Wang Xin, Cai Jiyu, Liu Yongqiang, Han Xiaoxiao, Ren Yang, Li Jianlin, Liu Yuzi, Meng Xiangbo
Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701, United States of America.
Beijing Advanced Innovation Center for Materials Genome Engineering, Beijing Key Laboratory for Magneto-Photoelectrical Composite and Interface Science, School of Mathematics and Physics, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, People's Republic of China.
Nanotechnology. 2021 Mar 12;32(11):115401. doi: 10.1088/1361-6528/abd127.
Ascribed to their higher capacity and lower cost compared to conventional LiCoO, the Ni-rich layered LiNiMnCoO (NMC622) is now considered as one promising cathode for lithium-ion batteries (LIBs). However, it still suffers from some evident performance degradation, especially under high cutoff voltages (i.e., >4.3 V versus Li/Li). The performance degradation typically is exhibited as capacity fading and voltage drop, mainly originating from an instable interface between the NMC622 and electrolyte as well as the evolution of the NMC structure. To improve the interfacial and structural stability of NMC cathodes, herein we deposited an ultrathin layer of AlO coatings (<5 nm) conformally over NMC622 composite electrodes directly using atomic layer deposition (ALD). It was found that, under different upper cutoff voltages (4.3, 4.5, and 4.7 V), the ALD AlO coatings enable enhanced performance of NMC622 cathodes with better cyclability and higher capacity. Particularly, the beneficial effects of the ALD AlO coatings are more remarkable at higher upper cutoff voltages (4.5 and 4.7 V). Furthermore, the ALD coatings can significantly improve the rate capability of NMC622. To this end, we utilized a suite of characterization tools and performed a series of electrochemical tests to clarify the effects of the ALD AlO coatings. This study revealed that the beneficial effects of the AlO ALD coatings are multiple: (i) serving as an artificial layer of solid electrolyte interphase to mitigate undesirable interfacial reactions; (ii) acting as a physical barrier to inhibit metal dissolution of NMC; and (iii) forming a reinforced networked overcoating to boost the mechanical integrity of NMC cathodes. This study is favorable for designing high-performance NMC cathodes.
与传统的LiCoO相比，富镍层状LiNiMnCoO（NMC622）因其更高的容量和更低的成本，现在被认为是锂离子电池（LIBs）一种很有前景的正极材料。然而，它仍然存在一些明显的性能退化问题，特别是在高截止电压下（即相对于Li/Li >4.3 V）。性能退化通常表现为容量衰减和电压下降，主要源于NMC622与电解质之间不稳定的界面以及NMC结构的演变。为了提高NMC正极的界面和结构稳定性，在此我们直接使用原子层沉积（ALD）在NMC622复合电极上共形沉积了一层超薄的AlO涂层（<5 nm）。研究发现，在不同的上截止电压（4.3、4.5和4.7 V）下，ALD AlO涂层能够提高NMC622正极的性能，具有更好的循环稳定性和更高的容量。特别是，ALD AlO涂层在较高的上截止电压（4.5和4.7 V）下的有益效果更为显著。此外，ALD涂层可以显著提高NMC622的倍率性能。为此，我们使用了一系列表征工具并进行了一系列电化学测试，以阐明ALD AlO涂层的作用。这项研究表明，AlO ALD涂层的有益作用是多方面的：（i）作为人工固体电解质界面层，减轻不良的界面反应；（ii）作为物理屏障，抑制NMC的金属溶解；（iii）形成增强的网络化包覆层，提高NMC正极的机械完整性。这项研究有利于设计高性能的NMC正极。
