Synergistic Defect Engineering in Ca‐Based Pellets for Durable and High‐Absorptance Solar Thermochemical Energy Storage

Solar thermochemical energy storage (TCES) holds immense promise for a carbon-neutral future. However, its large-scale, low-cost implementation is severely hampered by the poor solar absorptance, rapid performance degradation, and low volumetric energy density of conventional calcium carbonate/oxide materials. Herein, a multi-scale synergistic defect engineering strategy is proposed to resolve this conflict fundamentally. Guided by predictive ray-tracing models and density functional theory calculations that pinpoint dopant d-electron effects as the key modulator of optical properties, Mn/Mg co-doped pellets are rationally designed. These engineered pellets demonstrate a suite of outstanding properties: a dramatic leap in solar absorptance from a mere 3.4% to 78.5%, a 1.54-fold enhanced thermal conductivity, and exceptional cycling durability. Over 123 cycles, the pellets achieve a remarkable average volumetric energy density of 877.9 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>MJ</mml:mi> <mml:mspace></mml:mspace> <mml:msup><mml:mi>m</mml:mi> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$\rm {MJ\ m^{-3}}$</mml:annotation></mml:semantics> </mml:math> (2.1 times that of the pristine powder), maintaining a high average of 848.3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>MJ</mml:mi> <mml:mspace></mml:mspace> <mml:msup><mml:mi>m</mml:mi> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>3</mml:mn></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$\rm {MJ}\ {\rm m}^{-3}$</mml:annotation></mml:semantics> </mml:math> over 217 cycles. This unprecedented performance comes from a unique multi-scale defect synergy, where 0D point defects induce beneficial lattice strain, while in situ formed 3D nano-precipitates strategically pin 2D grain boundaries to suppress high-temperature sintering effectively. This work not only delivers a record-performing TCES material but also establishes a promising, theory-guided strategy for the intelligent design of next-generation energy storage materials.