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Enhancing Cycling Stability and Capacity Retention of NMC811 Cathodes by Reengineering Interfaces via Electrochemical Fluorination,Advanced Materials Interfaces
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High-capacity cathodes (LiNi0.8Mn0.1Co0.1O2) that can boost the energy density of lithium-ion batteries are promising candidates for vehicle electrification. However, several factors specific to high energy density materials entailing electrode reactions inhibit their application. Fluorination has shown a promising ability to combat the detrimental electrochemical performances of cathode materials, however, it remains difficult to achieve the desired functionality. Herein, a novel electrochemical fluorination (ECF) that demonstrates a promising electrochemical performance enhancement via stabilization of the cathode–electrolyte-interphase (CEI) by forming conformal LiF is proposed. Besides LiF surface layer formation, ECF reduces the degree of fluorination-induced Ni/Li disordering and enhances the layered structural stability as probed by X-ray diffraction. Because of the robust CEI, ECF-NMC811 cathodes deliver 203.0 mAh g−1 first discharge capacity at the current rate of C/10, with ≈98% capacity retention up to 100 cycles. Similarly, it delivers ≈180 mAh g−1 capacity at a 1 C rate with 86.4% capacity retention up to 200 cycles with average coulombic efficiency of > 99.5%. Comprehensive characterization with a multitude of probes reveals that ECF enhances the cycling stability of the electrode without altering bulk structure and morphology.
中文翻译：
高容量正极（LiNi 0.8 Mn 0.1 Co 0.1 O 2）可以提高锂离子电池的能量密度，是汽车电气化的有希望的候选者。然而，导致电极反应的高能量密度材料特有的几个因素阻碍了它们的应用。氟化已显示出一种有希望的能力来对抗阴极材料的有害电化学性能，但是，仍然难以实现所需的功能。在此，提出了一种新型的电化学氟化（ECF），通过形成保形LiF来稳定阴极-电解质界面（CEI），从而证明了有希望的电化学性能增强。除了形成 LiF 表面层外，ECF 还降低了氟化引起的 Ni/Li 无序程度，并增强了 X 射线衍射探测到的层状结构稳定性。由于强大的 CEI，-1在当前C /10 倍率下的首次放电容量，在 100 次循环中具有 ≈98% 的容量保持率。同样，它以 1 C 的速率提供 ≈180 mAh g -1的容量，在 200 次循环中具有 86.4% 的容量保持率，平均库伦效率 > 99.5%。使用多种探针进行的综合表征表明，ECF 在不改变体积结构和形态的情况下增强了电极的循环稳定性。 |
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