Moisture Adsorption Behavior in Anodes for Li‐Ion Batteries

Abstract

Excessive moisture adsorbed in electrodes and separators of a Li‐ion battery hampers its performance and is, therefore, removed to a certain amount in a post‐drying process. An insufficient understanding of the process results thereby in high process costs. Cost reductions can only be achieved efficiently with an improved process understanding by modeling this post‐drying process. As process modeling requires knowledge of sorption equilibria of water in the components of the battery, the sorption equilibria of water in different anodes are determined by means of a magnetic suspension balance and compared with different experimental setups. The measured data of the adsorption isotherms are described mathematically and give an impression of the amount of moisture, which is going to adjust at an equilibrium starting from a dry anode. Moreover, the materials of the anode are evaluated for their moisture sorption behavior. It is shown that mass‐weighted sorption equilibria of water in the materials yield a good approximation of equivalent equilibria in the anode. In the investigated anodes, the binder and rheology additive carboxymethyl cellulose (CMC) accounts for the most water uptake.

Current and future lithium-ion battery manufacturing

“…These side reactions also lead to inferior electrochemistry performance ( Stich et al., 2017 ). According to the investigations on the state-of-the-art electrodes, the graphite anode contains a much higher amount of moisture than the cathode because of the residual moisture in the aqueous CMC binder ( Stich et al., 2017 ; Eser et al., 2019 ). Current drying technology usually places the electrodes under a low-pressure environment with 60°C–150°C heating for over 12 h with the option of inert gas supply.…”

Design of Vacuum Post‐Drying Procedures for Electrodes of Lithium‐Ion Batteries

“…It aims at reducing the residual moisture in the cell components below a critical level to ensure a long battery cell life and high safety. On an industrial scale, post‐drying is most commonly conducted either in continuous roll‐to‐roll processes, where the electrodes or separators are often heated by infrared emitters, or batch‐wise by post‐drying whole coils in vacuum ovens [1–5] …”

Investigation of Drying Curves of Lithium‐Ion Battery Electrodes with a New Gravimetrical Double‐Side Batch Dryer Concept Including Setup Characterization and Model Simulations

“…The drying of the remaining solvent within the polymer was considered using sorption data from Eser et al, which were determined for battery electrodes. [ 16 ] The thermal conductivity of the dry film was assumed to be sufficiently high to lead to a uniform temperature of film and substrate over the film height.…”

“…The value of the activity is for high solvent loadings X and decreases as the solvent loading decreases. It can be integrated using the Brunauer–Emmett–Teller model (Equation (19)), as investigated by Eser et al [ 16 ] …”

“…The values of the fit parameters for an uncalendered anode were determined using a magnetic suspension balance, resulting in a value for the monolayer loading , k = 12.9, and z = 1.0. [ 16 ] With the knowledge of these parameters for each component within the electrode, the activity can also be calculated for different electrode compositions. [ 22 ] To implement the activity into Equation (18), the cubic Equation (20) was derived for a in dependency of X from Equation (19).…”