Self-assembled three-dimensional graphene/polyaniline/polyoxometalate hybrid as cathode for improved rechargeable lithium ion batteries

The energy crisis is currently a major concern worldwide due to the limited natural resources. Accordingly, lithium-ion batteries (LIBs) are in the focus of forefront energy storage investigations in our 21st century. Traditional lithium-insertion compounds for cathode materials, such as LiCoO2, LiMn2O4, LiNiO2 and LiFePO4, have been highly successful but they face serious limitations in energy storage density and production cost associated with their use. Therefore, the design of novel molecular cluster batteries (MCBs) as the next-generation energy storage device is an extremely important and hot topic of current research. Here, we first report preparation of zero-dimensional (OD) polyaniline/polyoxometalates [PW12O40]3− (PANI/PW12) nanospheres, and then have successfully embedded PANI/PW12 nanospheres into three-dimensional (3D) graphene sponge to construct a novel 3D graphene/polyaniline/polyoxometalates hybrid ([email protected]/PW12) as new cathode material in LIBs. The as-prepared [email protected]/PW12 hybrid in half-cell exhibits extraordinary electrochemical performances with high specific capacity (around 285 mAh g−1 at 50 mA g−1), excellent rate capability (140 mAh g−1 at 2 A g−1), and outstanding cycling stability (capacity fade rate of 0.028% per cycle even after 1000 cycles at 2 A g−1), representing the best performance for long-cycle POMs-based cathode in LIBs to date. Furthermore, a [email protected]/PW12-C lithium ion full-cell is first fabricated with an initial discharge specific capacity of 145 mAh g−1 at 2 A g−1, and then shows excellent cycling stability with a capacity decay rate of 0.035% per cycle over 1000 cycles at 2 A g−1. Importantly, the discharge and degradation mechanisms of [email protected]/PW12 cathode in LIBs are further deeply investigated. The electron-transfer (ET) from reduced PANI polymer to PW12 polyanion as well as the “electron reservoir” model on PW12 molecule both contribute to the high electroactivity. This study sheds thus new lights to the design of new generation electrode materials for lithium-ion batteries.