A non-Newtonian fluidic cellulose-modified glass microfiber separator for flexible lithium-ion batteries

The separator is of great importance for regulating ion transmission, maintaining electrode stability, and device safety in lithium-ion batteries. Despite their many advantages, glass microfiber separators have shortcomings that often give rise to poor cycle performance and fatal short-circuit risk when used in flexible batteries. Here, we propose the use of a scalable non-Newtonian fluidic cellulose permeation-diffusion strategy to develop a cellulose/glass microfiber composite film with an hourglass-gradient structure. Due to the unique gradient morphology resulting from the presence of cellulose macromolecules, the as-prepared composite film showed an improved surface mass density, adjustable pore structure, controllable ion transport, ideal mechanical flexibility, and robustness. When used as the separator in an assembled lithium-ion battery, the composite film exhibited rapid ion diffusion and Li dendrite inhibition, which endowed the battery with excellent cycle stability (specific capacity of 108.5 mAh g(-1) after 1000 cycles) and good rate performance. This composite film shows great potential application in flexible lithium-ion batteries including but not limited to pouch cells.