A joint of French science institutions just publish an article that claim they produced a rechargeable battery prototype using sodium ions (Na+). This battery has 90 Wh/Kg storage specific energy capacity, what is close to the early lithium batteries.
The sodium ions great advantage for making batteries, instead of lithium, is that sodium is cheap and common. The disadvantage is that it is less efficient as a charge carrier, so it´s necessary to develop materials that can work on higher voltages.
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