Back in 2009, when China’s economy was expanding at about twice today’s pace, a little-known private firm made a quiet bet on uncharted territory: Indonesia. The company was on a quest: to secure nickel, a vital industrial metal used in stainless steel production and, increasingly, to power advanced batteries. That bet proved lucrative. By leveraging Indonesia’s vast nickel reserves – the world’s largest – and securing greater control over upstream supplies, Tsingshan Group has grown into a...