Elucidating and Mitigating High-Voltage Interfacial Chemomechanical Degradation of Nickel-Rich Lithium-Ion Battery Cathodes via Conformal Graphene Coating
Elucidating and Mitigating High-Voltage Interfacial Chemomechanical Degradation of Nickel-Rich Lithium-Ion Battery Cathodes via Conformal Graphene Coating
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DOI：
10.1021/acsaem.1c01995
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发表时间：
2021-09-27
影响因子：
6.4
通讯作者：
Hersam, Mark C.
中科院分区：
文献类型：
--
作者：
Luu, Norman S.;Lim, Jin-Myoung;Hersam, Mark C.
锂镍锰钴氧化物（NMCs）是高性能锂离子电池极具潜力的正极材料。虽然这些材料通常在温和的电压窗（高达4.3 V vs Li/Li+）内循环，但由于严重的界面和化学力学降解，通常避免在高压（>4.7 V vs Li/Li+）下操作以获得额外的容量。在这些高电位下，NMC降解是由电解质分解反应加剧和化学力学应变的不均匀积聚导致颗粒断裂引起的。通过在NMC初级颗粒表面涂覆保形石墨烯涂层，我们发现电化学循环时高压循环寿命和库仑效率显著提高。尸检x射线衍射、x射线光电子能谱和电子显微镜显示，石墨烯涂层减轻了电解质分解反应，减少了颗粒断裂和电化学蠕变。我们提出了锂通量的空间均匀性与颗粒级机械降解之间的关系，并表明保形石墨烯涂层非常适合解决这些问题。总的来说，这些结果描绘了一条合理减轻富镍阴极高压化学力学降解的途径，可以应用于现有和新兴的电池材料类别。
Lithium nickel manganese cobalt oxides (NMCs) are promising cathode materials for high-performance lithium-ion batteries. Although these materials are commonly cycled within mild voltage windows (up to 4.3 V vs Li/Li+), operation at high voltages (>4.7 V vs Li/Li+) to access additional capacity is generally avoided due to severe interfacial and chemomechanical degradation. At these high potentials, NMC degradation is caused by exacerbated electrolyte decomposition reactions and non-uniform buildup of chemomechanical strains that result in particle fracture. By applying a conformal graphene coating on the surface of NMC primary particles, we find significant enhancements in the high-voltage cycle life and Coulombic efficiency upon electrochemical cycling. Postmortem X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy suggest that the graphene coating mitigates electrolyte decomposition reactions and reduces particle fracture and electrochemical creep. We propose a relationship between the spatial uniformity of lithium flux and particle-level mechanical degradation and show that a conformal graphene coating is well-suited to address these issues. Overall, these results delineate a pathway for rationally mitigating high-voltage chemomechanical degradation of nickel-rich cathodes that can be applied to existing and emerging classes of battery materials.