99.95% High Purity Manganese, page-751

The real battery demand for manganese might come from sodium batteries. The advantage of sodium over lithium is far greater abundance. However, sodium battery chemistries do not achieve the same mass or volume energy density that is possible with lithium. So lithium batteries will likely remain the best choice for EVs, but sodium could be a low cost, highly reliable option for large scale stationary batteries used for utilities.
Like lithium batteries, there are various sodium battery chemistries. The chemistry developed by Faradion depends on nickel which is ten times less abundant than lithium so the lithium bottleneck is traded for a nickel bottleneck. On the other hand, the major raw materials used for sodium batteries being produced by CATL are manganese and/or iron - both highly abundant which could allow unlimited scaling of sodium battery production.