Solar energy storage by dark Mn-doped CaO-based heat carriers

• Mn-doped CaO-based heat carriers with finely dispersed Ca2MnO4 inert support effectively resist CaCO3/CaO sintering, maintaining ~2000 kJ/kg energy storage density over 20 cycles. • The dark Ca2MnO4 phase markedly enhances direct solar absorption of CaO-based heat carriers, addressing the poor optical absorption of white CaO. • Granulated pellets exhibit excellent attrition resistance with only 9.85 wt% mass loss after 3200 mechanical cycles, supporting practical reactor applications. • The combined thermochemical and optical improvements position Mn-doped CaO carriers as promising candidates for concentrated solar power energy storage.