You may think that lithium-ion batteries are the best man can create, but researchers believe otherwise. There are other combinations of elements that are very promising. What about a cell with potential for seven times more energy density than Li-Ion could ever achieve? State of the art for current batteries would be 256 Wh/kg. Lithium-Carbon Dioxide batteries – or Li-CO2, for short – can theoretically reach 1,876 Wh/kg. Researchers at the University of Illinois at Chicago created the first usable Li-CO2 battery. It was tested to up to 500 cycles, and it worked, which is great news.