Projects

Problem Statement:

The relationship between how batteries are operated and their degradation and service life is complex and not well synthesized or communicated. There is a resulting lack of awareness about best practices related to responsible battery management that influence service life and degradation.

Project Objective:

The Center for Sustainable Systems (CSS) at the University of Michigan will review mechanisms, methods, and guidelines focused on preserving battery health and limiting degradation. The review will include academic literature as well as reports and information published by national labs and industry. Based on this review, we will synthesize and provide guidance for battery operation to minimize degradation and promote extended battery lifetime.

Project Scope:

The scope includes battery systems in vehicles, electronics (cell phones and laptops), and cordless power tools. The targeted audience is car owners and users of electronics and tools.

Project Overview: With support from RBC, researchers at CSS have developed a set of ten green principles for responsible management of batteries in mobile applications [1]. One of the most important principles is Principle #6: Design and operate battery systems to maximize service life and limit degradation. This project proposes an expansion of Principle #6 to provide guidance and strategies that promote battery health and lifetime extension.

The lifetime of a battery is dependent on several complex mechanisms relating to cell chemistry, charging and discharging conditions (e.g., fast charging and discharging cycles), temperature, and cycle depth [2], [3]. Battery service life is determined by battery degradation (or aging), which is characterized by a gradual decline in capacity and increasing internal impedance (resistance) [4]. Large changes in state of charge, high frequency of charge cycles, and extreme thermal conditions accelerate loss of anode / cathode active material and increase in resistance, which result in battery degradation.

Degradation causes more frequent battery replacement or vehicle (or electronic device) retirement, resulting in additional cost and environmental burdens associated with production and processing of new materials, as well as premature end-of-life burdens. Operating a battery system to minimize degradation, extend life, and prevent catastrophic failures delays these adverse environmental and economic impacts.

Battery lifetime can be increased though mechanisms such as reducing the target state of charge (SOC), minimizing rest periods at high SOC, or delaying battery charging until immediately before use [5], [6]. Since standby time dominates electric vehicle operation, battery lifetime can be significantly increased by implementing smart charging strategies (in terms of frequency and time of charging) [5]. If the next day’s battery energy requirement is known, the battery can be charged just-in-time and only to the extent required, rather than charging to a nominal maximum SOC as is typical. Spreading charging over time also reduces high temperatures associated with fast charging [6]. These are examples of strategies that minimize battery degradation and increase lifetime.

We propose to develop battery operation strategies that result in extended lifetime in support of the mission of the Responsible Battery Coalition (RBC) to promote sustainable and responsible battery management solutions. The goal is to provide practical guidance, metrics, and methods to accelerate environmental improvements of battery in electronics and vehicles and to inform multiple stakeholders including battery designers, suppliers, EV and electronics manufacturers, users, and material recovery and recycling organizations.

Read article posted February 2020 by U-M School for Environment and Sustainability:  Tips for Extending the Lifetime of Lithium-Ion Batteries.