Rational design of ultrathin composite solid-state electrolyte for high-performance lithium metal batteries

To address the safety and low energy density of conventional liquid electrolyte lithium-ion batteries, ultrathin solid-state electrolyte with high mechanical modulus and ionic conductivity has been widely concerned. Here, we report an ultrathin, mechanically robust and flexible composite solid-state electrolyte, composed of three-dimensional network host (polyimide (PI) film), ionic conductive inorganic particle (Li6.75La3Zr1.75Ta0.25O12), polymer binder (polyvinylidene fluoride), and lithium salt-ionic liquid solution. PI film guarantees the flexibility and thin thickness (∼25 μm) of the composite electrolyte. The introduction of high-content ceramic filler and ionic liquid enhance mechanical strength and room-temperature ionic conductivity (3.7 × 10−4 S cm−1) of composite electrolyte while reducing the interfacial impedance between the electrolyte and the electrode. The capacity retention (153 mAh g−1) of the LiNi0.5Co0.2Mn0.3O2|Li battery based on the prepared electrolyte is 88% after 100 cycles at 0.1C, which has high safety in practical applications.