Advances in Regulating Thermoelectric Properties of Ca ₃ Co ₄ O ₉ Materials through a Multiscale Strategy

As a competitive candidate for high-temperature direct thermoelectric conversion, Ca3Co4O9 holds significant implications for advancing the integration of low-carbon energy technologies, particularly in harnessing distributed waste heat, thereby supporting global carbon neutrality goals and optimizing the stability of multienergy systems. This review clarifies the preparation methods, structural defects, and texturation from nanoscale to bulks in recent years. There are various advanced processes to obtain Ca3Co4O9 materials, including nanoparticles, fibers, platelike templates, and hierarchical porous bulks. The latest research progress of Ca3Co4O9 exhibits that the multiscale defects, such as 0D (doping, vacancy), 1D (dislocation), 2D (grain boundary and phase boundary), and 3D (pores) defects, can independently regulate thermoelectric parameters to decouple the electrical/phonon transport. Furthermore, the strong anisotropic grain growth in textured Ca3Co4O9-based composites significantly improves the thermoelectric properties, suggesting the multiscale “structure design-performance regulation” strategy. The obviously decoupled electrical/thermal performance opens promising avenues for the sustainable energy application on deep space exploration, zero energy buildings, and electronic devices. The systematic exploration and critical discussion of Ca3Co4O9 can create some refreshing research works on oxide thermoelectric materials.