What is the lifespan of a lithium battery?
Cycle life
Cycle life is a crucial parameter for evaluating the techno-economic efficiency of batteries. One charge and discharge cycle is called a cycle or period. Under a given discharge regime, the number of cycles a battery can withstand before its capacity drops to a specified value is called its cycle life or service life.
Cycle life is affected by the battery's Depth of Discharge (DOD), therefore, the expression of cycle life must also indicate the DOD. For example, a battery cycle life of 400 cycles/100% DOD or 1000 cycles/50% DOD. Cycle life varies among different types of batteries, and even products of the same series and specifications can have significantly different cycle lives. Among commonly used batteries, zinc-silver batteries have the shortest cycle life, generally only 30-100 cycles; lead-acid batteries have a cycle life of 300-500 cycles; and lithium-ion batteries have a longer service life, with cycle lives exceeding 1000 cycles.
With increasing charge and discharge cycles, capacity decay of the secondary battery is an inevitable process. This is because during charge-discharge cycles, some irreversible processes occur inside the battery, causing a decrease in battery discharge capacity. These irreversible factors are mainly as follows:
1) The active surface area of the electrode decreases continuously during charge-discharge cycles, leading to an increase in operating current density and polarization.
2) Active material detaches or migrates from the electrode.
3) Some electrode materials corrode during battery operation.
4) Dendrites form on the electrode during cycling, causing micro-short circuits within the battery.
5) Aging and wear of the separator.
6) Irreversible crystal morphology changes occur in the active material during charge-discharge cycles, thus reducing its activity.
Storage life
Batteries experience capacity changes after prolonged storage; this characteristic is known as storage performance. Although no electrical energy is released during storage, self-discharge always occurs within the battery. Even in dry storage, inadequate sealing can allow moisture, air, and carbon dioxide to enter, triggering corrosion of the thermodynamically unstable active materials on the positive and negative electrodes, leading to oxidation-reduction reactions and energy loss. This is even more pronounced in wet storage. The magnitude of this self-discharge is expressed as the time it takes for the battery capacity to drop to a certain specified capacity, known as storage life (or shelf life).
