The initial state of charge (SoC) significantly impacts the number of charge and discharge cycles a battery can withstand, influencing its overall cycle life and degradation rate.
Impact of Initial State of Charge on Battery Cycle Life
- Narrow SoC Range Extends Cycle Life
Operating a lithium-ion battery within a narrow SoC window, such as charging only between 75% and 65% SoC, results in the longest cycle life, but with limited energy utilization. This tight cycling uses about 10% of the battery capacity but greatly reduces capacity loss and prolongs battery health. For example, cycling between 75% and 65% SoC offers the longest cycle life but only delivers a fraction of the total available energy. - Deeper Discharge and Full Charges Reduce Cycle Life
Fully charging to 100% and discharging deeply (e.g., down to 25% SoC) accelerates capacity loss and decreases the number of cycles. Cycling between 75% and 25% SoC allows utilization of roughly 50% of the battery but reduces cycle life relative to the narrower window. The largest capacity loss occurs when a lithium-ion battery is discharged fully from 100% to lower SoC levels like 25% or below. - Trade-off Between Utilization and Longevity
There is a trade-off between maximizing usable energy (depth of discharge) and maximizing the number of charge-discharge cycles. For example:
– Cycling from 75% to 65% SoC yields the highest cycle life but only 90,000 energy units (EU).
– Cycling from 75% to 25% SoC yields about 3,000 cycles and 150,000 EU, balancing cycle life and energy delivered. - High SoC and Temperature Stress
High voltages (close to 100% SoC) and elevated temperatures accelerate battery degradation, shortening cycle life. Maintaining the battery within moderate SoC limits and avoiding high SoC extremes helps preserve battery health. - Definition of a Cycle and Battery Lifespan
A full cycle typically describes a battery going from full charge to full discharge (100% to 0% SoC), and partial cycles count proportionally. The total cycle life is how many full cycles (or equivalent partial cycles) the battery can complete before capacity drops below about 80% of original capacity.
Summary
The initial state of charge or the SoC range used during battery operation critically determines cycle life:
- Keeping the SoC within a limited, moderate range (e.g., 75–65%) maximizes cycle count but limits energy use.
- Using a wider SoC range (e.g., 75–25%) increases usable energy but reduces cycle life.
- Fully charging to 100% or deep discharging hastens capacity loss and reduces cycles.
- High SoC and temperature stress degrade the battery more quickly.
Managing battery SoC to avoid deep discharges and full charges is key to extending the number of charge-discharge cycles a battery can withstand.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-the-initial-state-of-charge-impact-the-number-of-charge-and-discharge-cycles-a-battery-can-withstand/
