> Isn't lithium mineral the main cost in building these batteries?

No, and I have no idea why anyone would think that. Raw material costs are generally not that significant, most costs in manufacturing come from labor and capital.

The lithium in a $15000 75kWh battery pack costs around $1600 at current prices. There is a lot of room for the price to fall even with rising raw material costs, as manufacturing gets more efficient and capacity is built out.

And also, rising raw material prices will cause production to expand, which will eventually push prices back down.