Midstream: Accumulation and in-use stocks

Cobalt's in-use stock follows a distinctive midstream trajectory compared with the other materials examined in this study, as it is the only material whose total stock declines over the projection period. Chart 25 shows that, after expanding rapidly through the 2020s and 2030s, total in-use stock peaks at 2.1 million tonnes around 2040 before declining slightly towards 2050.

The changing composition of stock explains this pattern. Battery-related stock grows rapidly from a relatively small base and becomes the dominant component by the 2030s, before peaking and gradually declining. This is consistent with the substitution trends discussed earlier, as battery chemistries increasingly reduce cobalt content or eliminate it altogether. Superalloy stock, by contrast, continues to grow throughout the projection period, reflecting long-lived aviation and turbine applications where cobalt's high-temperature performance has no ready substitute. Yet alloyed cobalt still only accounts for around 24% of stock accumulation by 2050. Cobalt's in-use stock is therefore shaped by two opposing trends: a battery-driven expansion that slows down towards the end of the projection period, and continued accumulation in alloyed applications where cobalt remains technically indispensable.

This evolution has important implications for circularity. As in-use stock plateaus, end-of-life flows begin to converge with inflows, creating more favourable conditions for secondary supply than a system where stocks continue expanding indefinitely. At the same time, the composition of future secondary resources changes, with an increasing share of recoverable cobalt originating from superalloys and other long-lived applications rather than batteries. This changing material profile has important implications for the recycling infrastructure required to recover cobalt efficiently.