Keplerate-type polyoxometalate {MoFe} nanoparticle anodes for high-energy lithium-ion batteries

Li-ion batteries (LIBs), with high energy densities, have been explored in recent years. Polyoxometalates (POMs) have been proposed as promising anodes, with high capacity. Herein, we report a Keplerate-type POM [{Mo6O19}⊂{Mo72Fe30O254 (CH3COO)12(H2O)96}]·150H2O ({Mo72Fe30}) nanoparticle as a high energy anode material for LIBs for the first time. Employing synchrotron radiation X-rays, we conducted in operando and ex situ measurements to investigate the charge storage mechanisms of {Mo72Fe30}. The in operando X-ray absorption near edge structure (XANES) reveals that a single {Mo72Fe30} molecule can store 377 electrons. The {Mo72Fe30} anode exhibits a high capacity of ∼1250 mA h g-1 at 100 mA g-1, with 92% capacity retention after 100 cycles, and it also demonstrates an excellent rate performance (868 mA h g-1 at 2000 mA g-1). Li-ions can react with {Mo72Fe30} through surface-capacitive reactions and diffusion processes, and the Li-ion diffusion coefficient of {Mo72Fe30} is up to 10-10 cm2 s-1, resulting in high rate performance. Furthermore, a full-cell utilizing {Mo72Fe30} as an anode and LiFePO4 as a cathode was assembled, and it delivered a high energy density of 258 W h kg-1, which successfully demonstrates that {Mo72Fe30} is a promising anode material for LIB applications. This journal is