With the development of lithium ion battery (LIB) are recognized as a practical green option for the energy transportation and storage. Over the past decades, solid state batteries (SSB) have received the much attention among the LIB researchers, due to the development of electrolytes with high conductivity comparable to that of the liquid electrolyte. Additionally, the SSB have high energy density, non-flammability and large electrochemical window compared to the conventional liquid electrolytes. The electrolyte for SSB are classified as the oxide and sulphide. Among the solid electrolyte, the oxide electrolytes are considered to be chemically more stable whereas the sulphide electrolytes possessed relatively high ionic conductivity. With the development of the SSB, there is a need for the simulation tools in order to allow the battery engineers to explore the effects of various materials properties, geometries, etc. on the overall performances of the SSB. Simulation studies will provide an opportunity to explore the fundamental phenomena involved and the strategies to optimize the SSB performance. The objectives of this study are twofold. First is the identification of the bulk parameters of the SSB component materials. Second, the estimation of interfacial properties in SSB by utilizing the bulk parameters.

In this study, mass transport phenomena and the electrochemical reactions were considered by solving the numerical equations based on the finite element method. The model used includes the diffusion of the lithium in the active material (AM), diffusion of ions in the electrolyte and the charge kinetic transfer at the electrode-electrolyte interface. Firstly, numerical simulations were performed to identify the bulk parameters of the single particle of commonly used positive AM, i.e., LixCoO2 (LCO). The results of this study have been compared with the experimental study conducted by Dokko et al. (2009). The simulated models predict global discharge characteristics that were overall in a good agreement with the experimental result as shown in Figure 1.

In the second part of this study, complex three-dimensional micro-structure of the electrode (cathode) was taken into an account. For that purpose, an in-house code was used to model the composite electrode system of SSB, consisting of the idealized micro-structure, i.e., spherical, containing both the AM and solid electrolyte (SE). The simulation model assumes the transport number of the SE is unity, which is usually the case for the SE systems. Additionally, in this study, we have also taken into account the coating of the AM, which is usually done to reduce the contact resistance between the AM and the sulphide SE particles. The model predictions revealed that the concentration of lithium remain unchanged in the SE over a period of time. It is also found from the simulations that a significant concentration gradient developed among the positive AM particles at high discharge current.

Reference:

1. Dokko, N. Nakata, K. Kanamura, Journal of Power Sources, 189, (2009) 783–785