Structural and Chemical Insights into Conversion Reactions from in-situ Pair Distribution Function Measurements

摘要

In the search for new Li-ion battery electrodes that provide the best compromise between capacity, power, charge rates, and long-term stability, increasingly complex composite materials and reaction mechanisms have emerged. Amongst high capacity conversion electrodes based on highly abundant iron, mixed anion oxyfiuoride systems combine favorable performance characteristics of the simple oxides (e.g., Fe2O3, Fe3O4, FeO) and fluorides (e.g., FeF3, FeF2). Electrochemical reaction of the oxyfiuoride with lithium (FeOF + 3Li →Fe + Li2O + LiF) couples the higher output voltages and reaction potentials of the fluorides and the improved reaction kinetics, capacity and cyclability of the oxides to provide promising electrochemical performance.1 Identifying the fundamental basis for these performance advantages requires a comprehensive understanding of the electrochemical reaction mechanism and, accordingly, detailed knowledge of how the atomic structure transforms, how the electrode particles evolve, and how the chemical composition of different components change.