The continuous development of lithium-ion batteries (LIBs) manufacturing industry calls for the mass production of Li2CO3, which serves as a pivotal raw material for LIBs. In our previous study, Li was successfully precipitated as intermediate product Li2SiO3 from an alkaline solution containing Si by the hydrothermal precipitation method, realizing the preliminary separation of Li and impurities. In this research, H2SO4 digestion-water leaching-Na2CO3 precipitation process was proposed to manufacture Li2CO3 from the intermediate product Li2SiO3. Firstly, the reaction feasibility of H2SO4 digestion-water leaching and direct H2SO4 leaching for Li2SiO3 were comparatively evaluated through thermodynamic calculation and experimental research. Compared to direct H2SO4 leaching, H2SO4 digestion-water leaching process is preferred in view of its excellent filtration properties. Subsequently, systematic digestion and leaching experiments showed that up to 97.1 % of Li was extracted under the optimized conditions, and the concentration of Li in the leach liquor is as high as 29.33 g/L. After pH adjustment and Al removal, Na2CO3 precipitation were adopted for Li2CO3 production. The equilibrium relationship in Li2SO4-Na2CO3-H2O system was analyzed to predict the precipitation behavior of Li and select appropriate operation window for Li2CO3 preparation. Finally, with an additional carbonation-decomposition process, a Li2CO3 product with a purity of 99.51 % is produced. This process realizes efficient synthesis of battery-grade Li2CO3 from the intermediate product Li2SiO3.