Dive Brief:

• Safety science company UL is partnering with Hyundai Motor Company on a project to explore the safe deployment of used electric vehicle batteries for stationary energy storage.
• Under a memorandum of understanding signed in July, the two companies will collaborate on safety testing, assessments and a North American demonstration project for second-life battery energy storage systems. 
• UL participated in the development of UL 1974, the 2018 standard for evaluating batteries that are intended to be repurposed, which has been adopted in the United States and Canada. Ken Boyce, senior director of principal engineering in UL's Energy and Industrial Automation group, said the new work with Hyundai can help lead to "rigorous" and "non-destructive" evaluation standards that can further advance UL 1974.

Dive Insight:

Most electric vehicle batteries are replaced when they no longer meet performance standards of 80% of usable capacity. A handful of startups and utilities working in partnership with automakers have sought to repurpose those batteries for energy storage.

American Electric Power and Honda have explored possible uses for used batteries and Nissan piloted second-life battery use on the grid as early as 2015. General Motors has touted that its Ultium battery pack is designed with a second-life applications in mind. 

According to a 2019 report by McKinsey, by 2030 the rise of electric vehicles will result in a supply of second-life batteries totaling more than 200 GWh annually, higher than the demand for lithium-ion utility-scale storage for low- and high-cycle applications combined. However, the market has been held back by several factors, including the variety of battery size, design and the lack of clear industry standards. 

"No guarantees exist regarding second-life-battery quality or performance, and few industry standards focus on battery-management systems or state-of-health disclosures, let alone standard performance specifications for a battery that is to be used for a given application," McKinsey wrote. 

Boyce said that one particular concern for second-life batteries is the threat of thermal runaway, where the cells in a lithium-ion battery overheat and can cause a cascading fire. A number of factors can contribute to thermal runaway, ranging from manufacturing defects and blunt impact to excessive heat. Determining how much wear and tear or what use factors might put a battery at risk for a fire can help inform which batteries and designs are safest for reuse.F

"Before you start to give [a battery] a second life, you want to make sure you understand how safe it is," Boyce said, especially given the differing regulations that exist for motor vehicles and buildings. "There are aspects of the stationary infrastructure that can be more significant and consequential from a safety standpoint. For example, you can get out of a car if you needed to. But if you have an embedded energy storage system … and it's fixed to the structure in a building, you don't have that same kind of mobility response."

Boyce added that with startups exploring different ways to repurpose batteries — either by pairing them together or disassembling them to extract cells — it was especially important to have a consistent approach to "co-managing safety and sustainability."

The new research also comes amid new questions about the safety of lithium-ion battery storage. Australian fire officials are investigating the cause of a fire at the Victorian Big Battery storage project, built with Tesla Megapack units. Four emergency responders were injured in a 2019 explosion at Arizona Public Service's McMicken battery plant, an incident that forced state regulators to reconsider safety rules for the growing storage industry. 

Boyce said that research into recycling EV batteries can also inform standards and procedures for all types of stationary storage. 

"We always focus on a closed-loop system for gathering information from the field involving incidents or recalls or whatever may happen, and try to leverage that to try to drive for continued enhancement of safety standards," he said. "This is just a great source of information for us to understand how batteries respond to that aging process … and a rich set of data to understand what might cause degradation that can ultimately lead to a potential safety concern and then be more proactive about trying to mitigate that through safety practices and assessments."