Understanding the pore structure evolution of polyethylene separator with dissipative particle dynamics simulation

Abstract The commercialized lithium‐ion battery separators are mass‐produced by mixing ultra‐high molecular weight polyethylene (UHMWPE) and paraffin oil (PO). The dissipative particle dynamics method is utilized to investigate the extrinsic factors (shear rate and cooling rate) and the intrinsic factors (the molecular chain length) on the microstructure of the UHMWPE‐PO mixture. For the mixture with UHMWPE possessing the same chain length, the high shear rate promoted a lower porosity (~28%) and smaller pores. In contrast, the slow shearing led to a high porosity (~40%) and larger pores. For the mixture with UHMWPE possessing short and long chains, the shear rate hardly affects the porosity and the pore size: the porosity was kept at ~30%, and the pore size was reduced by ~35% compared to the model with the same‐chain‐length UHMWPE. The cooling rate after shearing is the dominant factor in determining the porosity and pore size: the fast cooling raised the porosity by ~33% but hardly increased the pore size, while the slow cooling raised the porosity by ~74%, and the pore size by ~105%. The current study provided a deep understanding of the pore structure evolution in separator processing. Highlights The effects of processing parameters on the pore structures are numerically illustrated. MD simulation and rheometer measurement assist DPD interaction parameters calibration for UHMWPE and PO. The low shear rate leads to a higher porosity and pore size. At the high shear rate, short UHMWPE chains reduce porosity but do not increase pore size. The fast‐cooling process slightly increases the porosity while keeping the pore size.