Simulation of the Impact of the Loss of Contact Area in All-Solid-State Battery

Abstract

Maintaining the physical contact between the solid-state electrolyte and the electrodes is important to improve the performance of the Li-ion battery. The initial interface contact depends on the fabrication process of the battery. Typically, the deposited thin-film battery would have better interface contact than the bulk-type (mixed powder) battery. Increasing the compression pressure during the fabrication process could lead to a better initial contact. On the other hand, the contact area would continuously lose due to the volume change of the electrodes during the cycling of the battery. To illustrate this problem, a 1-D continuum model was developed to simulate the discharging process of an all-solid-state Li-ion battery, which is composed of Li as the anode, LiCOO2 as the cathode, and Li3PO4 as the electrolyte. The parameters were taken from a thin-film battery model that has fitted to experimental data. We incorporated the effect of the imperfect contact into this model by assuming the current and Li concentration will be localized at the contacted area. We correlated the percentage of lost contact area with the discharging capacity and energy. We observed that the capacity and energy decrease with the loss of contact area and discharge rate. For example, when discharging at 1 C-rate, the capacity decreased 20% as the contact area losses 19.8%. At a higher discharging rate of 32 C, the capacity dropped quickly to be less than 20% when the contact area losses 1.52%. Since Li3PO4 and LiCOO2 are both ceramic materials and their initial contact area is non-perfect after the fabricating process. We applied the Johnson-Kendall-Roberts (JKR) model, which is appropriate for elastic deformation and adhesive contact, to estimate the applied pressure that can recover the loss of contact to the initial condition. We found that it is more effective to apply the pressure when the battery just starts to decay when the battery capacity loss is less than 10%. Therefore, in practical application, this model and method can be used to estimate the extent of the loss of contact area during the operation of the all-solid-state Li-ion battery, and further suggesting how much pressures should be applied to recover the capacity.