Centerpiece of all electric vehicles is a reliable traction battery, fulfilling customers’ requirements in terms of driving range, comfort and safety needs. Beyond optimization of these essential technological product characteristics, the cost-effective manufacturing of battery cells is of growing importance since the price premium for electric vehicles is predominantly due to battery cells. Thus, it seems necessary to analyze manufacturing processes as well as the resulting cost structure of battery cells in depth. While a multitude of publications cover purely technological improvements of lithium-ion battery cells, little attention has been paid to cost effects of manufacturing measures with respect to mass production of large-sized battery cells.

In light of the above, and to allow for comprehensive suggestions for cost reduction in mass production of large-sized battery cells, we derived a cost-oriented production model from step-by-step analysis of every technological operation along the manufacturing chain of battery cells [1]. This model reflects a stand-alone manufacturing plant under current industry practice, using modern automated production techniques. The model input consists of three major sets of parameters:

1. Product-related parameters, such as electrode composition and cell design
2. Production-related parameters, such as process sequence
3. Economy-related parameters, such as labor cost.

This model helps to identify the cost-relevant interrelations between battery cell (product), manufacturing process (production) and economic conditions. For instance, it enables to determine the changes in production costs for different scrap rate scenarios (Figure 1, left) or variations in electrode density, i.e., degree of compression in the calendering step (Figure 1, right).

Moreover, the present study includes recommendations for smart electrode processing based on practical experiments in technical-scale production, which disclose further pathways to lower the production costs for battery cells. The investigations focus especially on the slurry production process, carried out with significantly reduced solvent content [2] and shortened dispersing time, and the convective drying step: With a continuous extrusion process, battery slurries with halved solvent content can be produced, whereby duration and energy input of the subsequent electrode drying step are reduced notably without any losses in electrochemical cell performance.  This reveals significant manufacturing-oriented cost optimization potential since the coating and drying unit accounts for 8 % of the total machinery investment and consumes nearly 30 % of the total energy demand in manufacturing [1].

Both, model- and experiment-based investigations, suggest high savings potential in cell production by choosing an extrusion process with high solids content for slurry manufacturing.  

References:

[1] Jan-Hinnerk Schünemann: Modell zur Bewertung der Herstellkosten von Lithiumionenbatteriezellen, Dissertation,  iPAT-Schriftenreihe, Band 16, ISBN: 978‑3‑86844‑703‑3, Sierke-Verlag, Göttingen, 2015

[2] H. Dreger, H. Bockholt, W. Haselrieder, A. Kwade: Discontinuous and Continuous Processing of Low-Solvent Battery Slurries for Lithium Nickel Cobalt Manganese Oxide Electrodes, J Electron Mater, 2015, DOI: 10.1007/s11664-015-3981-4