[Objective] Compressed carbon dioxide energy storage (CCES) combines a high-density working fluid, closed-cycle operation, flexible siting, and the potential for long-duration energy storage, making it a promising physical storage option for power systems with high renewable-energy penetration. However, the reported performance of CCES varies substantially because liquid, transcritical, and supercritical routes differ in storage state, pressure level, heat-transfer process, low-pressure-side storage method, and evaluation boundary. This review aims to clarify the operating characteristics, performance ranges, equipment requirements, and engineering applicability of the main CCES routes, and to identify the technical barriers to large-scale deployment. 

[Methods] The literature was reviewed from the perspectives of thermophysical properties, system configuration, storage mode, key equipment, cycle optimization, multi-energy coupling, dynamic behavior, and demonstration projects. Liquid, transcritical, and supercritical CCES systems were compared in terms of operating boundaries, round-trip efficiency, energy storage density, storage-vessel requirements, heat and cold recovery, and component matching. Representative studies on underground storage, flexible gas holders, adsorption storage, hydraulic compensation, waste-heat recovery, heat-pump integration, cold-electricity cogeneration, and external heat or cold sources were summarized. Engineering projects in Europe and China were also examined to assess the transition from conceptual studies to demonstration-scale applications. 

[Results] CCES performance is primarily governed by the CO₂ storage state, low-pressure-side storage mode, pressure ratio, heat-exchanger matching, turbomachinery efficiency, and system boundary. Liquid or gas-liquid phase-change systems generally provide relatively high energy storage density, but require liquefaction, vaporization, cold storage, and phase-change heat transfer. Transcritical systems offer flexible ground-based deployment and can balance efficiency with siting adaptability, but are sensitive to thermophysical-property variations near the critical region and may require large low-pressure storage volumes. Supercritical systems are comparatively compact and avoid phase-change control, but impose stricter requirements on high-pressure vessels, sealing, materials, and turbomachinery manufacture. Typical transcritical and supercritical systems generally report round-trip efficiencies of 50%~70%. Nevertheless, direct comparison is difficult when external heat, cold-energy products, design values, or different storage boundaries are included. Waste-heat recovery, heat-pump coupling, cascaded thermal storage, and cold-electricity cogeneration can improve overall energy utilization, but often increase equipment count, control complexity, and capital cost. Existing megawatt-scale demonstrations and larger projects under construction indicate that CCES is progressing from thermodynamic verification toward engineering demonstration. 

[Conclusions] CCES has potential for long-duration energy storage and reduced dependence on large underground gas caverns, but different routes should not be evaluated using a single efficiency indicator. Future research should establish consistent performance boundaries and focus on transient control near the critical region, off-design turbomachinery performance, heat-exchanger network optimization, reliable sealing and material selection, low-cost storage devices, cascaded heat and cold utilization, and experimentally validated dynamic models. Long-term operating data, safety standards, economic assessment methods, and market mechanisms are also required to support commercial deployment.