Abstract Voltage and capacity decay problems of Li2MnO3-based lithium rich layered cathode materials are still unsolved, which are the major barriers for its practical application. Intensive investigations of their mechanisms have been proceeded in recent years, which clarify cation ordered arrangement and spinel deterioration are culprits in structural aspect. Herein, we conduct various analyses to a rocksalt type Li2Nb0·15Mn0·85O3, whose first charge process is along with primary oxygen redox as Li2MnO3, but subsequently shows much better capacity retention. This material suffers from severe voltage decay and overpotential during the cycle but hard X-ray diffraction indicates it can remain rocksalt structure without any tendency of spinel deterioration or cation ordering even with massive lithium vacancies. XAS results further show there is no evident oxygen redox activity from the second cycle, while the redox range of Mn nearly has no change during the cycle. Our results demonstrate that disordered lithium rich cathode materials could be promising to exhibit highly reversible capacity upon long cycling, and their voltage decay problem could be easier to be solved for different mechanism from layered one.

中文翻译：

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岩盐型 Li2Nb0.15Mn0.85O3 循环时无结构降解或氧化还原演化

摘要 Li2MnO3基富锂层状正极材料的电压和容量衰减问题仍未解决，是其实际应用的主要障碍。近年来对其机制进行了深入的研究，阐明了阳离子有序排列和尖晶石劣化是结构方面的罪魁祸首。在此，我们对岩盐型 Li2Nb0·15Mn0·85O3 进行了各种分析，其首次充电过程与初级氧氧化还原为 Li2MnO3，但随后显示出更好的容量保持率。这种材料在循环过程中会遭受严重的电压衰减和过电位，但硬 X 射线衍射表明它可以保持岩盐结构，即使存在大量锂空位，也不会出现尖晶石退化或阳离子有序的趋势。XAS 结果进一步表明，从第二个循环开始，没有明显的氧氧化还原活性，而 Mn 的氧化还原范围在循环中几乎没有变化。我们的结果表明，无序的富锂正极材料有望在长时间循环中表现出高度可逆的容量，并且它们的电压衰减问题可以通过与分层材料不同的机制更容易解决。