Assembly of Multifold Helical Polyoxometalate-Based Metal-Organic Frameworks as Anode Materials in Lithium-Ion Batteries.

For exploring the multifold helical fabrication of polyoxometalate (POM)-based hybrid compounds, four POM-based crystalline compounds with different meso-helices, H3[Ag27(trz)16(H2O)6][SiW12O40]2·5H2O (1), H[Ag27(trz)16(H2O)4][PW12O40]2·2H2O (2), [Ag23(trz)14(H2O)2][HSiW12O40] (3), and [Ag23(trz)14(H2O)2][PW12O40] (4), were successfully isolated by using the delicate 1,2,3-triazole ligand and silver ions in this work. Crystal analysis reveals that compounds 1 and 2 and compounds 3 and 4 are isomorphous and display 2-/4-fold mixed meso-helices and simple 2-fold meso-helices, respectively. In addition, due to the reversible multielectron redox behavior and electron storage functions of POMs, compounds 1 and 3 were studied as anode materials in lithium-ion batteries (LIBs). Compounds 1 and 3 show very high lithiation capacities (1356 and 1140 mAh g-1, respectively) in the initial cycle, which are much higher than those of (NBu4)4[SiW12O40] and commercial graphite at the current density of 100 mA g-1. More importantly, both compounds also show good stable performance after 100 cycles.