Multihierarchical Structure of Hybridized Phosphates Anchored on Reduced Graphene Oxide for High Power Hybrid Energy Storage Devices

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A multihierarchical structure with (NH 4 )(Ni, Co)PO 4 ·0.67H 2 O microplatelets and (Ni, Co) 3 (PO 4 ) 2 ·8H 2 O ultrathin nanopieces anchored on reduced graphene oxide (NCNP/RGO) is synthesized via a mild hydrothermal approach. This unique interface-rich structure is suitable for a high power energy storage device by providing efficient pathways for both electronic conduction and ionic transportation, which are effective ways to improve the electrochemical performance. Specifically, a specific capacity of 993 F g –1 is obtained in the three-electrode measurement, with ultrahigh capacity retention of 81.2% (807 F g –1 ) from 0.5 to 32 A g –1 . The hybrid device constructed with the as-prepared NCNP/RGO as anode and a hierarchical porous carbon (HPC) as cathode offers a very superior energy density of 42.1 Wh kg –1 at a power density of 73 W kg –1, which remains 32 Wh kg –1 at 14 kW kg –1 . Meanwhile, the as-prepared hybrid capacitor exhibits a remarkable cycling stability (96.5% capacitance retention after 10 000 cycles). The capacity contribution of capacitive behavior for the hybrid device is analyzed as 91.1% at 25 mV s –1 .