SK Inc. said Tuesday it has invested an additional 40 billion won ($35.7 million) into a next-generation lithium-metal battery developer Solid Energy Systems after making an initial investment of 30 billion won in 2018.

According to the holding firm of SK Group, the investment will allow the company to become the third-largest shareholder of SES after Singapore’s sovereign wealth fund Temasek and SES founder and CEO Qichao Hu.

SES, which started as a spinoff of the Massachusetts Institute of Technology in 2012, is one of the pioneers of next-generation lithium-metal batteries. After the successful development of a prototype, SES in March signed an agreement with General Motors to construct a test production facility in Boston by 2023 and commercialize the advanced battery by 2025.

Lithium-metal batteries use metal for anodes, or the negative side, while typical lithium-ion batteries use graphite. This increases lithium-metal batteries’ energy capacity 10 times greater than that of lithium-ion batteries.

By Kim Byung-wook (kbw@heraldcorp.com)