The surficial residual alkali is a key factor that leads to aggravated phase transition and decay in cobalt-free high-nickel cathode. In this paper, we develop a one-step in-situ modification technique to convert the residual alkali on the LiNiMnO (NM91) surface into LiMoO coating. As a fast ionic conductor, LiMoO coating not only facilitate Li diffusion, but also inhibits the transition from layered to rock salt phase on the cathode surface. Moreover, the multi-aperture architecture formed in the conversion promotes the high-valent Mo enter-into the lattice and realizes the gradient doping of Mo through thermodynamic diffusion. Due to the pillar effect, Mo doping increases c-axis spacing, mitigates cation mixing, and reduces the irreversible H2-H3 phase transition. As a result, both the Li diffusion kinetics and thermodynamic stability are improved. Consequently, the as-prepared Mo modified NM91 exhibits an increased capacity retention from original 62.3–75.6 % (100 cycles, 0.2 C) and enhanced rate capability of 131.96 mAh g at 5.0 C. This work provides a facile “reducing alkali” technological process, and lays foundation for the material design and performance optimization of high energy density cathodes in lithium-ion batteries.

中文翻译：

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将残留碱原位转化为快离子导体涂层并同步实现Mo4+梯度掺杂稳定LiNi0.9Mn0.1O2正极

表面残碱是导致无钴高镍正极相变和衰变加剧的关键因素。在本文中，我们开发了一种一步原位改性技术，将 LiNiMnO (NM91) 表面的残留碱转化为 LiMoO 涂层。作为快离子导体，LiMoO涂层不仅有利于Li扩散，而且抑制正极表面从层状相到岩盐相的转变。此外，转换过程中形成的多孔结构促进了高价Mo进入晶格，通过热力学扩散实现了Mo的梯度掺杂。由于柱效应，Mo 掺杂增加了 c 轴间距，减轻了阳离子混合，并减少了不可逆的 H2-H3 相变。结果，Li扩散动力学和热力学稳定性都得到改善。因此，所制备的 Mo 改性 NM91 的容量保持率从原来的 62.3% 提高到 75.6%（100 次循环，0.2 C），5.0 C 时的倍率性能提高到 131.96 mAh g。这项工作提供了一种简便的“还原碱”工艺流程，为锂离子电池高能量密度正极的材料设计和性能优化奠定基础。