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Cost Reduction Strategies for Lithium Ion Electrode Processing and Pouch Cell Formation Steps
Purchasing and handling the N-methylpyrrolidone (NMP) solvent used in much of the electrode formulation and coating steps add unnecessary manufacturing cost to the LIB pack. In addition, more processing energy (heated air flow) is required to remove NMP during drying of the electrode coatings than other solvents (such as water and lower alcohols) with much lower boiling points and higher vapor pressures. NMP recovery involves significant capital expense since multiple condensers or distillation towers are needed, and its use adds to the cost of the coating line equipment in making it explosion proof. Cathode thicknesses, which currently limit the cell specific capacity (mAh/g on a total-unit-cell weight basis) and energy density and indirectly add to cell cost, should also be significantly increased, so much fewer inactive components (current collectors and separators) are required per cell.
Electrode wetting and formation cycling also add significant process energy cost per kWh of usable energy, which is often neglected in LIB pack cost calculations. Furthermore, the wetting and formation steps are a huge process time bottleneck and add substantial capital cost to a LIB production plant. In a large-scale LIB manufacturing plant, the footprint associated with the wetting and formation steps can be as large as 20-25% of the entire layout.
There have been two useful LIB cost studies presented recently by Argonne National Laboratory (ANL)[2] and TIAX, LLC,[3]but these studies consider the entire 18650 cell production process without much granularity on individual processing and fabrication steps. These cost models are also heavy on contributions from material, labor, and capital equipment without detailed consideration of process energy requirements. This paper will give a more in depth review of the process energy consumption associated with electrode processing and formation cycling, two particularly costly elements of lithium-ion cell production, and how manufacturing cost savings could be realized.
The cell fabrication steps mentioned above contribute significantly to the current overall pack cost of $400-600/kWh and will be the focus of the calculations in this presentation. Formulation, coating, and drying aspects will be considered with respect to electrode processing cost, and wetting time and low-rate cycling will be addressed with respect to total cell formation time. This cost assessment approach will show the critical link between electrode processing aides, process energy consumption, and LIB pack cost. Initial calculations show that about 20% of the total battery pack costcan be saved by switching to aqueous electrode processing and doubling the electrode thicknesses.
Acknowledgment
This research at Oak Ridge National Laboratory (ORNL), managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) Applied Battery Research (ABR) subprogram (Program Managers: Peter Faguy and David Howell).
References
[1] D. Howell, “U.S. Battery R&D Progress and Plans,” DOE Annual Merit Review, May 14, 2013.
[2] K.G. Gallagher, D. Dees and P. Nelson, “PHEV Battery Cost Assessment,” DOE Annual Merit Review, May 9-13, 2011.
[3] B. Barnett, J. Rempel, C. McCoy, S. Dalton-Castor, and S. Sriramulu, “PHEV and LEESS Battery Cost Assessment,” DOE Annual Merit Review, May 10, 2011.