Capacity Fading of Ni-Rich NCA Cathodes: Effect of Microcracking Extent
Capacity Fading of Ni-Rich NCA Cathodes: Effect of Microcracking Extent
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DOI：
10.1021/acsenergylett.9b02302
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发表时间：
2019-12-01
影响因子：
22
通讯作者：
Sun, Yang-Kook
中科院分区：
文献类型：
--
作者：
Nam, Gyeong Won;Park, Nam-Yung;Sun, Yang-Kook
合成了富Ni Li[Ni 1-x-yCoxAly]O-2（NCA）正极材料（1 -x-y = 0.8，0.88和0.95），研究了其容量衰减机理。随着Ni含量的增加，阴极的容量保持率和热性能随着放电容量的增加而变差。容量衰减与由H2-H3相变引起的各向异性体积变化以及由此产生的微裂纹程度相关。尽管所有三个阴极在充电至3.9V后开始产生微裂纹，但微裂纹扩展到颗粒外表面的电位随着Ni含量的增加而降低。这些微裂纹破坏了阴极的机械完整性，并促进电解质渗透到颗粒芯中，这加速了内部初级颗粒的表面降解。因此，减轻或延迟H2-H3相变是改善富Ni NCA阴极的循环性能的关键。
Ni-rich Li[Ni1-x-yCoxAly]O-2 (NCA) cathodes (1 - x - y = 0.8, 0.88, and 0.95) are synthesized to investigate the capacity fading mechanism of Ni-rich NCA cathodes. The capacity retention and thermal property of the cathodes deteriorate as their discharge capacity increases when the Ni fraction is increased. The capacity fading correlates well with the anisotropic volume variations caused by the H2-H3 phase transition and the resulting extent of microcracking. Although all three cathodes start to develop microcracks after being charged to 3.9 V, the potential at which microcracks propagated to the outer surface of the particle decreases with increasing Ni content. These microcracks undermine the mechanical integrity of the cathode and facilitate electrolyte penetration into the particle core, which accelerates surface degradation of the internal primary particles. Therefore, mitigating or delaying the H2-H3 phase transition is key to improving the cycling performance of Ni-rich NCA cathodes.