Bipyridine carboxylic acid as a high-performance anode material for lithium- and sodium-ion batteries

Commercial lithium-ion batteries with carbon-based anodes exhibit low specific capacities and pose potential safety risks of lithium plating. As possible alternatives, conjugated carboxylic acid-based electrode materials have attracted extensive attention owing to their suitable discharge potential, low solubility in electrolytes, and low-cost reproducibility. However, their theoretical capacities are limited by the number of active sites. In this paper, we introduce 2,2′-bipyridine-5,5′-dicarboxylic acid (H2bpy) as a new anode material demonstrating high specific capacity, good cycle stability, and remarkable rate performance in both lithium- and sodium-ion batteries. In particular, H2bpy possesses an ultrahigh initial capacity of lithium-ion battery of 1200 mAh g−1 at a current density of 200 mA•g−1, and the specific capacity can maintain 550 mAh•g−1 after 100 cycles. Whereas the sodium-ion battery retains a specific capacity of 258 mAh•g−1 under the same conditions. We find, through density functional theory analysis, that the superior performance is due to the molecular structure and stacking form of H2bpy. Furthermore, we perform an ex situ spectroscopic analysis and find that the H2bpy electrode has good electrochemical stability. These findings suggest that bipyridine carboxylic acids can effectively broaden the application of heterocyclic carboxylic acids as anode materials.