A Zn ion hybrid capacitor with enhanced energy density for anode-free

Abstract Aqueous zinc-based energy storage system plays an increasingly important role in the energy storage field because of the low cost, high safety, and high capacity. At present, zinc-based cells developed use excessive zinc, which increases volume and mass and sacrifices some energy density. The anode-free construction is realized by effective interface modification layer to address these issues. Nitrogen doped porous carbon nanocages modulation layer facilitates the uniform distribution of electric field, promote the uniform transport of zinc ions, further optimize nucleation and inhibit dendrite growth. This strategy can realize the homogeneous zinc nucleation and growth to obtain efficient and stable zinc plating/stripping. The Cu/NPCNs electrodes keep stable Zn plating/stripping of 100 cycles at large current density of 5 mA cm−2 and still maintain high CE (99%). Based on this anode-free foundation, an anode-free Zn ion capacitor exhibits high specific capacity of 106 mAh g-1 at 1 mA cm−2 and maintains high-capacity stability of 98% after 2000 cycles at 1 mA cm−2. The energy density of 101 Wh kg−1 is higher than that of the zinc-metal anode system. This anode-free design strategy promotes the further development of zinc-based energy storage systems with high energy density.