“Electrodeposition is a versatile electrochemical process for the fabrication of metals/alloys and coatings of particulate and polymeric materials. The process also plays an important role in shortening microcircuits and battery-based electrochemical energy storage technologies. In commonly used Newtonian liquid electrolytes, the process is essentially unstable.
Electrodeposition is a versatile electrochemical process for the fabrication of metals/alloys and coatings of particulate and polymeric materials. The process also plays an important role in shortening microcircuits and battery-based electrochemical energy storage technologies. In commonly used Newtonian liquid electrolytes, the process is essentially unstable. Potential instability is associated with failure of microcircuits, dendrite formation on battery electrodes, and limiting conductance in ion-selective membranes. Therefore, it must be carefully studied in order to achieve stable and safe operation over a range of operating temperatures and current rates and multiple charge-discharge cycles.
Recently, Cornell University Lynden A. Archer’s (corresponding author) team found that viscoelastic electrolytes composed of semi-dilute solutions of very high-molecular-weight neutral polymers can suppress these instabilities through multiple mechanisms. The voltage window ΔV over which the electrolyte can operate without convective instability is shown to be significantly prolonged in viscoelastic electrolytes and satisfies the power-law function ΔV of the electrolytic viscosity η: η1/4. This power-law relationship is reproduced in the resistance to ion migration at the liquid/solid interface. After many experiments, it was observed that viscoelastic electrolytes enable stable electrodeposition of many metals, with the most profound effects on active metals such as sodium and lithium. Related results were published in Science Advances with the title “Stabilizing electrochemical interfaces in viscoelastic liquid electrolytes”.
Fig.1 Electrochemical properties of viscoelastic electrolytes
(A) IV curves of electrolytes with different polymer concentrations
(BD) Voltage versus time curves measured in electrolytes (B) without PMMA, (C) 2wt% PMMA and (D) 8wt% PMMA
(E) Average tracer particle velocity measured in optical lithium
(F) Average tracer particle velocity as a function of current density measured in control and viscoelastic liquid electrolytes
Figure 2 Physical properties of viscoelastic liquid electrolytes
(A) Frequency-dependent dynamic storage G’ (solid symbols) and loss G” of PMMA-EC/PC (v/v, 1:1)-1 M LiTFSI electrolyte as a function of polymer concentration
(B) Concentrations of zero shear viscosity and conductivity at 25°C
(C) Extended stability states in viscoelastic electrolytes as a function of electrolyte viscosity
(D) DC ionic conductivity of viscoelastic liquid electrolytes as a function of temperature
(E) Nyquist plots obtained from EIS measurements in electrolytes with different polymer concentrations
(F) ASR polymer concentration as a function of electrolyte viscosity for the electrolyte/Li interface
Fig. 3 Electrodeposition analysis of different metals in Newtonian and viscoelastic liquid electrolytes
(A) Average Li dendrite tip height as a function of time
(B) Average sodium dendrite tip height as a function of time
(C) Comparison of average dendrite growth rates for different metals
This work finds that viscoelastic electrolytes consisting of semi-dilute solutions of very high molecular weight neutral polymers can suppress the above-mentioned instabilities through multiple mechanisms. This finding has important implications for high-energy electrochemical energy storage.
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