Semco university – All about the Lithium-Ion Batteries # BATTERY IMPEDANCE MODEL AND ITS ROLE IN BMS Battery with internal resistance can be the reason behind your unbalanced battery pack. People think that batteries just die because of physical conditions like exposure to high and low temperatures, but chemical conditions like battery impedance can also lead to unbalanced batteries. If you think you are right, then do give the article a read as batteries with internal resistance can be a game changer while working with batteries.

## Introduction to Battery Impedance

Battery impedance refers to the resistance that a battery exhibits to the flow of electrical current. It is an important characteristic of a battery because it can affect its performance and lifespan. High impedance can cause voltage drops and reduce the battery’s ability to deliver power, while low impedance can lead to excessive current flow and overheating. Battery impedance can change over time due to factors such as temperature, age, and usage patterns. Therefore, it is important to monitor battery impedance regularly to ensure optimal performance and safety.

### Models of Battery Impedance

A combination of resistors, capacitors, and inductors represents the various physical and chemical processes that occur within the battery. The models typically include a series resistance to represent the internal resistance of the battery.

#### Electrochemical Impedance Model

The electrochemical impedance model is a mathematical model that describes the behavior of a battery’s impedance. It considers the battery as a combination of resistive and capacitive elements, which can vary depending on the battery’s state of charge, temperature, and other factors. The model uses complex impedance, which includes both magnitude and phase information, to represent the battery’s behavior over a range of frequencies. By measuring the impedance of a battery at different frequencies, the electrochemical impedance model can provide insight into the battery’s internal resistance, capacitance, and other characteristics. This information can be used to optimize battery performance, monitor battery health, and diagnose potential issues.

#### Equivalent Circuit Model

The equivalent circuit model of battery impedance is a simplified electrical circuit that represents the behavior of a battery’s impedance. It consists of a combination of resistive and capacitive elements that represent the battery’s internal components, such as the electrodes, electrolytes, and separators. The equivalent circuit model typically includes a resistor to represent the battery’s internal resistance, a capacitor to represent its capacitance, and other elements to account for factors such as polarization and diffusion. By measuring the impedance of a battery at different frequencies and fitting the data to the equivalent circuit model, it is possible to estimate the values of the circuit elements and gain insight into the battery’s internal behavior. The equivalent circuit model is commonly used in battery modeling and simulation, as well as in the design and optimization of battery management systems.

### Acquisition of Impedance

The acquisition of battery impedance typically involves measuring the battery’s response to an AC signal at different frequencies. This can be done using specialized equipment such as a battery impedance analyzer or a frequency response analyzer. The AC signal is applied to the battery and the resulting voltage and current responses are measured. The impedance of the battery can then be calculated using Ohm’s law, which relates the voltage and current to the impedance. By measuring the impedance at different frequencies, it is possible to obtain a frequency-dependent impedance spectrum that provides information about the battery’s internal behavior. This spectrum can be used to identify factors such as the battery’s internal resistance, capacitance, and other characteristics that can affect its performance and lifespan. The acquisition of impedance is an important tool for battery characterization, monitoring, and diagnosis.

#### Estimating Impedance

Estimating the impedance in a battery typically involves measuring the battery’s response to an AC signal and using mathematical models to interpret the resulting data. One common method is the electrochemical impedance spectroscopy (EIS) technique, which involves measuring the impedance of a battery at different frequencies using a sinusoidal voltage signal. The resulting impedance spectrum can be analyzed using mathematical models such as the equivalent circuit model to estimate the values of the circuit elements that represent the battery’s internal behavior. Other techniques, such as the impedance-based state-of-charge (SoC) estimation method, use the impedance of the battery to estimate its state of charge. This method involves measuring the impedance of the battery at different frequencies and using mathematical models to relate the impedance to the state of charge. Estimating the impedance in a battery is an important tool for battery characterization, monitoring, and diagnosis, and can provide valuable information about the battery’s internal behavior and performance.

### Measuring Resistance

Measuring impedance in a battery typically involves applying an AC signal to the battery and measuring the resulting voltage and current responses. This can be done using specialized equipment such as a battery impedance analyzer or a frequency response analyzer. The AC signal is typically a sinusoidal waveform with a known frequency and amplitude. The resulting voltage and current responses are measured and used to calculate the impedance of the battery using Ohm’s law. The impedance can be expressed as a complex number that includes both magnitude and phase information. By measuring the impedance at different frequencies, it is possible to obtain a frequency-dependent impedance spectrum that provides information about the battery’s internal behavior. This spectrum can be used to identify factors such as the battery’s internal resistance, capacitance, and other characteristics that can affect its performance and lifespan. Measuring impedance in a battery is an important tool for battery characterization, monitoring, and diagnosis.

### Application of Impedance

Impedance measurements and analysis have several important applications in batteries.

One of the primary applications is in battery characterization, where impedance measurements can provide valuable information about the battery’s internal behavior and performance. By measuring the impedance of a battery at different frequencies, it is possible to obtain a frequency-dependent impedance spectrum that can be used to identify factors such as the battery’s internal resistance, capacitance, and other characteristics.

Another important application of impedance measurements is in battery monitoring and diagnosis. Changes in the impedance of a battery over time can indicate changes in its internal behavior and performance, which can be used to diagnose potential issues such as aging, degradation, or damage.

Impedance measurements can also be used in battery modeling and simulation, where mathematical models such as the equivalent circuit model can be used to interpret the resulting data and predict the battery’s behavior under different conditions.

Impedance measurements can be used in battery management systems to optimize battery performance and extend its lifespan. By monitoring the impedance of a battery over time, it is possible to detect changes in its behavior and adjust the charging and discharging parameters accordingly to ensure optimal performance and safety.

### Troubleshooting

• Check the battery voltage using a multimeter. If the voltage is low, recharge the battery and check again.
• Measure the internal resistance of the battery using a battery impedance tester. If the resistance is high, it indicates that the battery is damaged and needs to be replaced.
• Check the battery terminals for corrosion or lose connections. Clean the terminals and tighten any loose connections.
• If the battery is still not functioning properly, try replacing it with a new one.

### Conclusion

Through the review of the progress in impedance modeling, acquisition, and application, it can be seen that impedance is frequently reported in battery management research and has broad application prospects, but there are still many engineering and scientific problems to be solved.