Reduced Drying Time of Anodes for Lithium‐Ion Batteries through Simultaneous Multilayer Coating

Abstract

The extended process chain starting from slurry mixing up to the operative lithium‐ion battery requires a deep understanding of each individual process step and knowledge of the interaction of the different process steps with each other. In particular, the intertwining of slurry mixing and drying determines the microstructure of the electrode, which in turn affects the performance of the cell. Herein, a scalable multilayer approach is used to tailor electrodes with improved mechanical and electrochemical properties, which disclose their advantages especially at high drying rates. Cryogenic broad ion beam scanning electron microscopy (Cryo‐BIB‐SEM) micrographs are used to reveal the influences of different process parameters, like slurry formulation, mixing device, and properties of the active material on the intrinsic network between active particles and binders in graphite‐based anode slurries. By a chosen combination of these slurries in a multilayer electrode, a tenfold acceleration of the drying time with favorable mechanical and electrochemical properties for full cells derived from these anodes is demonstrated.

Drying of NCM Cathode Electrodes with Porous, Nanostructured Particles Versus Compact Solid Particles: Comparative Study of Binder Migration as a Function of Drying Conditions

“…The adhesion force, measured by 90 peel tests, provides an indirect quantification of the binder migration and the mechanical properties of electrodes. [15,[35][36][37] The drying rate is varied for the same heat transfer coefficient by adjusting the isothermal drying temperature. For this purpose, the slurry is dried convectively via drying nozzles in a batch dryer with a heated plate.…”

“…The resistance increase, caused in particular by the non-uniform distribution of the components due to binder migration, has an effect on the potential curve and the discharge capacity at higher currents or C-rates. [18,[34][35][36] To investigate the influence of drying conditions and different degree of binder migration on the electrochemical properties of the cathodes, half cells were cycled at different C rates (Figure 13).…”

“…[15] At higher drying rates and, thus, shorter drying times, the binder concentration increases at the top of the electrode and decreases near the substrate, reducing adhesion and negatively influencing mechanical properties. [13,15,18,34,35] Faster drying and the resulting capillary transport in the electrode accelerate the migration of the binder. In addition, it is discussed in the literature that a shortened drying time might allow less time for concentration equilibration through Brownian molecular motion.…”

“…[29] In addition, the resulting concentration gradient of the binder leads to an inhomogeneous distribution of the carbon black particles and to an increase in electrical resistance, due to reduced electrical contact between the active material and the conductive additives as well as the formation of insulating binder layers and an accompanying increase in overpotential and, therefore, a decrease in specific capacitance, especially at higher currents. [17,18,20,[34][35][36] If capillary transport fails to maintain a wet electrode surface, the menisci retreat into the porous structure and the electrode dries out further. Consequently, the evaporation of the solvent no longer takes place at the upper surface but in the porous structure.…”

“…In addition, the resulting concentration gradient of the binder leads to an inhomogeneous distribution of the carbon black particles and to an increase in electrical resistance, due to reduced electrical contact between the active material and the conductive additives as well as the formation of insulating binder layers and an accompanying increase in overpotential and, therefore, a decrease in specific capacitance, especially at higher currents. [ 17,18,20,34–36 ]…”