Solid–gas thermochemical energy storage (TCES) systems represent one of the most promising pathways for achieving long-duration, loss-free thermal energy storage across a wide temperature spectrum, thereby addressing the mismatch between intermittent renewable energy supply and industrial, residential, and power-generation demands. This review provides a critical and integrative assessment of TCES materials, reactor concepts, thermochemical cycles, numerical modeling approaches, and real-world application cases, with the objective of identifying the dominant factors that govern practical performance, scalability, and technology readiness rather than theoretical potential alone. From a materials perspective, the review reveals that although salt hydrates, ammoniates, carbonates, hydroxides, metal oxides, and metal hydrides exhibit high intrinsic energy densities, their long-term viability is primarily limited by degradation mechanisms such as sintering, deliquescence, pore blockage, phase segregation, and sluggish reaction kinetics under cyclic operation. A key insight emerging from the literature is that marginal gains in theoretical energy density are far less impactful than improvements in cyclic stability, transport properties, and mechanical integrity. Composite materials, doped systems, salt-in-matrix formulations, and encapsulation strategies consistently outperform pure materials, indicating that future TCES development must prioritize stability-driven and cost-aware material design rather than thermodynamic optimization alone. At the reactor and cycle level, solid–gas configurations dominate current TCES implementations due to their operational flexibility and compatibility with wide temperature ranges. However, this review highlights that heat and mass transfer limitations, solid handling, and mechanical degradation remain the primary bottlenecks in scale-up. Advanced thermochemical cycles, including cascaded, resorption, and hybrid TCES configurations, demonstrate clear advantages in temperature matching, heat upgrading, and exergetic efficiency. Nevertheless, these gains are frequently offset by increased system complexity, multi-reactor layouts, and stringent control requirements, underscoring the need for simplified and robust cycle architectures co-designed with material properties. Application-oriented studies confirm that TCES performance under real operating conditions is governed less by material metrics measured in laboratory reactors and more by system-level integration losses, operating constraints, and component durability. Industrial decarbonization case studies—particularly calcium looping–based systems coupled with hydrogen production or CO₂ capture—illustrate the potential of TCES as a multifunctional energy technology, while also revealing the scarcity of long-term cycling data and standardized techno-economic benchmarks. Numerical modeling has become indispensable for TCES development, enabling reactor optimization and system integration analysis. However, the review identifies persistent gaps in multi-scale, multi-physics modeling and experimental validation, particularly for fluidized- and moving-bed reactors and advanced cycle configurations. Emerging AI-assisted modeling and material discovery frameworks are identified as transformative tools capable of accelerating design, reducing computational cost, and improving predictive reliability. Overall, this review concludes that the successful transition of TCES from laboratory research to commercial deployment will depend on prioritizing material durability, reactor robustness, system simplicity, and economic feasibility, supported by validated numerical tools and data-driven design methodologies. • Material stability, not energy density, limits scalable TCES deployment. • Advanced TCES cycles boost efficiency but increase system complexity. • Reactor design and integration losses dominate real-world TCES performance. • Numerical models guide TCES design, yet scale-up validation remains limited. • AI-assisted methods emerge as enablers for next-generation TCES systems.
Aliyari et al. (Fri,) studied this question.