A fully coupled electrochemical-mechanical-thermal model of all-solid-state thin-film Li-ion batteries

All-solid-state thin-film Li-ion batteries (ASSTFBs) have been regarded as a promising power source for microsystems. The main bottleneck of ASSTFBs is that its capacity degrades significantly with decreasing working temperatures, which has been ascribed to the huge mass-transfer overpotential across the solid-state electrolyte because of its low ion conductivity. In this work, a fully coupled electrochemical-mechanical-thermal model is established to investigate the behaviors of ASSTFBs with a typical LiCoO2/LiPON/Li ASSTFB configuration, especially at low temperatures. Numerical simulation is also performed based on this fully coupled model. The simulation results agree well with the experimental data in a wide temperature range (243 K–353 K) and current rate (30 μA cm−2 to 300 μA cm−2), verifying the effectiveness and accuracy of this fully coupled model. Moreover, based on this model, it is found that both mass-transfer overpotential across the electrolyte and charge-transfer overpotential at the cathode/electrolyte interface are the key factors determining the ASSTFB performance at room temperatures; for comparison, the charge-transfer overpotential at the cathode/electrolyte interface plays the dominant role at low temperatures. This work provides a deep insight into the ASSTFB behaviors as well as its performance optimization strategy, particularly at low temperatures.