Unified throughout-pore microstructure enables ultrahigh separator porosity for robust high-flux lithium batteries

Abstract

With small thickness, commercial polyolefin separators own low porosity to ensure sufficient thermomechanical properties, resulting in tortuous and enlarged Li+ diffusion pathways that induce large overpotentials and detrimental dendrite growth. As a dilemma, the exploration of highly porous separators has been challenged by their large thickness, impairing the applicability of such pursuits. Herein, an ultraporous architecture is designed to shorten Li+ transfer pathways by impregnating electrolyte-affinitive poly (vinylidene fluoride-co-hexafluoropropylene) into ultralight ∼3 μm 3D-polytetrafluoroethylene scaffold (abbreviated as UP3D). The UP3D separator with a porosity of 74% gives rise to 70% enhancement in Li+ transference and 77% reduction in Li+ transfer resistance (2.67 mΩ mm−1) and thus enables an ultrahigh Li+ flux of 22.7 mA cm−2, effectively alleviating Li+ concentration gradient across the separator. With the separator, the LiFePO4 half cell delivers a capacity of 118 mAh g−1 with an unparalleled capacity retention of 90% after 1000 cycles at 2 C, and a graphite || LiNi0.6Co0.2Mn0.2O2 pouch full cell delivers an areal energy density of 6.8 mWh cm−2 at 8.848 mA (1.4 mA cm−2) with a high cathode loading of 134.9 mg. Such results, together with the scalable production of the separator, reflect its promising potential in high-flux battery applications of separators that require both ultrahigh porosity and reliability.