Multiplex measurement of diffusion in zinc battery electrolytes from microfluidics using Raman microspectroscopy

Rechargeable zinc batteries have emerged as an inexpensive and safe post-lithium-ion battery technology and have received increasing research interest. Developing suitable electrolytes and understanding their transport properties lie at the heart of successful zinc battery technologies as the battery behaviour is a strong function of ion transport in the electrolytes. To accelerate the research and development process, herein we demonstrate a low-cost and high-throughput approach to measure the diffusion in zinc electrolytes at different concentrations simultaneously. The new approach combines Raman microspectroscopy and a multiplexed microfluidic chip with integrated micromixers, concentration gradient generators and a Y-sensor array. Aqueous-based zinc sulphate electrolytes, widely used in zinc batteries, were used for a proof-of-concept. The measured diffusion coefficients for different electrolyte concentrations show good agreement with literature values. With four electrolyte samples in this study, the developed approach requires minimum 0.5 mL of the electrolyte solutions and 30 mins, which is over ten times faster than a typical diffusion measurement with the conventional electrochemical approach in restricted-diffusion cells. The microfluidic chip is readily scalable to further increase the throughput, and can be extended to for use of measuring different (i.e. organic and aqueous) and even mixtures of electrolytes (i.e. ethylene carbonate and dimethyl carbonate) as well as salts (Li+, Na+, Mg2+, etc.).