Recent advances of polar transition-metal sulfides host materials for advanced lithium–sulfur batteries

Lithium sulfur batteries (LSBs) have been one of the most promising second batteries for energy storage. However, the commercialization of LSBs is still hindered by low sulfur utilization and poor cycling stability, resulting from shuttle effect and low redox kinetics of lithium polysulfides (LiPSs). Significant progress has been made over the years in enhancing the batteries performances and tap density with the transition-metal sulfides as sulfur host or additive in LSBs. In this review, we present the recent advances in the use of various nanostructured transition-metal sulfides applied in LSBs, and also focus on the interaction mechanisms of polar transition-metal sulfides with LiPSs and its catalysis for the redox of LiPSs. It may provide avenues for the application of transition-metal sulfides in LSBs. The challenges and perspectives of transition-metal sulfides are also addressed.

Critical enhancement of thermopower in a chemically tuned polar semimetal MoTe2

Ferroelectrics with spontaneous electric polarization play an essential role in today’s device engineering, such as capacitors and memories. Their physical properties are further enriched by suppressing the long-range polar order, as exemplified by quantum paraelectrics with giant piezoelectric and dielectric responses at low temperatures. Likewise in metals, a polar lattice distortion has been theoretically predicted to give rise to various unusual physical properties. However, to date, a “ferroelectric”-like transition in metals has seldom been controlled, and hence, its possible impacts on transport phenomena remain unexplored. We report the discovery of anomalous enhancement of thermopower near the critical region between the polar and nonpolar metallic phases in 1T′-Mo1−xNbxTe2with a chemically tunable polar transition. It is unveiled from the first-principles calculations and magnetotransport measurements that charge transport with a strongly energy-dependent scattering rate critically evolves toward the boundary to the nonpolar phase, resulting in large cryogenic thermopower. Such a significant influence of the structural instability on transport phenomena might arise from the fluctuating or heterogeneous polar metallic states, which would pave a novel route to improving thermoelectric efficiency.