We suggest that this previously unconsidered structure-redox coupling plays an important role in stabilizing anion redox in LMR-NMC. Thus the O redox chemistry in LMR-NMC cannot be understood as a static O 2– → O – + e – redox couple, but rather as a dynamic structure-redox coupled process described by + e –.
Lithium-rich layered oxide electrodes (Li 1+ xM 1− xO 2, 0 1 V. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.Ī more efficient and sustainable energy infrastructure requires a significant improvement in the cost and energy density of Li-ion batteries 1, 2. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. Here we reveal that in Li 1.17– xNi 0.21Co 0.08Mn 0.54O 2, these properties arise from a strong coupling between anion redox and cation migration. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries.
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