BEIJING, May 29 (Reuters) - China plans to invest more than 6 billion yuan ($830 million) in a government-led project to develop solid-state batteries with six firms eligible for state funding to work on the next-generation technology, a person with direct knowledge of the matter said.

Solid-state batteries hold the promise of improved safety, a longer lifespan and faster charging compared with conventional lithium-ion batteries that use flammable liquid electrolytes. But mass adoption remains some way off due to constraints in raw material availability, intricate manufacturing processes and the resultant high costs.

China is seeking to cement its lead in the global EV market after early and heavy investment in domestic supply chains helped it become the most cost-competitive battery and EV producer in the world.

Those picked as potential participants in the project include battery makers CATL and Nio-backed WeLion New Energy Technology, said the person.

BYD , which vies with Tesla for the title of the world's biggest EV seller and is a battery maker, as well as automakers FAW, SAIC and Geely have also been chosen, according to the person who was not authorised to speak to media and declined to be identified.

Geely declined to comment. The other companies did not immediately reply to Reuters' requests for comments.

Many auto industry officials and analysts expect solid-state batteries will determine the competitiveness of the next-generation EVs. Several global automakers are also looking into the technology, hoping to break China's dominance in the current EV battery technologies.

Japan's Toyota Motor, a laggard in EV development, has said it plans to launch vehicles powered by solid-state batteries in a couple of years.

Tesla has not detailed any solid-state development plans.

The official China Daily first reported news of the state-funded project.

($1 = 7.2475 Chinese yuan) (Reporting by Zhang Yan, Qiaoyi Li, Ethan Wang and Liz Lee; Editing by Edwina Gibbs)