Cheaper and far more abundant than lithium, sodium is increasingly appealing as a foundation for a next generation of high-voltage rechargeable batteries. Development of commercially viable sodium ion batteries lags significantly behind that of lithium batteries, which were widely adopted in the 1990s. But researchers worldwide aim to change that with the hope of eventually creating a more economical alternative to lithium. Advances in sodium ion battery performance could eventually lead to more widespread renewable energy adoption in power grids and drive down the cost of electric vehicles.