Converting Electrical Energy Storage Waste into Thermal Energy Storage Materials: A Novel and Sustainable Route for the Synthesis of Li ₄ SiO ₄ Heat Carriers

The widespread application of renewable energy depends on the development of efficient, large-scale, and cost-effective energy storage technologies. Lithium orthosilicate (Li 4 SiO 4 ) is a promising candidate for thermochemical energy storage (TCES) due to its high theoretical capacity and cyclic stability. However, its commercial feasibility is severely constrained by the high and increasing costs of its precursors. This study proposes an efficient and economical synthesis route for Li 4 SiO 4 using waste lithium batteries and natural diatomite. The derived material (LD-700) exhibited superior performance, achieving a high energy density of 490 kJ/kg with exceptional cyclic stability (only a 7% decay over 30 cycles). This enhancement could be attributed to a synergistic mechanism involving internal impurity elements from the precursors: alkali metals facilitated CO 2 diffusion, transition metals enhanced ionic mobility, and calcium contributed to higher storage density. LD-700 demonstrated a lower apparent activation energy in the chemical-controlled process compared to materials from conventional solid-state synthesis, leading to a broader operational temperature window. Comprehensive life cycle assessment (LCA) and techno-economic analysis confirmed the dual advantages of this strategy: reducing production costs and significantly decreasing the environmental footprint, achieving a net positive benefit in key impact categories such as global warming potential and acidification potential. This work not only presents a high-performance TCES material but pioneers a novel and economic concept of converting electrical energy storage waste into thermal energy storage materials, offering a compelling solution for efficient and sustainable thermal energy storage.