Nanocellulose Modified Polyethylene Separators for Lithium Metal Batteries

Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high-energy density Li metal-based batteries. Herein, a novel tri-layer separator design that significantly enhances the cycling stability and safety of Li metal-based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper-making process, is directly laminated on each side of a plasma-treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li⁺ flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri-layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose-based tri-layer separator design thus significantly facilitates the realization of high-energy density Li metal-based batteries.