What is a sodium-ion battery?

Sodium-ion batteries work on similar principles to lithium-ion batteries, but they use sodium, a far more abundant element. Because sodium is cheaper and widely available, these batteries are attracting attention for grid storage and some low-cost electric applications. They generally have lower energy density than lithium-ion cells, which means they store less energy for the same weight. Research and commercial production have expanded in the 21st century as demand for battery storage has grown.