The development of efficient and affordable electric vehicles is receiving ever greater interest from both industry and academia. This, indeed, is in the interest of migrating towards emission free vehicles. Arguably, one of the greatest barriers in the successful deployment of electric vehicles is the cost of the batteries inherent to such vehicles. In order to compete with the internal combustion engine (ICE) based vehicles, the current practices of producing the batteries need significant changes in technology and cost. The development of new materials and chemistries for more efficient and economic batteries is receiving a greater interest in the research community. However, for a successful commercialization and to bring down the overall cost, each processing step in the manufacturing of these batteries also needs to be improved and optimized.

            Argonne National Laboratory has developed, BatPac [1], a comprehensive spreadsheet tool for estimating the cost of Lithium Ion Batteries (LIB) with granularity to the cost contribution from each processing step. Analysis of each step, backed by thermal-hydraulic models where possible, offers the potential for quantifying and identifying the opportunities for reducing the cost and energy consumption of each processing step. Among the various processing steps in the production of LIBs, drying and solvent removal from the electrode coating is an energy and cost intensive process [2]. Solvent removal and drying of the coating is also a slow process, which is a potential bottleneck in the production line of LIBs. Thus, it is very useful to study and analyze this processing step in a greater detail. In general, solvent removal and drying has been widely studied [3-4]. However, few studies exist in the literature that focuses on the solvent removal and drying in the context of LIBs. This forms the focus of this study.

            In this work, we study and analyze the design aspects and energy requirements of solvent removal and drying in the electrode processing step of LIB production. The heat for the drying is derived from a combination of infra-red (IR) radiators and hot air injectors. We develop a mathematical model of the physical phenomena to understand the various factors affecting the drying rate. The solvent removal involves simultaneous heat and mass transfer with phase change. Our model considers capillary flow and gravity effects for liquid transport and diffusion for vapor phase transport. The model also accounts for the shrinkage of coating thickness with the removal of the solvent and so, the voidage is considered to be a function of solvent saturation in the coating. The system of non-linear partial differential equations is then solved numerically using a finite element method to predict the concentration and temperature profiles within the drying cathode layer. We finally study the effects of various factors such as drying temperatures and air conditions on the process performance.

Acknowledgement

The authors gratefully acknowledge support from the Vehicle Technologies Office, Hybrid and Electric Systems, David Howell (Team Lead), at the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.

Reference

[1]   P. Nelson, K. Gallagher and I. Bloom, "BatPaC (Battery Performance and Cost) Software," Argonne National Laboratory, 2012. [Online]. Available: http://www.cse.anl.gov/BatPaC/.

[2]   S. Ahmed, P. Nelson, K. Gallagher, D. Dees, “Energy impact of cathode drying and NMP recovery during LIB manufacturing.” Manuscript in preparation.

[3]   F. Chen, D. Pei, “A mathematical model of drying processes.” Intl. J. Heat Mass Transfer 32 (1989): 297-310.

[4]   Z. Przesmycki, “The mathematical modelling of drying process based on moisture transfer mechanism.” Drying’85 (1985): 126-134.

[5]   E. Gutoff, “Modelling solvent drying of coated webs including the initial transient.” Drying Technology 14 (1996):1673-1693.