There are several things that can shorten the lifespan of a lithium ion battery, but they all come down to heat. Heat is generated through several means and leads to a cascade of detrimental effects on the battery's chemistry and physical structure. The most common ways heat damages a battery are by leaving it in direct sunlight, running too much current for too long, or using the battery for prolonged periods towards the lower end of its voltage range. To extend the life of your lithium battery when not in use, learn the best storage methods from our other articles.

Heats Effect on Lithium-Ion Degradation

There are so many ways heat can affect a battery. Whether it's internally generated from an external source, heat is the primary factor affecting a lithium-ion battery’s overall lifespan. Something as simple as exposing a battery to direct sunlight for long periods of time can drastically shorten its lifespan. When a battery is left in direct sunlight, it absorbs energy from the sun, leading to an increase in its temperature. Another avenue is high current demands; drawing excessive current from a battery causes an increase in internal resistance, which in turn generates heat.

Also, low-voltage operations contribute to this issue. As the battery discharges and its voltage drops, the internal resistance increases, further elevating the temperature. These factors combined can significantly impact the efficiency and safety of lithium-ion batteries.

Chemistry & Heats Impact on Battery Lifespan

Lithium-ion batteries, based on complex chemical reactions, are highly sensitive to temperature variations:

  • Chemical Instability: The chemistry of lithium-ion batteries is inherently unstable and temperature-dependent. Elevated temperatures can disrupt these chemical processes, leading to efficiency losses and potential hazards.
  • Resistance and Heat: Electrical resistance in batteries increases with temperature. This increase in resistance can create a positive feedback loop, further raising the temperature and exacerbating the problem.

Internal Resistance and Its Consequences

Internal resistance plays a pivotal role in how heat affects lithium-ion batteries:

  • Resistance Measurement: A typical lithium-ion cell has an internal resistance ranging from 15 to 30 milliohms.
  • Heat Generation: Current flowing through this resistance generates heat. For instance, 3 to 5 watts of heat loss in a battery can significantly increase its temperature, reducing its lifespan.

Voltage Level Considerations

Voltage levels within a lithium-ion battery also influence its thermal behavior. As the voltage drops below certain levels (below around 3 volts), the internal resistance increases, causing more heat generation and accelerating battery degradation. 

So, however much heat your battery generates under a 30 amp load when it's fully charged will be a whole lot different than the same load when the battery is almost dead.

Extending Battery Life

To maximize the lifespan of a lithium-ion battery, several strategies can be employed:

  • Avoid Direct Sunlight: Preventing batteries from being stored or used in direct sunlight can significantly reduce heat-induced degradation.
  • Current Management: Avoiding excessive current draw prevents undue heat generation.
  • Optimal Voltage Operation: Keeping the battery within a safe voltage range (not too low) helps in maintaining its health.

Finding the Perfect Trade-Off

Balancing battery usage and preservation involves finding a middle ground:

  • Charge-Discharge Levels: Charging to 80% and discharging to 20% can extend the battery's life by 2.5 to 3 times while sacrificing some capacity.
  • Watt-Hour Efficiency: This strategy, while reducing immediate capacity, increases the total watt-hours extracted from the battery over its lifespan.

Heat is the primary factor that shortens the life of lithium-ion batteries. By understanding and mitigating the sources of heat generation, such as exposure to sunlight, high current demands, and low voltage operation, the lifespan of these batteries can be significantly extended. Managing the internal resistance, optimal charging, and discharging practices are key to preserving the health and efficiency of lithium-ion batteries, thereby enhancing their longevity and overall performance in various applications.

It’s important to remember that charging, discharging, and even storage are part of the heat cycle for lithium ion batteries. The closer you keep your battery to room temperature, the longer its going to last.