Single atom vacancy engineering with highly reversible N4 sites enable ultra-low overpotential for durable zinc-ion supercapacitors

Zn metal has delivered great promise as anode material for grid -level energy storage yet is challenged by dendrite growth. However, the overpotential, another important factor for energy conversion efficiency has been often overlooked, making the design of zincophilic substrates to guide the uniform deposition of Zn2+ with low overpotential are full of challenges. Here, inspired by density functional theory (DFT) that the N4 sites created by single atom vacancy with large binding energy with Zn2+ can induce the Zn2+ to form Zn-N4 bonds, according well with the electrochemical results that the Zn2+ can be reintroduced back into the electrolyte, demonstrating that the process is highly reversible. Extended X-ray absorption fine structure (EXAFS) combined with electron paramagnetic resonance (EPR) analysis certified the coexistence of both stable Zn-N4 sites and cation vacancies with high density in single atom Zn supported on nitrogen doped carbon materials (SA-Zn/CN-1). Most impressively, the SA-Zn/CN-1@Zn anode exhibits remarkable cycling stability at 1 mA cm -2 for over 3300 h with the ultra -low overpotential of about 22 mV in symmetric cells and a considerable capacity retention of 82% after 10000 cycles in capacitors assembled with active carbon. In a word, this work suggests a new approach to inhibit the growth of zinc dendrites with low overpotential through high reversible N4 sites provided by single atom vacancy engineering, which may be extended to inhibit other metal dendrites in the future.