Performance evaluation of liquid CO₂ battery for SOFC energy system load management

The integration of solid oxide fuel cell (SOFC) and energy storage mechanisms is a key method for achieving energy infrastructure transformation and energy conservation and emission reduction. When integrated with storage solutions, SOFC enables dynamic power output adjustment, facilitating a responsive match to variable electricity demands across the diurnal spectrum. This study pioneers the proposition of employing a novel carbon dioxide battery, based on the carbon dioxide liquefaction cycle, for application within SOFC power generation systems. The mathematical models of liquid carbon dioxide battery and SOFC system integrated with thermal energy recovery are developed. The system performance was comprehensively evaluated via energy and exergy analyses. The results of parameter sensitivity analysis indicate that the liquid carbon dioxide battery can achieve the maximum round-trip efficiency of 62.88 % and the energy storage density of 14.26 kW·h/m³, which indicate that it can well balance its round-trip efficiency and energy storage density, making it very competitive when compared to other other compressed gas energy storage configurations. Furthermore, the research findings indicate that elevating the maximum working pressure of the system can enhance both the cycle efficiency and the energy storage density. Nonetheless, beyond a threshold of 20 MPa, the incremental benefits to system performance diminish significantly, potentially introducing heightened safety concerns. Additionally, the strategic adjustment of the compression and expansion ratios is identified as a pivotal factor in optimizing system performance. Moreover, the modulation of the cooling water flow rate within the multiphase flow heat exchanger has been discerned to significantly influence the heat absorption by the liquid carbon dioxide battery, thereby impacting its operational strategy. In summary, the liquid carbon dioxide battery proposed in this study for application in SOFC power generation systems represents an efficient, compact, and environmentally benign energy storage solution.