Moisture behavior of lithium-ion battery components along the production process

Abstract

With the ongoing development of producing high-quality lithium-ion batteries (LIB), the influence of moisture on the individual components and ultimately the entire cell is an important aspect. It is well known that water can lead to significant aging effects on the components and the cell itself. Therefore it is urgent to understand the moisture behavior of the most important components anode, cathode and separator along the entire cell production as precisely as possible. This work is intended to realize just that, by creating application-related references, point out and explain difficulties as well as challenges and finally work out and provide solutions. At first it describes the amount of moisture these components can adsorb and desorb and which components of the electrodes take up particularly much or little moisture. On this basis the adsorption kinetics of anode, cathode and separator material are investigated, showing how quickly the described equilibrium moisture contents are achieved under typical manufacturing conditions. A linear time dependency was observed which shows that all components adsorb a high share of the equilibrium moisture in the first minutes. To give the reader a better impression for the overall process, real values of the various moisture contents of anode, cathode and separator material along the entire process chain during a production campaign are shown. Since moisture in the components cannot be completely avoided during manufacturing, a total of five different process variants for minimizing residual moisture are finally described, analyzed and compared with each other. General advantages and disadvantages, impact of the individual process parameters, residual moisture contents as well as energy and media consumption of electrode pack baking, coil baking, roll-to-roll baking, cell stack baking or pure exposure to dry room atmosphere are discussed. Finally an overall strategy to minimize water content in LIB components along the entire production is proposed regarding all established results.