Li-ion Electrode Microstructure Evolution during Drying and Calendering

Abstract

The drying process of electrodes might seem to be a simple operation, but it has profound effects on the microstructure. Some unexpected changes can happen depending on the drying conditions. In prior work, we developed the multiphase-smoothed-particle (MPSP) model, which predicted a relative increase in the carbon additive and binder adjacent to the current collector during drying. This motivated us to undertake the present experimental investigation of the relationship between the drying rate and microstructure and transport properties for a typical anode and cathode. Specifically, the drying rate was controlled by means of temperature for both an NMC532 cathode and graphite anode. The material distribution was analyzed using a combination of cross-section SEM images and the energy-dispersive X-ray spectroscopy elemental maps. The binder concentration gradients were developed in both the in- and through-plane directions. The through-plane gradient is evident at a temperature higher than 150 °C, whereas the in-plane variations resulted at all drying temperatures. The measurements identified an optimum temperature (80 °C) that results in high electronic conductivity and low ionic resistivity due to a more uniform binder distribution. Trends in transport properties are not significantly altered by calendering, which highlights the importance of the drying rate itself on the assembled cell properties.

Microstructure of Conductive Binder Domain for Electrical Conduction in Next‐Generation Lithium‐Ion Batteries

“…The CBD structure, such as pore morphology and carbon binder distribution along the vertical direction to the current‐collector, is highly influenced by the slurry colloidal interaction between PVDF, NMP, carbon black, and NMC622 through drying with particle aggregation and polymer migration driven by solvent evaporation. [ 36 ] Different colloidal interactions lead to different active material particle pile‐ups with varying porosities. Furthermore, different carbon‐binder forms different CBD structures such as sponges, bridges, and film, as well as the distribution of carbon‐binder throughout the electrode.…”

“…As a result, PVDF is more likely to move to the capillary formed by the aggregation of the particles causing PVDF to be attracted around the particles. The drying model can be referred to in the reference article published by Nikpour et al [ 36 ]…”

“…As a result, PVDF is more likely to move to the capillary formed by the aggregation of the particles causing PVDF to be attracted around the particles. The drying model can be referred to in the reference article published by Nikpour et al [36] It is clearly shown in Figure 5a,b that a large amount of CBD appears in the voids formed by particle aggregation. As shown in Figure 5c and the upper region of Figure 5d, the PVDF is present because of the voids where particle aggregation occurs.…”

Measuring Instruments for Characterization of Intermediate Products in Electrode Manufacturing of Lithium‐Ion Batteries

“…The drying condition, determined by the web speed and the temperature profile, in conjunction with the electrode thickness, can impact the electrode's microstructure [64][65][66] and its mechanical properties. [67] Indentation tests, on micro-and nanoscales, can be used to characterize the mechanical properties of the electrode.…”

Optimized LiFePO4-Based Cathode Production for Lithium-Ion Batteries through Laser- and Convection-Based Hybrid Drying Process

“…When the capillary transport no longer sufficiently wets the coating surface, pore dry-out begins. At this stage, the isolated solvent residues must overcome an additional transport resistance through the gas phase of the empty pores [19]. This leads to reduced mass transport, a falling drying rate, and an increasing coating temperature.…”