Old EV batteries could meet 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 disbursing electricity when demand exceeds supply.

Renewable energy production slows when the wind doesn’t blow and the sun doesn’t shine, which can lead to shortages at peak times, such as mornings and evenings and during the winter months. Gas and coal-fired power plants generally fill this gap. But countries like China, the US, the UK and Australia are building huge 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 electricity system more quickly and cheaply, argue Ruifei Ma of Tsinghua University in China and colleagues. These second-life batteries could meet 67% of China’s grid storage demand by 2050, while reducing costs by 2.5%, according to their study.

Electric vehicle batteries degrade as they are charged and discharged over the years, and they are typically retired from service when they reach about 80% of their original capacity. Although this degradation decreases a car’s range and acceleration, it has little impact on a grid storage system, where hundreds or thousands of batteries are charged and discharged over many hours.

“They still have a lot of energy left and, used as storage, they tend not to degrade as quickly,” says Gill Lacey of Teesside University, UK.

“We shouldn’t be throwing away these materials that are very expensive to extract, process and turn into batteries when we have 80% of usable capacity left in the cells,” says Rhodri Jervis of University College London. “So there’s a lot of desire to use obsolete batteries in second-life applications, from an economic standpoint, but I think it’s probably more important from a sustainability standpoint.”

Previous research has reached different conclusions about whether energy storage based on used batteries would be cheaper than new lithium-ion batteries, which have fallen in price.

But used batteries will likely become more economical as more electric vehicles go off the road. More than 17 million electric vehicles were purchased in 2024, about 20% of all car sales, and almost two-thirds of them were purchased in China.

The study found that in a scenario in which batteries of different chemistries are purchased across China and deployed until they reach 40% of their original capacity, second-life grid storage would begin to grow even faster after 2030, while new batteries would plateau. Total capacity would reach 2 trillion watts by 2050.

In a scenario where grid storage relies on new batteries and pumped hydropower – where water pumped into a reservoir flows downhill to drive a turbine – the total capacity is only about half that.

While second-life battery storage is not yet widely tested, US startup Redwood Materials has built a 63-megawatt-hour project using decade-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 reasonably offer.

But used batteries should be examined and grouped into units of similar capacity. Alternatively, the management system must be able to bypass individual batteries. Otherwise, the entire group will have to stop charging as soon as the most degraded battery has reached its capacity.

Damaged batteries must also be disposed of, and successful ones must be fitted with temperature and voltage sensors for each of their hundreds of cells. If a cell overheats, it can cause a massive, unextinguishable fire.

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