Zinc dendrite suppression in aqueous electrolytes saturated with aliphatic carbon-rich polyether additive

We report the underlying mechanism(s) for Zinc (Zn) dendrite suppression in aqueous electrolytes saturated with carbon-rich polyethylene glycol dimethyl ether (PEGDME) additives. Density functional theory (DFT) predicts a favorable adsorption of PEGDME molecules onto the oxidized Zn metal electrode (ZnO) surface, which was experimentally verified by fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy further indicates that without the PEGDME blocking layer, Zn metal reacts with water leading to zinc hydroxide (Zn(OH)₂) formation. This results in a heterogeneous (i.e., mixed ZnO/Zn(OH)₂) interface. Heterogeneity in the interface is responsible for non-uniform plating and stripping of Zn, triggering dendritic growth. However, with the PEGDME coating, Zn(OH)₂ formation is mitigated, leading to a relatively uniform ZnO interface that is less prone to dendrite-related problems. DFT also predicted a preferential adsorption of Zn-ions present in the electrolyte onto the PEGDME coating boosting the local concentration of Zn²⁺ at the electrode surface. The easy availability of Zn-ions in the electrode's vicinity mitigates the diffusion limited aggregation of dendrites. Owing to the above reasons, Zn||Zn symmetric cells with ∼75 % and ∼94 % PEGDME demonstrated extended durability over 2,000 cycles, without dendrite-induced shorting. Moreover, Zn ||V₂O₅ full cells assembled with ∼75 % PEGDME present in the electrolyte showed promising performance achieving ∼82.6 % capacity retention over 1,200 cycles, while maintaining a coulombic efficiency close to ∼100 %. This is attributed to the multifaceted and vital role played by PEGDME in passivating the Zn metal surface, boosting the local Zn-ion concentration at the metal-water interface and in suppressing parasitic side-reactions.