The Use of UV/vis Absorption to Measure Diffusion Coefficients in LiPF₆ Electrolytic Solutions

This work describes the measurement of the diffusion coefficient in lithium-battery electrolytic solutions. We have adapted the method of restricted diffusion to measure diffusion coefficients of LiPF₆ in various solvents using ultraviolet/visible (UV/vis) absorption. The use of UV/vis absorption provides a simple alternative to more arduous experiments and reduces the potential for experimental error due to side reactions. The diffusion coefficient was seen to decrease with concentration according to the following:

D = 3.018 x 10^-5 exp(-0.357c) for LiPF₆ in acetonitrile and D = 2.582 x 10^-5 exp(-2.856c) for LiPF₆ in ethylene carbonate/diethyl carbonate (with D in cm²s and c in mol/L). This technique may be useful for any liquid solution with a UV-active species of D greater than 10^-6 cm²s.