Unraveling the Critical Role of Ti Substitution in P2-NaxLiyMn1–yO2 Cathodes for Highly Reversible Oxygen Redox Chemistry,Chemistry of Materials

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Unraveling the Critical Role of Ti Substitution in P2-NaxLiyMn1–yO2 Cathodes for Highly Reversible Oxygen Redox Chemistry
Chemistry of Materials ( IF 7.2 ) Pub Date : 2020-01-17 , DOI: 10.1021/acs.chemmater.9b03765
Chao Li ₁ , Chong Zhao ₁ , Bei Hu ₁ , Wei Tong ₂ , Ming Shen ₁ , Bingwen Hu ₁

Affiliation

Monovalent Li-substitution has been proven to be an effective strategy to resolve the pivotal problems confronted with P2-type layered Mn oxides, such as cooperative Jahn–Teller distortions of Mn³⁺ ions and drastic P2-(OP4)-O2 phase transformations occurring during desodiation. However, the cycling stability of most Li⁺-substituted P₂-Na_xLi_yMn_1–yO₂ remains far from satisfactory. We herein develop a facile Ti-substitution method to improve the cyclability by taking Na_0.72Li_0.24Mn_0.76O₂ (NLMO) as an example. As expected, the novel layered oxide cathode Na_0.72Li_0.24Ti_0.10Mn_0.66O₂ (NLMTO-0.1) is able to deliver a very high reversible capacity of 165 mA h g^–1 for over 80 cycles within the voltage range of 1.5–4.5 V (vs Na metal), which is among the best for the reported Na-storage cathode materials. Moreover, the structure–property relationship of Ti⁴⁺ substitution is scrutinized by an arsenal of ²³Na/⁷Li solid-state nuclear magnetic resonance, dual-mode electron paramagnetic resonance, and synchrotron X-ray diffraction techniques. The results unequivocally substantiate that Ti substitution can effectively reduce the Li⁺/Mn⁴⁺ ordering in TMO₂ slabs, assist the reversible migration of Li⁺ during Na⁺ extraction/intercalation, and ultimately enhance the reversibility of the oxygen redox process. This work provides a comprehensive insight into the structure chemistry in developing high-capacity and high-stability layered oxide cathodes.

中文翻译：

揭示钛取代在P ₂ -Na _x Li _y Mn _{1- y} O ₂阴极中对高可逆氧氧化还原化学的关键作用

单价锂取代已被证明是解决P2型层状Mn氧化物所面临的关键问题的有效策略，例如Mn ³⁺离子的Jahn–Teller协同变形和剧烈的P2-（OP4）-O2相变的发生在灭绝期间。但是，大多数Li ⁺取代的P ₂ -Na _x Li _y Mn _{1- y} O ₂的循环稳定性仍然远远不能令人满意。我们在本文中开发了一种简便的Ti替代方法，通过使用Na _0.72 Li _0.24 Mn _0.76 O ₂来提高循环性。（NLMO）为例。正如预期的那样，新型层状氧化物阴极Na _0.72 Li _0.24 Ti _0.10 Mn _0.66 O ₂（NLMTO-0.1）能够在1.5-4.5的电压范围内提供超过80个循环的165 mA hg ^–1的非常高的可逆容量。V（相对于Na金属），是所报道的Na存储阴极材料中最好的V。此外，用²³ Na / ⁷的武库检查了Ti ⁴⁺取代的结构-性质关系Li固态核磁共振，双模电子顺磁共振和同步加速器X射线衍射技术。结果明确证实，Ti替代可有效降低TMO ₂平板中的Li ⁺ / Mn ⁴⁺有序化，在Na ⁺萃取/嵌入过程中协助Li ⁺的可逆迁移，并最终增强氧还原过程的可逆性。这项工作为开发高容量和高稳定性的分层氧化物阴极提供了对结构化学的全面了解。

更新日期：2020-01-17

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