Effect of functionalization on the interface transfer properties of CNT electrode in Li-air batteries by mesoscopic simulations

Li-air batteries have ultra-high theoretical capacity, but the actual discharge performance is not ideal. The morphology constraint formed by the cathode material in the electrolyte atmosphere is one of the factors affecting the transport performance of reactants. Coarse-grained simulation based on mesoscopic scale has inherent advantages in the study of system morphology and mass transfer characteristics by virtue of large spatial and temporal scales. Here, a polarizable water solvent coarse-grained model and carbon nanotube (CNT) pore coarse-grained model were constructed. The dynamic processes at the interface composed of CNT electrodes, different hydrophilic-functionalized CNT electrodes, and aqueous electrolytes were investigated by coarse-grain molecular dynamics (CGMD) simulations. The distribution and morphology of different functionalized CNTs, as well as the system and internal and external transport properties of the tube, were analyzed from the mesoscopic scale. The results show that CNTs can form a hydrophobic phase in aqueous electrolytes, and at the same time form a solvent phase that can provide favorable conditions for ion transport. By adding hydrophilic functional groups and uniform modification, the hydrophobic aggregation can be significantly improved, and the transport delay of CNTs to oxygen in the electrolyte can be weakened. The obtained simulation results of Li + and oxygen diffusion coefficients are consistent with the microscopic simulation results and experimental data. In addition, the optimal material transport condition of the composite cathode is obtained when the mass ratio of uniformly functionalized CNT to hydrophobic CNT is 1/3. Moreover, the transport within the CNT tube has a higher transport efficiency in a single direction. This study is of great significance for analyzing the mesoscopic morphology and mass transfer characteristics of oxygen electrodes in Li-air batteries in aqueous electrolytes.