How does the battery's internal resistance change with usage?

As a supplier of Lithium Ion UPS Batteries, I've witnessed firsthand the critical role these power sources play in various applications, from safeguarding communication networks to powering microgrids and generator cars. One of the most important factors that affects the performance and lifespan of a lithium-ion battery is its internal resistance. In this blog post, I'll explore how a battery's internal resistance changes with usage and what it means for battery users and suppliers.

Understanding Internal Resistance

Before delving into how internal resistance changes over time, it's important to understand what it is and why it matters. Internal resistance is the opposition to the flow of electric current within a battery. It's caused by several factors, including the resistance of the electrolyte, the electrodes, and the connections between them. When current flows through a battery, some of the electrical energy is converted into heat due to this resistance, which can lead to a voltage drop and a reduction in the battery's efficiency.

Internal resistance is a crucial parameter because it directly affects a battery's performance. A battery with high internal resistance will have a lower output voltage, reduced capacity, and a shorter lifespan. It can also cause the battery to heat up more during charging and discharging, which can further degrade its performance and safety.

Initial Internal Resistance

When a lithium-ion battery is new, its internal resistance is typically low. This is because the battery's components are in pristine condition, and there is minimal resistance to the flow of ions between the electrodes. The initial internal resistance of a lithium-ion battery can vary depending on several factors, including the battery's chemistry, design, and manufacturing process.

For example, lithium iron phosphate (LiFePO4) batteries generally have lower internal resistance compared to other lithium-ion chemistries, such as lithium cobalt oxide (LiCoO2). This makes LiFePO4 batteries more suitable for high-power applications, such as electric vehicles and power tools, where low internal resistance is essential for efficient operation.

Changes in Internal Resistance During Usage

As a battery is used, its internal resistance gradually increases. This is due to several factors, including:

1. Electrode Degradation

During charging and discharging, the electrodes in a lithium-ion battery undergo chemical reactions that can cause them to degrade over time. This degradation can lead to the formation of a solid electrolyte interphase (SEI) layer on the surface of the electrodes, which can increase the internal resistance of the battery.

The SEI layer is a thin film that forms on the electrode surface to protect it from further reactions with the electrolyte. However, as the SEI layer thickens over time, it can impede the flow of ions between the electrodes, increasing the internal resistance.

2. Electrolyte Decomposition

The electrolyte in a lithium-ion battery is a conductive liquid that allows ions to move between the electrodes. Over time, the electrolyte can decompose due to factors such as high temperature, overcharging, and over-discharging. This decomposition can lead to the formation of gases and other by-products, which can increase the internal resistance of the battery.

3. Lithium Plating

Lithium plating is a phenomenon that can occur when a lithium-ion battery is charged at a high rate or at low temperatures. During lithium plating, lithium metal deposits on the surface of the negative electrode, which can increase the internal resistance of the battery and reduce its capacity.

4. Mechanical Stress

Batteries can also be subjected to mechanical stress during use, such as vibration, shock, and compression. This mechanical stress can cause the electrodes and other components in the battery to shift or break, which can increase the internal resistance.

Impact of Internal Resistance on Battery Performance

The increase in internal resistance over time can have several negative impacts on battery performance, including:

1. Reduced Capacity

As the internal resistance of a battery increases, the voltage drop across the battery also increases. This means that less of the battery's stored energy is available for use, resulting in a reduced capacity.

2. Lower Efficiency

A battery with high internal resistance is less efficient because more of the electrical energy is converted into heat during charging and discharging. This can lead to increased energy consumption and higher operating costs.

3. Shorter Lifespan

The increased internal resistance can also accelerate the degradation of the battery's components, leading to a shorter lifespan. This means that the battery will need to be replaced more frequently, which can be costly for users.

4. Safety Risks

High internal resistance can cause the battery to heat up more during charging and discharging, which can increase the risk of thermal runaway and other safety issues. Thermal runaway is a self-perpetuating reaction that can cause the battery to overheat, catch fire, or explode.

Monitoring and Managing Internal Resistance

To ensure the optimal performance and safety of lithium-ion batteries, it's important to monitor and manage their internal resistance. This can be done using several techniques, including:

1. Battery Management Systems (BMS)

A BMS is an electronic system that monitors and controls the charging and discharging of a battery. It can measure the battery's internal resistance and adjust the charging and discharging parameters to optimize the battery's performance and lifespan.

2. Impedance Spectroscopy

Impedance spectroscopy is a technique that measures the impedance of a battery at different frequencies. This can provide information about the battery's internal resistance and other electrochemical properties.

3. Regular Maintenance

Regular maintenance, such as checking the battery's voltage, temperature, and state of charge, can help detect changes in internal resistance early on. This can allow users to take corrective actions, such as adjusting the charging and discharging parameters or replacing the battery, before significant damage occurs.

Applications and Considerations

The changes in internal resistance over time have different implications for various applications. For example:

1. Communication Base Station Battery

In communication base stations, reliable power supply is crucial to ensure uninterrupted communication services. Batteries with low internal resistance are preferred because they can provide high power output and maintain a stable voltage during power outages. As the internal resistance of the battery increases over time, it's important to monitor the battery's performance and replace it when necessary to avoid service disruptions.

2. Microgrid Energy Storage System

Microgrid energy storage systems use batteries to store excess energy generated by renewable sources, such as solar and wind, and release it when needed. Batteries with low internal resistance are essential for efficient energy storage and conversion. The increase in internal resistance over time can reduce the efficiency of the energy storage system and increase the cost of operation. Therefore, proper monitoring and management of internal resistance are critical for the long-term performance of microgrid energy storage systems.

3. Generator Car Lithium Battery

In generator cars, lithium batteries are used to power the electrical systems and start the engine. Batteries with low internal resistance can provide high cranking power and ensure reliable starting. As the internal resistance of the battery increases, the starting performance may degrade, and the battery may need to be replaced.

Conclusion

In conclusion, the internal resistance of a lithium-ion battery changes with usage due to factors such as electrode degradation, electrolyte decomposition, lithium plating, and mechanical stress. The increase in internal resistance can have a significant impact on the battery's performance, efficiency, lifespan, and safety. To ensure the optimal performance and safety of lithium-ion batteries, it's important to monitor and manage their internal resistance using techniques such as battery management systems, impedance spectroscopy, and regular maintenance.

As a supplier of Lithium Ion UPS Batteries, we understand the importance of providing high-quality batteries with low internal resistance and long lifespans. We are committed to helping our customers select the right batteries for their applications and providing them with the support and expertise they need to ensure the reliable operation of their power systems. If you're interested in learning more about our products or have any questions about battery internal resistance, please feel free to contact us for a purchase consultation.

References

• Arora, P., Zhang, Z., & White, R. E. (1999). Kinetics of lithium intercalation into carbonaceous materials. Journal of the Electrochemical Society, 146(2), 351-361.
• Broussely, M., Biensan, P., & Peres, J. P. (2004). Capacity fade mechanism and side reactions in lithium-ion batteries. Journal of Power Sources, 136(1-2), 33-41.
• Tarascon, J. M., & Armand, M. (2001). Issues and challenges facing rechargeable lithium batteries. Nature, 414(6861), 359-367.