Scalable Metal Phosphides as a Dual-Function Catalyst and Lithium–Metal Stabilizer for Lithium–Sulfur Batteries

Although lithium–sulfur batteries are a promising approach for achieving a high energy density, their commercial viability is limited by poor sulfur redox kinetics, polysulfide shuttling, and lithium metal instability. To resolve these issues concurrently, we utilize titanium phosphides (TiP x ) as dual-function materials to catalyze the sulfur redox kinetics at the cathode and stabilize the lithium metal at the anode. Importantly, these phosphides are synthesized via a facile, highly scalable, one-step mechanochemical ball-milling process that does not generate toxic phosphine gas as a byproduct, making it more viable compared with traditional synthesis routes. At the cathode, we find that higher phosphorus contents in the phosphide as in TiP 2 leads to superior redox kinetics and reduced polysulfide shuttling due to improved polysulfide adsorption ability. Meanwhile, at the anode, TiP 2 acts as a lithiophilic seed in a three-dimensional carbonaceous host that can be lithiated to form a Li-TiP 2 /C composite. This composite alleviates the volume changes of lithium metal by utilizing TiP 2 to form a more favorable solid–electrolyte interface. Full coin cells employing TiP 2 in the cathode and anode were assembled with a sulfur loading of 4 mg cm –2 and a negative to positive capacity (N/P) ratio of 6. After 50 cycles, the TiP 2 full cells retain a higher capacity of 643 mA h g –1 compared to 422 mA h g –1 for the conventional cell, despite the higher N/P ratio of 12 for the conventional cell. Overall, we showcase the viability of employing metal phosphides as catalysts in practical lithium–sulfur batteries.