Nanoporous Molecular Springs as Energy-Density Extenders for Liquid-Piston Compressed Air Energy Storage: A Performance and Techno-Economic Assessment

High-pressure liquid-piston compressed-air energy storage (LP-CAES) is mechanically simple and scalable, yet its value is limited by footprint-constrained energy density and utilization-dependent economics. This study evaluates an LP-CAES configuration augmented with zeolitic imidazolate framework (ZIF-8) molecular springs (MS), where pressure-driven water intrusion/extrusion into hydrophobic nanopores introduces an auxiliary work-storage pathway and modifies the gas-liquid volume dynamics during charge and discharge. A cycle-resolved lumped 0-D model couples real-gas thermodynamics, hydraulic pressure/flow losses, and physics-based component representations for a positive-displacement pump/motor set, Pelton turbine, and induction generator. For a 70–300 bar operating cycle, ZIF-8 integration, with a 2:1 dilution, increases the stored energy density by 32%. On a per-cycle basis, delivered electricity increases by 26.3%, while charging electricity rises by 30.5%, resulting in a reduction in roundtrip efficiency (RTE) from 55.7% to 53.9%. The MS channel exhibits 69.1% work recovery, with a net MS loss of 0.522 kWh per cycle, indicating that MS primarily acts as a capacity and energy-density extender rather than an intrinsic RTE enhancer. When scaled to a plant delivering 40 MWh per cycle, the baseline MS case reduces capital expenditure (CAPEX) by 16.3% and lowers the levelized cost of energy storage (LCOES) by 1.7% at daily cycling, while maintaining higher net present value (NPV) across three utilization scenarios, although the broader economic advantage remains scenario-dependent. These results suggest that ZIF-8 integration should be viewed as a vessel-level capacity extender, most attractive where storage footprint is constrained or additional charge acceptance can monetize curtailed or low-price electricity.