Open AccessMapping and Metastability of Heterogeneity in LiMn2O4 Battery Electrodes with High Energy Density
Author(s) -
Mark Wolfman,
Sara Khawaja,
Jordi Cabana
Publication year - 2020
Publication title -
journal of the electrochemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.258
H-Index - 271
eISSN - 1945-7111
pISSN - 0013-4651
DOI - 10.1149/1945-7111/ab6298
Subject(s) - electrode , microscale chemistry , materials science , cathode , anode , chemical physics , battery (electricity) , electrochemistry , lithium (medication) , metastability , relaxation (psychology) , diffusion , nanotechnology , analytical chemistry (journal) , chemistry , thermodynamics , medicine , psychology , social psychology , power (physics) , physics , mathematics education , mathematics , organic chemistry , endocrinology , chromatography
The hierarchical nature of the cathode in Li-ion batteries can result in phenomena determining electrochemical performance occurring at different length-scales, from individual atoms to the whole electrode. In architectures designed for high density of charge storage, transport limitations can emerge at the microscale that compromise effective utilization and accelerate degradation. These limitations manifest as chemical heterogeneity within the electrode. Micro-focused diffraction mapping using a laboratory X-ray source provides maps with sub-mm resolution of a whole electrode composed of commercial LiMn 2 O 4 . Evidence of disparate local utilization both laterally and along the depth of the electrode was obtained, especially at high rates and after multiple charge-discharge cycles. As a model to study the persistence of heterogeneity due to transport limitations, lateral gradients to lithium transport were introduced by cycling against Li anodes of small diameter. The resulting maps revealed the effects of anisotropic electric migration and diffusion to be separated, confirming that diffusion is the primary limitation for long-range kinetics. Tracking of subsequent relaxation revealed that the heterogeneity was metastable despite a strong thermodynamic driving force, maintained by poor lithium transport through the solid electrode matrix. This study enriches our understanding of transport across thick electrode architectures and the imposition of unique frustrated states, away from equilibrium.