Mechanical failure modes of a graphite/polyvinylidene difluoride (PVDF) composite electrode for lithium-ion batteries were investigated by combining realistic stress-stain tests and mathematical model predictions. Samples of PVDF mixed with conductive additive were prepared in a similar way to graphite electrodes and tested while submerged in electrolyte solution. Young's modulus and tensile strength values of wet samples were found to be approximately one-fifth and one-half of those measured for dry samples. Simulations of graphite particles surrounded by binder layers given the measured material property values suggest that the particles are unlikely to experience mechanical damage during cycling, but that the fate of the surrounding composite of PVDF and conductive additive depends completely upon the conditions under which its mechanical properties were obtained. Simulations using realistic property values produced results that were consistent with earlier experimental observations. © The Author An understanding of mechanical degradation in battery electrodes will support the design of batteries with longer cycle life. There are numerous studies that explore lithium-ion battery degradation mechanisms through both experimental and modeling work.1-9 Since commercial lithium-ion battery electrodes are typically composites consisting of active material, binder, and conductive agent, mechanical degradation of the electrode depends on the individual properties of the electrode components as well as their interactions. For instance, crack generation in anode particles (such as graphite and silicon) might accelerate self-discharge due to the exposure of new surface to electrolyte solvents, which leads to further solid electrolyte interphase (SEI) film growth. 4,7 As another example, damage to surrounding material might disrupt electrically conductive paths to the active material particles, resulting in battery capacity fade.Graphite is known to undergo a volume change of approximately 10% during cycling, 10 and previous modeling work 3,11 has explored the possibility of mechanical damage in isolated graphite particles due to such volume changes. However, in typical commercial graphite electrodes, active material particles are not isolated, but instead bound into a porous structure with polymer binder and conductive agent. This surrounding material experiences stress due to the expansion and contraction of active material, and in turn acts as a mechanical constraint on the active material particles.12-14 Moreover, the mechanical strength of a binder such as PVDF changes with exposure to electrolyte solution. 13,15 Hence, in predicting stress generation in these composite systems, one needs to consider volume changes and lithium concentration gradients within active material particles, as well as the influence of the surrounding material.This work combines, for the first time, experimental determination of mechanical properties of the binder and conductive agent composite under realistic conditions, with simulations t...

Anti-perovskites materials have recently attracted great interest as a family of solid state electrolytes with high ionic conduction.[1] Typical solid-state ionic conductors have temperature-dependent ionic conductivity following Arrhenius behavior over a substantial range of temperature, corresponding to a constant activation energy Ea. In the Na3OCl antiperovskite (Fig. 1), there are regimes of Arrhenius behavior separated by broad transitions, all while the structure remains cubic, Figure 2. Such non-Arrhenius ionic conductivity of Na3OCl has been observed in previous literature. [2][3] However, there is no clear explanation for this non-Arrhenius transition. Differential scanning calorimetry shows thermal transitions in the vicinity of these conductivity transitions, Figure 3, suggesting order/disorder phase transitions. Reitveld refinement on temperature dependent synchrotron XRD of Na3OCl suggests changes in octahedral tilt systems, which is CmCm in the low temperature region, Pnma in the medium temperature region, and P4/mbm in the high temperature geion, Figure 4. In this work, we use multiple temperature-resolved characterization methods including synchrotron XRD, transport measurements, and calorimetry, and modeling by AIMD and DFT, to understand this behavior and to gain insight into tuning antiperovskites for high ionic conductivity.This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Figure 1