Si-welding reinforced Mn-based light-absorbing shells to stabilize Ca-based pellets for durable thermochemical energy storage under prolonged ambient exposure

Abstract

The diurnal and seasonal intermittency of solar irradiation leads to unstable energy supply in concentrating solar power (CSP) systems, which necessitates long-term energy storage. Ca-based thermochemical energy storage (TCES) pellets have emerged as a promising solution. However, their ambient storage stability remains underexplored. Herein, the Al-stabilized Ca-based TCES pellets encapsulated with Mn-based shells reinforced by Si-welding and graphite dispersion are fabricated, and their long-term storage behaviors under ambient conditions are investigated. Atmospheric moisture and CO2 induce sequential hydration and carbonation of CaO in the pellets, degrading mechanical properties and heat release capacity. Notably, the reinforced TCES pellets exhibit excellent performance: the theoretical retained energy storage density reaches 0.91 MJ kg-1 (nearly 7.6 times that of pure Mn-based shells) and the shell shedding rate is only 10.25% after 90 days (less than one-fifth that of pure Mn-based shells). The enhanced stability arises from synergistic Si doping and graphite dispersion, which form uniformly dispersed low-temperature eutectic phases in the light-absorbing shells. These phases enhance core-shell interfacial adhesion, and effectively inhibit the intrusion of atmospheric moisture and CO2. Furthermore, long-term ambient-stored Ca-based TCES pellets can substantially recover their cyclic heat storage/release capability through re-calcination, with their energy storage density even exceeding the initial level. This innovative synergistic strategy provides potential opportunities for the future deployment of CaL-TCES systems in long-term energy storage and flexible energy utilization.