Investigation of the lithiation mechanism of tin phosphite SnHPO3 as anode for Lithium-ion batteries

Abstract

Phosphite-based anodes are attracting increasing attention in energy storage, especially for lithium-ion technology, due to their distinctive structures and their good electrochemical performances. Herein, the lithiation mechanism of tin phosphite SnHPO3 as lithium anode was examined for the first time. SnHPO3 has been synthesized through a soft hydrothermal route. Its structure was characterized by X-ray diffraction, Fourier Transform Infrared spectroscopy and 31P Nuclear Magnetic Resonance spectroscopy techniques. The reaction mechanisms of lithiation-delithiation of SnHPO3 anode was conducted using operando X-ray diffraction, ex-situ X-ray and ex-situ Fourier Transform Infrared spectroscopy techniques at room temperature. Both in-situ and ex-situ measurements show that SnHPO3 undergoes a conversion mechanism. The lithiation-delithiation of tin phosphite took place in a complex redox reaction sequence, and the reversible electrochemical phenomenon exclusively occurs through the alloying of tin at a low potential. The lithiation of tin phosphite begins by partial degradation of its structure, signifying the start of the conversion process. Then, the phosphite matrix becomes amorphous. The reversible capacity of the system is governed by the lithium‑tin alloying de-alloying process, produced at low potential.