LONDON (Reuters) - U.S. firm Ascend Elements and Poland's Elemental Strategic Metals have formed a joint venture to recycle electric vehicle batteries, with their first Polish plant already open and another plant planned in Germany, they said on Tuesday.

The companies did not disclose their planned investments via the joint venture, called AE Elemental, but said they are seeking European Union and local government funding.

The EU has mandated that over the next decade a growing proportion of materials in EV batteries must be recycled.

"Keeping battery materials in the local supply chain in Europe requires investment and infrastructure," Ascend Elements CEO Mike O'Kronley told Reuters. "That's what we're doing together."

The jointly developed plant in Zawiercie in southern Poland has the capacity to recycle up to 12,000 metric tons of batteries annually, equivalent to approximately 28,000 EVs.

EV batteries are shredded to create black mass, which is then further recycled to extract lithium and other battery materials for use in new EVs.

On the same site in Zawiercie, the venture will build a plant that will open in 2026 to extract lithium from black mass, processing up to 20,000 metric tons annually.

Ascend also plans a separate recycling plant for battery materials, O'Kronley said.

The companies said permitting has been completed for a plant in central Germany that will recycle up to 25,000 tons of batteries annually, but declined to disclose a location.

Ascend has raised around $700 million in equity funding and received $480 million in U.S. Department of Energy grants as part of Biden administration efforts to boost EV battery production. It has a battery recycling plant in Georgia and is building a second in Kentucky.

Elemental Strategic Metals, which is part of the Element Group, has raised $290 million in equity funding and said it was close to completing another round.

"This is a matter of speed," CEO Michal Zygmunt said. "Going together and sharing capex allows us to be more aggressive."