Influence of alkali ion doping on the electrochemical performances of tin-based composite materials

In this paper, we report an investigation of three tin-based composite materials as negative electrodes for lithium-ion batteries. Theses composites were synthesized by solid state reaction from dispersion of micrometric tin into BPO4, Li-doped BPO4 (LiBPO) and Na-substituted BPO4 (NaBPO) matrix, respectively. We have investigated more particularly the influence of the two alkaline ions (Li+, Na+) introduced into the matrix on electrochemical performances. The morphology of powders was observed by SEM and the composition studied by EDX analysis. The conductivity measurements showed that the modified BPO4 matrixes (Li or Na) exhibit improved conductivity (σRT = 2 × 10−11 S cm−1 for NaBPO). A focus of our interest was to relate the nature and structural composition of the composite interface between active tin and inactive matrix to the irreversible capacity in this type of composite materials. The electrochemical analysis shows a decrease of the irreversible capacity for the composite based on modified matrixes (around 150 and 190 mAh g−1 for SnNaBPO and SnLiBPO, respectively) with respect to the reference composite SnBPO (245 mAh g−1).