Study on the tolerance of cell inconsistencies in high-capacity liquid metal battery parallel modules

Liquid metal batteries (LMBs) are a novel battery technology with great potential for application in electrical large-scale energy storage systems. Parallel connection is one of the ways for battery formation, especially under large-scale applications which needs amount of energy. However, unbalanced current distribution on the branch is a critical issue for parallel modules. This paper takes fully consideration about the influence of module topology, connection resistance and cell inconsistency on the current distribution for parallel-connected LMBs, in view of its high-temperature working environment. The mechanism of connection resistance on current distribution are theoretically analyzed by a simplified Rint model, and the quantitative relationship between the ratio of connection resistance to battery internal resistance and current distribution are obtained. A mean-difference model (MDM) of the LMB is constructed and are extended to an equivalent circuit model (ECM) for module with n parallel-connected ( n p) LMBs. Factorial experiments are used to design 81 sets of experiments with four parameters of the number of parallel cells, the ratio of connection resistance to battery internal resistance, battery capacity difference and internal resistance difference as factors. Thereby, the branch current distribution in different factors is examined by models, and 10 2 Monte Carlo simulations are performed on each model to obtains highly reliable distribution results. The simulation results show that the branch current imbalance increases as the number of cells in parallel and the connection resistance grows, but an appropriate range of inconsistency between the cells can lessen the current distribution imbalance. As a result, this paper makes discussions on the tolerance of the LMB parallel module for the battery capacity and resistance differences.