Phosphorus boosts lithium-ion battery charge capacity

Using a solution-phase process to prepare red phosphorus in nanoparticle form, researchers in Taiwan have converted the inexpensive phosphorus allotrope from an electrochemically weak material to a highly promising one (Nano Lett. 2017, DOI: 10.1021/acs.nanolett.6b05081). The team, led by Hsing-Yu Tuan of National Tsing Hua University, demonstrated that the nanomaterial can be used to make lithium-ion-battery anodes with higher charge storage capacity than the graphite ones used commercially. Battery researchers have tried previously to take advantage of red phosphorus’s large theoretical charge capacity, which is roughly seven times as high as graphite’s. But phosphorus is a poor electrical conductor and swells drastically during lithiation cycles, causing anodes to crack. Blending phosphorus with carbon, which is a common approach, improves conductivity but dilutes the phosphorus, limiting the boost in charge capacity. So Tuan’s group formed iodine-doped red phosphorus nanoparticles by reacting PI₃ with ethylene glycol and cetyltrimethylammonium bromide. Pellets formed from the nanoparticles exhibit conductivities more than 10 billion times as high as that of commercial red phosphorus. Anodes made from the new material show an initial charge capacity that reaches red phosphorus’s theoretical value and falls slowly over hundreds of charge cycles.