Li-rich cathode materials are potential candidates for next-generation Li-ion batteries. However, they exhibit a large voltage hysteresis on the first charge/discharge cycle, which involves a substantial (up to 1 V) loss of voltage and therefore energy density. For Na cathodes, for example Na_0.75[Li_0.25Mn_0.75]O₂, voltage hysteresis can be explained by the formation of molecular O₂ trapped in voids within the particles. Here we show that this is also the case for Li_1.2Ni_0.13Co_0.13Mn_0.54O₂. Resonant inelastic X-ray scattering and ¹⁷O magic angle spinning NMR spectroscopy show that molecular O₂, rather than O₂²⁻, forms within the particles on the oxidation of O²⁻ at 4.6 V versus Li⁺/Li on charge. These O₂ molecules are reduced back to O²⁻ on discharge, but at the lower voltage of 3.75 V, which explains the voltage hysteresis in Li-rich cathodes. ¹⁷O magic angle spinning NMR spectroscopy indicates a quantity of bulk O₂ consistent with the O-redox charge capacity minus the small quantity of O₂ loss from the surface. The implication is that O₂, trapped in the bulk and lost from the surface, can explain O-redox.

富含锂的阴极材料是下一代锂离子电池的潜在候选材料。但是，它们在第一个充电/放电循环中表现出较大的电压滞后现象，这会导致电压的大量损失（高达1 V），从而导致能量密度降低。对于Na阴极，例如Na _0.75 [Li _0.25 Mn _0.75 ] O ₂，电压滞后现象可以通过在颗粒内的空隙中捕获的分子O ₂的形成来解释。在此我们表明，对于Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂也是这种情况。共振非弹性X射线散射和¹⁷ø魔角旋转NMR光谱表明，分子直径：₂，而不是Ô ₂ ^2-，对的O-氧化在颗粒内形成^2-在4.6V对Li ⁺ /锂上的电荷。这些O ₂分子在放电时还原为O ^2-，但在3.75 V的较低电压下，这解释了富锂阴极的电压滞后现象。¹⁷ O魔角旋转NMR光谱表明，大量的O ₂与O-氧化还原电荷容量一致，减去从表面损失的少量O ₂。这意味着O ₂，被困在大块中并从表面消失，可以解释O-氧化还原。