Ion‐Sieving Carbon Nanoshells for Deeply Rechargeable Zn‐Based Aqueous Batteries

As an alternative to lithium‐ion batteries, Zn‐based aqueous batteries feature nonflammable electrolytes, high theoretical energy density, and abundant materials. However, a deeply rechargeable Zn anode in lean electrolyte configuration is still lacking. Different from the solid‐to‐solid reaction mechanism in lithium‐ion batteries, Zn anodes in alkaline electrolytes go through a solid‐solute‐solid mechanism (Zn‐Zn(OH)4 2−‐ZnO), which introduces two problems. First, discharge product ZnO on the surface prevents further reaction of Zn underneath, which leads to low utilization of active material and poor rechargeability. Second, soluble intermediates change Zn anode morphology over cycling. In this work, an ion‐sieving carbon nanoshell coated ZnO nanoparticle anode is reported, synthesized in a scalable way with controllable shell thickness, to solve the problems of passivation and dissolution simultaneously. The nanosized ZnO prevents passivation, while microporous carbon shell slows down Zn species dissolution. Under extremely harsh testing conditions (closed cell, lean electrolyte, no ZnO saturation), this Zn anode shows significantly improved performance compared to Zn foil and bare ZnO nanoparticles. The deeply rechargeable Zn anode reported is an important step toward practical high‐energy rechargeable aqueous batteries (e.g., Zn‐air batteries). And the ion‐sieving nanoshell concept demonstrated is potentially beneficial to other electrodes such as sulfur cathode for Li‐S batteries. Rechargeable aqueous batteries using Zn anodes can serve as an alternative to lithium‐ion batteries with a better safety and lower cost. Zn suffers from passivation and dissolution‐induced problems due to the soluble intermediate and insulating product. These problems are simultaneously solved by designing an ion‐sieving carbon nanoshell coated ZnO nanoparticle anode, which shows high performance in a realistic working conditions.