High-performance lithium storage anode: Polypyrrole-coated microrods BiSBr with conversion-alloying dual mechanism

The construction of an anode material with a conversion-alloying dual mechanism is an efficient way to develop high energy density lithium-ion batteries (LIBs). Here, we report a novel conversion-alloying dual mechanism anode material of BiSBr for the first time, which significantly improves the efficient lithium storage. Owing to its unique open ribbon structure, BiSBr possesses a high Li⁺ diffusion and electrical conductivity of 141 S cm⁻¹ along the c-axis. In-situ X-ray diffraction and ex-situ transmission electron microscopy analyses verify that Li-ion intercalation/deintercalation proceeds via both conversion and alloying/dealloying reactions, enabling a volumetric capacity of 4231 mAh cm⁻³ and a theoretical specific capacity of 644 mAh g⁻¹ with an average working potential as low as 0.6 V. To tackle the problems of polysulfide dissolution and volumetric expansion, BiSBr nanorods were intimately encapsulated in flexible polypyrrole (PPy) shell to fabricate BiSBr-PPy core–shell composite, which demonstrates three times higher than that of BiSBr with a reversible capacity as high as 634 mAh g⁻¹ at 100 mA g⁻¹, maintaining 98 % theoretical specific capacity after 460 cycles. This work provides a feasible anode material with conversion-alloying dual mechanism that can be enhanced for high-performance lithium storage by polypyrrole coating.