Unraveling the Lithium/Sodium-Ion Diffusion Mechanism in Alloyed Phosphides for Lithium/Sodium Storage

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Phosphorus is a promising candidate for high energy density lithium/sodium-ion batteries due to its high capacity. However, the dynamics of carrier shuttling in the alloyed phosphorus anode are quite complex due to the multiple phase transitions during the lithiation/sodiation process. Here, we identify Li(Na)P and Li(Na) 3 P as stable phases from both ex situ and in situ X-ray diffraction measurements of black phosphorus (BP). Our results regarding the dynamics of lithiation/sodiation indicate that the entire reaction could be limited by sluggish lithium/sodium ion migration in the stable phases, Li(Na)P and Li(Na) 3 P, supported by ab initio molecular dynamics (AIMD) simulations. Additionally, Li 3 P has higher activation energies and correspondingly lower ion conductivity than LiP, making it the key role in the whole dynamics of lithium-ion transport during the lithiation process. In comparison, the dynamics of sodiation exhibit quite active behavior due to lower energy barriers for sodium-ion transport. However, the electrochemical performance of sodium-ion batteries suffers from a large charge transfer resistance at the electrode/electrolyte interface due to the generation of corrosive Na 3 P. Therefore, the construction of a stable solid electrolyte interphase (SEI) is crucial to improving the electrochemical performance of phosphorus anodes.

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