Vanadium-based polyoxometalate as electron/ion sponge for lithium-ion storage

Abstract Polyoxometalates with multiple redox reactions have been reported as electron/ion sponges for lithium-ion storage applications. Here we introduce a vanadium-based polyoxometalate, Na 7 H 2 [PV 14 O 42 ] (NPV), as an anode material for Lithium-ion batteries (LIBs). NPV exhibits a high reversible capacity up to 687 mA h g −1  at 100 mA g −1 with a good capacity retention of ~80% after 150 cycles. In operando synchrotron X-ray absorption near edge structure reveals the change of the valences of vanadium from V 4+ to V 1.87+ , indicating that it can transfer at least 30 electrons per molecule which leads to high capacity. In operando synchrotron X-ray diffraction confirms the crystal structure of NPV electrode converts to amorphous during charge/discharge processes. Therefore, the charge storage mechanism of NPV could be further proposed that Li ions insert into amorphous NPV electrode continuously and react with [PV 14 O 42 ] 9- molecules, and [PV 14 O 42 ] 9- is like an electron/ion sponge which can store at least 30 electrons.