Nanoscale morphological and chemical changes of high voltage lithium-manganese rich NMC composite cathodes with cycling.
Nanoscale morphological and chemical changes of high voltage lithium-manganese rich NMC composite cathodes with cycling.
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DOI：
10.1021/nl502090z
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发表时间：
2014-08-13
期刊：
影响因子：
10.8
通讯作者：
Nanda J
中科院分区：
文献类型：
--
作者：
Yang F;Liu Y;Martha SK;Wu Z;Andrews JC;Ice GE;Pianetta P;Nanda J
了解电池材料在电化学循环过程中化学成分和形态的演变对于延长电池循环寿命和确保安全性至关重要。这对于备受争议的高能量密度（高电压）的富锂锰阴极材料Li 1 + xM 1-xO 2（M = Mn、Co、Ni）的情况尤其如此。在这项研究中，我们结合联合收割机全场透射X-射线显微镜（TXM）与X-射线吸收近边结构（XANES）的空间分辨化学相，氧化态和形态的变化内的高电压阴极具有标称成分Li1.2Mn0.525Ni0.175Co0.1O2。具有化学/元素灵敏度的纳米级显微镜提供了阴极的直接定量可视化，并深入了解故障。单像素（约30 nm）TXM XANES揭示了Mn化学随着循环的变化，可能是尖晶石构象，可能包括一些Mn（II），从颗粒表面开始向内进行。颗粒的形态分析显示，高分辨率和统计采样，大多数颗粒采用非球形形状后，200个周期。多能断层扫描显示了一个更均匀的过渡金属协会在原始的粒子，隔离显着与循环。在阴极表面处的过渡金属的耗尽发生在仅仅一个循环之后，可能由表面处的电化学反应驱动。
Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium–manganese rich cathode material of composition Li1 + xM1 – xO2 (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (∼30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface.
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