Lithium-based rechargeable batteries are too expensive to use on a large scale because there is so little lithium available. But sodium is abundant and cheap, so why not base a battery on a sodium electrolyte?
The problem is that sodium ions are many times larger than lithium ones, and they gradually damage a battery's anode as they diffuse during charging and discharging. Another issue is that using a tin anode in such batteries would offer the highest power storage capacity, but this leads to the formation of a sodium-tin alloy that makes the battery swell, hastening what is known as "structural pulverisation". The upshot is that a sodium-ion battery with a tin anode can only be charged and discharged around 20 times.