Identification of carbon-wrapped Bi₅Nb₃O₁₅ as a viable intercalation/alloying high-performance lithium storage material

Bi-based transition metal oxide (Bi₅Nb₃O₁₅) has become a highly hopeful anode material for lithium-ion batteries (LIBs) due to its large theoretical capacity and affordable availability. Unfortunately, poor conductivity, as well as volume expansion and pulverization during repeated reactions will result in bad specific capacity and inferior cycling stability. Hence, Bi₅Nb₃O₁₅@C anode materials for LIBs were successfully synthesized using sucrose as a carbon source through a two-step high-temperature solid-phase method. Physical characterizations and electrochemical tests suggest that the highly conductive carbon shell derived from sucrose provides fast channels for Li⁺ transport and greatly reduces the charge transfer resistance. Moreover, ex situ scanning electron microscopy (SEM) indicates that the presence of carbon effectively suppresses the aggregation and pulverization of Bi₅Nb₃O₁₅ particles in the reaction process, effectively ensuring the integrity of Bi₅Nb₃O₁₅ particles. Benefiting from the above merits, the C-modified Bi₅Nb₃O₁₅, especially Bi₅Nb₃O₁₅@8%C (BNO-C3), holds charge capacity of 414.6 and 281.4 mAh·g⁻¹ at 0.1 and 0.5 A·g⁻¹, respectively. Additionally, the high specific capacity of 379.5 mAh·g⁻¹ is much greater than that of the bare Bi₅Nb₃O₁₅ (only 158.7 mAh·g⁻¹) after 200 cycles. Importantly, cyclic voltammetry (CV) combined with ex situ X-ray diffraction (XRD) confirms the conversion reaction between Bi₅Nb₃O₁₅ and Bi during cycling. This work provides a method for suppressing volume expansion and pulverization during cycling of Bi-based transition metal oxides and constructing high-performance LIBs anode materials.