Three-in-one strategy via anchored MoSe2 for construct stable conversion-type Na-Se batteries: Chemisorption, catalytic conversion and stress dispersion.

Abstract

Conversion-type selenium cathodes are considered a highly promising alternative to sulfur cathodes due to their high conductivity and similar theoretical capacity. However, stress-diffusion and shuttle effects during the conversion process remain significant challenges that urgently need to be addressed. Herein, a composite matrix of MoSe₂ anchored on the surface of N-doped hollow mesoporous carbon nanospheres (NHMCNS) was designed as a Se host to construct Se/C cathodes (Se/MoSe₂@NHMCNS). Anchored MoSe₂ successfully mitigated selenium loss by enhancing the chemisorption of polyselenides within the matrix. Meanwhile, polyselenides adsorbed on the Se/C cathode surface exhibit lower diffusion barriers and more negative Gibbs free energy during the conversion from chain polyselenides to Na₂Se. MoSe₂ accelerated the catalytic conversion of polyselenides to the final discharge products from both kinetic and thermodynamic perspectives. The huge stress induced by structural transformation during the conversion process is mitigated by MoSe₂ synergistic carbon walls, which effectively maintain the structural stability of the cathode. Based on this three-in-one strategy, the sodium-selenium battery assembled with Se/MoSe₂@NHMCNS exhibits stable cycling performance (400.6 mAh g^-1 at 2C after 500 cycles), and the pouch battery also demonstrates good practical performance.