The practical application of lithium silicate (Li4SiO4) in high-temperature CO2 capture is limited by its deteriorated sorption performance under low-concentration CO2 atmospheres and poor long-term cycling stability. Additionally, its inherent powder form poses significant challenges for industrial implementation. Meanwhile, as a thermochemical energy storage material, its stability is equally crucial. To address these issues, this study developed a novel Li4SiO4 sorbent featuring nanowire-like Li4SiO4 crystallites on the particle surface by utilizing mixed lithium sources (LiOH/LiNO3) and pumice (PU). The synthesized Li4SiO4 not only retains the porous granular structure of pumice but also exhibits excellent sorption performance and regeneration stability under low CO2 concentrations. The results demonstrate that when the molar ratio of LiOH/LiNO3 is 7:3, the synthesized Li4SiO4 particles (PU-Li4SiO4-0.7LH/0.3LN) exhibit nanowire-like Li4SiO4 crystallites on the particle surface. Under conditions of 600 °C and 20 vol% CO2 concentration, it achieves a sorption capacity of 29.5 wt% and a thermochemical storage capacity of 629.2 kJ/kg, significantly surpassing pure Li4SiO4. Moreover, PU-Li4SiO4-0.7LH/0.3LN demonstrates remarkable sorption-regeneration stability. After 150 cycles of reaction at 20 vol% CO2 concentration, the sorption capacity of PU-Li4SiO4-0.7LH/0.3LN decreased only from 21.4 wt% to 19.9 wt%. This excellent performance is attributed not only to the nanowire-like Li4SiO4 crystallites providing abundant sorption sites, but also to the natural porous structure of pumice offering stable gas transport channels.