Indeed. It is quite odd (perhaps to the point of being misleading) to use scientific notation ahead of "tonnes of kg", instead of just using scientific notation

Indeed. It is quite odd (perhaps to the point of being misleading) to use scientific notation ahead of "tonnes of kg", instead of just using scientific notation combined with Kg. I made this mistake reading the article–I divided 10^7 / 10kg per car --> only enough cobalt for about 10^6 cars (1 000 000) cars. Instead the calculation is 10^7 tonnes * 10^3 kg/tonne = 10^10 kg / 10kg per car = enough cobalt for 10^9 battery packs = 1 billion cars. I think we will be ok...