Why Do Rechargeable Batteries Stop Working?

The transition from a fully charged and functional battery to one that barely keeps your device running is a common but frustrating experience. This article will explore the reasons behind such issues, focusing on the physics and chemistry of rechargeable batteries, with a particular emphasis on lithium-ion batteries—a ubiquitous choice in modern devices.

Chemical Process: The Battery's Lifespan

The charging and discharging of a battery involve complex chemical reactions that occur within its cells. Each cycle of charging and discharging these reactions can become less efficient over time, leading to a decline in the battery's capacity and efficiency.

When a battery is new, the chemical reactions happen efficiently with minimal resistance. However, as the battery experiences more cycles, these reactions gradually lose their efficiency. Over time, the battery starts to take longer to charge, and it can no longer provide the required power or current, leading to the need for replacement.

Types of Battery Degradation

Not all rechargeable batteries degrade in the same manner. For example, liquid metal batteries may exhibit different characteristics compared to others like lead/acid or lithium-ion batteries.

In lead/acid batteries, the degradation process is more visible as the lead paste on the plate meshes starts to drop off, reducing the surface area available for the chemical reactions. This results in a decrease in both the capacity and the maximum amperage that the battery can deliver.

Understanding the Chemical Activity Surface

A fresh battery has a clean, optimal surface area that allows for maximum chemical activity. This surface area is crucial for defining the battery's capacity and maximum amperage. Over time, this active surface area gets clogged with chemicals from the liquid content within the battery, reducing the area available for effective reactions.

With each discharge and charge cycle, a tiny portion of the active surface gets "clogged," leading to a gradual decline in the battery's capacity. This process is exacerbated by factors such as age and storage conditions, including the state of charge (SOC) and temperature.

Specific Case: Lithium-Ion Batteries

Recent research by the U.S. Department of Energy has shed light on why lithium-ion batteries face performance decline over time. The deterioration is attributed to a specific undesirable chemical reaction that occurs more with each charge cycle.

An increase in the number of charge cycles leads to the formation of more crystals, which in turn reduce the battery’s efficiency and capacity. As a result, lithium-ion batteries eventually reach a point where they can no longer provide sufficient charge to power your device as effectively as when they were new. This explains why older lithium-ion batteries tend to charge slower and offer less run time on a full charge.

Understanding the underlying chemistry helps in managing your batteries more effectively. Proper storage and charging habits can help extend the life of your batteries, but the inherent limitations of battery chemistry will still take their toll over time.

Conclusion

Rechargeable batteries degrade over time due to the inefficiency of chemical reactions and the gradual clogging of active surfaces. While some battery types may not decline as much, the practical reality of modern devices leaves us dealing primarily with lead/acid and lithium-ion batteries. Understanding these issues can help in extending battery life and managing your energy consumption more effectively.