Juner Zhu

Porous electrodes couple electrical, chemical, mechanical, hydraulic, and thermal fields, yet conventional frequency-domain diagnostics interrogate only one of them: electrochemical impedance spectroscopy (EIS) the electrical response and dynamic mechanical analysis (DMA) the mechanical. Each reads a diagonal entry of the multiphysical constitutive matrix; the off-diagonal couplings—the basis of cross-domain transduction, and of degradation in electrodes—enter only implicitly. Starting from linear irreversible thermodynamics, we formulate a general theory of multiphysical impedance spectroscopy, in which perturbing one field and measuring the conjugate response of another probes off-diagonal entries explicitly. Specializing to the electro-chemo-mechanical pathway yields a closed-form theory of mechano-electrochemical impedance spectroscopy (MEIS), in which a small harmonic current is applied and the stack stress is measured. The impedance factorizes into a chemical-accumulation term multiplying the sum of a chemo-mechanical and a poro-mechanical kernel, with a porosity-accommodation bridge function derived from a Helmholtz free energy and a three-phase closure that interpolates between unsaturated and Biot-saturated limits. Because the mechanical kernel reduces to an equivalent spring—dashpot network, measured spectra can be fitted as in EIS or DMA with each element retaining a definite physical meaning, and MEIS emerges as one member of a broader family of cross-coupled spectroscopies.

Detecting and preventing lithium-ion battery failures remains a critical challenge, as failures degrade performance, damage materials, and pose safety risks. While catastrophic outcomes under extreme impacts or compression—such as short circuits, thermal runaway, and fires—have been extensively studied, batteries in real-world applications are more often exposed to moderate stresses. These conditions produce small internal changes with weak initial electrochemical signatures that can accumulate into severe damage over time. This work investigates how single-impact and compressive forces of varying intensities and orientations affect the structure and electrochemical behavior of 18650 NMC/graphite cylindrical cells. X-ray computed tomography (CT) provides direct visualization of damage to both active and inactive components, while open-circuit potential, impedance spectroscopy, and charge-discharge cycling collectively capture electrochemical consequences. The results reveal immediate yet modest capacity loss even after a single mechanical event, with damaged cells later showing cycling performance comparable to intact cells if only minor damage is introduced. However, repeated loading produces cumulative degradation, further aggravated by subsequent electrochemical cycling. CT imaging highlights structural changes invisible to conventional diagnostics, while electrochemical tests expose early functional impacts. Together, these complementary methods advance understanding of how moderate mechanical damage initiates, evolves, and compromises long-term reliability in lithium-ion batteries.

Background: Cylindrical lithium-ion batteries are tend to have an inward deformation during charge and discharge, which is called “core collapse”. This structural instability remains poorly quantified, and a deeper understanding of the underlying mechanics is essential for improving the structural integrity and safety of rechargeable cells. Objective: This study aims to investigate the deformation and buckling mechanisms of cylindrical lithium–ion battery jelly rolls under electrochemical cycling, with a focus on the interplay between geometry, interfacial constraint, and internal stress evolution. Methods: X-ray computed tomography (CT) imaging was employed to characterize the three-dimensional deformation of commercial cells, while a detailed finite element (FE) model explicitly incorporating current collectors, coating layers, and separators was developed to simulate chemo-induced stresses. The lithiation and delithiation processes were represented through an equivalent thermal-expansion surrogate to evaluate pre-buckling stress states. Results: CT analysis revealed negligible volumetric and hoop strains, confirming strong geometric constraint from the spiral architecture. Simulations showed that interface compatibility between current collectors and electrodes governs hoop-dominated stress fields, and that separator wrinkling can precede electrode buckling due to low bending stiffness and expansion mismatch. Conclusions: The results elucidate how hoop compression, interface constraint, and structural asymmetry collectively trigger jelly-roll instability. The findings establish a mechanistic foundation for analyzing confined expansion and guiding future multi-physics modeling of battery structural reliability.

Rechargeable batteries using electrodes based on intercalation chemistry exhibit notable cyclability, yet their performance still suffers from chemomechanical degradation. In this study, by combining a suite of operando microscopy methods, we explored electrode strain evolution and observed intricate particle cluster rearrangement under electrochemical stimuli. We show that early-stage strain accumulation in intercalation cathodes occurs during the period of interparticle charge transfer and redox reactions stemming from asynchronous coupling and decoupling between chemical (de)intercalation and physical grain motion. This interplay drives heterogeneous redox activity, localized charge equilibration, and multiscale strain cascades that propagate through an asynchronous network of chemical-mechanical interactions. Together, these findings reveal how collective particle dynamics and hierarchical strain transmission dictate electrode deformation and degradation in intercalation cathodes.

We developed a model that considers all components of a composite electrode. It integrates particle- and electrode-level behavior and enables simulation of the mechanical behavior of polymeric binders, which is critical for battery degradation.