High-temperature CO₂ adsorption has an attractive prospect in reducing CO₂ emissions efficiently. As the core of CO₂ adsorption technology, sorbents suffer from a well-known problem of capacity degradation as a result of sintering during cyclic CO₂ adsorption and desorption at high temperatures. This work aims to understand the microstructural evolution of Li₄SiO₄, one of the most typical and promising sorbents, during CO₂ capture. In-situ Transmission Electron Microscopy was used to directly capture the morphological variation of Li₄SiO₄ sorbents. Comprehensive characterization techniques were adopted to quantify microstructural parameters of Li₄SiO₄ under different conditions_. The real-time shrinkage of Li₄SiO₄ particles was demonstrated and equations on grain growth, specific surface area reduction, and pore volume evolution were established. The work can not only reveal the reason for the reduction of CO₂ capacity, but provide a theoretical guidance for the development of sintering-resistant CO₂ sorbents.