Dose Wesley M, Morzy Jędrzej K, Mahadevegowda Amoghavarsha, Ducati Caterina, Grey Clare P, De Volder Michael F L
Department of Engineering, University of Cambridge 17 Charles Babbage Road Cambridge CB3 0FS UK
Department of Chemistry, University of Cambridge Lensfield Road Cambridge CB2 1EW UK
J Mater Chem A Mater. 2021 Oct 11;9(41):23582-23596. doi: 10.1039/d1ta06324c. eCollection 2021 Oct 26.
The transition towards electric vehicles and more sustainable transportation is dependent on lithium-ion battery (LIB) performance. Ni-rich layered transition metal oxides, such as NMC811 (LiNiMnCoO), are promising cathode candidates for LIBs due to their higher specific capacity and lower cost compared with lower Ni content materials. However, complex degradation mechanisms inhibit their use. In this work, tailored aging protocols are employed to decouple the effect of electrochemical stimuli on the degradation mechanisms in graphite/NMC811 full cells. Using these protocols, impedance measurements, and differential voltage analysis, the primary drivers for capacity fade and impedance rise are shown to be large state of charge changes combined with high upper cut-off voltage. Focused ion beam-scanning electron microscopy highlights that extensive microscale NMC particle cracking, caused by electrode manufacturing and calendering, is present prior to aging and not immediately detrimental to the gravimetric capacity and impedance. Scanning transmission electron microscopy electron energy loss spectroscopy reveals a correlation between impedance rise and the level of transition metal reduction at the surfaces of aged NMC811. The present study provides insight into the leading causes for LIB performance fading, and highlights the defining role played by the evolving properties of the cathode particle surface layer.
向电动汽车和更可持续交通的转型取决于锂离子电池（LIB）的性能。富镍层状过渡金属氧化物，如NMC811（LiNiMnCoO），由于与低镍含量材料相比具有更高的比容量和更低的成本，是LIBs有前景的阴极候选材料。然而，复杂的降解机制限制了它们的使用。在这项工作中，采用了定制的老化方案来分离电化学刺激对石墨/NMC811全电池降解机制的影响。使用这些方案、阻抗测量和差分电压分析，结果表明容量衰减和阻抗增加的主要驱动因素是大的充电状态变化以及高的上限截止电压。聚焦离子束扫描电子显微镜突出显示，由电极制造和压延引起的广泛的微观尺度NMC颗粒开裂在老化之前就已存在，并且不会立即对重量容量和阻抗产生不利影响。扫描透射电子显微镜电子能量损失谱揭示了老化的NMC811表面阻抗增加与过渡金属还原程度之间的相关性。本研究深入了解了LIB性能衰退的主要原因，并突出了阴极颗粒表面层不断演变的特性所起的决定性作用。
