Unraveling the energy storage mechanism in nanostructured SnHPO3 anode through advanced operando and ex-situ characterizations

Nanostructured tin phosphite SnHPO3 was prepared via high-energy ball milling of hydrothermally synthesized powder to investigate its potential as an anode material for lithium-ion batteries. The nanostructuration process significantly reduced particle and crystallite sizes without altering the crystallographic structure or chemical composition. Electrochemical tests demonstrate that nanostructuration lowers kinetic barriers for lithium-ion transport, enabling the complete conversion of SnHPO3 into Sn nanoparticles, thereby facilitating its full lithiation. This results in a high reversible specific capacity of 645 mAh g−1 at 0.2 C over 70 cycles, with a coulombic efficiency exceeding 99 %. Operando X-ray diffraction, along with ex-situ TEM and XPS characterizations, reveals the complex interplay between morphological features and electrochemical storage mechanisms. The obtained high capacity is not only attributed to the classical LixSn alloys formation but also to a surface-related supercapacitive contribution and a potential overoxidation of Sn during delithiation. [Display omitted] •Lithiation mechanism of the nanostructured SnHPO3 anode for Li-ion batteries was thoroughly investigated.•Nanostructured SnHPO3 demonstrates a twofold increase in capacity compared to its micrometric counterpart.•Nanostructuration enables the complete conversion of SnHPO3 to ~8 nm Sn nanoparticles embedded within a phosphite matrix.