The Efficient K Ion Storage of M2P2O7/C (M=Fe, Co, Ni) Anode Derived from Organic-Inorganic Phosphate Precursors

Graphical Novel structured M 2 P 2 O 7 /C (M=Fe, Co, Ni) nanoflake composites are prepared via an organic-phosphors precursor assisted solvothermal method and a post high temperature annealing process, which could deliver superior potassium storage performance. Metal phosphates have been widely explored in lithium ion batteries and sodium ion batteries owing to high theoretical capacities, mild toxicity and low cost. However, their potassium ion battery applications are less reported due to the limited conductivity and the slow diffusion kinetics. Considering these drawbacks, novel structured M 2 P 2 O 7 /C (M=Fe, Co, Ni) nanoflake composites are prepared through an organic-phosphors precursor-assisted solvothermal method and a subsequent high temperature annealing process. The designed Co 2 P 2 O 7 /C composite exhibits the highest rate capacity with 502 mAh g −1 at 0.1 A g −1 and good cyclability for 900 cycles at 1 A g −1 and 2 A g −1 when compared with Ni and Fe based composites. The superior electrochemical performance can be attributed to their unique nanoparticle-assembled nanoflake structure, which can afford enough active sites for K + intercalation. In addition, the robust pyrophosphate crystal structure and the in situ formed carbon composition also have positive effects on enhancing the long-term cycling performance and the electrode's conductivity. Finally, this organic-phosphors precursor induced simple approach can be applied for easy fabrication of other pyrophosphate/carbon hybrids as advanced electrodes.