Mitigating the interfacial concentration gradient by negatively charged quantum dots toward dendrite-free Zn anodes

Aqueous zinc (Zn) batteries have shown great promise in energy storage systems as an intrinsically safe battery configuration. However, Zn dendrite and side reactions may impede their practical application. Here, we propose to mitigate interfacial concentration gradient by introducing N, S-doped carbon quantum dots (NSQDs) as an additive to achieve uniform Zn deposition. The dangling oxygen-containing groups of the NSQDs would be reduced by a Zn foil, thus interacting with the oxidized Zn2+ to form Zn-O bonds on the Zn surface. The formed NSQD layer provides abundant nucleation sites for Zn ions pre-seeding. Meantime, the NSQD layer in negative charge decreases the ion concentration gradient and uniformizes the electric field distribution near the Zn-electrolyte interfaces, facilitating dendrite-free Zn deposition, which is well evidenced by finite simulation results. Together with a decreased interfacial concentration gradient, the Zn metal anode exhibits good rate performances (20 mA cm−2 for nearly 6000 cycles). In addition, the assembled pouch full cell exhibits excellent cycling stability, and 81% of capacity retention is achieved after 250 cycles. This work not only offers a simple approach to modulate the interfacial concentration gradient for uniform Zn deposition but also paves the way for a practical dendrite-free aqueous Zn battery.