General Motors is prepaying Livent $198-million for a guaranteed six-year supply of lithium, a deal that reflects the auto industry's rising worry about a tightening market for the electric vehicle battery metal.

Prepaying cash for a guaranteed metal supply is unusual in the mining industry. The deal shows GM's eagerness to ensure it has sufficient raw materials to meet its goal of producing one-million EVs annually in North America by 2025.

Both companies announced the broad brushstrokes of the deal last week, but Livent announced financial terms on Tuesday as it posted a better-than-expected profit and raised its forecast for the year.

"GM is certainly thinking for the long term here," Paul Graves, Livent's chief executive, told investors on a Tuesday conference call. "By making the advanced payment, they are clearly giving us the commitment that we were looking for."

Graves has long prodded automakers to work closer with lithium producers. In an interview with Reuters last fall, Graves warned that unless the auto industry signed long-term deals, "there may be periods where there is just insufficient lithium."

Livent produces lithium in Argentina and has processing facilities in the United States.

Livent, which also supplies BMW, expects to receive the GM prepayment later this year. The company is set to start supplying GM in 2025 at a contractual price per tonne, though neither company disclosed volume.

Philadelphia-based Livent reported second-quarter net income of $60-million, or 31c a share, compared with $6.5-million, or 4c a share, a year ago.

Excluding one-time items, Livent earned 37c a share. By that measure, analysts expected earnings of 29c a a share, according to IBES data from Refinitiv.

Livent said expansion of its Argentina site is on schedule. The company's stock rose slightly in after-hours trading.