Tesla Semi Truck - Hype or Reality: Challenges in Electrifying Light Commerical Vehicles

Monday, 2 October 2017: 14:20
Chesapeake 12 (Gaylord National Resort and Convention Center)
S. Sripad and V. Viswanathan (Carnegie Mellon University)
While the electrification of the transportation sector is underway with a consistently increasing market share, segments like light commercial vehicles (LCVs) have not seen any significant market penetration. The major barriers are primarily in the shortcomings in specific energy, power, and cost associated with Li-ion batteries. With an initiative from several automakers to electrify other segments, there is a need to critically examine the performance requirements and to understand the factors governing such a transition in the near-term and long-term. In this study, we develop a systematic methodological framework to analyze the performance demands for electrification through an approach that couples considerations for battery chemistries, load profiles based on a set of vehicle-specific drive cycles, and finally applying these loads to a battery pack that solves a 1-D thermally coupled battery model within the AutoLion-ST framework. We evaluate four commercially available cathode chemistries, namely, LMO, LFP, NCA, and NMC, design cells for each of these systems, and characterize them on a 1-D thermally coupled battery model based on a comprehensive and experimentally validated materials database. This cell design effort is translated into a process-based and material specific battery cost model based on BatPaC, to obtain cost inputs for our framework. Using this framework, we analyze the performance of a fully electric LCV over its lifetime under various driving conditions and explore the trade-offs between battery metrics and vehicle design parameters. We find that in order to enable a driving range of over 400-miles for LCVs at a realistic battery pack weight, specific energies of about 350-400 Wh/kg or 200 Wh/kg at the pack-level needs to be achieved. A crucial factor that could bring down both the energy requirements and cost is through a vehicle re-design that lowers the drag coefficient to about 0.3. Finally, we evaluate the same trade-offs in the context of Beyond Li-ion systems like Li-S and Li-air, and observe a level off in the improvements gained with an increase in specific energy, while parameters like the pack-to-curb weight ratio (PTC) for LCVs that reflect on the overall efficiency of the vehicle are highly improved for high specific energies.

Figure Caption: Examination of future and beyond Li-ion systems for improvements in (a) Cost, (b) PTC, and (c) energy consumption for a fixed range of 200-miles and a cost of 150 $/kWh across chemistries. We see an improvement in the system level cost for an increase in pack specific energy up to 350 Wh/kg which signifies future Li-ion batteries and Li-S systems. The PTC at this specific energy is around a value of 0.15. Beyond this, the degree of improvement seen for the same increase in specific energy is reduced, since the pack weight does not remain a significant parameter for energy consumption. A similar trend is seen with the energy consumption (Wh/mile).