Revealing the inhomogeneous surface chemistry on the spherical layered oxide polycrystalline cathode particles

The hierarchical structure of the composite cathodes brings in significant chemical complexity related to the interfaces,such as cathode electrolyte interphase.These interfaces account for only a small fraction of the volume and mass,they could,however,have profound impacts on the cell-level electrochemistry.As the investigation of these interfaces becomes a crucial topic in the battery research,there is a need to properly study the surface chemistry,particularly to eliminate the biased,incomplete characterization provided by techniques that assume the homogeneous surface chemistry.Herein,we utilize nano-resolution spatially-resolved x-ray spectroscopic tools to probe the heterogeneity of the surface chemistry on LiNi0.8Mn0.1Co0.1O2 layered cathode secondary particles.Informed by the nano-resolution mapping of the Ni valance state,which serves as a measurement of the local surface chemistry,we construct a conceptual model to elucidate the electrochemical consequence of the inhomogeneous local impedance over the particle surface.Going beyond the implication in battery science,our work highlights a balance between the high-resolution probing the local chemistry and the statistical representativeness,which is particularly vital in the study of the highly complex material systems.

Data-Driven Lithium-Ion Battery Cathode Research with State-of-the-Art Synchrotron X-ray Techniques

CONSPECTUS:The lithium-ion battery(LIB)is a tremendously successful technology for energy storage thanks to its favorable characteristics including high energy density,long lifespan,affordability,and safety.It has been widely adopted in sectors including consumer electronics and electric vehicles,which are featured by an enormous market value.To meet the ever-increasing demands for energy density and cycle life,industry and academia are continuously devoting efforts to improve the current LIB technology.This requires an in-depth understanding of the electrochemical reaction processes and degradation/failure mech-anisms,to which advanced characterization is pivotal.Combining advanced synchrotron X-ray techniques with machine learning(ML)methods has been demonstrated as a powerful tool for uncovering the fundamental reaction and aging mechanisms in LIB and is emerging as an important research frontier.Our group’s research has been focusing on the battery cathode,which is a major limiting factor in today’s LIB technology.The degradation and failure of cathode materials in LIB are multiscale.The chemo mechanical processes at these different length scales are intertwined and mutually modulated.Therefore,it is crucial to understand the underlying mechanisms of charge−lattice−morphology−kinetics interactions in battery cathodes as a function of the electrochemical states.Synchrotron X-ray technology has unique advantages.It can detect lattice structure,electronic structure,chemical valence state,and multiscale morphology in different experimental modes,with high resolution and high efficiency.However,the large-scale experimental data bring great challenges in terms of reduction,analysis,and interpretation.Data-driven methods based on ML can greatly assist researchers to understand,control,and predict the electrochemical behavior of the complex battery cathode systems.In this Account,we focus on showcasing the integration of synchrotron and ML techniques for LIB cathode research.We review our recent findings on charge−lattice−morphology−kinetics in LIB cathode materials via this approach.First,the ML-based morphological study of cathode materials is discussed,highlighting a ML-assisted automatic feature recognition,particle identification,and statistical analysis of the prolonged cycling-induced particle damage and detachment from the carbon matrix.Second,we discuss the chemical heterogeneity and lattice deformation in cathode materials revealed by ML-assisted multimodal synchrotron characterizations.The role of ML tools in identifying and understanding chemical outliers and lattice defects in NCM cathodes is highlighted.Third,we provide our perspective on a future“dream”experiment for investigating the spatial distribution of cation−anion redox coupling effects in the battery cathode by means of resonant inelastic X-ray scattering(RIXS)imaging with ML.We anticipate that this new approach will provide new horizons for the development of novel high-energy and high-power-density LIB cathode materials.With an emphasis on the data-driven approaches for researching battery materials with synchrotron X-ray techniques,we hope that this Account will lead to more endeavors in this research field.