Yoo Sam (front row, left), head of Posco International's green materials department, signs documents with NextSource CEO Craig Scherba (front row, right), in Antananarivo, the capital city of Madagascar, Aug. 28. (Posco International)

Posco International said Monday that it has signed two agreements to secure some 90,000 metric tons of natural graphite, bolstering its supply chain for the key material for secondary batteries.

In a memorandum of understanding signed with Canada’s NextSource on Aug. 28, Posco agreed to invest in the company’s Molo Mine, one of the largest mines in Madagascar. The agreement is expected to help Posco secure 30,000 tons of natural graphite, or 15,000 tons of spherical graphite, on an annual basis for the next 10 years.

Flake graphite is natural graphite used to make electrodes, while spherical graphite, which has been reprocessed into a round shape, is used to make cathode. The output will be supplied to Posco Future M, a subsidiary specializing in the secondary battery business.

On Friday, Posco also signed a partnership with Australian company Black Rock Mining in Tanzania, under which it aims to participate in the miner’s rights offering and explore a potential off-take deal to increase the graphite supply to 60,000 tons a year. Black Rock Mining owns the world's second-largest natural graphite mine.

“By leveraging our global networks, we will continue to bolster the secondary battery value chain and contribute to national resource security," a Posco International official said.