In Situ Double Probe Beam Deflection Estimating Concentration Profiles of Battery Electrolytes

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 −1 CuSO 4 and ZnSO 4 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 CuSO 4 showed a systematic trend of increased response delay and decreased deflection with increased distance from the electrode, ZnSO 4 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.