Mechanism Understanding of Sodium Penetration into Anthracite Cathodes: A Perspective from Diffusion Coefficients

Sodium penetration into carbon cathodes is an important cause of cell failure and efficiency loss, but it is a formidable task to unravel the detailed mechanism experimentally. Combined with MD simulation and DFT calculation, several diffusion coefficients were acquired to quantitatively analyze the behaviors of sodium penetration for the first time. Especially, the transport diffusion coefficient of sodium vapor in the large-scale realistic anthracite cathode model was calculated as 6.132 * 10−10 m2/s, which was in outstanding agreement with experimental results. Owing to lower diffusion energy barrier, sodium was found to migrate faster along the grain boundaries than the other two solid diffusion pathways. The striking difference of corresponding diffusion coefficients in the order of magnitude indicated that sodium may migrate predominantly by vapor migration, rather than through solid diffusion, at least in anthracite cathodes with high porosity. This fundamental research would contribute to the understanding of sodium penetration mechanism and the optimization of cathode industry in the future.