NiP3: a promising negative electrode for Li- and Na-ion batteries

Abstract

Due to the abundance and low cost of sodium-containing precursors ambient temperature sodium ion batteries are promising for large scale grid storage. The low melting point of Na (97.7 °C) compared to 180.6 °C for Li represents a significant safety hazard for the use of Na metal anodes at ambient temperatures, which emphasizes the need for scientists and engineers to identify, design and develop new negative electrodes for Na-ion batteries. The identification of a suitable negative electrode is a crucial challenge for any further successful development of new cells, and to date efficient and competitive negative electrodes for NaB are still very rare. In this work we demonstrate that NiP₃ could be a good challenger for this purpose. NiP₃ based electrodes are evaluated as negative electrode materials for Li-ion batteries (LiB) and Na-ion batteries (NaB). The study of the reaction mechanism reveals the formation of a phase of composition close to Li₃P and Na₃P embedding Ni nanoparticles as the final reaction product after a full discharge. While the direct conversion of NiP₃ into Na₃P is identified for the reaction versus Na, it is still unclear whether an amorphous phase exists during the first discharge for the reaction versus Li before the conversion. Furthermore, thanks to the carboxymethyl cellulose/carbon black (CMC/CB) electrode formulation, the NiP₃ electrode possesses a very promising capacity with a reversible storage capacity higher than 1000 mA h g⁻¹ after 50 cycles for LiB and 900 mA h g⁻¹ after 15 cycles for NaB, which represents one of the highest capacities ever sustained in Na-ion batteries.