Midstream: Accumulation and in-use stocks

Nickel's in-use stock grows steadily throughout the projection period, peaking at almost 137 million tonnes in 2050, while its composition reveals a strong degree of structural inertia. Chart 32 below reveals that stainless steel feed remains the dominant stock throughout the period and increases its share slightly by 2050, totalling 80% of nickel’s stock accumulation. Battery-grade nickel expands by 1000% over the same period, reflecting the rapid growth of electric vehicles and energy storage applications. However, it starts from such a small base that it still accounts for only a modest share of total in-use nickel stock at the end of the projection. Although batteries represent the fastest-growing source of nickel demand, nickel remains overwhelmingly a stainless steel material. The majority of nickel therefore remains embedded in long-lived infrastructure, buildings, industrial equipment, and transport applications rather than battery systems.

The circularity implications follow directly. Nickel's circularity is fundamentally stock-based rather than flow-based. Most nickel remains locked within durable alloys that typically remain in service for several decades.^{131 132} Class I nickel, for example, is largely used in transport applications (see the Sankey diagram in the nickel Material flows and applications section), which have an average mean lifetime of 20 years, while Class II nickel (stainless steel feed) has a mean average lifetime of 50 years. This means future secondary supply depends not only on how efficiently end-of-life material is recovered, but also on how today's growing in-use stock is managed over its lifetime. Materials entering use today will form the recoverable resource of future decades.

This long service life also represents an often-overlooked contribution to circularity. Nickel-containing alloys¹³³ are used because they improve corrosion resistance, durability,¹³⁴ and performance in demanding environments, extending the lifetime of products used in applications such as hydropower, geothermal energy, and wave energy.¹³⁵ Delaying replacement and waste generation is itself a circular strategy, yet one that conventional recycling indicators do not capture. A nickel-containing product may therefore have a relatively low recycled content while still delivering greater resource efficiency over its full service life.