Quantification of Heterogeneous Degradation in Li‐Ion Batteries

Abstract

rechargeable batteries. Efforts have been devoted to studying different battery components (e.g., cathode, anode, electrolyte, and binder), aiming to improve energy and power densities, enhance safety, prolong lifetime, and reduce cost. An important aspect of the battery research is to identify the fading pathways of battery particles and electrodes at multiple length/time scales under practical operating conditions. [1] Redox reactions in batteries commonly involve phase transformation, lattice volume change, stress buildup, grain boundary weakening, and particle fracturing. These processes intertwine at multiple length and time scales, are termed as the chemomechanical interplay, and contribute to the complex fading mechanisms of composite battery electrodes. Mapping the chemomechanical transformation of battery particles and particle ensembles represents a promising methodology to establish the relationship among all these processes. Such a study will potentially provide insights into designing materials and electrodes whereThe multiscale chemomechanical interplay in lithium-ion batteries builds up mechanical stress, provokes morphological breakdown, and leads to state of charge heterogeneity. Quantifying the interplay in complex composite electrodes with multiscale resolution constitutes a frontier challenge in precisely diagnosing the fading mechanism of batteries. In this study, hard X-ray phase contrast tomography, capable of nanoprobing thousands of active particles at once, enables an unprecedented statistical analysis of the chemomechanical transformation of composite electrodes under fast charging conditions. The damage heterogeneity is demonstrated to prevail at all length scales, which stems from the unbalanced electron conduction and ionic diffusion, and collectively leads to the nonuniform utilization of active particles spatially and temporally. This study highlights that the statistical mapping of the chemomechanical transformation offers a diagnostic method for the particles utilization and fading, hence could improve electrode formulation for fast-charging batteries.

Surface regulation enables high stability of single-crystal lithium-ion cathodes at high voltage

“…X-ray fluorescence microscopy (XFM) provides unparalleled sensitivity for trace element distribution measurements in many micrometer-thick specimens (true microscale battery particles) and facilitates significantly improved sensitivity relative to electron probes 35 . With X-ray ptychrography, an emerging method that images ultrastructures at beyond-focus-optic resolution, a combined approach with XFM and ptychography can be employed to study elemental localization within the high-resolution structural context, which aids the elucidation of phase transition mechanisms [36][37][38] . The fluorescence maps (Mn, Co, Ni) in Fig.…”

Fracture behavior in battery materials

“…ion transport distance and rate lead to reaction heterogeneity at the electrode scale. Consequently, depth-dependent particle fracture is observed, which means a more sever crack occurs in the electrode near the separator more than near the current collector [92]. The experiment shows that the mechanical properties of a cathode degrade with a deep delithiation process and cycles [93], which is believed to be the consequence of state-of-charge heterogeneity and crack formation.…”

Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides

“…It has been reported that the surface chemistry plays a vital role during battery operation, although the battery operation is ultimately a bulk chemical process (i.e., the lithium ions (de)intercalate into the bulk of the active material). The undesired surface reactions include, but are not limited to the, reconstruction of the surface lattice structure 5 – 8 , the formation of a reaction passive interface 9 , dissolution and precipitation of metal cations 10 , growth of lithium dendrites from the particle surface etc 11 . These surface chemical processes lead to the development of local impedance and effectively cause the lithium ions and the electrons to detour through geometrically less optimal pathways, result in unwanted phenomena like cell polarization and capacity/voltage fade 12 .…”