On the rational development of advanced thermochemical thermal batteries for short-term and long-term energy storage

Thermal energy storage is an important means for achieving carbon neutrality. Absorption thermal battery is a promising solution for renewable energy utilization due to its excellent energy storage performance and operational flexibility. This study conducts comparative investigations among different absorption thermal battery cycles from a multi-criteria perspective, including energy storage efficiency, energy storage density, exergy efficiency, charging temperature, and initial cost. Except for the existing cycles (i.e., basic cycle, compression-assisted cycle, double-stage cycle, and double-effect cycle), a novel double-effect compression-assisted cycle is also included to cover a wider range of design options. The effects of charging/discharging/cooling temperatures on the storage performance are analyzed in three scenarios, i.e., short-term cold storage, short-term heat storage, and long-term heat storage. Results indicate that the compression-assisted cycle and the double-stage cycle can improve the energy storage density and lower the charging temperatures (e.g., below 70 °C); the double-effect cycle can enhance the energy storage efficiency; the double-effect compression-assisted cycle can achieve improvements in energy storage efficiency and density simultaneously, with a maximum energy storage efficiency above 1.30 and energy storage density over 300 kWh/m³, and bridge the temperature gap (i.e., 100 °C–140 °C) between the single-effect and double-effect cycles. The maximum energy storage efficiency, energy storage density, and exergy efficiency are 1.53, 365.4 kWh/m³, and 0.61, achieved by the double-effect cycle, the compression-assisted cycle, and the basic cycle, respectively. This work aims to facilitate the rational development of absorption thermal battery cycles for high-density and high-efficiency thermal energy storage towards carbon neutrality.