Keplerate-type polyoxometalate 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 [{Mo 6 O 19 }⊂{Mo 72 Fe 30 O 254 (CH 3 COO) 12 (H 2 O) 96 }]·150H 2 O ( {Mo 72 Fe 30 } ) 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 {Mo 72 Fe 30 } . The in operando X-ray absorption near edge structure (XANES) reveals that a single {Mo 72 Fe 30 } molecule can store 377 electrons. The {Mo 72 Fe 30 } 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 {Mo 72 Fe 30 } through surface-capacitive reactions and diffusion processes, and the Li-ion diffusion coefficient of {Mo 72 Fe 30 } is up to 10 −10 cm 2 s −1 , resulting in high rate performance. Furthermore, a full-cell utilizing {Mo 72 Fe 30 } as an anode and LiFePO 4 as a cathode was assembled, and it delivered a high energy density of 258 W h kg −1 , which successfully demonstrates that {Mo 72 Fe 30 } is a promising anode material for LIB applications. {Mo 72 Fe 30 } as an anode for lithium-ion batteries with a capacity of 1250 mA h g −1 , 92% retention up to the 100 th cycle, an excellent rate performance (868 mA h g −1 at 2 A g −1 ), and a high energy density of 258 W h kg −1 was studied by in operando measurements.