancy-mediated ion transport mechanisms for fast lithium-ion storage. The approach endows the TiSe2@CSA with a non-stacked structure, sufficient interlayer space and abundant Se vacancies for rapid ion transport. Through the theoretical analysis of density functional theory (DFT), this work confirms the significant role of Se vacancies in facilitating fast Li-ion storage. This is achieved by the enhancement of electron transfer and the reduction of the energy barrier for Li-ion diffusion. Moreover, the Li-ion storage mechanism and crystal phase evolution of TiSe2@CSA are investigated by the ex-situ XRD and HRTEM. The as-prepared TiSe2@CSA nanohybrid demonstrates a high capacity of 498 mAh g−1 at 0.05 A g−1 and an improved rate capability of 331 mAh g−1 at 5 A g−1, as well as long-term cyclability (80.5% capacity retention after 2000 cycles). When assembling TiSe2@CSA with activated carbon (YP-50) into a TiSe2@CSA//YP-50 LIC, a superior energy density of 96.7 Wh kg−1 is achieved at 410 W kg−1, and still retains 31.0 Wh kg−1 even at a high power density of 15700 W kg−1. The proposed MXene-derived selenization-conversion strategy can also be extended for other transition metal compounds to promote fast lithium-ion storage.