Dr.-Ing. Mingren Liu

Ether-based room-temperature sodium–sulfur (RT Na─S) batteries are a promising energy-storage system, yet hindered by the unregulated sulfur redox pathway, severe polysulfide shuttling and rapid capacity fading. Herein, highly unsaturated niobium-oxide sub-nanoclusters (≈0.7 nm) anchored on defective carbon black (NbOx-DCB) as a dynamic sulfur-conversion catalyst are introduced. The delocalized Nb d-electrons in the sub-nanocluster configuration create a mixed Nb4+/Nb5+ valence state that functions as a bidirectional electron reservoir, thereby enabling a distinct d-band-center self-regulation mechanism. The strong d–p orbital coupling enabled by a Nb4+-rich surface effectively captures sodium polysulfides and accelerates sulfur conversion kinetics during discharge, while a Nb5+-rich surface promotes facile solid-polysulfide decomposition during charging. Consequently, the NbOx-DCB/S cathode delivers a reversible capacity of 1184 mAh gS−1 at 0.1 A g−1 after 100 cycles and retains 547 mAh gS−1 after 3000 cycles at 2 A g−1, corresponding to a decay rate of 0.0027% per cycle. The general applicability of this approach is validated by high-performance tungsten and vanadium oxide sub-nanocluster-based sulfur cathodes. These findings highlight sub-nanoscale metal-oxide engineering as a versatile route to high-performance RT Na–S batteries.

Electrical double-layer capacitors offer high power density and long cycle life but are limited by moderate energy density. We investigate a strategy to improve their performance using quaternary electrolytes containing two distinct cations and two distinct anions. Our theoretical analysis shows that such electrolytes outperform pure ionic liquids and conventional mixtures sharing a common ion. We validate this approach experimentally using [EMIM][BF4] mixed with lithium salts, characterizing their local structure and electrochemical behavior via NMR, Raman spectroscopy, conductivity measurements, and electrochemical testing. We further demonstrate that the enhancement depends sensitively on electrode microporosity, underscoring the interplay between electrolyte composition and pore structure.