A Decision-Support Model for Retired Li-Ion Automotive Batteries

PI: Sally Benson, Simona Onori, Energy Resources Engineering. Will Chueh, Materials Science and Engineering
Benson Lab, Stanford Energy Control Lab, The Chueh Group

Today, electric vehicles (EVs) are the leading option for making transportation more sustainable, but with the ever-increasing growth of EVs, there is emerging concern about what to do with the retired batteries. The first wave of these retired batteries is expected by early EV adopters by 2025, with over 45,000 battery packs (containing tens of millions of Li-Ion cells) coming out of service. When batteries are retired from automotive service they still have from 50% to 70% of their initial capacity, which opens the possibility to repurpose them for other less demanding applications until they are eventually recycled. Possible applications include behind the meter energy storage for peak shaving, demand response, and power quality. Alternatively, grid-connected batteries also can provide frequency regulation, renewables smoothing, ramping support, and peak shaving, to name a few. Each of these 2nd life applications will place different demands on the battery, affecting its remaining useful life. There are four significant challenges to overcome to make repurposing or reusing retired batteries a viable option. Methods are needed to 1) quickly, affordably, and reliably assess the state-of-health of the battery pack/cells, 2) evaluate the remaining useful life of the pack/cells for different 2nd life applications, 3) determine the economic value of the pack/cells for sellers and buyers of repurposed batteries and 4) make repurposing batteries inexpensive enough to compete with the ever-declining costs of new Li-Ion batteries.  The goal of this project is to develop an integrated physics-based and technoeconomic model to assess whether a battery system coming out of automotive service should be recycled directly or has sufficient economic value to be repurposed for a particular 2nd life application, and if so, what is the value?