Towards an atomistic understanding of hard carbon electrode materials and sodium behaviors

Hard carbons are the primary candidate for the anode of next-generation sodium-ion batteries for large-scale energy storage, but the atomic scale cognition of materials and sodium storage behavior is still unclear. Combined annealing-MD simulations and Arrhenius framework, a series of large-scale molecular models for hard carbon anode were constructed to reproduce the main experimental characteristics at different annealing temperatures. From the simulations, we obtained the representative structural features and the detailed transformation information of each annealing stage at the atomic scale. Based on these reliable models, we used ReaxFF-MD to examine sodium behavior in hard carbon anodes with varying nanostructures. It was found that hard carbon will yield the highest ion diffusion rates of 1.99 × 10−10 m2/s and the minimum volume swelling of 7.4 % at low heat treatment temperature (1500 K). Finally, several optimization design strategies were proposed. These findings provide atomic insight into the future design and development of hard carbons for SIBs.