The team behind the sun-powered Solar Impulse 2 plane on Tuesday said it needed an additional 20 million euros ($22 million) to complete a historic round-the-world flight, after battery damage grounded it for months.

A spokeswoman for the record-breaking project told AFP this figure was just an "initial estimation" and that the funds would cover the salaries of 150 people, logistics and material for the coming year.

The plane suffered irreversible damage to parts of its battery system during a gruelling, five-day journey from Japan to Hawaii.

The project had initially hoped the repairs could be completed within weeks, but the extent of the damage grounded the plane in Hawaii until at least April of next year.

Solar Impulse 2 has been flown alternatively by Swiss businessman and pilot Andre Borschberg and his partner Bertrand Piccard, also a Swiss national and an aviator.

Piccard is reportedly in Europe seeking to raise the money to sustain the project which hopes to fly an aircraft around the world without using a drop of fuel.

Borschberg, who has also returned to Europe, smashed the previous record for a solo flight with his 118-hour journey across the Pacific Ocean.

The previous record of 76 hours and 45 minutes had been set by US adventurer Steve Fossett in 2006.

The Solar Impulse is currently parked at a hanger near to and monitored by the University of Hawaii.

Once repairs are completed, the plane is expected to cross the United States, stopping in New York before a trans-Atlantic flight to Europe.

From there, the pilots plan to make their way back to the point of departure in Abu Dhabi.