The development of sodium‐ion batteries is currently limited by the availability of high‐energy and low‐cost cathode materials. The energy density of cathodes can be maximized by expanding the voltage range for cycling, but this often leads to severe capacity degradation. Cathodes that demonstrate good long‐term cyclability at high voltage cut‐offs (>4.3 V vs Na/Na⁺) are scarce in the literature. In this work, layered P2‐Na_0.66Mn_1‐y Mg_y O₂ was synthesized by using a modified Pechini method at various compositions (y =0, 0.05, 0.1) and characterized after extended cycling between 2–4.5, 4.6, and 4.7 V vs. Na/Na⁺. Na_0.66Mn_0.95Mg_0.05O₂ displayed a similar initial discharge capacity to Na_0.66MnO₂ with significant improvements in cycle retention. It was most promising when cycled between 2 and 4.5 V, retaining 140 mAh g⁻¹ (82 % retention) and 116 mAh g⁻¹ (68 % retention) after 50 and 100 cycles, respectively, at low current (40 mA g⁻¹). A higher Mg dopant quantity led to improvements in cyclability and rate performance albeit with lower initial discharge capacity. Electrochemical and physical (ex situ XRD) characterizations were used to delineate the role of high‐voltage phase transitions, SEI layer formation, electrolyte solvent insertion into sodium slabs, and active material degradation/dissolution toward capacity loss.

中文翻译：

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钠离子电池P2-Na0.66Mn1-yMgyO2阴极的高压稳定性和表征

钠离子电池的发展目前受限于高能量和低成本阴极材料的可用性。可以通过扩大循环电压范围来最大化阴极的能量密度，但这通常会导致严重的容量下降。在高电压下（> 4.3 V vs. Na / Na ⁺）表现出良好的长期可循环性的阴极在文献中很少。在这项工作中，使用改进的Pechini方法在各种组成下（y = 0，0.05，0.1）合成了层状P2-Na _0.66 Mn ₁ - _y Mg _y O ₂，并在2-4.5、4.6和4.7 V vs.Na/Na ⁺。娜_0.66 Mn _0.95 Mg _0.05 O ₂的初始放电容量与Na _0.66 MnO ₂相似，循环保持率显着提高。当在2至4.5 V之间循环时，最有希望的是，在低电流（40 mA g-）下分别进行50和100次循环后，分别保持140 mAh g ^-1（82％保留）和116 mAh g ^-1（68％保留）^{。 1个}）。较高的Mg掺杂剂量虽然降低了初始放电容量，但可改善循环性能和速率性能。电化学和物理（非原位XRD）表征用于描述高压相变，SEI层形成，电解质溶剂插入钠板以及活性材料对容量损失的降解/溶解的作用。