Solid-State Supercapacitors with Enhanced Performance Using Al³⁺-Doped Li⁺ Ion Perovskite Electrolyte Integrated with...

We report the performance of solid-state ceramic supercapacitors (SSCs) based on a novel composite electrolyte comprising aluminum-doped lithium lanthanum titanate perovskite, Li_0.36La_0.56Ti_0.995Al_0.005O₃ (Al³⁺-doped LLTO), and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF₄). Rietveld refinement of X-ray diffraction data confirms the preservation of the tetragonal perovskite phase after Al³⁺ substitution, indicating structural stability of the host lattice. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy further corroborate the successful incorporation of Al³⁺ without forming secondary phases. The addition of ∼6 wt % EMIM BF₄ into Al-LLTO matrix significantly enhances the room-temperature ionic conductivity to ∼10^-3 Ω^-1 cm^-1, nearly 3 orders of magnitude greater than that of pristine LLTO, resulting into improved long-range electrical transport. Further, novel SSCs have been fabricated by sandwiching the composite electrolyte between high surface area freeze-dried carbon aerogel (FD-CA) coated copper electrodes and assembled using a low-cost hot-roll lamination approach. The devices at 35 °C exhibited a high specific capacitance of ∼370 F g^-1 at 1 mA/2 V, excellent cycling stability with ∼87% capacitance retention over 15,000 cycles at 2 V and 2 mA (1 A g^-1), and stable Coulombic efficiency of ∼99%. These symmetric SSCs demonstrate ideal electric double-layer capacitive behavior for operating potential ≤ 2 V. These results highlight the potential of Al³-doped LLTO/EMIM BF₄ composite electrolytes in combination with FD-CA-based electrodes for the development of safe, efficient, stable and scalable solid-state supercapacitors.