Polymer-in-Salt Electrolyte Enabled High-Performance Solid-State Hybrid Lithium-Ion Capacitor with 3D Conductive Nb2O5 Anode for Energy Storage

To address the safety limitations of liquid electrolytes and performance bottlenecks in conventional energy storage devices, a high-concentration polymer-in-salt polymer solid electrolyte (PiS-PSE) and a 3D conductive network-engineered niobium pentoxide (Nb 2 O 5 ) composite anode for solid-state hybrid lithium-ion capacitors (HLICs) are developed. The optimized lithium bis(trifluoromethanesulfonyl)imide/poly(vinylidene fluoride -co -hexafluoropropylene) (LiTFSI/PVDF-HFP) electrolyte (mass ratio 3:1) achieves an ionic conductivity of 2.09 × 10 − 3 S cm −1 at 20 °C with enhanced electrochemical stability (>4.5 V vs. Li/Li + ). Simultaneously, the Nb 2 O 5 /graphene-carbon nanotube hybrid anode (NGNT-90%) exhibits exceptional pseudocapacitive behavior and rate capability (171 mAh g −1 at 0.1C). The integrated solid-state HLIC delivers a high energy density of 108.3 Wh kg −1 at 100 W kg −1 and maintains 37.63 Wh kg −1 at 500 W kg −1 , which is comparable with reported liquid-based LICs. Critically, the device demonstrates >80% capacitance retention after 300 cycles at 5C with near-unity coulombic efficiency (≈99.0%), attributable to stable electrode/electrolyte interfaces and dendrite-suppressing characteristics of the PiS-PSE. This work provides a material design paradigm for next-generation safe, high-performance electrochemical energy storage systems.