Nel lithium battery industry, especially for LiFePO₄ (Lithium Iron Phosphate) batteries widely used in telecom, UPS , and energy storage systems , battery lifespan is usually evaluated from two critical dimensions: cycle life and calendar life. As a global leader in industrial battery solutions, EverExceed designs LiFePO₄ batteries with balanced optimization of both factors to ensure long-term reliability and maximum lifecycle value.

1. Cycle Life of LiFePO₄ Batteries

Definition:

Cycle life refers to the number of complete charge–discharge cycles a battery can perform under specified conditions—such as temperature, charge/discharge rate, and depth of discharge (DOD)—before its capacity degrades to a defined threshold, typically 80% of the rated capacity.

Core Focus:

Cycle life emphasizes “usage frequency” and “cumulative energy throughput.” It reflects how many times the battery can be actively used before performance becomes insufficient.

Aging Mechanisms:

• Loss of active materials and gradual structural degradation during repeated cycling.

• Repetitive expansion and contraction of cathode and anode materials, leading to material fatigue and micro-cracks.

• Continuous decomposition of electrolyte and the growth/restructuring of the solid electrolyte interphase (SEI) layer.

• Irreversible consumption of active lithium, forming “dead lithium” or participating in side reactions.

Testing & Representation:

Cycle life is typically evaluated through continuous laboratory charge–discharge testing. A common expression is:

“Capacity retention ≥80% after 3,000 cycles.”

Key Influencing Factors:

Depth of discharge (DOD), charge/discharge rate (C-rate), cutoff voltage settings, and operating temperature—especially during cycling.

2. Calendar Life of LiFePO₄ Batteries

Definition:

Calendar life refers to the total time a battery can maintain acceptable performance from the date of manufacture until capacity degrades to a defined level (typically 80%), under non-operating or storage conditions at a fixed temperature and state of charge (SOC).

Core Focus:

Calendar life emphasizes “storage duration” and “natural aging over time.” Even when not in use, battery aging continues.

Aging Mechanisms:

• Time-driven spontaneous chemical side reactions occurring even during idle storage.

• Slow oxidative decomposition of electrolyte at electrode interfaces, particularly at the cathode.

• Gradual thickening of the SEI layer, consuming active lithium and electrolyte.

• Dissolution or phase transition of electrode active materials.

Testing & Representation:

Calendar life is evaluated through long-term storage tests under controlled temperature and SOC conditions, for example:

“Capacity retention ≥80% after 10 years of storage at 25°C and 50% SOC.”

Key Influencing Factors:

Storage temperature (the most critical factor), storage SOC level, and time.

The Crucial Relationship Between Cycle Life and Calendar Life

In real-world applications, battery aging is the combined result of both cycle aging and calendar aging, occurring simultaneously.

• Interaction Effects:

Operating a battery at elevated temperatures accelerates both cycle aging (usage-induced stress) and calendar aging (time-driven stress).

• Practical Service Life:

Battery end-of-life may occur due to excessive cycling, prolonged storage time, or—more commonly—a combination of both. The actual service life is determined by whichever aging mechanism reaches the failure threshold first.

EverExceed Advantage:

EverExceed LiFePO₄ battery solutions are engineered with advanced cell chemistry, intelligent BMS, and optimized thermal management to effectively slow both cycle aging and calendar aging. This ensures long service life, stable performance, and lower total cost of ownership (TCO) for mission-critical applications such as telecom base stations, UPS systems, and energy storage projects.