From low-cost mineral to high-performance Li4SiO4 for solar energy storage and CO2 capture

The huge consumption of fossil fuels results in excessive CO2 emissions and its reduction has become a common concern. The combination of renewable energies (i.e., solar energy) and carbon capture, utilization, and sequestration are well recognized as two major routes to achieving carbon neutrality. Lithium orthosilicate (Li4SiO4) has been identified as one of the most promising candidates for solar energy storage and CO2 capture. However, the cost reduction and performance enhancement remain to be the main obstacles for its practical application. In this work, high-performance Li4SiO4 heat carriers have been synthesized using low-cost mineral as silicon source for solar energy storage and CO2 capture. Li4SiO4 derived from diatomite exhibited cyclic energy storage densities above 500 kJ/kg. The performance was further improved by doping alkali carbonates, particularly doping 3 wt% K2CO3 (LD-P-3K), which exhibited high and stable energy storage density of approximately 700 kJ/kg in the tested 10 cycles. Then, the mechanism of alkali doping was revealed through experiments and DFT calculations. The DSC results demonstrated that the improved performance was attributed to the formation of a eutectic melt which reduced the CO2 diffusion resistance. The DFT calculations showed that K-doped Li4SiO4 had lower adsorption energy and more significant charge migration, which meant stronger interaction. Additionally, diatomite-derived Li4SiO4 material is also a promising candidate for high-temperature CO2 capture, evidenced by its relatively high cyclic CO2 capture capacity (similar to 0.25 g/g). In general, satisfactory density/capacity and stability endows diatomite-derived Li4SiO4 with great prospects for both thermochemical energy storage and high-temperature CO2 capture.