Self-organization towards complex multi-fold meso-helices in the structures of Wells–Dawson polyoxometalate-based hybrid materials for lithium-ion batteries

Abstract

We utilised the rich coordination character of Wells–Dawson polyoxometalates (POMs) to explore the higher-level helical conformation of hybrids. Herein, two compounds, [Ag₂₆(Trz)₁₆(OH)₄][P₂W₁₈O₆₂] (1) and Na[Ag₁₆(Trz)₉(H₂O)₄][P₂W₁₈O₆₂]·H₂O (2) (Trz = 1,2,3 triazole), with multi-fold meso-helices were successfully isolated. Both 1 and 2 displayed two different types of four-fold meso-helices, which are composed of POMs and organic–metal subunits. The interesting thing is that the four-fold helixes of 2 sequentially evolve into the most complex eight-fold meso-helices by sharing the building blocks. In addition, the multi-chelate patterns of Wells–Dawson POMs in 2 represent the highest coordination numbers to date, which dominates the evolution from four-fold to eight-fold meso-helices. For the first time, the Wells–Dawson POMs-based hybrids 1 and 2 have been used as anode materials in lithium-ion batteries (LIBs). The initial specific capacities of 1077 mA h g⁻¹ for 1 and 1094 mA h g⁻¹ for 2 were much higher than those of (NBu₄)₆[P₂W₁₈O₆₂] and commercial graphite as reference anodes at a current density of 100 mA cm⁻². Also, both of them showed stable performance after 100 cycles.