(Invited) Recycling Zn for Rechargeable Zinc-Ion Batteries

Aqueous energy storage devices require highly reversible Zn electrodes, but this has been impeded by challenges including dendrite growth, low efficiency, hydrogen evolution, and metal corrosion. Here, we have successfully fabricated a reversible Zn powder electrode via engineering the growth of zinc crystals in different solvents from spent Zn foils. Theoretical calculations demonstrate that the adsorption energy gap of different solvents on the (002) or (100) facet of Zn metal varies and that a larger energy gap favors a higher orientation of Zn (002) plane. Highly oriented Zn (002) powder exhibits horizontal deposition, corrosion resistance, faster kinetics, and longer life under deep discharge (60%) in symmetric cells compared with less-oriented Zn. Under practical conditions including low N/P ratios (1–3), high-loading cathodes (10–18 mg cm −2 ), and lean electrolyte (5–9 μL mg −1 ), highly (002)-oriented Zn powder-based batteries and supercapacitors demonstrate large capacity (∼3 mAh cm −2 ) and energy/power density (108 Wh kg −1 /2,317 W kg −1 ), holding promise for applications. And for the first time, we have also upcycled spent alkaline batteries into rechargeable Zn metal batteries through a simple thermal treatment of electrode waste. The regenerated Zn powder anode shows super-zincophilicity and low overpotentials even under fast rates (8 mA cm −2 ) and high depth-of-discharge (50 %), which can be ascribed to coating of hydroxyl-rich organic layer with abundant nucleation sites as well as high orientation of favorable (002) plane and induced horizontal plating behavior. The regenerated cathode composed of MnO 2 and MnOOH manifests enhanced capacity in comparison to pristine ones. Under a low negative-to-positive capacity ratio of 3.8 and high loading of ~10 mg cm −2 , the regenerated electrodes are paired to fabricate zinc metal batteries which demonstrate high energy and power densities (94 Wh kg −1 , 1349 W kg −1 ), holding potential for practical applications. Given the sustainable, low-cost, environmental-friendly, and value-added features, the strategy proposed here will open a new pathway toward battery recycling/upcycling.