A molecular titration strategy: utilizing built-in electric field to detect lithium diffusion coefficient in LiFePO4

Abstract

Electrometric titration techniques have long been used to detect the Li+ diffusion coefficient of electrode materials. However, the influence of electrode additives, cell assembly methods, especially, inaccurate assessments of the reaction area often led to unreliable results. Here, we propose a molecular titration technique (MTT) to detect lithium diffusion coefficient (DLi) in LiFePO4. This MTT alleviates the tedious electrode preparation procedure, circumvents the influence of additives, amends the real reaction area errors, and shortens the testing time, making the testing more precise and efficient than the traditional titration techniques. In detail, [Fe(CN)6]3- solution is added into LiFePO4 solid dropwise, while potential change rate (rp) of the solution is recorded. Thereafter, a built-in electric field (BIEF) electron transferring model is established and the relationship between DLi and rp is formulated with Huggins-Weppner equation. Eventually, the de-lithiation diffusion coefficient of Li1-xFePO4 (1≤x≤0) is tested to be 1~8×10-15 cm2/s based on the recorded data and established formulations.