YONGIN, South Korea -- Hyundai Motor Group's plans for green cars are a costly array of hybrids, plug-ins, pure electrics and fuel-cell vehicles for both the Hyundai and Kia brands.

But the automaker's eco-car czar, Lee Ki-sang, expects a technological shakeout between 2020 and 2025 that will make it clearer whether a post-lithium ion battery breakthrough is on the horizon.

Lee, senior vice president for Hyundai Motor Group, said next-generation solid-state batteries seem to hold the greatest potential.

And if a breakthrough comes, Hyundai could rapidly shift its lineup toward electrics.

Much is riding on the direction of tomorrow's batteries because Hyundai aims to be the world's No. 2 eco-car maker by 2020, after Japanese rival Toyota Motor Corp.

To get there, it plans to launch 28 eco cars by then, consisting of 10 hybrids, eight plug-ins, eight electric vehicles and two fuel-cell vehicles, all of which require some kind of battery.

Eco cars make up about 2.5 percent of Hyundai Motor Group's global sales. But that could rise to between 20 percent and 40 percent of its total volume by 2025, Lee predicted.

"If a really new, next-generation battery appears, like magic, around 2025, then the market share of electric vehicles will go from 20 to 30 percent to 80 to 90 percent of the whole market," Lee said in an interview here at the South Korean manufacturer's fuel cell development lab.

The problem is diminishing gains from improvements in lithium ion batteries, the chemistry currently considered cutting edge in production cars.

If no successor technology can be found to lithium ion, then Hyundai-Kia should keep investing in fuel cells as a viable alternative, he said.

Lee expects the tipping point to occur sometime after 2025, based on what he hears from battery manufacturers' efforts to deliver a next-generation, high-storage power pack.

Today's lithium ion batteries will have run their limit by around 2022 or 2023, he said. Battery makers are already targeting 2025 for next-generation replacements.

Possible technologies include solid-state batteries, or batteries using a lithium-sulfur or lithium-air chemistry, Lee said.

"The problem is nobody can ensure the real possibility of building that kind of new battery technology," Lee said.

"Everybody is announcing, "We are developing it.' But to prepare a production line and to validate and to apply it to the vehicle, it will take some more time."

Hyundai-Kia hopes clues about the market direction will emerge around 2020.

"I can see some meaningful signal around 2020; that's my hope," Lee said. "Based on that meaningful signal, we have to modify our future plan. It can be a kind of turning point."

Lee said solid-state batteries seem to be the closest to reality.

Solid-state batteries use a solid electrolyte instead of the liquid electrolyte in today's cells.

They hold the potential for being lighter and more compact and for having a higher energy density. They also are more stable than lithium ion batteries and safer as a result, Lee said.

"Solid-state batteries are closest to realistic mass production," Lee said, adding that they are still a long way off. "We think solid-state batteries will be a strong candidate."