Research On Stability Of Cathode Materials Of Li-ion Battery Based On X-ray Spectro-microscopy

Novel synchrotron radiation facilities with higher brightness,higher collimation and tunable energy have facilitated groundbreaking improvements in nanoscale X-ray imaging methodologies.Compared with visible light and electrons,X-ray has the char-acteristics of short wavelength and deep penetration,which makes it suitably applied in non-destructive,high resolution imaging experiments.Additionally,taking advantage of the high flex characteristic of the synchrotron radiation facilities,in situ time-resolved X-ray imaging methods have been rapidly developed,which can effectively tackle the non-equilibrium scientific research.In order to understand the relationship between the morphology and functionality,X-ray spectro-microscopy has been broadly developed and become a well-recognized tool in different research fields including energy materials,industrial catalysis and envi-ronmental science.By combining X-ray near edge absorption spectroscopy and X-ray imaging,we can monitor the morphological and chemical evolution,such as valence state changes of the elements of interest,and then finish the correlation analysis,which can provide valuable insights beyond traditional imaging methods.In the research field of energy materials,with the growing need of the consumer electronics and the electronic vehicles,the world has an increasing demand for Li-ion batteries with higher energy densities and enhanced safety.Li-ion battery is a functional material with morphologically complex and chemically heterogeneous,thus characteri-zation methods in different time and spatial scale have been broadly applied in studying the Li-ion batteries to get fully understanding of the materials,such as using X-ray diffraction technique to get the information in macroscopic scale and using transmis-sion electron microscope to visualize the structure of the materials in microscopic scale.But only X-ray spectro-microscopy can effectively and efficiently tackle the intrinsi-cally complicated mesoscale chemistry.Thus,research on X-ray spectro-microscopic imaging technology and its applications on Li-ion batteries is very crucial not only in getting fully understanding of the Li-ion battery materials,but also can help to extend this method in more research areas beyond battery science.Thus,this dissertation has been focused on the study of working principle,failure mechanism and thermal stability of the cathode materials of Li-ion batteries by combin-ing X-ray spectro-microscopy and some other synchrotron-based experimental meth-ods,and proposed a new information retrieval method of X-ray spectro-microscopy to extend its applications on some specific material systems.The results provide valuable theoretical and experimental basis on new cathode materials design and modification.The main research contents and results of this dissertation are summarized as fol-lows:1.Combining X-ray spectro-microscopy,X-ray diffraction,neutron diffraction and DFT calculation to study the evolution of local structural ordering and chemical distribution upon delithiation of a rock salt-sturctured Li1.3Ta0.3Mn0.4O2(LTMO)cath-ode material,and developed the related experimental procedure and data processing and analysis methods,which opened a new way for Li-ion battery research.2.In situ study of thermally driven mesoscale chemomechanical interplay in Li0.5Ni0.6Mn0.2CO0.2O2(NMC622)cathode material through combining X-ray spectro-microscopy,soft X-ray spectroscopy,hard X-ray spectroscopy,Scanning Electron Mi-croscope and Energy Dispersive X-Ray Spectroscopy.We found thermal stress-induced oxygen release,crack formation and the extraction of Li protrusions.This study shows successful application of in situ imaging method on Li-ion batteries,which can be ex-tended to other research area beyond battery science.3.In situ study of thermal stress-induced charge and structure heterogeneity in LiNi0.8Mn0.1Co0.1O2(NMC81 1)at multiscale by combining X-ray spectro-microscopy,X-ray diffraction,hard X-ray spectroscopy,soft X-ray spectroscopy and X-ray raman,systematically studied the dynamics of thermal behavior of the charged NMC811 cath-ode material,including lattice phase transformation,transition metal cation migration,valence state change,and lithium redistribution.Besides,this study emphasizes the im-portant roles of the synchrotron-based characteration techniques in studing the Li-ion batteries and provides the methodological guide on related research.4.Exploration of using X-ray spectro-microscopy to study samples with highly anisotropic lattice structures.We did a three-dimentional XANES imaging experiment on a single-crystalline LiCoO2(LCO)particle and found X-ray absorption spectra on single-crystalline particles with highly anisotropic lattice structures was sensitive to the polarization configurations of the incident X-rays.We then developed a new informa-tion retrieval methodology by extracting the white-line peak energy in the X-ray ab-sorption near-edge structure spectra instead of edge energy as a key data attribute for representing the local state of charge.The proposed method demonstrates significantly improved accuracy and reveals the mesoscale chemical complexity in LCO particles with better fidelity.Meanwhile,the developed method is also broadly applicable to a wide range of scientific disciplines well beyond battery research.