Fig. 4: Lithium vulnerability index for a supply chain disruption in China.

Visualization of a vulnerability index for global LFP (Lithium Iron Phosphate [a–d]) and NMC (Lithium Nickel Manganese Cobalt [e–g]) cathode supply, for a lithium supply chain disruption in China. Table 1 defines the four sensitivity cases. The level of overall vulnerability at the cathode manufacturing step, added at each upstream step, is noted with a plus (+) sign. Sums may not add due to rounding. The solid horizontal black lines are visual aids to indicate separation of countries; semi-transparent red bars represent vulnerability that is propagated downstream. The Li supply chains differ between LFP and NMC cathodes because of differences in the distribution of countries that produce each cathode and the supply chain paths of each. Example solutions for the other NMC materials are in Supplementary Text S4-1. Indirect trade and unobserved trade do not count towards the measurement of vulnerability in the optimistic case, but are counted towards the pessimistic calculation in the case that includes uncertain data. For the minimum and maximum cases, one possible solution is presented, but other distributions with the same vulnerability index are possible. For all of these cases, we mask the distribution of production and trade upstream of China’s supply at each supply chain step because it does not affect the vulnerability index and may be distributed arbitrarily in the network flow optimization results.