锂(药物)
阴极
能量密度
结构精修
离子
衍射
分析化学(期刊)
材料科学
晶体结构
化学
工程物理
结晶学
物理
物理化学
有机化学
内分泌学
光学
医学
色谱法
作者
Lea de Biasi,Aleksandr Kondrakov,Holger Geßwein,Torsten Brezesinski,Pascal Hartmann,Jürgen Janek
标识
DOI:10.1021/acs.jpcc.7b06363
摘要
Two major strategies are currently pursued to improve the energy density of lithium-ion batteries using LiNixCoyMnzO2 (NCM) cathode materials. One is to increase the fraction of redox active Ni (≥80%), which allows larger amounts of Li to be extracted at a given cutoff voltage (Umax). The other is to increase Umax, in particular for medium-Ni content NCM materials. However, the accompanying lattice changes ultimately lead to capacity fading in both cases. Here the structural changes occurring in Li1.02NixCoyMnzO2 (with x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) during cycling operation in the voltage range between 3.0 and 4.6 V vs Li are quantified by means of operando X-ray diffraction combined with detailed Rietveld analysis. All samples show a large decrease in unit cell volume upon charging, ranging from 2.4% for NCM111 (33% Ni) to 8.0% for NCM851005 (85% Ni). To make a fair comparison of the structural stability of the different NCM materials, energy densities as a function of Umax are estimated and correlated with X-ray diffraction results. It is shown that NCMs with a lower Ni content allow for specific energies similar to that of, e.g., Ni-rich NCM811 (80% Ni) when operated at sufficiently high Umax, but still undergo less pronounced changes in structure. Nevertheless, as indicated by charge/discharge tests, the capacity retention of low- and medium-Ni content NCMs cycled to high Umax is also strongly affected by factors other than stability of the layered crystal lattice (electrolyte decomposition etc.). Overall, it is demonstrated that the complexity of the degradation processes needs to be better understood to identify optimal cycling conditions for specific cathode compositions.
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