Intrinsic Defect Energetics and Fluorine Doping Effects in Li2CO3 and Li2O2: A First-Principles Study

Abstract Lithium carbonate, Li2CO3, is a thermodynamically stable carbonate phase whose defect energetics are closely related to its stability and decomposition behavior in various lithium-based electrochemical systems. These properties of Li2CO3 are particularly important in lithium–oxygen battery environments. In these systems, Li2CO3 can form as a parasitic discharge product alongside Li2O2, the primary discharge product, leading to performance degradation. However, compared with Li2O2, the intrinsic defect thermodynamics of Li2CO3 and how chemical doping modifies its defect energetics remain insufficiently understood. In this study, first-principles calculations were performed to systematically analyze the intrinsic point-defect energetics of Li2CO3 and to evaluate the effects of fluorine doping on vacancy formation energies in Li2CO3 and Li2O2. Intrinsic defect analysis reveals that defect behavior is predominantly governed by lithium-related defects. Upon fluorine doping, the carbon vacancy formation energies decrease selectively, destabilizing the carbonate framework. Lithium vacancy formation energies decrease partially in Li2CO3 under certain conditions, while a reduction in neutral lithium vacancy formation energy is observed in Li2O2. These results suggest that fluorine doping modulates the defect energetics of both discharge products, potentially providing a thermodynamic basis for controlling the stability of Li2CO3 and Li2O2 under thermodynamic conditions representative of lithium–oxygen batteries.