In Situ Investigations on the Structural and Morphological Changes of Metal Phosphides as Anode Materials in Lithium-Ion Batteries

The binary metal phosphides (MP, M = Cu, Fe, Sn, Sb) compounds are of great interest as negative electrode materials for high energy density lithium-ion batteries. However, the morphology and structural changes at the nanoscale upon electrochemical (de)lithiation are not clear yet, which require further detailed investigation. In situ neutron scattering technique is utilized to investigate and compare the morphological changes of copper phosphide and tin phosphide during the initial cycle. By coupling with scanning electron microscopy investigation, the surface activities of the electrodes at different electrochemical states, including the solid electrolyte interphase formation, swelling and recovering, cracks appearance, and stripping at nanoscale of the material particles are evaluated. With in situ X-ray diffraction measurement, the energy storage mechanism is further explained. This work demonstrates useful techniques to analyze the detailed fatigue mechanisms of the active material, and provides new insights of the nanostructural changes of anode materials reacting with lithium via conversion and alloying.