Abstract P2-type Na0.67Ni0.33Mn0.67O2 (NNMO) is a state-of-the-art, high-energy and high-voltage cathode material in sodium-ion batteries. However, surface degradation effects, such as P2–O2 phase transformation, ordering of Na+/vacancy, electrolyte decomposition, and HF attack, limit its electrochemical stability. To counter these effects, we applied Mg1–xNixO (MgNiO) as a coating formed via wet-chemical coating to suppress unfavorable side reactions; surface doping of Mg2+ also occurs post-calcination, which is expected to reduce P2–O2 transition near the surface structure. MgNiO-NNMO exhibited outstanding cycling stability (70.08 mAh g−1 over 200 cycles) and rate capability (39.41 mAh g−1 at 5C over 800 cycles). The influence of Mg2+ doping was studied comprehensively through in situ and ex situ X-ray diffraction analysis. Furthermore, to characterize the protective role of the MgNiO coating in harsh conditions, we operated NNMO as Na half cells at a high temperature of 60 °C and high voltage of 4.5 V (vs. Na+/Na) for the first time; under these conditions, MgNiO-NNMO exhibited remarkable cycling stability (52.68 mAh g−1 over 100 cycles) as compared to pristine NNMO (7.213 mAh g−1 over 100 cycles). Surface analysis via X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy were also conducted to investigate the impact of electrolyte decomposition and HF attack.

中文翻译：

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Mg1-xNixO 涂层对 P2 型 Na0.67Ni0.33Mn0.67O2 的多重影响，生成高稳定性钠离子电池正极

摘要 P2型Na0.67Ni0.33Mn0.67O2（NNMO）是钠离子电池中最先进的高能高压正极材料。然而，表面降解效应，如 P2-O2 相变、Na+/空位的排序、电解质分解和 HF 侵蚀，限制了其电化学稳定性。为了应对这些影响，我们应用 Mg1-xNixO (MgNiO) 作为通过湿化学涂层形成的涂层，以抑制不利的副反应；Mg2+ 的表面掺杂也发生在煅烧后，这有望减少表面结构附近的 P2-O2 转变。MgNiO-NNMO 表现出出色的循环稳定性（70.08 mAh g-1 超过 200 次循环）和倍率性能（39.41 mAh g-1 在 5C 超过 800 次循环）。通过原位和异位X射线衍射分析综合研究了Mg2+掺杂的影响。此外，为了表征 MgNiO 涂层在恶劣条件下的保护作用，我们首次将 NNMO 作为 Na 半电池在 60 °C 的高温和 4.5 V（相对于 Na+/Na）的高压下运行；在这些条件下，与原始 NNMO（7.213 mAh g-1 超过 100 次循环）相比，MgNiO-NNMO 表现出显着的循环稳定性（52.68 mAh g-1 超过 100 次循环）。还通过 X 射线光电子能谱和飞行时间二次离子质谱进行了表面分析，以研究电解质分解和 HF 侵蚀的影响。68 mAh g-1 超过 100 次循环）与原始 NNMO（7.213 mAh g-1 超过 100 次循环）相比。还通过 X 射线光电子能谱和飞行时间二次离子质谱进行了表面分析，以研究电解质分解和 HF 侵蚀的影响。68 mAh g-1 超过 100 次循环）与原始 NNMO（7.213 mAh g-1 超过 100 次循环）相比。还通过 X 射线光电子能谱和飞行时间二次离子质谱进行了表面分析，以研究电解质分解和 HF 侵蚀的影响。