Ni–Sn intermetallics as an efficient buffering matrix of Si anodes in Li-ion batteries

Abstract

For a successful integration of silicon in high-capacity anodes of Li-ion batteries, its intrinsic capacity decay on cycling due to severe volume swelling should be minimized. In this work, Ni–Sn intermetallics are studied as a buffering matrix during reversible lithiation of Si-based anodes. Si/Ni–Sn composites have been synthesized by mechanical milling using C and Al as process control agents. Ni₃Sn₄ and Ni₃Sn₂ intermetallics and their bi-phasic mixture were used as constituents of the buffering matrix. The structure, composition and morphology of the composites have been analyzed by X-ray diffraction (XRD), ¹¹⁹Sn Transmission Mössbauer Spectroscopy (TMS) and scanning electron microscopy (SEM). They consist of ∼150 nm Si nanoparticles embedded in a multi-phase matrix, the nanostructuration of which improves on increasing the Ni₃Sn₄ amount. The electrochemical properties of the composites were analyzed by galvanostatic cycling in half-cells. Best results for practical applications are found for the bi-phasic matrix Ni₃Sn₄–Ni₃Sn₂ in which Ni₃Sn₄ is electrochemically active while Ni₃Sn₂ is inactive. Low capacity loss, 0.04% per cycle, and high coulombic efficiency, 99.6%, were obtained over 200 cycles while maintaining a high reversible capacity above 500 mA h g⁻¹ at moderate regime C/5.