A molten salt metallothermic reduction strategy is developed for preparing phosphorus (P) or phosphides controllably at low temperature, which is simple, energy-saving, and easy to scale up. Typically, synthesis of spongelike porous amorphous P (a-P) is realized through reduction of PCl5 with Zn (or Al) at 50 °C assisted by AlCl3. It is demonstrated that an adduct salt PCl5·AlCl3 composed of PCl4+ and AlCl4- ions with a low melting point below 50 °C is formed from covalent salts PCl5 and AlCl3. This system is also suitable for producing nanostructured phosphides by adding corresponding transition-metal (Co, Fe, and Cu) chlorides even at 50 °C. As a Li storage anode, the as-prepared a-P exhibits a capacity of 1605 mA h g-1 at 0.2 C, a good rate capability of 1283 mA h g-1 at 10 C, and a long-term cycling stability of 1082 mA h g-1 after 200 cycles. Additionally, the Na-/K-ion storage performance is investigated systematically.
Keywords: addition compound; alkali metal-ion batteries; amorphous P; molten salt; phosphides.