Zinc Electrode Cycling in Deep Eutectic Solvent Electrolytes: An Electrochemical Study

Abstract

Among post-lithium ion battery technologies, rechargeable chemistries with Zn anodes bear notable technological promise owing to their high theoretical energy density, lower manufacturing cost, availability of raw materials and inherent safety. However, Zn anodes, when employed in aqueous electrolytes, suffer from hydrogen evolution, passivation, and shape changes. Alternative electrolytes can help tackle these issues, preserving the green and safe characteristics of aqueous-based ones. Deep eutectic solvents (DESs) are promising green and low-cost non-aqueous solvents for battery electrolytes. Specifically, the cycling of Zn anodes in DESs is expected to be reversible, chiefly owing to their dendrite-suppression capability. Nevertheless, apart from a few studies on Zn plating, insight into the cathodic–anodic electrochemistry of Zn in DESs is still very limited. In view of developing DES-based battery electrolytes, it is crucial to consider that a potential drawback might be their low ionic conductivity. Water molecules can be added to the eutectic mixtures by up to 40% to increase the diffusion coefficient of the electroactive species and lower the electrolyte viscosity without destroying the eutectic nature. In this study, we address the electrochemistry of Zn in two different hydrated DESs (ChU and ChEG with ~30% H2O). Fundamental electrokinetic and electrocrystallization studies based on cyclic voltammetry and chronoamperometry at different cathodic substrates are completed with a galvanostatic cycling test of Zn|Zn symmetric CR2032 coin cells, SEM imaging of electrodes and in situ SERS spectroscopy. This investigation concludes with the proposal of a specific DES/H2O/ZnSO4-based electrolyte that exhibits optimal functional performance, rationalized on the basis of fundamental electrochemical data, morphology evaluation and modeling of the cycling response.

Highly improved aqueous Zn‖LiMn2O4 hybrid-ion batteries using poly(ethylene glycol) and manganese sulfate as electrolyte additives

“…To verify the stability of the PEG-modied electrolytes, we also performed LSV tests by using Ti foil as the current collector in ZL and modied ZL electrolytes. 38 The results shown in Fig. S3 † conrm that the electrolytes with PEG additives are more stable than the conventional ZL.…”

Effect of Water on Zn Electrodeposition from a Deep Eutectic Solvent

“…Little has been looked into DES in the presence of water for metal deposition. 20 However, the effect of Zn speciation in the electrolyte and the change in speciation in presence of water and its relation to electrodeposition has not yet been investigated in detail. Understanding the correlation between Zn solvation, electrodeposition parameters and morphology is important for the use of DES based electrolytes in Zn electroplating with controlled morphology as well as for Zn based batteries where dendrite-free deposition is an important criterion.…”