Lithium batteries lose charge even when they are not in active use, and understanding this phenomenon is key to optimizing battery storage and longevity. Lithium-ion technology has revolutionized energy storage, powering everything from smartphones to electric vehicles. However, if you’ve ever noticed that your battery seems to lose its charge despite being idle, there are underlying chemical reactions and storage conditions at play. In this article, we delve into the science behind why lithium batteries lose charge when unused, explore the effects of storing batteries at various charge levels, and offer best practices for maintaining optimal battery performance over time.

Chemical Reactions in Unused Lithium Batteries 

When a lithium battery is left unused for an extended period, several slow but persistent chemical reactions occur:

• Self-discharge and Electrolyte Decomposition:
  All batteries experience self-discharge—a natural phenomenon where charge is gradually lost. In lithium batteries, the electrolyte can decompose over time, leading to a reduction in available charge. This decomposition accelerates at higher temperatures, resulting in decreased performance.

• Formation and Growth of the SEI Layer:
  The Solid Electrolyte Interface (SEI) layer forms on the anode during initial battery use. While a stable SEI is beneficial, an unstable or excessively thick SEI—often resulting from long periods of inactivity—can impede lithium-ion flow, further reducing battery capacity and efficiency.

• Lithium Plating:
  In some conditions, especially when a battery is stored at a high state-of-charge, lithium can deposit or “plate” onto the electrode surfaces. This phenomenon not only contributes to capacity loss but can also increase internal resistance and, in severe cases, lead to safety issues.

Impact of Long-Term Inactivity on Battery Health

Leaving lithium batteries unused for long durations can lead to several detrimental effects:

• Capacity Fade:
  Over time, internal chemical reactions reduce the maximum capacity of the battery. Even when not in active use, these reactions slowly degrade the battery’s overall ability to hold a charge.

• Increased Internal Resistance:
  As unwanted chemical byproducts accumulate, the battery’s internal resistance can rise. This makes it less efficient at delivering power when eventually put back into service.

• Safety Concerns:
  In extreme cases, prolonged inactivity combined with inappropriate storage conditions (such as high temperatures) may increase the risk of swelling or even thermal runaway, although such instances are rare when batteries are stored correctly.

Effects of Storage Charge Levels: Charged vs. Uncharged

How a lithium battery is stored—whether fully charged, partially charged, or completely discharged—has a significant impact on its longevity:

• Fully Charged Batteries:
  Storing batteries at 100% charge can accelerate degradation due to higher internal voltage, which promotes chemical reactions like electrolyte oxidation. This can result in a thicker SEI layer and faster capacity fade over time.

• Completely Discharged Batteries:
  Conversely, leaving a battery in a deeply discharged state can lead to a condition known as “over-discharge,” where the battery voltage drops too low to recover. This can cause irreversible chemical changes that may render the battery unusable.

• Optimal Storage Charge:
  Experts generally recommend storing lithium batteries at about 40% to 60% charge. This mid-range state minimizes stress on the battery’s chemistry and helps extend its usable life.

Learn more about optimal battery charge levels from resources provided by the U.S. Department of Energy: DOE Battery Storage Guidelines.

Optimal Storage Conditions and Duration

How Long Can Lithium Batteries Be Stored?

When stored correctly, lithium batteries can maintain acceptable performance for 2-3 years. However, even under ideal conditions, natural degradation occurs due to self-discharge and chemical aging.

Key Factors Affecting Battery Storage:

• Temperature:
  Lower temperatures generally slow down chemical reactions. Storing batteries in a cool, stable environment is essential to reduce the rate of degradation. Extreme cold, however, may affect performance upon reactivation.

• Humidity:
  High moisture levels can lead to corrosion of internal components. It is best to store batteries in a dry environment with controlled humidity.

• State-of-Charge:
  As discussed, maintaining a charge level of 40-60% is optimal for minimizing chemical stress and extending the battery’s life.

• Storage Environment:
  Avoid direct sunlight, fluctuating temperatures, and areas prone to condensation. A climate-controlled storage facility is ideal for long-term storage.

For additional technical details on battery storage factors, ScienceDirect offers a comprehensive review on lithium-ion battery longevity: ScienceDirect on Battery Aging.

Best Practices for Storing Unused Lithium Batteries

To maximize the lifespan and performance of lithium batteries, consider the following guidelines:

• Maintain Optimal Charge:
  Charge batteries to between 40% and 60% before storage. This balance reduces stress on the battery and mitigates both overcharge and over-discharge risks.

• Store in a Cool, Dry Place:
  Ideal storage temperatures are typically between 15°C and 25°C (59°F to 77°F). Avoid high temperatures, which can accelerate degradation, and extremely low temperatures, which may affect battery chemistry.

• Regularly Monitor and Recondition:
  If batteries are stored for several months or longer, check their voltage periodically. Recharging to the optimal level when necessary can prevent deep discharge and extend overall battery life.

• Use Protective Packaging:
  Store batteries in anti-static, moisture-resistant containers. This protects against environmental factors and reduces the risk of accidental damage.

• Label and Organize:
  For businesses that handle multiple batteries, labeling each battery with its storage date and charge level can help track and manage the aging process efficiently.

Frequently Asked Questions (FAQs)

Q1: What causes lithium batteries to lose charge when they are not used?
A1: Lithium batteries lose charge due to self-discharge and chemical reactions such as electrolyte decomposition and SEI layer formation. These processes naturally occur even when the battery is idle.

Q2: What is the recommended state-of-charge for storing lithium batteries?
A2: It is best to store lithium batteries at a 40-60% charge. This level minimizes stress on the battery chemistry and helps reduce degradation over time.

Q3: How long can lithium batteries be stored without significant performance loss?
A3: Under optimal conditions—cool and dry environments with proper charge levels—lithium batteries can be stored for 2-3 years before noticeable capacity loss occurs.

Q4: How does temperature affect lithium battery storage?
A4: Higher temperatures accelerate chemical reactions, leading to faster degradation, while lower temperatures slow these reactions. However, extremely low temperatures can also affect battery performance when reactivated.

Q5: Should I store my lithium battery fully charged or completely discharged?
A5: Neither is ideal. Storing a battery fully charged can lead to overcharge stress, while a completely discharged battery risks over-discharge. A partial charge of around 40-60% is optimal for storage.

Conclusion

In summary, lithium batteries lose charge when unused due to inherent self-discharge and ongoing chemical reactions. The degradation process is influenced by factors such as storage temperature, humidity, and the battery’s state-of-charge. By maintaining batteries at an optimal charge level (40-60%) and storing them in controlled environments, you can significantly prolong their lifespan and ensure reliable performance when needed.