Environmental assessment and conductivity performance of calcium-based polymer electrolytes for the next generation of solid-state batteries

This study presents a comprehensive life cycle assessment (LCA) of calcium-based polymer electrolytes, aiming to advance sustainable solid-state post-lithium battery technologies. Despite calcium-based solid-state batteries offer safer and more reliable energy storage alternatives, research into their environmental and electrochemical performance remains limited compared to lithium-ion systems. In this work, three polymer electrolytes, based on a cross-linked polymer backbone doped with calcium salts (Ca (TFSI)₂, Ca(CF₃SO₃)₂, and CaI₂), are studied through LCA and characterized in terms of electrochemical and thermal properties. Notably, it is observed that the salts exhibit a significantly higher contribution to environmental impacts compared to the polymer. The LCA identifies CaI₂ as the most environmentally favorable, with climate change emissions of 8.01·10⁻⁵ kg CO₂ equivalent, particulate matter disease incidence of 3.12·10⁻¹² cases per kg PM_2.5, and negligible ozone depletion impacts (1.27·10⁻⁶ kg CFC11 eq). Although Ca (TFSI)₂ shows higher ozone depletion impact (2.68·10⁻⁴ kg CFC11 eq) it demonstrates superior ionic conductivity, achieving 0.09 mS⋅cm⁻¹ at 20 °C and 0.4 mS⋅cm⁻¹ at 90 °C. Moreover, differential scanning calorimetry confirms the fully amorphous structure of all electrolytes, with glass transition temperatures ranging from −19.61 °C (Ca (TFSI)₂) to −38.7 °C (CaI₂), which ionic conductivity at room temperature. These findings highlight a critical trade-off between environmental impact and electrochemical performance, providing actionable insights for the design of safer, more sustainable energy storage systems.