Batteries aren’t dead when they come to the end of their useful life in an electric vehicle.

Reused or “second-life” lithium-ion batteries still have a lot of juice left in them, but so far the concept of using these batteries in stationary applications has yet to gain real market traction. New research, growing automotive industry interest and an expanding startup ecosystem suggest that that could now finally be changing.

“There's definitely an uptick in the number of companies that are now trying this and getting serious about it, and I think it's becoming pretty clear what the main obstacles are that remain,” said MIT researcher Ian Mathews, who recently published a study on the economics of second-life battery systems coupled with grid-scale solar installations. “It's a very interesting time.”

EV batteries are typically replaced after they lose around 20 percent of their capacity, which means that there’s still up to 80 percent capacity remaining that can be used for stationary storage applications. Tapping into that remaining battery life has the potential to cut costs and greenhouse gas emissions, but it comes with several challenges.

Retrofitting lithium-ion batteries for reuse requires extensive testing and upgrades to ensure that the product will perform reliably in its new role. The nascent second-life battery market also needs a steady battery supply, customer demand and access to funding in order to be successful.

Solutions are within reach, with a growing group of technology startups and major automakers working to advance the second-life battery segment as EV sales continue to increase.

Dane Parker, chief sustainability officer at General Motors, said in an interview at the company’s EV Day event earlier this year that creating a circular supply chain for EV batteries is one of the company’s central efforts to reduce its environmental footprint. He said GM designed its new Ultium battery pack with second-life applications in mind and is currently working with partners to develop a business case around battery reuse.

"We actually believe it’s very viable,” he said of second-life batteries. “If you design them with that purpose…it becomes much easier to integrate later. And we’re doing that right now.”

Automakers under pressure to unlock value in used batteries

GM isn’t the only EV maker that’s looking closely at the second-life battery space. Nissan was one of the first major automakers to pilot second-life EV batteries in a grid-scale storage installation in 2015. That same year, BMW tested used batteries in demand response events during an 18-month pilot project in partnership with Pacific Gas & Electric.

Also in 2015, Daimler AG announced plans to build a 13-megawatt-hour second-life battery storage unit at a recycling plant in Lünen, Germany. Daimler subsidiary Mercedes-Benz Energy teamed up last year with Beijing Electric Vehicle, one of China’s largest EV makers, to build an energy storage system that uses retired EV batteries.

While it hasn’t ventured into the stationary storage space directly, American electric truck startup Rivian designed its battery packs from the outset to make end-of-life repurposing as easy as possible. Electric bus manufacturer Proterra took the same approach.

Automakers are “really, really interested” in second-life battery applications “because they know they have this huge store of value that is potentially going to come back to them when they have to take batteries out of cars,” said MIT's Mathews. “They know the cost of recycling is going to be huge for them if they're mandated to recycle these batteries, which they already are in some places.”

China and California already have EV battery recycling policies in place or under development. Repurposing EV batteries allows automakers not only to immediately generate additional revenue but also to delay when they need to take the batteries apart and recycle the materials.

The economic case for second-life batteries

Automakers aren’t the only companies paying attention to second-life batteries. A growing number of project developers are also starting to see second-life battery storage as a way to bring down the capital costs of commercial- and grid-scale battery installations, according to Mathews. This marks a shift away from the smaller residential and off-grid battery applications repurposed batteries were initially being tested for.

A study published in Applied Energy by Mathews and five other current and former MIT researchers concluded that lithium-ion batteries could have a profitable second life as backup storage for grid-scale solar photovoltaic installations, where they could operate for a decade or more in this less-demanding role.

The study results are based on a rigorous review of a hypothetical grid-scale solar farm in California, using real-world data on solar power availability, battery degradation and other factors. Mathews and his co-authors determined that a system of second-life battery installations coupled with a 2.5-megawatt solar project would be a profitable investment if the reused batteries were 60 percent or less than the original battery price. A separate McKinsey analysis found that second-life batteries could offer a cost advantage of 30 to 70 percent over new battery alternatives by the mid-2020s.

The same McKinsey report found that the supply of second-life EV batteries could surpass 100 gigawatt-hours per year by 2030, with the potential to meet half of the forecast global demand for utility-scale energy storage in that year.

Source: McKinsey, Second-Life EV Batteries: The Newest Value Pool in Energy Storage

Both the McKinsey and MIT studies note several challenges in repurposing EV batteries that must be overcome to unlock this new pool of battery supply.
Much more work needs to be done around second-life battery health and the best ways to control and monitor batteries from different vehicles and models once they’re grouped together in a new stationary pack, Mathews said. A growing number of startups are working on ways to overcome such hurdles. “[There's] a nice ecosystem building, but it is in the early stages."

