Dependence of Separator Thickness on Li-Ion Battery Energy Density

High energy density lithium-ion batteries are urgently needed due to the rapid growth demands of electric vehicles, electronic devices, and grid energy storage devices. There is still significant opportunity to improve the energy density of existing state-of-the-art lithium-ion batteries by optimizing the separator thickness, which is usually ignored. Here, the dependence of battery gravimetric and volumetric energy densities on separator thickness has been quantitatively discussed in different type Li-ion batteries by calculations combined with experiments. With a decrease in separator thickness, the volumetric energy density is greatly improved. Meanwhile, the gravimetric energy densities are significantly improved as the electrolyte soaking in the separator is reduced. The gravimetric and volumetric energy densities of graphite (Gr) ∣ NCM523 cells enable to increase 11.5% and 29.7%, respectively, by reducing the thickness of separator from 25 μ m to 7 μ m. Furthermore, the Li ∣ S battery exhibits an extremely high energy density of 664.2 Wh Kg −1 when the thickness of the separator is reduced to 1 μ m. This work sheds fresh light on the rational design of high energy density lithium-ion batteries.