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Sn x (Ca 0.05 B 0.975 P 0.975 O 3.95 ) 1− x /C composites as anode material for Li-ion batteries, with x =0.83 and x =0.71 were synthesized by a facile route including cellulose as carbon source. The composites were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and 119 Sn Mössbauer spectroscopy. In the latter case, different tin phases were found in the composite including the Sn II -based amorphous interface between metallic tin and borophosphate particles that improves the dispersion of the active species. The best electrochemical performances were obtained for x =0.71 that were further improved by ball-milled the composite with a small amount of carbon black. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB0.6P0.4O2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn0.72[BPO4]0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO4 matrix. The electrochemical responses of ATCO and Sn0.72[BPO4]0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530mAhg−1, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by 119Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous SnII composite oxide and shows that in the case of Sn0.72[BPO4]0.28, the surface of the tin clusters is mainly formed by SnII in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn0. The determination of the recoilless free fractions f (Lamb–Mössbauer factors) leads to the effective fraction of both Sn0 and SnII species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn x [BPO4]1− x composite materials (0.17