Accelerated Infrared Drying of NMP-Based Cathodes: Scaling Production for Efficient Battery Life Cycles

Objective
Electrode drying is the most energy-intensive bottleneck in the battery production life cycle, accounting for up to 48% of total manufacturing energy consumption. This work targets the production process of NMP-based NMC cathodes by implementing high-intensity infrared (IR) drying as a scalable technology to reduce specific energy consumption, dryer length, and cycle time, while maintaining adhesion and microstructure required for long-life cells.

Methodology
The study followed a two-phase practical approach: A) Discontinuous Trials (Emitter Investigation): Stationary experiments identified the impact of four types of IR emitter technologies on drying kinetics. Slurries of NMC (70 wt.% solids) were positioned 11 cm below the emitters to determine the relationship between optical power, wavelength, and adhesion. B) Continuous Trials (Production Scaling): Findings were scaled to a roll-to-roll (R2R) pilot coater (2m oven) using four carbon IR emitters (with Excelitas Noblelight patented quartz reflectors) in the first segment. We evaluated the Specific Radiative Heat Input by varying web speeds (1–3 m/min) and emitter power settings while monitoring film temperature via online IR pyrometers.

Results
Discontinuous trials revealed that total optical power is the dominant factor in drying kinetics; differences between Tungsten (short wave) and Carbon (mid wave) emitters were negligible when power levels were matched. Increasing power from 5 to 14 kW/m² achieved a 90% reduction in drying time (180 s to 15 s). A quality “sweet spot” was identified at 7 kW/m², yielding a 280% throughput increase while maintaining adhesion >1 N/mm². In R2R trials, web speed was successfully tripled, and at 2 m/min, energy demand was reduced by >50% (1.4 to 0.7 kWh/m²).

Discussion
The low saturation vapor pressure of NMP makes it highly sensitive to the air/IR balance. Our results align with KIT fundamental models, confirming that accelerated drying induces capillary-driven binder migration toward the surface. This results in binder depletion at the current collector interface, potentially reducing adhesion. However, IR-assisted convection proved more energy-efficient than induction or laser alternatives as the emitters provide convective heating without complex cooling-water infrastructure. Furthermore, shifts in color values and surface roughness were established as online markers to track pore closure and segregation during production.

Conclusion
This study establishes 7 kW/m² as the optimal benchmark for maximizing R2R cathode throughput. Implementing high-intensity IR emitters effectively reduces the dryer footprint and specific energy demand by half, offering a scalable solution for sustainable, giga-scale battery manufacturing.