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information is critical for developing sophisticated and predictive continuum models of battery degradation and failure. 103 100 10-3 10-6 10-9 10-12 10-12 μ –second Time-resolved XRD second hour day year Lifetime and length scale of Degradation mm In situ spectroscopy In situ NMR In situ PDF Charge transfer Interface events 10-9 10-6 10-3 Time Domain In situ a- TEM NEXT GENERATION ELECTRICAL ENERGY STORAGE Diffusion, Defects XRD μm Phase Transformation PDF TEM NMR Figure 2.5.5. Spatial and temporal responses of characterization tools. XRD = X-ray diffraction, PDF = pair distribution function, TEM = transmission electron microscopy, and NMR = nuclear magnetic resonance. Courtesy of Shirley Meng, University of California, San Diego, and Northeast Center for Chemical Energy Storage. Examples: The kinds of synergistic multimodal measurements needed to understand degradation are illustrated by recent studies of heterogeneous spatiodynamics of intercalation examined with operando X-ray microscopy (50 nm spatial resolution) in LixFePO4 cathodes.26,27 The experiments quantified local Li concentration through X-ray spectroscopy of the Fe valence states, revealed local structure through X-ray diffraction, and quantified lithiation kinetics by comparing sequential measurements. The latter revealed that the rate of lithiation within particles varies on nanometer length scales and depends on Li composition. In turn, this variation leads to domains of high and low lithiation, with the inhomogeneity amplified on delithiation and suppressed on lithiation. At equilibrium, such composition changes trigger structural phase transitions, but during lithiation, the kinetics suppress the phase transitions and replace them by a continuous solid solution. Left at rest, the solid solution relaxes to distinct phases with high local stresses at the phase boundaries, a precursor to fracturing. This interplay of composition, kinetics, structure, phase transformation, and stress is central to degradation behavior and may hold a key to fast charging and discharging dynamics in LiFePO4 batteries. Reaction inhomogeneities induced by electrode structure is another avenue to complexity. In LixMn1.5Ni0.5O4 , another surprisingly fast charging and discharging cathode, the lithiation rate depends strongly on the exposed crystallographic plane, which is higher for (100) than (111).25,26 The exposed crystallographic plane creates domains of inhomogeneous lithiation, with up to three distinct lithiation phases with different lattice constants in a single cathode particle. The local strains at the phase boundaries ultimately lead to fracture. As a further example, in situ transmission electron microcopy of lithiation-induced strain and fracture27 showed that, rather than progressing uniformly, lithiation nucleates at a few points and spreads laterally, with continuous grain nucleation occurring along the moving interface. This nucleation creates highly concentrated stresses at the phase boundaries, which ultimately fracture films after a few cycles, though at a stage of degradation before it is reflected in the electrochemical behavior. For these kinds of multi-phenomena, quantitative experiments only scratch the surface in uncoupling, quantifying, and recoupling the kinetic pathways of battery operation, degradation, and failure. Extension is needed to include thermal effects28 on ion mobility and defect formation and phase nucleation at nanometer spatial and perhaps femtosecond-picosecond temporal resolution. X-ray free-electron lasers and ultrafast 100 103 106 109 PRIORITY RESEARCH DIRECTION – 5 71 nm Length DomainPDF Image | Next Generation Electrical Energy Storage
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