Department of Chemistry, Brookhaven National Laboratory , Upton, New York 11973, United States.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China.
Nano Lett. 2016 Oct 12;16(10):5999-6007. doi: 10.1021/acs.nanolett.6b01609. Epub 2016 Sep 28.
Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layered-to-spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of X-ray diffraction (XRD), pair distribution function (PDF), X-ray absorption (XAS) techniques, and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries, on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compound LiRuMnO. It is found that the nanosized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nanosized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.
富锂和富锰（LMR）阴极材料由于具有高能量密度而被认为是储能应用的有前途的候选材料。然而，这些材料存在严重的电压衰减问题。氧损失和层状到尖晶石相转变是导致这种电压衰减的两个主要因素。在本文中，我们使用 X 射线衍射（XRD）、配分函数（PDF）、X 射线吸收（XAS）技术和像差校正扫描透射电子显微镜（STEM）相结合的方法，研究了微结构缺陷，特别是晶粒边界，对预锂化模型化合物 LiRuMnO 中氧损失和层状到尖晶石相转变的影响。研究发现，纳米级微结构缺陷，特别是预锂化产生的大量晶界，可极大地加速氧损失和电压衰减。缺陷（如纳米晶界）和氧释放形成正反馈循环，在循环过程中相互促进，加速了两种主要的电压衰减贡献者：过渡金属还原和层状到尖晶石相转变。这些结果清楚地表明了氧损失、微结构缺陷和电压衰减之间的重要关系。还建议保持 LMR 材料良好的结晶度和保护其表面的重要性。
