Dry Coating Technoeconomics – Chapter 2: How Materials Shape the Numbers

Gigafactory capacity is normally expressed as the gigawatt-hours (GWh) of cells produced annually under steady-state manufacturing conditions. Manufacturing energy is commonly stated as kilowatt-hours (kWh) of process energy consumed per kWh of cells produced (kWh/kWh).

Two factors determine this number:
1. The absolute energy required to complete the manufacturing process.
2. The amount of cell capacity produced from each kilogram of material processed.

This second factor is easy to overlook. Two coating lines may consume similar amounts of energy per kilogram of electrode, but their energy consumption per kWh of cells produced can differ greatly depending on which active materials are being processed. For cathodes, the principal driver is the cathode active material (CAM).

NMC811 cells typically require 1.35–1.45 kg of CAM per kWh of cells, whereas LFP cells require closer to 2.10–2.20 kg/kWh. All else being equal, this indicates that an LFP gigafactory must process around 1.5 times as much CAM to achieve the same cell capacity output. But all things are not equal.

An electrode slurry must contain enough solvent to achieve the rheological properties required for mixing, transfer, and high-throughput coating. The maximum achievable slurry solids content is influenced by the particle size, morphology, and surface area of the active material, binder and conductive additives.

Smaller, high surface area particles require more solvent to achieve the target slurry rheology – which has huge implications for the latest generations of LFP.

In Gen IV and V LFP, a significant proportion of the particle size distribution is sub-micron. As particle surface area increases, the slurry becomes more viscose. To keep the right rheology for a processable slurry, solids content must be lowered. When it comes to a techno-economically efficient process this matters – every additional kilogram of solvent must be heated, evaporated, extracted, captured and recycled.

State-of-the-art NMC cathode slurries can achieve solids contents of approximately 75 wt.%, while many LFP formulations operate closer to 60 wt.%. When this difference is combined with LFP’s lower material-level energy density, the result is around 2.4 times more NMP being processed per kWh of LFP cells produced, compared to NMC.
The impact of this flows through the entire electrode manufacturing system. Our model indicates that, when coating at 80 m/min, NMC811 requires an airflow rate of approximately 48,000 m³/h per coating side per oven to keep NMP concentrations safely below the lower explosive limit. For an equivalent LFP production line, the required airflow approaches 95,000 m³/h. More solvent means a greater evaporation duty.

Maintaining throughput therefore requires higher airflow, larger extraction and recovery systems, longer ovens, or additional parallel coating capacity.The result is a significant difference in capital cost, manufacturing footprint, and process energy, with slurry mixing, coating, drying and solvent recovery consuming approximately:*
• 4.4 kWh per kWh of NMC811 cells produced
• 13.4 kWh per kWh of LFP cells produced

Although the lower active material cost of LFP can outweigh this manufacturing energy penalty, it shows that applying a fixed energy factor across electrode materials is incorrect. Also, the comparison is a clear demonstration that eliminating solvent could have a huge impact. Without drying, the cost, carbon footprint and plant complexity of LFP electrode manufacturing would be driven down even more than it is for NMC.

Anode manufacturing follows the same basic process: formulate a slurry, coat it onto a current collector, and remove the solvent to create the finished electrode. The crucial difference is the solvent selection.

Most commercial graphite anodes use water instead of NMP. Water has no lower explosive limit, and doesn’t require the same near-total capture and recycling system as NMP. This removes much of the safety-driven airflow demand and solvent-recovery complexity associated with cathode manufacturing. But water introduces a different energy challenge.

Drying energy has two principal components: the energy required to heat the solvent and the latent energy required to convert it into vapour. Water has a specific heat capacity of approximately 4.18 kJ/kg·K and needs approximately 2,260 kJ/kg to vaporise. Its strong intermolecular bonding makes it intrinsically energy intensive to evaporate. Furthermore, the amount of water in the slurry adds to the challenge. Graphite, and increasingly graphite–silicon composite, slurries commonly operate at around 50–55 wt.% solids. Therefore, almost half of the wet coating mass is water which must be removed before the electrode exits the oven.

Although water does not need to reach 100 °C to evaporate inside a drying oven, rapid evaporation within the short residence time (~60 seconds) of a coating line requires substantial heat, effective mass transfer and sufficient ventilation to remove humid air and maintain the driving force for evaporation.

Consequently, anode drying is less dominated by airflow and solvent recovery than NMP-based cathode drying. Instead, the energy balance shifts away from safety-driven airflow and solvent recovery and towards the direct thermal duty of heating and evaporating water.

Typical anode ovens operate with air temperatures of approximately 90–110 °C and airflow rates of around 6,000–10,000 m³/h. Where the extracted water is treated as a waste stream rather than recovered for reuse, our model estimates anode manufacturing energy of approximately 2.5–3.2 kWh/kWh of cells, depending on the paired cathode and cell design.

Material selection does more than determine cell performance and raw material cost. It also determines how much material, and how much solvent, a gigafactory must process to produce each kWh of cells.

For cathodes, CAM energy density and achievable slurry solids content dictate the amount of NMP that must be removed and recovered. For anodes, many of the hazards and complexities of NMP disappear, but the thermal energy required to evaporate water becomes a fundamental process constraint.

These physical properties cannot be engineered away completely. Once heat recovery, airflow management and equipment efficiency have been optimised, slurry-based manufacturing approaches a practical energy floor. To go materially further, the industry must either adopt a different solvent system or eliminate solvent altogether.

Now we’ve established the techno-economic baseline for state-of-the-art slurry processing opex, the next edition will open the door to dry coating. We will examine the progress made so far, the challenges conventional dry electrode processes still face, and what still needs to be proven to compete with slurry-based manufacturing at gigafactory scale.

* These figures include mixing, coating, drying and solvent recovery under a consistent set of line-speed, coating-width and heat-recovery assumptions; they exclude downstream electrode processing and dry room energy.