California second-life startups gain momentum

In a step forward for the sector, California-based startups RePurpose Energy, Smartville Energy and ReJoule each received $2 million to $3 million in funding last month from the California Energy Commission Electric Program Investment Charge (EPIC) funding pool to validate their technology. All three startups previously received funding from the CalSEED program.
“Our mission is to reuse batteries from electric vehicles to store solar energy in lower-cost, more sustainable energy storage systems,” said Ryan Barr, chief operating officer at RePurpose.
“We can do better and need to do better,” Barr said of the energy storage industry’s greenhouse gas impact. “That's really what motivates our work.”
The mining and refining of lithium-ion battery materials, as well as the manufacturing of cells, modules and battery packs, requires large amounts of energy and can have a significant environmental impact. Second-life batteries could offer meaningful greenhouse gas emissions savings by eliminating the need to manufacture new batteries for every application.
One market analysis, which was commissioned by a European clean transportation organization, found that extending the life of a battery in a repurposed application has the potential to cut its embedded emissions in half.
RePurpose was born out of a decade of research at UC Davis and is led by Professor Jae Wan Park. The startup focuses its work on quickly and accurately disassembling EV batteries, usually from Nissan, determining their state of health, and then reassembling them with new controls and safety equipment.
By replacing the most degraded cells in the battery, it can be reused in another application outside of a vehicle for up to an additional 12 years based on RePurpose’s initial calculations. But first the bad cells have to be found. RePurpose has developed a way to test for battery degradation in about a minute — a process that traditionally takes a full day.
Safety is one of the biggest barriers to attracting more capital into the nascent second-life battery industry. RePurpose is also developing a “nondestructive fire suppression system” that can detect an imminent battery failure and prevent the battery from overheating without damaging any of the electrical components. Mitigating risks to investors should help boost access to project financing. 
Park raised around $5 million to develop the technology and deploy a 300-kilowatt-hour demonstration project at the UC Davis campus winery that’s shifting power use to offset the facility’s on-peak energy demand. The company has since raised another $4 million, including $3 million from the California Energy Commission’s EPIC funds, which will be used to deploy a second 1.2-megawatt-hour demonstration project at a food cooperative.
“We aim to replicate the food cooperative demonstration all over the state,” said Barr.

Smartville: The challenge of refurbishing different battery models

The diversity of EV battery packs available in the market creates another big hurdle for processing and reconfiguring the batteries for new applications, as it requires significant reverse-engineering even before the battery testing process can begin.
Smartville Energy, which spun out of UC San Diego’s Center for Energy Research, has developed a refurbishing process for different kinds of batteries, which researchers see as critical for enabling the technology to scale.
Rather than speed up the battery testing process like RePurpose and other players in the space are doing, Smartville’s specially designed power converters and conditioning process intentionally slows the testing down to balance the health of the batteries across the entire system. Because the health check involves charging and discharging the batteries many times over several weeks, this process creates the additional revenue stream of selling electricity services from the batteries during the testing process.
“Our control and power electronics design brings all of those different batteries from different vehicles, makes and models, as well as power-coupling formats, into the same modular design,” said Smartville CEO Antoni Tong. “Then each of them is cycled in a way that will improve their uniformity through the conditioning process, and at the same time those operations are synchronized with a grid service.”
With its $2 million in EPIC funding, Smartville is currently working to deploy its first real-world demonstration project at a store that sells rare and antiquarian books, whose inventory requires precise temperature and moisture control. “We often say that if we do our job right, there should be no new batteries going into stationary storage,” said Tong.


ReJoule: Starting at the very beginning

ReJoule, another California startup that received $2 million from the EPIC program, takes an approach to optimizing second-life batteries that starts within the vehicle itself. By installing ReJoule’s technology on a new battery, the battery system can be optimized over its entire life, allowing it to last even longer.
“The idea is that once our battery management system is embedded in the vehicle and we have this real-time state-of-health measurement, it would be much easier to transition from that first-life to a second-life application,” said founder and CEO Steven Chung.
“We wouldn’t need additional testing; we wouldn’t need to take the battery out of the vehicle, transport that battery to a specific test center, do the testing and then transport it to whatever second-life application,” Chung explained. “It can be much more streamlined.”