CAR Researchers Tackle Extreme Fast Charging of Electric Vehicles
An exploratory research program at the Center for Automotive Research (CAR) aims to evaluate the feasibility of Extreme Fast Charging (XFC) which would allow electric vehicles to be recharged as fast as conventional vehicles are refueled. XFC promises to accelerate the adoption of battery electric vehicles (BEVs) by designing high-performance, cost-effective, safe and affordable energy-storage systems.
CAR Senior Researcher Matilde D’Arpino and Professor Marcello Canova are heading the project which is contributing in understanding the technological barriers and potential solutions to achieve XFC. Zachary Salyer is the graduate research assistant working on the project while earning a master’s in mechanical engineering at The Ohio State University.
“It’s really working towards reducing the charging time, which is a huge concern for electric vehicle consumers, that’s one of the big challenges that the industry is facing,” Salyer said.
Starting from work done by the National Labs and US Department of Energy (US DOE), the CAR XFC research program is mapping the key technological barriers in charging infrastructure, battery pack design and electrical and thermal battery management which currently limit the maximum charging C-rate per cell. The C-rating is a way to rate batteries on how fast they can discharge or charge energy, in this case, the research could allow for an up to 6C rate which is a 10-minute charge time.
“Tesla's can charge from 20% to 80% state of charge in about 20 to 30 minutes. That would correspond to about a 1.5C rate, so getting that to 6C is a huge challenge because the increased charging rate is going to cause a lot of heating, and the cells are not necessarily able to withstand that high charging rate because of increased degradation,” Salyer said.
Several technical challenges need to be addressed at multiple levels, particularly in critical areas such as the understanding of the aging mechanism, thermal control and safety to enable XFC systems that would allow for maximum charging current per cell up to the 6C rate.
The researchers aim to produce a behavioral model of a Li-ion battery that they can use to predict the main factors that may pose constraints to fast charging, including cell degradation and heat generation.
“The ideal goal is that once we have a degradation model finalized and calibrated, we will be able to use the model to derive optimal charging strategies for specific cell chemistries and pack specifications. Moreover, we will be able to estimate the degradation that the cells will see using that specific profile and doing benchmarks between different cell technologies to understand their capabilities to withstand XFC,” D’Arpino said.
The researchers will conduct a simulation study aimed at exploring electro-thermal control optimization solutions that could mitigate potential degradation and thermal issues when performing fast charging. The study will explore how to dynamically charge a cell in order to optimize simultaneously for charge time, heat generation and cell cycle life. This would produce an algorithm that could be used to explore the impact of pack design parameters on the ability of the pack to tolerate fast charging at higher rates.
This research could be a valuable contribution in the knowledge of batteries and how small choices in cell design can impact the overall performance of a battery. The impact of the research could prove to be more resourceful than in just the realm of electric vehicles.
“It’s really a matter of focusing on reducing those charging times, and better understanding what’s happening within the cell, that can help you design better charging methods and extend the life of the batteries as well,” Salyer said.
Written by Muhammed Al Refai, CAR Marketing and Communications Intern