The present work proposes and establishes a universal strategy toward facilitating the development of desired structural types (viz., P-type vs O-type) of “layered” Na- transition metal (T_M) oxides, with the desired Na-content and properties. In this regard, the structure type, allowable Na-content, and Na-layer/“inter-slab” spacing have been found to depend on the “charge:size” ratio of the T_M-ions, concomitant electronegativity and covalency of T_M–O bonds, and the charge neutrality aspect. Overall, increases in the average “charge:size” ratio of the cation combination in the T_M-layer and concomitant T_M–O bond covalency result in a lower effective negative charge on the O-ions. This renders the prismatic coordination of O-ions around the Na-ions more favorable even at a higher Na-content, but with the latter needing some compromise over the charge neutrality aspect. Accordingly, by careful selection of the combination of non-T_M/T_M-ions in the T_M-layer, a high Na-containing (viz., ∼0.84 per formula unit) P2-type Na_0.84([]_0.06Li_0.04Mg_0.02Ni_0.22Mn_0.66)O₂ has been successfully developed here, which, as a cathode material for Na-ion batteries, exhibits a high desodiation capacity of ∼178 mAh/g (@ C/5; within 2–4 V vs Na/Na⁺), exceptional cyclic stability pertaining to a ∼98% capacity retention after 500 galvanostatic desodiation/sodiation cycles at a high current density (2.5C), and also stability upon exposure to air/water. The suitable combination of a high Na-content and “charge:size” ratio in the T_M-layer of the as-developed P2-type Na-T_M-oxide is again the factor responsible for the above properties/performances. Furthermore, going with the proposed scientific basis, mere replacement of Mn⁴⁺, having a higher “charge:size” ratio (∼7.5 Å^–1), with Ti⁴⁺, having a lower “charge:size” ratio (∼6.5 Å^–1), keeping everything else the same, has been found to yield the O3-type structure.

中文翻译：

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设计高含钠 P2 结构“层状”钠过渡金属氧化物作为钠离子电池高性能阴极材料的基本原理

_{目前的工作提出并建立了一种通用策略，以促进“层状”Na-过渡金属 ( TM ) 氧化物的所需结构类型（}即P 型与 O 型）的开发，具有所需的 Na 含量和特性。在这方面，已发现结构类型、允许的 Na 含量和 Na 层/“层间”间距取决于 T M 离子的“电荷：尺寸”比、伴随的电负性和 T 的共_价性_M –O 键和电荷中性方面。_{总体而言，T M}层和伴随的 T _M中阳离子组合的平均“电荷：尺寸”比增加–O 键共价导致 O 离子上的有效负电荷较低。这使得 O 离子围绕 Na 离子的棱柱配位即使在较高的 Na 含量下也更加有利，但后者需要在电荷中性方面做出一些妥协。因此，通过仔细选择T _M层中非 T _M /T _M离子的组合，高含钠量（即每个分子式单元约 0.84）P2 型 Na _0.84（[] _0.06 Li _0.04镁_0.02镍_0.22锰_0.66 )O ₂已在这里成功开发，作为钠离子电池的阴极材料，表现出高脱钠能力~178 mAh/g（@ C/5；在 2–4 V vs Na/Na + 内），出色的^循环稳定性在高电流密度 (2.5C) 下经过 500 次恒电流脱钠/钠化循环后，容量保持率约为 98%，并且在暴露于空气/水中时也具有稳定性。开发的 P2 型 Na-T _{M氧化物的 T M}层中高 Na 含量和“电荷：尺寸”比的适当组合再次是造成上述特性/性能的因素。此外，根据所提出的科学依据，仅用 Ti 替换具有更高“电荷：尺寸”比 (∼7.5 Å ^–1 )的 Mn ⁴⁺⁴⁺具有较低的“电荷：尺寸”比率 (∼6.5 Å ^–1 )，保持其他一切不变，已被发现产生 O3 型结构。