Easy to say; harder to support. I did my research beforehand: NiMH vs. Li-ion batteries - A battery Comparison
Its an interesting topic. I'd be interested if you have any other references as the one you quote has a few problems It focuses on tiny batteries, eg cell phones, not the size we have for traction batteries It says that NiMH has a higher energy density and then says the Li-ion is smaller It doesn't quantify what it means by hot temperatures or hot weather and it does not mention the nature of the problems which could presumably be anything from a slight voltage change which is a problem in some electronic applications to total battery failure. It makes assertions but does not support them by data or reasoning within the article or reference to sources where they can be verified