GM Comes Up With Model To Balance Energy Density & Fast Charging
High-energy density batteries usually struggle to accept high-power charging, while low-energy density batteries work just fine under high-power charging
GM thinks it may have a model to show the perfect compromise here.
Related – High Energy Density Battery Cells Brings Performance Trade-Offs Of Durability And Chargeability
General Motors researchers Mark W. Verbrugge and Charles W. Wampler picked up the topic of balancing two major parameters of electric cars – range and fast charging capability.
Manufacturers need to consider the trade-off between those two, as high range requires high-energy density cells that typically are unable to charge fast without significant degradation in cell life.
The model described in the article “On the optimal sizing of batteries for electric vehicles and the influence of fast charge” takes into consideration the cost of batteries, weight, charging, as well as cost of adaption – corresponding to the days a customer would need an alternative form of transportation, as the EV would not have sufficient range on those days.
The model could help to answer the question of what battery (type and size) would be optimal for each car.
“We provide a brief summary of advanced battery technologies and a framework (i.e., a simple model) for assessing electric-vehicle (EV) architectures and associated costs to the customer. The end result is a qualitative model that can be used to calculate the optimal EV range (which maps back to the battery size and performance), including the influence of fast charge. We are seeing two technological pathways emerging: fast-charge-capable batteries versus batteries with much higher energy densities (and specific energies) but without the capability to fast charge. How do we compare and contrast the two alternatives? This work seeks to shed light on the question. We consider costs associated with the cells, added mass due to the use of larger batteries, and charging, three factors common in such analyses. In addition, we consider a new cost input, namely, the cost of adaption, corresponding to the days a customer would need an alternative form of transportation, as the EV would not have sufficient range on those days.”
According to the Green Car Congress’ extended quotation, with fast charging capability (and a network of fast chargers), the older lower energy dense batteries would be more profitable – as the car would be cheaper and the owner would likely use alternative means for transport from time to time.
Besides there being no decent fast charging network, the major problem to us is that the car is related to the life style and range satisfies a peace of mind need. Consumers will often be willing to pay more for range higher than optimum from an economic standpoint.
“Of particular note is the cost of adaptation. When we exercise the model with inputs one can associate with a battery like that of the Chevrolet Bolt EV, we find that the net cell volume and the vehicle range are consistent with an adaptation cost of $165/day, three times the average cost per day to rent a car in the United States. This adaptation cost would be appropriate for customers having a strong desire to avoid relying on some alternative method of transportation for the days in which the EV could not supply the needed miles. … the Bolt EV’s 238 miles range would mean that the 75th percentile drivers would need an alternative form of transportation—that is, they would need to adapt—about 5 days per year.)
The results … allow one to assess whether fast-charge of a conventional lithium ion battery is superior to the implementation of a high-energy density cell that cannot be fast charged. For the parameters chosen, fast-charge of a conventional lithium ion battery offers superior value to the customer relative to the high-energy density cell.”