That’s a very good question.
In simply logical terms, Kristen Hall-Geisler of ‘How Stuff Works.com’ puts it in this way:
“The most obvious difference between Li-ion and NiMH batteries is the material used to store power. Lithium-ion batteries are made of carbon and highly reactive lithium, which can store a lot of energy. Nickel metal hydride batteries use hydrogen to store energy, with nickel and another metal (such as titanium) keeping a lid on the hydrogen ions”. Continue reading