Abstract
The regulation of anions and cations at the atomic scale is of great significance in membrane-based separation technologies. Ionic transport regulation techniques could also play a crucial role in developing high-performance alkali metal batteries such as alkali metal-sulfur and alkali metal-selenium batteries, which suffer from the non-uniform transport of alkali metal ions (e.g., Li
+
or Na
+
) and detrimental shuttling effect of polysulfide/polyselenide anions. These drawbacks could cause unfavourable growth of alkali metal depositions at the metal electrode and irreversible consumption of cathode active materials, leading to capacity decay and short cycling life. Herein, we propose the use of a polypropylene separator coated with negatively charged Ti
0.87
O
2
nanosheets with Ti atomic vacancies to tackle these issues. In particular, we demonstrate that the electrostatic interactions between the negatively charged Ti
0.87
O
2
nanosheets and polysulfide/polyselenide anions reduce the shuttling effect. Moreover, the Ti
0.87
O
2
-coated separator regulates the migration of alkali ions ensuring a homogeneous ion flux and the Ti vacancies, acting as sub-nanometric pores, promote fast alkali-ion diffusion.
An optimized transport of anions and cations is essential for the development of practical alkali metal batteries. Here, the authors report the use of Ti
0.87
O
2
nanosheets as coating material of polypropylene separators for Li-S, Li-Se and Na-Se cells.