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 (TiPx) 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 TiP2 leads to superior redox kinetics and reduced polysulfide shuttling due to improved polysulfide adsorption ability. Meanwhile, at the anode, TiP2 acts as a lithiophilic seed in a three-dimensional carbonaceous host that can be lithiated to form a Li-TiP2/C composite. This composite alleviates the volume changes of lithium metal by utilizing TiP2 to form a more favorable solid–electrolyte interface. Full coin cells employing TiP2 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 TiP2 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.