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

As an alternative to lithium-ion batteries, Zn-based aqueous batteries feature non-flammable electrolyte, 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 electrolyte 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 intermediate changes Zn anode morphology over cycling. In this work, we report an ion-sieving carbon nanoshell coated ZnO nanoparticle anode, synthesized in a scalable way with controllable shell thickness, to solve the problems of passivation and dissolution simultaneously. The nano-sized 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 than Zn foil and bare ZnO nanoparticles. The deeply rechargeable Zn anode reported is an important step towards 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.