A 12 μm-Thick, Mechanically Stable Ionogel Electrolyte with Directed Li⁺ Transport Channels for High-Performance...

The ionogel polymer electrolyte (IGPE) has emerged as a promising polymer electrolyte for lithium metal batteries (LMBs) due to its high safety and a wide electrochemical window. To achieve an energy density comparable to that of liquid electrolyte (LEs)-based cells, ultrathin IGPE electrolytes with high Li⁺ conductance are desired. However, their development still suffers from intrinsically poor mechanical stability and the low Li⁺ transference number (t_Li+) of IGPEs. Here, we design a 12 μm-thick, mechanically reliable, and highly Li⁺ conductive IGPE electrolyte (PET-IGPE) by incorporating a poly(butyl acrylate) (PBA)/solvate ionic liquid (SIL)-based ionogel with a polyethylene terephthalate (PET) track-etched membrane. The PET membrane as the scaffold enables the resultant IGPE electrolyte to have a high tensile strength of 65 MPa and a puncture strength of >340 gf mil^-1, preventing the Li symmetrical cell from short-circuiting for over 700 h of cycling. Meanwhile, the vertically aligned pores in the PET membrane function as the directional Li⁺ motion pathway, which enables an ultrahigh areal ionic conductance of 308.3 mS cm^-2, improves t_Li+ to 0.61, and steady Li plating/stripping without impairing the thermal and electrochemical oxidative stability of IGPEs. As a result, the Li|12PET-IGPE|LiFePO₄ cell shows high capacity, high cycling stability in a wide temperature range of 25-90 °C, and high tolerance to abuse, such as folding, cutting, or nail penetration.