Synthesis of dark Li4−3xFexSiO4 for simultaneous direct solar thermal conversion and durable thermochemical energy storage

Abstract

Thermochemical energy storage (TCES) technique based on Li4SiO4 looping system probably offers a mid-term if not near-term solution to the next generation concentrated solar power (CSP) plants featured with excellent stability and low regeneration temperature. However, traditional Li4SiO4 material commonly possesses dense microstructure with white superficial color, thus resulting in the unsatisfactory energy storage density and considerable radiant heat loss. This study involved doping Fe into Li4SiO4 to synthesize dark Li4−3xFexSiO4 heat carriers for thermochemical energy storage (TCES). By replacing Li+ with Fe3+, vacancies were created in the crystal lattice structure, resulting in the high energy storage density (456.14 kJ/kg) as well as the excellent cyclic long-term stability of I-Li3.7Fe0.1SiO4. Furthermore, Fe-doped dark Li4SiO4 showed obviously enhanced direct solar absorptance with the average solar absorptance of I-Li3.7Fe0.1SiO4 being 10 times higher than that of the undoped Li4SiO4. Such obvious enhancement in solar absorptance was attributed to the darkening superficial color through Fe doping. In summary, the synthesized Fe-doped Li4SiO4 heat carrier solved the encountered problems of traditional energy storage materials and exhibited as a promising heat carrier for practical thermochemical energy storage.