A nanoporous permselective polymer coating for practical low N/P ratio lithium metal batteries

Lithium metal batteries, in particular lithium–sulfur chemistries, hold great promise in energy storage from potentially increased gravimetric storage density and diminished reliance on transition metals, lowering resource demand and hence overall unit cost. However, these cells can have their feasibility improved to a greater extent by lowering the demand for lithium within their construction and reducing the polysulfide shuttling effect. Rising lithium costs and a lack of recycling options indicate the use of excess lithium to mitigate cycling stability issues is sub-optimal. Herein, the direct casting of a lithophilic, superglassy, nanoporous PTMSP polymer separator directly onto the lithium anode is described. PTMSP's bi-modal, sub-angstrom pore size distribution results in selective rejection of polysulfide species, while its high fractional free volume acts as a stabilizing matrix for deposited lithium as well as possessing a high ionic conductivity of 8.8 × 10^-4 S cm⁻¹. The coated anodes exhibit 5.7 times more dense lithium over controls, translating to improved cycling performance due to increased capacity retention and improved lithium utilization at low (< 3) N/P ratios for extended cycle life (> 250 cycles), at practical sulfur loadings (4 mg cm⁻²). These developments are promising steps for more widespread adoption of lithium sulfur batteries and other metallic lithium systems.