The Chinese - English dictionary translates 気
air, gas, steam, vapor; spirit
The interpretation of 気 as energy, live-energy ... is a daoistic term. It has it's roots in that relegion or philosphy and can not be understood without that background.
Well, I have the impression that the Chinese (maybe the Japanese, too) make some distinction between the simplified 気 and the traditional
- for example, see Wakan dictionary.
Certainly, Daoists give deep and complex meanings to qi, but I doubt that they were the first to do so. I don't think that it can be called a Daoist term only. It would probably be more correct to link its emergence to the book of the Yellow Emperor, the classic on Chinese traditional medicine.