Old EV batteries could cover most of China’s energy storage needs

Used electric vehicle batteries could meet two-thirds of China’s grid storage needs, charging when renewable energy is plentiful and releasing electricity when demand outstrips supply.

Renewable energy production slows down when the wind isn’t blowing and the sun isn’t shining, which can lead to shortages during peak times like mornings and evenings and winter months. This gap is usually filled by gas and coal-fired power plants. But countries like China, the US, the UK and Australia are building massive amounts of battery-based grid storage that can save renewable energy for later use.

As electric vehicles become more common, batteries from dismantled cars could be plugged into the grid to achieve a carbon-neutral energy system faster and cheaper, they say Ruifei Ma at Tsinghua University in China and colleagues. These second-life batteries could cover 67 percent of China’s grid storage demand by 2050, while cutting costs by 2.5 percent, according to their study.

EV batteries degrade over the years as they are charged and discharged, and are usually discarded once they reach about 80 percent of their original capacity. While this degradation reduces the car’s range and acceleration, it has little impact on a grid-connected storage system where hundreds or thousands of batteries are charged and discharged over many hours.

“They still have a lot of energy left in them, and when they’re used as storage, they don’t tend to degrade as quickly,” he says Gill Lacey at Teesside University in Great Britain.

“We shouldn’t be throwing away these materials, which cost a lot of money to mine, process and turn into batteries, when we have 80 percent usable capacity left in the cells,” he says. Rhodri Jervis at University College London. “So there’s a lot of desire to use discarded batteries in second-life applications from a cost savings perspective, but I think it’s probably more important from a sustainability perspective.”

Previous research reached different conclusions about whether energy storage based on used batteries would be cheaper than new lithium-ion batteries, the price of which was falling.

However, used batteries are likely to become more economical as more electric cars take off the road. It was more than 17 million EVs purchased in 2024, about 20 percent of all car sales, and nearly two-thirds of them were purchased in China.

The study found that in a scenario where batteries with different chemistries are procured across China and deployed until they reach 40 percent of their original capacity, second-life grid storage will begin to grow even faster after 2030, while new batteries stagnate. The total capacity would reach 2 trillion watts by 2050.

In a scenario where grid storage relies on new batteries and pumped hydro—where water pumped into a reservoir flows downhill to drive a turbine—total capacity only reaches about half of that.

While second-life battery storage is still largely untested, US start-up Redwood Materials has built a 63 megawatt-hour project from ten-year-old car batteries for a data center in Nevada. It claims its systems cost less than $150 per kilowatt-hour and can provide power for more than 24 hours, far longer than new lithium-ion batteries can realistically offer.

However, used batteries must be checked and grouped into units of similar capacity. Alternatively, the control system must be able to bypass individual batteries. Otherwise, the entire group will have to stop charging once the most degraded battery reaches its capacity.

Damaged batteries must also be shielded, and those that make the cut must have temperature and voltage sensors for each of the hundreds of cells. If the cell overheats, it can cause a massive, unextinguishable fire.

“Obviously the risks are higher, so you have to mitigate them with your security, your isolation and balancing, and making everything else more robust,” says Lacey.

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