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Abstract An in situ double probe beam deflection (PBD) technique has been developed using two laser beams to map the concentration profile of the diffusion layer in an electrochemical cell. A microscale moving upper probe and a fixed position secondary beam offer real-time concentration gradients to be profiled throughout the depth of the diffusion layer. The double PBD technique was used to plot concentration profiles for 0.1 mol/kg CuSO4 and ZnSO4 within a range of applied currents, showing increased magnitudes of gradients for higher currents. Both single and double beam PBD were explored, demonstrating the distance and time dependence of the developing concentration gradient. While CuSO4 showed a systematic trend of increased response delay and decreased deflection with increased distance from the electrode, ZnSO4 experienced some additional phenomena affecting the refractive index within the diffusion layer. The in situ double probe beam deflection was shown to be highly sensitive and offers future work in quantifying charge migration within this important region of the electrochemical cell. 

Abstract A thorough understanding of electrolyte transport properties is crucial in the development of alternative battery technology. As a key parameter, the diffusion coefficient offers important insights into the behavior of electrolytes, especially for fast charge of high-energy batteries. Existing methods of measurement are often limited by redox species or offer questionable accuracy due to side reactions and/or disruption of the diffusion profile. This work provides a novel optical method for measuring diffusion coefficients of liquid-phase concentrated battery electrolytes without electrochemical reactions. The method relies on the deflection of a refractive laser beam passing through an electrolyte of a minor concentration gradient in a triangular diffusion column. The diffusion coefficient, D, for a range of zinc sulfate electrolytes was successfully extracted by correlating the position of the laser beam to its concentration. Several other physicochemical properties of the same electrolytes are studied to correlate to the concentration-dependent diffusion coefficients, including viscosity, conductivity, and microstructure analysis based on vibrational spectroscopy (infrared and Raman). Also included is the future application of the triangular column for in situ electrochemical measurements.