Fig. 4: Structural, electrochemical performance, and mechanistic insights of liquid-state, solid-state, and quasi-solid-state Al–S batteries.

a Schematic representation of the solid-state Al–S pouch cell configuration, detailing the multilayer structure comprising Al anode, solid electrolyte, sulfur-based composite cathode, and encapsulating flexible packaging. b Comparative charge–discharge voltage profiles of liquid-state and solid-state Al–S pouch cells operated at 0.05 C, highlighting improved voltage polarization and stability in the solid-state configuration. c Discharge curves of the solid-state Al–S pouch cell under varying current rates, demonstrating rate capability and kinetics of sulfur redox processes within the solid-state matrix. d Galvanostatic Al plating/stripping profiles of symmetric Al|electrolyte|Al cells using either ionic liquid electrolyte (ILE) or a composite modified solid electrolyte (MSE@GPE), measured at a constant current density of 0.5 mA cm⁻², revealing lower overpotentials and improved reversibility in the MSE@GPE-based system⁹. e Long-term cycling behavior of Al|AE | S full cells using either untreated (u-Al) or previously cycled aluminum (pc-Al) anodes in AE-2Na electrolyte, illustrating the influence of surface conditioning and electrolyte compatibility on capacity retention and stability. f Corresponding voltage profiles of the 50th cycle for cells with u-Al and pc-Al, showing electrochemical maturity, reaction consistency, and improved voltage plateaus with the preconditioned Al anode. g Cycling performance of the Al–S battery using the AE-1K electrolyte at 100 mA g⁻¹, displaying gradual capacity evolution and stabilization indicative of interfacial adaptation and long-term integrity³⁷. h Cyclic voltammetry (CV) profiles of symmetric Al|electrolyte|Al cells under various electrolytic environments, providing insights into redox kinetics, ionic transport, and reversibility of Al electrodeposition/stripping. i Galvanostatic discharge–charge curves at the first cycle (1 A g⁻¹) for Al–S batteries comprising different sulfur composite cathodes, emphasizing the cathode-specific electrochemical behavior, including activation overpotential and specific capacity delivery³⁹. j Schematic of a quasi-solid-state Al–S battery and its working mechanism, delineating ionic transport, phase evolution, and electrochemical redox reactions in the hybrid electrolyte system combining solid framework and liquid infiltration for improved safety and performance. k Comparative cycling stability of liquid-state versus quasi-solid-state Al–S cells tested at 50 mA g⁻¹, underscoring the enhanced lifespan, Coulombic efficiency, and capacity retention of the quasi-solid-state design⁸. l Schematic illustration of the synthesis and integration of AlMo₄S₈/CNTs@S composite as an advanced cathode material, engineered to improve conductivity, structural confinement of polysulfides, and electrochemical activity. m Charge–discharge profiles of Al-ion batteries using AlMo₄S₈ cathodes at 100 mA g^-1 and 25 °C⁴⁰.