Sn-0.4BPO4 composite as a promising negative electrode for rechargeable lithium batteries

The structural and textural properties of a Sn-0.4BPO₄ composite material synthesized by ex situ dispersion of β-Sn in a BPO₄ matrix were investigated by using several complementary techniques to study the global order (XRD, TGA-DSC, SEM-XEDS) and the local order (FT-IR, ¹¹⁹Sn Mössbauer spectroscopy and X-ray absorption spectroscopy). The results reveal that the composite material consists of three main components: an electrochemically active species “Sn”, an inactive matrix “BPO₄”, and an amorphous Sn(II) borophosphate which acts as a link between the two former and which improves the cohesion of the composite. The electrochemical performances of the composite material were tested in Swagelok-type cells with metallic Li as counter-electrode. It shows a high reversible capacity of about 500 mAh g^?1 at a C/20 rate, and a very good stability under cycling even at very fast rates of C or C/1.3.