Enhancing the longevity of lithium-manganese-rich layered oxides by promoting oxygen redox reversibility.

To enable widespread adoption of electric vehicles, positive-electrode materials must fulfill high energy, long-term stability, and earth-abundant composition within large-format architectures. Lithium-manganese-rich layered oxides show promise through high energy enabled by oxygen redox chemistry and abundant manganese content while minimizing cobalt content. However, oxygen redox irreversibility and gas evolution present challenges in its adoption to large-format cells. Here, we reveal how applied voltage window governs oxygen redox reversibility through integrated X-ray spectroscopy and microscopy, electron microscopy, and in-situ mass spectrometry. An optimized potential window of 4.3-2.0 V vs. graphite confines oxygen redox to reversible regimes while ensuring complete reduction, minimizing electron deficiency and suppressing gas evolution and structural degradation. Building on these insights, our formation and cycling protocol achieves specific energy of 663 Wh/kg based on the mass of the positive electrode active material with 92.2% retention after 883 cycles in 40 Ah cells using cobalt-lean lithium-manganese-rich layered oxides (0.27 wt% cobalt), demonstrating viability for scalable and affordable electric-vehicle batteries.