Cycle life
The number of times a battery can be charged and discharged. It is usually counted up to the point where capacity has fallen to 80% of its original value.
With every cycle the electrode materials suffer slight damage and some lithium is lost to side reactions, so capacity gradually shrinks. A 2020 study that tested commercial lithium-ion cells under varied conditions found that lithium iron phosphate cells outlast other chemistries, and that temperature and depth of discharge change the lifetime greatly[1].
For a grid battery cycled every day, cycle life decides the cost per kilowatt-hour delivered. A battery of the same price that lasts twice as long is in effect half the price. Manufacturers' figures apply to specific conditions, so comparisons need matching temperature, charging rate and depth of discharge.
Related terms
- Lithium iron phosphateA type of lithium-ion battery with an iron-phosphate positive electrode. It uses no cobalt or nickel and is cheap, hard to ignite and long-lived.
- Sodium-ion batteryA battery that shuttles sodium ions instead of lithium. Its materials are plentiful and cheap, and it is entering use in grid storage.
- Grid batteryA large battery connected to the power grid that charges when electricity is plentiful and discharges when it is short.