Highly reversible and long-lived zinc anode assisted by polymer-based hydrophilic coating

Rechargeable aqueous zinc-ion batteries (AZIBs) are the most promising candidates for the energy storage due to their high safety, rich resources, and large specific capacity. However, AZIBs using neutral or slightly acidic electrolytes still face side effects and zinc dendrites on the anode surface. To stabilize the Zn anode, a chemically stable and multi-functional coating of polyvinylidene fluoride (PVDF) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was prepared on the Zn surface. The anhydride groups in 6FDA can improve the hydrophilicity, promoting the migration of zinc ions. Besides, PVDF is compatible with 6FDA because of the presence of organic F-containing groups, which can also effectively reduce the nucleation overpotential and exhibit the dendrite-free Zn deposition/stripping. The PVDF/6FDA@Zn symmetric cell can cycle for 5000 h at a current density of 0.5 mA·cm⁻², maintaining the extremely low polarization voltage and overpotential of 28 and 8 mV, respectively. The PVDF/6FDA@Zn∥MnO₂ full cell can remain a specific capacity of ∼90 mAh·g⁻¹ after 2000 cycles at 1.5 A·g⁻¹. This simple method achieves a reversible Zn anode, providing an inspiring strategy for ultra-long-cycle AZIBs.