Journal
ACS APPLIED ENERGY MATERIALS
Volume 4, Issue 10, Pages 11069-11079Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsaem.1c01995
Keywords
battery cathode; lithium nickel manganese cobalt oxide; electrochemical creep; cycle life; high voltage; chemomechanical degradation; Coulombic efficiency
Funding
- Exelon Corporation
- National Science Foundation Scalable Nanomanufacturing Program [NSF CMMI-1727846, NSF CMMI-2039268]
- National Science Foundation Future Manufacturing Program [NSF CMMI-2037026]
- Center for Electrochemical Energy Science, an Energy Frontier Research Center - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences [DE-AC02-06CH11357]
- Northwestern University
- Dow Chemical Company
- DuPont de Nemours, Inc.
- DOE Office of Science [DE-AC02-06CH11357]
- SHyNE Resource [NSF ECCS-1542205]
- IIN
- Northwestern University MRSEC program [NSF DMR-1720139]
- NASA Ames Research Center [NNA06CB93G]
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The study demonstrates that applying a graphene coating on NMC cathode materials significantly improves the cycle life and Coulombic efficiency at high voltages, mitigating electrolyte decomposition reactions and particle fracture. The research also establishes a relationship between the spatial uniformity of lithium flux and particle-level mechanical degradation in NMC cathodes.
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.
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