By Daniel Leussink and Maki Shiraki

KINOKAWA, Japan (Reuters) -Japanese Tesla supplier Panasonic Energy has finalised preparations for the mass-production of its high-capacity electric-vehicle batteries, the company said on Monday, as it seeks to start supplying the cell to automakers.

Panasonic Energy's renovated plant in the western prefecture of Wakayama will serve as the main factory for producing the 4680 cells, which the company says have five times the capacity of its smaller 2170 cylindrical batteries.

The unit of Panasonic Holdings has sent samples of the 4680 batteries to some automakers to which it is already a supplier, and intends to kick off production after getting the green light from clients, a Panasonic spokesperson said.

It had previously said it planned to start production of the 4680 cells at the Wakayama plant, where it formerly made parts for automotive batteries, in the first half of the current business year that started in April.

The bigger cells, which have a diameter of 46mm and an 80mm height, will allow automakers to extend the driving range of electric vehicles and use fewer cells to achieve the same battery pack capacity, Panasonic Energy said in a statement.

Tesla began delivering the Cybertruck in November 2023 after years of delay and a difficult production ramp-up.

While the automaker already produces its own 4680 batteries, one of the main bottlenecks it faces for the truck is the speed at which it can make them, sources told Reuters in late 2023.

Panasonic, one of Tesla's long-standing battery suppliers, is currently building its second U.S. battery plant in Kansas that is set to start production next year, in addition to one in Nevada.

Panasonic Energy held a ceremony to mark the completion of preparations to start mass-producing the batteries and showed an inspection line where trays stacked with the silver-coloured cells could be seen running through.

The company plans to start battery production at an annual capacity of several gigawatt hours, CEO Kazuo Tadanobu told reporters after the ceremony, adding the global EV market was likely to expand over the medium to long-term.

The Wakayama plant is expected to employ roughly 400 staff in the development and production of the new batteries by March 2025, and serve as a site for trying out processes that it could implement at other battery factories around the world, the company said.

Panasonic Energy already makes 2170 and 1860 cylindrical EV batteries at its Suminoe and Kaizuka plants in Japan.

The battery manufacturer and automaker Subaru, for which the U.S. is a key market, said last week they will set up a plant in Gunma prefecture north of Tokyo for the supply of automotive batteries from the 2028 business year.

(Reporting by Daniel Leussink and Maki Shiraki; Editing by Eileen Soreng, Jan Harvey and Louise Heavens)