Amorphous Sn2P2O7, Sn2B2O5 and Sn2BPO6 anodes for lithium ion batteries

BPO4 was used as an intimate mixture of B2O3 and P2O5 to react with SnO to form amorphous Sn2BPO6, and to alleviate the need for ternary reactions between SnO and the volatile oxides P2O5 and B2O3. The BPO4-synthesised amorphous Sn2BPO6 performed better than previous attempts, and amorphous Sn2P2O7 and Sn2B2O5 prepared similarly for comparison; even under conditions of high current density (150 mA/g) and high discharge potential limit (1.4 V). In Sn2B2O5 the clustering of Sn was evident by X-ray diffraction after charging and discharging. The good performance of Sn2BPO6 is perhaps due to the robustness of the BPO64− framework in repeated cycling. The reversibility in charge and discharge reactions from the second cycle onwards can be rationalised by the usual alloying mechanism. Both the initial decomposition reactions of the glasses and the passivation of the anode surface by electrolyte solution components are believed to contribute to the observed first cycle irreversibility.