Promotional role of B₂O₃ in enhancing hollow SnO ₂ anode performance for Li-ion batteries

A composite anode consisting of hollow SnO₂ microspheres covered by glass-like B₂O₃ layers was prepared via a combined hydrothermal-impregnation method, which results in much improved electrochemical performance in lithium ion batteries, relative to pristine SnO₂ anodes. The cycling and rate capabilities of the SnO₂-B ₂O₃ composite anodes were investigated as a function of B₂O₃ content. The balance between increased electron-acceptor effect and compromised electronic conductivity due to addition of B₂O₃ is maximized around 20 wt% B₂O ₃ loading. The best performing SnO₂-B₂O ₃ composite anode exhibits a specific capacity of 622.7 mAh g ^-1 up to 160 cycles, and is able to maintain a capacity above 528.6 mAh g^-1 at rate of 5C. These enhanced performance characteristics are attributed to the unique composite structures consisting of the hollow SnO ₂ cores and the B₂O₃ buffer layers, which likely are beneficial for reducing the overall volume changes. Importantly, the decreased charge transfer resistance and increased Li⁺ diffusion coefficient, resulting from B₂O₃ coating, lead to overall improvement of rate performance for the composite anodes. Such-fabricated composite structures are stable during the Li⁺ insertion/extraction, thereby promoting cycling stability.