I thought the price differential was not going to happen as there was a serious drop in the price of Lithium over the past year; but I looked it up and the lithium price drop is more a 5 year trend, with the last few months having a sudden surge in the price.
Increased production of Lithium is why. However, that only drains the (very limited) reserves of Lithium more quickly. Currently we have about 75 years left of it at previous extraction rates. More could be found, that is unlikely.