Using coarse-grain MD to study the trade-off between surface area and mass transport in aqueous Li-O2 battery using functionalized CNT

The discharge performance of lithium-oxygen battery with ultrahigh theoretical capacity is not satisfactory, and its mass transfer process is restricted by many factors such as cathode structure and hydrophilic/hydrophobic properties. Here, the mass transfer process at the interface composed of hydrophobic carbon nanotubes (CNTs) electrode, hydrophilic carboxylic carbon nanotubes (COOH-CNTs) electrode, composite electrode and aqueous electrolyte was studied by coarse-grain molecular dynamics (CGMD) simulation. The mesoscopic scale simulation method enabled this study to discuss the hydrophilicity/hydrophobicity of the two-phase interface on the cathode side in order to improve the mass transfer and diffusion of reactants. The morphology of hydrophobic/hydrophilic electrode in aqueous electrolyte and the mass transfer conditions of reactants under different hydrophilic conditions were analyzed. The results showed that hydrophobic CNTs exhibited aggregation behavior and formed pore channels in aqueous electrolyte, which was conducive to the transport of ions and dissolved oxygen, while hydrophilic COOH-CNTs had stronger dispersion under aqueous electrolyte conditions, which could provide more reaction sites. Under certain hydrophobic conditions, non-polar force had cutoff effect on the diffusion of dissolved oxygen. The simulation results of electrolyte density showed good consistency with the experimental data, and the oxygen diffusion coefficient obtained was also consistent with the microscopic simulation results. This study was of great significance for the analysis of the mesoscopic morphology and mass transfer characteristics of the oxygen electrode during the charging and discharging process of lithium-oxygen battery.