Effective Bidirectional Mott-Schottky Catalysts Derived from Spent LiFePO 4 Cathodes for Robust Lithium-Sulfur Batteries.

It is deemed as a tough yet profound project to comprehensively cope with a range of detrimental problems of lithium-sulfur batteries (LSBs), mainly pertaining to the shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur conversion. Herein, a Co2 P-Fe2 P@N-doped carbon (Co2 P-Fe2 P@NC) Mott-Schottky catalyst is introduced to enable bidirectionally stimulated sulfur conversion. This catalyst is prepared by simple carbothermal reduction of spent LiFePO4 cathode and LiCoO2 . The experimental and theoretical calculation results indicate that thanks to unique surface/interface properties derived from the Mott-Schottky effect, full anchoring of LiPSs, mediated Li2 S nucleation/dissolution, and bidirectionally expedited "solid⇌liquid⇌solid" kinetics can be harvested. Consequently, the S/Co2 P-Fe2 P@NC manifests high reversible capacity (1569.9 mAh g-1 ), superb rate response (808.9 mAh g-1 at 3C), and stable cycling (a low decay rate of 0.06% within 600 cycles at 3C). Moreover, desirable capacity (5.35 mAh cm-2 ) and cycle stability are still available under high sulfur loadings (4-5 mg cm-2 ) and lean electrolyte (8 µL mg-1 ) conditions. Furthermore, the as-proposed universal synthetic route can be extended to the preparation of other catalysts such as Mn2 P-Fe2 P@NC from spent LiFePO4 and MnO2 . This work unlocks the potential of carbothermal reduction phosphating to synthesize bidirectional catalysts for robust LSBs.