A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB 0.6 P 0.4 O 2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn 0.72 [BPO 4 ] 0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO 4 matrix. The electrochemical responses of ATCO and Sn 0.72 [BPO 4 ] 0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g À 1 , respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by 119 Sn M össbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn II composite oxide and shows that in the case of Sn 0.72 [BPO 4 ] 0.28 , the surface of the tin clusters is mainly formed by Sn II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn 0 . The determination of the recoilless free fractions f (Lamb-M össbauer factors) leads to the effective fraction of both Sn 0 and Sn II 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 [BPO 4 ] 1 À x composite materials (0.17 o xo 0.91). The cell using the compound Sn 0.72 [BPO 4 ] 0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g À 1 at C/5 rate).